Distribution of twist along the threadline in a fluid-jet, false-twist system

A false-twist system uses a false twist process that is designed to give texture to a yarn. The process involves twisting a yarn at a fixed rate and then heating the yarn followed by rapid cooling. The twisting and heating relaxes the stresses built up in the twisting process, but subsequent cooling forces the yarn into new stress patterns that cause the yarn to kink, giving it texture. False twist theory is well-known and given with equations in this report. However the theory predicts that there will be no twist applied downstream of the twister. In practice twist has been observed. Experiments here confirm that simple twist theory is incomplete, since downstream twist has been observed. Results indicate that an upstream twist is formed that passes through the twister and re-appears downstream. The authors also demonstrate that a false twist system with no moving parts can be designed.