Prepared By Amirul Eahsan

WHAT IS IRREGULARITY OR UNEVENNESS OF FIBER?

The mass per unit length variation due to variation in fiber assembly is generally known as "IRREGULARITY" or "UNEVENNESS". It is true that the diagram can represent a true reflection of the mass or weight per unit length variation in a fiber assembly. For a complete analysis of the quality, however, the diagram alone is not enough. It is also necessary to have a numerical value that represents the mass variation. The mathematical statistics offer 2 methods

TYPES OF METHODS

1. The irregularity U%: It is the percentage mass deviation of

unit length of material and is caused by uneven fiber

distribution along the length of the strand.

2. The coefficient of variation C.V%

Imperfections

Yarns spun from staple fibers contain imperfections. They are

also referred to as frequently occurring yarn faults. They can be

subdivided into three groups

1. Think place

2. Thick place

3. Neps

The reasons for these different types of faults are due to raw

material or improper preparation process. A reliable analysis of

these imperfections will provide some reference to the quality of

the raw material used

The standard sensitive levels are as follows :

Thin place: -50% Thick place: +50% Neps: +200%

Thin places and thick places in a yarn can thin places and thick places refer to a particularly valuable indication that the raw, on the one hand, quite considerably affect the appearance of a woven or knitted fabric. Furthermore, an increase in the number of material or the method of processing has become worse

IRREGULARITY OF YARN IS RECOGNISED AS:

1. Variation of liner density 2. Variation of linear thickness 3. Variation of linear twist 4. Variation of linear strength 5. Variation of linear color

Periodic variation:

Inspection of some traces express definite sequences of thick

place in the strand of material. These forms of irregularity refer to

as periodic variation.

Classification of periodic variation:

Classified according to their wavelength, using the fiber length as

a length unit,

i. Short terms variation:1 to 10 times the fiber length.

ii. Medium term variation: 10 to 100 times the fiber

length.

iii. Long term variation: 100 to 1000 times the fiber

length.

Classification of the causes of yarn

irregularity given by Martindle:

Properties of raw materials.

Inherent shortcomings in yarn making & Preparatory

machinery.

Mechanically detective machinery.

External causes due to working conditions & inefficient

operation.

Properties of raw materials:

There are some variables in the properties of natural fibre which

causes variety of problems for the spinners. Fibre length is the

major variable of them. There are others variables which have

some effect on the yarn properties such as; surface character,

fineness, shape of cross-section, maturity, crimp etc.

Inherent shortcoming in yarn making & preparatory

machinery:

Variation in fibres hamper the fibre manipulation by rollers,

aprons, gills & other machine parts. To give the best result the

machines is set within the limitations imposed by the materials.

The ‘Drafting Wave’ is one example of irregularity due to the

inability system to control each fibre. Short fibres are formed due

to this kind of irregularity which float in the drafting zone & move

forward in an irregular but cyclical manner which results in the

drafted strand having thick & thin places.

Mechanically detective machinery:

An efficient maintenance system in machinery is essential to

keep the level of irregularity within bounds/minimum. Many

defects hampers the mechanism of machinery such as; machine

draft out of adjustment, bearings become worn, components get

damaged, lubrication systems clog/stops, and dirt etc.

External causes due to working condition & insufficient

operation:

Men & women working in a mill must be aware of their duties,

their lack of responsibilities may decrease the quality control.

Operatives can spoil yarn too, by poor piecing, careless oiling &

clearing, & general slack work.

Effect of irregularity in weight per unit

length:

1. Strength

2. Fabric appearance

3. Stripy Knitted goods

4. Dyeing & finishing faults

1. Strength:

Thin places in slivers, roving or yarns are the weakest places.

During the process when the strand has to support itself during its

passage from one point to another, more irregular strand will have

the greater chance to breaks usually means the introduction of

other faults e.g. thicker sliver or roving of the piecing or knots in

yarn.

2. Fabric appearance:

A certain amount of irregularity is unavoidable & these causes

irregularity in appearance of fabric. Excess variation in irregularity

will produce an objectional appearance on the fabric surface. This

effect of irregularity depends on some factors like, the types of

variations(periodic or non-periodic), fabric structure, fabric

dimensions, use of yarn(as warp or weft),& fabric finish. Fabric

appearance can be classified as below-

i. Diamond bars &

ii. Weft bars or block bars

3. Stripy Knitted goods:

Weaver fares are better than the knitter the irregularity in one

set of threads may concealed/hid by other side. Knitting m/c are

set to produce a given quality of fabric from a known count to

cone or where one cone contains yarn of different count, the

result is stripy knitted fabric.

4. Dyeing & finishing faults:

The thicker & soft parts of the yarn take up more size than the

thinner & harder regions. As a result during the dyeing process

the distribution of the residual size may be uneven & cause

difficultly in achieving a level dyeing.

Methods of measuring irregularity:

Visual method

Cutting & weighing method

Variation in thickness under compression

-W.I.R.A roving evenness tester

-LINRA roller yarn diameter tester

Electric capacitance tester

-Fielden-walker yarn evenness

recover

-USTER evenness tester

Photo electric tester

-W.I.R.A photo electric tester

-LINRA tester

Miscellaneous method:

-Airflow

-Mercury displacement.

Premier evenness Tester:

Imperfections/km- No.of mass increases (Thick place).Mass

reduction (Thin place) & short mass increase (Neps) measured

simultaneously at the following values-

Thin places: -30%,-40%,-50%,-60% etc.

Thick places:+30%,+50%,+70%,+100%etc.

Neps places:+140%,+200%,+280%,+400%etc.

