Sizing Recipe Cost Reduction and Loom Efficiency Loss
A weaving mill runs 240 air-jet looms at 700 picks/min on 100% cotton poplin, 40s x 40s, 133 x 72, 63 in width. To cut sizing cost, the size recipe was changed from 70% PVA/30% modified starch to 40% PVA/60% modified starch, and size add-on was reduced from 12.0% to 9.5%. Size-box temperature is 85 C and squeeze pressure 22 kN/m. Loom-shed RH is 68%. Weaving efficiency fell from 92% to 81%, warp breakage rose from 0.8 to 2.6 per 100,000 picks, concentrated at the shedding zone, and sized-yarn abrasion resistance dropped about 30% while elongation at break fell from 5.2% to 4.1%. Sized-yarn hairiness increased. The recipe change was projected to save PKR 3.2 million per year. Fabrics are sold greige at an average contribution of PKR 45/m; the mill runs 7,200 hours per year. The customer has not yet complained, but the mill is behind schedule.
1. Quantify the production and contribution loss caused by the efficiency drop and compare it with the projected sizing saving. Then diagnose the technical cause of the warp breakage pattern.
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Production calculation At 700 picks/min and 133 picks/in, theoretical production = 700 x 60 / 133 = 315.8 in/h = 8.02 m/h per loom. At 92% efficiency: 8.02 x 0.92 = 7.38 m/h. At 81% efficiency: 8.02 x 0.81 = 6.50 m/h. Loss = 0.88 m/h per loom. For 240 looms and 7,200 h/year: 0.88 x 240 x 7,200 = 1.52 million m/year. At PKR 45/m contribution, the loss is about PKR 68.4 million/year, over 20 times the PKR 3.2 million saving. Even if only half the lost metres can be sold, the change is not economic.
Diagnosis Reducing PVA from 70% to 40% and add-on from 12.0% to 9.5% lowers film cohesion, abrasion resistance, and elongation. Hairiness rises because fibres are less encapsulated. The breakage concentration at shedding is consistent with abrasion between warp ends and heddles/reed, aggravated by lower elongation and higher tension peaks. The problem is the size film, not loom setting alone.
2. Propose a corrected sizing and loom-shed plan, with a trial protocol and measurable acceptance criteria, before the balance of the order is woven.
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Restore film strength without returning blindly to the old cost: raise PVA to 55-60% or add 10-15% acrylic binder to the starch/PVA blend; increase size add-on to 11.5-12.5%; raise size-box temperature to 90-92 C; increase squeeze pressure to 25-27 kN/m; and raise loom-shed RH to 72-75% for this poplin. Check sized-yarn elongation at break, abrasion resistance, and hairiness against the old acceptable reference.
Trial on 20 looms for 48 hours, with the same warp and pick density. Measure efficiency, warp breakage per 100,000 picks, break position, sized-yarn elongation, abrasion loss, and hairiness. Acceptance: efficiency at least 90%, warp breakage no more than 1.0 per 100,000 picks, sized-yarn elongation at least 4.8%, abrasion resistance within 10% of the old reference, and no size shedding at the droppers. If the trial passes, cascade to all looms; if not, revert to the original recipe for the remaining order and continue development offline.
3. The mill manager wants to keep the cheap recipe because the customer has not complained. Give your recommendation and the decision rule you would use.
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Recommend immediate reversion for the balance of the order. The customer has not complained because greige fabric may still meet the visual contract, but the mill is paying for the change through lost production. The decision rule is: a sizing change is acceptable only if the contribution lost through efficiency and breakage is less than the sizing saving plus any quality risk. Here the loss is roughly PKR 68 million/year against PKR 3.2 million/year saving, so the cheap recipe fails by a wide margin.
Do not wait for a customer claim. Revert, then run the corrected recipe as a controlled cost-reduction project. A cheaper recipe can be reconsidered only when a 20-loom trial shows efficiency at or above 90% and warp breakage at or below 1.0 per 100,000 picks for at least one full beam set. Keep the customer informed only if delivery is affected; otherwise correct internally and protect the schedule.