textile testing

Textile TestingFor

DH & TT Students

ByEr.P.Rangari

Reader (Processing)I.I.H.T. Champa

E mail:[email protected]

Textile Testing By P. Rangari Page 1

UNIT –IIntroduction Textile Testing is the application of Engineering knowledge and science to the measurement of properties and characteristics of and conditioning affecting textile fibres, yarn and fabrics. It involves the use of techniques, tools, instruments and machines in the laboratory for evaluation of the properties of different forms of textiles.

Quality control is concerned with the evaluation of test data and its application to the control of textile process, raw materials, intermediate products and final products. It concerned not only with quality level but also cost of maintaining this level.

Testing provides back ground and data and quality control applies the results.

1. Objectives & Importance of Textile Testing

Textile Testing has attained important position in the textile industry. It is just as applicable to the analysis of finished fabrics as it is to the raw materials. It is useful for the measure of house hold fabric as for army fabrics. It is necessary for the cotton spinner in controlling the quality of his product as it is to the rayon producer in controlling quality product. It is valuable tool in the hands of textile manufacturer as it is in the hands of the research technicians.

Many form of textile all differ in their characteristics just as people differ in personality. Ex. yarn may be strong, heat resistance, elastic etc. The laboratory equipped for textile testing is providing ground for the determination, measure and comparison such standards.

It is also necessary to know the other conditions or forces influence the result. For ex. Cotton yarn being hygroscopic is strengthened by increase in moisture contents. To understand inter relationship of many properties of textile materials knowledge of individual test methods and procedures is essential.

Standards are established by an individual organization. For example staple length of raw cotton, size of rowing, strength of yarn, number of filaments in the rayon etc. Textile testing helps to establish scientific specification. Textile testing is also playing role in analysing the market requirements or consumer demand.

2. Sampling techniques Inspection for acceptance purpose is carried out at many stages in manufacturing. There may be inspection of incoming materials, process inspection at various points in the manufacturing operation, final inspection by the manufacturer of its own products and ultimately inspection of finished products by one or more purchasers. Inspection in the sense of sorting product that conforms to specification from


non-confirming products and inspection cannot be relied on to ensure that all accepted product relay conforms.

Inspection fatigue on repetitive, inspection operations often will limit the effectiveness of 100% inspection. No sampling procedures eliminate all non-confirming products. It follows the best way to be sure that accepted products confirm to the specification is to have the product made right to first place.

Purpose of Sampling Most of the acceptances in inspection are necessarily on a sampling basis. The purposes of samplings are

All the acceptance tests that are destructive of items tested must be inevitably done by sampling.

In many other instances sampling inspection is used because of the cost of 100% inspection is prohibitive and

The influence of inspection is fatigue in 100% inspection.

Often happen that the striking quality improvements can be caused outright rejection of entire lots of products on the basis of non- confirming products found in sample. The rejections of entire lots bring much strong pressure for quality improvement.

Some Weakness in Acceptance Sampling Inspectors often use a working rule that is influenced by knowledge of past quality

history of the product being sampled. For instance same article purchased from two or more sources, an inspector may check only one or two items in a lot from source considered reliable but might give critical examination to a lot from a source considered to be unreliable. Inspector memories of past quality may be short or inaccurate.

These limitations suggest need of definite working rules regarding size and frequency of sample and basis for acceptance or rejection. Defect & Defective

These words are used in their technical sense dealing with lack of conformity to specification. It is common for specification to contain margin of safety. Therefore some products does not meet specification can be satisfactory for its intended use.

A defective item is one that does not confirm to specification in some respect; a defect is a non conformity to some specification.

Factors Governing SamplingSampling methods are governed by the following factors.

1. Form of the material: The material could be in the form of fibre, yarn or fabric. It could also be an intermediate product such as sliver, roving, etc. A sampling method useful for fibre may not be suitable for a yarn.


2. Amount of material available: If sufficient amount of material is available, we can perform minimum number of tests required for accuracy of the test.

3. Nature of the test: The nature of test depends upon the characteristic being evaluated. In some test the test specimen is destroyed, in others it is not. Some test use small sample, while others use a relatively large sample.

4. Type of testing instrument: To asses a particular characteristic of a material one or more than one instrument are used. Under such circumstances the sampling methods are different.

5. Information required: the sampling method used for a given textile material will be influenced by the amount of information required.

6. Degree of accuracy required: the sampling method need not to be elaborate if only approximate information is required.

Types of SampleThere are two types of sample. These are

1. Random sample2. Biased sample

Random SampleThe probability assumes that the samples are drawn at random, that is, each item in the

lot is assumed to have an equal chance to be selected in the sample. If the items in a lot is mixed thoroughly a sample is chosen anywhere in the lot meet the requirements of randomness. However a common condition is that there is no reason to believe that the items have had a through mixing. More over it may be impracticable to carry out.

It is practicable to assign a different number to each item in a lot and draw an item from any place of the lot; a formal scheme for drawing a random sample may be adopted. Such scheme may use a table of random numbers or some mechanical device for generating random number needed. Computer generated random numbers may be used

Random digits can be generated in any way that gives each digit from 0 to 9 an equal chance to be selected. Table No. 1.2.1 contains 2500 random digits reproduced. The table is prepared by the Random Corporation.

Assume that it is desired to select a sample of 15 from lot of 750 items. Each item of the lot is identified by a number from 1 to 750. Therefore, it is necessary to select 15 random three digit numbers from 001 to 750.

First it is necessary to determine the starting point in the table. The table contains 50 rows and 50 columns digit listed in pairs. Assume the pencil point is placed at random in the table and the first two digits number to the right from 1 to 50 determines the row to be selected. The procedure is repeated to determine the starting column. Assume that the 8th row and 39th column


are chosen. Assume the decision was made in advance that the starting point chosen will be the first digit of three digit numbers read to right and succeeding numbers will be read down the table. The following numbers are obtained.

471, 098, 443, 335, 015, 106, (932), 682, (864), 531, 379, (909), 225, 233, 404, (812), 392, (820), (934), 183, (929), 592.

Numbers that are not between 001 to 750 must be discarded. These are shown in brackets. A number that has already occurred must also be discarded. The selections of the sample between 001 to 750 are rearranged in the increasing size as follows.

015, 098, 106, 183, 225, 233, 335, 379, 392, 404, 443, 471, 531, 592, 682

Biased SampleIt may sometimes happen that the selection of sample is influenced by factors other than

chance. In such cases the sample may not be the representative of the bulk. This kind sample is called “biased” sample. A few factors influencing sample are

Bias due to specific physical characteristic of the individual in bulk: The person selecting the sample may be unconsciously influenced by a specific physical characteristic of the individual. The sampler has selected knowingly or unknowingly due to ease or convenience of selection.

Bias due to position of individuals in the bulk relative to the sample: Some time position of the individual members of the bulk relative to the person doing the sampling may give the sample a bias.

Bias due to some other factor: Occasionally, some other subconscious bias could be introduced. The person selecting the sample may unconsciously select only the cleaner portion of the bulk.

Yarn and Fabric Sampling Method

A. Methods used for sampling FibersIt was mentioned earlier that sampling techniques have to consider the form of the

material available for test e.g. fiber, yarn or fabric. Going a step further, the sampling method used for selecting a fibre sample for testing depends upon the form in which the fibre is available. Thus, fibres in bales or sliver or card web or yarn will demand different techniques.

Some sampling techniques used for the determination of fibre properties are discussed in what follows.

1. The squaring technique:

This technique is used for the selection of a random sample from a sliver. In using this technique, the sliver is first opened out into the form of a web and placed on a black velvet pad. The end of the sliver is then ‘squared off. This is achieved by placing a glass plate over the fibres to act as a

Textile Testing By P. Rangari

control, allowing only a small fringe to project beyond the leading edge ofbelow Figure.Next, all the protruding fibres are removed and discarded. The plate is moved back asecond fringe is removed. These last two steps eliminate the extentfibres have terminated in a given volume of the fibre web.

The above operation is repeated until the final position of the plate edge is at least aequal to the length, from its original position, of the longest fbecause whenever a sliver is broken there is a bias of long fibres at each

The plate is then moved back a millimetre or so one last timethe leading edge of the plate are removed and taken as the numerical ora test, e.g. a length test on a comb sorter.

2. The cut squaring method

When the material is composed of fibres in a modified squaring technique, called the cuttwists in the material are removed. The material is then gently openedparallel on a black velvet pad. A glass plate is placedangles to the strand axis. This arrangement is depicted in

The protruding fringe of fibres is cut across with scissors as close to the glass plate asand the fibres whose cut ends project are removed by forceps and discarded.then shifted back about one millimetre and again the projecting fibresdiscarded. This operation is repeated. Finally, after a third mowhole fringe is pulled out and used as the test sample.

control, allowing only a small fringe to project beyond the leading edge of the plate, as shown in

Next, all the protruding fibres are removed and discarded. The plate is moved back asecond fringe is removed. These last two steps eliminate the extent-bias since all the ends of

inated in a given volume of the fibre web.

The above operation is repeated until the final position of the plate edge is at least aginal position, of the longest fibre present. This

because whenever a sliver is broken there is a bias of long fibres at each broken fringe.

The plate is then moved back a millimetre or so one last time and all the fibresthe leading edge of the plate are removed and taken as the numerical or representative sample for

omb sorter.

The cut squaring method

When the material is composed of fibres in parallel order, e. g. drawframe sliver, rove anda modified squaring technique, called the cut-squaring technique, may be used.twists in the material are removed. The material is then gently opened out a little, and laid

a black velvet pad. A glass plate is placed-over the fibres with its leading edge at right angles to the strand axis. This arrangement is depicted in below Figure.

The protruding fringe of fibres is cut across with scissors as close to the glass plate asand the fibres whose cut ends project are removed by forceps and discarded. The glass plate is then shifted back about one millimetre and again the projecting fibres are removed and discarded. This operation is repeated. Finally, after a third movement of the glass plate, the whole fringe is pulled out and used as the test sample.

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e plate, as shown in

Next, all the protruding fibres are removed and discarded. The plate is moved back a little and aall the ends of the

The above operation is repeated until the final position of the plate edge is at least a distance ibre present. This step is essential

broken fringe.

and all the fibres protruding from representative sample for

parallel order, e. g. drawframe sliver, rove and yarn, squaring technique, may be used. First of all any

out a little, and laid with its leading edge at right

The protruding fringe of fibres is cut across with scissors as close to the glass plate as possible The glass plate is are removed and

the glass plate, the


3. Zoning Technique

The selection of representative samples from a large lot ofa bale of cotton, for example, the fibres may notfibre have to be pulled out from as many places in the balethe fibres form a highly heterogeneous mass, a veryselected from the bale at random so that all its

In such cases, an elaborate system called the zoning technique is used. This techniqueinvolves selection of tufts of fibre from all possible parts ofsamples prepared by different persons show results between which thestatistically insignificant. In other words, sampling on a given bulk ofmethod gives samples that are similar in characteristics, andThe zoning technique is thus one recommendedthe use of the technique in prepaof a comb sorter it is given in theBelow Figure represents a pictori

1. A sample of about 50 grams is prepared from the bulk material by selecting about 80tufts chosen, as practicably as is possible, from all portions of the bulk.

2. The sample is then divided into four quarters.3. Next, 16 small tufts of about 20 mg each are selected at random from each quarter4. (a) One of the small tufts is taken and divided in to two nearly equal parts by hand. The right

hand side is discarded and the one

representative samples from a large lot of material presents specialcotton, for example, the fibres may not form a homogenous mixture and small tu

ibre have to be pulled out from as many places in the bale as is practically possible, Further, ifthe fibres form a highly heterogeneous mass, a very large number of tufts would need to be

ale at random so that all its parts have been represented.

In such cases, an elaborate system called the zoning technique is used. This techniqueinvolves selection of tufts of fibre from all possible parts of the bulk. But it issamples prepared by different persons show results between which thestatistically insignificant. In other words, sampling on a given bulk of material by the zoning method gives samples that are similar in characteristics, and therefore representative of the bulk. The zoning technique is thus one recommended first by the British Standards. A brief account of

preparing a sample for evaluating the length characteristics by means e following.rial representation of the method used.

A sample of about 50 grams is prepared from the bulk material by selecting about 80tufts chosen, as practicably as is possible, from all portions of the bulk.

sample is then divided into four quarters.Next, 16 small tufts of about 20 mg each are selected at random from each quarter

One of the small tufts is taken and divided in to two nearly equal parts by hand. The right hand side is discarded and the one in the left is turned through a right angle.

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material presents special problems. In mixture and small tufts of

as is practically possible, Further, iflarge number of tufts would need to be

In such cases, an elaborate system called the zoning technique is used. This technique too the bulk. But it is reliable in that

differences are material by the zoning resentative of the bulk.

irst by the British Standards. A brief account ofsample for evaluating the length characteristics by means

A sample of about 50 grams is prepared from the bulk material by selecting about 80 large

Next, 16 small tufts of about 20 mg each are selected at random from each quarter.One of the small tufts is taken and divided in to two nearly equal parts by hand. The right


(b) This tufts is than split into two nearly equal parts by hand; the half in the left hand is now discarded and the and the remaining portion turned through a right angle.(c) The third halving is then carried out on the portion that remains in the hand. The right hand portion is discarded this and remaining portion is turned through a right angle.(d) Now a fourth halving is done on the remaining portion of the fiber. The left hand half is discarded and small tuft that remains is preserved. Remaining 15 tufts of step 3 are halved four times in exactly the same manner as above to give 15 small tufts, or wisps, that are preserved. 16 wisps are similarly separated from each of other quarters of step 2. Now we have 16 wisps from each quarters of original sample

5. The set of l6 wisps from each quarter is combined into tufts. This gives us four tufts.

6. Each of the four tufts is thoroughly mixed by hand by drawing and doubling between the fingers.

7. Each of these mixed tufts is then divided into four parts, splitting the tuft in a direction perpendicular to the fibre length. Splitting in a lengthwise direction could result in two parts of differing in length characteristics. Hence this precaution is important. Care is also taken to see that the parts are as nearly equal to each other as possible.

8. Once part is taken respectively from each of the tufts and combined to give a new tuft. This is repeated with the remaining parts of each tuft. We now have four new tufts, each containing a part of the previous four tufts (Step 6).

9. Each of the new tufts is thoroughly mixed again by manual drawing and doubling.10. A quarter portions is then taken from each of the four new tufts to make the final sample,

again taking care to split the tuft in a direction perpendicular to the fibre length.

This sample can now be regarded as a representative sample possessing all the length characteristics of the bulk material.


B. Method Used For Sampling YarnsYarn samples are selected according to the type of test and the form in which the yarn is

available. The yarn could be ring bobbin, a double flanged bobbin, a bundle of hanks and so on. Some sampling methods for the determination of yarn count, twist and strength are discussed below.

Sampling for the determination of count of yarn in package form: 16 packages are selected from the concerned machine for spun yarn in the form of cops, ring-frame bobbins, tubes or other forms of primary package. Skeins are then wound form the top portion of eight packages, next skeins is wound from about the middle portion of the remaining packages.

Large packages such as cones and cheeses, take eight packages. Prepare two skeins from each; it is preferable to take one skein form the outer portion and another from a part near the middle. For continuous filament yarn, only one skein is taken from the outside of each of sixteen cones or cheeses.

Sampling for the determination of count from the yarn removed from the fabric: From the conditioned fabric, cut at least two rectangular strips, about 20 inch long containing different warp threads for determining the count of yarn. Similarly take at least five rectangular 20 inch strips representing different weft for determining count of weft yarn. The strip width should be such as t contain at least fifty lengths of either warp or weft yarn.

Sampling of yarn for the determination of twist in yarn in package form: Take test specimens in equal numbers form ten packages, taking care that no specimen is taken from within one yard of the end of the package. Discard a length of about one yard of yarn between two consecutive specimens.

Sampling for the determination of lea strength of spun yarn: A lea of yarn is taken from each of twenty packages. If only a small number of packages, withdraw lea from a smaller multiple of four packages such that a total of twenty leas are obtained.

Sample for determination of single strength: If single yarn and two ply yarns of medium count are being evaluated, not less than 50 test specimens are taken from the available material. Yarn may be from a package, or from a warp, or from a woven or knitted fabric. In case two ply yarn and for cabled yarns, the number of test specimens may be reduced to thirty.

C. Methods Used In Sampling of FabricsSampling for fabrics will vary from one kind of fabric to another. Three different types of

fabric commonly encountered in testing laboratory. They are

Narrow type of fabrics like brides, laces, ribbons etc.

Woven fabric of regular width.

Knitted fabricThe following points are too kept in mind while removing samples from fabrics for test.


At least two inches near the selvedge should be avoided. This is, because, the fabric properties of the fabrics at the selvedge differ from those at the body of the fabric. This is due to extra strain is imposed in the yarn near the selvedge.

No two samples should contain the same threads.

The weft wary fabric strips of samples should include fabric from two weft packages. During weaving weft tension will vary at the top and bottom ends of pirns and give rise to “cop end effect”, which may affect the fabric strength, and causes changes in fabric structure and other properties.

3. Elementary Statistics

The term “statistics” refers to both a set of data (information) and methods used to analyze the data. In making physical tests on textile sample, we must remember that we are dealing with variable substances. For example, we make several determinations of strength on a piece of cloth; we may find no two test give the same result.

Measured quality of the manufactured product is always subject to a certain amount of variations as result of chance. Some stable system of chance causes is inherent in any particular scheme of production and inspection. Variation with in this stable pattern is inevitable. The reason for variation outside this stable pattern may be discovered. This makes possible the diagnosis and correction of many production troubles and often being substantial improvement inproduct quality and reduction in spoilage and rework.

Measurements are seldom, if ever, exact, confusion exists in the mind of many people, because they associate with the exact number of units or counts with the answer of the


measurements. No number is likely to be exact, but all might be good approximation. This situation develops data and is collected from these test results.

The attractive and effective presentation of data is essential if the data are to be of utmost value. Practically all data can be presented in the form of either table or charts and one or both of these methods are recommended.

Measures of Central Tendency Most measurements in textile testing consist of a set of repeat measurements that have

been made on a number of identical individuals constituting a sample taken from the bulk of the material. Certain statistical measures are used to dspread.A short guide to the terms employed is given below. For a more comprehensive

textbook of statistics should be consulted.

1. Arithmetic mean or averageThe arithmetic mean is the measure mostsample. It is obtained by adding together the individualsum by the number of individual’s

Where

X= Mean or average. n = Number of test results. ∑= Sum of test results. Example:-Calculate the average TPI ofof 10 test specimens.33.8, 34.2, 33.5, 33.8, 33.6, 34.7,

Mean = 33.8 + 34.2 + 33Mean or Average = 33.87Advantages of arithmetic mean or averageIt is simple to understand, it is easy to calculatedistribution.

likely to be exact, but all might be good approximation. This situation develops data and is collected from these test results.

The attractive and effective presentation of data is essential if the data are to be of utmost value. Practically all data can be presented in the form of either table or charts and one or both of these methods are recommended.

Central Tendency Most measurements in textile testing consist of a set of repeat measurements that have

been made on a number of identical individuals constituting a sample taken from the bulk of the material. Certain statistical measures are used to describe the average of the results and their

A short guide to the terms employed is given below. For a more comprehensivetextbook of statistics should be consulted.

Arithmetic mean or averageThe arithmetic mean is the measure most commonly chosen to represent the central value of a sample. It is obtained by adding together the individual values of the variable x

individual’s n.

Calculate the average TPI of a yarn, given the following individual values of

33.8, 34.2, 33.5, 33.8, 33.6, 34.7, 34.2, 33.8, 33.5 and 33.6.

33.5 + 33.8 + 33.6 + 34.7 + 34.2 + 33.810Advantages of arithmetic mean or average

is easy to calculate, it is the most popular method of locating a

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likely to be exact, but all might be good approximation. This

The attractive and effective presentation of data is essential if the data are to be of utmost value. Practically all data can be presented in the form of either table or charts and one or both of

Most measurements in textile testing consist of a set of repeat measurements that have been made on a number of identical individuals constituting a sample taken from the bulk of the

escribe the average of the results and their

A short guide to the terms employed is given below. For a more comprehensive explanation a

the central value of a x and dividing the

a yarn, given the following individual values of the TPI

+ 33.5 + 33.6

is the most popular method of locating a


2. MedianA second measure of central tendency is the median. The median is defined as the middle value of series of values arranged in the order of magnitude either in the ascending order or in the descending order of magnitude. It lies at the centre of the distribution. Fifty percent of the distributions are above the value and other fifty percent of them are below the value.

Properties of median Although the median is not as popular as the arithmetic mean, it does have advantage of

being both easy to determine and easy to explain.

The number of observations rather than the values of the observations affect the median; hence it will be less distorted as a representative value than the arithmetic mean.

Advantage and disadvantage of median An additional advantage of the median is that it may be computed for an open-end

distribution.

The major disadvantage of the median is that it is a less familiar measure than the arithmetic mean. However, since the median a positional average, its value is not determined by each and every observation. Also, the median is not capable of algebraic treatment.

Example: - The following are the test results of single yarn strength in grams: 210, 220, 218,216, and 222. Determine the median.

The observations, arranged in ascending order, are 210, 216, 218 220 and 222. The value of the middle of the observations (the third value in this case is) is the median.Median = 218.

3. ModeThe mode is a typical or commonly observed value in a set of data. It is defined as the value occurs most often, or the value with the greatest frequency. The dictionary meaning of the term mode is ‘most usual’Example: - Seven threads are tested for TPI, gave the following value 15, 14, 14, 17, 14, 15, 16,find the mode value.In the above given problem the TPI value 14 is occurs most frequently. So the mode value is 14

Measures of DispersionIn order to describe the variability of measured characteristic of the material tested, the

following terms used to indicate the dispersion.1. Range 2. Mean deviation3. Standard deviation4. Co-efficient of variation5. Standard error


1. Range As defined earlier, the range is defined as the difference between the highest (numerically largest) value and the lowest (numerically smallest) value in a set of data. It is rough measures of dispersion in the data. In symbols, this may be indicated as,R = H – LWhere R = Range, H = Highest value and L = Lowest value.

Example: - The single thread strength values in grams of a yarn are given below. Find the range.115, 100,122,110,120.Here the highest value is 122 gm and lowest value is 100 gm. Thus

Range =122-100 =22 gm.

2. Mean Deviation The mean deviation is the more accurate indication of variation in a set of given values than the range. The ‘deviation’ is difference between each value and arithmetic mean. In other words, mean deviation is the sum of deviation (taken as positive) values from an average divided by the number of observations.

Where x – arithmetic mean, x – observed values, n – number of observations.

Percentage mean deviation (PMD)This is the ratio between the mean deviation and mean, expressed as a percentage. This is used to compare two samples with different mean values.

3. Standard deviationThe average gives little or no indication as to the amount or type of variation in the quality of the material nor does it indicate the variation is due to the process or inherent in the product. To find answer to these questions, it is only necessary to calculate Standard Deviation.


The Standard deviation “is defined as the root of mean square deviation of number from average”. In other words Standard deviation is the measure of the amount of variation from the average set of data.

Merits The standard deviation is rigorously defined.

It is based on all observations of a series.

It is capable for further algebraic treatment.

It is least affected by fluctuations in sampling and hence stable.

It is free from the mathematical weakness of ignoring the sign of

It is the most important means of absolute dispersion and is a keystone in samplingcorrelation.

Demerits It is difficult to compute as compared to other measures.

It attaches more weight to extreme values and less to those nearer the mean.

In a distribution with openregarding the size of the class interval of the open

4. Co-efficient of variationA frequently used relative measure of variation is the coefficient of variation, denoted by CV. This measure is the ration of standard deviation to the mean expressed as the percentage.

Coefficient of Variation CV = (SD

Where SD – standard deviation, x

5. Standard ErrorThe Standard error of the mean by dividing the standard deviation of the sample by the square root of the number in the sample.

Where SE – Standard error, SD –

The Standard deviation “is defined as the root of mean square deviation of number from average”. In other words Standard deviation is the measure of the amount of variation from the average set of data.

The standard deviation is rigorously defined.

It is based on all observations of a series.

It is capable for further algebraic treatment.

uctuations in sampling and hence stable.

mathematical weakness of ignoring the sign of the deviations.

It is the most important means of absolute dispersion and is a keystone in sampling

It is difficult to compute as compared to other measures.

to extreme values and less to those nearer the mean.

In a distribution with open classes, its value cannot be calculated without regarding the size of the class interval of the open-end classes.

tive measure of variation is the coefficient of variation, denoted by CV. This measure is the ration of standard deviation to the mean expressed as the percentage.

SD/ x) x 100

standard deviation, x - mean

The Standard error of the mean by dividing the standard deviation of the sample by the square root of the number in the sample.

– Standard deviation, n- number of observations.

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The Standard deviation “is defined as the root of mean square deviation of number from average”. In other words Standard deviation is the measure of the amount of variation from the

he deviations.

It is the most important means of absolute dispersion and is a keystone in sampling and

to extreme values and less to those nearer the mean.

classes, its value cannot be calculated without assumptions

tive measure of variation is the coefficient of variation, denoted by CV. This measure is the ration of standard deviation to the mean expressed as the percentage.

The Standard error of the mean by dividing the standard deviation of the sample by the square

number of observations.


4. Atmospheric Conditions

Conditioning & Textile TestingMost of textile materials are hygroscopic in nature. They have ability to absorb or give up

moisture. The moisture is picked up or absorbed by hygroscopic material from atmosphere, if the relative amount of moisture in the air is greater than in the material. Conveniently, the moisture will be given up by the material if the relative amount of moisture in the air is less than that in the material. Equilibrium is said to be established between the material and atmosphere, when one way of flow is obtained it, that is whatever is given up by the material to the atmosphere the same thing is taken from the atmosphere, by equilibrium with the atmosphere in which it is placed known as conditioning.

Humidity Humidity is defined as the amount of moisture present in the atmosphere.

Absolute Humidity & Relative HumidityHumidity is the term used to describe moisture existing in the atmosphere. Humidity term

is used to describe the dampness of the atmosphere. The amount of moisture contents in the air may be expressed namely

1. Absolute humidity (AH)Absolute humidity is defined as the weight of water vapour in a unit volume of moist

air and is expressed as grains per cubic foot or grams per cubic meter. Absolute humidity is the actual density of water vapour in the atmosphere.

2. Relative Humidity (RH)Relative humidity is defined as the ratio between actual vapour pressure and saturated

vapour pressure at the same temperature and this is normally expressed as a percentage. The ability of air to hold moisture depends upon its temperature. Higher the temperature more moisture can hold. Relative humidity can be defined by the following equation.

Standard Testing Atmosphere Standard atmospheric condition for nearly all textile materials is RH 65%±2% and temperature - 20° ± 2° or 68° ± 4° . In tropical and sub-tropical countries, the difficulties of achieving the temperature 20° are understood and so the higher standard temperature may beused, say 27° ± 2° or 81° ± 4° . ISI (Indian Standard Institute presently known as Bureau of Indian Standard) standards are RH 68%±2% and temperature 27° ± 2° .


Recommended optimum conditions for different textile manufacturing process are: 40% to 45% RH at 72° to 75° Blow room, 65% RH at 75° for carding, 53% RH at 75° for spinning. During knitting and weaving high RH is helpful to reduce breakages.

Conditioned weight is the weight of the material when it is conditioned.

Measurements of Atmospheric ConditionsInstruments used in determination of Relative Humidity are known as hygrometer. The

following methods may be used to measure the atmospheric conditions.

1. Wet & Dry bulb hygrometer

PrincipleIf it can be so arranged that a thin film of moisture (water) always surrounds of a

thermometer, the temperature indicated by the thermometer would the humidity of the surrounding atmosphere. If the surrounding air is not saturated moisture, water evaporates from the bulb into the air at a rate that is proportional difference between the actual humidity and 100% humidity. Since cooling takes with evaporation, the temperature indicated by the thermometer will be less than the room temperature.

The drier the atmosphere the greater the amount of moisture evaporating from the bulband the greater will be the cooling. The thermometer will thus show a much lower temperature atmosphere were relatively humid. It is this principle of gauging the humidity of a given atmosphere that is used in the design and working of a wet and dry bulb hygrometer.Description

Wet & dry bulb hygrometer is shown in figure. It consists of a frame A on which two identical thermometers, B & C are mounted. A muslin sleeve D, which is dipped into a container E containing distilled water F, covers the bulb of thermometer C. This thermometer is therefore called the ‘wet bulb thermometer’. The bulb of the other thermometer B is left open to the atmosphere. This thermometer is thus called the ‘dry bulb thermometer’ and the temperature it shows is referred to as the dry bulb temperature, which is of course the room temperature. The wet bulb temperature is on most occasions lower than the dry bulb temperature. In an atmosphereof 100 % RH, both the thermometers would indicate the same temperature.

The instrument comes with an RH table that displays a series of values of the dry bulbtemperatures in the extreme left column and increasing values of the difference between the wet and dry bulb temperatures along the top row.Determination of relative humidity

A wet and dry bulb hygrometer is usually mounted on the wall of a testing room or anyplace where the relative humidity is to be monitored. The procedure of determining the RH of an atmosphere is simple. The wet bulb and dry bulb thermometer is placed in the atmosphere until the mercury levels in both of them attain constant positions. The wet bulb and dry bulb temperatures are then noted. The difference between these two temperatures is worked out.


The RH table is then used to read out the RH of the atmosphere being evaluated. This is done by locating the dry bulb temperature in the left-most column and then moving rightward along the row till the column corresponding to the difference between the dry and wet bulb temperatures is reached. The RH value at the meeting point is the RH of the atmosphere.

An exampleDry bulb temperature = 30.6°CWet bulb temperature = 22.2°CDifference = 8.4°CRH% read from the table = 43%

2. Hair Hygrometer

Principle of workingThe hair hygrometer, as the name suggests, uses a strand of human hair as an important

element in the instrument. A significant characteristic of human hair is that its length varies with changes in the humidity of the surrounding air. If the humidity is high it elongates and if it is low it contracts. In order to utilise this property to good effect it is necessary to connect a thin bundle of human hair to a suitable lever system, so that the humidity can simple be read off a dial.


DescriptionA typical arrangement of the components of a hair hygrometer is depicted in Figure. The

principle parts are a circular glass cover A, a graduated RH% scale B and a pointer C. Thepointer is connected to a band of human hair.Determination of relative humidity

The instrument is normally kept in the testing room itself The RH% of the atmosphere isindicated on the scale and can be read off easily at any time. The fact that this instrument does not use distilled water may be an advantage. However the hair hygrometer is rarely used today as it responds very slowly to changes in the surrounding humidity. This is a major disadvantage and the hygrometer has therefore to be checked and calibrated often. The RH % indicated by it can best be taken only as an approximation of the actual value.

3. Thermo hygrographA thermo hygrograph is accomplished by hair hygrometer and it has the additional

feature of measuring the room temperature. A helical coil of a bimetallic strip has the distinctive property of increasing or decreasing in length as the temperature of the surrounding air increases or decreases. If a bimetallic coil is connected suitably to a lever system, it can be used to measure the room temperature.


A schematic diagram of a thermal-hygrograph is shown in the figure No. 2.2.2. This instrument records both temperature and RH% on a graph paper chart. A sensitive bimetallic coil that is connected to a lever records the temperature while a band of human hair attached to another lever record the RH%.

The Instrument consists of two-pen A and B, actuated by two levers C and D, and respectively records the temperature and RH% on a graph sheet or chart E. The graph sheet is fixed around a cylinder or drum F. A clockwise system connected to a bimetallic coil H and the other pen B on a band of hair G. The chart is divided into two portions. The upper portion is used for recording temperature and lower portion is used for recording RH%. The chart is further divided into seven columns, each column representing a day of 24hours.

This system rotates the cylinder automatically at a definite speed. At the same time the pens record temperature and RH% on the chart according to the prevailing condition of atmosphere. The readings are noted at periodic intervals of a time every day. After a week time the chart is removed and day to day variation in temperature and humidity is noted and analysed.

Advantages:1. It is a direct reading instrument.2. It records both temperature and RH%.3. It records temperature and RH% value and later it is analysed.4. The use of distilled water is eliminated.


4. Electrolytic hygrometerIn an electrolytic hygrometer, variations in the electrical resistance of lithium chloride

with varying humidity are converted by a suitable arrangement to give a direct reading of the surrounding humidity.

