Sliver Deformation
Periodic thickness variations arising during the draw-frame stage of yarn preparation stem from the uncontrolled movement of short fibers between roller nips. This drafting wave irregularity appears as a cyclical variation in the linear density of the sliver, roving, or spun yarn. It occurs because fibers shorter than the roller setting are not gripped by either roller simultaneously, leading to cluster-like movements that create thick and thin zones.
Analysis Pattern
Spectrogram analysis of yarn running through an electronic tester displays a characteristic hill-like curve that denotes this specific defect. A drafting wave irregularity produces a wave pattern that repeats over a length of several times the average fiber length. This periodic variation increases the overall coefficient of variation of the yarn.
Machine Tuning
Optimizing the pressure on the top drafting rollers and adjusting the roller settings to suit the fiber length distribution reduces this defect. Eliminating drafting wave irregularity is critical for producing yarn with high break-strength consistency. This adjustment reduces loom stoppages during weaving.
Fabric Impact
Uneven yarn containing these periodic thick and thin spots produces a cloudy appearance in the woven or knitted fabric. When the drafting wave irregularity is not controlled, the finished cloth exhibits horizontal bands that become highly visible after the dyeing process. This leads to commercial rejections by garment makers.
