Abstract

The tensile properties of spun yarn are accepted as one of the most important parameters for assessment of yarn quality. The tensile properties decide the performance of post spinning operations; warping, weaving and knitting; hence its accurate technical evaluation carries much importance in industrial applications. An important aspect of dynamic tensile testing of spun yarns is the possibility of predicting the performance of yarn in subsequent processes. Continuous tensile testing of spun yarn involves transporting the yarn under constant tension at constant output speed. Thus, in continuous testing every inch or millimeter of yarn is tested to generate true elongation of yarn at specific dynamic tension & speed condition, and the tensile characteristics are continuously assessed. Dynamic tensile properties measured by continuous testing simulate actual manufacturing conditions more closely than the static tensile testing.

Keywords: Constant tension transport (CTT), dynamic yarn strength, lint loss, spun yarn, yarn friction

Introduction

Standard measurement of yarn strength is executed on a gauge length of 500mm. A clamped yarn breaks in its weakest place according to the so-called principle of the weakest link and this strength value is assigned to the whole length. As the test sample is gripped at the two ends and maintain that static state during the testing process, the evaluated tensile properties are often treated as static tensile properties and the strength measured by single thread tensile test method is referred to as static yarn strength. Standard evaluation is the result of a measured strength file of the weakest links, while the strength of the other places situated on clamping lengths is not measured. The basic characteristics of distribution (average value, standard deviation and coefficient of variation) of the measured values are as a rule calculated but the order of the measured values and the relations between these values and the length of links are not usually examined.

An important aspect of dynamic tensile testing of spun yarns is the possibility of predicting the performance of yarn in subsequent processes. Researchers have experimentally determined that the static yarn strength measured at 500mm length is more appropriate to simulate the mechanical properties of fabrics and cannot accurately predict the running behaviour of yarn on subsequent machines; warping, weaving and knitting. Continuous tensile testing of spun yarn involves transporting the yarn under constant tension at constant output speed. Thus, in continuous testing every inch or millimeter of yarn is tested to generate true elongation of yarn at specific dynamic tension & speed condition, and the tensile characteristics are continuously assessed. Thus, dynamic tensile properties measured by continuous testing simulate actual manufacturing conditions more closely than the static tensile testing. Dynamic yarn strength is the maximum tension level under which the yarn is transported without any break for a length of 200m, at a speed of 40m/min. The measured extension at this maximum tension level is considered as the dynamic extension.

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About the Authors

B. R. Das is associated with the Department of Textile Technology, Indian Institute of Technology, New Delhi, India and S. Hati is with Utkal University of Culture, Bhubaneswar, Orissa, India.