Strength at “Theoretically Null Twist” of Acrylic and Polyester/Cotton Rotor Spun Yarns: Application to Prediction of “Machine Twist”

Acrylic staple rotor spun yarns (172) obtained from a BD 200 rotor machine fitted with twelve different spinning heads that combined four different rotors and three different yarn extraction nozzles were tested for strength at a theoretically null twist. A high correlation existed between the theoretically null twist strength and the apparent loss of twist or residual twist. We propose a method for assessing the total twist or machine twist of the yarn from the apparent yarn twist measured in a twist tester and from the yarn strength at a theoretically null twist. Tests on fourteen polyester/cotton yarns obtained from a RU 11 machine seem to indicate that this method of assessment may be applied to other materials and other rotor machines.