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Yarn Technology and Quality

By Wang Xungai

Zhang Shangyong

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Module 1

Fundamentals of Yarn Technology

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Overview

Overview of the unitA yarn is a relatively strong and flexile asse!ly of fires or fila!ents "ith or "ithoutt"ist# $t is an i!%ortant inter!ediate %roduct et"een fires and farics# The inter&relationshi%s et"een the structure and %ro%erties of fires' yarns' and farics areillustrated in (igure 1#

(igure 1 $nterrelations of fires' yarns' and faric structure and %ro%erties

The area encircled y the ro)en line in figure 1 indicates the real! of yarn technology#*enerally s%ea)ing' yarn technology deals "ith the !anufacture of various ty%es of yarns

consisting of different fires and fire arrange!ents' and the %ro%erties of these yarns#

$n this unit' the )ey yarn !anufacturing %rocesses "ill e discussed in detail' together"ith the +uality as%ects of yarn !anufacture# This unit is organised into the follo"ing!odules,

Module 1 (unda!entals of Yarn TechnologyModule 2 Yarn -vennessModule . (ire /re%arations for S%inningModule 0 Yarn S%inning Syste!sModule Yarn Technology -xtension

This first !odule deals "ith the asics of yarn technology' including yarn count syste!s'yarn t"ist' and designation of yarn structures#

The second !odule addresses the )ey +uality as%ect of yarns' i#e# yarn evenness#-venness is the !ost funda!ental %ro%erty of yarns' ecause it affects other i!%ortantyarn %ro%erties' such as yarn strength# A good understanding of yarn evenness "ill hel%us a%%reciate the fire %rocessing re+uire!ents for !a)ing +uality yarns#

$n the follo"ing !odule on fire %re%arations for s%inning' the %re%aratory %rocessingstages efore the actual s%inning %rocess are discussed in detail# -!%hasis is %laced on

cotton %rocessing and "orsted to% !a)ing#

.

Properties of fibre

polymer ormolecule

+Fibre structure

Fibre

properties

+

Yarnstructure

Yarnproperties

+

Fabricstructure

Fabric

properties

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$n !odule 0' the !aor syste!s of sta%le fire s%inning are discussed' including rings%inning' rotor s%inning' friction s%inning and air et s%inning#

(inally' the extension !odule covers other relevant yarn technologies that are not

discussed in %revious !odules# These technologies include the "oollen and se!i&"orstedsyste!s as used in car%et yarn !anufacture' fila!ent yarn texturing technology' fancyand other s%ecialty yarn %roduction#

This unit uilds on the !aterials covered in the yarn technology !odule in the first unit &$ntroduction of (ire Science and Textile Technology# You are encouraged to revie" that!odule efore you start this unit#

Overview of the module

Yarns co!e in different si3es and sha%es# But for textile a%%lications' t"o for!s of yarnare !ost co!!on# They are single yarn 4or singles yarn5 and %lied yarn' as indicated infigure 2#

A single yarn re%resents the si!%lest continuous strand of fire !aterial# $f this strandconsists of sta%le fires' it is a sta%le yarn or s%un yarn# $f the strand is a singlecontinuous fila!ent' it is called a !ono&fila!ent yarn or si!%ly !ono&fila!ent# $f thestrand is !ade of a s!all undle of single fila!ents' then this strand is )no"n as a !ulti&fila!ent yarn or si!%ly !ulti&fila!ent# The ta%e yarn sho"n in figure 2 is different toother yarns# $t is a flat rion' slit fro! a thin fil!# (inally' a single strand could also e!ade of a co!%osite of fila!ents and sta%les' "ith the fila!ents staying in the centre'

"ra%%ed around y the sta%le fires# Such a yarn is called a core yarn' "hich is a for! ofco!%osite yarns#

The %lied yarn is also )no"n as a folded yarn' or a t"isted yarn# $f t"o single yarns aret"isted together' they !a)e a t"o&%ly or t"o&fold yarn as sho"n in figure 2# $f !orethan t"o single yarns are involved' "e get a !ulti&%ly yarn#

$n this !odule' "e discuss the different "ays of descriing the si3e or thic)ness of yarns#We also discuss the role t"ist %lays in yarns since fires in !any yarns are si!%ly heldtogether y t"ist# (inally' "e descrie the designations of various yarn structures#

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(igure 2 A s)etch of different ty%es of yarn

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To%ic 1

Yarn count

Introduction

Yarns co!e in different si3es# They can e +uite thic)' or they can e very thin# Since ytheir very nature textile yarns are soft and s+uashy' the 6thic)ness7 of a yarn can not eeasily !easured y yarn dia!eter# But textile yarns are often sold on a "eight asis' so itis natural to ex%ress the si3e of a yarn in ter!s of its "eight or !ass# The t"o asic "aysof doing this are y indicating either ho" !uch a given length of yarn "eighs 4the directsyste!5 or "hat the length of yarn "ill e in a given "eight 4the indirect syste!5# Theset"o road yarn count syste!s are ex%ressed elo"'

lengthGiven

yarnofWeight

countyarnDirect = '

weightGiven

yarnofLengthcountyarnIndirect =

Because a textile yarn is usually a very slender asse!ly of tiny fires' it is conceivalethat the "eight of a yarn in a given length "ill e very s!all "hile the length of a yarn ina given "eight "ill e +uite large# 8onse+uently' the yarn count figures "ould get eitherincredily s!all 4direct syste!5 or large 4indirect syste!5 unless s%ecial units are used#9ver the years' !any different units have een used in different sectors of the textile

industry# This to%ic descries these different units and the conversions involved#

