process control spinning

8/11/2019 Process Control Spinning

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PROCESS CONTROL IN SPINNING

Raw Material SelectionFibre Quality Index (FQI

In view of the large number of inuencing quality parameters

and their unpredictable correlations, it is always helpful if an indexbased on all major parameters is calculated to give an overall idea ofcotton quality. This is done by nding !ibre quality Index", a commonsingle parameter giving idea of bre quality. The !#I should correlatewell with spinnability and important yarn properties if it has to serveas a quality index of bre.

There have been e$orts to develop !#I and one developed by%outh India Textile &esearch 'ssociation is as follows(

FQI !f

msul"

where lu ) *+ span length in mm- s ) stelometer bre bundle

strength at mm gauge in g per tex- m ) maturity coe$icient and f )micronaire value /air ow0.1owever no universally established formula of !#I" is developed.

Control o# $bre len%t&2hile blending of di$erent varieties, it is common practice not

to blend cotton types di$ering in staple length more than 34356. 'llspinners usually understand the requirement of maintaininguniformity in length. 7nless bre lengths are matched it is ratherimpossible to optimi8e settings particularly in drafting. 2ide variationin length can create havoc in spinning.

Control o# 'icronaire ran%e and aera%e9icronaire variation between bales within the same varieties often

reects variation in maturity. The variation in average maturitybetween mixing of the same lot therefore results in serious defectsparticularly, dyeing defects. :ye absorption depends on cellulosecontent in bre and variation in maturity is therefore responsible forvariation in dye penetration. In case yarns of same lot from di$erentmixings with wide variation of micronaire, then that can be one of thecauses of barriness in fabric.

If cotton of di$erent varieties are used then micronaire variationusually indicates variation in neness rather than maturity. The

variation in neness may results in following problems( ;ossible drafting defects as drafting behaviour depends on

bre neness :yeing defects as dye absorbency depends on bre

neness


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%egregation particularly during air transport throughducts if neness range is very large resulting above twoproblems.

Therefore it is important not only to maintain neness andmaturity average between mixings but also to maintain a narrow

range between bales within a mix. 1owever often spinners forgetabout micronaire range in a mixing. In all mixings, micronaire rangeof bales used should be


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as that of the overall mixing. The position of a bale for micronaireand colour should be xed for the group and it should repeat in thesame order for all the groups.

Leel o# Moi+ture,i%& leel o# Moi+ture

The higher level of moisture in bre results in di$iculty inopening and therefore cleaning. @xcessive moisture may often be acause of increase in neps particularly in ne bres.Low leel o# Moi+ture

Aow level of moisture in bre results in poor strength as cottongains strength with increase in moisture regain. Therefore, with lowmoisture, there is chances of excessive brea


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/b0The cleaning e$iciency of blow room machines for seed coats ismuch less than for leafy matter and sandCdust taoth, the total trash as well as the proportion of seed C coats inthe trash, thus determines the cleaning e$iciency of the blowroom.

/d0The excess of waste over total trash is more with greaternumber of machines used in the blow room.' sequence of blow room machines responses to the type of cotton

feed to it almost entirely in terms of the amount of trash in the feed.The bre prperties such as length and its variation have almost noe$ect on the amount of waste that falls down at each machine.

If a blow room that has been found to be optimum performance ata particular level to trash is fed with a mixing containing as much as=* more trash the blow room responds to it by a correspondingincrease in the waste extracted and a slight increase in cleaning sothat it maintains its optimum performance. %imilarly, if the trash in

the mixing decreases, the optimum performance is maintained. It isimportant to note that the performance remains optimum even in theabsence of and changes in the settings and speeds, or in the numberof machines in the blow room line. 's a result, once a blow line isadjusted to give optimum results, its performance remains optimumover a su$iciently wide range of trash content. !requent adjustmentson the machinery are not necessary.

If two widely di$erent mixings, say a medium count mixing with* trash and a superne mixing with about = trash are wor


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Ste* 32 Dlean the blow room line thoroughly by removing all wastefrom and under all the machines. %pread large brown papers undereach machine for collecting the waste. ;rocess the =++


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micron ire immature cottons. They damage the bres causing them tobecome matted. 'ir currents should be controlled and no windsshould be allowed to form during the passage of cotton from onmachine to another. The use of same type of cleaning point insequence can increase neps signicantly.

