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Textile Research Journal

http://trj.sagepub.com/content/44/2/111The online version of this article can be found at:

DOI: 10.1177/004051757404400205

1974 44: 111Textile Research JournalN. Balasubramanian and V.K. Bhatnagar

Effect of Mechanical Processing Variables in Drawing on Sliver Irregularity

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111

2. Birenbaum, E. I., The Predetermination of the Strength ofYarn Made from a Two-Component Blend, Tekhnol. Tekstil.Prom. No. 4, 35-41 (1961); Tech. of Textile Industy,U. S. S. R. (Engl. Edn.) No. 4, 34-41 (1960).

3. Hamburger, W. J., The Industrial Application of the Stress-Strain Relationship, J. Textile Inst. 40, P700-P720 (1949).

4. Hearle, J. W. S., Grosberg, P., and Backer, S., StructuralMechanics of Fibers, Yarns, and Fabrics, Chap. I, Wiley,1969.

5. Hearle, J. W. S. and Thakur, V. M., The Breakage ofTwisted Yarns, J. Textile Inst. 52, T49-T63 (1961).

6. Kemp, A. and Owen, J. D., The Strength and Behavior ofNylon/Cotton Blended Yarns Undergoing Strain, J. Textile

Inst. 46, T684-T698 (1955).7. Owen, J. D., The Strength and Stress-Strain Behavior of

Blended Yarns, J. Textile Inst. 53, T144-T167 (1962).8. Platt, M. M., Klein, W. G., and Hamburger, W. J., Mechanics

of Elastic Performance of Textile Materials. Part IX: FactorsAffecting the Translation of Certain Mechanical Propertiesof Cordage Fibers into Cordage Yarns, Textile Res. J. 22,641-667 (1952).

Effect of Mechanical Processing Variables in Drawing on Sliver Irregularity

N. BALASUBRAMANIAN AND V. K. BHATNAGAR

The Bombay Textile Research A ssociation, Lal Bahadur Shastri Marg Ghatkopar (West), Bombay 86, India

ABSTRACT

The present work examines the influence of draft distribution at the drawframe upon sliver irregularity under varyingconditions of drawframe processing. The investigations were made at the first and second passage of drawing in cardedmixings and at post-combed drawings in combed mixings, on slow-speed drawframes with Shirley draft distribution andhigh-speed Whitin drawframes.

Eccentricity of top roller is shown to be one of the causes of slippage and sliver irregularity in slow-speed drawframes.Increasing the top roller loading is helpful in overcoming to some extent the deterioration in irregularity caused by aneccentric top roller. Roller slip at the front position caused by eccentricity in the roller has the most detrimental effectson sliver irregularity. Use of lower break draft under these conditions increases the sliver irregularity considerably.Eccentricity in the top roller in the second and third position causes more slippage, but the effect on irregularity of sliveris only marginal. Reduction of break draft increases slippage of front, second, and third top rollers even when they aretrue, but it does not affect sliver irregularity.The optimum roller setting at the front zone in conventional and high-speed drawframes depends upon the break

draft and lies at a higher level at lower break draft. Thus, at close front zone setting, higher break draft gives a moreregular sliver, while at wide setting, lower-break draft gives better results. The sliver irregularity at the optimum settingis, however, not much affected by the break draft.

Introduction

Earlier studies [1, 2] have shown that top roller

slippage is a serious source of Irregularity in conven-tional drawframes with graduated draft distribution.Redistribution of draft and improved fluting designincorporated in Shirlev draft distribution have beenfound beneficial in reducing the second top roller slip.In Shirley draft distribution, the drafting is carried outat the front and back zones and only tension draft is

kept in the middle zone. Even in modern high-speeddrawframes, drafting is essentially carried out in twozones comprising a break .draft zone and a main draftzone. The distribution of draft between- the two zones

is often claimed to have a significant influence on

sliver irregularity. :Butter and Slater [3J claimed thatthe thick and thin portions in adjoining slivers tend tomove into phase in post comber drawframes and in thefinisher head of carded drawframes; when this occurs,

the full benefits of doublings are not realized. Theywere further of the view that reduction of the breakdraft or concentration of draft in a single zone helps toreduce the phasing tendency and thereby leads to amore even sliver. T~1M [4] have indicated similarresults for post comber drawings.