Objectives

At the end of this to%ic you should e ale to,

understand the definitions for different yarn count syste!s

)no" the conversion et"een yarn counts

a%%reciate the effect of !oisture on yarn count results

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Direct Count Systems

The direct syste!s are ased on the "eight or !ass %er unit length of yarn# So!e ty%icaldirect syste!s are given elo"' together "ith their definitions# /lease note that "hile the

"eight unit is gra!' different lengths are used in the definitions#Tex g!"###m$This is the !ass in gra! of one )ilo!etre' or 1';;; !etres' of the %roduct#

$f one thousand !eters of yarn "eigh 2; gra!s or one hundred !eters of the yarn "eigh2 gra!s' the yarn "ould e 2; tex# 9n the other hand' if 1;; !etres of yarn "eigh gra!s' then the count of the yarn "ill e ; tex#

Dtex g!"#%###m$This is called deci&tex# $t is the !ass in gra! of ten )ilo!etre' or 1;';;; !etres' of the

%roduct# $t is a s!aller unit than tex 41 tex < 1; dtex5' and is usually used for fires andfila!ent yarns#

A 1:= dtex %olyester fila!ent "ould "eigh 1:= gra!s for every 1;';;; !eters of thefila!ent#

'tex g!m$This is called )ilo&tex# $t is the !ass in gra! of one !etre of the %roduct# $t is a !uchlarger unit than tex 41 )tex < 1';;; tex5' and is usually used for heavy %roducts such asslivers#

$f a sliver "eighs gra!s %er !etre' then the count of this sliver "ould e )tex#

The tex syste! 4tex' )tex' dtex5 is the %referred standard syste!# By definition'

1 )tex < 1';;; tex < 1;';;; dtex

Denier g!(%###m$>enier is also used extensively in the industry' %articularly for !anufactured fires andsil)# $t is the !ass in gra! of nine )ilo!etres' or ?';;; !etres' of the %roduct#

By definition'

1 dtex < ;#? denier

$f a .;; denier yarn is !ade u% of 1# denier individual fila!ents' there "ill e a total

nu!er of 2;;#1

.;;= fila!ents in the yarn#

=

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Indirect Count Systems

$ndirect count syste!s are not as straightfor"ard as the direct ones# $n the early historyof yarn !anufacture' different s%inners' often geogra%hically and culturally isolated fro!

one another' devised their o"n "ays of !easuring yarn thic)ness# 8onse+uently' thereare nu!erous indirect count syste!s that have een' and continue to e' used in theindustry# So!e exa!%les are given elo"' together "ith the !ass and length conversions'

Commonly used

& Metric 4@!5 !g

& -nglish 8otton 4@ec5@o# of 0; yard han)s %er %ound

& Worsted 4@"5 @o# of :; yard han)s %er %ound

The !etric count 4@!5 is relatively straightfor"ard# $t is the length in !etre of one gra!of the %roduct# (or exa!%le' if one gra! of yarn !easures 0; !etres' then the !etriccount of this yarn "ould e 0; @!#

Si!ilarly' if one %ound of cotton yarn !easures 1':; yards' or t"o han)s of 0; yards'

the -nglish cotton count of this yarn "ill e 2 @ec# /lease note that a han) of yarn is an

unsu%%orted coil consisting of "ra%s of yarn of a certain length#

The conversions et"een different units "ill e discussed later#

)ess commonly used

& linen' he!%' ra!ie @o# of .;; yard han)s %er %ound& asestos C C ; C C C C& glass C C 1;; C C C C& s%un sil) C C 0; C C C C& ra" sil) 4dunce5 C C 1;;; C C C ounce

Occasionally used in the woollen industry

& Yor)shire s)ein @o# of :; yard han)s %er %ound& West of -ngland C C .2; C C C C& A!erican cut C C .;; C C C C& A!erican run C C 1;; C C C ounce

& >e"sury C C 1 C C C ounce& *alashiels C C .;; C C C 20 ounces

You !ay "onder ho" the strange length units such as 0; yard han) and :; yard han)ca!e aout# The first !ass&%roduction s%inner D the s%inning&enny "as ale to s%inyarns si!ultaneously onto several oins and filled the oins u% at the sa!e ti!e# The

oins "ere changed after 0; yards of cotton yarns "ere "ound onto the!# Toesti!ate the thic)ness of the yarns' the s%inner si!%ly counted ho" !any full oins"ere needed to alance a "eight of one %ound# (or exa!%le' if : oins "ere needed to!a)e u% one %ound' the yarn "ould e called a :s yarn# Si!ilarly a 2;s "orsted yarn!eans one %ound of this yarn "ould fill u% 2; oins' each "ith :; yards of yarn

"ound on#

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Conversion between Different Yarn Counts

$t is often necessary to !a)e conversions et"een different yarn count syste!s# (or this%ur%ose' the follo"ing !ass 4"eight5 and length conversions are needed,

1 yard 4yd5 < ;#?100 !1 %ound 4l5 < ;#0.: )g1 ounce 4o35 < 11: l1 dra! ?dr5 < 11: o31 grain 4gr5 < 1=;;; l

Wor)ed -xa!%les

Question,What is the conversion factor et"een "orsted count 4@"5 and tex E

Solution,According to definition' one "orsted count 4@"5 < one :; yard han) %er %ound' or

pound

yardNw

:;11

=

Since 1 yard 4yd5 < ;#?100 ! and 1 %ound 4l5 < ;#0.: )g' the aove e+uationeco!es'

g

m

g

m

g

mNw

12B?2#1

:#0.

;:0#12

:#0.