Gne of the major reasons in blow room for the creation ofexcessive neps is the repeated treatment of bres that are stic


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It has been observed that mills generally to not use correct typeof wire suited to a given quality of mixing. Gne inevitable reason forthis is that multiple counts are produced in a mill. %imilarly, di$erenttypes of bres are processed in the same card. 9ills are generallyindi$erent to the type of feed plate used in spite of the fact that it has

considerable bearing in yarn quality. !eed C plate to ta


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to =.*m in brea


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@xcessive top roller pressure. 7se of varnishes to the top roller cots. . Inadequate suction in the pneumatic.

&oller settings too close or too wide for the type of materialprocessed.

@xcessive trash in the feed material.

End .rea9+ in :rawin%Improper piecing at bac< process.:oubled sliver in feed.

Thin card sliver due to web falling at cards. Incorrect trumpet si8e. Dottons having excessive honey dew content. Inadequate top roller pressure4brea< draft. :amaged surfaces i drafting4 calendar rollers. Gver lling of cans, and poor material handling practices.

Bery wide setting between drafting rollers.:eeply meshed gears. Improper ambient conditions in the department.

Proce++ Control in Co'bin%I'*roe'ent in Fibre len%t& a#ter Co'bin%

The average bre length is expected to increase after combingdue to the removal of short bres. The following table gives theexpected increase in mean length as determined by a sorter diagramprocess.

Nor'+ #or i'*roe'ent in Mean Len%t& a#terCo'bin%

Dount /Fe0Aevel of comber

waste

Increase in meanlength/mm0

=+s K +sH K L 3.+ K 3.=

3+ K 3= 3.= K 3.J+s K E+ 33 C 3 =.+ K =.*

5+s 3= K 3E =.* K .+J+s 3 K 3* =.* K .+3++s 3E K 35 .+ K E.+

If a mill has brograph instrument to measure the bre lengthcharacteristics, the improvement in mean bre length can be assessedquite fast and more objectively. The following guideline could be usedto assess the improvement in the bre length.

Dombing e$iciency ) (%)100*%noilComber

lengthspan50%intImprovemen%

'n improvement of 3.H, 3.* and 3. is considered to begood, average and poor. 2henever these norms are applied, one


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should also ta


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han< of sliver or excessively worn out, replace it with narrowertrumpet

@nsure proper coiling at the nisher draw frame and test springplates for smooth functioning because they result inentanglements of the sliver during withdrawal from the can and

cause brea


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=+s=+ x

E*3=*+

+

+s3HJ x

E33*+

+

+s c3HJ x

E3

3E++

+E+s

3HJ xE3

3E+++

E+s c3HJ x

E33E*+

+

*+s3HJ x

E33E*+

+

5+s3HJ x

E33E*+

+

5+s c3HJ x

E33*++

+

The choice of spindle lift and ring diameter is an importantfactor a$ecting the end brea


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Gbservation of the balloon formed at various heights of the buildof the ring bobbin brings out the accurateness of the spindle gauging.The prole of the balloon should not touch the pac


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that can be done is to ensure that the variation in the number of bresper crossCsection is the barest minimum. The variability of mass perunit length, both within and between bres and the minimumconceivable variability in the number of bres per crossCsection in ayarn set the minimum limit for yarn irregularity. This limit, expressed

as the coe$icient of variation is ) 3+54 N , where F is the averagenumber of bres per cross section. ?iven the yarn count, the averagenumber of bres per crossCsection is inversely proportional to theaverage bre mass. The minimum attainable coCe$icient of variation/DB 0 can be shown to be +.J5*P inchperg*Ne , where Fe is thecount of yarn spun. >ased on this, one can calculate the theoreticalminimum DB for various counts of yarn and they are given in Table.

Table 42 T&eoretical Mini'u' Irre%ularity o# ;arn+

Qarn

count/Fe0

DB of yarn spun from bres of

inchperg

Einchperg

*inchperg

=+s 5.H H.H J.5E+s L.* 3+.L 3=.=J+s 3.E 3*.* 3H.

