COMBED YARN FOR KNITTING - 2
- If the micronaire is low, blowroom process parameters become very critical.
- It is better to do a perfect preopening and reduce the beater speeds in fine opening. If required one more fine opener can be used with as low as beater speed, instead of using very high speed in only one fine opener
- If the micronaire is lower than 3.8, it is not advisable to use machines like CVT4 or CVT3
- Nep increase in cotton after blowroom process should be less than 80%.(i.e 180 % of rawcotton nep)
- If the nep increase is more, then beater speeds should be reduced instead of feed roller to beater setting
- If the trash percentage in cotton is less and the neps are more in the sliver, no of beating points can be reduced. 3 beating points should be more than enough.
- variation in feed roller speed should be as low as possible especially in the feeding machine
- beater types and specification should be selected properly based on the positions of the beater and the type of raw material (fibre micronaire and trash percentage)
- the material pressure in the ducts should be as high as possible to reduce feeding variation to the cards
- feed rollers in the chute should work continuously without more speed variation if pressure filling concept is used.(i.e. balancing of the chute should be done properly). For others, the feed roller should work at the maximum speed for a longer time.
- material density between different chutes should be same. The difference should not be more than 7%
- The difference in duct pressure should not be more than 40 pascals in chute feed system.
- air loss should be avoided in the chute feed system, to reduce the fan speed and material velocity
- blow room feeding should be set in such a way that the draft in cards is same for all the cards and the variation in feed density is as low as possible
- fibre rupture in blowrrom should be less than 2.5%
- 70% of the quality will be achieved in carding, if the wires are selected properly
- following table can be used as a guide line for cylinder wire selection
|carding production||wire height||angle of wire(degrees)||points per square inch|
|less than 30 kgs/hr||2 mm||30||around 840|
|more than 30 kgs||2mm||35 to 40||900 to 1050|
- Flat tops with 400 to 500 points per square inch should be used
- if the micronaire is lower than 3.5, the cylinder speed should be around 350rpm. If the micronaire is between 3.5 to 4.0, it can be around 450 rpm. If the micronaire is more than 4.0, it can be around 500 rpm.
- Lower the micronaire, lower the lickerin speed. It should range from 800 to 1150 rpm depending upon the micronaire and proudction rate
- pointed wires should be used for cyliner
- TSG grinder should be used once in 2 months for consistent quality
- Flat tops should be ground frequently (once in 3 months) for better yarn quality. Because, flat tops plays a major role in reducing neps and kitties in the yarn. Emery fillet rollers should be used for flat tops grinding, instead of using grinding roller grinding stone
- Licker-in wire should be changed for every 150000 kgs produciton in carding
- stationary flats should be changed for every 150000 kgs production in carding
- Individual card studies upto yarn stage should be conducted regularly, and if the quality is deteriated by 25% from the average quality. card should be attended (wire mounting, grinding, full-setting etc to be done)
- setting between cylinder and flat tops should be as close as possible, depending upon the variation between cylinder and flat tops. Care should be taken so that , wires do not touch each other.
- Card autolevellers should be set properly. Nominal draft should be correct. Draft deviation should not be more than 5% during normal working.
- card stoppages should be as low as possible
- slow speed working of cards should be avoided. slivers produced during slow speed should be removed
- 10 meters C.V% of card sliver should be less than 2.0
- Sliver weight difference between cards should not be more than 2.5%
- Sliver U% should be less than 3.5 and spectrogram peaks should be attended
- cylinder loading should be nil. If cylinder is loaded, wire should be inspected. If required grinding should be done or wire should be changed
- sliver diameter difference should be less. Calender roller pressure should be same in all the cards
- trash in sliver should be less than 0.1%
- uiformity ratio of sliver should be same or better than raw cotton
- if kitties or seed coat fragments are more, higher flat speeds should be used and as much as flat waste should be removed to reduce seed coat fragments in the yarn
- in general sliver hank varies from 0.12 to 0.14
- individual card studies should be conducted upto yarn stage, if the quality from a particular card is bad, immediate action to be taken to rectify the problem. Lower the variation better the yarn quality.
- In lap preparation, total draft, fibre parallelisation ,no of doublings, lap weight etc should be decided properly(based on trial)
- higher the lap weight(grams /meter) lower the quality. It depends upon the the type of comber and the fibre micronaire
- if fine micronaire is used, lap weight can be reduced to imrpove the combing efficiency
- if coarse micronaire is used, lap weight can be increased
- if fibre parallelisation is too much, lap sheets sticking to each other will be more( It will happen if the micronaire is very low also). If the lap sheets are sticking to each other, the total draft between carding and comber should be reduced
- If the draft is less, fibre parallelisation will be less, hence loss of long fibres in the noil will be more
- top comb penetration should be maximum for better yarn quality. But care should be taken so that top comb will not get damaged.
- damaged top comb will affect the yarn quality very badly
- setting between unicomb and top nipper should be same and it should be around 0.4mm to 0.5 mm
- feed weight is approximately 50 to 58 grams for combers like E7/4 and is 65 to 75 grams for combers like E62 or E7/6
- lower the feed length, better the yarn quality. Trials to be conducted with different feed lengths and it should be decided based on quality and production requirement
- required waste should be removed with the lowest detaching distance setting
- for cottons with micronaire upto 3.5, top comb should have 30 needles/cm and for cottons with more than 3.8 micronaire, the top comb should have 26 needles/cm
- Trials to be conducted to standardise the waste percentage
- piecing wave should be as low as possible. Piecing index should be decided based upon cotton length and feed length
- spectrograms should be attended. Comber sliver uster should be less than 3.5
- head to head waste percentage should be as low as possible
- variation in waste percentage between combers should be as low as possible( less than 1.5%)
- If cotton with low maturity coefficient is used, it is better to remove more noil to avoid dyeing variation problem
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