Yarn Evenness and Imperfection Testing
category
Yarn evenness testing measures mass variation along yarn length using capacitive or optical sensors at 100–400 m/min test speed, providing CV% of mass variation, thin and thick place counts per km, nep counts per km, and hairiness index — the most comprehensive and commercially significant group of quality parameters in spun yarn testing. USTER Tester 6 (capacitive measurement, sensing slot 8 mm × 1 mm, 10–400 m/min test speed, 1 km test length standard) is the globally dominant evenness instrument used for USTER Statistics benchmarking — capacitive signal proportional to fibre mass in sensing slot, sampling frequency 4,000 Hz at 400 m/min providing 600 measurements/m. Premier Tenso LAB (optical sensor alternative: LED source, photodetector, 200 m/min, CV% measurement, imperfection count) provides cross-check capability. Key output parameters: CV% of mass variation (global evenness, USTER benchmark for Ne 30 ring cotton: 50th percentile CV% = 14.8%, 25th percentile = 13.5%, 5th percentile = 12.0%); thin places per km (−50% threshold: 50th percentile = 40/km, 5th percentile = 4/km); thick places per km (+50% threshold: 50th percentile = 120/km, 5th percentile = 18/km); neps per km (+200% threshold: 50th percentile = 180/km, 5th percentile = 55/km). CVm% correlation with fabric quality: ring-spun Ne 30 cotton CVm% 13.0% produces woven fabric with 95th percentile appearance grade; CVm% 17.0% produces 50th percentile grade — 4 percentage point CVm% improvement equals one grade step in fabric appearance.
Role
Yarn evenness testing is the single most commercially important quality test in spinning mill production — Uster CV%, thin places, and thick places measured on the evenness tester predict with high statistical confidence (R² 0.85–0.95) the woven fabric horizontal bar defect rate and knitted fabric pilling grade that determine whether fabric meets retail buyer acceptance specifications or requires renegotiation and price penalty.