Warp breaks after a sizing change at a Bhiwandi powerloom
A powerloom unit in Bhiwandi weaves 40s combed cotton poplin with 6,000 warp ends on a 63-inch reed, running at 600 picks per minute. The quality target is a warp break rate of 1.0 per 10^5 picks; the current rate is 2.5. Sized yarn elongation has fallen from 5.5% to 4.2%, size add-on is 9%, size-box temperature is 85 °C, squeeze pressure is 18 kN/m, and the loom shed relative humidity is 55%. The sizing master proposes raising add-on to 12% and adding extra binder. The weaving master reports size patches, reed marks, and frequent warp stops near the selvedges. The buyer has already complained about small size spots visible after dyeing. The order is for 40,000 m, and only ten beams can be trialled before the full 200-beam set is sized.
1. Calculate the current and target warp breaks per loom-hour and comment on the size of the gap.
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At 600 picks per minute, one loom makes 600 × 60 = 36,000 picks per hour, which is 0.36 × 10^5 picks.
- Current rate: 2.5 × 0.36 = 0.90 warp breaks per loom-hour.
- Target rate: 1.0 × 0.36 = 0.36 warp breaks per loom-hour.
- Gap: 0.54 breaks per loom-hour, so the current rate is 2.5 times the target.
Over a 24-hour day this is about 21.6 breaks against a target of 8.6 per loom. That is a large gap, not a marginal one. It means the unit cannot solve the problem by tightening monitoring alone; the sizing and weaving conditions need a trial. Because only ten beams can be trialled before 200 are sized, the trial must be planned to test the likely causes rather than simply adding more size.
2. Evaluate the proposal to raise size add-on to 12% and add extra binder. What is the more likely diagnosis?
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Raising add-on is likely to make the problem worse. An add-on of 9% is already substantial for a 40s combed cotton warp, and the elongation has fallen from 5.5% to 4.2%. More size and more binder would build a thicker, stiffer film, not necessarily a better-penetrated one. A brittle film sheds in the loom, producing the size patches and size spots seen after dyeing, and it can increase reed marks rather than reduce breaks.
The low humidity is a strong suspect. Cotton size films need moisture to remain flexible. A loom shed at 55% RH is dry for cotton weaving; 70–80% RH is the usual aim. Dry film cracks and abrades, especially near the selvedges where the reed and droppers work hardest.
Check penetration before adding size. Use an iodine test on a yarn cross-section to see whether size has penetrated the yarn core or sits mostly on the surface. Also check squeeze pressure, size-box temperature, yarn hairiness and the size recipe. The correct trial is probably a lower add-on with better penetration, a lubricant or softener, and raised shed humidity, not 12% add-on.
3. What data should the ten-beam trial record, and what decision rule would you use before sizing the full 200-beam set?
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Record per beam: size add-on, wet and dry elongation, abrasion resistance, hairiness, moisture regain, size penetration by iodine test, size-box temperature, squeeze pressure, and loom shed RH. On the loom, record breaks per 10^5 picks, break location (selvedge, dropper, back rest), loom efficiency, and visible size spots after dyeing a trial piece.
Decision rule: accept the recipe only if the break rate is at or below 1.0 per 10^5 picks, elongation is at least about 5%, there are no visible size spots after dyeing, and efficiency has not fallen. If the trial improves elongation but not breaks, examine the loom accessories and humidity rather than adding more binder. If breaks fall but size spots remain, the recipe is not acceptable to the buyer.
Commercial discipline: do not size 200 beams on a hope. The trial is cheap compared with reprocessing 40,000 m. Record the trial conditions so the accepted recipe can be repeated, and keep a sized yarn sample from each trial beam.