The above table clearly brings out the e$ect of bre neness onthe minimum achievable yarn evenness for a given count in terms ofcoe$icient of variation. The irregularity considered above is MrandomirregularityN.

:rafting on ring frames is carried out by means of rollers and

aprons, where the rollers are


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stage is li


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imperfections can occur as frequently as once a metre. The presenceof imperfections as well as faults may cause di$iculties in subsequentprocesses and can lead to poor appearance of the fabric. 2hile faultscan to some extent be removed in winding, the imperfections are sosmall and so numerous that to extract and replace them by rea


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3. &ingframes

/Dont.0

counts EEs to J+s, and=.* mm for counts3++s and above

:raftingDondition

s!ront toproller

condition

'void wobbling, greasytop rollers- bu$ every

5 months- minimumdiameter =* mm- forpolyester blendedyarn, bu$ morefrequently

Top rollercondition critical

Traverse

9ust operate- cover twoCthirds if the roller width-do not let the roving toslip outside drafting 8oneon any spindle.

&ollerpressure

@qual on all arms and asrecommended bymanufacturers- top armsetting important

%hould not gobelow =+ of therecommended

value on morethan =+ of thespindles

=. Dards

=. Dards/Dontinu

ed0

Dylinderspeed

9aintain the maximumpossible asrecommended bymachinerymanufacturer /1;;roduction cards( ++to *++rpm depending

on the technology levelof the cards0

;roduction rate

Aowest commensuratewith availability ofcards

7se of lowproduction rateshelps inreducing theneps- trialsneeded to decidethe level ofproduction- over5+ reduction

may benecessary toprocessimmature breswith largelength variability


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:o$erspeed

1igh do$er speed withlight han< for any

given production rate-adjust han< at the rst

head of drawing by

reducing the draftDylinderC

do$ersetting

E thou- as uniform aspossible

Donditionof wirepoints

9aintain the wirepoints sharp by regulargrinding

Dritical factor

.Dombers

Improvement inmeanlength

's per standards-

Timing ofpiecing

@nsure that is as permachinerymanufacturerNsrecommendations

%etting offront 8one

in drawbox

9aintain minimumpossible distancewithout causing brebrea


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C&ec9 li+t #or control o# Ne*+ in yarn

Sta%e o#Pro>

ce++in%

C&ec9*oint

Generalreco''endation

Re'ar9+

3. Dards

#uality ofgrinding

7se a low powermicroscope to ensurethat grinding wirepoints is proper

!lat stripswaste

1igher than 3.*sometimes helps inreducing the neps

;roduction

parameters and

conditionof wirepoints

%ame as in previoustable

Dleaninge$iciency

Doncentrate on theremoval of seed coatparticles- sliver may betested for number oftrash particles pergrams similar to nepsper gram to reducetrash neps

;ressureon cross

rolls%elect maximumpressure

Fot e$ective forseed coatsbecause ofattached bres

=.Dombers

9achinecondition

%ame as in previoustable

Gptimum

comberwaste

1igher levels of wastesgenerally result in

reduction in neps- costand considerations

If card sliver hashigh level ofneps and if theyarn qualityrequirementsare stringent,assumes moreimportance

. >lowroom

!anspeeds

?enerally =++ to =*+rpm more than thebeater speed


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Gmissionof beaters

'void usage of harshbeaters unlessinevitable

9achine

condition

Dondition of beatingpoints, grid bars,

opening elementscritical

Dleaninge$iciency

Doncentrate onopening in blow roomand achieve highestpossible combinedblow room and cardingcleaning e$iciency

9odern blowroom linesconcentratemore onopening- highcleaninge$iciencies arenot generallyachievable in

modern lines.