?100#;:;11 ==

=

Therefore' for a yarn of @" "orsted count' each gra! of this yarn "ould !easure1#12?2 ti!es @" !eters# Since tex is the !ass in gra! of a 1';;; !eters of yarn' "eneed the nu!er of gra!s in 1;;; ! of the yarn#

( )NwNw

texmpergramsofNo B#BB

12B?2#1

1;;;1;;; ==

The aove e+uation can also e "ritten as,tex

Nw B#BB

=

So the conversion factor is ##

Question,$f a yarn is 2; tex' "hat is the "orsted count of this yarnE

Ans"er,

Fsing the conversion factor given aove' the "orsted yarn count is Nw.#002;

B#BB= #

8onversion et"een other count syste!s can e "or)ed out in a si!ilar "ay# Tale 1#1lists co!!only used conversion factors# You !ay try to "or) the! out yourself#

Tale 1#1, (actors for Yarn 8ount 8onversion

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>$G-8T 89F@T $@>$G-8T 89F@T

To Tex To>enier

To Metric8ount 4@!5

To 8ottoncount 4@ec5

To Worsted8ount 4@"5

(ro! Tex Tex?

Tex

1;;;

Tex

#?;

Tex

B#BB

(ro! >enier denie111#;

denier

?;;;

denier

1.

denier

=?=2

(ro! Metriccount 4@!5 Nm

1;;;

Nm

?;;; N?;#; NBBB#;

(ro! 8ottoncount 4@ec5 Nec

#?;

Ne

1. Nec:?.#1 Nec#1

(ro! Worstedcount 4@"5 Nw

B#BB

Nw

=?=2 Nw12?#1 N::::#;

*oisture and Yarn Count

Gegardless of the yarn count syste! used' it is necessary to !easure the "eight andlength of a yarn in order to deter!ine its count# But !ost fires' %articularly naturalfires' asor !oisture fro! at!os%here# The "eight of the yarn "ill e different atdifferent !oisture level# The "ater content in textiles can e ex%ressed as either moisturecontentor as regain# Their definitions are,

1;;54

5454Ge =

DspecimendryofMass

WspecimeninwaterabsorbedofMassRgain

1;;54

5454

+

=

DWspecimenundriedoriginalofMass

WspecimeminwaterabsorbedofMassMcontentMoisture

(ro! these definitions' the conversion et"een regain 4G5 and !oisture content 4M5 cane "or)ed out according to the e+uation elo",

R

RM

+

=

1

$n co!!ercial transactions' the !ass to invoice is "or)ed out on the asis of an agreedconventional regain level' not on the actual regain of the yarns 4or other textiles5 eingtraded# This is very i!%ortant# Because' in the asence of an agreed conventional regainlevel' s!art sellers !ay ta)e advantage of the !oisture asor%tion %ro%erty of theirtextiles and ri% the uyers off "ith large +uantity of "ater in their %roducts# Theconventional regain levels' to e used for calculation of the legal co!!ercial !ass' have

een estalished y national or international standards# These co!!ercial regain valuesare %urely aritrary values arrived at for co!!ercial %ur%oses for interested %arties' andthey often vary fro! fire to fire and fro! country to country# $n Australia' theconventional regain rates for so!e fires are given in Tale 1#2#

Tale 1#2, 8onventional regain rate for selected fires(ire 8onventional regain 4H5

1;

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Wool and hair fires

8o!ed 4"orsted5

8arded 4"oollens5

8otton @or!al cotton

Mercerised cotton

Sil)

/olyester

Sta%le fire

8ontinuous fila!ent

1#21=

#1;#

11

1#1#

8onditioning the "hole lot of yarns or other textile !aterials to the conventional regainrates given aove is not %ractical' ecause of the ti!e re+uired etc# $n calculating theco!!ercial !ass to invoice for a lot' the follo"ing %rocedures are often follo"ed,

415 -xtract a sa!%le of !ass 4g"5 fro! the lot 4"hose total gross "eight is *W5425 >eter!ine the dry "eight 4d"5 of the sa!%le y oven drying to co!%letely eva%orate

the !oisture contained in it#4.5 8alculate the co!!ercial !ass to invoice 4c"5' ased on a conventional regain GH'

y !eans of the for!ula,

1;;H1;; R

gwdwGWcw +=

The follo"ing exa!%le illustrates this %oint#

-xa!%le,

Su%%ose a lot of "orsted yarn is to e shi%%ed to a uyer' and the gross "eight of lot is1;;; )g# We no" need to "or) out the co!!ercial !ass to invoice for the lot of yarn#

Ans"er,

We first extract a s!all sa!%le 4say ;; gra!s5 fro! the lot# After oven drying of thiss!all sa!%le' the dried !ass eco!es' say' 0; gra!s# (or "orsted yarn' theconventional regain rate is 1#2H according to Tale 1#2# Therefore' the co!!ercial!ass to invoice should e,

542#1;:01;;

2#1B1;;

;;

0;1;;; g=

+

This suggests that the !erchandise is actually drier than the conventional value# Iad1;;; )g een used as the !ass to invoice' the su%%lier "ould have een at a loss#

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You !ay try to "or) out the actual regain of this lot of yarn using the values given in thisexa!%le#

+eview ,uestions

1# Su%%ose you have t"o cotton yarns# The count of yarn A is 2; tex' and that of

yarn B is 2; @ec# Which yarn is a thic)er oneE You need to ustify your ans"er via

%ro%er count conversions#2# $f a "orsted yarn has a count of 0; @" 4"orsted count5 at a regain level of 2;H'

"hat "ould e the count of this yarn' in tex' "hen it is oven&driedE

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To%ic 2

Yarn twist

Introduction

$n the !anufacture of sta%le fire yarns' t"ist is inserted into the fine strand of fires tohold the fires together and i!%art the desired %ro%erties to the t"isted yarns# Withoutt"ist' the fine strand of fires "ould e very "ea) and of little %ractical use# A change inthe level of t"ist also changes !any yarn %ro%erties' such as strength and softness# Thisto%ic descries the nature of yarn t"ist' the effect of t"ist on yarn %ro%erties' as "ell ast"ist !easure!ent#

