COMBED YARN FOR KNITTING
Yarn quality requirement is changing everyday. Quality requirement is different for different end uses and it is different for different customers.
It is easy to make the highest quality yarn just for the sake of achieving the best yarn results. But it is difficult to produce a good quality yarn with a minimum deviations. Very high fluctuation in yarn quality is an EVIL for any enduse. Some times it is better to keep same level of yarn quality ( around 25% USTER STANDARDS) by strict quality control than achieving 5% USTER STANDARD but without consistency. Consistent quality will be very much appreciated by the clients.
"I often say that when you can measure what you are speaking about and express it in numbers, you know something about it. But when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the stage of science, whatever the matter may be" (attributed to Lord Kelvin, 1883).
Hence it is advisable to fix the standards for different yarn characteristics for cotton spun yarns for different end uses. The following table gives the quality requirement for KNITTING YARNS.
Table: Quality Standard for4 Ringframe Cop
|Yarn Characteristic||required value for 30S Combed||other combed counts|
|Average count||30 ( 29.6 to 30.4)||nominal count plus or minus 1.3%|
|Count C.V%||less than 1.5||less than 1.5%|
|Twist Multiplier||3.5 to 3.6||3.5 to 3.6|
|TPI C.V%||less than 2.5||less than 2.5%|
|U%||9.2 to 9.8||5 to 10 % Uster Stat . value|
|-50% thin place / 1000m||less than 4||5 to 10 % Uster Stat . value|
|-30% thin place / 1000m||less than 650||5 to 10 % Uster Stat . value|
|+50% thick place / 1000 m||less than 30||5 to 10 % Uster Stat . value|
|+200 Neps / 1000m||less than 50||5 to 10 % Uster Stat . value|
|Total Imperfection / 1000 m||less than 85||5 to 10 % Uster Stat . value|
|RKM ( tenacity) gms /tex||more than 16.5||more than 16.5|
|RKM C.V%||less than 7.5 %||5 to 10 % Uster Stat . value|
|Elongation %||more than 5.5||more than 5.5|
|Hairiness H||4.0 to 4.5||< 50% value of Uster Statistics|
|Hairiness Standard Deviation||less than 1.5||25% Uster stat value|
|Objectionable classimat faults(both short and long)||less than 1 per 100 km||less than 1 per 100 km|
|Total classimat faults||less than 150||5 to 10 % Uster Stat . value|
|H1- thin faults||less than 5 per 100 km||5 to 10 % Uster Stat . value|
|shade variation on cones in UV lamp||no shade variation||no shade variaition|
GUIDE LINES TO ACHIEVE THE ABOVE:
Raw material should be selected properly. There is a direct relationship between certain quality characteristics of the fibre and those of the yarn. 70 to 80 % of basic yarn quality is decided by cotton.
- Short fibre content is very important for yarn quality. Uniformity Ratio should be more than 47%. Fibres of length 4 to 5 mm will be lost in porcessing (as waste and fly). Fibres upto 12 to 15mm do not contribute to strength but only to fullness of the yarn. Only the fibres above these lengths produce the other positive characteristics in the yarn.
- 2.5% span length should be more than 28 mm. Span length affects yarn strength and yarn uniformity. End breakage rate also depends upon the fibre length. Longer the fibre, lower the end breakage rate, better the yarn quality.
- Average Microaire should be between 3.8 to 4.3 for counts 24s to 40s (Ne). It can be between 4.1 to 4.7 for counts coarser than 24s.
- If the micronaire is coarse, the number of fibres in the yarn cross section will be less. This always results in lower strength and lower elongation. But it is easy to process coarse micronaire fibres in blowroom and cards.
- Nepping tendency is less for coarse micronaire fibres. On the contrary, spinnability (in both speed frame and ringframe) is not good with coarser micronaire fibres.
- U% is affected by Micronaire. Coarser the micronaire, higher the U%. Coarser the fibre , higher the end breakage rate in spinning.
- Uster Thin place( -30%) in the yarn vary depending upon the fibre micronaire. Lower the micronaire, lower the thin places vice versa
- Strength of the fibre should be more than 23 grams/tex
- Elongation of the fibre should be more than 6%.
- No of neps per gram should be less than 250
- should not mix two cottons with wide Reflectance value (Rd value) and yellow ness value (+b)
- sticky cotton should not be used. If cotton is sticky, it is better to reduce the percentage of sticky cotton in the mixing. Low humidity and high temperature should be maintained in the departments
- cottons with less contamination should be used (cottons like Andy, SJV, alto etc)
- 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
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