Determining Recovered Yarn Linear Density from Woven Fabrics
Determining recovered yarn linear density involves unraveling measured lengths, removing crimp under standardized tension, and correcting dry mass for size.
Twist Contraction Factor
Contraction Ratio
The proportional reduction in yarn length that occurs when fibers are twisted together during the spinning process. Calculating the twist contraction factor allows engineers to predict the final length of yarn that will be wound onto a bobbin. This value is expressed as a percentage of the original untwisted length.
Twist Impact
Twisting increases the density of the yarn but reduces its linear output from the spinning frame. The twist contraction factor increases as more turns per inch are inserted into the fiber assembly. High-twist crepe yarns exhibit a very high contraction, whereas low-twist yarns experience minimal shortening.
Measurement Formula
Determination involves measuring the length of a twisted yarn and then measuring its straightened length after removing the twist. The twist contraction factor is computed using the difference between these two lengths divided by the untwisted length. This measurement requires a twist tester equipped with a sensitive tension gauge.
Production Setting
Spinners use this contraction percentage to adjust the feed roll speeds on spinning frames to achieve the target yarn count. When the twist contraction factor is calculated accurately, the machine drafts the fiber roving to the correct thickness. This adjustment prevents the production of yarns that are too heavy or too thin for the intended knitting or weaving application and optimizes spindle speeds to lower energy costs.