Objectives

At the end of this to%ic you should e ale to,

understand the effect of t"ist on certain yarn and faric %ro%erties

a%%reciate the i!%ortance of surface t"ist angle and of selecting the right t"ist factor

for different yarns

)no" ho" to calculate the t"ist contraction

)no" the asic rules that a%%ly to t"ist !easure!ents

-ature of twist

Ty.es of twistThere are t"o ty%es of t"ist, real t"ist and false t"ist#

415 Gead t"istTo insert a real t"ist into a length of yarn' one end of the yarn should e rotated relativeto the other end' as indicated in figure 2#14a5#

S%un yarns usually have real t"ist' "hich holds the fires together in the yarn#

425 (alse t"istWhen inserting false t"ist into a length of yarn' oth ends of the yarn are cla!%ed'usually y rollers' and t"ist is inserted "ith a false t"ister et"een the cla!%ing %oints'as indicated in figure 2#145#

$f the yarn is not traversing along its axis' the t"ist "ill e in o%%osite directions aoveand elo" the false t"ister# $f the false t"ister is re!oved' the o%%osite t"ists "ill cancelout one another' leaving no real t"ist in the length of yarn# $f the yarn is traversing alongits axis' then the section of the yarn !oving a"ay fro! the false t"ister "ould have nonet t"ist' as indicated in figure 2#145#

(alse t"isting is a very i!%ortant %heno!enon' "hich has considerale %ractical

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i!%lications in yarn technology# (alse t"isting is featured in !any )ey %rocesses that "e"ill discuss later' including "oollen ring s%inning' o%en&end rotor and friction s%inning'air et s%inning' and fila!ent yarn texturing#

(igure 2#1 Geal t"isting and false t"isting

Twist directionA t"ist can e either in Z direction or S direction as indicated in figure 2#2' de%ending onthe orientation of the surface fire in relation to yarn axis#

(ig# 2#2, T"ist direction

$t is "orth noting that t"ist direction affects faric %ro%erties# (or exa!%le' (igure 2#.sho"s t"o identical t"ill&"eave farics "ith the "ar% yarn of different t"ist direction#(aric A "ill e !ore lustrous than faric B' ecause light reflected y fires in the "ar%and "eft is in the sa!e direction# (aric A "ill e softer "hile faric B fir!er' ecause in

(aric B' the surface fires on the "ar% and "eft in the region of contact are aligned in

S-Twist Z-Twist

False

twister

(a)

Inserting real twist

(b)

Inserting false twist

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the sa!e direction and they !ay 6get stuc)7 inside each other and reduce the !oility ofthe intersection# Whereas for faric A' the surface fires on the "ar% and "eft in theregion of contact are crossed over' and they can !ove aout easily# The freedo! of!ove!ent at the yarn intersections is the )ey for faric softness#

(ig# 2#., -ffect of t"ist direction on faric %ro%erties

Self&loc/ing effectBecause of t"ist in a yarn' the fires on yarn surface ta)e a roughly helical configurationaround the yarn# When the yarn is under tension' these surface fires are also undertension# Io"ever' ecause of the helical configuration' %art of the tension is divertedradially' "hich creates a radial %ressure# This is illustrated in figure 2#0#

(igure 2#0 Ielical fire under tension 4Jord 1?1' %# =5

The radial %ressure tends to %ac) the fires together' increasing the nor!al forceet"een the!' and so increasing their frictional resistance to sli%%ing %ast each other#The !ore tension is a%%lied to the yarn' the !ore it loc)s together' hence Kself&loc)ingK#An analogy is' "hen you "ind a string around your ar!' as you %ull the string along thear! and a"ay fro! each other' the string ites dee%er into the flesh#

Without t"ist' there "on7t e any self&loc)ing effect to %revent fire sli%%age#8onse+uently the yarn "ould have no strength#

0ffect of twist level on yarn strength

Twill directionS twist Z twist

() (!)

(S"ort arrows indicate direction of lig"t

reflected from t"e warp and weft yarns)

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The level of t"ist is usually ex%ressed in nu!er of turns %er !etre 4t%!5# @u!er ofturns %er inch or t"ist %er inch 4t%i5 is also used in the industry#

More t"ist gives greater radial co!%onent to any a%%lied tension' so increases resistance

of fires to sli% and the strength of yarn increases as a conse+uence# This is de%icted ythe Kcoherence curve1 in figure 2##

9n the other hand' if a undle of %arallel fila!ents is t"isted' the t"ist "ill %ut theindividual fila!ents under torsional stress# This stress "ea)ens the fila!ents and thestrength of the fila!ent "ould decrease as the level of t"ist increases# This is de%icted ythe 1obli,uity curveK in figure 2##

(or sta%le fire yarns' these t"o curves co!ine to give the actual 1twist&strengthcurve1 for a sta%le fire yarn as sho"n y the heavy line in figure 2##

(ig# 2#, -ffect of t"ist level on the strength of sta%le 4s%un5 yarn

(igure 2# indicates that for sta%le fire yarn' increasing the t"ist level "ill increase yarnstrength to a !axi!u! level' eyond "hich further increase in t"ist "ill reduce yarnstrength#

$t should e noted that for continuous fila!ent yarn' the oli+uity curve a%%lies# $n other"ords' t"isting a continuous fila!ent yarn only reduces the yarn strength' regardless ofthe t"ist level used# $f a continuous !ulti&fila!ent yarn is t"isted' the reason for thet"ist is to )ee% the individual fila!ents together' not for strength#

