Draft Ratio Calculation and Distribution
topic
Total draft (TD) = roving count (Ne) × yarn count (Ne)⁻¹, distributed as mechanical draft across zones. Break draft in the back zone (1.1–1.5) opens the roving twist for smooth drafting; main draft (15–45) performs the actual attenuation. Actual draft equals mechanical draft corrected for roller slip. Draft distribution is optimised by balancing fibre load across zones to prevent over-drafting in one zone causing irregularity.
Role
Correct draft ratio distribution is fundamental to producing on-count yarn within ±1.5% count variation (CVcount%). Count variation directly affects fabric weight consistency, which is a contractual specification in every yarn sale and fabric production agreement. Miscalculation leads to rejected lots and financial penalties.