Proce++ Control in Rotor S*innin%Eenne++

The evenness of the rotor yarn is inuenced by the followingfactors( neness of bres evenness of feed sliver accumulated dirt and dust in the rotor groove damaged or worn out opening roller deposits in the transport channel damaged or worn out navel damaged or worn out draw o$ roller

The rotor spinning system has an inherent advantage ofnullifying very short term unevenness of slivers. This is achieved bythe intensive doubling obtained at the rotor groove at the level ofindividual bres. 1owever this levelling is e$ective only to the extentof yarn lengths equivalent to the circumference of the rotor- anyfurther unevenness in the sliver is faithfully reproduced in the nalyarn. Therefore, feed sliver evenness needs to be controlled with

7ster DB between =.* to .*. 'chieving this level of evennessdepends on the proportion of short bres in the raw material, settingof drafting rollers, availability of draft control elements such aspressure bars, selection and distribution of draft etc.

1igh rotor speeds in general result in more uneven yarn- withincrease in rotor speed, the throughput rate increases, which a$ectseparation of bres by the opening roller. The bres released on the


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rotor may not slide down in a smooth fashion to the groove and thusmay a$ect arrangement of bres in the groove.

The deposition of dirt and dust in the rotor groove interfere withthe transformation of bre band into yarn through twisting and a$ectthe yarn evenness.

The wear of the rotor groove can also increase the unevennessas it disturbs the ow of torque and deposition of bres in the groove.Gpening roller individualises the bres and feeds them into the

rotor groove. 2rong type of opening roller, damaged teeth of openingrollers need attention here. The speed of the roller should be adjustedaccording to the sliver han< and the feed rate. ' higher opening rollerspeed /not being too excessive0 would in general be more conducivefor producing even yarn.

:eposition of waxy materials or spin nishes in the transportchannel causes hindrance to the free ow of bres through thechannel and thereby into the groove. &egular cleaning action as part

of routine maintenance is a solution to this problem.The navel in the rotor assembly acts as a false twist generatorby its abrasive action on the rotating yarn. The rubbing action of thenavel may become too aggressive if it gets damaged or worn. Thiscould lead to high unevenness and faults in the yarn.

The draw o$ roller should ensure a steady and smoothwithdrawal of yarn from the rotor at a constant rate. If the rollers aredamaged or eccentric, the withdrawal of the yarn will be jerig trash particles within the


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groove will hamper the ow of twist and uniform deposition of bresin the groove where the trash is present leading to periodicity of yarn.The damaged rubber covering of the twinCdisc drive to the rotorcauses the rotor speed to vary in a periodic and jerad sliver joints

could be a source of long thic< places.&esidual trash level in the sliver is an extremely important

factor in rotor spinning. The more is the residual trash the more willbe its quic< deposition into the rotor groove. 'ny contaminants orundrawn bres would be potential fault generator. %ome amount ofdust and dirt generally nd their way into the rotor groove and llthem up gradually. The rotor needs to be cleaned periodicallydepending on the rate of build up of deposit. 2hen the grooves arenot cleaned at regular intervals, the grooves get gradually cho


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Sa'*lin%Dollect a suitable number of bobbins every day from each group

of ring frames wor


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Control o# Slier Eenne++

The unevenness of card sliver is generally between = Cwhich increases to around * CH after the rst passage of drawing.The second passage of draw frames, used invariably for spinningcarded yarns, reduces this value to between C* depending upon

the bre length characteristics of the mixing being processed and thetype of draw frame.

In the case of carded material, the two contributes to theunevenness of the drawing sliver are the drafting waves and the rollerslip waves. The drafting wave has a variable wavelength even in anygiven layers ranging between = and times the staple length. 'part from these specic measures for controlling theunevenness of the carded and combed slivers on conventional andmodern draw frames, it is necessary to pay close attention to twoother factors which are often ignored in mill practice. These are thecreel draft between the lifter rollers and the bac< rollers, and the web

draft between the front rollers and the coiler calendar rollers. >oththese are essentially tension drafts which are normally not ta


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Stren%t& and Stren%t& -ariation!actors '$ecting Qarn %trength

The factors which a$ect yarn strength will now be listed in theorder of their importance.

-#uality of drafting at ring frames

- #uality of carding- #uality of combing- #uality of mixing- Gther processing factors

The control of the variability of lea strength can serve a numberof useful purposes. ' low level of strength variability is indicative ofuniform performance of the yarn. !urther it helps in reducing theamount of testing required to ensure the conformity of the averagestrength with standards.

process control spinning

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