PROCESS CONTROL IN SPINNING Raw Material Selection Fibre Quality Index (FQI In view of the large number of inuencing quality parameters and their unpredictable correlations, it is always helpful if an index based on all major parameters is calculated to give an overall idea of cotton quality. quality. This is done by nding !ibre quality Index", a common single parameter giving idea of bre quality. The !#I should correlate well with spinnability and important yarn properties if it has to serve as a quality index of bre. There have been e$orts to develop !#I and one developed by %outh India Textile &esearch 'ssociation 'ssociation is as follows( FQI !
lusm f
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where lu ) *+ span length in mm- s ) stelometer bre bundle strength at mm gauge in g per tex- m ) maturity coe$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$ering in staple length more than 34356. 'll spin spinne ners rs usua usuall lly y unde unders rsta tand nd the the requ requir irem emen entt of main mainta tain inin ing g uniformity in length. 7nless bre lengths are matched it is rather impossible to optimi8e settings particularly in drafting. 2ide variation in length can create havoc in spinning. Control o# 'icronaire ran%e and aera%e 9icronaire variation between bales within the same varieties often ree reect cts s vari variat atio ion n in matu maturi rity ty.. The The vari variat atio ion n in aver averag age e matu maturi rity ty between mixing of the same lot therefore results in serious defects particularly particularly,, dyeing defects. defects. :ye absorptio absorption n depends on cellulose cellulose content in bre and variation in maturity is therefore responsible for variation in dye penetration. In case yarns of same lot from di$erent mixings with wide variation of micronaire, then that can be one of the causes of barriness in fabric. If cotton of di$erent varieties are used then micronaire variation usua usuall lly y indi indica cate tes s vari variat atio ion n in nen nenes ess s rath rather er than than matu maturi rity ty.. The The variation in neness may results in following following problems( ;ossible ;ossible drafting defects as drafting behaviour depends on bre neness :yei :yeing ng defe defect cts s as dye dye abso absorb rben ency cy depe depend nds s on bre bre neness •
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%egreg %egregati ation on partic particular ularly ly during during air transp transport ort throu through gh ducts if neness range is very large resulting above two problems. Ther Theref efor ore e it is impo import rtan antt not not only only to main mainta tain in nen nenes ess s and and maturi maturity ty averag average e betwee between n mixing mixings s but also also to mainta maintain in a narrow narrow range range betwee between n bales bales within within a mix. mix. 1owev 1owever er often often spinne spinners rs forget forget about micronaire range in a mixing. In all mixings, micronaire range of bales used should be
etween mixing variation in average micronaire in such case should not be more than +.3 to have a perfect control over fabric barre. •
Control o# Colour ran%e and aera%e &ange of colour of cotton bales used should should be same for all the mixings of a lot 'verage of colour of cotton cotton bales used should be same for for all the mixings of a lot The control of colour is very important to maintain uniform shade and avoid to dyeing defects due to variation between and within mixings in a lot. •
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Control o# Maturity coe)icient ran%e and aera%e In general, maturity is indirectly measured by micronaire and so in mill, maturity is not directly measured. 1owever, in case of mixing bre bres s of di$e di$ere rent nt orig origin in4v 4var arie iety ty,, micr micron onai aire re vari variat atio ion n does does not not nece necess ssar aril ily y indi indica cate te matu maturi rity ty vari variat atio ion. n. Ther Theref efor ore e it is alwa always ys advisable to measure maturity coe$icient directly from each bale if such such a facili facility ty exits exits.. 'vailab vailabili ility ty of cotto cotton n bre bre nenes neness s maturi maturity ty inst instru rume ment nt such such as 9icr 9icrom omat at test tester er now now allo allow w mill mills s to incl includ ude e maturity as one of the parameter to consider while mixing. I'*ortant *oint+ #or &o'o%eneou+ 'ixin% The following points are worth considering to maintain minimum variation and to obtain a homogeneous homogeneous and uniform uniform mix. !eeding of thin layers from each bale should be preferred. 9aximum number of bales should be used in a mix as this increases the number of layers in a mix. ?rouping of >ales( %upp %uppos ose e ther there e are are ve ve di$e di$ere rent nt micr micron onai aire res s and and ve ve di$erent colours in the mix and *+ bales are used in the mixing. 9ore groups should be made by grouping the bales in a mixing so that each group will have average micronaire and average colour •