Twist angle

This is the angle of fires to yarn axis' and this angle varies throughout yarn' fro! 3eroat centre to !axi!u! at yarn surface# The fires on yarn surface are the !ost i!%ortant'as they ind the others into the yarn 4refer to self&loc)ing effect discussed earlier5#

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While it is not co!!on %ractice to !easure the yarn t"ist angle' the surface t"ist angle!ade y the surface fires in relation to yarn axis is a very i!%ortant %ara!eter# $tdeter!ines the essential yarn characteristics such as yarn softness' yarn ul) etc' "hich inturn govern !any essential faric %ro%erties# The follo"ing exa!%le illustrates the %oint#

$n figure 2#:' yarn 1 and yarn 2 have the sa!e t"ist level D one turn each# But the surfacefire on the thic)er yarn is oviously stretched !ore to acco!!odate this t"ist# This"ould !ean the thic)er yarn is !ore closely %ac)ed# As a conse+uence' yarn 2 "ill not

e as soft as yarn 1# $n other "ords' even though the t"ist level is the sa!e in these t"oyarns' the yarn characteristics are +uite different# Therefore' "e can not si!%ly use t"istlevel to re%resent yarn character# Io"ever' the surface t"ist angles of yarn 1 415 and

yarn 2 425 are different# They can etter reflect the yarn characteristics' regardless of the

difference in yarn thic)ness#

(igure 2#: T"o yarns of the sa!e t"ist level' ut different surface t"ist angles

#

Yarn $ Yarn %

d$ d%

$%

d$d%

#

1=

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Twist factor Twist multi.lier$

This is a very i!%ortant factor that relates to the angle of t"ist helix the surface fireshave in a yarn# As "e "ill see later' this factor is very i!%ortant for a s%inner ecause of

the follo"ing reasons,

Ji)e surface t"ist angle' it governs the yarn characteristics

$t is used to "or) out the t"ist to use in s%inning' in order to !aintain the sa!e

surface t"ist angle and si!ilar yarn characteristics "hen the yarn count is changed#The t"ist "or)ed out fro! t"ist factor is also needed for setting u% the s%inning!achine#

But ho" do "e relate the t"ist factor to surface t"ist angle and ho" to choose the rightt"ist factor thenE

+elate twist factor to twist angleBecause it is !uch easier to !easure t"ist level in turns %er !etre than t"ist angle' "eshould relate t"ist level to t"ist angle#

(ro! figure 2#:' "e get'

L

d"

tan

Also fro! figure 2#:' the height 4%itch5 of one turn of t"ist is J# Since the t"ist level isnor!ally s%ecified as the nu!er of turns %er !etre' the t"ist level in one !etre of theyarn "ould e,

L

#"twist

so

twistxd"tan 415

We also )no" fro! ex%erience that yarn dia!eter is also very hard to !easure' ecausetextile yarns y their very nature are soft and s+uashy# 9n the other hand' yarn count isnor!ally used as "e have discussed in the first to%ic of this !odule# But "e can relate

yarn dia!eter to yarn count using the ex%ression elo",

cubic density $ 2 linear density Tex$ ! cross&sectional area 3$

Assu!ing a circular cross section for the yarn' "e get'

$%d

#&xTex"

'm()

(g$m'#&xTex"'m(g$

*

+,

*

+,,

Solve for d,

#&xTex%

"d

+,*

425

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8o!ining e+uations 415 and 425,

$#&xtex*

"twist

,+

tan

ortex

-"twist "here 'tex(t.p.m$#&&./"- , tan

L is called the t"ist factor' and is %ro%ortional to if re!ains constant#

Thus' L is a factor relating t"ist level to yarn count# The derivation sho"s that if t"oyarns have the sa!e t"ist factor' they "ill have the sa!e surface t"ist angle' regardlessof count# Since surface t"ist angle is the !ain factor deter!ining yarn character' thent"ist factor can e used to define the character of a yarn#

$t is "orth noting though there are !inor errors associated "ith the use of t"ist factorfor the follo"ing reasons,

- The cuic density !ay e different for different yarns# $t is assu!ed in the aovecalculation that this "ill not change for yarns of the sa!e surface t"ist angle#

- >ifferent fires "ith different frictional and other %ro%erties "ill create different yarncharacter#

@evertheless' the relationshi% "e have ust derived et"een t"ist' t"ist factor and yarncount is one of the !ost i!%ortant in the study of yarn technology# This relationshi% is-x%ressed in different "ays for different yarn count syste!s#

(or the tex syste!,

tex

-0actorTwist"metreperturnsTwist t

5454

(or the !etric count 4@!5 syste! 4the t"ist factor for the !etric count syste! is also)no"n as al.ha metric & 4m5,

Nm)lphaTwist"metreperturnsTwist m 5454

(or -nglish cotton 4@ec5 count syste!,

Nec-0actorTwist"inchperturnsTwist e 5454

(or "orsted count 4@"5 syste!,

Nw-0actorTwist"inchperturnsTwist w 5454

/lease note the unit for t"ist is also different in the aove ex%ressions of t"ist factor# $naddition' t"ist factor is also )no"n as t"ist !ulti%lier' t"ist al%ha' or t"ist coefficient#

Choice of twist factorsYarns intended for different end uses have different characteristics# Since t"ist factor

