The crimp in a yarn is defined as the mean difference between the actual length of any yarn and its apparent length in the fabric after weaving. It is usually expressed as a percentage of the apparent length of the yarn in the fabric.
Determination of the crimp of yarn is carried out by marking a known length on the fabric, removing the marked yarn in such a manner that it does not loose its twist, holding it between two grips at the marked points, and slowly extending it till it is subjected to a specified straightening tension. The increase in length of the yarn is determined and expressed as a percentage of marked length to obtain the value of crimp.
The Crimp Tester is designed to determine the crimp of yarns taken out of fabrics. One end of the yarn is held in a pivoted loading grip on which the desired tension load is applied by means of a sliding weight acting on a lever arm, while the other end is held in a movable grip which is mounted on a screw and can move along the direction of the yarn, stretching it in the process. The distance moved through by this grip gives the extension of the yarn, and can be measured on a scale fixed by the side of the grip assembly.
IS 3442 - 1966 : Method for Determination of Crimp and Count of Yarn Removed from Fabrics