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as that of the overall mixing. The position of a bale for micronaire and colour should be xed for the group and it should repeat in the same order for all the groups. Leel o# Moi+ture ,i%& leel o# Moi+ture The higher level of moisture in bre results in di$iculty in opening and therefore cleaning. @xcessive moisture may often be a cause of increase in neps particularly in ne bres. Low leel o# Moi+ture Aow level of moisture in bre results in poor strength as cotton gains strength with increase in moisture regain. Therefore, with low moisture, there is chances of excessive brea
/b0The cleaning e$iciency of blow room machines for seed coats is much less than for leafy matter and sandCdust taoth, the total trash as well as the proportion of seed C coats in the trash, thus determines the cleaning e$iciency of the blow room. /d0The excess of waste over total trash is more with greater number 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 no e$ect on the amount of waste that falls down at each machine. If a blow room that has been found to be optimum performance at a particular level to trash is fed with a mixing containing as much as =* more trash the blow room responds to it by a corresponding increase in the waste extracted and a slight increase in cleaning so that it maintains its optimum performance. %imilarly, if the trash in the mixing decreases, the optimum performance is maintained. It is important to note that the performance remains optimum even in the absence of and changes in the settings and speeds, or in the number of machines in the blow room line. 's a result, once a blow line is adjusted to give optimum results, its performance remains optimum over a su$iciently wide range of trash content. !requent adjustments on the machinery are not necessary. If two widely di$erent mixings, say a medium count mixing with * trash and a superne mixing with about = trash are wor
In order to assess whether a blow room is in fact doing adequate cleaning without taesides this lot,
Ste* 32 Dlean the blow room line thoroughly by removing all waste from and under all the machines. %pread large brown papers under each machine for collecting the waste. ;rocess the =++ eaters must be set with correct clearance to prevent damage to bres and consequent formation of neps. Aong and curved conveying pipes with rough inner surfaces and vends are to be avoided to reduce napping potential of cottons. 1arsh treatments with cleaning points li
micron ire immature cottons. They damage the bres causing them to become matted. 'ir currents should be controlled and no winds should be allowed to form during the passage of cotton from on machine to another. The use of same type of cleaning point in sequence can increase neps signicantly. Gne of the major reasons in blow room for the creation of excessive neps is the repeated treatment of bres that are sticlunt stri
It has been observed that mills generally to not use correct type of wire suited to a given quality of mixing. Gne inevitable reason for this is that multiple counts are produced in a mill. %imilarly, di$erent types of bres are processed in the same card. 9ills are generally indi$erent to the type of feed plate used in spite of the fact that it has considerable bearing in yarn quality. !eed C plate to ta
to =.*m in brea
@xcessive top roller pressure. 7se of varnishes to the top roller cots. . Inadequate suction in the pneumatic. &oller settings too close or too wide for the type of material processed. @xcessive trash in the feed material. End .rea9+ in :rawin% Improper piecing at bac< process. :oubled sliver in feed. Thin card sliver due to web falling at cards. Incorrect trumpet si8e. Dottons having excessive honey dew content. Inadequate top roller pressure4brea< draft. :amaged surfaces i drafting4 calendar rollers. Gver lling of cans, and poor material handling practices. Bery wide setting between drafting rollers. :eeply meshed gears. Improper ambient conditions in the department. Proce++ Control in Co'bin% I'*roe'ent in Fibre len%t& a#ter Co'bin% The average bre length is expected to increase after combing due to the removal of short bres. The following table gives the expected increase in mean length as determined by a sorter diagram process. Nor'+ #or i'*roe'ent in Mean Len%t& a#ter Co'bin%
