Twist-less and Self-twist yarns

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Twist-less yarns

Principles of staple yarn production

l Fiber consolidationl Fiber parallelizationl Drawing

Improve the inter fiber cohesionl Improve the inter fiber cohesion

Fiber Consolidation

• “Is the process where the fiber is opened to a individual level”

Fiber consolidation cont.

l Fiber consolidation is carried out in carding machine.

l Consolidated fiber flow is known as the carded sliver.carded sliver.

l Fibers are opened and oriented along the sliver axis.

Fiber parallelization

• “Is the process where fibers are more paralleled along the sliver axis”

Fiber parallelization cont.

l Fiber parallelization is carried out in draw frame machine.

l Paralleled fiber flow is known as the draw frame sliver.frame sliver.

l Fibers are paralleled by drafting.l Due to the relative fiber movement, along

the sliver axis improve the fiber orientation and straighten the hooked and folded fibers.

Carded Vs Draw frame sliver

• Draw frame sliver Carded sliver

Drawing

• “Is the process where the linear density of the yarn is reduced to the required level to

spin a yarn”

Drawing Cont.

l Drawing is carried out in Speed frame and Ring frame in conventional ring spinning.

l Output is the thin parallel fiber flow which has near linear density to the final yarn.has near linear density to the final yarn.

l Process of drawing is drafting (roller drafting/drafting with air flow).

l Sliver is stretched, so that length increases while thickness decreases ultimately reducing linear density.

Improve inter fiber cohesion

• “Process of improving the cohesion between fibers so that fibers confirm in to one unit

(Yarn)”

Improve inter fiber cohesion cont.

• Twisting : Improving the fiber cohesion by friction by introduction of twist to the yarn.

– True twist/Pure twist : Ring spinning, OE spinning, [Friction]

– False twist : Air jet spinning, Water jet spinning.

• Twistless methods : Improving the fiber cohesion by another means than twisting.

– Adhesive bonding– Continuous felting

Twist-less spinning methods

• Adhesive Bonding : Strand is held together by an adhesive instead of the twist.

• Continuous felting : Fibers are bond • Continuous felting : Fibers are bond together by using the felting effect of fibers.

Tek-Ja process

• Drawing unit• Press roll• Carrier roller• Rub cylinder• Rub cylinder• Presser cylinders• Dryer• Pump

Tek-Ja process cont.

Drawing (Roller Drafting)

Introduction of adhesiveMixture (carrier cylinder)

Winding(Winding unit)Mixture (carrier cylinder)

Introduction of false twist(Rub cylinder)

Drying(Drying unit)

(Winding unit)

Production speed : 3-5 times than ring spinning

Control factors in adhesive spinning

• Fiber control in roller drafting• Adhesive percentage• Condensation• Fiber support in the material path• Fiber support in the material path• Drying

Fiber control in roller drafting

• Simple drafting system is used(Two coupled rollers)rollers)

• High drafting is required in greater speed levels(3-5 times the normal spinning speed)

Fiber control in roller drafting Cont.

• Wet spinning of cellulosic fibers : Fibers are introduced with some amount of moisture prior to drawing. This significantly increases the inter-fiber significantly increases the inter-fiber cohesion resulting greater fiber control.

• Additional fiber control devices such as aprons.

Wet spinning

• Yarn evenness is not significantly varying with the production speed.

• Drafting settings has very less effect on yarn evenness.

Adhesive percentage

• Strength of the yarn according to the requirement.

• Determines the stiffness of the yarn• Depend on the count• Depend on the count• 4-8 per cent ; produces yarn which is not

too stiff, and has sufficient strength for normal counts.

Condensation

• Improve the packing of the fibers after introduction of adhesive solvent.

• Yarn is subjected to a mechanical forces to achieve near circular cross section.achieve near circular cross section.

• Rubbing rollers and air jet twisting devices.

Fiber support in material path

• Yarns are very weak in the material path and needed to be supported.

• Yarn is always supported by another surface or rollers.surface or rollers.

• Yarn is given a false twist to improve the strength.

Drying

• Drying is the process where the water in the adhesive solution is vaporized leaving the adhesive in the yarn.

