The Roving-Space Sweet Spot in Siro-Spun Ring Spinning

Siro-spun ring spinning produces a two-strand twisted yarn by feeding two roving’s simultaneously through a single drafting system. The roving space d — the centre-to-centre separation at the front-roller nip — is the single most influential geometric variable unique to this process: it governs the spinning triangle geometry and thereby affects all twelve measurable yarn quality parameters. Since these twelve parameters do not all reach their optimum at the same d, this constitutes a genuine multi-objective optimisation problem. This article presents a complete, self-contained physical and engineering framework derived from first principles. The central original contribution is the replacement of conventional fibre-length-based estimates of the spinning triangle height L with a rigorous machine-state derivation: L = Cₘₐₕₕ × (1000/TPM), where TPM is twists per metre and Cₘₐₕₕ is a dimensionless machine calibration constant determined by a single direct measurement on the running frame. This yields the generalised sweet-spot equation d* = (1800 × Cₘₐₕₕ × tan(θ_max)) / TPM, valid across fibre types, yarn counts, and machine geometries without any fibre staple length input. A four-group mechanistic taxonomy classifies all twelve quality parameters, a Harrington desirability framework identifies the composite optimum, and a DMAIC control plan with EWMA charting closes the loop for production.