Recommended Values:

For ring spun yarn:-50%,+50%,+200%

For open end:-50%,+50%,+280%

Fig. Premier Evenness Tester

The ‘USTER’ evenness tester

Definition : The instrument or M/C by which unevenness (U%) ,

co-efficient of variation of mass (CV%), yarn hairiness,

imperfection index (IPI) and thick, thin place, neps etc of yarn,

roving sliver can be measured or calculated is called Uster

Evenness Tester or Uster Tester .

Fig. USTER Evenness Tester

Two oscillators A and B have equal frequencies when there is no

material in the measuring capacitor C. When the two frequencies

are superimposed the difference in frequency is zero.

The presence of material in the capacitor causes its capacity to

change and so alter the frequency of the oscillator. A there will be

a difference between the two frequencies which changes

according the to the amount of material between the capacitors

plates. The suitable circuits D translate these frequencies

differences into signals which are indicated on the meter M , drive

the pen of recorder , and are fed into the integrator which

indicates the average irregularity either as percentage mean

deviation or coefficient of variation according to the model used.

The actual tester is illustrated following external features:

The ‘comb` of eight measuring capacitors of different sizes.

The creel and guides to control the material.

The traverse roller which can control the material speed over

a range from 2-100 yd per minute.

The control switches.

The mater on the main unit which indicate the momentary

variations in the material.

The indicator which indicates P.M.D or C.V.

The high speed pen recorder whose chart speed can be

varied between 1 and 40 in/min.

Advantage of Uster Evenness Tester:

The CV% measured by USTER give a measure of variation of weight per unit length.

This instrument measure the irregularity of material at high speed (2-100ft/min)

It can show both % of M.D & C.V. of material. The recorder of pen can work at a high speed of 100yds/min

Disadvantages of Uster Evenness Tester:

The result obtained by this M/C is affected by moisture content of material.

This M/C can't detect the thick and thin place. In this instrument material up to a certain thickness can be

tested.

Uses of Uster Evenness Tester:

1. Evenness measurement of yarn, roving and sliver. 2. Measurement of imperfection ( thick, thin place) 3. Mass analysis. 4. Spectrogram analysis/frequency analysis. 5. Yarn hairiness measurement 6. Fabric simulation i,e before making fabric.The yarn gathering

knowledge about the quality of the fabric. 7. Variation of trend analysis.

PHOTOELECTRIC EVENNESS TESTER:

When a beam of light is directed on to a photoelectric cell an

electric current is produced. The magnitude of the current is

directly proportional to the intensity of light falling on the light-

sensitive part of cell. If part of the light is cut off by a yarn passing

between its source and the photoelectric cell, the current following

will vary as thickness of yarn varies.

Irregularity testers based on this principle usually consist of the

following parts:

Fig: schematic diagram of a photoelectric evenness tester

1. A stabilized source of light (A).

2. An optical system to control the light (B).

3. A slit of variable width through which the yarn passes (C).

4. A photoelectric cell (D).

5. Suitable meters and recording instruments to measure the

current variations and produce an irregularity trace (E).

6. A yarn-control device.

The coefficient of variation measured by photoelectric methods

does not give a measure of the variation of weight per unit length.

In the papers referred to, the coefficients of variation obtained by

photoelectric testers and the cutting weighing of 1 in. lengths have

been compared for a number of yarns. The conclusions reached

that yarns of comparable cont and construction are graded by a

photoelectric tester in the same order as by cutting and weighing

1 in. lengths, and that the numerical value of the coefficient of

variation measured optically is greater than that of short term

weight variation.

Difference between the Electronic Capacitance

Tester and Photo Electric Tester:

Electronic Capacitance Tester Photo Electric Tester

1) Main part of this tester is a

capacitor.

1) Main part of this tester is photo

electric cell.

2) In this tester the evenness is

measured by the variation in

frequencies between the two

oscillators.

2) Evenness is measured by the

variation in the intensity of light of

different yarns.

3) This tester is based on the

mechanism of the capacitor.

3) Based on the optical system.

4) Consists of a yarn controlling

device, light source etc.

4) Consists of yarn controlling

device, light source and suitable

meter.

5) Comparatively slow in giving the

value of irregularity in PMD or CV.

5) Gives quick and accurate value

of irregularity in terms of CV.

6) The results are affected by the

m/c of material.

6) The results are not affected by

the m/c of material.

7) Figure

7)Figure

The LINRA roller:

An instrument developed by the Linen Industry Research

Association.

The yarn passes round a series of rollers so that it lies between

four nips.

The pressure of each roller being 5g.

The four thickness so measured are equally spaced within 1

inch.

The top roller supports a small anvil on which the plunger of

micrometer rests.

A series of measurements may be taken along the yarn.

Modifications to such an apparatus can convert from a hand

operated instrument with intermittent measurement to a

continuous tester with the movement of the top roller being

used to actuate mechanical or electrical pen recorders.

This instrument works satisfactorily with coarse and medium

flax yarns up to about 60s lea (27.5tex) and on rayon staple

yarns with twist factor of 1.5 or more.

Conclusion

The evenness of yarn is an important index of quality control of

textiles, so the researches about the yarn evenness test method

have been the hotspot in the textile measurement for recent

years. From this assignment we got an opportunity to learn more

about the importance of evenness. We have discussed about the

factors which affects the evenness of yarn. Most important thing is

that, we have gathered a clear concept about some of the major

methods and machines or tester to determine the evenness of

yarn. All the knowledge we have acquired from our analysis which

we made to perform this assignment successfully will help us to

understand more about the necessity of various textile testing

especially the evenness testing.