Textile Testing and Quality Control
The exam tests standard test conditions, the correct instrument for each property, how test results are expressed, and simple quality-control arithmetic such as count, CSP and coefficient of variation. Statistical quality control terms - control charts, AQL, 4-point grading - are also fair game.
Standard conditions and sampling
- Conditioning: 65 ± 2% relative humidity and 20 ± 2 °C (27 ± 2 °C in tropical practice), with preconditioning and adequate relaxation time before testing.
- Sampling must be random and zone-wise across the lot; test specimens are taken from different positions to capture variation.
Tests to know
- Fibre: micronaire (fineness with maturity), staple length, single-fibre or bundle strength.
- Yarn: count by wrap reel or skein (840 yd = 1 lea = 1 lb for Ne), lea strength, count-strength product, evenness by capacitive evenness tester giving CV% and thin/thick/neps per 1000 m, twist by untwist–retwist.
- Fabric: strip and grab tensile, Elmendorf tear, bursting by diaphragm or ball, Martindale abrasion and pilling, crease recovery angle, dimensional stability after washing, GSM, EPI/PPI, colour fastness to wash, light, rubbing and perspiration.
Worked example
A 120-yard lea of 40s Ne cotton breaks at 80 lb. CSP = lea strength (lb) × count (Ne) = 80 × 40 = 3200. Check the count: if 14.8 tex were given instead, Ne = 590.5 ÷ 14.8 ≈ 40. The lea is one-tenth of 840 yd, so the strength is a lea value, not a single-thread value.
QC tools
- Mean and range control charts for count and strength; specification limits separate from control limits.
- AQL sampling for lot acceptance; 4-point system for grading fabric defects per 100 square yards.
Traps
- Calculating CSP with tex instead of Ne.
- Treating a 120-yard lea as 840 yards.
- Testing without conditioning, or reporting CV as a percentage of the wrong mean.