An electrolytic hygrometer consists essentially of a plastic frame carrying electrodes covered with platinum. The electrodes are wound with a skein of fine fibres impregnated with lithium chloride. The electrodes are wound with fine fibres impregnated with lithium chloride. An electric supply of constant voltage is connected to the electrodes. A graduated circular dial for RH% and a pointer to indicate the ambient RH are also connected.

When the instrument is switched on, the current flowing through the element is subject to changes in the humidity in the atmosphere. Variations in the current are translated into appropriate movements of the pointer, which shows the RH reading on circular scale.


5. Measurement of moisture Regain &Moisture Content

There are two ways of expressing the amount of moisture in the textile material.

Moisture Content: Moisture content or moisture is the weight of moisture (water vapour) present in the textile material expressed as a percentage of its total weight.

Moisture Regain: Moisture regain is defined as the weight of moisture in a textile material is expressed as a percentage of its oven dry weight.

The moisture content and moisture regain of a fibre can be determined in the laboratory by means of the following instruments:

1. Moisture Measuring oven- a direct method 2. Shirley Moisture Meter - an indirect method

1. Moisture Measuring Oven This is a direct method of assessing the amount of moisture in textile materials.Principle: - A sample of known weight is heated in a special oven at a temperature of 105 ± 3ºCfor 1.5 to 2 hours to constant weight or oven-dry weight. The difference between the original weight and the oven-dry weight of the sample gives the weight of moisture present in the sample.

The moisture in the sample is expressed as a percentage of its original weight to get themoisture content of the sample. Similarly, expressing the moisture in the sample as a percentage of the oven-dry weight of the sample gives its moisture regain.

Description: - below Figure shows a moisture-testing oven. It consists of a double-walled chamber A, the walls of which are packed with an insulating material like glass wool to minimise loss of heat. Two portions can be identified with regard to the chamber, the upper portion C and lower portion D.

The lower portion houses the heating elements, a temperature-set knob E and a thermostatic control. The thermostat consists of the typical bimetallic rod which senses and controls the temperature inside the chamber. It is connected both to a red light G and a green light H. A main switch I is connected to the power supply. A blower fan F is provided inside the instrument at the right-hand side of the chamber circulating the hot air inside. The middle portion of the chamber has accommodating a cage J that carries the sample under test.

The upper portion of the chamber has a balance K; the right-hand side pan L of balance carries a standard weight of 50 grams (M). The left-hand side pan N is connected to the cage. Weights corresponding to the loss in weight of the sample as it dries can be put in this pan to counterpoise pan L. This arrangement helps to determine the weight of water inside the chamber without disturbing the sample.


Procedure to determine fibre moisture content and moisture regain: - 50 grams of the sample are placed in the cage inside the chamber, so as to balance the 50-g weight in the righthand pan. The oven is switched on and the heating elements are turned on. A continual How of air at the correct RH (ideally air at standard RH and temperature) is passed through the oven. The thermostatic control is set at 105°C.

The air flowing into the chamber starts getting heated and when the temperature issufficiently high the moisture in the fibre sample will start evaporating. Care is taken that the thermostatic arrangement maintains the temperature inside the chamber within ± 2°C of the set temperature of 105°C.

After about 1.5 hours of heating, the weight of material will have reduced due to themoisture being evaporated from it. A suitable weight is now placed in the left-hand side pan such that it exactly balances the other pan. Weighing is done at every 10 minutes until a constant weight is obtained. This means that all the moisture from the sample has been removed. The total of the weights in the left-hand pan is the amount of moisture present in 50 grams of the sample.

The oven-dry weight of the sample is calculated as the difference between the original weight of the sample and the weight of the moisture present in it.


Moisture content & regain can be calculated by using the following formula:

Moisture content (M)

= Weight of moisture in the sample / Original weight of the sample X 100

Moisture Regain (R)

= Weight of moisture in the sample / Oven weight of the sample X 100

The main advantage of a regain-testing oven is that all the, weighing is carried out inside the oven. This means that the instrument avoids the need to carry the sample to a separate balance, in which case it could gain in moisture and lead to erroneous results.Further large samples can be tested. In fact this is by far the most accurate method estimating regain of a large sample. It serves as a benchmark for accurate testing of fibre regain and other methods can be checked against it for accuracy.

Conditioning ovenA modified version of the moisture testing oven has also been in use. This has an

additional feature. In this version, the relative humidity of the air in the oven can be set to a desired value within a given range. This improvement allows both the temperature and the humidity in the chamber to be set. Known as the ‘conditioning oven’ this equipment permits the determination of moisture of a given sample at specific values of humidity. The sample is allowed to ‘condition’ at the set value of RH for a few hours and its weight is determined. Next its oven-dry weight is determined as explained above. The difference between these weights expressed as a percentage of the oven-dry weight gives the regain of the RH in which it was conditioned.

2. Shirley Moisture Meter - an indirect method

This instrument is based on an indirect method of measuring amount of moisture in textiles. It used the principle of variation in electrical resistance with moisture. When the fibre is dry, the resistance to flow of electrical current will be at the practical maximum and when it is wet the resistance will be at maximum level. This property of the textile fibre permits the use on an electrode by means of which the electrical resistance of a given fibre can be measured and its moisture regain can be read off a suitably calibrated dial.

DescriptionThe regain indicating unit and a sectional view of the two electrodes are shown

respectively in the below. The Shirley moisture meter consists of an electrode A fixed in a holder B. the electrode consists of an insulating material in between central and outer conducting materials. It is connected by means of cable C to the regain indicating unit.


The regain indicating unit has two dials D & E. Dial covers the normal range of regain values from 7% to 11%. The other dial E, has two ranges, one with a range 9 to 15% regain for testing damp or wet fibres and other with a range 5% to 9% for testing dry fibres.

Out of two electrodes, one is designed for the use of raw cotton fibre and the other for yarns. The angular space between the conducting elements in the electrode is greater for yarns than it is for cotton.

Procedures for the determination of sample regain The instrument is switched on

Depending upon whether loose fibre or cotton yarn is tested, the appropriate electrode us selected and fitted into holder.

The scale – select knob, S is set to the required scale depending upon whether the test sample is wet or dry.

Then the Zero-set position under the chosen scale is selected using the same knob and the pointer on the chosen scale is checked to see whether it indicates exactly zero. If not, Zero adjust knob (F) is turned till the pointer reads Zero.

Next, knob S is turned to the max-set position and the pointer is checked to whether it accurately coincides with the maximum reading on the scale.

Once the selected scale has been calibrated, knob S is turned to the testing mode.

A sample is pressed by the sensing end of the electrode. A firm pressure is applied to the holder in order to bring the electrode and sample in close contact.

The moisture in the sample is noted on the chosen scale.

The numbers of readings are taken at various parts of the material and the average value of regain is recorded.

Advantages: 1. this instrument over the moisture testing oven is the speed of the test. 2. It has easy-to-read scales. 3. The instrument is compact and portable. 4. It is suitable for the routine test of bleached or undyed fibres or yarn.

6. Effects of Moisture Regain on Fibre Properties

Under the natural condition, the amount of moisture in the atmosphere is continuously changing. These results in varying amount of moisture contained by the hygroscopic material exposed to the atmosphere. Many physical properties of textile materials are affected by amount of moisture contained in it. Fundamentally the weight of the material is depends upon the humidity of the atmosphere in which it is exposed. The greater the humidity is greater the weight of the material. The greater the moisture contents greater the loss to the buyer of the material.


So the textile transaction, when the weight is in consideration, like cotton, silk trade etc., it is very much necessary to standardize the moisture contents.

Apart from the weight, the moisture also affects in dimension, tensile strength, elastic recovery, electrical resistance, rigidity etc., of textile materials. Cotton absorbs moisture readily when exposed to high humidity and as results, the weight as well as strength increased and other properties change. Linen shows substantially increase in strength as the moisture content is increased. Rayon generally shows reduction in strength with corresponding increase in elongation as the moisture contents are increased. These changes are high on viscose rayon and low on nylon & Dacron. Animal fibres show slight decrease in strength with increase in moisture contents. Practically all textile material show increase pliability and greater immunity to static electric influence with increase in moisture contents.

Textile manufacturing operations are conducted to large extent in a humidity atmosphere. Under ideal humidity condition the following advantages realized in.

1. Reduction in generation of static electricity.2. Materials are more easily workable due to increased pliability.3. Reduction in amount of dust and fly.4. Allows for the retention of the moisture already within the material. 5. Permits greater bodily comfort for personnel in cool weather.

Some of the man-made textiles fibres have high relative regain where as other resist the absorption of water. Fibres that absorb moist readily are classified as “HYDROPHYLIC” material, ex. Cotton, and that do not are classified as “HYDROPHOBIC” material, ex. Terylene, nylon.

Effects of Regain on Fibre properties It has been mentioned in the preceding sections that fibre properties are affected,

sometimes dramatically, by regain. The major effects of regain on fiber properties discussed in the following.

Fibre dimensionsAbsorption of moisture changes the dimensions of fibres. It is well known that fibres

swell with increasing moisture absorption. Swelling causes a greater increase in the width of the fibre and a marginal increase in its length.

As the water molecules enter and penetrate the fibre, they break a number of the intermolecular hydrogen bonds in the fibre, and separate the molecules and thus swell the fibre in a width-way direction. As the molecules are now in a more relaxed state, they tend to cause some increase in the length of the fibre. With regard to the effect of moisture on a textile fabric, the net result of absorbed moisture is a decrease in length i.e. shrinkage


Mechanical propertiesThe strength of fibres is affected by moisture. In the case of vegetable fibres such as

cotton and flax, the strength is increased from 8 to 10 per cent. In the case of viscose rayon, the strength is decreased by about 50 per cent. All other fibres show a drop in strength with increasing moisture except for polyester and polypropylene fibres, which are unaffected.

Similarly Extensibility, crease recovery, pliability (opposite of stiffness) and the abilityto be set by finishing processes are the other mechanical properties affected by regain. Fabric handle and drape is associated primarily with the stiffness of the fabric. The drier the fabric the stiffer it will be and vice versa.

Electrical propertiesThe electrical resistance of a fiber varies with different regain values. When the sample

is dry, resistance to the flow of electrical current will be at a practical maximum. When it is wet, the resistance will be minimum. The dielectric characteristics and the susceptibility to static troubles are also affected by the amount of moisture in the material.

The hydrophobic synthetic fibres are notorious for their proneness to static problems on account of their negligibly low moisture regains.

Thermal effectsWhen textile materials absorb moisture, heat is generated, i.e. they tend to be

exothermic. This heat is referred to as the ‘heat of absorption’ or sometimes ‘heat of wetting’.An example of clothing is cited to explain this effect. In a place which normally

experiences severe winter, if a person goes from a warm room with a low RH% into a cold environment with a higher RH% (i.e. from indoor to outdoor) the clothes worn by the person absorb more moisture and heat is generated. This heat acts like a warm blanket around the person and shield her/him body from the sudden large drop in temperature suffered in process. Wool is ideal in this respect as the heat of moisture absorption it produces is high.

Factors Affecting fiber regainThere are four major factors that can affect the regain of textile fibres. These are

explained below.

1. Relative humidityThe regain of a fibre increases rapidly at low humilities, and then it increases at a low

rate, showing an almost linear portion in the absorption curve. Finally, it rises at more rapid rate at high humilities. This behaviour can be easily seen in the absorption curves of the fibres shown in to cite a real life instance; a towel that is dry in normal air would feel moist after some time in a Turkish (steam) bath, where the humidity is usually very high.2. Time

A relatively dry fibre placed in a given atmosphere takes a certain amount of time toreach an equilibrium regain value. Beyond the equilibrium time, the fibre continuously gains and


losses small quantities of moisture such that it maintains equilibrium regain. This result isobtained so long as the relative humidity of the surrounding atmosphere is maintained constantly at a given value.

Standard Regain Value of Textile MaterialsStandard regain is the regain of the material is obtained under standard test condition

when absorbed from dry side. Standard regain of different textile materials are1. Cotton - 8.5%2. Silk - 11.0%3. Wool (Carbonised) - 17.0%4. Scoured wool - 16.0%5. Yarn (woollen/worsted) - 18.25%6. Cloth (woollen/worsted) -16.0%7. Viscose – Cupramonium rayon -11.0%8. Jute -13.25%9. Flax and Hemp - 12.0%10. Nylon - 4.5%11. Orlon - 2.0%12. Dacron - 0.4%

“Commercial Regain” is the standard adopted for commercial transaction. These are arbitrary figures and generally very closed to standard conditions.

Corrected Invoice weight When textile materials are bought and sold by weight, it is necessary for there to be

agreement between buyer and seller on the exact weight that has to be paid for. This value can vary considerably with the moisture content of the material which in turn varies with type of material, the atmospheric moisture content at the time and how wet or dry the material was before it was packed, among other factors. The buyer certainly does not wish to pay for excess water at the same price per kilogram as the textile material. A 'correct invoice weight' is therefore determined according to. In this procedure the consignment is considered to contain a percentage of water known as the standard regain allowance and the weight of the consignment is calculated as if it contained this amount of water.

When a consignment of textile material is delivered and weighed, a sample is taken from it on which tests are made which enable the correct invoice weight to be calculated. Samples of at least 200gm are selected according to adequate sampling procedures and immediately stored in airtight containers so that no moisture is lost. The samples are weighed and then the oven dry weight is determined as described above. In some cases other non-textile materials, such as oils, grease, wax and size, are removed before drying.


If M — mass of consignment at time of sampling, D = oven dry mass of sample, S = original mass of sample and C = oven dry mass of the consignment:

The regain allowances vary depending on what physical state the material is in, for example woollen yarn 17%, worsted yarn 18.25% , oil combed tops 19% , wool cloth 16% .

Where R1 is Commercial regains value

If the samples are dried after cleaning a different set of allowances is used for moisture and oil content, etc:

Where R2 is the moisture regains which may differ from R1, A2 is the allowance for natural grease and B2 is the allowance for added oil. In most cases an overall allowance is given which includes the values for moisture and natural and added fatty matter.

In the case of a blend the overall allowance is calculated from the fraction of each component in the blend multiplied by its regain value, for example: 50/50 wool / viscose (dry percentages)


Unit II

1. Measurement of linear Density (Yarn Count)

Yarn Fineness or Count In practice, yarn fineness is typically described by terms such as yarn count, yarn number, or yarn size. The subject of yarn fineness can be treated in a similar manner to that of fiber fineness in the sense that both the fiber and the yarn may not have perfectlycircular cross sections and they both exhibit thickness variability. Therefore, the linear density or mass per unit length is commonly used as an alternative measure of actual fineness or thickness.

In general, three yarn count systems are commonly used:1. The direct system and2. The indirect system.3. Universal Count System

Yarn count is an important characteristic. All the purchases and sales are made on the basis of count of yarn. A type of machinery and also setting of the machinery depend on count of yarn. A setting is made to spin particular count cannot be employed to spin different count. Adjustments are to be made at every stage of processing so as to get required count of yarn, so for manufacturing of the fabric. The setting of the machinery depends upon count of yarn. So from the point of view of the buyer and seller, technologist’s point of view, and also from point of view of imitation and quality control, testing of yarn is necessary.

Count denotes size of the yarn, i.e. whether the yarn is thick or thin, heavy or light. Owing to the fact the material from which is made is highly variable and process also to some extent imposes further unevenness. The count of yarn is not absolutely constant throughout the length of yarn. The size of the yarn is a measure of diameter. But measurement of diameter is not easy for many reasons. Any instrument used to find out the diameter could compress the yarn so the result obtained depends upon force applied. Therefore, usual methods of measuring the size of the yarn are either ratio to length and weight or weight to length.

Technically ‘yarn count’ signifies the relationship between length and mass of yarn and it is from this relationship that the term ‘linear density’ is also much in use. Linear density is the general term, used more frequently for fibres. Both the terms count and linear density have been used interchangeably in the textile world, difference exists between the two. While count is a number indicating “length (of yarn) per unit mass, linear density is a number signifying “the mass (fibre or yarn) per unit length.

The following methods are used for count determination1. Wrap reel and weighing balance method 2. Direct reading count balance – Knowles balance, Quadrant balance, Beesley’s Balance, Auto

sorter.


1. Wrap Reel & Weighing Balance Method

Wrap reel (Length measurement)common type of wrap reel is shopackage B, a traverse guide C and a swift D. The perimeter of swift varies from one model to another and it may be 1 yard or 1½ yard or one meter. The wrap reel also has a length indicator E and a warning bell F to tell the operator when the set number of revolutions has been obtained. Wrap reel may be hand driven, by means of handle G, or motor may be used to drive them.

In general, where cotton yarns are to be evaluated, the swift normally has yard) perimeter so that 80 revolutions of the reel produce a ‘lea’ of 120 yards.

Where the use of metric and Tex system of yarn numbering, a wrap reel with a one meter perimeter is used and 100 metres or 50 metres skeins are reeled for deter

In order to obtain accurate results, the following three conditions are necessary.

Yarn must be spread out on the reel so that each revolution will reel off exactly the same length of yarn.

Tension must be constant and neither too much

The speed of the reel must be constant.

Wrap Reel & Weighing Balance Method

Wrap reel (Length measurement): The length of yarn is obtained by the use of wrap reel. A common type of wrap reel is shown in below figure. It consists of a creel A to hold a yarn package B, a traverse guide C and a swift D. The perimeter of swift varies from one model to another and it may be 1 yard or 1½ yard or one meter. The wrap reel also has a length indicator E

warning bell F to tell the operator when the set number of revolutions has been obtained. Wrap reel may be hand driven, by means of handle G, or motor may be used to drive them.

In general, where cotton yarns are to be evaluated, the swift normally has yard) perimeter so that 80 revolutions of the reel produce a ‘lea’ of 120 yards.

Where the use of metric and Tex system of yarn numbering, a wrap reel with a one meter perimeter is used and 100 metres or 50 metres skeins are reeled for determination of count.

In order to obtain accurate results, the following three conditions are necessary.

Yarn must be spread out on the reel so that each revolution will reel off exactly the same

Tension must be constant and neither too much or too little.

The speed of the reel must be constant.

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: The length of yarn is obtained by the use of wrap reel. A . It consists of a creel A to hold a yarn

package B, a traverse guide C and a swift D. The perimeter of swift varies from one model to another and it may be 1 yard or 1½ yard or one meter. The wrap reel also has a length indicator E

warning bell F to tell the operator when the set number of revolutions has been obtained. Wrap reel may be hand driven, by means of handle G, or motor may be used to drive them.

In general, where cotton yarns are to be evaluated, the swift normally has a 54 inch (1½

Where the use of metric and Tex system of yarn numbering, a wrap reel with a one meter mination of count.

Yarn must be spread out on the reel so that each revolution will reel off exactly the same


Weight Measurement Weighing of the yarn may be made by

i. Grain scales at room conditions.ii. Analytical balance at room conditionsiii. Analytical balance and drying oven.

The grain scales are used in general for determining weight of skeins of yarn at room conditions. These are calculated in grains and a simple calculation gives the count of the yarn if standard skein is weighted.

Analytical balance gives more accuracy than is usually necessary and are valuable principally determining count or denier form small lengths of yarn.

A more accurate method is to weigh the skein, when they are oven dry. So called conditioning ovens, usually supplied to the Textile industry, consist of an oven with analytical balance accurate to 1 centigram or to 1/10th of grain mounted on it. These are sufficiently accurate for count determination.

Calculation of Counts The formulae for calculating counts and denier from length and weight determination

are as follows

Where, N – Count or Number, L – length in yards, W – Weight at standard regain in grains, H –length of standard hank in yards

2. Knowles balance (A direct Reading Method)

This is direct-reading yarn count balance. It is only suitable for the test specimen can be prepared in the form of lea. Yarn Knowles balance uses fixed mass and a fixed length of test yarn to give a direct reading of yarn count on a special scale. A 120 yard length of yarn is counterpoised against a standard mass in a modified version of an ordinary two pan balance. The yarn count is simply read off the scale graduated in Ne. Description

A Knowles balance is shown in fig. It is an ordinary physical balance with slight modifications. C is the main beam of the balance and D is the pointer, behind the beam, is a rectangular board F mounted on pillar G. The board contain seven scales, marked from A to G and graduated in different ranges of English Cotton count, as shown in the table below. E is a scale knob connected to the count board and helps the board to move up and down to select any required count scale.


Table:Scale

DesignationABCDEFG

Standard Weights and Rider WSeven circular standard weights are a part of the Knowles balance. Each of these weights

are marked respectively A to G, to correspond to the seven count scales A to G. If for example, Scale C is selected for use, then standard weight C should be usdesigned that any chosen weight, corresponding to a particular count scale, has to be used in the left-hand pan. Procedure to Determine the Count of Yarn1. The approximate count of the test2. The scale-select knob is then operated to choose scale corresponding to the visual estimated

count. Ex. If the test yarn is approximately 40

Scale Designation

NeC Count Range

2s to 8s

6s to 24s

20s to 40s

35s to 65s

58s to 88s

80s to 110s

100s to 130s

Rider WeightsSeven circular standard weights are a part of the Knowles balance. Each of these weights

are marked respectively A to G, to correspond to the seven count scales A to G. If for example, Scale C is selected for use, then standard weight C should be used and so on. The balance is so designed that any chosen weight, corresponding to a particular count scale, has to be used in the

Procedure to Determine the Count of YarnThe approximate count of the test yarn is first assumed visually.

select knob is then operated to choose scale corresponding to the visual estimated the test yarn is approximately 40s , then the scale D is selected.

Page 31

Seven circular standard weights are a part of the Knowles balance. Each of these weights are marked respectively A to G, to correspond to the seven count scales A to G. If for example,

ed and so on. The balance is so designed that any chosen weight, corresponding to a particular count scale, has to be used in the

select knob is then operated to choose scale corresponding to the visual estimated , then the scale D is selected.


3. Standard weight corresponding to the chosen scale is placed in the left hand pan of the balance.

4. The rider corresponding to the chosen scale is placed on the beam, at its middle.5. At least 10 leas of the test yarn are prepared on a wrap reel, taking the precaution mentioned

earlier.6. One of the leas is placed on the right hand pan of the balance. The balance knob is turned

clockwise and the lea is counterpoised against the standard weight in the other pan by sliding the rider to the left or the right as required, so that the two pans are evenly poised as indicated by the even swing of the pointer.

7. The count of lea is then read off on the chosen scale at the point coinciding with the position of the rider on the beam.

8. Remaining leas are tested as above and the mean value of the count is reported as the count of the test yarn.

Advantages This kind of balance is easy to use and requires no special practice in operation.

The test can be done very quickly, as no calculation is required.

Knowles balance is a good choice for routine count test in spinning mill.

The balance can be adapted to other count system by appropriately changing the count scales.

3. Quadrant BalanceLike Knowles balance the quadrant balance too is a direct reading yarn count balance. It

gets the name from the fact that its scale is shaped like the arc of a quadrant. A standard length of yarn is hung from a hook attached to one end of the main beam of the quadrant balance. The count is directly read off on the scale that corresponds with the length of the specimen.

The salient feature of the quadrant balance is shown in the below fig. The main beam A, of the balance has a hook B at one end and a counter weight at the other end. The beam is pivoted at the end of the horizontal rod fixed to a rigid pillar D, on which is also mounted curved plate E, referred to quadrant scale. Three scales are engraved on the plate, Pointer F is fixed to the beam at the point where the beam itself is pivoted. When the sample hook is empty and beam is at rest, the pointer hangs freely and so lower end coincides with a vertical datum line G on the curved set of scales.

The graduations on the three scales of the curved plate are as follows.i. The upper most scale is for reading the mass per square yard of the test fabric in

ounces. ii. The middle scale is for reading yarn count for 8-yard length of the test yarn.iii. The bottom scale is for reading of yarn count using 40-yard lengths of yarn.


Procedure to Determine the Count of YarnLevelling: Before the start of the test, the instrument is checked to see that it is levelled properly. This is achieved by ensuring that the pointer coincides with the datum line when the main beam is at rest and its hook is empty.Calibration: The instrument is calibrated by using the standard weight H marked 40s and supplied with the instrument. The weight is hung on the sample hook of the beam. The pointer should read 40s on 40-yard scale. For 8-Yard test specimen:

An 8 – yard test specimen is drawn in one of the two ways.i. By measuring the yarn against a yard scaleii. By winding the yarn around a one-yard template.

Care should be taken uniform tension is maintained. The pointer swings along the scale and comes to rest. Finally the yarn count is read off and recorded.

For 40-yard test specimen A 40 – yard sample is drawn as explained above.

It is coiled up and hung on the sample hook. This time the count is read off. Nine more specimens are tested and mean count of yarn is calculated.

Mass per unit Area of fabric The upper most scale of the balance is used to determine the mass per unit area of fabric. A

square or circular standard template with an area of one-hundredth of a square yard (12.96 sq. inch) is used to cut off test specimens of the fabric. The specimen is placed on the sample hook and the reading of the pointer noted on the mass-of-fabric scale in terms ounces per square yard.


Advantages and disadvantages of the quadrant balance:1. The quadrant balance is an easy-to-use balance.2. Tests can be done very quickly, as no calculations are required.3. The balance can be adapted to the other count systems by appropriately changing the

count scales. Some quadrant balances are available these days in which mass per unit area of fabric can be read off in grams per square metre.

4. Short lengths of yarn up to 40 yards or so and fabric pieces of about 100 cm2 are enoughfor tests on this balance.

5. The accuracy of the balance is definitely lower than the Knowles balance and is limited to the graduations on the count scale. This is especially so in the larger count range for both the 8-yard and the 40-yard scales, where the graduations are so close that intermediate values can be assessed only approximately. It is therefore suitable only for an approximate estimate of yarn count.

4. Beesley’s BalanceA Beesley’s-type balance is used to find out the count of yarn removed from a small

sample of cloth. It therefore uses much shorter lengths of yarn for a test than the Knowles and quadrant balances. The special advantage of this kind of balance is that it is available in a compact size so it is portable.Principle:

The principle of a Beesley's balance is similar to a common balance, except that no pans are used here. Standard lengths of warp or weft threads removed from a fabric of specific dimensions are counterpoised against a standard weight. The number of threads that exactlybalances the standard weight is the count of the yarn under test.Description:

A typical appearance of this kind of balance is shown in the figure. 'A' is the beam of the balance pivoted at C on a rigid pillar B. The beam has three features. The first is that there is a sample hook D attached to its right end; the second is that it has a tapered left end that also serves as a pointer E; and thirdly, it has a notch F about midway on its left-hand section. Thestandard weight, G that comes as a part of the balance is hung on the notch during a test. With no sample on the hook and no weight in the notch, the pointer E of the beam coincides with an index mark H on another pillar I.

The instrument also comes with a template K. The edges of the template are the standard lengths to which the warp or weft threads in a test fabric are cut under different systems of yarn count. For example, the edge WP of the template represents a "full-cotton" length. If only a very small piece of the test fabric is available, the edge PQ of the template is used to measure off the threads. This is the "half-cotton" length. Similarly, the other edges ST, VW, XS and QYrepresent the standard lengths meant for woollen, linen, worsted and metric count systems respectively.


The standard weight G is used for all tests of yarnsystem. For the "half-cotton" length alone a smaller standamass than G is used. As the beam is light, air draughts could interfere withdoes in a physical balance. The instrument is therefore always enclosed in a glassbe temporarily open at the front for

A –Beam B- PillarC- PivotD-HookE-Pointer F-Notch G-WeightH-Index MarkI-PillarJ-ScrewK- Template

The standard weight G is used for all tests of yarn count determination irrespective of the cotton" length alone a smaller standard weight of correspondingly lower

As the beam is light, air draughts could interfere with accurate testing as it instrument is therefore always enclosed in a glass

be temporarily open at the front for operator convenience.

K

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count determination irrespective of the correspondingly lower

accurate testing as it instrument is therefore always enclosed in a glass casing that can


Procedure to determine yarn count

a. Levelling the instrument: When the beam is free of test specimen and the standard weight, its pointer should be exactly in line with the index mark H. Any deviations can be set right by adjusting the levelling screw J.b. Determination of count: First of all, place the standard weight G on the notch of the beam; if the half-cotton length on the template is to be used, use the smaller standard weight instead. Next, the test fabric is laid flat and a square of fabric is cut off with a sharp blade. The side of the square should be about 1 1/2 times longer than the standard yarn length required to be used. The warp and weft threads are unravelled from the fabric, taking care to keep them separately.

The warp threads are then taken, a few at a time, aligned parallel to each other, and straightened to just remove crimp. The straightened set of threads is held parallel to the required edge of the template and cut off using a sharp blade. A number of warps threads are cut off thus from the unravelled threads.

The warp threads of the required standard length are placed on the hook of the beam, one by one,until the standard weight on the beam is exactly counterpoised, as indicated by the coincidence ofthe pointer with the index mark.

The threads on the sample hook are removed and counted. The total number of threads is equal to the count of the warp yarn in the test fabric. For example, if there are 20 warp threads, the yarncount is 20s if the warp consists of single yarn and 2/40s, if it is double yarn. The weft threads unravelled from the test fabric are tested in exactly the same manner as described for the warp threads and the weft yarn count determined.Advantages and disadvantages of the Beesley's balance The balance is easy to operate and the counts of the threads in a fabric can be quickly

estimated.

This instrument is the only alternative if only a small sample of fabric is available for analysis and speed of test is important.

The accuracy is not high as the yarn is decrimped manually for cutting it off to standard length and operator errors could therefore easily occur.


2. Study of twistTwist is the measure of spiral turn given to the yarn to hold the consequent fibres or

threads together. Twisting refers to operation of laying the fibres of single yarn at one angle to the axis of yarn itself. The fundamental purpose of twist enables a long and continuous thread being formed from discontinuous short fibres as they are naturally occurring. It is essential to give binding force to the fibres so that the yarn which enables to withstand stress and sduring the process of manufacture. To make continuous yarn there is no other mean except twisting.

In cotton spinning twisting starts from sliver. In woollen process the condenser webbing will have no twist actually. Twist is to put in only in the fispinning twist is put inserted in final drawing, where the mule frame has a flyer attached to it which inserts twist. In jute and spun silk process twist is first inserted at roving frame. Definition of Twist

Twist may be defined as the hold the component fibres or strands together. Twist is also defined as the helical disposition of the components of a yarn, be they fibre or threads.

Directions of twistThe twist in a yarn may be an S

has S-twist or Z-twist, hold it vertically and observe the direction instrands lie.

S-Twist:The yarn has S-twist if its component fibres or threads

are inclined to the axis of the yarn and are disposed in the same general direction of the central segment of the letter S. This is depicted in the figure.

Z-Twist:Similarly, the yarn has Z-twist if the constituent

or threads are inclined to the yarn axis and lie inthe same direction as the central segment ofshown in the figure.In textile practice, it is customary to have Zyarns and S-twist for weft yarns.

Quantification of Twist (Amount of Twist)Twist has been defined as the number of spiral or helical turns given to a strand in order

to hold the component fibres or yarns together. Therefore twist maof turns per unit length. The length unit is either inch or meter; so “turns per inch” (tpi) or "turns per meter" (tpm). Thus a yin terms of tpm, have a twist of 25

Twist is the measure of spiral turn given to the yarn to hold the consequent fibres or threads together. Twisting refers to operation of laying the fibres of single yarn at one angle to

The fundamental purpose of twist enables a long and continuous thread being formed from discontinuous short fibres as they are naturally occurring. It is essential to give binding force to the fibres so that the yarn which enables to withstand stress and sduring the process of manufacture. To make continuous yarn there is no other mean except

In cotton spinning twisting starts from sliver. In woollen process the condenser webbing will have no twist actually. Twist is to put in only in the final stage of processing. In the worsted spinning twist is put inserted in final drawing, where the mule frame has a flyer attached to it which inserts twist. In jute and spun silk process twist is first inserted at roving frame.

may be defined as the number of spiral or helical turns given to a yarn in order to hold the component fibres or strands together. Twist is also defined as the helical disposition of the components of a yarn, be they fibre or threads.

The twist in a yarn may be an S-twist or a Z- twist. To quickly find out whether a yarn twist, hold it vertically and observe the direction in which its component fibres or

component fibres or threads are inclined to the axis of the yarn and are disposed in the same general direction of the central segment of the letter

twist if the constituent fibres threads are inclined to the yarn axis and lie in general in

the same direction as the central segment of the letter Z, as

In textile practice, it is customary to have Z-twist for warp

(Amount of Twist)Twist has been defined as the number of spiral or helical turns given to a strand in order

hold the component fibres or yarns together. Therefore twist may be quantified as the number turns per unit length. The length unit is either inch or meter; so twist is expressed in terms of

turns per meter" (tpm). Thus a yarn having a twist level of 25 tpi would, tpm, have a twist of 25 × 39.37 = 984.25 tpm.

