Controlling count variation in yarn
Posted: Tuesday, September 13, 2005
by Bala
http://bala.bravehost.com/Balasubramanian.html
Importance of count variability in yarn hardly needs any emphasis. Higher count variability invariably leads to higher strength variability. The weak patches in the yarn lead to frequent end break in further processing, which often reaches annoying levels leading to rejection of bobbins and cones. In latest autoconers, which have settings for rejecting bobbins with count of yarn exceeding beyond certain limits of the nominal, processing of yarns with even slightly high count variations becomes extremely difficult. Winding efficiency reaches unacceptably low levels with such yarns. Higher count variability especially of medium to long length range results in moire like appearance in fabric and increases warp way streaks and weft bars. Ring cuts and soiled ring packages is another problem with higher count CV. To overcome this, wider clearance is kept between ring diameter and full package leading to lower doff weights. With higher count variability, percentage of bobbins exceeding tolerance limits of nominal count increases, leading to sales rejections and market complaints. In shuttleless looms, problem of weft tear is encountered during weaving when count of weft changes abruptly beyond certain limits at the time of pirn change. High count variations in weft are also a cause of warp way fabric creases in processed fabrics like dyed poplins.
Location of source of count variability will be greatly facilitated if wrappings and estimate of CV from the same are based on corresponding wrapping lengths of material at different stages. Thus wrappings and CV of wrappings may be based on 5yd instead of the traditional 15 yd length at Inter. 5 yd length at Inter after drafting will be closer to 120 yd length in yarn than 15 yd length and CV estimates based on the former will be more helpful to show if ring frame is contributing to additional variation. At draw frames, CV of wrappings based on 0.5 yd length will be more useful from the same consideration. Estimation of CV of such lengths can be obtained from modern Evenness testers like Uster tester 3.
Estimation of variability by assessment of the percentage of yarn which is beyond a certain weight has several merits. For example, one of the conditions stipulated in purchase of yarn is that not more than 5% of bobbins will have a count beyond mean ± specified percentage. Supplies that do not meet this specification are liable to rejection.
Example Count = 30s, Buyer stipulates that only 5% of bobbins should fall outside 30 +/- 1.5
MILL A - CV of Count = 1.7%, Standard Deviation = 0.51, % bobbins falling outside 30 +/- 1.5 = 2.7
MILL B - CV of Count = 2.5%, Standard Deviation = 0.75, % bobbins falling outside 30 +/- 1.5 = 5
MILL C - CV of Count = 3%, Standard Deviation = 0.9, % bobbins falling outside 30 +/- 1.5 = 10
MILL D - CV of Count = 5%, Standard Deviation = 1.5, % bobbins falling outside 30 +/- 1.5 = 31.7
In Table 1 % of bobbins with count outside +/- 1.5 of 30s is shown for mills with different levels of count variation. As count CV increases, % of bobbins falling beyond +/- 1.5 of mean increases. This shows that only mills with low count variation will be able to fulfill rigorous standards set by highly quality conscious buyers.
| Count CV% | % of bobbins exceeding +/- 1.5 of 30s |
|---|---|
| 1.7 | 2.7 |
| 2.5 | 5 |
| 3 | 10 |
| 5 | 31.7 |
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