• Drying is the major limitation in producing • Drying is the major limitation in producing adhesive spun yarn in higher production rates.

• High speed production requires dryers with larger size and complex design.

• Adhesive bonding is not feasible than the rate of 100m/min with conventional drying.

Inactive starch

• Starch which is in inactive state is applied as the adhesive and later in the process starch is activated.

• After wet drawing the inactive starch is • After wet drawing the inactive starch is applied and wound in to a package.

• Package is then steamed to activate the starch and improving inter fiber cohesion.

• Package is then unwound and rewound in to a smaller package.

Inactive starch cont.

Inactive starch process

Drawing

Applying inactive inactiveAdhesive mixture

Unwinding

Adhesive mixture

Introduction of false twist Cone winding

Steaming

Bobtex process

• Wetting device• Roller assembly• False twister• Cross wound • Cross wound

package• Feed roller• Stirrer

Air jet twisting device

Control parameters

• Fiber control in roller drafting

• Adhesive percentage

• Condensation

• Fiber support in the material path• Fiber support in the material path

• Drying

Bobtex filament process

Continuous felting

• Wool fibers have strong cohesive forces between them which is caused by scale structure of wool structure of wool fibers.

• Continuous felting is the process where the felting is improved and used as a cohesive force to spin a yarn.

Continuous felting cont.

• Fibers are forced to move uni-directionally under a mechanical force.

• The resistive force caused by fiber scales finally result in fiber entanglement increasing frictional forces.forces.

• Felting of yarn readily occurs in suitable liquid medium when the fibers are mechanically agitated. Liquid acts as a lubricant improving fiber relative movement, thereby increasing felting effect.

Periloc process• Tension less wool

sliver• Rotating rollers

and rotating and rotating circular plate.

• Squeeze rollers• Drying and

winding

Periloc process cont.• A: Felting tube• B: Felting liquid

medium• C: False twister• D: Sliver• D: Sliver

Properties & End-uses

Twist-less yarn characteristics

• Flat and ribbon like flexible yarn• Depends on the fibre type and the adhesive

type

Top View

Front View

Twist-less yarn fabric properties• Strength

– When twist-less yarn is washed to remove adhesive, virtually there is no strength.

– Depends upon the friction at fibre crossing points

– So the structure of the fabric becomes important– Strength of twist-less yarn fabrics is higher than – Strength of twist-less yarn fabrics is higher than

normal fabrics

Twisted Yarn Fabric Twist-less Yarn Fabric

• Strength…

N.C. = Normally twisted yarnsTwl.C. = Twistless yarns

• Cover factor– Twist-less yarns increase the cover factor

of fabric– Because the twist-less yarn (flat & ribbon

like) is not thin as normal twisted yarns and the yarns flatten within the fabric structurestructure

– Can match a normal fabric with much lighter fabric made with twist-less yarns by decreasing the number of yarns per centimeter

• Luster– Fabrics made from twist-

less yarns have an attractive and characteristic luster.

– Following figure shows results of a quantitative assessment using Zeiss glossmeter

– Luster of twist-less yarn – Luster of twist-less yarn fabrics lies between bright rayon and normal finished cotton poplin

– Due to no twist in yarn, light is reflected without scattering

• Bulkiness– Twist-less yarn is very bulky– Fibres are loosely arranged in the twist-less yarn

fabrics– Changed disposition of the fibers tends to give a

softer hand in twist-less yarn fabrics

• Water & air permeability– Open structure of twist-less yarn fabrics allows

more water & air transmission

• Effect of laundering

– Fabric loose strength on washing in two ways,• By chemical degradation of fibres• By loss of fibres from the yarn

– Since the chemical degradation of fibres can be considered very small, the loss of strength can considered very small, the loss of strength can be attributed to loss of fibres

• Effect of Laundering…– In twist-less yarn fabrics the fall in strength

due to fibre loss is counter-balanced by increase in friction between fibres as a result of fabric shrinkage

