Guidelines for selection of yarn part 2 12.02.14

YarnYarn

Technical Specifications & selection Technical Specifications & selection guidelinesguidelines

Technical SpecificationsTechnical Specifications

Yarn Twist Yarn Twist

Twisting is the primary binding mechanism of spun Twisting is the primary binding mechanism of spun yarns. yarns.

In general, twist is defined as a measure of spiral turns In general, twist is defined as a measure of spiral turns given to a yarn in order to hold the constituent fibers given to a yarn in order to hold the constituent fibers together. together.

In practice, yarn twist is described using three main In practice, yarn twist is described using three main parameters: parameters:

• (a) twist direction, (a) twist direction, • (b) twist level (turns/unit length), and (b) twist level (turns/unit length), and • (c) twist factor(c) twist factor

Yarn TwistYarn Twist

The amount of twist inserted in the yarn can influence The amount of twist inserted in the yarn can influence many yarn characteristics.many yarn characteristics.

It is, perhaps, the only It is, perhaps, the only binding mechanismbinding mechanism that allows that allows the structure to retain a great deal of the structure to retain a great deal of its flexibilityits flexibility (as (as compared to glue or adhesive chemicals which result in compared to glue or adhesive chemicals which result in more stiff structures).more stiff structures).


Highly twisted yarn is “Lively” and tends to twist upon it Highly twisted yarn is “Lively” and tends to twist upon it and produce “Snarls”. and produce “Snarls”.

Fabrics made from highly twisted yarns will possess a Fabrics made from highly twisted yarns will possess a lively handle. lively handle.

In general, the higher the level of twist in the yarn the In general, the higher the level of twist in the yarn the greater the tendency for the greater the tendency for the knit fabric to skew or knit fabric to skew or torque.torque.

An increase in the amount of twist produces an increase An increase in the amount of twist produces an increase in the in the yarn strengthyarn strength, if yarn strength is increase, the , if yarn strength is increase, the fabric strength will be increased. fabric strength will be increased.


The warp yarns are the yarns with highest twist.The warp yarns are the yarns with highest twist.

The twist of weft yarns is approximately 4 - 5 % below The twist of weft yarns is approximately 4 - 5 % below the twist of warp yarns.the twist of warp yarns.

The twist of hosiery yarns is approximately 12 – 15 % The twist of hosiery yarns is approximately 12 – 15 % below the twist of warp yarns.below the twist of warp yarns.

A fine yarn requires more twist than a coarse yarn for the A fine yarn requires more twist than a coarse yarn for the same application.same application.

Twist Multiplier ( TM)Twist Multiplier ( TM)

The twist multiplier is an expression of the twist level The twist multiplier is an expression of the twist level adjusted for yarn count.adjusted for yarn count.

The commonly used formula to determine the twist The commonly used formula to determine the twist multiplier of yarn for a given yarn count and a given twist multiplier of yarn for a given yarn count and a given twist level is:level is:

TM = TPI / TM = TPI / √ Ne√ Ne

The twist factor is also named twist multiplier in some The twist factor is also named twist multiplier in some countries.countries.

Twist &Twist MultipliersTwist &Twist Multipliers

The threshold between weaving and knitting yarn has The threshold between weaving and knitting yarn has been determined to be the following twist multipliers: been determined to be the following twist multipliers:

• • Combed cotton yarn αe = 3.7 Combed cotton yarn αe = 3.7

• • Carded cotton yarn αe = 3.9 Carded cotton yarn αe = 3.9

Yarns with twist multipliers below these values have Yarns with twist multipliers below these values have been classified as knitting yarns. been classified as knitting yarns.

This is the standard adopted by UsterThis is the standard adopted by Uster

Twist &Twist MultipliersTwist &Twist Multipliers

The cloths were woven from the 10s cotton The cloths were woven from the 10s cotton yarn. yarn. ( W – Warp, F – Filling, and the TM)( W – Warp, F – Filling, and the TM)

Twist DirectionTwist Direction


When the yarn is woven or knitted into a fabric, the When the yarn is woven or knitted into a fabric, the direction of twist influences the direction of twist influences the appearanceappearance of fabric and of fabric and the the hand feelhand feel..


Fabric A will be more lustrous than Fabric B, because Fabric A will be more lustrous than Fabric B, because light reflected by fibres in the warp and weft is in the light reflected by fibres in the warp and weft is in the same direction. same direction.

Fabric A will be softer while fabric B firmer.Fabric A will be softer while fabric B firmer.

Twist Direction & SpiralityTwist Direction & Spirality

Twist direction will also have a great influence on fabric Twist direction will also have a great influence on fabric stability,stability, which may be described by the amount of which may be described by the amount of skew skew or "torque" in the fabric.or "torque" in the fabric.

Twist Direction & SpiralityTwist Direction & Spirality

One of the solutions to solve the problem of Spirality is to One of the solutions to solve the problem of Spirality is to coordinate the direction of twist with the direction of coordinate the direction of twist with the direction of machine rotation. machine rotation.

With other factors being similar, yarn of Z twist is found With other factors being similar, yarn of Z twist is found to give less skew with machines rotating to give less skew with machines rotating counterclockwise. counterclockwise.

Fabrics coming off the needles of a counterclockwise Fabrics coming off the needles of a counterclockwise rotating machine have courses with left-hand skew, and rotating machine have courses with left-hand skew, and yarns with Z twist yield right-hand wale skew. Thus, the yarns with Z twist yield right-hand wale skew. Thus, the two effects offset each other to yield less net skew. two effects offset each other to yield less net skew.

Clockwise rotating machines yield less skew with S twist.Clockwise rotating machines yield less skew with S twist.