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4li)e surface t"ist angle5 deter!ines yarn characteristics' the choice of t"ist factor isoften governed y the intended use of the yarns# $f !axi!u! yarn strength is of theut!ost i!%ortance' one "ould oviously choose the o%ti!u! yarn t"ist 4see figure 2#5and the o%ti!u! t"ist factor for strength# Io"ever' the end&use of yarn !ay e such

that other %ro%erties !ay e !ore i!%ortant# (or exa!%le' a yarn to e used for "eft orfor hosiery !ay e re+uired to e soft and ul)y and therefore a lo" t"ist factor is used#A yarn to e used for the %roduction of voile or cre%e faric "ill necessitate the use of ahigh t"ist factor# $f one considers sta%le yarns for the %roduction of %lied or caledse"ing threads then soft t"isted single yarns are used and this results in the higheststrength in the final thread# Another i!%ortant feature to consider is that the %roductivityfor s%inning yarns of lo"er t"ist factor is higher# (or these reasons' the !aority of yarnsare s%un "ith a t"ist factor lo"er than the o%ti!u! t"ist factor for !axi!u! strength#Tale 2#1 sho"s the t"ist factor !ost co!!only used for the various ty%es of yarns#

Tale 2#1, T"ist factors !ost co!!only used 4Bona 1??0' %22:5

Yarn Tex count

54 tpmtex-t

Metric count54

Nm

tpm-m

4al%ha !etric & !5

-nglish cottoncount

54Ne

tpi-

e

89TT9@- Soft )nit"ear- Weft- War%- War%extra strong- 8ris%

20;; & 2?;;2?;; & .0;;.?;; & 0.;;.;; & :.;;:;; & =;;

== & ?2?2 & 1;120 & 1.?1=; & 2;121: & 2=

2# D .. D .#0 D 0## D :#= D ?

W9GST->

-Lnit"ear

- Soft- Mediu!- Strong- -xtra strong

1=;;2;;;2.;;2:;;2?;;

0:.=.2?2

/lease note these are reference values only' and the reco!!ended values vary fro!source to source#

9nce a t"ist factor is chosen' the level of t"ist re+uired for the yarn can e calculatedfor a given yarn count# This t"ist level is then used to set u% the s%inning !achine for

yarn %roduction#

The distribution of twist in sta.le s.un yarns

$f so!eone t"ists your head' it is your nec) that suffers !ost# That is ecause the nec) isa 6thin7 %lace and offers little resistance to eing t"isted# By analogy' if a yarn of varyingthic)ness is t"isted' it is usually the thin s%ot in the yarn that gets t"isted the !ost#$nvarialy' yarns s%un fro! sta%le fires 4eg# "ool' cotton5 are not %erfectly unifor!' andthere are thic) and thin s%ots along the yarn length# This variation in yarn thic)ness "illlead to variation in the t"ist level along the yarn length' ecause t"ist tends to

accu!ulate in the thin %lace#

The fact that t"ist tends to accu!ulate in the thin s%ot along the yarn has several

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i!%ortant i!%lications,

$t exacerates the variation in yarn linear density

While variation in yarn linear density is the funda!ental cause of t"ist variation'concentration of t"ist in the thin %laces "ill !a)e those %laces even thinner'exacerating the %role! of yarn unevenness#

$t i!%roves the evenness of a fire asse!ly during Ndrafting against t"istO

$n the drafting stage of "oollen ring s%inning' the "oollen sluing is drafted "hilet"ist is inserted into the sluing 4drafting against t"ist5 to control fires duringdrafting# Because t"ist tends to accu!ulate in the thin s%ots' the fires in thin regionsin the sluing are !ore difficult to draft than those in the thic) %laces' "hich haveless t"ist# As a result' the thic) %laces are drafted !ore than the thin %laces' thus

i!%roving the evenness of the drafted !aterial# This is de%icted in figure 2#=#

(igure 2#= K>rafting against t"istK i!%roves evenness

$t has i!%lication for t"ist !easure!ents

Because the t"ist level varies along the yarn length' the t"ist !easured at a shortlength of yarn !ay not reflect the true average t"ist of the yarn# Standard test

%rocedures should e follo"ed to !easure the yarn t"ist accurately#

The relationshi% et"een t"ist and yarn count !ay e ex%ressed y the follo"ingfor!ula,

Tex

#Twist

p

"here % is usually greater than 1 ut less than 2 for !ost yarns#

Twist contraction

When a undle of %arallel fires is t"isted' the distance et"een the t"o ends of a fire

T"in place wit"

more twist

(a) !efore drafting (b) fter drafting against twist

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"ill decrease' %articularly for fires near the surface of the t"isted undle# As a result'the overall length of the t"isted undle is shorter than its length efore t"ist insertion#The reduction in length due to t"ist insertion is )no"n as t"ist contraction#

The follo"ing for!ula is used to calculate the a!ount of t"ist contraction,

1#&&xL

L+L"ncontractio1

o

fo

"here Jo < original length efore t"istingJf < final length after t"isting

$t should e noted that ecause of t"ist contraction and the associated change in length'the count of a yarn "ill change slightly "hen t"ist in the yarn is changed# T"istcontraction increases yarn count 4tex5' ecause the "eight of the yarn is distriuted overa shorter length# The follo"ing for!ula can e used

2+#

N"N o

f

"here @o < count 4tex5 efore t"isting@f < count 4tex5 after t"isting8 < Hcontraction

*easurement of twist

T"ist !easure!ent is a routine test for yarns# Because of the variation in t"ist alongyarn length as discussed earlier' care should e ta)en in !easuring the t"ist of sta%les%un yarns# So!e asic %rinci%les are discussed here#

Sam.ling rulesThe follo"ing rules should e oserved "hen !easuring yarn t"ist,

a# Tests should not e li!ited to a short length of the yarn %ac)age#

# Be"are of Co%erator iasC & tendency to select either thic)er or thinner regions#Ta)ing sa!%les at fixed intervals along the yarn length "ill reduce the ias#

c# >iscard first fe" !etres fro! %ac)age# Being a free end' it could have lost t"ist#

d# Ge!ove yarn fro! side of %ac)age' not over end# Ge!oving yarn over end "illchange the t"ist level in the yarn#

e# Tension in Yarn during teste#g# (or single "orsted yarns, P 1 !@tex

5rinci.les of measuring methods

The t"o co!!on !ethods used in t"ist !easure!ent are straightened fibre methodand untwist!retwist!ethod#