’rhe mechanism of phasing has not been satisfactorilyunderstood and the experimental evidence as to theeffect of break draft upon phasing tendency is scanty.When the break draft is altered, the interfiber cohesionand drafting forces in both zones are affected, and theroller setting should be optimized to take these intoaccount. Further, roller slip is not altogether elimi-nated in Shirley draft distribution, and a considerableamount of variation in regard to roller slip is observedin the mills drawframes equipped with the same draftdistribution and having the same amount of weighting.Apparently, the mechanical condition of the drawframehas also a considerable influences over roller slip and



112

should be’taken into accaunt whi~le examining the effectsof break draft. Very jittle information is available inliterature in regard to the contribution of mechanicalfaults upon roller slip. &dquo;

’ ’

. The present studies have been undertaken to provide’ guidelines in regard to opt.imum draft distribution atthe drawframe under varyi.n.g, conditions of processing.For this, purpose, the effect of break draft upon sliverirregularity has been examined in conjunction with thatof roller setting,. top roller eccentricity, and top rollerpressure:., The studies have been made on carded andcombed cotton slivers and man-made fiber material onconventional (Platts MP F2),. as well as high-speeddraw frames (Whitin M6). .. Fiber properties of cottonsused in the studies are given~ in the Appendix. Roller

settings cannot be sometimes’ reduced below a certainlevel because of the dimensions of the rollers and gears.Similarly, m.echanical defects like eccentricity in draft-ing rollers cannot be altogether eliminated in mill

processing. A knowledge of optimum drawing condi-tions under varying conditions of processing is, there-fore, likely to be of considerable benefit to the mills.

, .

&dquo;

~

Effect_ of Break Draft Upon Roller Slip and Sliver.,

.

, Irregularity in Carded Mixing ’

. ’ (Conventional Drawfrarne -with Shirley’

, Draft Distributions . .

The effect of break draft upon roller slippage was. first investigated. The roller slip at different positionswas assessed with the help d~,’a Shirtey roller slip meter.

It will be seen from the results (Table I) that rollerslip is higher at second and third positions than at thefirst and fourth positions. The amount of roller slipalso varies with the type of fiber, being more pronouncedwith long staple man made fiber. The roller slip at allpositions is lower at the second passage of drawing thanat. first passage. The improved loarallelizaticm ofmaterial accompanying a passage of drawing reducesthe drafting force and, thereby, results in less roller slip-Reduction of break draft increases the roller slip at all

positions, the effect being more prominent at first,second, and third positions. With reduction of breakdraft, the drafting force at the back zone and the sliverweight under the third roller are increased, which resultsin an increased roller slip of the third top roller. At thesame time, the sliver weight at the sccond roller is alsoincreased, and despite the increased draft there is moreinterfiber cohesion at the front zone because: (1) fibersare less parallelized and (2) the strand under the secondroller js coarser, although of the same width. As a

. result, the drafting force at the front zone is increased,resulting in -more slippage (of the top roller) at thefront and second positions.

’

Although the break draft is found to alTect the rollerslip, no significant effect upon sliver irregularity is found(results of which are not given). The extent of increasein slippage is presumably not large enough to affect.

irregularity. An alternative explanation is that the

improved fiber control associated with improved inter-fiber cohesion compensates for the effects of slippage.

..,&dquo; TA 13.LE 1. Effect of break draft upon top roller slip at different positions..

&dquo; ’ (Conventionatdrawframe with Shirley draft distribution)



113

Effect of Eccentricity in the Top Roller Upon RollerSlip and Sliver Irregularity in

. Shirley Draft Distribution

Top roller eccentricity is a common defect encoun-tered in the mills drawframes. ’I’he eccentricity arisesfrom : the bend developed in the rollur over a period ofworking, defects in manufacturing, and inaccuracies inmounting and bulfing of the cots. It is to be expectedthat eccentricity will increase the roller slippage and,thereby, lead to more irregularity. Very little pub-lished work is available rotating eccentricity with rollerslippage. Detailed studies were, therefore, undertakenon this subject cm Mt)F2 drawframe which has Shirleydraft distribution. A top roller having an eccentricityof ahout 1<)~&dquo;l<XX) in. was used for this purpose. Aneccentric rollers was prepared by turning down the endpins and fitting an eccentric slc~we on it (Fig. 1). &dquo;

Roller slip was measured when the eccentric rollerwas used in different positions while processing cardsliver of 30s mixing.

Ivtc~. 1. Eccentric sleeve for top roller; .B - center of roller;li-center of rotation; (’ sleeve (eccentric); I) top roller endpin.

