Mechanisms of Yarn Twist Blockage

Yarn twist blocking occurs when a yarn slides over a yarn guide or other machine part. This paper reviews previous investigations on twist blockage, the influence of yarn and guide conditions, and especially twist blocking mechanisms. The twist block ing mechanisms so far suggested are all based on a continuum yam model—a yarn treated as a flexible and laterally deformable cylindrical body. The validity and draw backs of these mechanisms are discussed. A further mechanism based on the continuum yarn model—twist blocking due to biased normal pressure distribution across the yarn—is proposed, and yarn twist blocking phenomena are then re-examined by treat ing the yarn as an array of mobile fibers. The yam-to-guide frictional force pushes the fibers in front of the guide to increase their helix angles, and pulls the fibers behind the guide to decrease their helix angles. The new mechanism is put to the test by comparing predicted twist blockage with previous observations, and is found to offer satisfactory interpretations.