Shrink

• Wet ability– Wet ability is high in twist-less yarn fabrics– Yarns are not twisted and don’t have a tight

structure in yarns

• Wicking property– Wicking property is high than normal twisted

yarn fabrics– Twist-less yarns has more open structure

allowing easy capillary action

• Shrinkage– Both knitted and woven fabrics of twist-less

yarns suffer much less shrinkage in the fabric forming process

• Crease resistance• Crease resistance– Crease resistance property of the twist less

yarn fabric is same as the normal fabric

End-uses• Towels

– Bath towels, hand towels and baby blankets– Twist-less towels are more bulky and softer– Good absorbency properties

• Twist-less pyjamas and cotton bath wear– Light weight, comfortable permeability

properties and luxury look due to better luster

• Twist-less shirts– Light weight, comfortable to wear

• Tent fabrics– Light twist-less yarn fabric is almost equal to

normal heavy tent cloth in respect of air & water permeability

– Tearing strength of twist-less yarn fabrics are higher than normal fabrics

• Composites– Twist-less yarns with long, aligned fibers are

using for;• load-bearing applications (an added advantage of

having a lower weight than conventional reinforcements)

• To reinforce naturally derived plastics• To reinforce naturally derived plastics• Interior parts for the automotive industry

Self-twist yarnsSelf-twist yarns

Introduction • Staple yarns have been given strength by the

use of continuous, unidirectional twist• No alternative technique has been developed

Unidirectional Twist• Comparatively slow process

oTraveler speedoBalloon tensiono Power to rotate the bobbinso Power to rotate the bobbins

• Spinning process is expensive • Necessary to rotate the yarn take-up package

Alternating twist

Alternating Twist• Twist alternating in S and Z direction • Necessary only to rotate strand of fibres• Possible to rotate the strand at high speed

Alternating twist yarn

Draw backs of Alternating twist• Also inserts an alternating untwisting torque• Application of tension cause to reduce the

strength of the yarn

Concept of Self Twist• Allow to assemble to two alternative twisted

yarns• Untwisting torque in two strands cause them

to ply about one anotherto ply about one another• Untwisting torque is balanced by the plying

torque

Principal of Self Twist

Self Twisting• Assembly of at least two strands, at least one

of which has alternating twist along its length

• In practice, assembly of two identical strand • In practice, assembly of two identical strand having identical level of alternating twist

Self Twist Spinner

Process of Self Twist Spinner• Drafting system present two strand of fibres

to a pair of rubber covered reciprocating and rotating rollers

• reciprocating and rotating rollers insert • reciprocating and rotating rollers insert alternating region of S and Z twist

• Two strands are immediately converged and allow to self twist

• Twisted yarn is wound on to a take-up package

Twisting region of self twister

Twisting region of self twister cont…

Twisting region of self twister cont…

• The twist in u always in the same direction but varies cyclically in intensity

• The twist in v varies cyclically in direction

Self Twist Yarn

Self Twist Yarn cont…• Zero phased yarn

both strands are converged with their twist structures in phase

• Phased yarn • Phased yarn assembly of to strands out of phased

Phased yarns are stronger than zero phased yarns

Methods of inserting Alternating Twist

• Centrifugal-jaw Twister• Intermittent Nip Twister• Disc Twister• Fluid-vortex Twister• Fluid-vortex Twister• Oscillating Roller Twister

CategorizationIntermittently

Centrifugal-jaw TwisterIntermittent Nip TwisterDisc Twister

ContinuouslyFluid-vortex TwisterOscillating Roller Twister

Centrifugal-jaw Twister

Factors Effected to Twist • Twist intensity is governed by the magnitude

of the centrifugal – jaw forces.• Relative speed of the strands through the

twister.twister.• Rotational speed directly effected to the

twist cycle length.

Centrifugal-jaw Twister cont…

Limitations • Production rate is limited

it has not been possible to design such complex twisting tube to run at the high speed, in practical situation is 10000 r.p.m.speed, in practical situation is 10000 r.p.m.

• Frictional forces generated in pulling the strand through the jaws.

Intermittent Nip Twister

Merits & Demerits• Merits

– High production speed– Twisting of heavy continuous - filament– low variation intermittency– low variation intermittency

Demerits– Difficulties in threading– Sliver slippage

Disc Twister

Disc Twister cont…..

