Brittle sized beam in Barpeta
A small weaving unit in Barpeta is preparing a warp of 1,440 ends, 40 m long, in 2/60s cotton on a sectional warping drum. The weaver mixes the size paste at 4% concentration instead of the 6% in the recipe, because the paste "looks thick enough"; dries the beam in the sun for two days until it is bone dry; and winds with a wooden brake that slips under tension. On the loom, ends start breaking within the first 3 m, mainly at the selvedges and in the region wound last. The broken ends show a dry, powdery, brittle film, and there are hairy patches where fibres have abraded. Twelve beams are needed for a 480 m order, and the store holds 25 kg of sizing starch. The weaver asks whether to add more starch or more oil to the paste.
1. Calculate the dry size required per beam and for all twelve beams. Is 25 kg of starch sufficient?
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Warp weight. 2/60s cotton = Ne 30 equivalent. Total yarn length = 1,440 × 40 = 57,600 m. Using metres per gram = 1.6933 × Ne:
- weight = 57,600 / (1.6933 × 30) = 57,600 / 50.8 = 1,134 g of dry warp per beam.
Size at 8% add-on: 1,134 × 0.08 = 90.7 g of dry size per beam.
Paste at 6% concentration: 90.7 / 0.06 = 1,512 g of paste per beam. With 10% for pick-up and leftovers, about 1.7 kg of paste per beam.
Twelve beams: 12 × 90.7 = 1,088 g ≈ 1.09 kg of dry size, i.e. about 18 kg of 6% paste plus allowance.
The 25 kg of starch in stock is more than enough. Quantity is not the problem - concentration control, drying and tension are. The answer to the weaver is: neither more starch nor more oil; correct the concentration and the process.
2. Diagnose the brittle film and the pattern of end breaks. Rank the causes in order of importance.
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The break pattern is the clue. Breaks at the selvedge plus breaks concentrated where the beam was wound last point to a film and tension problem, not to bad yarn.
- Under-sizing. A 4% paste instead of 6% delivers roughly two-thirds of the intended add-on - about 5% instead of 8%. The film is too thin to protect the yarn from abrasion at the heald and reed, hence the hairy patches.
- Over-drying in the sun. Bone-dry size film loses its flexibility and cracks; the powdery, brittle fragments on the broken ends are characteristic. Cotton should leave sizing at near its natural regain, not oven-dry.
- Slipping brake. Uneven beam tension leaves slack and tight ends. Slack ends abrade and fail first; the last-wound region also suffers because it dried hardest and was wound at inconsistent tension.
- Poor penetration. If the paste was cold or lumpy, size sits on the surface, flakes off and does not bind the fibres.
- Selvedge strain. Selvedge ends take the highest tension at the flanges and fail first when the film is weak.
Adding oil may plasticise the film but will not repair under-sizing; adding starch to a 4% paste without weighing invites lumps and shedding faults.
3. Set out the corrected sizing and warping procedure, with the checks the unit should record for each beam.
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Corrected procedure
- Weigh, don't judge by eye. Mix size to exactly 6% by weight of dry starch, cook at 70–80 °C until the paste is clear and free of lumps, and add a softener/binder only as per the recipe.
- Control add-on. Dip and squeeze (nip) uniformly; verify by weighing a 1 m length of sized yarn against the unsized length - target 8% ± 1%.
- Dry under shade or controlled warmth, not two days of direct sun, to a flexible film. Check by feel and, if available, a moisture meter; cotton should stay near 8% regain.
- Fix the brake. Service or replace the slipping brake and use a tension guide so the beam winds firm and even from flange to flange; taper tension slightly at the selvedges.
- Sectional warping discipline: equal ends per section, identical tension per section, lease sticks in place, and the drum tension checked before transfer.
Record per beam: lot number, yarn count, ends, length, paste concentration, wet pick-up, measured add-on, drying time, beam tension, and breaks per 10,000 ends during weaving. That record is how the unit learns which variable caused a fault - and it is what a buyer's audit will ask for.