Simulation And Experimental Investigation Of The Dynamic Yarn Behavior During Weft Insertion

Wetf insertion is the most distinctive and important part of air-jet loom, which depends onthe friction between airflow and yarn to lead the yarn moving. The quality of weft insertion has adirect effect on the loom speed, production eiffciency and textile quality. However, the action ofyarn during weft insertion is quite complicated and controlled by multiple factors. It bringstremendous diiffculties for further research on weft insertion process and has been a main factorrestricting the development of air-jet looms in our country. So the research on dynamic yarnbehavior during wetf insertion has become an urgent and important project.In this paper, the domestic and international research in related fields are reviewed atbeginning. The dynamic yarn under the airflow based on the theory of aerodynamics and yarnmovement is established. Beside, a high speed camera is used to observe actual yarn motion duringweft insertion and the main factors effect on yarn motion is discussed. This paper includesfollowing contents:(1)Analyze the structure and flow channel of main nozzle and acquire the flow fielddistirbution inside and outside of main nozzle by simulation. In addition，this paper focuses on theflow velocity and static pressure of the throat，the mixed air area, the acceleration tube and thetube exit of main nozzle.(2)Establish the dynamic yarn model under the friction of weft air. Since the yarn can beregarded as straight movement approximately, it is only affected by airflow traction, air resistanceand balloon tension ignoring the vertical forces. Separate forces are analyzed to obtain the yarnvelocity and acceleration in any position. If time is small enough, treat the yarn as uniform motion.The kinetic characteirstic of yarn can be acquired by step iterative method knowing initialconditions.(3)Obtain the characteirstic parameters of yarn to get the yarn motion under the friction ofwetf air，which including yarn density, yarn diameter and the friction coefficient between yarn andair flow. A measurement system for yarn tension is special considered to get the friction coefficientand the effect of different fabric structure on friction coeiffcient is analyzed. (4) Plug flow field distribution acquired by fluid simulation into Matlab and establish thenumerical model of yarn motion to obtain the kinetic characteristic curve of yarn during wetfinsertion. From the result，the speed of yarn motion will be increased with the addition of distanceand eventually stabilized; the acceleration trend increases at first and then sharply decreases asdistance increases. The kinetic characteristic curve obtained by theoretical and high speed camerais compared and analyzed. On this basis，the effect of gas supply, yarn linear density and frictioncoefficient on yarn motion features are selective analysis.By studying the dynamic yarn model duirng wetf insertion, it helps to increase the cognize ofyarn motion features and lays a foundation for further optimizing on weft insetrion process andenergy-saving emission reduction of air-jet loom.