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Twist is the measure of spiral turn given to the yarn to hold the consequent fibres or threads together. Twisting refers to operation of laying the fibres of single yarn at one angle to

The fundamental purpose of twist enables a long and continuous thread being formed from discontinuous short fibres as they are naturally occurring. It is essential to give binding force to the fibres so that the yarn which enables to withstand stress and strain during the process of manufacture. To make continuous yarn there is no other mean except

In cotton spinning twisting starts from sliver. In woollen process the condenser webbing nal stage of processing. In the worsted

spinning twist is put inserted in final drawing, where the mule frame has a flyer attached to it which inserts twist. In jute and spun silk process twist is first inserted at roving frame.

given to a yarn in order to hold the component fibres or strands together. Twist is also defined as the helical disposition of

twist. To quickly find out whether a yarn which its component fibres or

Twist has been defined as the number of spiral or helical turns given to a strand in order be quantified as the number

twist is expressed in terms of arn having a twist level of 25 tpi would,


If a yarn is designated as 23 Z 16/5 S11 Cotton, it means that the yarn is a 5-ply cotton yarn having a doubling twist of 11 tpi in the S-twist direction; the component single yarns are each of 23 S count and have a twist of 16 tpi in the Z-twist direction.

Relationship between Yarn Count and Twist:One of the important relationships that influence machinery settings in the spun yarn process

is that between yarn count and yarn twist. These two yarn parameters are related by an important factor known as the ‘twist factor ‘or the ‘twist multiplier‘. The relationship is derived in what follows.

The figure shows a schematic diagram of a single element or fibre of a spun yarn as it lies on the surface the yarn. On account of the twist in the yarn, the fibre assumes a helical shape about the fibre axis. So the full line represents the part of the fibre visible in front and the broken line that part of the fibre that spirals around on the other side.

The figure shows one unit length l of the yarn. The fibre AB is shown making one complete turn of the helix around the yarn axis. Let d be the diameter of the yarn and the angle between a tangent to the fibre and the yarn axis (twist angle or helix angle).

Given this information, imagine now that the yarn surface is slit open along a line passing through the ends of fibre AB and the yarn is opened out. It will be realised that the opened out surface layer of the yarn assumes the shape of rectangle ABCD, as shown in the figure.It will also be clear that the fibre is in fact the hypotenuse AB of the right-angled triangle ABC. ABC is the helix (or twist) angle and the circumference of the yarn is equal to AC. The yarn length l is represented by BC.


Let C be the count of yarn, n the twist in the yarn in terms of turns per inch and d the yarn diameter. In A ABC, tanθ = AC/BC

tanθ = πd/ l ..... .. (1)As the yarn twist is n turns per inch and the length of the yarn

twist is l,We have nl = 1(inch) or n = 1

Considering C in terms of Nec, the diameter d of the yarn can be expressed d = 1/ (28 \ √C)Putting these values of n and d in Equation 1, we have, tan θ = π×n×1/ (28 \ √C)

n = tanθ × 28√C / π…….. (2)n = m×√C/π, where m = 2

The factor m is called twist multiplier or the twist factor. This is the relationship between the count and twist in a yarn and the twist multiplier and it can be stated genera

Twists per inch = Twist Multiplier

Twist Angle:As illustrated above, the yarn twist angle is the an

formed by a fibre on the yarn surface and the yarn axis. If the twist multiplier of a known, the twist angle can easily be calculated.Example: Calculate the twist angle of a spun cotton yarn twisted to give a twist factor of 5.Twist factor = 28 tanθ/π 5= 28 tanθ/π tanθ = 5π/28 tanθ = 29o18

be the count of yarn, n the twist in the yarn in terms of turns per inch and d the yarn = AC/BC = (circumference of the yarn) / l = πd / l

As the yarn twist is n turns per inch and the length of the yarn accommodating one turn of

have nl = 1(inch) or n = 1/ I.Considering C in terms of Nec, the diameter d of the yarn can be expressed as

Putting these values of n and d in Equation 1, we have,C)

π…….. (2)where m = 28tanθ/π

The factor m is called twist multiplier or the twist factor. This is the relationship between the and twist in a yarn and the twist multiplier and it can be stated generally as follows.

inch = Twist Multiplier × √Count in Ne.

As illustrated above, the yarn twist angle is the angle between a tangefibre on the yarn surface and the yarn axis. If the twist multiplier of a

angle can easily be calculated.Calculate the twist angle of a spun cotton yarn twisted to give a twist factor of 5.

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be the count of yarn, n the twist in the yarn in terms of turns per inch and d the yarn

mmodating one turn of

The factor m is called twist multiplier or the twist factor. This is the relationship between the lly as follows.

ngent to the helix fibre on the yarn surface and the yarn axis. If the twist multiplier of a cotton yarn is

Calculate the twist angle of a spun cotton yarn twisted to give a twist factor of 5.


Significance of the twist multiplier:

The twist multiplier is used to calculate the amount of tpi to be given to the cotton yarn during spinning. If yarns of soft feel and a pliable behaviour is required twist factors around 3.0 is used while at the other extreme, hard twisted, stiff and twist lively yarns will have twist factors of around 6.0.

It describes the nature and character of a yarn i.e. characteristics like softness, smoothness, hardness, etc of yarns. If yarns of different counts were spun with the same twist factor,their characteristics would be similar. Conversely, if yarns of the same count differed in twist factor, they would have markedly different characteristics.

Function of twist in yarn structure: The main function of twist is to bind the fibers together and helps to keep them in their

respective positions. It thus gives coherence to the yarn.

Without twist a strand of fibres has very little strength and in the first instance a yarn must have sufficient tensile strength to withstand the stresses of preparation and fabric manufacture.

The main function of twist is to give coherence to the yarn. In order to develop strength in a twisted strand of discontinuous fibres and so resist breakage, the individual fibres must grip each other when the strand is stressed. This cohesion arises mainly from the twist, which presses the fibres together as the stretching force is applied and so developing friction between adjacent fibres.

Twist is also used to bring about novel effects that are prominently visible when the yarn is converted to fabric. This is achieved primarily by having a combination of yarns with different twist levels and twist directions in the fabric.

Twist & Yarn Strength:

The strength of a yarn twisted from staple fibers increases with increasing twist but up to the certain limit beyond that limit yarn starts loses strength. In the lower portion of the curve (Fig.), this strength will be due solely to sliding friction, i.e. under tensile loading the fibers slide apart. Cohesive friction arises only in the middle-to-upper regions of the curve. This is caused by the high tension, and thus high pressure, and finally becomes so considerable that fewer and fewer fibers slide past each other and more and more are broken.

This continues up to certain Maximum, i.e. to the optimal exploitation of the strength of the individual C) - is dependent upon the raw material. Normally, yarns are twisted to levels below the critical twist region (A – knitting, B – warp); only special yarns such as voile (C) and crêpe (D) are twisted above this region. Selection of a twist level below maximum strength is appropriate because higher strengths are mostly unnecessary, cause the handle of the end product to become too hard, and reduce productivity.


Fig. – Relationship between the number of turns of twist T/m, turns of twist per meter in the yarn; PES, polyester fibers; Co, cotton fibers

Optimum twist factor:The twist factor that gives maximum strength

‘optimum twist factor‘. This would naturally be a function of fibre characteristics such as length, fineness, rigidity, surface and frictional properties, etc. of course yarns not always manufactured to have maximum strength; when visual or other effects are of more importance, a compromise is inevitable. Crepe yarns have very high twist factors in the range 6.0 to 9.0 and these yarns when woven into fabric impart the characteristic crepe surface to the fabric.

Factors Affecting Twist:The twist introduced in the yarn during spinning depend

The count of yarn to be spun the yarn count.

The quality of cotton used -less twist than the shorter ones.

The use to which the yarn is put knitting yarn or any other yarn.

The fineness of the fibre being spun for the same count compared to shorter and coarser cottons.

The kind of machine in which the yarn will subsequently be used weaving on power looms and automatic looms will be higher than that used for hosi

Relationship between the number of turns of twist and the strength of a yarn; F, strength; T/m, turns of twist per meter in the yarn; PES, polyester fibers; Co, cotton fibers

The twist factor that gives maximum strength in any given staple yarn is called the ‘optimum twist factor‘. This would naturally be a function of fibre characteristics such as length, fineness, rigidity, surface and frictional properties, etc. of course yarns not always manufactured

strength; when visual or other effects are of more importance, a compromise is Crepe yarns have very high twist factors in the range 6.0 to 9.0 and these yarns when fabric impart the characteristic crepe surface to the fabric.

The twist introduced in the yarn during spinning depends upon a number of factors.

The count of yarn to be spun - the twist level in a yarn is proportional to the square root of

- all other parameters remaining the same, longer fibres require ter ones.

The use to which the yarn is put - is the yarn meant to be used as warp yarn, weft yarn, knitting yarn or any other yarn.

The fineness of the fibre being spun - the finer and longer staple cottons need a lower twist for the same count compared to shorter and coarser cottons.

The kind of machine in which the yarn will subsequently be used - the twist in yarns used for weaving on power looms and automatic looms will be higher than that used for hosi

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and the strength of a yarn; F, strength; T/m, turns of twist per meter in the yarn; PES, polyester fibers; Co, cotton fibers.

in any given staple yarn is called the ‘optimum twist factor‘. This would naturally be a function of fibre characteristics such as length, fineness, rigidity, surface and frictional properties, etc. of course yarns not always manufactured

strength; when visual or other effects are of more importance, a compromise is Crepe yarns have very high twist factors in the range 6.0 to 9.0 and these yarns when

s upon a number of factors.

the twist level in a yarn is proportional to the square root of

all other parameters remaining the same, longer fibres require

is the yarn meant to be used as warp yarn, weft yarn,

s need a lower twist

the twist in yarns used for weaving on power looms and automatic looms will be higher than that used for hosiery.


The softness of the fabric into which the yarn is to be converted - yarns required for soft-surfaced fabrics are given only a slack twist.

The smoothness of the fabric into which the yarn is to be converted - yarns required for smooth-surfaced fabrics are given many twists per inch. They are hard twisted yarns and they give strength, smoothness, elasticity and some crease-resistance of fabrics.

Any other special attribute of the fabric into which the yarn is to be converted - yarns required for crepe fabrics with rough, pebbly or crinkled surfaces are given a maximum amount of twist. The crepe yarns also confer enhanced crease resistance to the fabric.

Effects of twist on fabric properties:The twist in yarns can be caused to affect the properties of the fabric in which the yarns

are included. Major fabric properties that are influenced by yarn twist are listed below. 1. Visual appearance2. Handle3. Mechanical characteristics

1. Visual Appearance:

When yarns are incorporated in a fabric such that adjacent sets of yarn vary in the direction of twist, different effects like the shade effect, stripe effect etc., can be produced.

Prominence of twill lines in a fabric largely depend upon the direction of twist in warp and weft yarns.

2. Handle: Yarn with higher twist levels is smooth. They are hard yarns that are less hairy and therefore relatively lustrous. When such yarns are woven into fabric, the fabric feels smooth, hard and stiff. Very highly twisted yarn will be lively and tend to twist upon itself to produce snarls. Fabric from such yarns will also lively handle. The handle of yarn with low twist will be comparatively softer and limp.

3. Mechanical Properties: Properties like tensile strength, abrasion resistance and tearing strength are affected. When strand of parallel fibres are twisted, fibres get closer to each other and their movement is becomes difficult as the twist increases. Thus inter fibre friction increases so too strength. This continues until the maximum strength is reached. The yarn has optimum twist. Increase in the twist fall in strength as the fibres now have very high twist angle.

Twist in general, causes an increase in yarn lustre and reduction in yarn hairiness, the better will be the abrasion resistance. Influence of the twist to yarn strength, the stronger the yarn better is the tearing strength.

In a highly twisted yarn the fibres at the surface are incapable of sharing a load with those nearer the core of yarn unless they straighten under the effect of the tensile load. By the time this happens, many of the fibres at the core have already broken.


The net result is a lower breaking load. All the fibres in the yarn act in a concerted manner when the yarn approaches the optimum twist and result in optimum strength. This is not possible when this twist level is exceeded and many of the fibres, especially those at the yarn surface, are too oblique to the yarn axis. As stated above, twist in general, causes an increase in yarn lustre and a reduction in the yarn hairiness. The lower the yarn hairiness, the better will be its abrasion resistance, everything else remaining constant.

Measurement of twist:The most obvious way to measure the number of twists per unit length of yarn is simply

to untwist a known length of the yarn and check visually to see whether the twist has beencompletely removed.

Sampling of yarns for twist testingWith regard to twist testing, as with all physical tests, sampling is very important. This is

so because twist can be found to vary along the length of any given yarn. It can be realised fromcommon experience that a thicker strand needs to be twisted to a greater extent than a thinnerstrand to achieve the same level of twist. Speaking technically, it can be stated that the amount oftwist in a material is inversely proportional to its thickness. Thick places in a strand would have less twist than thin places, i.e. twist α (1/yarn thickness).

In twisting staple fibre strands, it is impossible to give variable twist along different portions of a given strand to end up with even twist throughout the strand. The net result is that the places of normal thickness would have the intended twist level, the thick places would have lower twist and the thin places would be tightly twisted. The thin places would be hard twisted and the thick places soft twisted.Number of tests and general specifications

To obtain representative values of the mean twist in given yarns, standards organisations always specify that a certain minimum number of tests have to be performed. They also indicate the precautions to be followed while drawing test specimens from a yarn package. In general, the following points may be followed.

In the case of plied and cabled spun yarn and continuous filament yarn, at least ten specimens are to be tested if the test length is 500 mm according to Bureau of Indian Standards (BIS). The British Standards Institution (BSI) recommends testing up to 20 specimens of 250 mm each.

In the case of single spun yarn, BIS specifies that a minimum of 100 specimens of 25 mm length each be tested while using the ‘direct count method’ of twist measurement and 20 tests for specimens of 250-500 mm if the untwist-retwist method is used. BSI recommends 50 specimens of 25 mm each.

The test yarn package is to be mounted vertically on a peg that permits smooth withdrawal of the yarn at right angles to the package. The package should be free to rotate about the peg as the yarn is withdrawn gently from it.


If the yarn is removed from the top of the package there would tend to be a twisting or untwisting action on the yarn depending upon whether the yarn is S-twisted or Z-twisted. This action would therefore certainly alter the twist and the results would not be true.

The actual test specimen should be handled manually such that the fingers do not touch the length over which the twist is actually measured.

The tension in the test specimen must be constant. BSI recommends a yarn tension level of tex /2 ± 10% grams. To cite an example, a 40s Nec count (i.e. about 15 tex) yarn would be maintained at a tension in the range 635- 8.25 grams. BSI also specifies the same level of tension.

Techniques of twist MeasurementsTwist testing equipment have not changed radically over the years except that actual test

uses electronic devises to measure the twist. The most common techniques that have been used for measuring yarn twist are listed below.

Straightened fibre technique or the direct count method.

Twist contraction technique or the untwist and retwist method.

Twist to break technique.

Microscopic technique.

1. The straightened fibre technique

A. Straightened twist tester

Principle: Used only for testing single spun yarns, this technique involves the untwisting of the test specimen until all of the twist is removed. The completeness of the untwisting is verified byvisual examination of the straightening of all of the fibres in the strand - this is why the name ‘straightened fibre technique‘. The number of turns required for the untwisting is counted and the number is divided by the length of the test specimen to arrive at the twist of the test yarn turnsper unit length.

This technique is also known as the ‘direct count method‘, as the twist in the yarn is directlycounted.Construction: The below figure depicts the salient features of a single yarn twist tester incorporating the straightened fibre technique. The instrument consists of two pillars, A and B, mounted on a rigid base C. On pillar A are mounted a fixed jaw D, a guide pulley E, a tensioningarrangement F, a magnifying lens G and a blackboard H. Pillar B carries a jaw I that can be rotated manually either way by means of handle K and the number of revolutions is recorded in the revolution counter J. A length of 25 mm (or one inch), the test length normally used, separates the faces of the jaws D and I. A test specimen L can be seen mounted between the twojaws.


Test Procedure: The first step is to set the revolution counter to zero.

Next clamp the test yarn in the rotatable jaw. Open the static jaw and lead the yarn through it and then over the guide pulley; attach a small weight to the yarn to give it the required tension and then close the jaw to clamp the yarn.

Check, by means of lens G if necessary, the twist direction of the test specimen. Then using the handle, rotate jaw I in a clockwise or anti

Note the twist in the yarn being removed. When most of the twist has been removed, push sharp needle through the middle of the partially untwisted strand so it nearly touches thestatic jaw; then, looking through lens G, gently move the needle towards the other jaw.

Give the handle a final rotation either way until the needle is in the closto the rotatable jaw.

Finally, the number of turns of the rotatable jaw required to untwist the test specimen is read off the revolution counter and recorded.

At least 50 tests are conducted in this manner and the mean tpi and CV% are

Test Results: The mean instrument reading is first calculated and then the twist is expressed either in terms of turns per inch (tpi) or turns per metre (tpm) as follows.

If the mean instrument reading is 'm' turns and the test length is yarn is m tpi or 39.37 m tpm. If the test length is 25 mm, the twist is (25.4m/25) tpi or 40m tpm.

The first step is to set the revolution counter to zero.

Next clamp the test yarn in the rotatable jaw. Open the static jaw and lead the yarn through and then over the guide pulley; attach a small weight to the yarn to give it the required

and then close the jaw to clamp the yarn.

ens G if necessary, the twist direction of the test specimen. Then using handle, rotate jaw I in a clockwise or anti-clockwise direction so as to untwist the yarn.

Note the twist in the yarn being removed. When most of the twist has been removed, push sharp needle through the middle of the partially untwisted strand so it nearly touches thestatic jaw; then, looking through lens G, gently move the needle towards the other jaw.

Give the handle a final rotation either way until the needle is in the closest possible position

Finally, the number of turns of the rotatable jaw required to untwist the test specimen is off the revolution counter and recorded.

At least 50 tests are conducted in this manner and the mean tpi and CV% are

The mean instrument reading is first calculated and then the twist is expressed turns per inch (tpi) or turns per metre (tpm) as follows.

ng is 'm' turns and the test length is one inch, then the twist in them tpm. If the test length is 25 mm, the twist is (25.4m/25) tpi or 40m tpm.

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Next clamp the test yarn in the rotatable jaw. Open the static jaw and lead the yarn through and then over the guide pulley; attach a small weight to the yarn to give it the required

ens G if necessary, the twist direction of the test specimen. Then using clockwise direction so as to untwist the yarn.

Note the twist in the yarn being removed. When most of the twist has been removed, push asharp needle through the middle of the partially untwisted strand so it nearly touches thestatic jaw; then, looking through lens G, gently move the needle towards the other jaw.

est possible position

Finally, the number of turns of the rotatable jaw required to untwist the test specimen is

At least 50 tests are conducted in this manner and the mean tpi and CV% are calculated.

The mean instrument reading is first calculated and then the twist is expressed

n the twist in them tpm. If the test length is 25 mm, the twist is (25.4m/25) tpi or 40m tpm.


B. Continuous Twist Tester

Principle: This twist tester is a modification of the abovetesting of a number of one-inch test specimens without undueinstrument is therefore capable of giving more reliable results on the shorttwist in the yarn.

It works on the same principle as the abovethe test specimen has to be static during a twist test,one-inch lengths of the test yarn can be evaluated an extended length of the yarn.

Construction: The figure shows a continuous twist tester. It has amounted from left to right a peg to support a lens E, a fixed jaw F, a rotatable jaw G,reading on a dial, a handle I and a winding drum J.translational motion either to the left or to the right, in a slotinstrument. This arrangement allowsshown mounted between the two jaws. A zeroin the dial to zero.

This twist tester is a modification of the above instrument and permits the continuous inch test specimens without undue handling of the

capable of giving more reliable results on the short- term variation in

It works on the same principle as the above instrument, viz. the straightened- fibre principle. Asthe test specimen has to be static during a twist test, the term 'continuous' simpl

lengths of the test yarn can be evaluated successively and quickly, one after another, on

The figure shows a continuous twist tester. It has a broad base A, on which are a peg to support a yarn package C, a thread guide D, a

lens E, a fixed jaw F, a rotatable jaw G, connected to a revolution counter H that indicates thereading on a dial, a handle I and a winding drum J. Both the jaws can be moved, in a

either to the left or to the right, in a slot provided ininstrument. This arrangement allows specimen lengths of 1", 5" or 10". A test specimen K isshown mounted between the two jaws. A zero-set knob in the instrument helps to set the pointer

Page 46

instrument and permits the continuous handling of the yarn. This

term variation in

fibre principle. Asthe term 'continuous' simply implies that

, one after another, on

broad base A, on which are arn package C, a thread guide D, a magnifying

connected to a revolution counter H that indicates theBoth the jaws can be moved, in a

the base of the specimen lengths of 1", 5" or 10". A test specimen K is

in the instrument helps to set the pointer


Test Procedure:1. Using 1-inch test specimens

The distance between the two jaws is set at one inch by moving the rotatable jaw appropriately.

The test yarn sample is drawn from the sample package and passed through the guide, the fixed jaw and the rotatable jaw, and finally wound on to the take-up drum.

The jaws are closed to clamp an inch length of the specimen.

The revolution counter is set to zero by adjusting the zero-set knob.

The twist direction in the test yarn is identified by means of the magnifying lens. The rotatable knob is then rotated to untwist the yarn.

After the major portion of the twist is removed, a sharp needle is inserted into the untwisted strand as close to the fixed jaw as possible and moved towards the rotatable jaw while looking through the magnifying lens. Complete untwisting is achieved by rotating the jaw one way or the other until it is possible to push the needle right up to it.

The tpi of the test specimen can now be directly read from the dial and recorded as m1.

The yarn is then twisted back to its original level of twist, as indicated by the zero reading on the dial. The original twist is thus put back into the test specimen.

The rotatable jaw is then opened and moved leftward to the fixed jaw until the two jaw faces touch each other.

The fixed jaw is now opened and the rotating jaw is closed and pulled back to its original position. This brings in a new 1-inch specimen in between the jaws. The fixed jaw is now closed.

The take-up drum is rotated to take up the slack yarn at its left.

The new test specimen is then evaluated for twist. Let its reading be m2.

The above procedure is repeated until the required number of tests is completed.

The mean tpi value is then calculated from the individual readings ml, m2, m3, m4…mn and reported.

2. Test lengths greater than one inchThe above general procedure can be used to test yarn for twist using 5-inch and 10 inch

test specimens. The greater the test length the fewer will be the number of test specimens to be tested.

Advantages of this instrument Unnecessary handling of material between successive tests is avoided.

Shorter variations in tpi values along a continuous length of yarn can be assessed.


2. Twist contraction technique or the untwist and retwist method

Principle: Also known as the twistthat the twist in a given length of ycauses the yarn to extend in length. The original level of tthe opposite direction. As a result, the yrequired to untwist and retwist the ylength when a strand of parallel fibres is twisted in a given direction will generallthe contraction it suffers when it

Twist contraction: The twisting together of two strands causes a contraction effect that must be known in order to calculate the count of the plied yarn accurately. The twist contraction principle holds good even when a strand of parallel fibres (or filaments) is twisted.

In general, if the length of the strand before twisting is L and upon twisting the contractedlength is L1, the twist contraction C is given by C = L

Extension on Untwisting: remains, the resulting strand would have a length equal to L.

Contraction on Retwisting:opposite direction of its original twist, such that the same level of twist is attained, the length of the resulting yarn would again be L

Figure: Contraction on Twisting

Twist contraction technique or the untwist and retwist method

Also known as the twist-and-retwist method, this technique works on the principle given length of yarn, under specified tension, is removed by untwisting. This extend in length. The original level of twist is then inserted into the y

direction. As a result, the yarn reverts to its original length. The number of turns and retwist the yarn is noted and the tpi is calculated. The contraction in

lel fibres is twisted in a given direction will generallis twisted in the opposite direction.

The twisting together of two strands causes a contraction effect that to calculate the count of the plied yarn accurately. The twist

contraction principle holds good even when a strand of parallel fibres (or filaments) is

In general, if the length of the strand before twisting is L and upon twisting the contracted, the twist contraction C is given by C = L - L1.

Extension on Untwisting: If the above yarn of length L1 were untwisted so that no twist remains, the resulting strand would have a length equal to L.

Contraction on Retwisting: Further, if the untwisted strand above were twisted in the opposite direction of its original twist, such that the same level of twist is attained, the length of the resulting yarn would again be L1.

Contraction on Twisting Extension on Untwisting

Page 48

retwist method, this technique works on the principle by untwisting. This

en inserted into the yarn but in arn reverts to its original length. The number of turns

arn is noted and the tpi is calculated. The contraction in lel fibres is twisted in a given direction will generally be equal to

The twisting together of two strands causes a contraction effect that to calculate the count of the plied yarn accurately. The twist

contraction principle holds good even when a strand of parallel fibres (or filaments) is

In general, if the length of the strand before twisting is L and upon twisting the contracted

were untwisted so that no twist

untwisted strand above were twisted in the opposite direction of its original twist, such that the same level of twist is attained, the

Extension on Untwisting


Tension type Twist tester

A typical tension-type twist tester is shown in the figure. It is specifically designed to apply the twist contraction principle to single spun yarns. Essentially, it consists of two pillars, mounted on a solid base. A fixed jaw is mounted on a pillar. This jaw is connected to a tension scale that has a sliding weight that can be set at any required point on the scale, the lower end of which is a pointed tip. The whole scale is in effect a small pendulum. At the base of this pillar is a fixed index mark.

The other pillar carries the rotatable jaw I, which is connected to handle and a revolution counter through gears. The gear ratio is such as to display the tpi of the test specimen at the end of thetest. The mechanical counter displays four digits. The first two digits represent whole numbers while the next two indicate two decimal places. A zero setting knob is connected to the counter.The test specimen mounted in between the fixed and rotatable jaws. The specimen length in this instrument is a fixed 10". In some testers of this kind there is an arrangement to change the specimen length by sliding the fixed jaw pillar along a slot in the base.

Test Procedure:-The sliding weight on the tension scale is first set according to the count of the test yarn and the instrument constant, which will usually be provided by the concerned instrument manufacturer. For example, a particular manufacturer recommends that the following formula be used to arrive at the tension setting.

Tension scale reading = 156/English count

Yarn from the test package is first gripped in the fixed jaw and then led through the rotatable jaw. It is pulled through the latter jaw until the knife-edge tip of the pendulum pointer is exactly in line with the fixed index mark at the base. This jaw too is then closed.


At this stage, the test specimen is under recommended tension and has a test length or gauge length of 10".

The mechanical counter is now set to zero using the zero-set knob.

The twist direction of the test specimen is ascertained, if necessary by means of a magnifying lens and the handle is rotated so as to untwist the yarn.

As the twist in the 10 inch specimen is removed, the yarn extends and the tension in it falls; as a result, the pendulum pointer moves away from the index mark and eventually reaches its position of rest (i.e. the vertical position). At this stage, all the twist has been removed from the sample.

The jaw is kept rotating in the same direction until sufficient twist has been inserted to bring the pointer gradually back to coincide with the index mark.

Thus, in this method, the twist is first removed by untwisting and then put back by retwisting -the untwist-and-retwist principle.

The revolution counter reading is noted and recorded. As stated earlier, this is the value of the tpi of the test specimen.

3. Twist-to-Break Technique of Twist MeasurementsThe twist-to-break technique is not a reliable method for everyday tests with yarns and is

therefore not much used these days. Its mention here is merely for historical interest.Principle

A specific short length of yarn is twisted in a twist tester until it breaks. Another specimen of the same length is then twisted to break by twisting it in the opposite direction. If NS

are the number of turns required in the first case and N2 those in the second instance, the tpi of the yarn is given by (NS - N2)/ 2.

4. The microscopic techniqueThis technique is more suitable for research work on special model yarns rather than for

routine yarn testing. The fact that only a very small portion of the yarn is tested at a time and that the technique is therefore very slow makes it inconvenient for regular testing. However, the textile technologist is encouraged to be aware of this technique.

Principle:-A microscope equipped with a graduated rotary sample stage is used to measure the helical angle of the twist in the yarn. The yarn diameter is also measured. From these two quantities the twist per unit length is calculated.

The microscopic arrangement:-Line diagrams depicting the principle of the technique are shown in the figures (a) and (b). Note the circular rotary stage A of the microscope withgraduations in degrees at its periphery. The rotary microscopic stage can be fixed at any desired position by means of a small screw catch B. Note also the fixed index mark C close to the circular stage against which the angular


positions of the stage can be read off. The eyepiece used should be a crosswire eyepiece haying a built-in micrometer scale to measure the yarn diameter. A magnified view of the yarn as seen through the eyepiece is superimposed at the centre of the diagrams. The two perpendicular cross wires can be clearly seen in these views.

Test Procedure The circular rotary stage is first set so as to have its 'zero' mark coinciding with the index

mark. It is then fixed in this position.

A length of yarn mounted on a microscopic glass slide is placed on the rotary stage and held in position by the catches normally available on the stage itself.

The yarn is brought into sharp focus and the eyepiece is turned one way or another so that one of the cross wires of the eyepiece is parallel to the yarn axis.

The stage catch is released and the stage rotated slowly until the crosswire is tangential to the helix formed by the twisted fibres on the yarn surface. The stage catch is again turned on to fix the stage in this new position.

The angle through which the stage is rotated is noted. This is the yarn twist angle.

Now the eyepiece is rotated so that the micrometer scale is perpendicular to the yarn axis. The width of the yarn is read off on the scale. The yarn diameter is then calculated in terms of inches.


Calculations:-Let the yarn angle as determined by the above procedure be θ°. Let the yarn diameter be d inches. Consider one complete turn of the helical twist on the yarn surface. Let I in. be the length of this helix measured parallel to the yarn axis.Referring to the figure, we have I = π d /tanθSince turns per inch = 1/I,

Twist per inch = tan q/ π θThe values of θ and d are known, so the yarn tpi can be calculated.

DisadvantageAs stated earlier, this method has disadvantages. These are listed below.

Accurate determination of the yarn twist is not possible as a very small portion of the yarn isexamined at a time. A very large number of readings would have to be taken to haverepresentative values of the twist.

The technique is tedious and considering the large number of tests, operator fatigue could affect the results.

This technique is therefore unsuitable for routine testing and quality control.

Twist determination in Folded yarns (Doubled & Cabled Yarn)

Doubled yarns containing two or more plies and cabled yarns are evaluated for twist in a slightlydifferent type of twist tester known as the take-up twist tester. This twister derives its name from the term ‘twist take-up‘, used frequently in yarn twisting. This term is a further refinement of the term ‘twist contraction‘, which has been defined earlier.

Definition of ‘twist take-up’Twist take-up may be defined as the twist contraction suffered by a strand being twisted expressed as a percentage of the original length of the strand before twisting.

Twist take-up % = 100 × (twist contraction) / (strand length before twisting)

=100 × (strand length before twisting - strand length after twisting) Strand length before twisting

The twist contraction is a function of the count of the strand and the level of twist inserted. The take-up twist tester primarily measures the twist in plied or cabled yarns. Indirectly, it permits the measurement of the twist take-up in such yarns.


The take-up twist tester

Principle:-This twist tester works on a simple principle. A specific length of the plied yarn under test is untwisted completely to zero twist. The number of turns required to separate the yarn into its component single yarns is observed. This number divided by the initial test length in inches gives the tpi of the test yarn. From the final untwisted length of the yarn and its initial twistedlength it is possible to calculate the twist take-up percentage.

Parts of the instrument:-The figure shows the main parts of a take-up twist tester. It consists of two pillars A and B fixed to a solid base C on which is embedded a scale to measure the distance between the two jaw faces, i.e. the yarn test length. Pillar A is attached to a rod D in the base of the instrument by means of pin E. This arrangement permits it to be moved and set in any one of three positions from the other pillar B. The three positions correspond to yarn test lengths 1", 5" or 10". Yarn can thus be tested at any of these test lengths. At the top of pillar A is mounted a non-rotatable jaw F, an extension scale or ‘take-up‘ scale G, a catch H, a guide pulley I, and a serrated lever J. The lever carries a tension weight K and a guide L. When required, jaw F can slide on a pair of smooth rods M. The jaw has an index mark N etched on it.

