The evenness of yarn is an important index of quality control of textiles, so the researches about the yarn evenness test method have been the hotspot in the textile measurement for recent years. In this article, two main yarn evenness testing methods including the Uster method and the CTT (Constant Tension Transport) method which are important in the present textile industry are compared and studied. Though comparing and analyzing the testing principles of two methods, adopting the method of statistical analysis to correlatively analyze the testing data obtaining from two different testing measures, the method of CTT can more visually and exactly describe the appearance quality of yarns.
Keywords: Yarn evenness, CTT, Uster, Value of CVThe evenness of yarn is one of main indexes to measure the quality of yearns. The unevenness of yarns will deteriorate the mightiness of yarns, and increase the end breakage rate in the spinning, and the increase of the end breakage rate will directly limit the speed of the machines and reduce the productivity. In addition, the unevenness of yarns will seriously influence the appearance quality of textiles.The usual yarn evenness testing methods mainly include the length measurement and weight measurement method, the visual measurement method and the Uster evenness tester method. Because of large computation, the length measurement and weight measurement method is only used in the research works requiring higher nicety or adjusting and measuring unevenness instruments, and it is rarely adopted in general tests. Because the visual measurement method is quick and convenient, and it can comprehensively evaluate the appearance quality of yarns, and it is a very usual method in productions, but it has many deficiencies such as large man-made factor influences, random character, non-objectivity and bad repetition character, and its testing results are hard to be reserved. So the application range of above two testing methods will be narrower and narrower, and they will be finally replaced by other testing methods. The Uster evenness tester can get rid of the influence of man-made factors to the testing results, and it can quickly and objectively measure the unevenness of yarns, so it is applied widely. However, as viewed from its testing principle, it still has certain deficiencies. First, the Uster CV value of yarn evenness can only denote the unevenness degree of yarns, but can not reflect the uneven structure of yarns. Second, the Uster CV value of yarn evenness only considers the average of the unevenness degree of yarns, and can not reflect the uneven waves with different characters on yarns, i.e. it ignores the discrete character of yarn unevenness. But these uneven waves of yarns would largely influence the unevenness of cloth cover. Third, when measuring blended yarns, because both the properties of fiber materials and the dielectric coefficients are different, and if the blended evenness of fibers in yarns is bad, the capacitance will change, which will influence the CV...
