Grip Strength
Mechanical grip in composite yarns prevents the external staple fibers from sliding along the central elastic core. In core-spun yarns, the sheath fiber clamping force is a critical quality factor that prevents core exposure and yarn stripping during downstream weaving or knitting. It depends on the yarn twist, the coefficient of friction of the fiber blend, and the elastane draft ratio.
If the force is too low, the sheath can bunch up and form thick slubs, leaving the bare elastic core exposed to mechanical abrasion.
Twist Influence
Increasing the twist multiplier on the spinning frame directly enhances the sheath fiber clamping force by squeezing the sheath fibers more tightly against the core. However, excessive twist can make the yarn too harsh and reduce the production speed. Spinners must find the optimal twist for each fiber blend.
Processing Failure
Low clamping force leads to yarn failure on high-speed weaving looms. The yarn experiences high tension and abrasion as it passes through the heald eyes and reed. Under these conditions, the sheath can slide back and cause yarn breaks that stop the loom.
Laboratory Assessment
Yarn friction testers measure the force required to slide the sheath relative to the core. This test provides a reliable measure of the sheath fiber clamping force before the yarn is sent to the weaving shed. It helps prevent costly fabric defect claims from garment manufacturers.