The other pillar B carries a rotatable jaw O. The shaft of this jaw has a worm P activated by pinion Q, a handle wheel R and a handle S. The jaw can be rotated in any chosen direction, clockwise or anticlockwise, by rotating the handle appropriately.


The worm combines with two worm wheels (discs T and U) to form a mechanical counter that counts the number of revolutions of the rotatable jaw. The top disc (worm wheel) of the counter has 100 teeth that represent 100 divisions or graduations. A pointer is attached to the bottom disc but it moves over the top disc to indicate the readings on it. As the bottom disc has only 99 teeth, every revolution it makes causes the pointer also to move across 99 teeth. The pointer therefore would always lag by one tooth for every revolution of the top dial (which moves through 100teeth per revolution). The lag of the pointer by one tooth enables readings to be taken beyond 100 revolutions of the rotatable jaw.

The rotating jaw assembly has a spring-loaded knob V, which when pushed causes the two discs of the counter to be disengaged from the worm. This arrangement helps to set the top dial to zero reading against an index mark W etched on the frame of the rotatable jaw assembly. At ‘zero-setting‘, the pointer and the zero mark of the counter should both be in line with this index mark.X is a test specimen fixed between the two jaws.

Procedure The required tension at which the yarn is to be held in between the jaws is calculated on

the basis of the test yarn count. This is usually (tex/2) grams. The tension weight is adjusted on the serrated lever appropriately.

The mechanical counter is then set to zero using the spring-loaded jaw as explained above.

Pillar A is set at the chosen distance from pillar B to give the desired test length of 1, 5 or 10 inches.

The non-rotatable jaw is adjusted to coincide with the zero mark on the take-up scale and the catch is released.

The plied or cabled yarn from the test package is threaded through the guide, the non-rotatable jaw and then through the rotatable jaw.

After ensuring that the yarn is at the right tension, both of the jaws are closed so as to grip the test specimen.

The twist direction of the test yarn is checked and the handle is rotated in such a direction as to untwist the yarn.

The twist in the yarn gets removed gradually and when most of it is removed, the rotation of the jaw is stopped and a sharp needle is inserted into the yarn so as to separate the plies and as close to the face of the sliding jaw as possible. The needle is then moved towards the rotatable jaw to push any residual twist towards it. The jaw is then caused to rotatedagain to remove all the twist completely from the yarn.

Two readings are then noted. One is the reading of the pointer on the dial and the other isthe extension of the yarn on the extension scale. The former denotes the total number of turns that were required to untwist the test length of the yarn and the latter denotes the extension of the yarn upon complete removal of the twist.


Calculations The twist per inch and the take-up per cent of the test yarn are calculated as follows.

1. Twist per inch = Dial reading / test length2. Take-up % = (Extension scale reading) / (untwisted length of yarn)

Twist determination in individual pliesThe twist direction and the twist level in a plied or cabled yarn will not necessarily be the

same as those in the individual plies of the yarn. In most cases the twist direction and the twist level would be the same in the final singles yarn composing the plied or cabled yarns.

The twist direction in the plied yarns can be easily determined. However, determination of the twist per inch takes a little more effort.

Plied YarnIf it is a two-ply yarn, follow the procedure described above to determine the doubling twist, using a take-up twist tester and a test length of 10 inches. At the end of the test there will be twoindependent plies between the jaws.Next, using sharp blade carefully cut off one of the plies close to the jaw faces. Without undue handling, mount the single yarn carefully on a single-yarn twist tester using a 10 inch test length, if possible, or a one-inch test length and determine the twist level as explained earlier. The second ply left on the take-up twist tester is then cut off and tested similarly on a single-yarn twist tester.If a three-ply yarn is to be tested, follow the above procedure until all the three plies have been tested.

Cabled yarnIf a cabled yarn is to be tested, first determine the cabling twist direction and cabling twist using a take-up twist tester and a test length of 10 inches as explained for the plied yarn. At the end of the test, the component (doubled) yarns will be separated. All of them but one is cut off flush with the jaw faces.The doubled yarn left uncut between the jaws will be slack and of a length greater than 10 inches on account of the extension due to the untwisting of the parent cabled yarn. One of the jaws is opened and the doubled yarn is tensioned and then clamped again. The doubling twist direction and level of twist is then determined. Finally, the component single yarn twist is determined as explained above.

Electronic Twist Tester (Microprocessor twist tester)The electronic twist tester is an automated version of the conventional manually-operated

twist testers described above. This instrument is capable of evaluating the twist in both single and doubled yarns.Principle:-The instrument uses the untwist-and-retwist principle for single yarns and the principle of the take-up twist tester (untwisting only) for doubled yarns.


Construction:-The essential features of the instrument are shown in the figure. Yarn from a test package is first taken to a disc unit mounted on a solid base, which also has a scale along its length to measure the distance between the two clamps (i.e. test specimen length). The scale is graduated both in inches (1-20") and in centimeters (1 to 50 cm).The disc unit consists of a graduated disc pivoted at its centre and mounted on a moveable support. The disc unit is thus capable of being moved anywhere along the scale to set any desired yarn test length.At the top of the disc is a non-rotatable clamp to hold one end of the test specimen. The tension in the specimen can be set by adjusting a pointer to any desired position on the scale, the graduations of which indicate yarn tension in grams force. This is the arrangement for setting the tension in single yarns. In the case of doubled yarns, an additional weighting device is added to the disc.The right side of the instrument has a microprocessor unit to which is attached a rotatable jaw. The unit houses a motor to rotate the jaw in the clockwise or anticlockwise direction. It also has the following features.

A digital display unit for displaying yarn tpi or tpm.

An lamp to indicate zero position

Tpi / tpm selection switch

Motor switch

Twist direction selection switch (S / Z switch)

Forward / backward rotation switch

Test Procedure for single yarn The disc unit is slid along the scale and fixed to give the desired test length.

The required yarn tension, calculated on the basis of the yarn count, is set on the graduated dial. The pointer is moved appropriately so that it reads the set yarn tension.

Make the required selections of the tpi I tpm switch and the S / Z switch.

The yarn sample from the test package is led through a guide and clamped in between the two jaws. When this is done correctly the forward direction switch light up.


Before the test is started, the digital display should read zero and the concerned indicator lamp lights up. If not, the zero setting is obtained by using the reset knob.

The motor switch is now turned on. When the motor runs the zero-set indicator light normally turns off at a display value of l tpi (or tpm).

When the yarn has been untwisted and retwisted the motor stops automatically.

The tpi or the tpm value of the test specimen is then read off the digital display unit and noted.

20 such readings are taken and the average value of twist is reported.

Test procedure for doubled yarnThe additional weight arrangement is used to get the right test yarn tension. The tension pointer is set to the maximum value on the scale. The digital display is set to zero. All of the other steps are the same as those for single yarn. When the motor stops automatically the display shows 2 to 3 tpi (or 20 to 25 tpm). A sharp needle is now inserted in between the ply yarns close to the face of the non-rotatable jaw and any residual twist is pushed towards the rotatable jaw. The motor is then run slowly until the needle can be freely pushed right up to the face of the rotatable jaw.The twist reading is then noted and at least 10 such readings are obtained in all to arrive at themean value of the yarn twist.


Yarn Evenness

IntroductionThe spinning of yarns from natural fibres is a difficult task for any spinner because of the

natural variations in fibre properties like length, fineness, strength, crimp, cross sectional area, etc. Right through the spinning systems developed by man, the textile technologists have constantly been putting their efforts into the production of an ideally even yarn by manipulating the process parameters and machine design. There has always been an endeavour to enhance the evenness of spun yarn. Yarn evenness contributes immensely to the quality of woven and knitted fabrics. Other applications where yarn is used also calls for good evenness. Hence yarn evenness plays a very important role in the quality of most textile products.

Evenness, unevenness, regularity and irregularity are common terms used to describe thedegree of uniformity of a textile product. In the textile field, the uniformity of products like thelap, sliver, roving or yarn is expressed in terms of evenness or regularity or in terms of unevenness o irregularity.

In actual practice, it is not easy to produce a yarn of perfectly uniform characteristics such as uniformity in weight per unit length, uniformity in diameter, twists per inch, strength, etc. This is mainly due to the inherent variation in natural fibre characteristics such as fineness, maturity, length, color, diameter etc.The following yarn properties are usually subject to variation.

Weight per unit length

Twists per inch

Diameter

Strength

Importance of Yarn Evenness on process and product qualityIrregularity can adversely affect many of the properties of textile materials. The most

obvious consequence of yarn evenness is the variation of strength along the yarn. If the average mass per unit length of two yarns is equal, but one yarn is less regular than the other, it is clear that the more even yarn will be the stronger of the two. The uneven one should have more thin regions than the even one as a result of irregularity, since the average linear density is the same. Thus, an irregular yarn will tend to break more easily during spinning, winding, weaving, knitting, or any other process where stress is applied.

A second quality-related effect of uneven yarn is the presence of visible faults on the surface of fabrics. If a large amount of irregularity is present in the yarn, the variation in fineness can easily be detected in the finished cloth. The problem is particularly serious when a fault a thick or thin place appears at precisely regular intervals along the length of the yarn. In such cases, fabric construction geometry ensures that the faults will be located in a pattern that is very clearly apparent to the eye, and defects such as streaks, stripes, barre, or other visual groupings develop in the cloth.


Such defects are usually compounded when the fabric is dyed or finished, as a result of the twist variation accompanying them. Twist tends to be higher at thin places in a yarn. such locations, the penetration of a dye or finish is likely to be lower twist. In consequence, the thicker yarn region will tend to be deeper in shade than the thinner ones and, if a visual fault appears in a pattern on the fabric, the pattern will tend to be emphasized by the presence of colorresistance controlled by a finish.

Other fabric properties, such as abrasion or pillabsorbency, reflectance, or lustre, may also be directly influenced by yarn eveffects of irregularity are widespread throughout all areas of the production and use of textiles, and the topic is an important one in any areas of the industry.

Classification of yarn irregularityWhen dealing with yarns, especially spun yarn, two types of variation are

encountered.1. Random Variation2. Periodic Variation

1. Random Variation: - Variation that occurs randomly in a textile material order or pattern is called random variation. This is caused mainly due to the natural variations in the fibre properties.

If a yarn were cut into onedetermined and then the weights are plotted in a graph against the lengths. Aone shown in the figure would berepresents an irregularity trace. A mean line isof the one-inch lengths of yarn.

Thus the deviation of each point or value from the meandeviations from the mean are of aseen in the figure, then the variation is called

s are usually compounded when the fabric is dyed or finished, as a result of the twist variation accompanying them. Twist tends to be higher at thin places in a yarn. such locations, the penetration of a dye or finish is likely to be lower than at the thick regions of lower twist. In consequence, the thicker yarn region will tend to be deeper in shade than the thinner ones and, if a visual fault appears in a pattern on the fabric, the pattern will tend to be

color or by some variation in a visible property, such as crease

Other fabric properties, such as abrasion or pill-resistance, soil retention, drape, absorbency, reflectance, or lustre, may also be directly influenced by yarn evenness. Thus, the effects of irregularity are widespread throughout all areas of the production and use of textiles, and the topic is an important one in any areas of the industry.

irregularityWhen dealing with yarns, especially spun yarn, two types of variation are

Variation that occurs randomly in a textile material withoutorder or pattern is called random variation. This is caused mainly due to the natural variations in

cut into one-inch lengths and the weight of each consecutive length is weights are plotted in a graph against the lengths. A graph such as the

would be obtained. When the plotted points are joined to form arepresents an irregularity trace. A mean line is drawn to indicate the average value of the weight

Thus the deviation of each point or value from the mean can be observed. If the deviations from the mean are of a random nature and no definite pattern of variation isseen in the figure, then the variation is called ‘random variation.

Page 59

s are usually compounded when the fabric is dyed or finished, as a result of the twist variation accompanying them. Twist tends to be higher at thin places in a yarn. Thus, at

t the thick regions of lower twist. In consequence, the thicker yarn region will tend to be deeper in shade than the thinner ones and, if a visual fault appears in a pattern on the fabric, the pattern will tend to be

by some variation in a visible property, such as crease-

resistance, soil retention, drape, enness. Thus, the

effects of irregularity are widespread throughout all areas of the production and use of textiles,

When dealing with yarns, especially spun yarn, two types of variation are commonly

without any definite order or pattern is called random variation. This is caused mainly due to the natural variations in

each consecutive length is graph such as the

obtained. When the plotted points are joined to form a graph, it drawn to indicate the average value of the weight

can be observed. If the andom nature and no definite pattern of variation is visible, as


2. Periodic Variation: - Periodic variation is a variation that in the textile material. The periodic variations are of two types namely short term periodic variation and long term periodic variation.

A-AmplitudeM- Mean ValueD- Distance between two consecut

Suppose a yarn is cut into oneof yarn are determined. If the crosssuch as the one depicted in the figure would beshown and a line indicating the mean value is drawn

Periodic variation is usuallfigure, the distance from one peak of the wave to the next on the same sidecalled wavelength. Amplitude is athe deviations from the mean are in a definitevariation‘.Periodic variations are listed below

Short term periodic variationthe fibre length, the variation is called short

Medium tern periodic variationtimes the fibre length, the variation is referred

Long tern periodic Variation1000 times and above the fibre length,

Expression of irregularityTwo terms are used to express the irregularity

spinning mill to asses and quantify the uniformity or regularity

1. Percentage of mean deviation2. Co-efficient of variation.

Periodic variation is a variation that occurs at definite length sequences in the textile material. The periodic variations are of two types namely short term periodic variation and long term periodic variation.

consecutive amplitudes.is cut into one-inch lengths and the cross sections of consecutive lengths

of yarn are determined. If the cross sections were plotted against the successive lengths, asuch as the one depicted in the figure would be obtained. The plots are joined to form a graph as

and a line indicating the mean value is drawn.Periodic variation is usually denoted by the terms 'wavelength' and ‘amplitude’. In the

from one peak of the wave to the next on the same side of the mean line is called wavelength. Amplitude is a measure of the size of the deviation from the mean level.the deviations from the mean are in a definite sequence, the variation is called ‘periodic

Periodic variations are listed below

Short term periodic variation:- If the wavelength of the periodic variation is 1 to the fibre length, the variation is called short-term variation.

Medium tern periodic variation:- If the wavelength of the periodic variation is times the fibre length, the variation is referred to as medium term variation.

tern periodic Variation:-Lastly, if the wavelength of the periodic variationtimes and above the fibre length,the variation is called long term variation.

Two terms are used to express the irregularity of yarns & intermediateto asses and quantify the uniformity or regularity.

Percentage of mean deviation..

Page 60

occurs at definite length sequences in the textile material. The periodic variations are of two types namely short term periodic

consecutive lengths sections were plotted against the successive lengths, a graph

obtained. The plots are joined to form a graph as

'wavelength' and ‘amplitude’. In the of the mean line is

measure of the size of the deviation from the mean level. If sequence, the variation is called ‘periodic

odic variation is 1 to 10 times

If the wavelength of the periodic variation is 10 to 100 to as medium term variation.

gth of the periodic variation is 100 to the variation is called long term variation.

intermediate products of


Basic irregularity: - The basis irregularity is the certain amount of irregularity found even in most uniform material. Basic irregularity is also referred to as “difficult to bring the irregularity to zero. The basic irreexpression

Where Vr – CV% of weight per unit of length of strand, N cross section of the strand and Vm shows that for given fibre and yarn count, timproved by the spinning machinery.

Index of Yarn Irregularity: -material and the calculated basis irregularity. Using this index it iquantify the spinning quality of yarn. It is given by the formula.

Where I – Index of irregularity, Va irregularity Accordingly the best yarn have a value of I = 1. Higher the value of I indicate that the yarn is more irregular.

Number of fibres in yarn cross sectiona good measure of the evenness of spun yarn. Of course this would depend upon variation in fibre fineness. In general, finer the fibre the greater the number of fibres in the yar

Methods used for Measurement of Yarn Evenness

The following methods have been used to measure yimportant property that determines ysection.

basis irregularity is the certain amount of irregularity found even in most uniform material. Basic irregularity is also referred to as “limit irregularity

to bring the irregularity to zero. The basic irregularity is given by the following

CV% of weight per unit of length of strand, N – the average number of fibres in the cross section of the strand and Vm – CV% of the fibre weight per unit length. shows that for given fibre and yarn count, there is a basic or limit irregularity which improved by the spinning machinery.

This is the ratio between the actual irregularity present in the material and the calculated basis irregularity. Using this index it is possible to assess and quantify the spinning quality of yarn. It is given by the formula.

Index of irregularity, Va – The actual irregularity measured, Vr – the calculated limit the best yarn have a value of I = 1. Higher the value of I indicate that

n yarn cross section: The average number of fibres in a yarn cross section is a good measure of the evenness of spun yarn. Of course this would depend upon variation in fibre fineness. In general, finer the fibre the greater the number of fibres in the yar

Measurement of Yarn Evenness

hods have been used to measure yarn evenness. As stated earlier, the mostrtant property that determines yarn evenness is the mean number of fibres in the cross

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basis irregularity is the certain amount of irregularity found even in limit irregularity” (Vr) as it is

gularity is given by the following

the average number of fibres in the This relationship

here is a basic or limit irregularity which cannot be

This is the ratio between the actual irregularity present in the s possible to assess and

the calculated limit the best yarn have a value of I = 1. Higher the value of I indicate that

: The average number of fibres in a yarn cross section is a good measure of the evenness of spun yarn. Of course this would depend upon variation in fibre fineness. In general, finer the fibre the greater the number of fibres in the yarn cross section.

arn evenness. As stated earlier, the mostarn evenness is the mean number of fibres in the cross-


1. Visual AssessmentIn this method, the test yarn is wound on a black board or a drum with a black surface. The parallel array of yarns is compared with a set of standard yarns wound in a similar manner. The test yarn is then accordingly graded for its appearance.Examples: Blackboard method, drum method, photographic technique, projector method, lap meter method.

2. Gravimetric techniqueIn this technique, also called the cutting-and-weighing method, the test strand in the form of a lap, sliver, rove or yarn is cut to a known length and its mean count is calculated from the results of a number of test specimens. The standard deviation, coefficient of variation and the percentage mean deviation are computed and then analysed for evenness.Examples: Lap scale; lap meter; sliver, roving and yarn wrapping.

3. Electronic capacitance testersIn this type of a device, the sliver, rove or yarn is passed through a capacitor head. The variation in the weight per unit length is monitored continuously as the strand moves at constant speed through the capacitor. The variation is continuously measured and electronic circuits record the degree of unevenness of the test strand.Examples: Fielden-Walker evenness tester and User Evenness Tester.

4. Measuring the thickness of a strand under compressionIn this technique, the test strand runs through a rectangular groove, where it is compressed and its thickness is monitored using photocells. The variation in thickness is a measure of theevenness of the material.Examples: WIRA roving levelness tester and LINRA roller yarn diameter tester.

5. Photoelectric testersIn this method, a beam of light is passed through the textile strand. The light emerging from thestrand falls on a photoelectric cell. This produces an electric current, the magnitude of which willdepend upon the thickness of the material. The output is converted into values that denote theevenness of the test strand.Examples: WIRA photoelectric tester and LINRA tester.

1. Visual Assessment Methods (Blackboard method)

This is probably the most economical and widely used everyday test for yarn unevenness. In this method, the test yarn is wound uniformly on a black surface (which may be a black board as shown in the figure or a black drum). The appearance of the parallel array of threads is examined visually against standard appearance boards of yarn similar to the test yarn. When a black painted drum is used instead of a cardboard, the size of the drum would depend upon the


requirement. Drums of fairly large diameter that canhave been used in practice. However, the blackboard technique is

In a typical test, the yarn is wound on a blackboard ofappearance board winder. This winder is shown in the figure.carry the test yarn package, a tensiongrooved spindle, which is drivenby a holder and is flipped in a continuousrequired action through stepped set of pulleysinch, which is selected according to the test yarn count.

The American Society for Testing and Materials (ASTM) supplies a set of Standard Yarn Appearance Boards for cotton that standard boards are prepared with a definite number of wraps per inch for different count ranges as indicated in the table below.

For example, if a 30s Nec yarn is to be examined by this blackboard to a wrapping density of 26 wraps/inch.

fairly large diameter that can display the entire contents of a cop of yarn used in practice. However, the blackboard technique is the more frequently method.

In a typical test, the yarn is wound on a blackboard of size 91/2"X 51/2" on a device called the yarn board winder. This winder is shown in the figure. The winder consists of a peg

, a tension type yarn guide and a traverse guide. The, which is driven manually by rotating handle. The blackboard is held

and is flipped in a continuous manner by operating the handle which causes thethrough stepped set of pulleys. Each pulley gives a specific number of winds per

selected according to the test yarn count.

The American Society for Testing and Materials (ASTM) supplies a set of Standard Yarn Boards for cotton that is used for comparing the appearance of the test yarn. These

boards are prepared with a definite number of wraps per inch for different count ranges

mple, if a 30s Nec yarn is to be examined by this method; it should be wound on theblackboard to a wrapping density of 26 wraps/inch.

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display the entire contents of a cop of yarn the more frequently method.

" on a device called the yarn The winder consists of a peg to

. The guide sits on a is held in position

manner by operating the handle which causes thepulley gives a specific number of winds per

The American Society for Testing and Materials (ASTM) supplies a set of Standard Yarn used for comparing the appearance of the test yarn. These

boards are prepared with a definite number of wraps per inch for different count ranges

it should be wound on the


Interpretation of results: A blackboard is fixed to the holder in a yarn appearance board winder. The test yarn is wound with uniform tension on to the board using the handle. When the board is full of yarn, it is taken out and assessed for its appearance by grading it. In order to identify the grade of the yarn, it is compared with the ASTM standard boards. The boards are photographs of yarns of different counts wound similarly and classified into four main grades asA, B, C and D according to visual appearance of yarn. There are also intermediate grades like B+, C+ and D+. Lastly, there is a grade referred to as BG.

Description of the ASTM yarn grades1. Grade A Yarn

No large neps those are three times more than the normal diameter of the yarn.

Must have good uniformity from inch to inch.

Should have good cover without excessive fuzziness.

No leaf and other foreign matters are present.

2. Grade B Yarn No large neps but may have a few small ones.

May have a maximum of three small pieces of foreign matter per board.

This yarn will be slightly more irregular and slightly more fuzzy than Grade A yarn3. Grade C Yarn

Will have more neps.

More fuzziness and a greater amount of foreign matter than Grade B yarn.

More thick and thin places than in Grade B yarn.

Over-all rougher appearance.4. Grade D Yarn

Has some slubs, which are more than three times the average diameter of the yarn

Has more neps of large size.

Have more thick and thin places.

Have more fuzz and more foreign matter than Grade C yarn.

Has an overall rougher appearance than Grade C yarn.5. Yarn Below Grade D (BG grade)

Has more defects

Overall rougher appearance than Grade D yarn

Grading:-The boards prepared for a test yarn are compared with the ASTM boards of the same count group. The sample is graded on both the sides of the board (front and reverse) and the grade of the poorer side is taken as the grade of the sample. Three graders should grade each board independently. When all the three graders assign the same grade then that is taken as the final grade. In case of disagreement, then the grade given by any two of the graders will be taken


as final provided that the grade assigned by the tgrade from the grade assigned by the other twIn situations where a comparisongrade of each specimen is convindex value is calculated. Qualitative designations that can be assigned to yarn and the yarn appearance index corresponding

2. Gravimetric technique

As mentioned earlier, the basis of this technique is that strands are first cut to specific known lengths and each of them weighed accurately in a sethe lengths is analysed and the yarn uniformity is assessed. This technique is uslaps, slivers, rovings and yarns.

Lap Uniformity: The first stage at which the weight per unit length can be controlled in spinning is the lap stage. Variation in lap is found out in terms Yard-to-yard variation in the lap

Lap-to-lap variation: In this commonly fixed length, is weighed and itspermitted. Any lap that exceeds this tolerancetaken at the blow room Scutcherway, the lap-to-lap variation is kept within tolerable limits.

Yard-to-yard variation or withinis cut into one-yard lengths and weighed. The resvariation is found, the mechanical defects in the blow roomidentified and these can be rectified to avoid the production of faulty

Uniformity of Sliver or rovemass per unit length. The methodweighing them in an accurate balance. The count (hank) of the test specimens iscalculated. The test procedure has been explained in detail in the section on yarn count. Anyvariation in the mass per unit length of the strand is

as final provided that the grade assigned by the third grader does not differ by.grade from the grade assigned by the other two.

n of the average quality of different lots of yarnverted to its equivalent yarn appearance index

calculated. Qualitative designations that can be assigned to yarn and the yarn g to each of the above grade are given in Table.

As mentioned earlier, the basis of this technique is that strands are first cut to specific known and each of them weighed accurately in a sensitive balance. The mass per unit length of

is analysed and the yarn uniformity is assessed. This technique is us

first stage at which the weight per unit length can be controlled in Variation in lap is found out in terms of Lap-to

in the lap

In this commonly practiced method, the full lap, which is usually a fixed length, is weighed and its weight recorded. A tolerance of 250 grams per lap is permitted. Any lap that exceeds this tolerance limit is rejected and suitable measures are

Scutcher to rectify the variation. By controlling the lap weight in this lap variation is kept within tolerable limits.

yard variation or within-lap variation: To study the yard-to-yard variation, a lap yard lengths and weighed. The results are recorded and analysed. If any undue

variation is found, the mechanical defects in the blow room scutcher responsible for it can be identified and these can be rectified to avoid the production of faulty laps.

Uniformity of Sliver or rove: Slivers and rovings are checked routinely for variation in mass per unit length. The method consists of measuring off standard lengths of the strand weighing them in an accurate balance. The count (hank) of the test specimens iscalculated. The test procedure has been explained in detail in the section on yarn count. Anyvariation in the mass per unit length of the strand is computed in terms of standard deviation

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hird grader does not differ by. More than one

n is involved, theand the average

calculated. Qualitative designations that can be assigned to yarn and the yarn

As mentioned earlier, the basis of this technique is that strands are first cut to specific known nsitive balance. The mass per unit length of

is analysed and the yarn uniformity is assessed. This technique is used widely for

first stage at which the weight per unit length can be controlled in to-lap variation &

od, the full lap, which is usually a weight recorded. A tolerance of 250 grams per lap is

limit is rejected and suitable measures are controlling the lap weight in this

yard variation, a lap recorded and analysed. If any undue

scutcher responsible for it can be

Slivers and rovings are checked routinely for variation in consists of measuring off standard lengths of the strand and

weighing them in an accurate balance. The count (hank) of the test specimens is then calculated. The test procedure has been explained in detail in the section on yarn count. Any

computed in terms of standard deviation


(SD) and coefficient of variation (CV). If the variation is on the plus side, suitable corrections in the process or machinery are made to get a strand of acceptable uniformity.

Uniformity of Yarn: Yarn is also monitored for variation in mass per unit length. The method consists of wrapping a standard length of the test yarn (120 yards or 100 metres) and weighing them in an accurate balance. The count or the linear density of the test specimens is calculated and any variation in it is assessed in terms of SD and CV. In the event of excessive variation, suitable remedial action is then taken to get yarn of tolerable evenness.

3. Electronic Capacitance Testers

Principle: These testers consist essentially of a measuring device that is a parallel-plate air capacitor. Strands such as sliver, rove or yarn are passed through the capacitor. The capacitance of the capacitor will vary depending upon the variation in the mass per unit length of the strand under test. The change in the capacitance will be proportional to the weight of the material in between the plates of the capacitor. As the material is passed continuously, changes in capacitance are measured and converted into unevenness values and irregularity traces by suitable electronic circuits and electro-mechanical devices.The electronic capacitance testers are influenced by certain material and instrumental factors that are briefly discussed below.

Strand ThicknessIn order to ensure the right sensitivity and working performance of the capacitor in the evennesstester, the thickness of the test strand should not occupy more than 40% of the distance between the capacitor plates. So different capacitors are necessary to evaluate different strands like sliver, rove coarse yarns and fine yarns.

Capacitor LengthThe shorter the length of the capacitor the better the evaluation of the strand, as variations overshort lengths is measurable. In the Uster Tester the capacitor length varies from 20 mm to B mm, to accommodate the testing of sliver, rove and yarn.Assessment of yarn evenness

Cross-sectional shape of the strandWhen the cross-sectional shape of the test strand changes, the capacitance of the capacitor toochanges. It is therefore important that the cross-sectional shape of the material tested remains thesame throughout the test. Soft strands, slivers in particular, should be prevented from becoming flat randomly along their length.

Effect of moisture content in the strandChanges in the atmospheric conditions alter the moisture content of the sample; the mass of the material will consequently be affected. This in turn would cause changes in the capacitance values of the capacitor. The higher the moisture content in the sample the greater is the change in capacitance value and vice-versa. Therefore tests are always performed on conditioned samples in standard testing atmosphere.


Yarn Faults & there lengths

Nep: This is a yarn fault of length 1 mm and a cross

Thick place: This is a yarn fault of length approximately equfibre. The cross-sectionalaverage cross sectional area of the yarn.

Thin place: This is a yarn fault of length approximately equal to the staple length of the fibre. The cross-sectionalcross sectional area of the yarn.number of neps, thick places and thin

As an example their standards for the number of neps/1000 meteres the yarn count range 20-80S Nec

The Uster Evenness Tester (Electronic Capacitance principle

The Uster evenness tester was among the earliestcommercial success. The tester gives an output of the unevennessrove and yarn and the imperfections in Principle: The instrument works on the ‘capacitance principle‘,strand is passed through a parallelcross-sectional area of the test strand.which are amplified and converted byinformation, of which a printout can be obtained.

U% (Unevenness %)

Imperfections - Neps, thick places and thin places.

CV % (Variation)

SpectrographDescription: This is a fairly recent model of the Uster tester the figure. The instrument consists of three main units. These and Printer.

This is a yarn fault of length 1 mm and a cross-section of 200% the average value.

This is a yarn fault of length approximately equal to the staplesectional area of a thick place is approximately 50% greater than the

average cross sectional area of the yarn.

This is a yarn fault of length approximately equal to the staple length of the sectional area of a thin place is approximately 50% less than the average

cross sectional area of the yarn. The Uster Company has recommended standards for the of neps, thick places and thin places in cotton yarn.

andards for the number of neps/1000 meteres is included |n the table for Nec.

Electronic Capacitance principle)

The Uster evenness tester was among the earliest of the capacitance testers to find great success. The tester gives an output of the unevenness (U%) of the test strands sliver,

imperfections in yarn.The instrument works on the ‘capacitance principle‘, mentioned above. The textile

parallel-plate capacitor. The capacitance of the capacitorsectional area of the test strand. Change in the capacitance is transformed into

which are amplified and converted by suitable circuits to give an output of the followinginformation, of which a printout can be obtained.

Neps, thick places and thin places.

This is a fairly recent model of the Uster tester and its salient features are shown in consists of three main units. These are, The Tester,

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section of 200% the average value.

al to the staple length of the area of a thick place is approximately 50% greater than the

This is a yarn fault of length approximately equal to the staple length of the area of a thin place is approximately 50% less than the average

The Uster Company has recommended standards for the

cluded |n the table for

of the capacitance testers to find great (U%) of the test strands sliver,

mentioned above. The textile plate capacitor. The capacitance of the capacitor varies as the

transformed into signals suitable circuits to give an output of the following

salient features are shown in Signal Processor


Tester: The tester consists of a peg A to hold a test are available for holding and guiding larger and softer strands like thestrand is led through a regular guide C, tension guides D and a adjustable bar E. Thepushed leftwards or rightwards so as toA magnetic-control tension device F adjusts itselfThe instrument also consists of measuring head G,push- button switch J and a manometer K. The measwidth for accommodating the following specimens.Slot No 1 - For sliver.Slot No 2 - For rove.Slot No 3 - For yarns up to 30s NeSlot No 4 - For yarns of count greater than 3

The rubber-covered rollers are positively driven rollers that draw the test material through theinstrument. They can be run at any one of the following speeds, 25, 50, The speed is usually varied according to the test material. Thsuction circle, which is a hole into which the material is sucked for disposal. The pushswitch is used for getting the initial pressure during testing. The manometer indicates the pressure of the air in the suction tube;

Signal Processor: The signal processor consists of a processing unit with video screen, a keyboard and push button switches. The following information is keyed in for every test.