Increase in mean Dount /Fe0 length /mm0 HKL 3.+ K 3.= =+s K +s 3+ K 3= 3.= K 3.J +s K E+ 33 C 3 =.+ K =.* 5+s 3= K 3E =.* K .+ J+s 3 K 3* =.* K .+ 3++s 3E K 35 .+ K E.+ If a mill has brograph instrument to measure the bre length characteristics, the improvement in mean bre length can be assessed quite fast and more objectively. The following guideline could be used to assess the improvement in the bre length. Aevel of comber waste
Dombing e$iciency )
% Improvement in 50% span length Comber noil %
* 100 (%)
'n improvement of 3.H, 3.* and 3. is considered to be good, average and poor. 2henever these norms are applied, one
should also ta
The standard method consists of feeding full laps for all the heads after cleaning the machine and removal of waste from the machine. 'll the laps are fully run in the comber. The laps fed, the sliver fed and the waste removed are all weighed to obtain the waste . This is quite a time consuming process, but the results are quite reliable. In the short method, the test is conducted only for ve minutes of comber running. The machine is cleaned of the waste and the laps are weighed and the test is started. 'fter ve minutes, the lap weights and the waste collected and /sometimes, the sliver produced0 are measured and calculations are done to nd out the waste . 2hen an overall waste is required for machine setting, the second method could be followed. 2hen the quality improvement is the objective where factors such as head to head variation are required to be studied in detail, the rst method would be appropriate. Proce++ Control in Fly #ra'e Fly Fra'e End brea9a%e
' total brea
han< of sliver or excessively worn out, replace it with narrower trumpet @nsure proper coiling at the nisher draw frame and test spring plates for smooth functioning because they result in entanglements of the sliver during withdrawal from the can and cause brea
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Proce++ Control in Rin% S*innin% Control o# End .rea9+ in Rin% S*innin% The rst major process control activity for any spinner is perhaps the control of end brea
=+ x 3=*+ E* + 3HJ x 3*+ +s E3 + 3HJ x 3E++ +s c E3 + 3HJ x 3E++ E+s E3 + 3HJ x 3E*+ E+s c E3 + 3HJ x 3E*+ *+s E3 + 3HJ x 3E*+ 5+s E3 + 3HJ x 3*++ 5+s c E3 + The choice of spindle lift and ring diameter is an important factor a$ecting the end breaalloon control rings should be used to reduce the tension of the yarn that is being twisted, which thus reduces the end brea
Gbservation of the balloon formed at various heights of the build of the ring bobbin brings out the accurateness of the spindle gauging. The prole of the balloon should not touch the pac
that can be done is to ensure that the variation in the number of bres per crossCsection is the barest minimum. The variability of mass per unit length, both within and between bres and the minimum conceivable variability in the number of bres per crossCsection in a yarn set the minimum limit for yarn irregularity. This limit, expressed as the coe$icient of variation is ) 3+54 N , where F is the average number of bres per cross section. ?iven the yarn count, the average number of bres per crossCsection is inversely proportional to the average bre mass. The minimum attainable coCe$icient of variation /DB 0 can be shown to be +.J5*P Ne * µ g per inch , where Fe is the count of yarn spun. >ased on this, one can calculate the theoretical minimum DB for various counts of yarn and they are given in Table . Table 42 T&eoretical Mini'u' Irre%ularity o# ;arn+ DB of yarn spun from bres of Qarn count E * µ µ µ g per inch g per inch g per inch /Fe0 =+s 5.H H.H J.5 E+s L.* 3+.L 3=.= J+s 3.E 3*.* 3H.
The above table clearly brings out the e$ect of bre neness on the minimum achievable yarn evenness for a given count in terms of coe$icient of variation. The irregularity considered above is Mrandom irregularityN. :rafting on ring frames is carried out by means of rollers and aprons, where the rollers are y dividing the wave length of an irregularity in the yarn by the drafts introduced onwards of a particular stage, one can chec< whether the particular
stage is li
2ave length ) Number of ! patterns on both sides of the board at that idth . The presence of periodicities beyond the wave length of 3* cm can be detected with the use of the spectrograph equipment of the electronic yarn evenness testers. The spectrograph shows a single pea< at the appropriate length when the irregularity is periodic. >etween the two extreme types of purely random and purely periodic lies another type of periodicity which is called as quasi periodic. ' quasi periodic variation has a varying wave length and amplitude. #uasi periodic variation is inevitable with the current level of technological development and only its magnitude has to be controlled within reasonable limits. The source of this inevitable quasi periodic variation is roller drafting. In roller drafting, the bres which are shorter than the nip to nip distance oat in the drafting 8one without any control during their stay and they are pulled out of order by the front nip leading to production of thic< and thin places alternately. The wave length varies from about 5 to J cm and the amplitude of the variation depends on the amount or proportion of short bres. These variations do not show as pea