It will be seen (’rable II) that Toller slip is increasedwith the eccentric top roller. The increase in slippageis due to excessive friction at the bush caused by theeccentricallv moving roller.

It will be useful to know if the adverse effects of

eccentricity can be overcome by a proper choice ofbreak draft. The results of studies conducted in thisconnection are discussed below. In these studies,an eccentric roller was used in the front, second, andthird position.

l:c-c-eulri<ily ill Frolll Top Kullor -

’I’he studies have been made with two medium stapleIndian cottons, a long staple Egyptian cotton, and aman-made fiber (Polyno). The effect of eccentricitywas examined at two break drafts at the first and second

passage of drawing in carded mixings and at post comberdrawing in combed mixing. The results of the toproller slippage and sliver irregularity are given in1’able III. -t

.

It will be seen from the results that use of eccentricroller in front position leads to increased slippage of theroller. Use of low break draft under these conditionscauses the slippage to increase further.

*

This is because,as pointed out earlier, the interfiber cohesive forcesincrease with a reduction of t’he break draft and,thereby, result in more roller slip. Use of eccentric toproller in front position also adversely affects sliver

irregularity and the deterioration is more prominentwhen break drafts are kept low. This effects is clearlymarked with first-hassage drawing sliver and in the



114’ -1 ’ r ’- ’ i

. ’

’..

TABLE III.

Effect of eccentricity in front top roller and break draft upon roller slil) and sliver irregularity

I ..- , .

’ ~ I ~ .

in Shirley· draft distribution.

’

.’ TAHLE IV. Effect of eccentricity in second top roller and break draft upon roller slip and sliver irre~;ularity.. ’ , ’ ’

, - in Shirley draft distrihution. ’

-- -, - .,L - :.--.)= -~ ’- -- - ,--- ---- ---.. ,,,,- ----- - ,----- ...- - - -- _n. ,- . - .



115

drafting of polynosic material. ’rhus, when there is

eccentricity in the front top roller, low break drafts arenot preferable as they lead to more sliver irregularity.The spectrograms of drawing slivers prepared with

eccentric top roller in front position are given in Figures2 and 3. The spectrograms show a periodicity with awavelength equal to circumference of front roller. ’I’he

FIG. 2. Spectrogram of drawing sliver with eccentric front topruller; cotton C02; 0.14 hank second passage of drawing ; break-(Ira’ft-2.0; U% of sliver = 4.6.

I,1&dquo;’IG. 3. 51)ectrograin of drawing sliver with eccentric front top

rUler; cotton (’02; 0.14 hank second passage of drawing; breakdraft 1.2; l’cJo ctf sliver =5.4. ~

, I

amplitude of the wave will lo found to be higher at lower

I

break drafts, which explains the poorer rre~u!aritB.

I:c~Prttricit;v ill Secou~l 7’op Roller

1t will be seen from TaMe 11’ that en:t’n,tricity insecond top r<>llor leads to a substantial increase in roller 4



116, ’&dquo;

.

slippage. The slippage is also found to be higher withI the coarser sliver. However, the deterioration in ir-’

regularity caused by slippage is only marginal. This isbecause at the low tension drafts operating in the

.

middle zone, speed variations of second roller do notcontribute to -Iarge variations of draft in the middlezone. But second roll slip will result in an uneven

, feed of material to the ’zone, which accounts forthe marginal increase m irregularity. Reduction of,break draft increases roller slip, but does not have anyeffect over sliver irregularity. .

_ ’ &dquo;&dquo;

’ .

’ ’’ ’ .... ’

f~;ccenlricily iti Third Tv ~ Raller’.

l

- Effect of eccentricity in third top roller was next

investigated at different break drafts. Investigationswere made at first and s cond, passage of carded draw-

ings and post comber dra ing~ using two medium stapleIndian.. cottons, , rrian-~ ade fiber, and a long stapleEgyptian cotton . ’ he esults are given in Table V.The results mileage that, as ,in the- earlier studies,

eccentricity in t(p roller increases the slippage of therollers. Reduction of break draft generally results in

-

more roller slipptage with both normal and eccentricrollers The slippage is more prominent at the first

passage of drawing .than at the second; possibly becauseof higher drafting forces in the’former. Again for thesame reason, the slippage is of a low order during thedrafting of combed slivers. The extent of roller slip isgenerally more with coarse hank than with 6ner hank.