Test Programmes - This push but

Test parameters - This push button is used to select the test particulars.

ists of a peg A to hold a test yarn package B. Separate creeling devicesholding and guiding larger and softer strands like the sliver and rove. The test

guide C, tension guides D and a adjustable bar E. Thepushed leftwards or rightwards so as to increase or decrease the gap between the

control tension device F adjusts itself according to the test yarn count.The instrument also consists of measuring head G, rubber-covered rollers H, a suction circle I, a

button switch J and a manometer K. The measuring head consists of four slots of varying accommodating the following specimens.

s Nec count.For yarns of count greater than 30s Nec.

covered rollers are positively driven rollers that draw the test material through theinstrument. They can be run at any one of the following speeds, 25, 50, 100, 200 and 400 mThe speed is usually varied according to the test material. They deliver the test material into thesuction circle, which is a hole into which the material is sucked for disposal. The push

used for getting the initial pressure during testing. The manometer indicates the tion tube; this is usually kept at 1 kg/cm2.

The signal processor consists of a processing unit with video screen, a switches. The following information is keyed in for every test.

This push button sets the required test programmes.

This push button is used to select the test particulars.

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package B. Separate creeling devicessliver and rove. The test

guide C, tension guides D and a adjustable bar E. The bar can be ween the tensions guides. arn count.

covered rollers H, a suction circle I, a head consists of four slots of varying

covered rollers are positively driven rollers that draw the test material through the, 200 and 400 m/mm.

ey deliver the test material into thesuction circle, which is a hole into which the material is sucked for disposal. The push-button

used for getting the initial pressure during testing. The manometer indicates the

The signal processor consists of a processing unit with video screen, a switches. The following information is keyed in for every test.


Report parameters - The parameters required for getting a printed report are selected by this push button.

Video results - If the results are required on the video screen, they can be seen by usingthis button.

Test Series - This button is for selecting the number of samples to be tested and also series to be tested.

Start/stop button - This is to start or stop the instrument.

A key for initialising the signal processor; this is indicated by a red bulb indicator.

Printer: A printer is connected to the signal processor. It gives a printout of the test results when required. All the results are stored in the signal processor and immediately after the tests have been completed the results can be printed.Testing Procedure for Yarns

The instrument is switched on.

At least 30 minutes are allowed for warm up.

The test programmes, test parameters, test series and report parameters are selected by operating the keyboard and the other buttons of the signal processor. The selections are made to include the following information.

a. Test material particularsb. Results required on printer / videoc. Operator and other reference data required.

Yarn from the creel is passed through guides, the tension device, the measuring slot (capacitor) and finally fed into the suction circle.

The pressure in the manometer is checked to ensure the correct pressure.

When all of the above has been set, the instrument is ready for a test.

The start button is now pressed and the guide at the measuring head moves automatically to guide the yarn into the 3rd or 4th slot according to the yarn count.

The yarn passes continuously through the slot and it is monitored for a pre-selected period of one minute at a pre-selected speed of 400 m/min (for yarns).

The normal stroke diagram (variations with respect to the mean level) and the U% can be seen on video screen.

When the first test has been completed, the next specimen is threaded through the parts asbefore and the second test is started.

The test procedure is repeated until the selected number of tests is completed.

If there is any problem during a test, the signal processor clearly indicates it and the operator rectifies it before resuming the test.

After completing all the tests, the printer is switched on and the test reports are printed out. Printout normally provides the following information both in numerical and in graphical form.


1. Data relating to the test material, machine and test house particulars2. U%, CV% and imperfections3. Spectrogram4. Variance - length curves.

Table shows the Uster values for carded cotton yarn

Test Procedure for Sliver and RoveThe creel unit of the instrument is suitably modified to accommodate the sliver or rove. The testprocedure for these strands is the same as that described for yarn. The test programmes, parameters, video and printer results, etc are selected in accordance with the test material.test strand is then threaded through the instrument, the test performed and the results like theU%, CV%, Spectrogram, etc are printed out.

Analysis of Periodic VariationThe following are the major causes of periodic variations in yarn.

Poor fibre control - leading to drafting waves and

Mechanical defects in the machinery.The wavelength of the periodic variation plays a vital role in identifcause(s) variation. The example given under the next topic clarifies this.For a given strand, it is one of the previous machinery that introduces variation in the material. The following formula is used to find out the wavelength of periprevious machine.

Wavelength of variation introducedMachine by a previous (e.g. simplex)

1. Data relating to the test material, machine and test house particulars

values for carded cotton yarn:

Test Procedure for Sliver and Rove:The creel unit of the instrument is suitably modified to accommodate the sliver or rove. The testprocedure for these strands is the same as that described for yarn. The test programmes, parameters, video and printer results, etc are selected in accordance with the test material.test strand is then threaded through the instrument, the test performed and the results like theU%, CV%, Spectrogram, etc are printed out.

(U %)The following are the major causes of periodic variations in yarn.

leading to drafting waves and

Mechanical defects in the machinery.The wavelength of the periodic variation plays a vital role in identifying the source(s) that

variation. The example given under the next topic clarifies this.For a given strand, it is one of the previous machinery that introduces variation in the material.

following formula is used to find out the wavelength of periodic variation introduced by a

Wavelength of variation introduced Wavelength of variation in the yarnby a previous (e.g. simplex) =

Draft in the current machine (e.g. ring frame)

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The creel unit of the instrument is suitably modified to accommodate the sliver or rove. The testprocedure for these strands is the same as that described for yarn. The test programmes, testparameters, video and printer results, etc are selected in accordance with the test material. The test strand is then threaded through the instrument, the test performed and the results like the

he source(s) that

For a given strand, it is one of the previous machinery that introduces variation in the material. odic variation introduced by a

Wavelength of variation in the yarn

the current machine (e.g. ring frame)


Causes of Irregularity in Yarn: The causes of yarn irregularity can be broadly traced to the following factors.

1. Variation in the properties of the raw material.2. Inherent drawbacks of the machinery.3. Mechanical defects in the machinery.4. Extraneous causes.

Classimat System –Yarn FaultsThis is a system for evaluating yarn for faults. It classifies the faults into specific categories so that a clear picture of the number and type of defects in the yarn is obtained. Yarn faults Yarn irregularity can be broadly grouped into two categories namely the frequently occurring faults and the seldom-occurring faults. The frequently occurring faults are analysed by the Uster evenness tester and accessories whereas the seldom-occurring faults are scanned by the Uster classimat system.

Frequently Occurring FaultsThe frequently occurring faults are thin places, thick places and neps. These faults are defined as those deviating from the average value by a pre-determined reference value. Generally these imperfections are measured at density levels of 50, 3,3. With reference to these levels, a thin place is a region where the cross-section is less than half the cross-sectional size of the yarn average. Similarly a thick place is that region where the cross-sectional size is greater by 50% of the yarn average. A small, but sharp thick place is defined as a nep.

Rarely-occurring faultsFaults such as slubs, spun-in fly, loose fly, hard piercings, and long thin place constitute the not-so-frequent faults. These faults are to be avoided for two reasons.

They contribute to end breaks in processes such as winding, warping, weaving and knitting.

They take away the aesthetic appeal of the fabrics.The frequency of the infrequent faults is generally estimated in the industry by the number of breaks that occur and the faults that are ‘cleared’ by the clearers. The frequency of these faults varies widely between 5% and 75%. The use of this general information for determining the frequency and classification of the faults becomes practically meaningless. This is where the Uster classimat system comes in.

The Uster classimat system enables a quick, objective and comprehensive estimate of the infrequent yarn faults. The system is fundamentally designed to measure very large yarn imperfections like slubs, bad piecing, spun-in lint and not the conventional imperfections as those measured by the Uster Imperfections Indicator, namely thin places, thick places and neps. As the type of imperfections scanned by the classimat is rare occurrences in the yarn, they are referred to as infrequent faults.


The Classimat classification of faultsof yarn faults on the basis of the length and dimensionresults of fault classification in the format shown in the figure.faults. A letter of the English alphabet and a number identify each fault. Thelength range in which the fault liesthe fault lies.A-type faults are those that have alength range 1-2 cm; C-type faults, 2faults while the letters 'H' and 'I' represent the thin faults.

Figure: Classes of yarn fault as given by the Classimat

The number 1 represents a fault of size +of the yarn in the case of thick places and 30% to 45% in the casedenotes +150% to +250% for the thick places and 45% to 7numerals are attached to the E to G types of faultE-type of fault represents faults that are +1yarn and of length equal to or greater than 8

The F and G faults characterise faults that have crossthe mean transverse area of the yarn but the lengthfaults in the length range 8-32 cm while the Gclassimat system is programmelength class. Very simply, this mthe lower categories also. The table explains th

The Classimat classification of faults: The Uster classimat (UCM) provides a detailed breakof yarn faults on the basis of the length and dimension of the faults. This instrument presents the

fault classification in the format shown in the figure. There are totally 23 types of English alphabet and a number identify each fault. The letter represents the

e fault lies and the number indicates the transverse size range in

type faults are those that have a length in the range 0.1-1 cm; similarly, B-type faults aretype faults, 2-4 cm and so on. The letters A to G denote the thick yarn

the letters 'H' and 'I' represent the thin faults.

Classes of yarn fault as given by the Classimat

The number 1 represents a fault of size +100% to +150% over the nominal crossin the case of thick places and 30% to 45% in the case of thin places; number 2

the thick places and 45% to 75% for the thin places andnumerals are attached to the E to G types of faults since they are generally few in number. The

fault represents faults that are +100% and above the average cross-sectional area of the equal to or greater than 8 cm.

The F and G faults characterise faults that have crosssections in the range +45% to +1transverse area of the yarn but the length ranges are different; the F-type faul

32 cm while the G-type fault includes those aboveclassimat system is programmed to perform a cumulative counting of the faults within each

Very simply, this means that the bigger faults are automatically included as faults in also. The table explains this feature of the classimat for the A

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lassimat (UCM) provides a detailed break-uplts. This instrument presents the

There are totally 23 types of letter represents the

and the number indicates the transverse size range in which

type faults are in the A to G denote the thick yarn

cross-sectional size n places; number 2

5% for the thin places and so on. No since they are generally few in number. The

sectional area of the

ions in the range +45% to +100% over type fault includes

type fault includes those above 32 cm. The cumulative counting of the faults within each

automatically included as faults in the A-type faults.


*al, a2 and a3 are the absolute faults in the respective categories.the length classes. The cumulative indication of the faults facilitates thevalue of all disturbing yarn faults for each lengtgrouped into three categories. These are listed below.

Short thick faults: A1 + B1 + C

Long thick faults: E + F + G

Long thin faults: H1 +I1

Causes of the short thick faults Presence of large amount of trash

resulting in insufficient opening and cleaning at blow

Use of low-micronaire cottons with high level of immaturity

Use of cotton lots containing a high proportion of short fibres

Excessive fibre entanglements while opening and cleaning in blow

Use of improper settings between cylinder and flats in cards

Damaged wire points in cylinder, doffer and flats in cards

Absence of top roller clearers in speed frame

Use of broken and damaged surface of the floating condensers and roving guides

Use of too wide or narrow settings in ro

Use of improper spacers in speed and ring frame

Causes of the long thick faults Presence of unopened rovings in the blow

Folding or overlapping of the blowcards.

Use of improper settings in draw frames

Too low a web or creel draft in draw frame resulting in improper drafting

Loose bottom and top apr

Improper seating of floating and fixed condensers in speed frames

Improper piecing in speed and ring frames

Occurrence of lashing-in and excessive end breaks in speed frames

Absence of top or bottom roller clearers in speed and ring

Occurrence of short fibre choking in the hollow leg fly

Too close a setting between traveller clearer and traveller in ring frames

are the absolute faults in the respective categories. The above is applicable for all the length classes. The cumulative indication of the faults facilitates the evaluation of the sum value of all disturbing yarn faults for each length class. The 23 classes of faultsgrouped into three categories. These are listed below.

+ C1

Long thick faults: E + F + G

Causes of the short thick faultsPresence of large amount of trash or high proportion of seed coat fragments in the mixing resulting in insufficient opening and cleaning at blow-room and carding.

micronaire cottons with high level of immaturity.

Use of cotton lots containing a high proportion of short fibres.

xcessive fibre entanglements while opening and cleaning in blow-room

Use of improper settings between cylinder and flats in cards.

Damaged wire points in cylinder, doffer and flats in cards.

Absence of top roller clearers in speed frame.

damaged surface of the floating condensers and roving guides

Use of too wide or narrow settings in roving and spinning machines.

Use of improper spacers in speed and ring frame.

Presence of unopened rovings in the blow-room lap or card slivers.

Folding or overlapping of the blow-room layers while feeding to the licker

Use of improper settings in draw frames.

Too low a web or creel draft in draw frame resulting in improper drafting

Loose bottom and top aprons in speed frames.

Improper seating of floating and fixed condensers in speed frames.

Improper piecing in speed and ring frames.

in and excessive end breaks in speed frames.

Absence of top or bottom roller clearers in speed and ring frames.

re choking in the hollow leg flyer of speed frames

Too close a setting between traveller clearer and traveller in ring frames.

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The above is applicable for all evaluation of the sum

h class. The 23 classes of faults are further

or high proportion of seed coat fragments in the mixing

room.

damaged surface of the floating condensers and roving guides

room layers while feeding to the licker-in of the

Too low a web or creel draft in draw frame resulting in improper drafting.

er of speed frames.


Use of narrow spacer in ring frames resulting in non

Use of fibres having excessivin the yarn.

Causes of the long thin faults Excessive incidence web falling (partial or full) in cards

Too high a break/creel draft or web drafts in draw frames

Excessive variation in top ro

Loose top roller end bushes in draw frames

Disturbance to the free rotation of creel calender rollers in draw frames

Sliver stretch of the creel in speed frames due to too high a creel draft

Too high a break draft in speed

Benchmarks for classimat faultsfaults present in Indian yarns as reported by SITRA. The values serve as benchmarks to compare the occurrence of the infrequentexport yarn were evaluated by means of classimat system II.

Use of narrow spacer in ring frames resulting in non-drafted ends.

Use of fibres having excessive variation in fibre length resulting in formation of crackers

Excessive incidence web falling (partial or full) in cards.

Too high a break/creel draft or web drafts in draw frames.

Excessive variation in top roller pressure in draw frames.

Loose top roller end bushes in draw frames.

Disturbance to the free rotation of creel calender rollers in draw frames.

Sliver stretch of the creel in speed frames due to too high a creel draft.

Too high a break draft in speed frames.

Benchmarks for classimat faults: The table gives the average occurrences of different type of reported by SITRA. The values serve as benchmarks to compare yarn faults in spinning mills. The seldom occurring faults in the

means of classimat system II.

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e variation in fibre length resulting in formation of crackers

The table gives the average occurrences of different type of reported by SITRA. The values serve as benchmarks to compare

mills. The seldom occurring faults in the


UNIT-III

1. Tensile Testing of textiles –introduction terminology and definitions.

Introduction: The level of strength required from a yarn or fabric depends on its end use. For some end uses it is the case that the higher the strength of the materials, the better it is for its end use. This is particularly true for yarns and fabrics intended for industrial products. However, fabrics intended for household or apparel use merely need an adequate strength in order to withstand handling during production and use. It is generally the case that a higher-strength product can only be obtained by either making a heavier, stiffer fabric or by using synthetic fibres in place of natural ones. In either case changes are produced in other properties of the material, such as the stiffness and handle, which may not be desirable for a particular end use.

Terminology & Definitions: Units: It is important when measuring strength to be clear about the distinction among mass,

weight and force. The SI unit of mass is the kilogram (kg). Force can only be defined in terms of what it does. Force is that which changes a body's state of rest or of uniform motion in a straight line. In other words a force causes a body to accelerate. The SI unit of force the Newton (N) is defined in terms of the acceleration produced when the force acts on a mass of one kilogram.

Breaking strength; tensile strength: This is the maximum tensile force recorded in extending a test piece to breaking point. It is the figure that is generally referred to as strength. The force at which a specimen breaks is directly proportional to its crosssectional area, therefore when comparing the strengths of different fibres; yarns and fabrics allowances have to be made for this. The tensile force recorded at the moment of rupture is sometimes referred to as the tensile strength at break.

Stress: Stress is a way of expressing the force on a material in a way that allows for the effect of the cross-sectional area of the specimen on the force needed to break it:

Stress = force applied / cross-sectional area

In the case of textile materials the cross-sectional l area can only be easily measured in the case of fibres with circular cross-sections. The crosssections of yarns and fabrics contain an unknown amount of space as well as fibres so that in these cases the cross-sectional area is not clearly defined. Therefore stress is only used in a limited number of application s involving fibres.

Tenacity: Tenacity is defined as the specific stress corresponding with the maximum force on a force/extension curve. The nominal denier or Tex of the yarn or fibre is the figure used in the calculation; no allowance is made for any thinning of the specimen as it elongates.

Breaking length: Breaking length is an older measure of tenacity and is defined as thetheoretical length of a specimen of yarn whose weight would exert a force sufficient to break the specimen. It is usually measured in kilometres.


Elongation: Elongation is the increase in length of the specimen from its starting length expressed in units of length. The distance that a material will extend under a given force is proportional to its original length; therefore elongation is usually quoted as strain or percentage extension. The elongation at the maximum force is the figure most often quoted.

Strain: The elongation that a specimen undergoes is proportional to its initial length. Strain expresses the elongation as a fraction of the original length:

Strain = Elongation / Initial Length

Extension percentage: This measure is the strain expressed as a percentage rather than a fraction

Extension = (Elongation / initial length) X 100% Breaking extension is the extension percentage at the breaking point.

Work of rupture: The work of rupture is a measure of the toughness of a material as it is thetotal energy required to break the material. Consider a small section of the force extension curve. Within this small section the force can be considered to be constant at a value F. This force increases the sample in length by an amount d/, therefore

Work done = force X displacement = FdI

From this the total work done in breaking the material which is the work of rupture is:

2. Load & Elongation Curve- the stress strain curve.

When an increasing force is gradually applied to a textile material so that it extends and eventually breaks, the plot of the applied force against the amount that the specimen extends is known as a force-elongation or stress-strain curve. The curve contains far more information than just the tensile strength of the material. The principal features of a force elongation curve, in this case of a wool fibre, are shown in Fig. The use of the force elongation curve as a whole allows a better comparison of textile materials to be made as it contains more information about the behaviour of the material under stress than do the simple figures for tensile strength and elongation.The most important features of the curve are as follows.

Yield point: Depending on the material being tested, the curve often contains a pointwhere a marked decrease in slope occurs. This point is known as the yield point. At this point important changes in the force elongation relationship occur. Before the yield point the extension of the material is considered to be elastic that is the sample will revert to its original length when the force is removed. Above the yield point in most fibres, some of the extension is non-recoverable, that is the sample retains some of its extension when the force is removed.


Young's modulus: This value is obtained from the slope of the least squares fit straightline made through the steepest linear region of the curve as shown in Fig.

Breaking point: when loading is continuing a point will come where the yarn will break as shown in the figure and that load or force is known as breaking force.

3. Elastic Recovery- instantaneous and time depended effects.

The effects of time are important in the mechanical behaviour of textile fibres. For example, if a rope were made to carry a heavy fixed load for a long time, how would it respond or behave?Similarly, how would be the behaviour of a fibre material (e.g. rubber fibre), which is maintained at constant strain for an extended period of time?Three variables are always present in a tensile test of textile fibres, load, elongation and time. Ofthese three, time is the variable that can never be kept constant! So it is usual to study the effects of time in one of two ways.

Keeping the load constant and observing the change in elongation with time - the effect is known as creep.

Keeping the elongation constant and observing the change in load with time - this effect is called stress relaxation.

Creep: Creep may be defined as the gradually increasing elongation shown by a fibre specimen with respect to time when subjected to a constant load. The study of the creep behaviour of a fibre can be split into two aspects.1. Instantaneous creep effect2. Time dependent creep effect


The creep behaviour of a fibre under a constant loadillustrated schematically in the figure, in which the constant loadof time OC.

The figure (a) is the load-time relationship. Loadconstant over the time period of the test as shown bybetween strain and time and depicts the creep behaviour of the fibre specimen.specimen extends rapidly and this is calledextension slows down gradually with time and this is thereforeThe total extension is thus made up of two components, the insdependent extension. This time dependent extension is called creep.

On removal of the load at point B in the figure,more slowly with perhaps a small amount of residualThe instantaneous extension is composed of two1. The elastic extension which is recoverable and2. The plastic or permanent extension, which is not

The creep behaviour of a fibre under a constant load and its recovery under zero schematically in the figure, in which the constant load on the specimen is for a period

time relationship. Load OA is applied to the fibre and this remainsconstant over the time period of the test as shown by the line AB. The figure (b)

and depicts the creep behaviour of the fibre specimen.specimen extends rapidly and this is called the ‘instantaneous extension‘. Thereafter the

slows down gradually with time and this is therefore called the time dependent effect. thus made up of two components, the instantaneous extension and the time

dependent extension is called creep.

On removal of the load at point B in the figure, the specimen recovers rapidlywith perhaps a small amount of residual extension referred to as ‘permanent set

The instantaneous extension is composed of two quantities.1. The elastic extension which is recoverable and2. The plastic or permanent extension, which is not recoverable.

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and its recovery under zero loads is on the specimen is for a period

OA is applied to the fibre and this remains) is a relationship

and depicts the creep behaviour of the fibre specimen. Initially the the ‘instantaneous extension‘. Thereafter the

called the time dependent effect. extension and the time

y at first and thenn referred to as ‘permanent set.


Similarly, the time dependent extension is a combination of two parts; primary creep which isrecoverable and the secondary creep, which is not recoverable.

In the figure b,Instantaneous extension = a — bTotal creep = b — cPrimary creep = e — f (recoverable)Secondary creep = g—h(Non-recoverable or permanent deformation)Instantaneous recovery on removal of load =d—e

One of the classic examples of the effects of creep is that of the behaviour of an automobile tyrereinforced with nylon continuous filament tyre yarn. After a long drive in a car running on nylon-yarn reinforced tyres, the tyres get quite hot. When the car is stopped for a while to rest them, the weight of the car acting on the tyres constitutes constant large load acting on the tyres. Due to the heat and the creep effect of the nylon, the tyres acquire a flat shape at the point of contact with the ground. When the car resumes its journey, a ‘thumping’ sound is heard because of the partly-flattened tyres. The noise stops after a while when the circular shape of the tyre is regained.

4. The Mechanism of strength testing machines –CRL, CRE & CRT.Principles of applying load to yarn test specimens in the section on Fibre Strength, it has been discussed in some detail that three ways of applying the load to the test specimen are prevalent in tensile testing. These are listed below. Just as fibre strength testers have one or another of these principles inbuilt in their design, so too do yarn tensile testers incorporate them. Yarn tensile testers that include the principles in their design are indicated in each case.

Constant rate of loading (CRL) e.g. Scott I. P. Tester and Uster Dynamat.

Constant rate of extension (CRE) e.g. Instron Tensile Tester, Uster Tensorapid.

Constant rate of traverse. (CRT) e.g. Pendulum lever type single thread and lea strengthtesters.

The student is referred to the earlier discussion on the three alternatives to load a test specimenand their implications in testing practice. However, the principles alone are illustrated here andbriefly explained below for the convenience of the student.

CRLThe ends of a test specimen A are mounted respectively in an immovable jaw J1 and a traversable jaw J2. A gradually increasing force F, starting from zero but increasing at a constant rate, is applied to the specimen. The applied force causes the specimen to extend until it breaks. In this case, the loading causes elongation. Since the load on the specimen increases at a constant rate, this principle of loading is called the Constant Rate of Loading (CRL) principle.


CRESpecimen B has its ends mounted respectively in a nonjawJ4. The latter is moved downwards at a constant rate of speed by a screwinitial tension in the specimen is zero,specimen suffers extension and this would cause it towould go on increasing until it is so high that the specimen breaks.elongation is responsible for the tension or loading in the specimen. So this prinis called the Constant Rate of Elongation

CRTSpecimen C is fixed exactly like Specimen 2, buttruly fixed as in the above cases,pulley at the top to operate a load indicating mechanism. The lower jawa constant rate to elongate therelative to that of the lower jaw preverate. This principle of loading is therefore referred to as theprinciple. Though in this case too, specimen extension causes loading, it isCRE principle.

unted respectively in a non-traversable jaw J3 and a traversable moved downwards at a constant rate of speed by a screw

initial tension in the specimen is zero, but when the bottom jaw moves downward, thers extension and this would cause it to be loaded; the tension in the specimen

increasing until it is so high that the specimen breaks. In this case, the applied the tension or loading in the specimen. So this prin

is called the Constant Rate of Elongation (CRE) principle.

Specimen C is fixed exactly like Specimen 2, but between Jaws J5 and J6. The upper jaw is not as in the above cases, but due to an instrumental design feature, is connected to a

operate a load indicating mechanism. The lower jaw traverses downward at a constant rate to elongate the specimen, exactly like J4. The movement of the upperrelative to that of the lower jaw prevents the extension of the specimen at a precisely constant

This principle of loading is therefore referred to as the Constant Rate of Traverse (CRT) this case too, specimen extension causes loading, it is different from the

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traversable jaw J3 and a traversable mechanism. The

but when the bottom jaw moves downward, thebe loaded; the tension in the specimen

In this case, the applied the tension or loading in the specimen. So this principle of loading

. The upper jaw is not design feature, is connected to a

traverses downward at specimen, exactly like J4. The movement of the upper jaw

extension of the specimen at a precisely constant Constant Rate of Traverse (CRT)

different from the


5. Factors influencing yarn strength – factors affecting the test results obtained from testing instruments.

Factors influencing yarn strength: Staple length: Long staple fibre will normally give stronger yarn than short staple fibre as

more twist can be inserted in a strand of long fibres. Increased twist gives rise to increased strength. Even at low twist factors, a yarn consisting of long fibres will be stronger than one with short staple fibre. The effect of twist in binding the fibres will be greater when long fibres are present than if short fibres were present.

Fibre fineness: Fine fibres produce stronger yarn than coarse fibres for a given count of yarn. The finer the fibre, the greater the number of fibres in the yarn cross-section and consequently, the greater will be the inter-fibre friction. Thus the finer the fibre the greater in general will be the yarn strength. In the case of cotton this effect is the more pronounced as the finer fibres are also the stronger fibres.

Fibre strength: Stronger fibres produce stronger yarn. For the reasons explained in the previous point, even with relatively weak fibre, increased fineness of the fibres will produce a yarn of acceptable strength.

Twist: In the section on yarn twist, it was mentioned that the strength of a staple fibre yarn increases with twist until the optimum level of twist is reached when the yarn shows maximum strength. The optimum twist level is also a function of the twist angle and the twist multiplier (TM). The right TM is chosen for yarns of different types and meant for different end uses.

Evenness: The strength of a yarn is directly related to its uniformity. The more uniform a yarn is the higher is its strength and vice-versa. Poor uniformity leads to a greater number of weak places in the yarn and a correspondingly lower strength.

Fibre length variation and distribution: In the case of staple fibre with inherent natural variation, like cotton, the strength of yarn spun from it is greatly influenced by short fibre content. The greater the short fibre content the weaker the yarn and vice versa. The fibre length distribution should also be uniform to get optimum strength.

Fibre finish: The following finishes are usually applied to synthetic staple fibres during the early stages of spinning to improve their processing performance. Spin finish & Anti-static finish. The type and amount of chemicals in the finish composition will have a definite influence on the strength of the resulting yarn. Not only would the characteristics of the fibre be altered but also the strength of the yarn may increase or even decrease.

Factors affecting the test results obtained from testing instruments.The tensile properties of textile materials are influenced by the following factors.1. Test specimen length: In a tensile test, the longer the test specimen the lower in general is

its strength. The breaking load of a specimen at different gauge lengths. Actually the strength of the weakest point in the specimen. When the material is tested using shorter gauge lengths,


the breaking loads .yarn tested at a shorter gauge length shows greater strength because it would have relatively fewer weak points. As the test length increases, the possibility of there being a greater number of weak point’s increases and the mean strength would not reflect the actual strength of the material. This is called the “weak link effect”. This effect is overcome in tensile testing by standardising the length of the test specimen.

2. Speed of test or time to break the specimen: the section on fibre strength it was discussed that the speed of a tensile test influences the breaking load high speed test is one in which the specimen is loaded at a rapid rate and it breaks very quickly. A slow tensile test is the opposite; the rate of loading is low and the specimen takes a long time to break with yarns too, a rapid test would result in a greater breaking load than a slow test.

3. Capacity of the tensile tester: The capacity of a tensile tester would depend upon the breaking load of the sample being investigated. If a yarn is tested in a machine with a very high capacity, meant for very strong strands, it would break at a low time-to-break and a higher than expected breaking load would result.

4. Effects of Humidity and Temperature: The atmosphere moisture influences the structure and mechanical behaviour of textile fibres. So, for routine tensile testing, it is essential that the standard testing atmosphere is always maintained, i.e. 65 ± 2% RH and 27 ± 2° C, in the case of a tropical country like India.

5. Previous history of the specimen: Textile materials are subjected to various forms of stress and strain during the following processes. Various stages in the yarn manufacture & Chemical processing the tensile strength of textile materials will vary depending upon its exact previous history. Some examples are cited below. A mechanically conditioned or a work-hardened textile would be stronger than one that is not conditioned thus. The strength of a sized yarn would generally be stronger than the original unsized yarn. A bleached textile would in general be weaker than the original grey material.

6. Form of the test specimen: The material for test may be available in different forms, namely single yarn, double yarn, etc. These yarns will have different tensile strength. Further factors associated with the form and structure of the yarn would also influence the results. For example, a six-ply yarn produced in one single doubling operation could have a different strength compared with a six-ply cabled yarn made up of the same singles count, but which consists of three strands of two-ply yarn, produced in two doubling operations.


6. The Pendulum Lever Yarn Strength Tester

The pendulum lever principle of instrumentas well as lea testing on a regular basis. These areprinciple of loading the test specimen.

The pendulum lever principle: J1 and a lower jaw J2. The upper jaw ispulley C, of radius r. The lower jaw is given a constantby means of the screw mechanitransmitted to the small pulley via the steeland causes the pendulum P to swing away from itspivoted at the same point as the pulley and it swings over an arcwhile it moves thus, it pushes a pointer along the scale. When the specimenpendulum stops moving and the position of

Let M be the mass of pendulum and let itsE. Assuming for the moment that the specimen is

The Pendulum Lever Yarn Strength Tester

of instrument design has been in popular use for both singleas well as lea testing on a regular basis. These are sturdy instruments that operate on the CRT

loading the test specimen.

: The figure shows a specimen A fixed in between anJ1 and a lower jaw J2. The upper jaw is attached to a steel band B, which runs over a smallpulley C, of radius r. The lower jaw is given a constant rate of traverse in a downward direction

screw mechanism D. This causes tension in the specimen. The tensiontransmitted to the small pulley via the steel band. The pulley rotates in an anticlockwise directionand causes the pendulum P to swing away from its vertical position of rest. The pendulum is

same point as the pulley and it swings over an arc-shaped load scale at its free end; pushes a pointer along the scale. When the specimen

pendulum stops moving and the position of the pointer indicates the specimen‘s breaking load.

Let M be the mass of pendulum and let its- centre of gravity lie at a distance R from itsAssuming for the moment that the specimen is inextensible and that there are no dynamic

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design has been in popular use for both single-yarn sturdy instruments that operate on the CRT

imen A fixed in between an upper jaw attached to a steel band B, which runs over a small

rate of traverse in a downward direction This causes tension in the specimen. The tension is

band. The pulley rotates in an anticlockwise directionvertical position of rest. The pendulum is

shaped load scale at its free end; pushes a pointer along the scale. When the specimen breaks, the

imen‘s breaking load.

centre of gravity lie at a distance R from its pivot at inextensible and that there are no dynamic


forces acting on it at any chosen instant, let radians be the angle through which the pendulum has moved. Given these conditions, the following relationship may be derived.The system will be in equilibrium if the moment exerted by the load is balanced by the moment exerted by the weight of pendulum. Taking moments about the pivot of the small pulley, we get,

F×r = Mg×x =Mg R Sin θSince Mg, R and r are constant we can substitute (MgR)/r by the constant K.F = K Sin θ i.e. F∞ Sin θ

As the force F acting on the tape is equal to the tension in the specimen, the tension in thespecimen is proportional to the sine of the angle through which the pendulum moves from its initial vertical position. As increases, so too does Sinθ. Thus the force in the specimen goes on increasing until it breaks.

