Preparatory is Heart of the process

Basic process requirements for good yarn quality

GMT 11:00 2016 Monday ,20 June

Sriyadithatextile - Basic process requirements for good yarn quality

Mr. Pratap - GM at M M Yarns, Rajkot
TFA

In Textile yarn preparation, the heart of the process is Mixing, Blowroom & Carding, which will decide the final output yarn quality according to the end use requirement. In this Casual discussion regarding process basic requirements for good yarn quality, Mr. Pratap - GM at M M Yarns, Rajkot - has given very elaborately guidelines by departmentwise.


MIXING:
• Average Micronaire of the mixing should be same for the entire lot. The difference in average micronaire of   different mixings of the same lot should not be more than 0.1
• The micronaire C.V% of a mixing should be less than 10%
• The micronaire Range should be same
• Cottons with two different origins should not be mixed
• Cottons with too wide micronaire range should not be mixed
• Cottons with too wide reflectance value(Rd) and Yellowness value(+b) should not be mixed
• immature fibre content should be minimum as it will affect dyeiing and will result in white-specks
• If automatic bale openers are used, bale laydowns should be done properly, so that different micronaire         bales and colors are getting mixed up homogeneously even if small quantity is being checked
• If manual mixing is carried out, bales should be arranged and mixed properly so that different micronaire     bales and colors are getting mixed up homogeneously even if small quantity is being chekced
• for manual mixing, the tuft size should be as low as 10 grams
• If cottons with contamination is used, the best way is to open the bales into small tufts and segregate the       contaminants. There are mills who employ around 60 to 80 persons to pick up contamination from a mixing   of 20tons.
• Japanese insist on mixing atleast 36 bales for one mixing to avoid Barre problem

BLOWROOM:
• 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%


CARDING:
• 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              Less than 30 kgs/hour             More than 30 kgs/hr

 Wire height                                  2 mm                                2 mm

 Angle of wire (degrees)                  30                                   35 to 40

 Points per sq.inch                      Around 840                         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%
• uniformity 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.

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