imperfections can occur as frequently as once a metre. The presence of imperfections as well as faults may cause di$iculties in subsequent processes and can lead to poor appearance of the fabric. 2hile faults can to some extent be removed in winding, the imperfections are so small and so numerous that to extract and replace them by *oint ce++in% :rafting paramete rs Total draft
3. &ing frames
control o# <= " t&ic9 and t&in *lace+ General reco''endation
Re'ar9+
@qual to count for 5s to 3Es, 3E to 3L for counts 3*s to =+s =+ to =* for counts ==s to 5s and =* to * for counts E+s to 3++s
Dhanges in twist, spindle speed, traveller count and mechanical condition of rings, travellers have no inuence
'bout 3. for drafts >rea< upto =*, about 3.* for draft higher drafts 'pron E.* mm for counts upto spacer 3Js, E.+ mm for =+s to =5s, .* mm for counts =Js to E+s, .+ mm for
:rafting Dondition s !ront top roller condition
Traverse
3. &ing frames /Dont.0
=. Dards
=. Dards /Dontinu ed0
&oller pressure
counts EEs to J+s, and =.* mm for counts 3++s and above 'void wobbling, greasy top rollers- bu$ every 5 months- minimum Top roller diameter =* mm- for condition critical polyester blended yarn, bu$ more frequently 9ust operate- cover twoC thirds if the roller widthdo not let the roving to slip outside drafting 8one on any spindle. @qual on all arms and as recommended by manufacturers- top arm setting important
%hould not go below =+ of the recommended value on more than =+ of the spindles
9aintain the maximum possible as recommended by machinery Dylinder manufacturer /1; speed ;roduction cards( ++ to *++rpm depending on the technology level of the cards0 ;roductio Aowest commensurate 7se of low n rate with availability of production rates cards helps in reducing the neps- trials needed to decide the level of production- over 5+ reduction may be necessary to process immature bres with large length variability
:o$er speed DylinderC do$er setting Dondition of wire points Improve ment in mean length
. Dombers
E. !ly frames
*. :raw frames
1igh do$er speed with light han< for any given production rateadjust han< at the rst head of drawing by reducing the draft E thou- as uniform as possible 9aintain the wire points sharp by regular Dritical factor grinding 's per standards-
@nsure that is as per Timing of machinery piecing manufacturerNs recommendations 9aintain minimum %etting of possible distance front 8one without causing bre in draw brea
7 roving
7 of sliver
5 to J for carded counts and * to H for combed counts- ta
Donduct trials to obtain low 7
!ollow up trials upto ring frame stage before choosing a draft or spacer as optimum
's per standardsmaintain minimum possible nip to nip Fo inuence on distance without causing yarn thin and bre brea
C&ec9 li+t #or control o# Ne*+ in yarn Sta%e o# Pro> ce++in%
3. Dards
C&ec9 *oint
Re'ar9+
#uality of 7se a low power grinding microscope to ensure that grinding wire points is proper 1igher than 3.* !lat strips sometimes helps in waste reducing the neps ;roductio n paramete %ame as in previous rs and table condition of wire points Dleaning Doncentrate on the e$iciency removal of seed coat particles- sliver may be tested for number of trash particles per grams similar to neps per gram to reduce trash neps ;ressure Fot e$ective for on cross %elect maximum seed coats rolls pressure because of attached bres 9achine %ame as in previous condition table
=. Dombers Gptimum comber waste
. >low room
General reco''endation
!an speeds
1igher levels of wastes generally result in reduction in neps- cost and considerations
?enerally =++ to =*+ rpm more than the beater speed
If card sliver has high level of neps and if the yarn quality requirements are stringent, assumes more importance
'void usage of harsh Gmission beaters unless of beaters inevitable Dondition of beating 9achine points, grid bars, condition opening elements critical
Dleaning e$iciency
Doncentrate on opening in blow room and achieve highest possible combined blow room and carding cleaning e$iciency
9odern blow room lines concentrate more on opening- high cleaning e$iciencies are not generally achievable in modern lines.