7. Inertia EffectsIn an instrument in which there are a number of parts that move due to mechanical forces,

errors related to inertia, acceleration, etc will occur. It cannot therefore be assumed that theinstrument is free from dynamic forces acting on the specimen. In actual practice, two effects ofinertia namely overthrow and acceleration affects the final results. Appropriate corrections have thus to be made.

Overthrow errorIn pendulum type testers, even after the specimen breaks, the pendulum will continue to move until all the kinetic energy possessed by the pendulum has been dissipated. So, the instrument tends to show a higher breaking load. The additional load would depend upon the angular velocity of the pendulum at the moment of specimen break.

Called the overthrow error, it is naturally found to be the greatest in the case of low breaking loads. This error can be overcome to a great extent by using a lower rate of traverse. It is also for this reason that materials showing breaking loads less than 10% of the tester capacityshould not be tested. Further inextensible materials will give rise to higher overthrow errors as inthis case the velocity of the upper jaw will be about the same as the velocity of the lower jaw andthus give the pendulum a higher angular velocity.

Acceleration errorIn the pendulum-lever tester, there will be a tendency, at the start of a test, for the specimen to stretch before any load is recorded. Tension develops in the specimen increasingly until it issufficient to overcome the inertia of the pendulum. The initial force required to move the pendulum is greater than the force required to keep the pendulum moving at its required angular velocity. Hence, there will be a tendency for the pendulum to overshoot or accelerate; the tension in the specimen reduces as a result and it slackens even as an increasing load is being indicated.If the above points are kept in mind and appropriate corrections are made for the errors stated,


the pendulum lever tester is the most economicaand the lea strength of spun yarns.

The Pendulum Lever Single Thread Strength The principle on which this instrument works when using it have been discussed above. The parts of the instrument andnormally followed are discussed asDescription of the instrumentThe salient features of the instrument are shown in theupper jaw J1 and a lower jaw J2. A yarn specimen ‘A’ taken from supplythrough the thread guide C and isthread spindle-rod D, driven by a motor E through aH.

pendulum lever tester is the most economical method of finding out the singlethe lea strength of spun yarns.

Lever Single Thread Strength Tester (CRT)principle on which this instrument works is CRT and some of the factors to be b

been discussed above. The parts of the instrument and the test procedure rmally followed are discussed as follows.

The salient features of the instrument are shown in the figure. The instrument consists of an lower jaw J2. A yarn specimen ‘A’ taken from supply package B passes

through the thread guide C and is clamped at the jaws. The lower jaw is driven by a screwrod D, driven by a motor E through a gear box F, a stepped pulley G and a c

Page 85

l method of finding out the single-thread strength

of the factors to be borne in mind the test procedure

figure. The instrument consists of an package B passes

clamped at the jaws. The lower jaw is driven by a screw-gear box F, a stepped pulley G and a clutch


A traverse speed control handle I connected to a ' variable stepped-pulley drive enables the bottom jaw to be traversed in two ranges namely: i) 50 to 150 mm / minute and ii) 150 to 500 mm / minute. The clutch can be used to lower or raise the lower jaw. This jaw is connected to a rod and a pin arrangement (J and K) that can be raised or lowered to accommodate testspecimens of desired gauge lengths from 0 to 500 mm. The rod on which the lower jaw is mounted is housed inside the screw-thread spindle rod D. The upper jaw is connected to a chain L, which in turn is connected to a sector M and a pendulum N. The sector replaces the pulley in some of the older versions.

The arm of the pendulum is connected to a pointer O, such that when the pendulum moves, along the serrated quadrant scale P, the pointer too is pushed along with it. The quadrant scale is graduated in two ranges. The upper range includes the breaking strength values from 0 to 2000 g and the regular pendulum is used. The lower scale is graduated to read from 0 to 10 kg and asmall additional weight Q is added to the pendulum when this scale is required to be used. When the instrument is at rest, the pendulum arm and the pointer are in line with the zero reading on the scale.The pendulum is held in this position by means of a catch R. A set of pawls S, attached to the arm of the pendulum, work on the serrations on the top face of the quadrant scale when the pendulum is in motion. As soon as the test specimen breaks the pawls fall into the serrations and the movement of the pendulum is arrested.A pointer T, connected to the upper jaw, helps to read the specimen elongation on the elongation scale U. A catch V, inserted below the lower jaw rod, keeps the specimen under tension at the start of a test. The instrument is usually set to give a specimen breaking time of 20 i 3 seconds. The rate of traverse of the lower jaw is normally set at 300 mm I min (or 12 inches per minute in the older models of the instrument).

Testing ProcedureThe required specimen length is set by using the rod and pin (J & K). The traverse speed is set byusing traverse speed control handle (I). The pointers on the strength scale and elongation scale are brought to zero position. The pendulums and the movement of the upper jaw are arrested with a catch. The specimen to be tested is taken and clamped between the upper jaw and thelower jaw. The extra material is cut off exactly at the jaw position and then the catch is taken out.So the yarn is under tension before testing. When the instrument is started, the lower jawtraverses downward imposing tension on the specimen and thereby pulling the upper jaw; this in turn will make the pendulum to move over the quadrant scale. When the specimen ruptures, the pendulum arm is retained in the position by a set of pawl working over the serrated portion of the quadrant. The position of pendulum arm gives the breaking load of the specimen. This is read bythe pointer (O). 50 tests are done for single yarns and 25 for plied yarns. Every time thependulum arm is brought to zero position and the movement of the upper jaw is arrested. Then the tenacity is calculated using the formula


Mean breaking load in kg ×1,000Tenacity in g/tex = Count of yarn in tex

Apart from the breaking load, the elongation is also measured by noting down the relativeposition of the upper jaw. The elongation scale pointer (T) directly reads the difference in themovement of both the lower and upper jaws. This can be calculated in terms of percentage by: Elongation scale readingElongation % = x 100 Gauge length or specimen length

Since small samples are being tested, the range in the strength value will be very high and thereby increase the CV%. The number of spun yarn samples to be tested in the standard test procedure for 20 inches is 50.

Scales in the pendulum lever type strength testing instrumentsIn pendulum lever type of strength testing instruments, the force acting on the specimen is directly proportional to the sine of angle through which the pendulum has moved.So

If the recording strength scale is circular, the graduations for reading strength will be even.

If the scale is a serrated quadrant, the graduations are initially closely spaced and further on they are spaced more widely. An additional pendulum positioned at the top pivot has beenused to overcome this effect and have regularly spaced graduations.

Advantages over a single-thread strength test The time required to test a lea is much less.

The lea strength is useful for comparing the quality of yarns spun from different cottons

The yarn count can be determined subsequently using the ruptured lea from a test.

The effects of yarn irregularity can be seen more clearly in a lea strength test.

Any errors due to sampling are not really significant.

Yarn leas Strength Tester

The lea tester is a popularly used instrument and is a common sight in the test houses of yarnmanufacturing organisations. It is a very sturdy machine and works on the pendulum lever principle. It uses the CRT principle of loading the specimen, which is a 120-yard skein or a lea of yarn. Both the pendulum lever and the CRT principles have already been explained above.

Description of the instrument: A typical lea tester is shown in the figure. The entire set-up is exactly like that of the single-thread tester, except that this machine is heavier and of a higher capacity, as a lea is to be tested. This instrument is also motor-driven but it requires a bigger motor.


In a lea tester, there are no typical jaws to ‘clamp’ the test specimen. Instead there is an upperhook H1 and the lower hook H2. ‘A’ is the specimen inserted over them. The lower hook is traversed by a screw mechanism driven at constant speed by motor C.The rate of traverse in a lea tester is usually 12 inches (300 mm) per minute. The upper hook is connected to a steel band D, which in turn is connected to pulley E and pendulum F. The pendulum has a heavy bob G. Pawl I is attached to the pendulum. It moves over a serrated quadrant K. The pawl works in the serration on the quadrant scale and helps the pendulum to stop at the precisely when the lea breaks. Pointer L is connected to the arm of the pendulum via a gear mechanism. The pointer moves over a dial M and indicates the lea strength in pounds (in older models) or in kilograms (in more recent models).

Test Procedure: From the test cops or cones, at least fifteen 120-yard leas are prepared using a standard wrap reel. The precautions to be observed when using wrap reels. One of the leas is slipped over the hooks of the tester so that it forms a flat, evenly-spread sheet of yarn. The following precautions are taken while preparing leas and mounting them in the tester.


The yarns should be reeled under uniform tension.

The yarns should be reeled such that the individual strands forming the lea make up anarrow sheet of yarn with the strands parallel to each other; grouping or bunching ofthreads is to be avoided.

The lea should be mounted on the hooks of the tester as a flat even sheet of yarn; none of the strands should be in a twisted state or should ride over adjacent threads.

The pointer should initially read zero on the dial. If not, the pendulum and the pawl aresuitably adjusted to ensure this.

The lower hook is engaged with the screw mechanism and the motor is switched on. The hook -now traverses downwards at a constant rate. The threads in the test specimen straighten up and start getting elongated and pulled down by the screw. As the yarns are pulled down, there is apull on the upper hook. This causes the pendulum to be pulled and this in turn moves the pointer over the dial. As all of this happens, one or two threads break and many of them therefore slip around the hooks. When the lea offers no further resistance, the pendulum stops instantly and the pawls working in the serration on the quadrant prevent it from swinging back to its original position of rest. At the same time the pointer also stops moving and indicates the breaking load of the lea on the dial. The lea strength reading is now taken and recorded. The lower hook is then reversed back to its previous position and the broken lea is removed from the hooks. The remaining 14 leas are then tested in like manner and the mean breaking load is calculated.

Capacity of the Lea Tester: When performing tests on a lea tester, it must be ensured that the breaking load value of the test leas lie between 10 and 90 per cent of the breaking load range of the instrument used. If the values fall outside this range, an instrument of a different appropriate capacity is to be selected.Drawbacks of the lea-strength tester

1. The lea strength of a yarn is not truly representative of the combined strengths of the 80 individual threads in the lea. It is only a near approximation of the combined strength.

2. The following human errors lead to unreliable lea strength values like uneven yarn tension during wrapping of the test material. If the threads are inclined during a test, the lea strength value obtained will not be accurate.

3. Lea strength values serve little purpose in winding or weaving operations. In theseprocesses, the yarn is used as individual strand and not as a skein.

4. The rupture of a single thread at a weak place affects the results of the whole skein.5. As the lea tester is of the CRT-type, inertia errors may affect the results.6. The skein test does not give an indication of the extensibility and elastic properties of the

yarn; these are important characteristics of the yarn that greatly influence the weavingprocess.


The merits of a lea tester A lea tester is a simple instrument that is easy to use. Most textile industry personnel are

accustomed to using one for routine testing. So it is still very much prevalent.

The broken lea remaining after a lea strength test is used to determine the yarn count. The lea strength and the yarn count are combined into a parameter called the Count-Strength-Product or the CSP, the values of which are useful to both buyer and seller.

Though a lea test is not a particularly sensitive test to identify the weakest point in the yarn, it is sensitive enough to detect changes in yarn quality. For example, incorporation of cotton waste in mixing, changes in settings, changes in the weighing system, etc, can be detected.

A lea tester does not contain any complicated part or mechanism. It is a strong and robustinstrument and gives long period of service without trouble.

Many samples can be tested in a short duration of time to have a comparative idea of the material emerging from the spinning room. So the lea test is still regarded as a handy testby the spinner in general.

The Inclined Plane Principle

Constant rate of loading (CRL) test conditions are obtained in the inclined plane type of testers.The figure shows the basic features of this principle. A yarn specimen ‘A’ is clamped between a fixed jawJ1 and a movable jaw J2. Jaw J1 is fixed to a plane or rail BC and jaw J2 is fixed to a freely movable carriage D. The plane is pivoted at E and lowering its right end can therefore tilt it. The right end of the rail is linked to a rack and pinion drive F, which is driven by a motor. At the start of a test, the plane is horizontal and its right end is at C. When the rack is set in motion, the end C descends to position C‘.

Let the rail swing through an angle θ when its right end moves from position C to position C‘. This is also the angle of inclination of the rail from the horizontal. Let W be the weight of the carriage acting downwards. The force P acting on the yarn specimen can be calculated by resolving the vertical force W in two directions, one parallel to the plane and the other perpendicular to it.If P is the force parallel to the plane i.e. the force applied to the specimen due to the carriage rolling on the inclined plane, then P = W sin θ, P α sin θHence, the load on the specimen is directly proportional to the sine of the angle of inclination ofthe rail. Now consider the triangle E C'C,Sin θ = CC’/ EC’For a given machine EC’ is a constant and therefore sin is proportional to CC’. Thus, if sin is θincreased at a constant rate, the load on the specimen can be increased at a constant rate.


This is easily achieved by increasing CCand the Uster Dynamat Instrument, the rightsmall pedestal or platform, as shown in the figure. Thedrive mechanism. It can be seen here that the rate ofthe specimen. Apart from this, the instrument can bea material and also the effect of loading and

The Inclined Plane Single-Thread Strength Tester

The Scott IP Tester and the Uster Dfor evaluating single thread strength. Both theseabove.The Scott Inclined Plane TesterThis instrument is used to find single the “inclined plane principle” and is designed to give aspecimen.Description of the instrument: instrument consists of a creel A to hold thea dead-weight-and-lever arrangement D can be adjustedspecimen. A fixed jaw E is attached to one end of a long rail G (thefixed jaw can be adjusted to set any desired specimen H. The rail is graduated up to 500 mm.Another jaw F is attached to a carriage or trolley I thatcan take on an additional weight J, to

This is easily achieved by increasing CC’ at a constant rate. In the Scott Inclined Plane Tester and the Uster Dynamat Instrument, the right end C of the plane is actually a wheel that sits on a small pedestal or platform, as shown in the figure. The platform is lowered or raised by a gear drive mechanism. It can be seen here that the rate of loading is not affected by the extension of

cimen. Apart from this, the instrument can be used to study the stress-strain properties of a material and also the effect of loading and unloading at various stages.

Thread Strength Tester

the Uster Dynamat Instrument are two examples of inclined plane testers evaluating single thread strength. Both these instruments work on the principle explained

The Scott Inclined Plane Testerfind single yarn strength and its RKM value. The instrument works on

“inclined plane principle” and is designed to give a constant rate of loading to the test

: The figure shows the major features of the Scott IPinstrument consists of a creel A to hold the test yarn package B. A tension device C consisting of

lever arrangement D can be adjusted to apply a fixed pre-tension to the test fixed jaw E is attached to one end of a long rail G (the left end in the figure). The

set any desired specimen length. The rail can swingH. The rail is graduated up to 500 mm.Another jaw F is attached to a carriage or trolley I that can roll freely on the rail.can take on an additional weight J, to increase the capacity of the instrument. A pen K

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In the Scott Inclined Plane Tester plane is actually a wheel that sits on a

platform is lowered or raised by a gear loading is not affected by the extension of

strain properties of

are two examples of inclined plane testers instruments work on the principle explained

and its RKM value. The instrument works on constant rate of loading to the test

The figure shows the major features of the Scott IP tester. The test yarn package B. A tension device C consisting of

tension to the test left end in the figure). The

rail can swing about fulcrum

can roll freely on the rail. The carriage increase the capacity of the instrument. A pen K can be


attached to the carriage. During a test, the pen can trace the load-elongation curve of the test specimen on a chart or graph paper L. The chart holder M is fixed to a balance frame, a balance rod N and balance weight O.This set-up balances the frame when the instrument is working. Four guide pulleys P manipulate the chart holder.

The extreme right end of rail is connected to a roller Q, which rests on a platform R. This end of the rail is moved down by screw mechanism S, activated by a motor and clutch. The clutch can be operated either way to raise the rail or lower it.Test Procedure

The left-hand jaw is positioned and fixed on the rail to give the desired gauge length ortest specimen length.

The dead weight close to the fixed jaw is positioned on the lever to give a yarn pre-tension corresponding to the nominal count of the test yarn.

Any additional weight is attached to the carriage unit depending upon the breaking loadrange of the test yarn.

Ensure that the pen contains enough ink and then place it in the pen holder of the carriage.

Insert a fresh chart paper in the chart holder.

Set the rail in the horizontal position. If required use the operator handle and bring it to the horizontal position.

Open the fixed and movable jaws.

Fix one end of the yarn in the fixed jaw and clamp it.

Pass the other end of the yarn via the tension discs, pull it until the tension-discs unit isvertical and clamp the specimen to the movable jaw.

The specimen is now set for the test.


The screw rod is now lowered. The rail starts inclining as a result. The carriage rolls onthe inclining rail and load is thus applied to the yarn.

As the rail tilts, the chart and pen system come into operation and the pen records a curveon the paper. As the load is applied to the yarn it extends. When the load is too much tobear the yarn breaks.

As soon as the yarn breaks, the carriage rolls quickly down the rail to the right end.

The screw drive is reversed to raise the rail back to its horizontal position and the motor is switched off.

The above procedure is repeated for another 49 test specimens.

The charts are analysed to arrive at the following information and the mean values are calculated.1. The breaking load: the point of specimen break on the curve is noted and depending on thecalibration of the load scale, the breaking load is worked out.2. The RKM value or the breaking length in kilometres is calculated by using the followingformula.

Breaking load in gramsRKM = -------------------------------- Yarn count in tex

The Strain Gauge Principle

The strain gauge principle is relatively a more recent one that is used extensively nowadays intextile testing. The technique uses the well-known ‘Wheatstone bridge‘principle.

A beam ABCD, which is actually a flat stiff spring, is mounted like a cantilever, as shown in the figure. The free end of the beam is connected to an upper jaw J1 at which is clamped one end of a test specimen E. The other end of the specimen is clamped at a lower jaw J2, which can be caused to traverse vertically, up or down, by means of screw mechanism M.If J2 is moved downwards, a tensile force is developed in the specimen and this causes the free end of the beam BC to be deflected.

If a resistance wire R were fixed to the upper face AB of the beam, the effects of the deflectionof the beam will be transmitted to it (R) such that it would be possible to measure the magnitude of the load on the specimen.

A deflection in the beam would cause an increase in length of its upper face AB and a decrease in length of its lower face CD. The resistance wire being attached to the upper face of the beam would also suffer an increase in length. Recalling his/her knowledge of basic electricity, the student will realise that, in the above situation, the following two statements hold good.


When a length of resistance wire is stretched, its electrical resistance increases and whenit contracts, its resistance decreases.

The change in the resistance of the wire is proportional to its change in length.

Thus, the resistance of R increases and the increase is proportional to the amount of load applied to the specimen and therefore to the beam. Now this change in resistance has to be converted to ameaningful record of the load applied to the specimen and the response to it. This is achievedadmirably by means of a typical Wheatstone bridge circuit.

The circuit includes four resistances, two attached to the upper face AB of the beam and the other two to its lower face CD. The interconnections between the four resistances are as in a Wheatstone bridge, as shown in the figure.

All the resistors are of equal resistance and with no strain on the beam, if a voltage is appliedacross AB, there will be no voltage drop across CD. When the beam suffers a strain imposed on it by the load applied to the specimen, it would result in changes in the resistances of the resistors attached to it and this in turn would lower the output voltage across CD. This voltage drop would be proportional to the load applied to the specimen. This output is electronically processed and recorded automatically as visible information.

Instron Tensile Tester

This instrument is capable of evaluating the tensile properties of single, plied and cabled yarns. It is also used to determine the tensile strength of fabrics. It is a universal tensile testing machine that can test a whole range of fibres, yarns and fabrics.Principle: The instrument works on the ‘strain gauge principle, explained above. The yarn specimen is clamped between a traversable upper jaw and a fixed lower jaw. The upper jaw is traversed at a constant speed to extend the specimen. This causes a load to develop in the yarn. The load is transmitted to the resistance wires in a load cell. The changes in the load cell are transformed via appropriate electronic circuits to tensile data.Description: A typical Instron tensile tester is shown in the figure. J1 is the traversable upper jaw and J2 the lower fixed jaw. In the earlier versions of the tester, the upper jaw was connected to the top cross bar of the instrument via the load cell and the lower jaw was mounted in atraversable crosshead. ‘A’ is the yarn test specimen clamped at the jaws. The instrument comes with different types and sizes of jaws that can be used according to the type of material for test. There are very light jaws for fibres, slightly heavier ones for yarns and cords and very heavy ones for fabric and very strong material. A load cell B is housed in a moving crosshead C thatcan be traversed along two screw rods D located in the side columns of the instrument. The crosshead speed can be varied in the range 50 to 500 mm / minute.


The upper jaw is attached to the load cell.model to accommodate materials of varnormally range from 0-50 grams (material.

A range of specimen grips or clamps is also supplieddepend upon the material being tested, lighter ones being used forones for strong material.

The load cell is connected to a load cell amplifier, whichconstant sensitivity. The instrument is also provided with a stripcontrol panel and a pen to record the load. The chart is moved at a selectedrecords the load-elongation curve,varied in the range 50 to 1000 mm/minute.Working: The correct load cell and the jaws are selectedrequired gauge length, the crosshead speed (i.e. the rate ofselected on the main control panel of the instrumentthe two jaws and the crosshead is traversed. The upper jaw moves

The upper jaw is attached to the load cell. A range of load cells is supplied with the universal accommodate materials of varying tensile properties. The capacities of the

50 grams (0-0.5 N) for fibre testing 0 -500kg (0-5 KN

A range of specimen grips or clamps is also supplied with the instrument. The grips selected the material being tested, lighter ones being used for fibre testing and the heavier

The load cell is connected to a load cell amplifier, which keeps the electronic circuit unit at a sensitivity. The instrument is also provided with a strip chart recorder s

to record the load. The chart is moved at a selected speed and the pen elongation curve, in a normal tensile test, on the chart. The chart speed

varied in the range 50 to 1000 mm/minute.correct load cell and the jaws are selected according to the test material. The length, the crosshead speed (i.e. the rate of extension), the chart speed, etc are main control panel of the instrument. The yarn specimen is mounted in between

and the crosshead is traversed. The upper jaw moves up and the specimen is

Page 95

load cells is supplied with the universal The capacities of the load cells

KN) for very strong

the instrument. The grips selected fibre testing and the heavier

keeps the electronic circuit unit at a chart recorder system with a

speed and the pen e chart. The chart speed can be

according to the test material. The extension), the chart speed, etc are

arn specimen is mounted in between up and the specimen is


the output voltage in the circuit. The electronic circuitry converts the output data into a load-elongation curve that is drawn on the chart. The chart paper is traversed so that fresh paper comes into the test area. Further specimens are tested as described above and the mean values of the breaking load, breaking elongation, etc are calculated.Range of tests possible on the Instron TesterThe following tests are possible on the Instron tensile tester.

Load-elongation

Compression

Fabric tearing strength

Cyclic loading

Elastic recovery

Stress Relaxation

The Ballistic Tester

Why a ballistic tester?During processing and usage, some textile materials will be required to withstand an impact orsudden high load acting for a mere fraction of a second. Sometimes this may be repeated loading. For example, when a yarn is caught in a heald or in a dent of the reed, during weaving, it could be subjected to sudden high loads. Similarly a sewing thread may get caught in the eye of a needle during high-speed stitching. The energy required by yarns and threads to withstand the resulting load or stress can be evaluated by subjecting them to a ballistic load or an impact load (or a shock load!), and the energy required to break or rupture them can be measured.

Description of the testerThe figure shows the salient parts of a typical ballistic tester. It consists of a semicircular scale A fixed to a solid stand B. The scale is calibrated either in in.lb. or cm kg to indicate the energy of rupture of the test specimen. A pendulum C, with a very heavy bob, has its fulcrum at D. Two fixed jawsJ1 and J2 are attached to the base E of the instrument. Jaw J1 is used for yarns and jaw J2 is used for fabric specimens. A jaw J3 is fixed to the pendulum bob.

A pointer F is also pivoted at G and it is free to move about the pivot. During a test the pendulum pushes it to a point on the scale where the reading of the work of rupture of the test specimen can be read off. A catch H at the top right hand side of the frame holds the pendulum up at the start of every test.Test Procedure: The test sample of yarn is first converted into the form of full leas, half leas or quarter leas depending upon the yarn count. For counts above 605 full leas are used, for counts between 205 and 605, half leas are used and for counts less than 205, quarter leas are used for testing. The instrument is first calibrated properly as follows.


The pointer is brought to the vertical position. Then, without attaching any yarn sample to the pendulum, raise it up to the top right-hand position (Position 1) and lock it in place using the catch. Next release the pendulum and note the position to which the pointer is pushed up at the top left.

If the pointer shows zero on the scale, the instrument is ready for the test. If not, the position of catch H is adjusted, moving it either higher or lower as required, until the pointer is in line with the zero on the scale when the pendulum falls freely without restraint. When the instrument is set for the test, the pendulum is raised to the top right and the catch is operated to hold up the pendulum. The pointer is then positioned close to its anticipated position when the specimen breaks.One end of the test yarn skein is then attached to the fixed jaw on the base of the instrument and the other end to the jaw on the pendulum bob. Care is taken to see that the specimen is mounted properly and free of twists. The catch is then released and the pendulum swings to the other side pulling the sample with it and finally rupturing it. The position of the pointer on the scale shows the energy spent in rupturing the sample in inch lb or cm kg. The above procedure is repeated for another 15 samples and the mean work of rupture is calculated.Merits of the Ballistic TestThe ballistic test has the following advantages.

It is a simple test and it tests a large sample of yarn. The operator need not have a greatdeal of practice to perform tests with an acceptable degree of accuracy.

It is a very fast test. So several sample can be tested quickly on it and more quickly than it would take the same number of samples on a lea tester.

As the operation is easy and simple, there are neither operator errors nor operator fatigue.A little care has nevertheless to be taken to keep the operator safe from injury due to therapidly falling heavy pendulum during the test.

There is hardly any effect of yarn friction on the final results.

Every thread in the test skein contributes to the final result, unlike the lea test.


The ruptured lea may be used for determination of yarn count. So like the lea tester, twoproperties are simultaneously evaluated.

The ballistic test is capable of highlighting weak places in the yarn and yarn evenness with greater consistency than a lea test.

The work of rupture is a good indicator of the breaking load and the breaking extension of a yarn. The ballistic test thus indirectly provides a combined measure of these twoimportant yarn properties.

CSP & CORRECTED CSP

Lea Count Strength Product (Break Factor or Yarn Factor)The product of the count of a yarn in Ne and its lea strength in pounds is called the Lea Count Strength Product or the Lea CSP. It has also been referred to as the break factor or the ‘yarn factor‘. The lea CSP is used even today as an important yarn parameter. It has been found to be very useful in the assessment of the character of a given cotton yarn from the strength point of view. It also enables comparisons to be made between yarns of similar, but not necessarily, identical count. The count strength product of a yarn tested under a given set of conditions can be calculated for another set of conditions. The formula given below can be used. 80 x N x SCount Strength Product (CSP) = ————— WWhereS — Average yarn breaking load (lea strength) in lb (kg 2 206)N — Average yarn count in an indirect system W — number of wraps (strands) in skein

Simplified FormulaCSP = N×S

Corrected CSPThe actual count of a spun yarn would generally be slightly different from its nominal count, i.e. the desired count. A yarn of 40s nominal count could turn out to have a mean actual count of 39.7 or sometimes 40.2, and so on. The yarn manufacturer usually labels all the yarn bundles produced with the CSP values in terms of the nominal count of the yarn. The actual mean CSP of a given yarn thus needs to be corrected to the nominal yarn count.The following ASTM formula, applicable to American Upland-type cottons, is used to get thecorrected strength.

S2 = [N1S1-18.27 (N2-N1)] / N2

Where, N1 = actual count, S1 = actual strength in lb, N2 = nominal count, S2 = corrected strengthin lb. The CSP corrected to nominal yarn count = N2S2.


UNIT – IV

1. Fabric strength testing

Introduction: The level of strength required from a yarn or fabric depends on its end use .For some end uses it is the case that the higher the strength of the materials, the better it is for its end use. This is particularly true for yarns and fabrics intended for industrial products. However, fabrics intended for household or apparel use merely need an adequate strength in order to withstand handling during production and use. It is generally the case that a higher-strength product can only be obtained by either making a heavier, stiffer fabric or by using synthetic fibres in place of natural ones. In either case changes are produced in other properties of the material, such as the stiffness and handle, which may not be desirable for a particular end use.

Definitions Stress: Stress is a way of expressing the force on a material in a way that allows for the

effect of the cross-sectional area of the specimen on the force needed to break it. In the case of textile materials the cross-sectional area can only be easily measured in the case of fibres with circular cross-sections. The crosssections of yarns and fabrics contain an unknown amount of space as well as fibres so that in these cases the cross-sectional area is not clearly defined. Therefore stress is only used in a limited number of application s involving fibres.

Stress = Force applied / cross-sectional area

Specific (mass) stress: Specific stress is a more useful measurement of stress in the case of yarns as their cross-sectional area is not known. The linear density of the yarn is used instead of the cross-sectional area as a measure of yarn thickness. This allows the strengths of yarns of different linear densities to be compared. It is defined as the ratio of force to the linear density:

Specific stress = force / linear density The preferred units are N/tex or mN/tex,

Tenacity: Tenacity is defined as the specific stress corresponding with the maximum force on a force/extension curve. The nominal denier or tex of the yarn or fibre is the figure used in the calculation; no allowance is made for any thinning of the specimen as it elongates.

Breaking length: Breaking length is an older measure of tenacity and is defined as thetheoretical length of a specimen of yarn whose weight would exert a force sufficient to break the specimen. It is usually measured in kilometres.

Elongation: Elongation is the increase in length of the specimen from its starting lengthexpressed in units of length. The distance that a material will extend under a given force is proportional to its original length therefore elongation is usually quoted as strain or percentage extension. The elongation at the maximum force is the figure most often quoted.


Strain: The elongation that a specimen undergoes is proportional to its initial length. Strain expresses the elongation as a fraction of the original length:

Strain = elongation / initial length Extension percentage: This measure is the strain expressed as a percentage rather than a

fraction Extension = (elongation / initial length) X 100% Breaking extension is the extension percentage at the breaking point.

Gauge length: The gauge length is the original length of that portion of the specimen overwhich the strain or change of length is determined.

Fabric strength

The breaking strength is a measure of the resistance of the fabric a tensile load or stress in either warp or weft direction. “To measure the breaking strength,’ there are three tests that may beused. They are:1. Ravelled strip method2. Cut strip method3. Grab method

1. Ravelled Strip Method: it is a tension test on a strip of fabric in which the specified specimen width is secured by ravelling away yarns. The specimen should be of 2 inches and 8 inches test length. For these samples of 12×2.5 inches are cut, the bigger dimension is in the direction of testing. The extra length is allowed for gripping in the jaws. From these samples, threads from both the edges are removed until the width is reduced to 2 inchesexactly. Rate of traverse for the bottom clamp is 12 inches/min.

2. Cut Strip Method: It is a tension test on a strip of fabric in which the specimen width is secured by cutting the fabric. This method of fabric strength is identical to ravelled strip method. The sample width is 2 inches and test length is 8 inches. The test specimens are cut for exact width and no ravelling of the sample is necessary. This method is used only for coated or heavily sized fabrics, where ravelling of the threads would be difficult. Procedure of doing the test la the same as that for ravelled strip test.

Method of Measuring Tensile StrengthThe tensile strength of the fabric can be determined using the instrument cloth tensile strength tester and is shown in Fig 4.8.Description: This is a motor driven, pendulum type strength tester. A dial plate, calibrated in kgsand lbs, is provided at the top and a pointer is made to move over the dial plate. The-pointer shaft is connected to the upper clamp by connecting rod and steel tape against a heavy pendulum. The pendulum carries a pawl which moves over a toothed quadrant. This acts as a catch and prevents the heavy pendulum from dropping back after the breakage of the material takes place.


This also helps to note the reading at ease. A red pointer is provided in the upper clamp and an elongation scale in the lower clamp to note the elongation of the specimen. Downwardmovement is given to the lower clamp by a screw rod and lever at the rate of 18 inches/minute. A catch is provided for the upper clamp to mount the sample without disturbing the pointer on the dial.

Procedure: Inspect the tester for the proper size of the clamps, distance between the clamps, and any

other parts or settings that are necessary. (If a pendulum - type tester is used, select the proper pendulum weight so that the pendulum will be between approximately 9 and 45 degrees with the vertical when the specimen breaks).

If stress-strain curve is to be drawn, place the chart and pen in positioned align the chart properly.

Place the sample in the clamps. The specimen should be so placed that yams are broken perpendicular to the load.

