Ends-Down Spike After a Roving Hank Change on 40 Ne Cotton

Draft = yarn hank / roving hank. Before: 40/1.00 = 40. After: 40/0.85 = 47.1. The total draft has increased by 7.1, or 17.6%. In tex terms, 1.00 Ne roving is 590.5 tex and 0.85 Ne roving is 694.7 tex; the front zone must now attenuate a heavier roving to the same 14.8 tex yarn. If the break draft, spacer, roller setting and top-roller pressure were left as they were, the drafting zone is being asked to control more fibres with the same geometry. Floating fibres increase, thick and thin places appear, and breaks concentrate at the front roller and spinning triangle, which is exactly the reported pattern. The slubs and long thin places in winding are consistent with a drafting wave, not with a random roving fault.

The RH fall from 55% to 45% compounds the problem. At low RH, cotton fibres are stiffer, static increases, and fibre-to-fibre cohesion in the roving and the spinning triangle falls. The yarn has less elongation at break, fly increases, and the spinning triangle is less stable. Therefore the roving change and the dry atmosphere together explain a rise from 35 to 110 ends down per 1,000 spindle-hours. Rejecting the roving lot is not justified unless its count CV, neps or thick-place count is also out of specification; the draft and climate must be corrected first.

Production scales roughly with spindle speed: 14,000/16,500 = 0.848, a loss of 15.2% before any efficiency gain. Twist increases from 25.3 to 27.8 tpi. The twist multiplier changes from 25.3/√40 = 4.00 to 27.8/√40 = 4.40. A 4.40 TM is high for a knitting yarn; it will raise tenacity somewhat but reduce elongation, increase yarn torque and fabric spirality, and make the yarn harsher. It does not correct the increased drafting wave. It may also raise spinning tension and traveller friction; with the same 3/0 traveller, the yarn may break more often at the traveller or balloon rather than fewer times at the triangle.

Slowing the frame by 15.2% may reduce ends down by lowering centrifugal force and traveller speed, but it is an expensive way to buy stability and will not remove the root cause. A 15% speed loss on a frame is a direct 15% production loss, and the mill will still have poor yarn quality. My assessment is: reject both proposals as permanent fixes. Use a temporary speed reduction only as a containment measure while the draft distribution and humidity are corrected; do not add 10% twist to a knitting yarn without a knitting trial.

First, restore the roving to 0.95–1.00 Ne or re-set the draft distribution for 0.85 Ne: check break draft (typically 1.15–1.25), main draft, spacer size, roller gauge and top-roller pressure. The spacer must match the yarn count, not the roving hank. Second, restore RH to 52–55% at 27–30°C with adequate humidification; low RH is a controllable variable, not a seasonal excuse. Third, keep 15,500 rpm as an intermediate speed, not 16,500 rpm, and check spinning tension before changing the traveller. If tension is low, a slightly heavier traveller may stabilize the balloon; if tension is high, a lighter traveller may be needed. Do not change traveller and twist at the same time.

Run a 24-spindle, 8-hour trial on at least two frames. Record ends down per 1,000 spindle-hours, classimat faults, yarn CVm, IPI thick places (+50%), thin places (−50%), neps, tenacity, elongation and hairiness. Accept the trial only if ends down is ≤50 per 1,000 spindle-hours, IPI values are within 25% of the original baseline, tenacity is no more than 5% below baseline, and CVm is no more than 0.5 points above baseline. If these are met, ramp speed in 500 rpm steps and re-test. If not, examine roving CV and fibre maturity before blaming the roving lot.