Warp Breakage After a Sizing Change
A powerloom unit has 48 rapier looms weaving a 40s × 40s cotton poplin, 110 ends/inch, 90 picks/inch, 63-inch width. After changing the sizing recipe from a maize-starch/PVA blend to a lower-cost all-maize recipe, warp breakage rose from 1.5 to 3.8 per loom per shift. The cloth shows short warp streaks and size marks near the selvedges. Size add-on fell from 6.2% to 4.4%; size box temperature is 85°C; squeeze pressure is 2.2 kN; sizing speed is 65 m/min; sized yarn moisture regain is 6.0%. Loom shed RH is 48%, against a target of 60–65% for cotton. The size kitchen uses 4% maize starch, 1% tallow and 0.2% wetting agent, with no binder. The mill has 20 days of production committed to an export order and cannot stop all looms. A warp beam contains 6,930 ends and is 6,000 m long.
1. Rank the likely causes of the breakage increase and justify your ranking using at least three pieces of data. Is the all-maize recipe viable at 4.4% add-on?
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Ranking: first, the size recipe and add-on; second, the low weave-room RH; third, possible squeeze or size-mark problems near the selvedge.
The change from a maize/PVA blend to all-maize removed the flexible binder that gives abrasion resistance. At the same time, add-on fell from 6.2% to 4.4%, a drop of 1.8 percentage points. For a 40s poplin with 110 ends/inch and 90 picks/inch, the warp is subjected to heavy abrasion and repeated shedding, so a brittle all-maize film at low add-on is unlikely to protect it. The breakage rose from 1.5 to 3.8 per loom per shift immediately after the change, which points strongly to sizing. The RH of 48% is well below the 60–65% target for cotton, making the yarn brittle and increasing static and tension. Size marks near the selvedges suggest uneven squeeze or size migration, which can also cause local weak spots.
All-maize at 4.4% add-on is not viable for this fabric. Maize starch alone forms a brittle film with poor adhesion; the recipe needs a binder such as PVA or an acrylic size, or a modified starch, and the add-on must return to about 6.0–6.2%.
2. Calculate the additional size solids required per 6,000 m beam to return to 6.2% add-on. Show your assumptions and comment on whether size cost is the main issue.
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For 40s cotton, the linear density is 590.5 / 40 = 14.76 tex, i.e. 14.76 g/km. Beam yarn length = 6,930 ends × 6,000 m = 41,580,000 m = 41,580 km. Yarn mass = 41,580 × 14.76 / 1,000 = 613.7 kg per beam.
The add-on must rise by 6.2% − 4.4% = 1.8% of yarn mass. Additional size solids = 0.018 × 613.7 = 11.05 kg per beam.
If the size formulation costs about ₹100/kg, the extra cost is about ₹1,105 per beam, or ₹1,105 / 6,000 = ₹0.18 per metre of warp. Even if a PVA-containing size costs more than all-maize, the added size cost is small compared with the cost of warp stops, loom downtime, repair of streaks and rejection of export fabric. The cheap recipe is a false economy. The calculation assumes add-on is expressed on dry yarn mass and ignores small losses in the size box.
3. Propose a two-week recovery plan that avoids stopping all looms, and state one measurable acceptance criterion.
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Immediate action: raise the weave-room RH to 62–65% and check humidification distribution; reduce loom speed by 5–8% on the affected looms to lower warp tension while the trial runs. Sizing action: restore a binder, for example 1.5–2% PVA or an acrylic binder, or switch to a modified starch; target 6.0–6.2% add-on, size-box temperature 85–90°C, and sized-yarn moisture regain around 7–8%. Check the squeeze rolls for crown and pressure balance to remove the selvedge size marks. Run the revised recipe on one beam and six looms first, then inspect for size shedding, streaks and breakage before extending it to the rest of the order. Acceptance criterion: within 10 days, warp breakage on the trial looms should fall to 2.0 or fewer per loom per shift, with no size marks or short warp streaks, and add-on should be 6.0–6.2% at 62 ± 3% RH.