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415 Straightened fire !ethod

This !ethod involves counting of the nu!er of turns re+uired to unt"ist the yarns until

the surface fires a%%ear to e straight and %arallel to yarn axis# This !ethod is !ainlyused for %ly and continuous fila!ent yarns#

425 Fnt"ist Get"ist Method

This is the co!!on !ethod used for sta%le fire yarns# $t is ased on t"ist contraction4hence also )no"n as t"ist contraction !ethod5#

(or this !ethod' it is assu!ed that the contraction in length' due to insertion of t"ist' isthe sa!e for oth direction of t"ist 4S and Z5# Su%%ose "e "ant to !easure the t"istlevel in a yarn "ith Z t"ist' the yarn is first unt"isted 4y a t"ist tester5' and a counter

on the t"ist tester "ill record the nu!er of turns# >uring unt"isting' the yarn "ouldincrease in length fro! its original length J to a ne" length J7# $f the o%eration iscontinued' the yarn "ould have its t"ist co!%letely re!oved first and then t"isted u%again in S direction# As the yarn gets t"isted' its length "ill decrease 4t"ist contraction5fro! J7 to"ards its original length J# When its original length is reached' the totalnu!er of turns received y the yarn' as recorded y the counter on the t"ist tester'"ould e e+ual to t"ice the t"ist in the original yarn 4"ith a length of J5#

Auto!atic t"ist testers are no" availale' such as the Z"eigle auto!atic t"ist tester#

+eview ,uestions1# C(or a sta%le fire yarn' the higher the t"ist' the stronger the yarnC# $s this

state!ent trueE WhyE

2# A yarn of 0; @! 4!etric count5 has a t"ist factor of .';;; 54 tpmtex #

What is the t"ist level' in turns %er !etre' of this yarnE.# $f a yarn has an al%ha !etric 4!5 of 1;;' "hat is the t"ist factor in the tex syste!

4Lt5 and the -nglish cotton count syste! 4Le5E You need to sho" your "or)ing#0# Assu!ing after t"isting' the count of a !ulti&fila!ent yarn is increased fro! 1;

dtex to 1; dtex' "hat is the a!ount of t"ist contraction ex%erienced y this!ulti&fila!ent yarnE

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To%ic .

The designation of yarn structures

Introduction

This to%ic descries a !ethod of indicating the co!%osition of yarns# The yarns can es%un yarns or fila!ent yarns# They !ay e single' folded or caled yarns# This to%ic isada%ted fro! NIandoo) of textiles standards for studentsO' %ulished in 1? y theStandards Association of Australia#

Objectives

At the end of this to%ic you should e ale to,

descrie a yarn according to its designation

designate a yarn ased on a detailed descri%tion of the yarn

Systems and rules

T"o syste!s can e used for yarn designation#

Single&to&fold notation .referred$

This is the %referred syste!' "here single co!%onent of the yarn is descried first'follo"ed y a descri%tion of ho" the co!%onents are co!ined together to !a)e u% theresultant yarn#

Fold&to&single notationThis notion is o%%osite to the single&to&fold notation# The "hole structure is descriedfirst' follo"ed y a descri%tion of its co!%onents#

6eneral rulesThe follo"ing general rules should e noted,

Fse tex for sta%le s%un yarns and dtex for fila!ent yarns CfnC indicates n fila!ents in a single !ono 4n

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elo"#

S.un yarnsThe details used in the designation of s%un yarns include,

4a5 Jinear density 4tex545 >irection of t"ist 4S or Z54c5 A!ount of t"ist 4turns %er !etre5

(or exa!%le' the designation 0; tex Z ::; descries a s%un yarn that has a count of 0;tex' "ith a t"ist level of :;; turns %er !etre' and the t"ist is a%%lied in Z direction#

*ono&filament yarnsThe details used in the designation of !ono&fila!ent yarns include,

4a5 Jinear density 4dtex545 Sy!ol f4c5 Sy!ol t; if not t"isted other"ise t"ist direction and a!ount

(or exa!%le' the designation 1= dtex f1 t; descries a !ono&fila!ent 4f15 yarn "ith acount of 1= dtex' "ith any t"ist 4t;5 in the yarn#

Si!ilarly' the designation 1= dtex f1 S;; G1=#0 dtex descries a !ono&fila!ent yarn"ith an initial count of 1= dtex# After a%%lying a t"ist of ;; turns %er !etre in the Sdirection' the resultant count of the fila!ent eco!es 1=#0 dtex# /lease note that theincrease in count is due to t"ist contraction#

*ultifilament yarnsThe details used in the designation of !ulti&fila!ent yarns include,

4a5 Jinear density45 Sy!ol f4c5 @u!er of fila!ents4d5 Sy!ol t; if not t"isted other"ise t"ist direction and level4e5 Gesultant linear density

(or exa!%le' the designation 10; dtex f0; t; !eans a !ulti&fila!ent yarn "ith a count

of 10; dtex' consisting of 0; individual fila!ents "hich are not t"isted# /lease note thatthe linear density of each individual fila!ent "ill e dtex#.

