Fabric Formation (Weaving, Knitting, Nonwoven)
Fabric Formation covers weaving, knitting and nonwoven engineering. The exam tests fabric geometry, cover, areal mass, structure-property relationships and the effect of machine settings.
Core concepts
- Woven fabric is formed by interlacing warp and weft; the loom cycle is shedding, picking and beating. Crimp interchange affects handle and mass.
- Knitted fabric is built from loops; wales are columns, courses are rows, and gauge is needles per unit width.
- Nonwoven webs are formed by carding, spunlaying or wetlaying, then bonded mechanically, thermally or chemically.
- Fabric mass depends on yarn linear density, thread density and crimp; cover factor describes tightness, not mass.
- Air-jet, rapier, projectile and water-jet looms differ in insertion rate and yarn quality demands.
Worked example
A plain woven fabric has 20 ends/cm and 18 picks/cm, both 30 tex, with 5% warp crimp and 3% weft crimp. Uncrimped warp mass = ends/cm × tex/10 = 20 × 30/10 = 60 g/m2; with crimp, multiply by 1.05 = 63 g/m2. Weft = 18 × 30/10 = 54; × 1.03 = 55.6 g/m2. Total ≈ 118.6 g/m2. Ignoring crimp underestimates mass.
Traps
- Confusing cover factor with areal mass.
- Using yarn diameter instead of tex in mass calculations.
- Forgetting crimp and finishing shrinkage.
- Confusing wales with courses, or gauge with machine width.