Wool Staple Strength and Length Testing
topic
Wool staple strength (SS, N/ktex) and staple length (SL, mm) are measured by the Staple Breaker instrument (IWTO-30) or OFDA2000 (BSC Electronics, IWTO-47 variant) clamping 100+ individual wool staples at 30 mm jaw separation and applying tensile force to break — SS = breaking force (N) / staple linear density (ktex), SL = measured distance between crimp crests. SS classification: strong >35 N/ktex (processing loss <10%, first quality); sound 30–35 N/ktex; mid-staple tender 20–30 N/ktex (10–20% processing loss, second quality); tender <20 N/ktex (>20% processing loss, severe card breakage — must be blended or processed at reduced card speed). Position of break (POB%, IWTO-30): tip break (weathering damage at fibre tip, 0–33% from tip), mid-staple break (nutritional stress during growth — most damaging, 33–66%), or base break (recent nutritional stress, 66–100% from tip). Mid-staple tender wool causes 2–3× higher card breakage and 15–25% more noil at combing, directly raising processing cost by $0.30–0.80/kg clean. OFDA2000 simultaneously measures MFD along staple length (5 mm intervals), identifying diameter minima correlated with break position and strength. Staple length (SL 65–120 mm for Merino apparel wool, >120 mm for crossbred carpet wool) determines worsted spinning count potential: maximum achievable yarn count Nm ≈ SL (mm) / 3.5 for ring spinning.
Role
Wool staple strength testing predicts processing performance and yield loss in worsted spinning — SS below 30 N/ktex directly triggers tender wool penalties at auction of $1–3/kg clean and requires mill process adjustments (reduced card speed, higher combing noil) that increase processing cost by $0.30–0.80/kg, making staple strength the second most commercially significant wool fibre test after fibre diameter.