0;

10;= #

Si!ilarly' the designation 10; dtex f0; S1;; G10: dtex !eans the sa!e !ulti&fila!entyarn as descried aove# But this ti!e' the 0; individual fila!ents are t"isted in Sdirection "ith a t"ist level of 1;; turns %er !etre# Because of t"ist contraction' theresultant count of this !ulti&fila!ent yarn eco!es 10: dtex#

*ulti.le wound yarns

These are the yarns that have several co!%onents "ound u% together' "ithout inserting

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any t"ist# This is also )no"n as assembly woundyarns

*ulti.le wound yarns with similar com.onentsThe details used in the designation of such yarns include,

4a5 @otation according to single yarn used45 Multi%lication sign' #4c5 @u!er of single yarns laid together4d5 Sy!ol t;

-xa!%le, 0; tex S1 2 t;4t"o 0; tex yarns' each "ith 1 turns %er !etre in S direction' "oundtogether "ithout t"ist5

*ulti.le wound yarns with dissimilar com.onents

The details used in the designation of such yarns include,

4a5 @otation according to single yarn used' connected y the addition sign P and %ut inrac)ets

45 Sy!ol t;

-xa!%le, 42 tex S02; P :; tex Z;5 t; 48an you descrie this yarnE5

Folded or .lied yarns

These are the yarns that have several co!%onents t"isted u% together#

Folded yarns having similar com.onentsThe details used in the designation of such yarns include,

4a5 @otation according to single yarn used45 Multi%lication sign' #4c5 @u!er of single yarns t"isted together4d5 >irection of folding t"ist4e5 A!ount of folding t"ist4f5 Gesultant linear density

-xa!%le, .0 tex S:;; 2 Z0;; G:?#. tex4a singles yarn of .0 tex "ith a t"ist of :;; turns %er !etre in S directionis t"isted together "ith another yarn of the sa!e descri%tions# Thefolding t"ist is 0;; turns %er !etre in Z direction' and the resultant yarncount is :?#. tex 4slightly higher than .0 x 2 due to t"ist contraction#5

Folded yarn having dissimilar com.onentsThe details used in the designation of such yarns include,

4a5 @otation according to single yarn used' connected y the addition sign P and %ut in

rac)ets45 >irection of folding t"ist

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4c5 A!ount of folding t"ist4d5 Gesultant linear density

-xa!%le, 42 tex S02; P :; tex Z;5 S.:; G?#2 tex

48an you descrie this yarnE5

Cabled yarns

8aled yarns have several co!%onents' "hich can e either si!ilar or dissi!ilar instructures#Cabled yarns having similar com.onentsThe details used in the designation of such yarns include,

4a5 @otation according to folded yarn used45 Multi%lication sign' #4c5 @u!er of folded yarns caled together4d5 >irection of caling t"ist4e5 A!ount of caling t"ist4f5 Gesultant linear density

-xa!%le, 2; tex Z=;; 2 S0;; . Z2;; G1.2 tex

Cabled yarns having dissimilar com.onentsThe details used in the designation of such yarns include,

4a5 @otation according to single and folded yarns used' connected y the addition sign Pand %ut in rac)ets#

45 >irection of caling t"ist4c5 A!ount of caling t"ist4d5 Gesultant linear density

-xa!%le, 42; tex Z=;; . S0;; P .0 tex S:;;5 Z2;; G?: tex

Single&to& fold versus fold&to&single notations

So far "e have used the %referred single&to&fold notation for yarn designation# -xa!%les

of fold&to&single notation are given elo"' together "ith their e+uivalent single&to&foldnotation#

-xa!%le one &

1.. dtex f0; S 1;;; G 1.: dtex 4single&to&fold5G 1.: dtex f 0; S 1;;; 1.. dtex 4fold&to&single5

This descries a !ultifila!ent yarn of 1.: dtex after t"isting to 1;;; t! in the Sdirection# Before t"isting' the count "as 1.. dtex' and the individual fila!ent lineardensity is 1..0; < .#. dtex#

-xa!%le t"o

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2; tex Z =;; x 2 S 0;; x . Z 2;; G 1.2 tex 4single&to&fold5G 1.2 tex Z 2;; . S 0;; 2 Z =;; 2; tex 4fold&to&single5

This descries a caled yarn uilt u% fro! a singles yarn of 2; tex "ith =;; t! Z' %lied"ith itself "ith 0;; t! S' "hich is suse+uently three&%lied "ith 2;; t! Z t"ist#

-xa!%le three

42 tex S 02; P :; tex Z ;5 S .:; G ?#2 tex 4single&to&fold5G ?#2 tex S .:; 4S 02; P Z ;5 2 tex P :; tex 4fold&to&single5

This descries a t"o %ly yarn "ith dissi!ilar co!%onents' %lied together in the Sdirection "ith .:; t!#

(inally' the follo"ing %oints are "orth noting,

415 The resultant count is of !ost use to the user of the yarn425 $n textile !ills' areviated notations are often used' i#e# G0;2 tex4.5 (or indirect count syste!s' the single yarn count is nor!ally given' i#e#

22; or 2;2 42&fold 2;s5 .2:; 4.&fold' 2&fold :;s' caled yarn5#

+eview ,uestions

1# >escrie yarns "ith the follo"ing designations,4a5 42 tex S02; P :; tex Z;5 S.:; G?#2 tex

45 42 tex S02; P :; tex Z;5 t;4c5 42; tex Z=;; . S0;; P .0 tex S:;;5 Z2;; G?: tex4d5 2; tex Z=;; 2 S0;; . Z2;; G1.2 tex

+eferences

Bona' M# 1??0' Textile 3uality' Texilia' $taly#

Jord' /# 1?1' The 4conomics5 6cience and Technology of 7arn 8roduction' The Textile$nstitute' Manchester' FL#

Standards Association of Australia 4SAA5' 1?' 9andboo of Textiles 6tandards for6tudents' Standards Association of Australia' @orth Sydney#