Limitations• Slippage can be occur between twisting

surface and strand.• Increases the possibility of wear of twisting

surfacesurface

Fluid-vortex Twister

Air jet valve

Characteristics of air jet • Air twister mechanically simple and easy to

set up• Twist insert Continuously• For staple fibres the size of twisting chamber • For staple fibres the size of twisting chamber

must be large• High production speed

Compare with convergence tube & guide

Convergence guideConvergence tube

Oscillating Roller Twister

Oscillating Roller Twister

Conventional roller twister

Features• Suitable for the staple fibers• Simple twisting mechanism• Bulk production • Continuous preventive maintains• Continuous preventive maintains

– Consider the nip roller and gap conditions

Alternative spinning Systems utilizing self twistutilizing self twist

ST yarn

• ST is the abbreviation used for in phase yarn or low phase angle yarn from basic self twist machine.

• It is a two or more strand structure wherein each strand has same count.

Shortcomings of Staple ST in processing to fabrics…

• Unable to withstand as warp yarn in weaving- Inter yarn abrasion in a warp sheet cause fibres trapping between yarns and entangled fibres tend to unpeel or untwist the self twist structure at twist change overs.

• The cyclic nature of self twist structure manifested as patterning in a fabric. - Due to the difference of reflectance in different twist sections shows a patterning effect.Hide the patterning

- Use of yarn dyed or printed patterns.- Raising or Brushing.

STm

• One strand of self twist yarn is reduced in weight, the untwisting torque of the other strand tends to predominate at the self twisting and the heavy strand tend to wrap twisting and the heavy strand tend to wrap the lighter about it self in an alternative manner.

• STm refers to the situation where heavier strand is staple and other is a monofilament.

• The resultant STm structure is a strand of staple fibres having a very low alternating twist bound together by a monofilament spiraling helically in reversing direction about the outside.

• Advantages: Spinning limit is extended.• Advantages: Spinning limit is extended.Increase productivityPatterning would be less.

Duplex self twist yarn

1) 2ST yarn• Two ST yarns are assembly wound on the

one package at the self twist spinner .• The final 2ST yarn is a 4 ply structure.• The final 2ST yarn is a 4 ply structure.• Certain superior properties.• Count range is restricted.• Production is impaired.

2) 2STm yarn• Two STm yarns are assembly wound on to

the spinning package .• No of strands twisted from twisting rollers • No of strands twisted from twisting rollers

are reduced at the expense of inconvenience of handling monofilaments.

Double twister Systems

1) ST2 Yarn-Involves self twisting together

of self twisting structures.-Weaves exceptionally well.-Weaves exceptionally well.-Patterning still prevail.-Count range is limited.-Output is limited compared to

ST yarn.

• Below shows the way the yarn is incorporated in ST2 structure.

2) (STm)2 yarn• Two STm yarns are self

twisted together to give (STm)2 yarn.

• The substitution of fine • The substitution of fine monofilaments for two of the strands extend the available count ranges.

• Weave Exceptionally well and less patterning.

3) (ST)m yarn• Add a monofilament to ST

yarn in its second twisting stage.

• The resultant yarn is stable enough to withstand enough to withstand weaving.

4) STmm yarn• The second

monofilament serves to bind the first monofilament and the stability and robustness stability and robustness of resultant yarn structure are enhanced compared to STm yarn.

STT yarnConcept• Alternative way of the ST system where

spinning two singles on to an assembly wound and transfer to the twisting process.

• The output of ST spinner need to have • The output of ST spinner need to have sufficient tenacity to ensure the satisfactory level in the next process of twisting.

• The operation of ST spinning within the STT system is similar to conventional spinning.

• The commercial development of spinning system was undertaken by Repco Research Incorporation, Australia.

• Yarn characteristics depend on ply twist and added twist.

• Properties of STT include high extension to • Properties of STT include high extension to break (STT yarns are more extensible and have a lower modulus) .

• Tenacity increase with added twist to a certain level and then decrease.

• Irregularity reduces with added twist.

Recap

• Twist-less yarns– Principles of staple yarn production– Twist-less spinning methods– Properties & End-uses– Properties & End-uses

• Self-twist yarns– Unidirectional & Alternating Twist– Draw backs Alternating twist– Self –twist and self-twist yarn production– Alternative spinning Systems utilizing self twist

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