Abstract


The tensile properties of spun yarn are accepted as one ofthe most important parameters for assessment of yarn quality. The tensileproperties decide the performance of post spinning operations; warping, weavingand knitting; hence its accurate technical evaluation carries much importancein industrial applications. An important aspect of dynamic tensile testing ofspun yarns is the possibility of predicting the performance of yarn insubsequent processes. Continuous tensile testing of spun yarn involvestransporting the yarn under constant tension at constant output speed. Thus, incontinuous testing every inch or millimeter of yarn is tested to generate trueelongation of yarn at specific dynamic tension & speed condition, and thetensile characteristics are continuously assessed. Dynamic tensile propertiesmeasured by continuous testing simulate actual manufacturing conditions moreclosely than the static tensile testing.


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


Introduction


Standard measurement of yarn strength isexecuted on a gauge length of 500mm. A clamped yarn breaks in its weakest placeaccording to the so-called principle of the weakest link and this strengthvalue is assigned to the whole length. As the test sample is gripped at the twoends and maintain that static state during the testing process, the evaluatedtensile properties are often treated as static tensile properties and thestrength measured by single thread tensile test method is referred to as static yarn strength. Standard evaluationis the result of a measured strength file of the weakest links, while thestrength of the other places situated on clamping lengths is not measured. Thebasic characteristics of distribution (average value, standard deviation andcoefficient of variation) of the measured values are as a rule calculated butthe order of the measured values and the relations between these values and thelength of links are not usually examined.


An important aspect of dynamic tensile testing of spun yarnsis the possibility of predicting the performance of yarn in subsequentprocesses. Researchers have experimentally determined that the static yarnstrength measured at 500mm length is more appropriate to simulate themechanical properties of fabrics and cannot accurately predict the runningbehaviour of yarn on subsequent machines; warping, weaving and knitting.Continuous tensile testing of spun yarn involves transporting the yarn underconstant tension at constant output speed. Thus, in continuous testing everyinch or millimeter of yarn is tested to generate true elongation of yarn atspecific dynamic tension & speed condition, and the tensile characteristicsare continuously assessed. Thus, dynamic tensile properties measured bycontinuous testing simulate actual manufacturing conditions more closely thanthe static tensile testing. Dynamic yarn strength is the maximum tension levelunder which the yarn is transported without any break for a length of 200m, ata speed of 40m/min. The measured extension at this maximum tension level isconsidered as the dynamic extension.


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About the Authors


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