Warp breakage after an over-sized and over-dried beam
A powerloom shed weaves 63-inch reed-space cotton shirting with 40s warp and weft, 110 ends/inch and 56 picks/inch at 220 rpm and 82% efficiency. After a new sizing lot, warp breaks rose from 4 to 14 per 100,000 picks. The sized warp has 12.5% size pick-up, 4.1% elongation, 5.0% moisture and a size-bath viscosity of 18 s by Ford cup against a standard of 12 s. The recipe is starch/PVA 70:30 and the drying cylinders are at 130°C. Weave-room RH is 62%, and sized beams have been stored for 10 days. Operators report cloudy size on the beam and brittle yarn at the back rest; drop wires show abrasion. The order is 50,000 m of 120 GSM fabric with a delay penalty. The size kitchen proposes adding more softener to the bath.
1. Calculate fabric production per loom per hour at 82% efficiency and the weft yarn consumed per hour, assuming 6% weft crimp.
Read the worked answer
Picks per minute = 220 × 0.82 = 180.4. Picks per hour = 180.4 × 60 = 10,824.
Fabric length per hour = picks per hour / picks per inch = 10,824 / 56 = 193.3 in/h = 4.91 m/h.
Weft length per hour = picks per hour × reed width × (1 + crimp) = 10,824 × 63 in × 1.06 = 722,827 in/h = 18,360 m/h.
40s Ne weft linear density = 590.5 / 40 = 14.76 tex = 14.76 g/km. Weft mass = 18.36 km × 14.76 g/km = 271 g/h.
So each loom produces about 4.9 m of 63-inch fabric per hour and consumes about 271 g of weft yarn per hour at the stated efficiency. At 14 breaks per 100,000 picks, the breakage rate is 10,824 / 100,000 × 14 = 1.52 warp breaks per loom-hour, which is high for a plain cotton shirting.
2. Diagnose the warp breakage increase. Explain why adding softener alone is not a cure.
Read the worked answer
The sizing data point to a brittle, over-penetrated and over-dried film. At 12.5% pick-up, the add-on is above the normal 8–10% range for a 40s cotton warp. The 18 s viscosity is also high, so the size sits on the surface rather than penetrating uniformly; that gives cloudy size and later flakes off at the back rest and drop wires. Drying at 130°C with only 5.0% moisture drives the film glassy and reduces elongation to 4.1%, well below the 5.5–6.5% needed for loom abrasion resistance.
Ten days of storage makes the film harder and less flexible. The 62% RH weave-room air cannot re-plasticise a badly over-dried beam quickly enough. The result is abrasion at the drop wires, brittle yarn at the back rest and a rise from 4 to 14 breaks per 100,000 picks.
Softener alone would reduce surface friction but would not correct high add-on, poor penetration or over-drying. It can also plasticise the film unevenly and cause tackiness on the beam. The cure is to reduce viscosity and add-on, lower cylinder temperature, retain 7–8% moisture and shorten beam storage.
3. The size kitchen can reduce pick-up to 9.5% and viscosity to 12 s. Calculate the size saved per 1,000 m of warp and over the 50,000 m order. State two quality checks before releasing the trial beams.
Read the worked answer
Warp ends = 110 × 63 = 6,930.
Mass of 1,000 m of unsized warp = 6,930 × 1,000 m × 14.76 g/km = 102.3 kg. At 12.5% pick-up, size = 102.3 × 0.125 = 12.8 kg per 1,000 m. At 9.5%, size = 102.3 × 0.095 = 9.7 kg. Saving = 3.1 kg per 1,000 m.
For 50,000 m, saving = 3.1 × 50 = 155 kg of size solids. This is a material saving, but the purpose is quality: the lower add-on must still protect the yarn.
Before releasing the trial beams, check: (1) sized yarn elongation at least 5.5% and moisture 7–8% across the beam width; (2) size uniformity and abrasion resistance, for example a sized-yarn abrasion test and a visual check for cloudy or flaky size. Run the trial on at least two looms against a control beam for 100,000 picks and require warp breaks at or below 6 per 100,000 picks before releasing the whole order.