Apply load to the sample and when the sample breaks, reverse the movement of the lower clamp and raise the pen from the chart if a stress-strain chart is being made. If a stress-strain chart is not being made,

Record the breaking strength and return the pendulum to the zero position.


3. Grab Test Method: It is a tension test on the fabric in which only a part of the width of the specimen is gripped in the clamps. For example, if the specimen width is 4 inches and the width of jaw is 1 inch the specimen is gripped centrally in the clamps as shown in the figure.

Test samples of size 4 x 6 inches are cut from the master sample. The 6 inch length is parallel to the yarn to be tested and it is depended on the gauge length. In setting the testing instrument, the clamps must be set 3 inches apart. The lower jaw moves at a rate of 12 inches per minute.Procedure: Inspect the tester for the proper size of the clamps, distance between the clamps etc.

If stress-strain curve is to be drawn, place the chart and pen in positioned align the chart properly.

Place the sample in the clamps. The specimen should be so placed that yams are broken perpendicular to the load.

Apply load to the sample and when the sample breaks, reverse the movement of the lower clamp and raise the pen from the chart if a stress-strain chart is being made. If a stress-strain chart is not being made,

Record the breaking strength and return the pendulum to the zero position.

Five breaks are made both for warp and weft.

Tearing Strength testsA fabric tears when it is snagged by a sharp object and the immediate small puncture is

converted into a long rip by what may be a very small extra effort. It is probably the most common type of strength failure of fabrics in use. It is particularly important in industrial fabrics that are exposed to rough handling in use such as tents and sacks and also those where propagation of a tear would be catastrophic such as parachutes. Outdoor clothing, overalls and uniforms are types of clothing where tearing strength is of importance.


Measuring tearing strength: The fabric property usually measured is the force required to propagate an existing tear and not the force required to initiate a tear as this usually requires a cutting of threads. As part of the preparation of the fabric specimens a cut is made in them and then the force required to extend the cut is measured. This is conveniently carried out by gripping the two halves of the cut in a standard tensile tester. The various tear tests carried out in this manner differ mainly in the geometry of the specimen. The simplest is the rip test where a cut is made down the centre of a strip of fabric and the two tails pulled apart by a tensile tester. The test is sometimes referred to as the single rip test, the trouser tear or in the US as the tongue tear test Fig. 5.24(a). What is understood in the UK as the tongue tear test has the specimen cut into three tails Fig. 5.24(b) and (c), the central one is gripped in one jaw of the tensile tester and the outer two in the other jaw. This test is also known as the double rip as two tears are made simultaneously.

Single rip tear test: In the US Standard 10 specimen s are tested from both fabric directionseach measuring 75mm X 200mm (3 X 8 in) with an 80mm (3.5 in) slit part way down the centre of each strip as shown in Fig. (a). One of the 'tails ' is clamped in the lower jaw of a tensile tester and the other side is clamped in the upper jaw, the separation of the jaws causes the tear to proceed through the uncut part of the fabric. The extension speed is set to 50mm/min (2in/min) or an optional speed of 300mm/min can be used. There are three ways of expressing the result:1. The average of the five highest peaks.2. The median peak height.3. The average force by use of an integrator.

Depending on the direction the fabric is torn in the test is for the tearing strength of filling yarns or of warp yarns. If the direction to be torn is much stronger than the other direction, failure will occur by tearing across the tail so that it is not always possible to obtain both warp and weft results.


(All Dimensions are in Inches)

Wing rip tear test: The wing rip test overcome s some of the problem s which are found withthe single rip test as it is capable of testing most types of fabric without causing a transfer of tear. During the test the point of tearing remains substantially in line with the centre of the grips. The design of the sample is also less susceptible to the withdrawal of threads from the specimen during tearing than is the case with the ordinary rip test. The British standard uses a sample shaped as in Fig. 5.25 which is clamped in the tensile tester in the way shown in Fig. 5.26. The centre line of the specimen has a cut 150mm long and a mark is made 25mm from the end of the specimen to show the end of the tear.


The test is preferred to the tongue tear test though it is not suitable for loosely constructed fabrics which would fail by slippage of the yarns rather than by the rupture of threads. Five specimens across the weft and five specimens across the warp are tested. The test is carried out using a constant rate of extension testing machine with the speed set at 100mm/min. The tearing resistance is specified as either across warp or across weft according to which set of yarns are


broken. The results can be expressed as either the maximum tearing resistance or the median tearing resistance. The median value is determined from a force elongation curve such as that shown in and it is the value such that exactly half of the peaks have higher values and half of them have lower values than it. The median tearing resistance value is close to the mean value but it is an easier value to measure by hand methods as it can be determined by sliding a transparent rule down the chart until half the peaks are above the edge of the rule and half below it, at which point the load can be read from the chart.

Elmendorf tear testerThe Elmendorf tear tester is a pendulum type ballistic tester which measures energy loss during tearing. The tearing force is related to the energy loss by the following equation:

Energy loss = tearing force X distanceLoss in potential energy = work doneThe apparatus which is shown in Fig. consists of a sector-shaped pendulum carrying a clamp which is in alignment with a fixed clamp when the pendulum is in the raised starting position, where it has maximum potential energy. The specimen is fastened between the two clamps and the tear is started by a slit cut in the specimen between the clamps. The pendulum is then released and the specimen is torn as the moving jaw moves away from the fixed one. Thependulum possesses potential energy because of its starting height. Some of the energy is lost in tearing through the fabric so that as the pendulum swings through its lowest position it is not able to swing to the same height as it started from. The difference between starting height and finishing height is proportional to the energy lost in tearing. The scale attached to the pendulum can be graduated to read the tearing force directly or it may give percentage of the original potential energy.

The apparatus tears right through the specimen. The work done and hence the reading obtained is directly proportional to the length of material torn. Therefore the accuracy of the instrument depends on very careful cutting of the specimen which is normally done with a die. The range of the instrument is from 320 gf to 3840 gf in three separate ranges obtained by using supplementary weights to increase the mass of the pendulum. When a fabric is being torn all the force is concentrated on a few threads at the point of propagation of the tear. This is why the forces involved in tearing are so much lower than those needed to cause tensile failure. Depending on the fabric construction, threads can group together by lateral movement during tearing, so improving the tearing resistance as more than one thread has to be broken at a time.

The ability to group is a function of the looseness of the yarns in the fabric. Weave has an important effect on this: twill or a 2/2 matt weave allows the threads to group better thus giving better tearing resistance than a plain weave. High sett fabrics inhibit thread movement and so reduce the assistance effect.


Resin treatments such as crease resistance finishes which cause the yarns to adhere to one another also have the same effect. The tensile properties of the constituent fibres have an influence on tearing resistance as those with a high extension allow the load to be shared whereas fibres with low extension such as cotton tear easily.

Bursting strength: Tensile strength tests are generally used for woven fabrics where there aredefinite warp and weft directions in which the strength can be measured. However, certain fabrics such as knitted materials, lace or non-woven s do not have such distinct directions where the strength is at a maximum. Bursting strength is an alternative method of measuring strength in which the material is stressed in all directions at the same time and is therefore more suitable for such materials. There are also fabrics which are simultaneously stressed in all directions during service, such as parachute fabrics, filters, sacks and nets, where it may be important to stress them in a realistic manner. A fabric is more likely to fail by bursting in service than it is to break by a straight tensile fracture as this is the type of stress that is present at the elbows and knees of clothing.

When a fabric fails during a bursting strength test it does so across the direction which has the lowest breaking extension. This is because when stressed in this way all the directions in the fabric undergo the same extension so that the fabric direction with the lowest extension at break is the one that will fail first. This is not necessarily the direction with the lowest strength. The standard type of bursting strength test uses an elastic diaphragm to load the fabric, the pressure of the fluid behind the diaphragm being used as the measure of stress in the fabric. The general layout of such an instrument is shown in Fig. 5.29. The bursting strength is then measured in


units of pressure. As there is a sizeable force needed just to inflate the diaphragm this has to be allowed for in the test. The usual way is to measure the increase in height of the diaphragm during the test and then to inflate the diaphragm to the same height without a specimen present. The pressure required to inflate the diaphragm alone is then deducted from the pressure measured at the point of failure of the sample. The relationship between the diaphragm height and the fabric extension is quite complex so that the method is not used to obtain an estimation of fabric extension.

Diaphragm bursting test: The fabric to be tested is clamped over a rubber diaphragm by meansof an annular clamping ring and an increasing fluid pressure is applied to the underside of the diaphragm until the specimen bursts. The operating fluid may be a liquid or a gas. Two sizes of specimen are in use, the area of the specimen under stress being either 30mm diameter or 113mm in diameter. The specimens with the larger diameter fail at lower pressures (approximately one-fifth of the 30mm diameter value). However, there is no direct comparison of the results obtained from the different sizes. The standard requires ten specimens to be tested.In the test the fabric sample is clamped over the rubber diaphragm and the pressure in the fluid increased at such a rate that the specimen bursts within 20 ± 3 s. The extension of the diaphragm is recorded and another test is carried out without a specimen present. The pressure to do this is noted and then deducted from the earlier reading.The following measurements are reported:

Mean bursting strength kN/m2

Mean bursting distension mm


The US Standard is similar using an aperture of 1.2 2 ± 0.3 in (31 ± 0.75mm) the design of equipment being such that the pressure to inflate the diaphragm alone is obtained by removing the specimen after bursting. The test requires ten samples if the variability of the burstingstrength is not known.The disadvantage of the diaphragm type bursting test is the limit to the extension that can be given to the sample owing to the fact that the rubber diaphragm has to stretch to the same amount. Knitted fabrics, for which the method is intended, often have a very high extension.

Abrasion resistance

Introduction: A garment is considered to be serviceable when it is fit for its particular end use. After being used for a certain length of time the garment ceases to be serviceable when it can no longer fill its intended purpose in the way that it did when it was new. The particular factors that reduce the service life of a garment are heavily dependent on its end use. For instance overalls worn to protect clothing at work would be required to withstand a good deal of hard usage during their lifetime but their appearance would not be considered important. However, garments worn purely for their fashionable appearance are not required to be hard wearing but would be speedily discarded if their appearance changed noticeably. An exception to this generalisation is found in the case of denim where a worn appearance is deliberately strived for.If asked, many people would equate the ability of a fabric to 'wear well' with its abrasion resistance, but 'wear', that is the reduction in serviceable life, is a complex phenomenon and can be brought about by any of the following factors:

Changes in fashion which mean that the garment is no longer worn whatever its physical state.

Shrinkage or other dimensional changes of such a magnitude that the garment wills no longer fit.

Changes in the surface appearance of the fabric which include: the formation of shiny areas by rubbing, the formation of pills or surface fuzz, the pulling out of threads in the form of snags.

Fading of the colour of the garment through washing or exposure to light. The bleeding of the colour from one area to another.

Failure of the seams of the garment by breaking of the sewing thread or by seam slippage.

Wearing of the fabric into holes or wearing away of the surface finish or pile to leave the fabric threadbare. Wearing of the edges of cuffs, collars and other folded edges to give a frayed appearance.

Tearing of the fabric through being snagged by a sharp object.

These changes are brought about by the exposure of the garment to a number of physical and chemical agents during the course of its use. Some of these agents are as follows:


Abrasion of the fabric by rubbing against parts of the body or external surfaces.

The cutting action of grit particles which may be ingrained in dirty fabrics and which may cause internal abrasion as the fabric is flexed.

Tensile stresses and strains which occur as the garment is put on or taken off and when the person wearing it is active.

The laundering and cleaning processes which are necessary to retain the appearance of the garment.

Attack by biological agents such as bacteria, fungi and insects. This is a particular problem for natural materials.

Degradation of the fabric by contact with chemicals which can include normal household items such as bleach, detergents, anti-perspirants and perfumes.

Light, in particular ultra-violet light can cause degradation of polymers leading to a reduction in strength as well as causing fading of colors.

Contact of the garment with sharp objects leading to the formation of tears.

The above causes of wear are often acting at the same time. For instance, chemical or bacterial attack may so weaken a fabric that it can then easily fail through abrasion or tearing. Laundering of a fabric taken together with the abrasion that it encounters during use may lead to much earlier formation of pills or failure through abrasion than would be predicted from any pilling or abrasion tests undertaken on the new material.

Factors affecting abrasion resistanceThe factors that have been found to affect abrasion include the following.

Fibre type: It is thought that the ability of a fibre to withstand repeated distortion is the key to its abrasion resistance. Therefore high elongation, elastic recovery and work of rupture are considered to be more important factors for a good degree of abrasion resistance in a fibre than is a high strength. Nylon is generally considered to have the best abrasion resistance. Polyester and polypropylene are also considered to have good abrasion resistance. Blending either nylon or polyester with wool and cotton is found to increase their abrasion resistance at the expense of other properties.

Fibre properties: One of the results of abrasion is the gradual removal of fibres from the yarns. Therefore factors that affect the cohesion of yarns will influence their abrasion resistance. Longer fibres incorporated into a fabric confer better abrasion resistance than short fibres because they are harder to remove from the yarn. For the same reason filament yarns are more abrasion resistant than staple yarns made from the same fibre. Increasing fibre diameter up to a limit improves abrasion resistance.

Yarn twist: There has been found to be an optimum amount of twist in a yarn to give the best abrasion resistance. At low-twist factors fibres can easily be removed from the yarn so that it is gradually reduced in diameter. At hightwist levels the fibres are held more


tightly but the yarn is stiffer so it is unable to flatten or distort under pressure when being abraded. It is this ability to distort that enables the yarn to resist abrasion.

Fabric structure: The crimp of the yarns in the fabric affects whether the warp or the weft is abraded the most. Fabrics with the crimp evenly distributed between warp and weft give the best wear because the damage is spread evenly between them. If one set of yarns is predominantly on the surface then this set will wear most; this effect can be used to protect the load-bearing yarns preferentially. One set of yarns can also be protected by using floats in the other set such as in a sateen or twill weave. The relative mobility of the floats helps to absorb the stress. There is an optimum value for fabric sett for best abrasion resistance.

Factors that can affects the Abrasion testsVery many different abrasion tests have been introduced. Poor correlation has been found both between the different abrasion testers and between abrasion tests and wear tests. The methodsthat have survived to become standards are not necessarily the 'best' ones. Among the factors which can affect the results of an abrasion test are the following.

Type of abrasion: This may be plane, flex or edge abrasion or a combination of more than one of these factors.

Type of abradant: A number of different abradants have been used in abrasion tests including standard fabrics, steel plates and abrasive paper or stones (aluminum oxide or silicon carbide). The severity as well as the type of action is different in each case.

Pressure: The pressure between the abradant and the sample affects the severity and rate at which abrasion occurs. It has been shown that using different pressures can seriously

alter the ranking of a set of fabrics when using a particular abradant. Speed: Increasing the speed of rubbing above that found in everyday use also brings the

dangers of accelerated testing as described above. A rise in temperature of the sample can occur with high rubbing speeds; this can affect the physical properties of thermoplastic fibres.

Tension: It is important that the tension of the mounted specimen is reproducible as this determines the degree of mobility of the sample under the applied abradant. This includes the compressibility of any backing foam or inflated diaphragm.

Direction of abrasion: In many fabrics the abrasion resistance in the warp direction differs from that of the weft direction. Ideally the rubbing motion used by an abrasion machine should be such as to eliminate directional effects.

Method of assessment:Two approaches have been used to assess the effects of abrasion:

1. Abrade the sample until a predetermined end-point such as a hole, and record the time or number of cycles to this.


2. Abrade for a set time or number of cycles and assess some aspect of the abraded fabric such as change in appearance, loss of mass, loss of strength change in thickness or other relevant property.

The first approach corresponds to most people’s idea of the end point of abrasion but the length of the test is indeterminate and requires the sample to be regularly examined for failure in the absence of a suitable automatic mechanism. This need for examination is time consuming as the test may last for a long time. The second approach promises a more precise measurement but even when the sample has rubbed into a hole the change in properties such as mass loss can be slight. However none of the above assessment methods produces results that show a linear or direct comparison with one another. Neither is there a linear relationship between successive measurements using any of these methods and progressive amounts of abrasion.

Martindale Abrasion Tester This apparatus is designed to give a controlled amount of abrasion between fabric surfaces at comparatively low pressures in continuously changing directions. The results of this test should not be used indiscriminately, particularly not for comparing fabrics of widely different fibre composition or construction.In the test circular specimens are abraded under known pressure on an apparatus, shown in, which gives a motion that is the resultant of two simple harmonic motions at right angles to one another. The fabric under test is abraded against a standard fabric. Resistance to abrasion is estimated by visual appearance or by loss in mass of the specimen.

Method: Four specimens each 38mm in diameter are cut using the appropriate cutter. They are then mounted in the specimen holders with a circle of standard foam behind the fabric being tested. The components of the standard holder are shown in. It is important that the mounting of the sample is carried out with the specimens placed flat against the mounting block.


Fig. Standard Holder for abrasion tester

The test specimen holders are mounted on the machine with the fabric under test next to the abradant. A spindle is inserted through the top plate and the correct weight (usually of a size to give a pressure of 12kPa but a lower pressure of 9kPa may be used if specified) is placed on top of this. The standard abradant should be replaced at the start of each test and after 50,000 cycles if the test is continued beyond this number. While the abradant held flat by a weight as the retaining ring is tightened. Behind the abradant is a standard backing felt which is replaced at longer intervals.

Assessment: The specimen is examined at suitable intervals without removing it from its holder to see whether two threads are broken. If the likely failure point is known the first inspection can be made at 60% of that value. The abrading is continued until two threads are broken. All four specimens should be judged individually. The interval for inspection are given below

The individual values of cycles to breakdown of all four specimens are reported and also the average of these.Assessment by Average rate of loss in mass: This is an alternative method of assessing abrasion resistance which requires eight specimens for the test. Two of these are abraded to the endpoint as described above and then the other pairs are abraded to the intermediate stages of 25%, 50% and 75% of the end point. The samples are weighed to the nearest 1 mg before and after abrasion so that a graph can be plotted of weight loss against the number of rubs. From the slope of this graph, if it is a straight line, the average loss in mass measured in mg/1000 rubs can be determined.


Figure: One station of Martindale Abrasion Tester

Pilling of fabrics & its Causes –Measurement of picking by using ICI pilling box tester

Pilling:Pilling is a condition that arises in wear due to the formation of little 'pills ‘of entangled

fibre clinging to the fabric surface giving it an unsightly appearance. Pills are formed by a rubbing action on loose fibres which are present on the fabric surface. Pilling was originally a fault found mainly in knitted woollen goods made from soft twisted yarns. The introduction of man-made fibres into clothing has aggravated its seriousness.The initial effect of abrasion on the surface of a fabric is the formation of fuzz as the result of two processes, the brushing up of free fibre ends not enclosed within the yarn structure and the conversion of fibre loops into free fibre ends by the pulling out of one of the two ends of the loop.

The greater the breaking strength and the lower the bending stiffness of the fibres, the more likely they are to be pulled out of the fabric structure producing long protruding fibres. Fibre with low breaking strength and high bending stiffness will tend to break before being pulled fully out of the structure leading to shorter protruding fibres.


Pilling tests:After rubbing of a fabric it is possible to assess the amount of pilling quantitatively either

by counting the number of pills or by removing and weighing them. However, pills observed in worn garment s vary in size and appearance as well as in number. The appearance depends on the presence of lint in the pills or the degree of colour contrast with the ground fabric. These factors are not evaluated if the pilling is rated solely on the number or size of pills. Furthermore the development of pills is often accompanied by other surface changes such as the development of fuzz which affect the overall acceptability of a fabric.

It is therefore desirable that fabrics tested in the laboratory are assessed subjectively with regard to their acceptability and not rated solely on the number of pills developed. Counting the pills and/or weighing them as a measure of pilling is very time consuming and there is also the difficulty of deciding which surface disturbances constitute pills. The more usual way of evaluation is to assess the pilling subjectively by comparing it with either standard samples or with photographs of them or by the use of a written scale of severity. Most scales are divided into five grades and run from grade 5, no pilling, to grade 1, very severe pilling.

ICI pilling box:For this test four specimen s each 125mm X 125mm are cut from the fabric. A seam

allowance of 12mm is marked on the back of each square. In two of the samples the seam is marked parallel to the warp direction and in the other two parallel to the weft direction. The samples are then folded face to face and a seam is sewn on the marked line. This gives two specimens with the seam parallel to the warp and two with the seam parallel to the weft. Each specimen is turned inside out and 6mm cut off each end of it thus removing any sewing distortion. The fabric tubes made are then mounted on rubber tubes so that the length of tube showing at each end is the same. Each of the loose ends is taped with poly (vinyl chloride) (PVC) tape so that 6mm of the rubber tube is left exposed as shown in below Fig.

All four specimen s are then placed in one pilling box. The samples are then tumbled together in a cork-lined box as shown in Fig.7.5. The usual number of revolutions used in the test is 18,000 which take 5 h. Some specifications require the test to be run for a different number of revolutions.


Assessment: The specimens are removed from the tubes and viewed using oblique lighting in order to throw the pills into relief. The samples are then given a rating of between 1 and 5 with the help of the description s in above Table.

Figure: line diagram of ICI Pilling Box


Crease Resistance & Crease Recovery

Creases are a fold in a fabric introduced unintentionally. The definition of a wrinkle is less clear, however. Some define wrinkles as three-dimensional creases, whereas others define them as short and irregular creases. They form when fabrics undergo double curvature, which occurs when a flat material is bent in both of its planes. Sufficient force must be applied that the change is permanent to some degree. Some people use the terms ‘wrinkle’ and ‘crease’ interchangeably.Wrinkles and creases are distinct to pleats, because pleats are introduced intentionally and over regular intervals. They are usually sharp folds, often running lengthways to give a decorative effect. Crease marks are marks left in a fabric once the crease has been removed and are usually caused by mechanical damage.Crease resistance is the ability of a material to resist, or recover from, creasing. Crease recovery is a specific measurement of crease resistance that determines the crease recovery angle. It is therefore a quantitative method of analysis.Crease is a fold in fabric introduced unintentionally at some stages of processing. Crease or crushing of textile material is a complex effect involving tensile, compressive, flexing and tensional stresses. Crease recovery is a fabric property which indicates the ability of fabric to go back to its original position after creasing.Measurement by Shirley Crease Recovery tester: Crease recovery is a measure of creases resistance, specified quantitatively in terms of crease recovery angle. To measure this, the popular instrument is Shirley crease recovery tester. The instrument consists of a circular dial which carries the clamp for holding the specimen. Directly under the centre of the dial there is a knife edge and an index line for measuring the recovery angle. Crease recovery is determined depending upon this recovery angle. If the angle is 0o then recovery is zero and if the angle is 180o then recovery is full. Crease recovery depends on the construction, twist of yarn, pressure, time etc. Usually crease recovery is more in warp way than in weft way. This is because warp yarns are well in quality, strength, treated with sizing, kept in more tension during weaving etc.Apparatus: Crease recovery tester, Scissor, Glass plates, Steel plates, Weight.Sample: Cotton woven fabric Size: 4.4 X 1.5cm.Atmosphere: Temperature – 25oC and relative humidity – 67% Standard atmosphere: temperature – 20oC and relative humidity - 65%.

Figure: Shirley Crease Recovery Tester.


Procedure:

1. The specimen is cut by template and carefully creased by folding in half. 2. The crease is imparted on fabric by placing it between two glass plates and adding to

500gm weight on it. 3. After 1 min the weight is removed and the creased fabric is clamped on the instrument. 4. Then it is allowed to recover from the crease. The recovery time may vary to suit

particular creases. Usually it is 1 min. 5. When crease recovers the dial of the instrument is rotated to keep the free edge of the

specimen in line with the knife edge. 6. The recovery angle is read from the engraved scale. 7. In this way 10 tests are done in warp way and 10 for weft way. 8. The mean value of recovery angle is taken and thus crease recovery is measured.

Crease recovery is determined depending upon the recovery angle. If the angle is 0o then recovery is zero and if the angle is 180o then recovery is full. Here the recovery angle for the given fabric sample is the middle of the range. So it is to say that the crease recovery of the sample fabric is average.

Fabric stiffness, Handle & Drape-Bending length, flexural rigidity, bending modulus-Shirley stiffness tester.

Handle: 'Handle', the term given to properties assessed by touch or feel, depends upon subjective assessment of the fabrics by a person. Terms such as smooth, rough, stiff or limp depend strongly on the type of fabric being assessed, for instance the smoothness of a worsted suiting is different in nature from that of cotton sateen. Because of the subjective nature of these properties attempts have been made over the years to devise objective tests to measure some or all of the factors that go to make up handle. Fabric stiffness and drape were some of the earliest properties to be measured objectively.

Bending lengthA form of the cantilever stiffness test is often used as a measure of a fabric's stiffness as it

is an easy test to carry out. In the test a horizontal strip of fabric is clamped at one end and the rest of the strip allowed hanging under its own weight. This is shown diagrammatically shown in below Fig. The relationship among the length of the overhanging strip, the angle that it bends to and the flexural rigidity, G, of the fabric is a complex one which was solved empirically by Peirce to give the formula:


Where L = length of fabric projecting,θ = angle fabric bends to,M = fabric mass per unit area.

From this relationship Peirce defined a quantity known as the bending length as being equal to the length of a rectangular strip of material which will bend under its own mass to an angle of 7.1°. The bending length is dependent on the weight of the fabric and is therefore an important component of the drape of a fabric when it is hanging under its own weight. However, when a fabric is handled by the fingers the property relating to stiffness that is sensed, in this situation, is the flexural rigidity which is a measure of stiffness independent of the fabric weight.The bending length is related to the angle that the fabric makes to the horizontal by the following relation:

Where C = bending length.When the tip of the specimen reaches a plane inclined at 41.5° below the horizontal the

overhanging length is then twice the bending length. This angle is used in the Shirley apparatus to increase the sensitivity of the length measurement and the slide on this instrument is directly calibrated in centimeters.

Shirley stiffness testerThis test measures the bending stiffness of a fabric by allowing a narrow strip of the

fabric to bend to a fixed angle under its own weight. The length of the fabric required to bend to this angle is measured and is known as the bending length.The test specimens are each 25mm wide and 200mm long; three are cut parallel to the warp andthree parallel to the weft so that no two warp specimens contain the same warp threads, and no two weft specimens contain the same weft threads. The specimens should not be creased and those that tend to twist should be flattened.

Before the test the specimens are preconditioned for 4h (500C >10 % RH) and then conditioned for 24 h. If a specimen is found to be twisted its mid-point should be aligned with


the two index lines. Four readings are taken from each specimen, one face up and one face down on the first end, and then the same for the second end.weft is calculated. The higher the bending length, the stiffer is the fabric.

Flexural rigidity: The flexural rigidity is the ratio of the small change in bending moment per unit width of the material to the corresponding small change in curvature:

Where C = bending length (mm), M = fabric mass per unit area (g/m

Bending modulus: The stiffness of a fabric in bending is very dependent on its thickness, thethicker the fabric, the stiffer it is if all other factors remain the same. The bending modulindependent of the dimensions of the strip tested so that by analogy with solid materials it is a measure of 'intrinsic stiffness'.

Where T = fabric thickness (mm).

Fabric Drape –Drape Co-efficient & Drape Meter

Drape: Drape is the term used to describe the way a fabric hangs under its ownimportant bearing on how good a garment looks in use. The draping qualities required from a fabric will differ completely depending on its end be classified as either good or bad. Knitted fabrics are relatively floppy and garments made from them will tend to follow the body contours. Woven fabrics are relatively stiff with knitted fabrics so that they are used in tailored clothing where the fabric hangs away from

the two index lines. Four readings are taken from each specimen, one face up and one face down on the first end, and then the same for the second end. The mean bending length for warp and weft is calculated. The higher the bending length, the stiffer is the fabric.

The flexural rigidity is the ratio of the small change in bending moment per unit width of the material to the corresponding small change in curvature:

here C = bending length (mm), M = fabric mass per unit area (g/m2).

The stiffness of a fabric in bending is very dependent on its thickness, thethicker the fabric, the stiffer it is if all other factors remain the same. The bending modulindependent of the dimensions of the strip tested so that by analogy with solid materials it is a

fabric thickness (mm).

Figure: Shirley Stiffness Tester

efficient & Drape Meter

Drape is the term used to describe the way a fabric hangs under its ownimportant bearing on how good a garment looks in use. The draping qualities required from a

completely depending on its end use; therefore a given value for drape cannot be classified as either good or bad. Knitted fabrics are relatively floppy and garments made from them will tend to follow the body contours. Woven fabrics are relatively stiff with knitted fabrics so that they are used in tailored clothing where the fabric hangs away from

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the two index lines. Four readings are taken from each specimen, one face up and one face down The mean bending length for warp and

The flexural rigidity is the ratio of the small change in bending moment per

The stiffness of a fabric in bending is very dependent on its thickness, thethicker the fabric, the stiffer it is if all other factors remain the same. The bending modulus is independent of the dimensions of the strip tested so that by analogy with solid materials it is a

weight. It has an important bearing on how good a garment looks in use. The draping qualities required from a

therefore a given value for drape cannot be classified as either good or bad. Knitted fabrics are relatively floppy and garments made from them will tend to follow the body contours. Woven fabrics are relatively stiff when compared with knitted fabrics so that they are used in tailored clothing where the fabric hangs away from


the body and disguises its contours. Measurement of a fabric s drape is meant to assess its ability to do this and also its ability to hang in graceful curves.

Cusick drape test: In the drape test the specimen deforms with multi-directional curvature and consequently the results are dependent to a certain amount upon the shear properties of the fabric. The results are mainly dependent, however, on the bending stiffness of the fabric.In the test a circular specimen is held concentrically between two smaller horizontal discs and is allowed to drape into folds under its own weight. A light is shone from underneath the specimen as shown in Fig. 10.4 and the shadow that the fabric casts, shown in Fig. 10.5, is traced onto an annular piece of paper the same size as the unsupported part of the fabric specimen. The stiffer a fabric is, the larger is the area of its shadow compared with the unsupported area of the fabric. To measure the areas involved, the whole paper ring is weighed and then the shadow part of the ring is cut away and weighed. The paper is assumed to have constant mass per unit area so that the measured mass is proportional to area. The drape coefficient can then be calculated using the following equation:

The higher the drape coefficient the stiffer is the fabric.

Figure 10.4 Cusick Drape Test


At least two specimens should be used, the fabric being tested both ways up so that a total of six measurement s are made on the same specimen. There are three diameters of specimen that can be used:• A 24cm for limp fabrics; drape coefficient below 30% with the 30cm sample; • B 30cm for medium fabrics;• C 36cm for stiff fabrics; drape coefficient above 85% with the 30cm sample.It is intended that a fabric should be tested initially with a 30cm size specimen in order to see which of the above categories it falls into. When test specimens of different diameter are used, the drape coefficients measured from them are not directly comparable with one another.


UNIT –V

1. Crimp of yarn in fabric – crimp and fabric properties, measurement of crimp percentage

When the linear density of a yarn has to be determined from a sample of fabric, a strip of the fabric is first cut to a known size. A number of threads are then removed from it and their uncrimped length is determined under a standard tension in a crimp tester. All the threads are weighed together on a sensitive balance and from their total length and total weight the linear density can be calculated.

Yarn from a finished fabric may have had a resin or other type of finish applied to it so that its weight is greater than that of the original yarn. Alternatively it may have lost fibres during the finishing process so that its weight may be lower than that of the original yarn. For these reasons the linear densities of yarn from finished fabrics can only represent an estimate of the linear density of the yarn used to construct the fabric.

There are several important effects of crimp on Fabric Properties:

Abrasion Resistance: If crimp percentage is high then the resistance of the fabric will be higher.

Shrinkage: If crimp percentage is high then the shrinkage of the fabric will be lower.

Handle Properties: When the crimp percentage is higher, the softness of the fabric will be fiber. Simultaneously stiffness of the fabric will be lower.

Fabric Design: Required extensibility is achieved by controlling crimp.

Shirley crimp tester:When yarn is removed from a fabric it is no longer straight but it is set into the path that

it took in the fabric. This distortion is known as crimp and before the linear density of the yarn can be determined the crimp must be removed and the extended length measured.

The crimp tester is a device for measuring the crimp-free length of a piece of yarn removed from a fabric. The length of the yarn is measured when it is under a standard tension whose value is given in Table 4.3.


