Dynamic Tension Characteristics Of Yarns On High-speed Warp Knitting Machine

Yarn tension has always been a hot topic in the textile industry.Too high or too low tension can directly affect the quality of finished products.In the warp knitting,the control of the yarn tension generally relies on the experience of the processors,but the value and the change of the tension they don't know.In terms of theoretical research,there are a few researches on the tension of warp yarn,and the system is poor.There is still a lack of inductive factors which influencing the yarn tension,and the trend and degree of influence are not involved.This paper carried out a series of studies.The yarn tension under different machine parameters and technological parameters were tested and analyzed.The influence laws were discussed and the solution of theoretically optimized tension was proposed which lays a foundation for stabilizing yarn tension and reducing tension fluctuations.First of all,the high-frequency test method of warp yarn tension was introduced,and the testing principle,requirements,test methods and steps were described.Based on the characteristics of warp knitting yarn tension curve,the maximum value and average value were selected from the general evaluation indicators to describe the yarn tension level,and the standard deviation was used to evaluate the discrete degree.In addition,the probability density curve,kurtosis and skewness were also proposed to describe the distribution of the yarn tension.The average value of the slope after derivation from the tension curve was used to evaluate the overall fluctuation of the yarn tension.In this way,a scientific evaluation method was established to conduct a comprehensive evaluation of warp yarn tension.Secondly,based on the spindle angle and the movement of the knitting elements,the change of the yarn tension waveform was analyzed,and the reason of the height change of the adjacent peaks was explained by the difference in the direction of the guide bar movement.In addition,combining with the general evaluation indicators,kurtosis,skewness,slope average,and the change of the yarn tension curve,it was explored that the influence of machine parameters including the tension compensation device,machine speed,shogging system and the position of the guide bar on yarn tension level,discrete degree,tension distribution,and the degree of overall fluctuation.And the reason of these changes were analyzed.Thirdly,combined with practical experience and warp knitting conditions,the appropriate level range was selected,and the yarn tension of the three main technological parameters: warp run in,draw off density and structures were tested.The test results combine with the evaluation indicators were analyzed and compared.The influence of each technological parameters on yarn tension and its influence degree were summed.Finally,using the method of multiple regression analysis,the relationship between the yarn tension and the warp run in,draw off density,structures and machine speed were studied.The influence degree of these four factors on the yarn tension was proposed.The calculation equations for yarn tension levels,discrete degree and the degree of overall fluctuation were established.By summing up the influence law of various factors on yarn tension,the index of suitable tension was defined.Combined with practice and multiple regression equations,theoretical solutions to optimize yarn tension were given.