Twist Direction & StrengthTwist Direction & Strength

No No consistentconsistent differences in strength differences in strength for the cloths for the cloths made from yarns with S-twist and Z- twists yarnmade from yarns with S-twist and Z- twists yarn

Yarn Twist & Cover FactorYarn Twist & Cover Factor

Since thousands of ends or wales are presented side-by-Since thousands of ends or wales are presented side-by-side in the woven or the knit fabrics, a slight change in side in the woven or the knit fabrics, a slight change in yarn diameter can result in a substantial change in the yarn diameter can result in a substantial change in the overall overall cover factorcover factor of fabric. of fabric.

Differences in yarn twist lead to deviations in yarn Differences in yarn twist lead to deviations in yarn diameter. A reduction is yarn twist increases the yarn diameter. A reduction is yarn twist increases the yarn diameter and decreases the densitydiameter and decreases the density

The yarns with low twist numbers are bulkier and softer, The yarns with low twist numbers are bulkier and softer,

the the fabric producedfabric produced has a higher cover factor and softer has a higher cover factor and softer hand.hand.


Knit fabric strength is depends upon yarn strength and Knit fabric strength is depends upon yarn strength and stitch (loop) length.stitch (loop) length.


Higher TPI yarn is more rigid and have higher resistance Higher TPI yarn is more rigid and have higher resistance to bending while loop forming in knitting, than Low twist to bending while loop forming in knitting, than Low twist yarn; hence, the radius of their curvature is longer. yarn; hence, the radius of their curvature is longer. Hence, we can not have small loop length.Hence, we can not have small loop length.

An optimum combination of strength and flexibility can An optimum combination of strength and flexibility can be achieved through many options including a proper be achieved through many options including a proper level of twist.level of twist.

Twist & ElongationTwist & Elongation

Increasing twist factor will leads to an increase of yarn Increasing twist factor will leads to an increase of yarn elongation, which in turn the increase of the knitted elongation, which in turn the increase of the knitted fabrics elongation. fabrics elongation.

Good elongation values in the yarn will reduce fabric Good elongation values in the yarn will reduce fabric holes. holes.

Also, the increased twist fabric causes the increase in Also, the increased twist fabric causes the increase in seam elongationseam elongation

Yarn HairinessYarn Hairiness

The reduction of twist increases the hairiness The reduction of twist increases the hairiness because the number of protruding fibers because the number of protruding fibers increases. increases.

Consequently the pilling tendency is also Consequently the pilling tendency is also affected.affected.

The effects of loop length and yarn twist The effects of loop length and yarn twist factors on seam performancefactors on seam performance

Seam elongation was positively affected by loop length Seam elongation was positively affected by loop length and yarn twist factor. and yarn twist factor.

By contrast, seam strength and seam efficiency were By contrast, seam strength and seam efficiency were negatively affected by loop length and yarn twist factors .negatively affected by loop length and yarn twist factors .

i.e. As the loop length and yarn twist factor increases, i.e. As the loop length and yarn twist factor increases, seam strength and efficiency decreases. seam strength and efficiency decreases.

Increasing yarn twist factor will increase the strength of Increasing yarn twist factor will increase the strength of constituent yarns, which in turn increases the knitted constituent yarns, which in turn increases the knitted fabric strength. Thus, the increased twist factor will lower fabric strength. Thus, the increased twist factor will lower seam efficiency.seam efficiency.

Yarn twist CV%Yarn twist CV%

In handling large quantities of data statistically, the In handling large quantities of data statistically, the coefficient of variation (C.V.%) is commonly used to coefficient of variation (C.V.%) is commonly used to define variability and is thus well-suited to the define variability and is thus well-suited to the problem of expressing twist variation. problem of expressing twist variation.

It is currently probably the most widely accepted It is currently probably the most widely accepted way of quantifying irregularity. way of quantifying irregularity.

It is given by :It is given by :

coefficient variation (C.V.%) = coefficient variation (C.V.%) = (standard deviation/average) x 100(standard deviation/average) x 100

Yarn twist CV%Yarn twist CV%

The variation of yarn twist CV should not exceed 3.5% to The variation of yarn twist CV should not exceed 3.5% to avoid quality problems which can be recognized by the avoid quality problems which can be recognized by the human eye.human eye.

Yarn twist for a specific end useYarn twist for a specific end use

Alpha e is for English countAlpha e is for English count

SummarySummary

Cotton spun yarns for knitting should exhibit good hand Cotton spun yarns for knitting should exhibit good hand or softness, therefore need less twist. or softness, therefore need less twist.

This lower twist leads to softer yarn and fabric. This lower twist leads to softer yarn and fabric.

Yarn Torque or liveliness should be at a minimum to help Yarn Torque or liveliness should be at a minimum to help prevent excessive fabric shrinkage, skew, and torque. prevent excessive fabric shrinkage, skew, and torque.

SummarySummary

The formation of spirality may be prevented by The formation of spirality may be prevented by various yarn-related methods. various yarn-related methods.

Some of these methods include :Some of these methods include :

a) low-twist-lively yarns; a) low-twist-lively yarns;

b) balanced plied yarns can be preferred, b) balanced plied yarns can be preferred,

c) and S-twist and Z-twist single yarns arec) and S-twist and Z-twist single yarns are

used at alternate feeders, respectively used at alternate feeders, respectively


We will discuss other parameters in next edition.We will discuss other parameters in next edition.

Until then, Until then,

Bye Bye.Bye Bye.

Note:Note:

This is a Training material prepared for internal This is a Training material prepared for internal training purpose.training purpose.

Guidelines for selection of yarn part 2 12.02.14

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Transcript of Guidelines for selection of yarn part 2 12.02.14