The instrument is shown diagrammatically in Fig. 4.3 and consists of two clamps, one of which can be slid along a scale and the other which is pivoted so as to apply

The sample of yarn removed from the fabric isinto the clamp. This is because the length of yarn in the clamps has to bemeasurement. The right hand clamp can be moved along the scale and it has an engraved line on it at which point the extended yarn lewith a pointer arm attached. On the pointer arm is a weight which can be moved along the arm to change the yarn tension, the set tension being indicated on aleft hand clamp assembly is balanced and the pointer arm lines up against a fixed mark. As the weight is moved along the arm the clamp tries to rotate around the pivot, so applying a tension to the yarn. When a measurement is being made the movable clamp ipointer is brought opposite the fixed mark. At this point the tension in the yarn is then the value which was set on the scale. The length of the yarn can then be read off against the engraved line.

The crimp, which is the difference between the extended length and the length of the yarn in the fabric, is defined as:

Where L0 = distance between ends of the yarn as it lies in the fabric L1 = straightened length of yarn

2. Fabric shrinkage and its measurementThe dimensional stability of a fabric is a measure of the extent to which it keeps its

original dimensions subsequent to its manufactureincrease but any change is more likely to be a decrease or gives rise to a large number of customer complaints. Some fabric faults such as colour loss or pilling can degrade the appearance of a garment but still leave it usable.Other faults such as poor abrasion resistance mextent their appearance may be anticipated by

The instrument is shown diagrammatically in Fig. 4.3 and consists of two clamps, one of which can be slid along a scale and the other which is pivoted so as to apply tension to the yarn.

The sample of yarn removed from the fabric is placed in the clamps with each end a set distance into the clamp. This is because the length of yarn in the clamps has to be allowed for in the

. The right hand clamp can be moved along the scale and it has an engraved line on it at which point the extended yarn length can be read. The left hand clamp is balanced on a pivot with a pointer arm attached. On the pointer arm is a weight which can be moved along the arm to change the yarn tension, the set tension being indicated on a scale behind it. At zero tension the left hand clamp assembly is balanced and the pointer arm lines up against a fixed mark. As the weight is moved along the arm the clamp tries to rotate around the pivot, so applying a tension to

When a measurement is being made the movable clamp is slid along the scale untile the fixed mark. At this point the tension in the yarn is then the value

which was set on the scale. The length of the yarn can then be read off against the engraved line.

difference between the extended length and the length of the yarn in the

= distance between ends of the yarn as it lies in the fabric.d length of yarn.

2. Fabric shrinkage and its measurements.The dimensional stability of a fabric is a measure of the extent to which it keeps its

s subsequent to its manufacture. It is possible for the dimensions of a fabric to increase but any change is more likely to be a decrease or shrinkage. Shrinkage is a problem that gives rise to a large number of customer complaints. Some fabric faults such as colour loss or pilling can degrade the appearance of a garment but still leave it usable.Other faults such as poor abrasion resistance may appear late in the life of a garment and to some extent their appearance may be anticipated by judging the quality of the fabric. However,

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The instrument is shown diagrammatically in Fig. 4.3 and consists of two clamps, one of which tension to the yarn.

with each end a set distance allowed for in the

. The right hand clamp can be moved along the scale and it has an engraved line on ngth can be read. The left hand clamp is balanced on a pivot

with a pointer arm attached. On the pointer arm is a weight which can be moved along the arm to scale behind it. At zero tension the

left hand clamp assembly is balanced and the pointer arm lines up against a fixed mark. As the weight is moved along the arm the clamp tries to rotate around the pivot, so applying a tension to

s slid along the scale until the e the fixed mark. At this point the tension in the yarn is then the value

which was set on the scale. The length of the yarn can then be read off against the engraved line.

difference between the extended length and the length of the yarn in the

The dimensional stability of a fabric is a measure of the extent to which it keeps its . It is possible for the dimensions of a fabric to

shrinkage. Shrinkage is a problem that gives rise to a large number of customer complaints. Some fabric faults such as colour loss or

ay appear late in the life of a garment and to some judging the quality of the fabric. However,


dimensional change can appear early on in the life of a garment so making a complaint more likely. A recent survey of manufacturers rated shrinkage as one of the ten leading quality problems regardless of the size of the company.

Fabric shrinkage can cause problems in two main areas, either during garment manufacture or during subsequent laundering by the ultimate customer. At various stages during garment manufacture the fabric is pressed in a steam press such as a Hoffman press where it is subjected to steam for a short period while being held between the upper and lower platens of the press.

Laundering is a more vigorous process than pressing and it usually involves mechanical agitation, hot water and detergent. Tumble drying can also affect the shrinkage as the material is wet at the beginning of the drying process, the material being agitated while heated until it is dry. Dry cleaning involves appropriate solvents and agitation; the solvents are not absorbed by the fibres so they do not swell or affect the properties of the fibres. This reduces some of the problems that occur during wet cleaning processes.There are a number of different causes of dimensional change, some of which are connected to one another. Most mechanism s only operates with fibre types that absorb moisture, but relaxation shrinkage can affect any fibre type. The following types of dimensional change are generally recognised:1. Hygral expansion is a property of fabrics made from fibres that absorb moisture, in

particular fabrics made from wool. It is a reversible change in dimensions which takes place when the moisture regain of a fabric is altered.

2. Relaxation shrinkage is the irreversible dimensional change accompanying the release of fibre strains imparted during manufacture which have been set by the combined effects of time, finishing treatments, and physical restraints within the structure.

3. Swelling shrinkage results from the swelling and de-swelling of the constituent fibres of a fabric due to the absorption and desorption of water.

4. Felting shrinkage results primarily from the frictional properties of the component fibres which cause them to migrate within the structure. This behaviour is normally considered to be significant only for fibres having scales on their surface such as wool.

The dimensions of fabrics can become set while they are deformed if they are subjected to a suitable process. Fibres that absorb water can be set if they are deformed while in the wet state and then dried at those dimensions. Thermoplastic fibres can be set if they are deformed at a comparatively high temperature and then allowed to cool in the deformed state. The set may be temporary or permanent depending on the severity of the setting conditions. During relaxation shrinkage it is temporary set that is released. It is generally the case that deformation that has been set can be released by a more severe treatment than the setting treatment. Conversely if it is wished to make the dimension s of the fabric permanent it is necessary to carry out the setting at conditions that the fabric will not meet in use.


Hygral expansion: Hygral expansion refers to the property of certain fabrics that absorb moisture, where the fabric expands as the moisture content increases, owing to the swelling of the constituent fibres. This is particularly a property of wool fabrics. All of the expansion is subsequently reversed when the fabric is dried to its original moisture content. The increase in dimensions takes place in both warp and weft directions and its magnitude is related to the amount of moisture in the material. Figure 6.2 shows the increase in dimensions of two wool fabrics with increasing atmospheric moisture content; in one case the expansion increases with regain almost up to the maximum value for wool, whereas in the other fabric the expansion reaches a maximum at around 20% regain. This is considered to be due to the tighter weave of the second fabric which causes the width ways expansion of the warp yarn to interfere with the lengthways expansion of the weft yarn.

Hygral expansion is believed to be caused by the straightening of crimped yarn as it absorbs moisture. This is due to the fact that wool fibres swell to 16% in diameter and 1% in length when wet. The swelling causes fibres which have been permanently set into a curve to try to straighten out due to the imbalance of forces. When the fibres dry out they revert to their former diameter and so take up their original curvature.

Hygral expansion of a fabric in a finished garment can cause problems when the garment is exposed to an atmosphere of higher relative humidity than that in which it was made. The expansion can cause pucker at seams and wrinkling where it is constrained by other panels or fixed interlining.


Relaxation shrinkage: when yarns are woven into fabrics they are subjected to considerable tensions, particularly in the warp direction. In subsequent finishing processes such as tentering or calendering this stretch may be increased and temporarily set in the fabric. The fabric is then in a state of dimensional instability. Subsequently when the fabric is thoroughly wetted it tends to revert to its more stable dimensions which results in the contraction of the yarns. This effect is usually greater in the warp direction than in the weft direction.Relaxation shrinkage in wool fabrics is caused by stretching the wet fabric beyond its relaxed dimensions during drying. A proportion of the excess dimensions are retained when the dry fabric is freed of constraint. The fabric will, however, revert to its original dimensions when soaked in water. This effect is related to the hygral expansion value of a fabric in that a fabric with a high value of hygral expansion will increase its dimensions more when it is wetted out so that it subsequently needs to contract to a greater extent when it is dried. Merely holding such a fabric at its wet dimensions will thus give rise to a fabric that is liable to relaxation shrinkage.

Swelling shrinkage: This type of shrinkage results from the width ways swelling and contraction of the individual fibres which accompanies their uptake and loss of water. For instance viscose fibres increase in length by about 5% and in diameter by 30-40 % when wet. Because of the fibre swelling, the yarns made from them increase in diameter which means that, for instance, a warp thread has to take a longer path around the swollen weft threads. This is shown diagrammatically in Fig. 6.3 where the swelling of the yarns from the dry state (a) to the wet state (b) causes an increase in the length of the path the yarn must take if the fibre centers remain the same. In a fabric the warp yarn must either increase in length or the weft threads must move closer together. In order for the warp yarn to increase in length, tension needs to be applied to the fabric to stretch it. In the absence of any tension, which is usually the case during washing, the weft threads will therefore move closer together. Although the fibre dimensions will revert to their original values on drying, the forces available for returning the fabric to its original dimensions are not as powerful as the swelling forces so that the process tends to be one way. The overall effect of the swelling mechanism on a fabric's dimensions is dependent on the tightness of the weave. This mechanism is the one that is active when viscose and cotton fabrics shrink.


Felting shrinkage: Felting shrinkage is a mechanism of shrinkage that is confined to woolfabrics and it is a direct consequence of the presence of scales on the wool surface as shown in Fig. 6.4. Deliberate use of this effect is made in milling to increase the density of structures. Felting is related to the directional frictional effect (DFE) which is found in wool fibres. The coefficient of friction of wool fibres is greater when the movement of the fibre in relation to another surface is in the direction of the tip than when it is in the direction of the root. This effect can be measured directly. Shrinkage is caused by the combined effects of DFE and fibremovement promoted by the elasticity of wool. The behaviour is promoted if the fibres are in warm alkaline or acid liquor.When alternating compression and relaxation are applied to the wet material, the compression force packs the fibres more tightly together but on relaxation of the force the DFE prevents many of the fibres from reverting to their original positions. Wool can be made shrink resistant by treatment to reduce the effect of the scales on friction. Chlorine treatments tend to remove the scales; however, too drastic a treatment can reduce the strength of the fibres. Resin treatments are used to mask the scales. The most successful treatments use a combination of the two approaches.

Methods of measuring dimensional stability

Marking out samples: The general procedures for preparing and marking out of samples are laid down in the British Standard. Many dimensional stability tests follow very similar lines differentiated only by the treatment given to the fabric, so that these procedures may be followed if no specific test method exists.For critical work the recommended sample size is 500mm X 500mm and for routine work a minimum sample size of 300mm X 300mm is considered sufficient. The samples are marked with three sets of marks in each direction, a minimum of 350mm apart and at least 50mm from all edges as shown in Fig. 6.5. In the case of the smaller sample the marks are made 250 mm apart and at a distance of 25 mm from the edge. For critical work it is recommended that the


samples are preconditioned at a temperature not greater than 500C with a relative humidity of between 10% and 25%. All samples are then conditioned in the standard atmosphere. After measurement the samples are subjected to the required treatment and the procedure for conditioning and measuring repeated to obtain the final dimensions.

Figure 6.5 Marking out sample

WIRA steaming cylinder: The WIRA steaming cylinder is designed to assess the shrinkage thattakes place in a commercial garment press as steam pressing is part of the normal garment making up process. The shrinkage that takes place when a fabric is exposed to steam is classifiedas relaxation shrinkage not felting or consolidation shrinkage.In the test the fabric is kept in an unconstrained state and subjected to dry saturated steam at atmospheric pressure. These conditions are slightly different from those that occur in a steampress where the fabric is trapped between the upper and lower platens while it is subjected to steam.Four warp and four weft samples are tested, each measuring 300mm X 50mm. They are first preconditioned and then conditioned for 24 h in the standard testing atmosphere in order that the samples always approach condition from the dry side. Markers (threads, staples, ink dots) are then put on the fabric so as to give two marks 250mm apart on each sample.The four specimens are then placed on the wire support frame of the apparatus shown in Fig. 6.6 and steam is allowed to flow through the cylinder for at least one minute to warm it thoroughly. The frame is then inserted into the cylinder keeping the steam valve open and the following cycle carried out:• Steam for 30 s• Remove for 30 s

This cycle is performed three times in total with no additional intervals. The specimens are then allowed to cool, preconditioned and then conditioned for another 24 h to bring them into


the same state they were in when they were marked. They are then remeasured on a flat smooth surface and the percentage dimensional change calculated. The mean dimensional change and direction is reported:

3. Inspection of fabrics- American 10 point system-method of grading – 4 point system for knitted fabrics.

Fabric inspection methods: The inspection of fabric has two primary functions; first to classify the products according to the different quality based on the demands of the buyer/market or client and second to provide the information about the quality being produced. During the inspection the fabric may be found to contain different defects.

The defects depending on the magnitude, frequency of occurrence, position, importance, effect on the purpose, consequence in the further process etc., shall be classified and graded under various systems. During the inspection, the occurrences of various defects need to be examined and graded based on their magnitude and dimension as per the required system. There are two most common types of systems for grading the defects:

4 – Point System 10-Point System.


4 – Point system:

It is an inspection method used for the visual checking of fabric quality; faults are scored with penalty points of 1, 2, 3 and 4 according to the size and significance. The 4-point system, also called the American Apparel Manufacturers’ Association (AAMA) point-grading system for determining fabric quality, is widely sued by producers of apparel fabrics and by the Department of Defense in the United States and is endorsed by the AAMA as well as the ASQC. Defect can be in either length or width direction, the system remains the same. Only major defects are considered. No penalty points are assigned to minor defects.

In this system, one should inspect at least 10 per cent of the total rolls in the shipment and make sure to select at least one roll of each colour way. Fabric defects are assigned points based on the following:

Size of defect Penalty3 inches or less 1 points

Over 3 but not over 6 2 points

Over 6 but nor over 9 3 points

Over 9 inches 4 points

Total defect points per 100 square yards of fabric are calculated and the acceptance criteria are generally not more than 40 penalty points. Fabric rolls containing more than 40 points are considered "seconds".

The formula to calculate penalty points per 100 square yards is given by:

= (Total points scored in the roll × 3600) / Fabric width in inches × Total yards inspected

the following are noteworthy points for this system:

No more than 4 penalty points can be assigned for any single defect. The fabric is graded regardless of the end-product. This system makes no provision for the probability of minor defects. 4 point system is most widely used system in apparel industry as it is easy to teach and

learn.


10-point method Fabric Inspection systemThe earliest inspection system and is designed to identify defects and to assign each defect a value based on severity of defect. Published in 1955 by Textile Distributors Institute and National Federation of Textiles.

Ten Points System (Woven): Warp Defects

10-36 inches 10 points

5-10 inches 5 points

1-5 inches 3 points

up to 1 inch 1 point Weft Defects

Full width 10 points

5 inches to half width 5 points

1-5 inches 3 points

up to 1 inch 1 point

Notes:-Standards for examination of finished goods (woven mainly). Penalties to be assigned for imperfection of warp and weft defects. Grading is designed to apply to every imperfection according to size, regardless of type. For print cloth, any piece of grey which contains less than 50% more penalty. No one yard should be penalized more than 10 points. Any warp or weft defect occurring repeatedly throughout the entire piece makes it “second”. A combination of both warp and weft defects when occurring in one yarn should not be penalized more than 10 points.

Ten Point System Grading:

First Quality’s: piece is graded as “first” if the total quality points do not exceed the total yardage of the piece. Example: 100 yard piece got the penalized of 70.Second Quality’s: piece is graded a “second” if the total penalty points exceed the total yardage of the piece.


Quality Assurance:Quality Assurance (QA) is a way of preventing mistakes or defects in manufactured

products and avoiding problems when delivering solutions or services to customers. QA is applied to physical products in pre-production to verify what will be made meets specifications and requirements, and during manufacturing production runs by validating lot samples meet specified quality controls.

Quality Assurance refers to administrative and procedural activities implemented in a quality system so that requirements and goals for a product, service or activity will be fulfilled. It is the systematic measurement, comparison with a standard, monitoring of processes and an associated feedback loop that confers error prevention. This can be contrasted with quality control, which is focused on process output.

Two principles included in Quality Assurance are: "Fit for purpose", the product should be suitable for the intended purpose; and "Right first time", mistakes should be eliminated. QA includes management of the quality of raw materials, assemblies, products and components, services related to production, and management, production and inspection processes.

Suitable quality is determined by product users, clients or customers, not by society in general. It is not related to cost, and adjectives or descriptors such as "high" and "poor" are not applicable. For example, a low priced product may be viewed as having high quality because it is disposable, where another may be viewed as having poor quality because it is not disposable.

Definition: QA is a set of activities for ensuring quality in the processes by which products are developed.

Focus on: QA aims to prevent defects with a focus on the process used to make the product. It is a proactive quality process.

Goal: The goal of QA is to improve development and test processes so that defects do not arise when the product is being developed.

How: Establish a good quality management system and the assessment of its adequacy. Periodic conformance audits of the operations of the system.

What: Prevention of quality problems through planned and systematic activities including documentation.

Responsibility: Everyone on the team involved in developing the product is responsible for quality assurance.

Example: Verification is an example of QA.

Statistical Techniques: Statistical Tools & Techniques can be applied in both QA & QC. When they are applied to processes (process inputs & operational parameters), they are called Statistical Process Control (SPC); & it becomes the part of QA.

As a tool: QA is a managerial tool.


Quality Control:

Refers to quality related activities associated with the creation of project deliverables. Quality control is used to verify that deliverables are of acceptable quality and that they are complete and correct. Examples of quality control activities include inspection, deliverable peer reviews and the testing process.

Controls include product inspection, where every product is examined visually, and often using a stereo microscope for fine detail before the product is sold into the external market. Inspectors will be provided with lists and descriptions of unacceptable product defects such as cracks or surface blemishes for example.

The quality of the outputs is at risk if any of these three aspects is deficient in any way.Quality control emphasizes testing of products to uncover defects and reporting to management who make the decision to allow or deny product release, whereas quality assurance attempts to improve and stabilize production (and associated processes) to avoid, or at least minimize, issues which led to the defect(s) in the first place. For contract work, particularly work awarded by government agencies, quality control issues are among the top reasons for not renewing a contract.

Definition: QC is a set of activities for ensuring quality in products. The activities focus on identifying defects in the actual products produced.

Focus on: QC aims to identify (and correct) defects in the finished product. Quality control, therefore, is a reactive process.

Goal: The goal of QC is to identify defects after a product is developed and before it's released.

How: Finding & eliminating sources of quality problems through tools & equipment so that customer's requirements are continually met.

What: The activities or techniques used to achieve and maintain the product quality, process and service.

Responsibility: Quality control is usually the responsibility of a specific team that tests the product for defects.

Example: Validation/Software Testing is an example of QC.

Statistical Techniques: When statistical tools & techniques are applied to finished products (process outputs), they are called as Statistical Quality Control (SQC) & comes under QC.

As a tool: QC is a corrective tool.


Total quality management (TQM)

TQM consists of organization-wide efforts to install and make permanent a climate in which an organization continuously improves its ability to deliver high-quality products and services to customers. While there is no widely agreed-upon approach, TQM efforts typically draw heavily on the previously developed tools and techniques of quality control. TQM enjoyed widespread attention during the late 1980s and early 1990s before being overshadowed by ISO 9000, Lean manufacturing, and Six Sigma.

The main features of TQM are:

Customer-oriented: TQM focuses on customer satisfaction through creation of better quality products and services at lower costs.

Employee involvement and empowerment: Teams focus on quality improvement projects and employees are empowered to serve customers well.

Organization-wide: TQM involves every department or division.

Continuous improvement: Quality improvement is a never-ending journey.

Strategic focus: Quality is viewed as a strategic, competitive weapon.

Process management: TQM adopts the concept of prevention through process management.

Change in corporate culture: TQM involves the creation of a work culture that is conducive to quality improvement.

There is no widespread agreement as to what TQM is and what actions it requires of organizations; however a review of the original United States Navy effort gives a rough understanding of what is involved in TQM. The key concepts in the TQM effort undertaken by the Navy in the 1980s include:

"Quality is defined by customers' requirements." "Top management has direct responsibility for quality improvement." "Increased quality comes from systematic analysis and improvement of work processes." "Quality improvement is a continuous effort and conducted throughout the organization."

Total Quality Management (TQM) Tools

Total quality management (TQM) tools help organizations to identify, analyze and assess qualitative and quantitative data that is relevant to their business. These tools can identify procedures, ideas, statistics, cause and effect concerns and other issues relevant to their organizations. Each of which can be examined and used to enhance the effectiveness, efficiency, standardization and overall quality of procedures, products or work environment, in accordance with ISO 9000 standards (SQ, 2004). According to Quality America, Inc. the number of TQM tools is close to 100 and come in various forms, such as brainstorming, focus groups, check lists,


charts and graphs, diagrams and other analysis tools. In a different vein, manuals and standards are TQM tools as well, as they give direction and best practice guidelines to you and/or your staff. TQM tools illustrate and aid in the assimilation of complicated information such as:

1. Identification of your target audience2. Assessment of customer needs3. Competition analysis4. Market analysis5. Brainstorming ideas6. Productivity changes7. Various statistics8. Staff duties and work flow analysis9. Statement of purpose10. Financial analysis11. Model creation12. Business structure13. Logistic analysis.

The list goes on, though essentially TQM tools can be used in any situation, for any number of reasons, and can be extremely effective if used properly.

TQM ToolsThe following are some of the most common TQM tools in use today. Each is used for, and identifies, specific information in a specific manner. It should be noted that tools should be used in conjunction with other tools to understand the full scope of the issue being analyzed or illustrated. Simply using one tool may inhibit your understanding of the data provided, or may close you off to further possibilities.

Pie Charts and Bar Graphs: Used to identify and compare data units as they relate to one issue or the whole, such as budgets, vault space available, extent of funds, etc.

Histograms: To illustrate and examine various data element in order to make decisions regarding them Effective when comparing statistical, survey, or questionnaire results.

Run Chart: Follows a process over a specific period of time, such as accrual rates, to track high and low points in its run, and ultimately identify trends, shifts and patterns.Pareto Charts / Analysis Rates issues according to importance and frequency by prioritizing specific problems or causes in a manner that facilitates problem solving. Identify groupings of qualitative data, such as most frequent complaint, most commonly purchased preservation aid, etc. in order to measure which have priority.· Can be scheduled over select periods of time to track changes. They can also be created in retrospect, as a before and after analysis of a process change.

Force Field Analysis : To identify driving and restraining forces occurring in a chosen process in order to understand why that particular process functions as it does. For example, identifying the driving and restraining forces of catering predominantly to


genealogists. To identify restraining forces that need to be eradicated, or driving forces that need to be improved, in order to function at a higher level of efficiency.

Focus Groups: Useful for marketing or advertising organizations to test products on the general public. Consist of various people from the general public who use and discuss your product, providing impartial feedback to help you determine whether your product needs improvement or if it should be introduced onto the market.

Brainstorming and Affinity Diagrams: Teams using creative thinking to identify various aspects surrounding an issue. An affinity diagram, which can be created using anything from enabling software to post-it notes organized on a wall, is a tool to organize brainstorming ideas.

Tree Diagram: -To identify the various tasks involved in, and the full scope of, a project.

-To identify hierarchies, whether of personnel, business structure, or priorities.-To identify inputs and outputs of a project, procedure, process, etc

Flowcharts and Modeling Diagrams: Assist in the definition and analysis of each step in a process by illustrating it in a clear and comprehensive manner. Identify areas where workflow may be blocked, or diverted, and where workflow is fluid.Identify where steps need to be added or removed to improve efficiency and create standardized workflow

Scatter Diagram: To illustrate and validate hunches. To discover cause and effect relationships, as well as bonds and correlations, between two variables . To chart the positive and negative direction of relationships

Relations Diagram: To understand the relationships between various factors, issues, events, etc. so as to understand their importance in the overall organizational view.

PDCA: The Plan-Do-Check-Act style of management where each project or procedure is planned according to needs and outcome, it is then tested, examined for efficiency and effectiveness, and then acted upon if anything in the process needs to be altered.

This is a cyclical style to be iterated until the process is perfected. All of these TQM tools can be easily created and examined by using various types of computer software or by simply mapping them out on paper. They can also be easily integrated into team meetings, organizational newsletters, marketing reports, and for various other data analysis needs. Proper integration and use of these tools will ultimately assist in processing data such as identifying collecting policies, enhancing work flow such as mapping acquisition procedures, ensuring client satisfaction by surveying their needs and analyzing them accordingly, and creating an overall high level of quality in all areas of your organization.


ISO : ISO (International Organization for Standardization) is an independent, non-governmental membership organization and the world's largest developer of voluntary International Standards.ISO is made up of 165 member countries who are the national standards bodies around the world.What are standards?

International Standards make things work. They give world-class specifications for products, services and systems, to ensure quality, safety and efficiency. They are instrumental in facilitating international trade.ISO has published more than 19 500 International Standards covering almost every industry, from technology, to food safety, to agriculture and healthcare. ISO International Standards impact everyone, everywhere.Benefits of International Standards: International Standards bring technological, economic and societal benefits. They help to harmonize technical specifications of products and services making industry more efficient and breaking down barriers to international trade. Conformity to International Standards helps reassure consumers that products are safe, efficient and good for the environment.Benefits of standards: the ISO Materials: ISO has developed materials describing the economic and social benefits of standards, the ISO Materials. They are intended to be shared with decision makers and stakeholders as concrete examples of the value of standards.

Facts and figures about the benefits of standards:The repository of studies on economic and social benefits of standards provides an insight of the approaches and results of the studies untertaken by different authors, such as national and international standards bodies, research institutes, universities and other international agencies.

For business: International Standards are strategic tools and guidelines to help companies tackle some of the most demanding challenges of modern business. They ensure that business operations are as efficient as possible, increase productivity and help companies access new markets.

Benefits include: Cost savings - International Standards help optimise operations and therefore improve the

bottom line.

Enhanced customer satisfaction - International Standards help improve quality, enhance customer satisfaction and increase sales.

Access to new markets - International Standards help prevent trade barriers and open up global markets.

Increased market share - International Standards help increase productivity and competitive advantage.

Environmental benefits - International Standards help reduce negative impacts on the environment.


How does ISO develop standards?An ISO standard is developed by a panel of experts, within a technical committee. Once

the need for a standard has been established, these experts meet to discuss and negotiate a draft standard. As soon as a draft has been developed it is shared with ISO’s members who are asked to comment and vote on it. If a consensus is reached the draft becomes an ISO standard, if not it goes back to the technical committee for further edits.

Key principles in standard development:

1. ISO standards respond to a need in the market: ISO does not decide when to develop a new standard. Instead, ISO responds to a request from industry or other stakeholders such as consumer groups. Typically, an industry sector or group communicates the need for a standard to its national member who then contacts ISO. Contact details for national members can be found in the list of members.

2. ISO standards are based on global expert opinion: ISO standards are developed by groups of experts from all over the world, that are part of larger groups called technical committees. These experts negotiate all aspects of the standard, including its scope, key definitions and content. Details can be found in the list of technical committees.

3. ISO standards are developed through a multi-stakeholder process: The technical committees are made up of experts from the relevant industry, but also from consumer associations, academia, NGOs and government. Read more about who develops ISO standards.

4. ISO standards are based on a consensus: Developing ISO standards is a consensus-based approach and comments from stakeholders are taken into account.

ISO Elements

Management Responsibility

Quality System

Contract Review

Design Control

Document & Data Control

Purchasing

Control of Customer Supplied Product

Product Identification and Traceability

Process Control

Inspection and Test Status

Control of Inspection, Measuring and Test Equipment.

Inspection and Test Status

Control of Nonconforming Product

Corrective & Preventive Action

Handling , Storage, Packaging,Preservation and Delivery

Control of Quality Records

Quality Audits

Training

Servicing

Statistical Techniques


What is Six Sigma ? Six Sigma's aim is to eliminate waste and inefficiency, thereby increasing customer

satisfaction by delivering what the customer is expecting. Six Sigma is a highly disciplined process that helps us focus on developing and

delivering near-perfect products and services. Six Sigma follows a structured methodology, and has defined roles for the participants. Six Sigma is a data driven methodology, and requires accurate data collection for the

processes being analyzed. Six Sigma is about putting results on Financial Statements. Six Sigma is a business-driven, multi-dimensional structured approach to:

o Improving Processeso Lowering Defectso Reducing process variabilityo Reducing costso Increasing customer satisfactiono Increased profits

The word Sigma is a statistical term that measures how far a given process deviates from perfection. The central idea behind Six Sigma is that if you can measure how many "defects" you have in a process, you can systematically figure out how to eliminate them and get as close to "zero defects" as possible and specifically it means a failure rate of 3.4 parts per million or 99.9997% perfect.

Key Concepts of Six Sigma: At its core, Six Sigma revolves around a few key concepts. Critical to Quality: Attributes most important to the customer. Defect: Failing to deliver what the customer wants. Process Capability: What your process can deliver. Variation: What the customer sees and feels. Stable Operations: Ensuring consistent, predictable processes to improve what the

customer sees and feels. Design for Six Sigma: Designing to meet customer needs and process capability.

Our Customers Feel the Variance, Not the Mean. So Six Sigma focuses first on reducing process variation and then on improving the process capability.

The Benefits of Six Sigma: There are following six major benefits of Six Sigma that attract companies.

Six Sigma: Generates sustained success. Sets a performance goal for everyone. Enhances value to customers. Accelerates the rate of improvement.


Promotes learning and cross-pollination. Executes strategic change.

Key Elements of Six Segma: There are three key elements of Six Sigma Process Improvement. Customers Processes Employees

The Customer: Customers define quality. They expect performance, reliability, competitive prices, on-time delivery, service, clear and correct transaction processing and more. Today, Delighting a customer is a necessity. Because if we don't do it, someone else will!

The Processes: Defining Processes and defining Metrics and Measures for Processes is the key element of Six Sigma. Quality requires to look at a business from the customer's perspective, In other words, we must look at defined processes from the outside-in. By understanding the transaction lifecycle from the customer's needs and processes, we can discover what they are seeing and feeling. This will give a chance to identify week area with in a process and then we can improve them.

The Employees: The company must involve all employees in Six Sigma Program. Company must provide opportunities and incentives for employees to focus their talents and ability to satisfy customers.

Methodologies of Six Sigma: the following two key methodologies:

DMAIC: refers to a data-driven quality strategy for improving processes. This methodology is used to improve an existing business process.

DMADV: refers to a data-driven quality strategy for designing products & processes. This methodology is used to create new product designs or process designs in such a way that it results in a more predictable, mature and defect free performance.

There is one more methodology called DFSS - Design For Six Sigma. DFSS is a data-driven quality strategy for designing design or re-design a product or service from the ground up.Sometimes a DMAIC project may turn into a DFSS project because the process in question requires complete redesign to bring about the desired degree of improvement.

DMAIC Methodology: This methodology consists of following five steps.

Define --> Measure --> Analyze --> Improve -->Control Define : Define the Problem or Project Goals that needs to be addressed. Measure: Measure the problem and process from which it was produced. Analyze: Analyze data & process to determine root causes of defects and opportunities.


Improve: Improve the process by finding solutions to fix, diminish, and prevent future problems.

Control: Implement, Control, and Sustain the improvements solutions to keep the process on the new course.

In the subsequent session we will give complete detail of DMAIC Methodology

DMADV Methodology:This methodology consists of following five steps.Define --> Measure --> Analyze --> Design -->Verify

Define : Define the Problem or Project Goals that needs to be addressed. Measure: Measure and determine customers needs and specifications. Analyze: Analyze the process for meet the customer needs. Design: Design a process that will meet customers needs. Verify: Verify the design performance and ability to meet customer needs.

DFSS Methodology: DFSS - Design For Six Sigma is a separate and emerging discipline related to Six Sigma quality processes. This is a systematic methodology utilizing tools, training and measurements to enable us to design products and processes that meet customer expectations and can be produced at Six Sigma Quality levels. This methodology can have following five steps.

Define --> Identify --> Design --> Optimize -->Verify Define : Identify the Customer and project. Identify: Define what the customers want, or what they do not want. Design: Design a process that will meet customers needs. Optimize: Determine process capability & optimize design. Verify: Test, verify, & validate design.

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