Drawing — Parallelisation and Levelling
topic
Drawing (draw frame) attenuates and combines 6–8 card slivers into one sliver of similar linear density, using 3-over-3 roller drafting at draft ratios of 6–8, at delivery speeds of 400–1000 m/min. Two passages are standard (breaker and finisher) with auto-leveller on the finisher (closed-loop or open-loop), correcting sliver mass variation at wavelengths of 0.5–10 m. Finisher sliver CVm% target: 2.0–3.0%; without leveller, 3.5–5.0%.
Role
Drawing auto-leveller performance is the primary control over long-term yarn count variation. Without levelling, sliver mass variation from carding propagates to ring frame output as count variation (CVcount%) and long-period evenness faults (Uster CVL%). Understanding draw frame leveller calibration and its effect on ring-spun count consistency is essential for quality engineers managing lot-to-lot count variation — a key specification in yarn sales contracts.