Combed Yarn Quality Crisis After Sliver Change
A ring-spinning mill produces 30 Ne combed cotton yarn for a knit fabric customer. Over three days the carded neps in the comber feed sliver rose from 28 to 61 per gram, and the comber noil extraction was reduced from 18% to 14% to improve yarn realisation. Simultaneously, the yarn's Uster CVm rose from 11.2% to 13.6%, thin places (-50%) rose from 18 to 54 per km, and the knitting department reports frequent needle breaks and fabric holes. The spinning master wants to compensate by increasing twist from 3.9 to 4.2 twist multiplier to make the yarn 'stronger'. The customer's specification allows CVm of 12.0% maximum and thin places of 30 per km maximum. The mill has one week of delivery buffer.
1. Diagnose the most probable root cause of the quality deterioration and evaluate whether increasing twist will solve the problem.
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The simultaneous jump in neps and thin places points to the fibre-preparation stage rather than spinning. Reducing noil extraction from 18% to 14% leaves more short fibre and neps in the combed sliver, so the comber is no longer performing its core function of short-fibre removal. Short fibres cluster and create thin places when drafting, and residual neps pass through into yarn. The rise from 28 to 61 neps/g in feed sliver is a direct fingerprint of inadequate combing.
Increasing twist cannot fix this. Twist improves yarn tenacity by increasing fibre-to-fibre friction, but it does not remove short fibre, does not eliminate thin places, and does not reduce neps. In fact higher twist on a neppy yarn can worsen fabric appearance by locking neps into the structure and increasing the risk of kink and snarling. Twist multiplier above 4.0 also reduces production and may push the yarn outside the customer's hand-feel requirements. The correct response is to restore noil extraction to at least 18% and verify combing efficiency before touching twist.
2. Recommend a corrective and verification plan within the one-week buffer, including what to measure and in what order.
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Step 1: Restore the comber to 18% noil and re-check the combing efficiency and nep removal efficiency. Step 2: Test the comber sliver for neps per gram and short-fibre content (AFIS or similar) to confirm the feed is back within the historical baseline of about 28 neps/g. Step 3: Spin trial bobbins and test Uster CVm, thin places (-50%), and neps (+200%) against the customer limits of 12.0% CVm and 30 thin places/km. Step 4: Only after yarn data is acceptable, run a knitting trial of at least 200 kg to confirm needle breaks and fabric holes have stopped.
Do not release the three days of suspect yarn to the customer; segregate and either sell as a lower grade or re-process if feasible. Update the realisation calculation so that noil reduction is not treated as a free gain - the true cost of the 4% noil saving is the rejected yarn and the customer claim.
3. Explain how the mill should justify the noil decision economically to management.
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Management sees a 4% noil reduction as a 4% raw-material saving. The mill should present a full cost comparison: the value of recovered noil versus the cost of rejected yarn, knitting downtime, fabric seconds, and potential claim. If, for example, 3 days of output at 1,200 kg/day equals 3,600 kg of suspect yarn, and even half is downgraded at a loss of, say, 40 currency units per kg, that is 72,000 units - likely far exceeding the noil value. The argument is that noil is a controlled, priced loss, while quality failure is an uncontrolled loss with reputational cost. Recommend that any change to noil extraction be trialled on a small lot with full testing before production release.