Eccentricity in third top rpller generally leads to

more irregularity in the output sliver but the increaseis relatively small compare.d to that at front position.Eccentricity in the roller leads to more irregularities. because of toller nip movement and increased slippage

~ of roller, and the irregularity caused by - both would_

increase with draft. But at the same time the extentof slippage increases ’with ’reduction of draft, and the &dquo;

ultimate effect of break draft over sliver irregularity is-

a compromise between the two opposing influences.This explains why the effect of break draft upon irregu-larity is of generally low magnitude with eccentricityin third top roller. &dquo;.

’

’

Specjtbgrams ~

_

~

.

.

’

’

.

Spectrograms of second passage slivers obtained witheccentrit roller in. third position are given in Figures 4and 5. The sp.ectrogr4.mq do not show prominentperiodicities as in the earlier studies.

.. ~ Top Roller Loading

, ’. ~, . ,

Lt would be of interest to know the influence of toproller loading upon sliver, irregularity. when there is

eccentricity in top roller as this will help to isolate thecontribution of roncr nip’movement from that of rollerslip’ towards irregularities. Experiments were con-

F~c. 5. Spectrogram of sliver with eccentric roller in thirdposition; cotton C02; 0.14 hank second passage of drawing; break-(iraft~1.2; U% of sliver = 3.8.

ducted on Kalyan, L-14i, C02, and Digvijay cottonsfor this purpose. Both normal and eccentric top rollerswere used at the front position in these studies and theload was increased by putting on additional weights.The first three cottons were investigated at the first

passage of drawing on MDF2 drawframe, while the lastcotton was used at the second passage of drawing onT & S bicoil drawframe. The results are given inTable VI.

’

The results confirm the adverse effects of eccentricityupon roller slip as well as sliver irregularity. Applyingadditional load to the. eccentric rollers reduces roller

slippage and improves the regularity of sliver. How-

ever, with the normal roller where roller slippage is oflow magnitude, application of additional load does notcontribute to any improvement in evenness of sliver. Q

The adverse effects of eccentricity upon sliver irregu-larity therefqre seems to arise more because of itscontribution to slippage than because of its influenceover roller nip movement, as the latter is not affected by’the load applied to the roller.

Spectrograms ’

’’

The spectrograms of drawing slivers prepared witheccentric front top roller and with normal and increasedweightings are given in Figures 6 and 7. It will beseen that application of. extra load has resulted in areduction in amplitude of the periodicity, which shouldbe attributed to the reduced slippage of the eccentrictop roller.



117

TABLE VI. Effect of top roller load upon roller slip and sliver irregularily (with cct’cntri< and normal top rollers).



118

Medium Term Variations in the Sliver

To investigate if mediums term variations in the

sliver are also affected by eccentricity and break draft,further investigations were made, using the &dquo;inert test&dquo;on the ’Uster -even.ness tester, &dquo;Inert test&dquo; measure-ments were made at a material speed of 2 m/min, andthe results obtained correspond- to variations betweenlerfgths of roughly 11.5 cm. , ,

.

’

~ .

The results from ARBP52 cotton (Table VII) showsthat the break draft has no effect on medium termvariations of sliver (as indicated by inert test values)with , normal top rollers. This means that the irregu-,~larities introduced in the’ break draft zone are com-,parable at the two breik-drafts. Eccentric front top

. roller leads to a deterioration of &dquo;inert test&dquo; irregularityat the lower break draft with both ARBP52 and (’02cottons,. Eccentricity-In the front top roller results ina periodicity of wavelength 8-9 cm, which should

normally not have any effect over the &dquo;inert test&dquo;

irregularity. It wquld appear that the roller slipencountered with eccentric roller varies (rom time totime and this in turn contributes to medium termvariations in the sliver. An increase in &dquo;inert test&dquo;

irregularity is also seen with ’the eccentric roller at thethird position, but this is to be expected, as the irregu-larities introduced in the break draft zone appear asmedium term variations in the sliver. .

Effect of Roller Setting and Break Draft.

’

Upon Sliver Regularity &dquo;

-

,

~

Roller Settings in the Front Zone’

. (Shirley Draft Distribution) .

