Warp and Weft Crimp Exchange Mechanics in High Density Weaving
Warp and weft crimp exchange in high-density weaving shifts structural waviness across processing, dictating finished sett, shrinkage, and air permeability.
Yarn Packing Coefficient
Density Coefficient
The ratio of the volume occupied by solid fibers to the total volume of the yarn provides a direct measure of the yarn’s internal density. Utilizing the yarn packing coefficient, textile designers can estimate the air permeability and thermal resistance of the resulting fabric structure. This metric ranges from zero for completely open space to a theoretical maximum of one for a solid rod of polymer.
Twist Parameter
Yarn twist is the primary factor that determines the density of the fiber packing within the yarn core. An increase in twist raises the yarn packing coefficient by pulling the outer fibers closer to the center, which decreases the yarn diameter. However, excessive twist eventually decreases the coefficient as the fibers buckle.
This occurs at very high twist levels.
Quality Measurement
Optical cross-section analysis and liquid displacement methods are used to determine the actual volume occupied by the fibers. Comparing the measured yarn packing coefficient to theoretical models helps spinners optimize the twist multiplier for specific fabric applications. Quality audits check this value to ensure consistency across different yarn lots.
Consistency ensures uniform dyeing.
Spinning Limit
Very low coefficients yield soft, bulky yarns that are prone to piling and shedding during subsequent knitting or weaving processes. When the yarn packing coefficient falls below a critical threshold, the lack of fiber-to-fiber friction leads to yarn slippage and weak spots. Spun yarns must maintain a balance between a high coefficient for strength and a low coefficient for softness.
The optimal value is determined by the final application of the fabric, with shirtings requiring higher coefficients than hosiery. Spun yarns require precise adjustment of the twist to hit this balance.