Warp Preparation and Sizing
This domain covers the warp route from winding and warping through sizing, drawing-in and tying-in, with emphasis on size add-on, yarn strength and size machine control.
Core rules
- Winding removes faults and builds a stable package. Warping transfers ends to a beam with uniform tension and correct end count.
- Sizing coats and penetrates warp yarns to reduce hairiness and abrasion, improving weaveability. Size recipes use starch, PVA, CMC, binders, waxes and lubricants.
- Size add-on or size pick-up is the dry size mass as a percentage of dry unsized yarn mass. It must be calculated on an oven-dry basis when regain differs.
- Sizing machine stages: size box, squeeze rolls, drying cylinders, lease rods, headstock and beam winding. Squeeze pressure and size concentration control add-on; drying controls elongation and size film quality.
- Over-sizing causes brittle yarn and shedding problems; under-sizing causes hairiness, warp breaks and reed entanglements.
- Drawing-in threads ends through droppers, healds and reed. Tying-in joins a new warp to the old warp to reduce style-change time.
Worked example
Oven-dry unsized warp mass = 100 g. Oven-dry sized mass = 120 g. Size add-on = (120 - 100) / 100 × 100 = 20%. If the sized sample were 120 g at 10% regain, its dry mass would be 120 / 1.10 = 109.09 g, giving 9.09% add-on against 100 g dry unsized yarn, not 20%.
Traps
- Calculating add-on on as-is mass without regain correction.
- Confusing size concentration in the box with add-on on yarn.
- Assuming more size always improves weaveability.
- Ignoring squeeze-roll pressure and drying effect on elongation.
- Mixing warp and weft preparation routes.