Effect of Different Let-off Mechanisms on Fabric Formation and Dimension of Fabric in the Loom

Abstract

This paper presents an analysis of the crimp-making forces and the forces required to locate the picks in their proper positions within the cloth-fell region at the moment of beat-up and after beat-up. These forces and certain factors inherent in the process of fabric formation affect the dimensions of a particular fabric. The factors considered in this paper are closed shed warp tension, warp tension at the moment of beat-up, weaving resistance, and the effect of these on the dimensions of fabric produced in a Hattersley loom fitted with semi-positive and WIRA/Poole fully positive let-off devices. The uniformity of the fabric dimensions is discussed with respect to the warp and weft thread spacings obtained in the loom state using the two let-off mechanisms. The effect of weft unwinding tension is also considered. There is little to choose between the two let-off systems when considering the control of fabric dimensions: both systems produce irregularities in the dimensions of the fabric. The effect of warp tension changes is more critical when weaving with the WIRA/Poole roller than with the Hattersley semi-positive let-off device. The findings clearly demonstrate the influence of the warp elastic constant on the dynamic forces and, finally, on the dimensions of the fabric. There is no significant effect of changes in the weft tension on the forces and the fabric dimensions.