Proce++ Control in Rotor S*innin% Eenne++ The evenness of the rotor yarn is inuenced by the following factors( 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 of nullifying very short term unevenness of slivers. This is achieved by the intensive doubling obtained at the rotor groove at the level of individual bres. 1owever this levelling is e$ective only to the extent of yarn lengths equivalent to the circumference of the rotor- any further unevenness in the sliver is faithfully reproduced in the nal yarn. Therefore, feed sliver evenness needs to be controlled with 7ster DB between =.* to .*. 'chieving this level of evenness depends on the proportion of short bres in the raw material, setting of drafting rollers, availability of draft control elements such as pressure bars, selection and distribution of draft etc. 1igh rotor speeds in general result in more uneven yarn- with increase in rotor speed, the throughput rate increases, which a$ect separation of bres by the opening roller. The bres released on the
rotor may not slide down in a smooth fashion to the groove and thus may a$ect arrangement of bres in the groove. The deposition of dirt and dust in the rotor groove interfere with the transformation of bre band into yarn through twisting and a$ect the yarn evenness. The wear of the rotor groove can also increase the unevenness as 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 opening rollers need attention here. The speed of the roller should be adjusted according to the sliver han< and the feed rate. ' higher opening roller speed /not being too excessive0 would in general be more conducive for producing even yarn. :eposition of waxy materials or spin nishes in the transport channel causes hindrance to the free ow of bres through the channel 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 generator by its abrasive action on the rotating yarn. The rubbing action of the navel may become too aggressive if it gets damaged or worn. This could lead to high unevenness and faults in the yarn. The draw o$ roller should ensure a steady and smooth withdrawal of yarn from the rotor at a constant rate. If the rollers are damaged or eccentric, the withdrawal of the yarn will be jerig trash particles within the
groove will hamper the ow of twist and uniform deposition of bres in the groove where the trash is present leading to periodicity of yarn. The damaged rubber covering of the twinCdisc drive to the rotor causes 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 will be its quic< deposition into the rotor groove. 'ny contaminants or undrawn bres would be potential fault generator. %ome amount of dust and dirt generally nd their way into the rotor groove and ll them up gradually. The rotor needs to be cleaned periodically depending on the rate of build up of deposit. 2hen the grooves are not cleaned at regular intervals, the grooves get gradually cho
Table 62 Factor+ a)ectin% ;arn Quality Quality c&aracteri+tic Factor+ 7nevenness /7, DB0 @venness of feed sliver :irt and dust in rotor groove :amaged4worn opening roller :amaged4worn navel :amaged4worn do$ing o$ roller ;eriodic variation :irt and dust in rotor groove :amaged or worn opening roller :rive to feed rotor 7nevenness of feed sliver ;resser and feed plat arrangement Tensile property &aw material characteristics !eed sliver Twist Gpening roller &otor /speed, diameter, groove0
Control o# Count and Count -ariation (C-
Sa'*lin% Dollect a suitable number of bobbins every day from each group of ring frames wor bobbin count ariation Cau+e+ o# ,i%& -ariation( The most important single cause of within C bobbin count variation is defective draw frame drafting. ;oor drafting introduces pronounced di$erences in the weight of J cm pieces of rst leas sliver of EJ cm pieces of nisher sliver which leas to variations in count between consecutive leas of the yarn form the same bobbin. The contribution to within C bobbin count variation from y frames can be from two sources( irregular drafting and irregular stretching. Gf these the e$ect of irregular draft is not much.This is because irregular drafting will introduce variability between small lengths of roving. %uch variability will be averaged out in a * m piece of roving which roughly corresponds to a lea of yarn. The e$ect of irregular stretching caused by improper regulation of bobbin speed can introduce di$erences in the weight of roving over di$erent layers of the roving bobbin. To the extent that di$erent leas from a ring bobbin originate from di$erent layers of the creel roving bobbin, therefore, the e$ect of irregular stretch can a$ect the within C bobbin count variation. The rst and last lea of a ring bobbin is normally separated by about J to 3+ layers for roving. This means that irregular stretch at y frame can a$ect within C bobbin count variation if such irregularity is li
Control o# Slier Eenne++
The unevenness of card sliver is generally between = C which increases to around * CH after the rst passage of drawing. The second passage of draw frames, used invariably for spinning carded yarns, reduces this value to between C* depending upon the bre length characteristics of the mixing being processed and the type of draw frame. In the case of carded material, the two contributes to the unevenness of the drawing sliver are the drafting waves and the roller slip waves. The drafting wave has a variable wavelength even in any given layers ranging between = and times the staple length. 'part from these specic measures for controlling the unevenness of the carded and combed slivers on conventional and modern draw frames, it is necessary to pay close attention to two other factors which are often ignored in mill practice. These are the creel draft between the lifter rollers and the bac< rollers, and the web draft between the front rollers and the coiler calendar rollers. >oth these are essentially tension drafts which are normally not taesides improper choice of processing parameters and poor mechanical- conditions of the machine, the behaviour of the raw material can , contribute signicantly to high within C bobbin count variation although this is extremely rare. Two examples of such problematic behaviour are ( roller lapping and bre shedding. .etween > bobbin count ariation :i$erence in the average han< of inter bobbins can originate from( Cdeference in blow room lap weight Cdraft di$erences between groups of cards or combers, Chan< di$erences between draw frames slivers, draft di$erences between y framesCexcessive han< di$erences between front and bac< row of bobbins in y framesThis list of causes immediately suggests also the remedies for high between C bobbin count variation 't ring frames, it is necessary to ma
Stren%t& and Stren%t& -ariation !actors '$ecting Qarn %trength The factors which a$ect yarn strength will now be listed in the order 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 number of useful purposes. ' low level of strength variability is indicative of uniform performance of the yarn. !urther it helps in reducing the amount of testing required to ensure the conformity of the average strength with standards.