Investigations were~,mad~’~to elucidate the effect ofbreak draft upon sliver Irregularity as the roller settingat front zone is varied..’-, The studies were made using197/3, L-147, ARBPS2 cottons, and a 60s mixing onMDF2 drawframe with Shirley- draft distribution. Thestudies were made at second passage of drawing after

carding with the first three cottons and at post comberdrawing with the last material. The results are givenin Table VIII.An examination of the results indicates that the

relative merits of the break draft upon sliver irregularityis dependent upon the front zone setting. With 197/3cotton; the sliver irregularity is nearly unaffected bybreak draft at close settings but, with a widening ofsetting, the lower breakdraft gives a slightly betterevenness. With L-147 and ARBI’52 cottons, roller

setting has no significant effects over irregularity at thehigher break draft, but at the lower break draft (i.e.,1.2) a significant deterioration of sliver irregularity isfound at the closest setting. As a result, the sliverirregularity is poorer with lower break draft at close

settings. A similar result is also found in post combeddrawing of 60s mixing. ’rhe sliver irregul.arity is ob-served to deteriorate with a reduction of break draft atclose settings, but at wider settings the lower breakdraft is found to give better results. In fact, at theclosest setting of 38/32 in., drafting was not possible atthe lower break draft, while no dimculty was ex-

perienced at the same setting with an increased breakdraft.

These findings can be explained as follows. Whenthe break draft is reduced, the front zone draft is in-creased but, at the same time, there is more bulk ofmaterial under the second top roller while there is noalteration in the width of the ingoing individual strands.This means that a greater degree of interfiber cohesionwould operate in the front zone at the lower break draftat any given roller setting. This is supported by theroller slip measurements reported earlier, where a higherroller slip was always found at the lower break draft.When the interfiber frictional forces increase beyond acertain level, slippage of the material under the draftingrollers or plucking of the same takes place, leading tomore sliver irregularity. This explains the poorerirregularity of sliver at low break draft when the

settings are kept close. But the improved control over/

I

-- .. 1’AHf:F VII. EtTe(,:l of break draft on medium term variations in the sliver’

I.

~

(Second passage of drawing, carded mixing)



119

the fibers obtained with low break drafts contributes toa better sliver regularity at wider settings. Thus, theoptimum roller setting from the point of view of sliverirregularity shifts with break draft, being displaced toa higher level at lower break draft, as clearly illustratedin Figure 8. I’rovided optimum front zone settings areused, there is not much to choose between the two breakdrafts in regard to irregularity of sliver.

Roller Setting in Front Zone (NN*hitin Drawframe)Studies were carried out on a Whitin drawframes (M6)

to determine optimum front zone setting from the pointof view of sliver regularity and its dependence uponbreak draft. Three materials: L-147, ARH’S2, and(~iza 45 were examined for the effect of front zone

setting.and break draft upon sliver irregularity. Thefirst two cottons were carded while the last was combed, .and the studies were carried out at second passage of

drawing in carded mixings and at post comber drawingsin combed mixing. The break draft was varied between1.2 and 1.9. The results of sliver irregularity are givenin Table IX.

The results for 1.-I~7 cotton indicates that at close

settings break draft does not have a significant effectover sliver irregularity but, at wide settings, lowerbreak draft results in slightly more even sliver. WithARBP52 and (~fza 45, lower break draf t. resui ts in amore Irregular sliver at close setting, but at wide settingsthere is not much difference in irregularity of sliverbetween the two break drafts. ’rhus, the results arebroadly in conformity with the trend observed onMDF2 drawframe, and reasons advanced earlier are

equally applicable here.

Roller Setting in the Back Zone

(Shirley Draft Distribution)

The control over the fibers in the back zone is de-

pendent upon the back zone setting and, hence, while



120

- -- -.. -- - -.. - --..- -.. - - -

examining the effect of back draft, the back zone settinghas to be taken into. account. ’I’he effect of break draftupon sliver irregularity was investigated with mediumstaple Indian cottons at a;,‘ range’ of .back zone roller

settings, i.e., from 44/32 in. to 52132 in. The, results(not given) showed that within this range, back zonesetting has only little or marginal influence over sliverirregularity and the choice-,of break draft is, therefore,,not critically affected by the back zone setting. ...

’i &dquo; ,

. Conclusions .

The studies have emphasized the need for maintain-ing a close tolerance in regard to eccentricity in toproller for getting an even drawing sliver. At the

drawframe, eccentricity in the top roller adverselyaffects sliver irregularity primarily because of its in-fluence.over slippage. The slippage caused by eccentricroller is,periodic in nature with a periodicity correspond-irig to sliver made during one revolution of the roller.

.--.. - - - - --. - - .- -

Increasing the top roller weighting therefore helps toimprove sliver regularity when the roller is eccentric.Higher weighting reduces the slippage found with aneccentric roller and contributes to an improvement ofsliver regularity. The amplitude of the periodicityobserved with an eccentric roller is also reduced withan increase in weighting.

,

The use of lower break drafts in Shirlev draft dis-

tribution increases the roller slip of the top roller at thefirst, second, and third position.

()ther factors remaining the same, slippage of toproller is found to be more at the first passage of drawingthan at ,second passage. ’rhis is because of the higherdrafting forces in the former. As a result, eccentricityin the top roller has a more prominent effect upon

slippage as well as sliver irregularity at the first passagedrawing than at second passage of drawing.With Shirley draft distribution, roller slip at front

position caused by eccentricity in roller is found to have

. ’ ... ~ Appendix. Fiber Properties of Cottons.



121

most detrimental effects upon sliver irregularity. Ec-

centricity in top roller at second and third position alsoincreases the slippage but the effects on irregularity isonly marginal.

In Shirley draft distribution, use of lower break draftleads to a more irregular sliver when the front top rolleruis eccentric. This is because of higher roller slip andlarger front zone drafts.

Reduction of break draft is also found to increase themedium term variations in the sliver when the toproller at front or third position is eccentric. Slippagecaused by eccentricity seems to vary- with time, therebycontributing to medium term variations.The optimum roller setting at the front zone in draw-

frames with Shirley draft distribution and Whitin draw-frames is dependent upon the break draft. The

optimum lies at a wider setting with low break drafts.As a result, low break draft leads to a more irregularsliver at close settings and to a more regular sliver atwide settings. This is explainable from the higher

interfiber cohesive forces in the front zone at the lowbreak draft at any given setting. The break draft isnot found to have much influences over sliver irregularityat the optimum ’roJlet settings.. ,

:lckncne·declgme~tl. The authors are’thankful to Mr.’r. 1’. Ananthan, Director, BTRA, for his keen interestin the work and for his permission to publish the paper.

Literature Cited ’

1. Dakin, G., Foster, G. A. R., and Locke, J., Irregularities inCotton and Rayon-Staple Slivers Caused by Roller Slip atthe Drawframe, J. Textile Inst. 43, T545-T562 (1952).

2. Foster, G. A. R., Roller Slip and the Irregularity of Cotton andRayon-Staple Drawframe Slivers, II. ’I’he Nature of RollerSlip and the Theory of I)raft Distribution, J. Textile Inst. 44, T570-T579 (1953).

3. Nutter, W. and Slater, W. J., A Critical Assessment of Recent Progress in the Technology of Cotton Spinning, J. TextileInst. 50, P397-P425 (1959).

4. Platts Bull. 9, P277-P295 (1952).

A Technique for Measuring the Specific Volume of a Yarn, with Particular Reference to Wool Carpet Yarns

G. A. CARNABY

Wool Research Organisation of New Zealand (Inc.), Christchurch, New Zealand

ABSTRACT

A new technique for measuring the diameter and the specific volume of a yarn using simple laboratory apparatus is de-scribed. The results obtained with this technique on metal rods are compared with micrometer measurements. Sometypical measurements on a range of wool carpet yarns are given. The technique appears to have advantages over existing methods, particularly on compressible yarns of noncircular

cross section, where objective values are required. It is also suitable for testing twist lively yarns.

-~~------ -

’

Introduction ’

The specific volume of a solid object is defined asthe ratio of its volume to its mass. Since textile yarnsconsist of fibers with large spaces between them, thespecific volume of a yarn may be considered as theapparent space-filling capacity of unit mass of fibers.

This physical property of a textile yarn is importantin many circumstances. In the wool carpet industry,for example, yarn specific volume affects the frequencyof doffing during spinning and twisting, the choice ofhank rather than package processing routes, the

density and spacing of tufts in the carpet pile, andfinally, the &dquo;cover&dquo; of the carpet produced. A crimp-ing machine has been developed for increasing the

specific volume of wool carpet yarns in industry E8].

=- - - - -

The fundamental problem in measuring the specificvolume of a yarn is to determine the dimensions of theyarn while it is in an unstrained state. This is because,in general, the surface is not clearly defined and alsobecause the initial strain moduli are very small.

Previous techniques have relied on mechanical or op-tical devices. The latter include microscopic [4],projection [1, 3], photographic [10], and photoelectricE2, 6] methods. The major criticism of these tech-niques is that they assume a circular yarn cross section.Such an assumption is often inappropriate,for yarns oflow compressional resistance and is certainly not correctfour ply yarns, especially two-fold yarns as normallyused for carpets. In addition, some of these techniqueshave problems caused by operator dependency, the



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