Simulation And Experimental Study Of Pneumatic Yarn Splicing Behavior

Pneumatic technology has found a variety of applications in textile industry. Among these applications, pneumatic yarn splicing is a key technology to realize yarn breakage piecing and enable knot-free splicing. As a complex process, pneumatic splicing can be obviously divided into an untwisting process and a mingling process. First, a high-speed airflow generated in the untwisting chamber is used to untwist two yarn ends intermingled by fibers in a helical manner, causing the yarn ends to become individual fibers. The two untwisted yarn ends are then dragged into a mingling chamber in an overlapping relationship. Meanwhile another strand of airflow is applied to join the two separated yarn ends together to form a neat strong yarn. Therefore, the effectiveness of the airflow is the dominating factor on the final splicing quality, no matter during untwisting process or mingling process. It is thus that the study of the characteristics of airflow in the untwisting or mingling chamber and the effect of airflow on the multi-filaments motion become more important and meaningful.Starting from the market requirement of knot-free yarn and the advantage of pneumatic technology, this paper analyzes the importance of the pneumatic splicing technology. Additionally, the current research state research method of pneumatic splicing internationally and nationally is introduced respectively, such as research method and direction. The primary contents and significance of this paper is also clarified according to the comparing of studying. After that, the working process and principal theory of pneumatic splicing is expounded on the basis of the splicing model.Next, the CFD software was adopted to simulate the characteristic of airflow in the untwisting chamber with three different structural parameters, namely the chamfer angle of the intake nozzle ?, the rotation angle of the intake nozzle ?, and the eccentric distance between the intake nozzle and untwisting tube e. Thereinto, the chamfer angle ? is mainly used to induce some part of the axial airflow from the intake nozzle to convert into a radial airflow. The rotation angle ? and eccentric distance e affect the intensity of the circumferential airflow by changing the incidence angle. Because the effect of key factor on the untwisting performance of yarn ends is the circumferential airflow, the velocity circulation in different rotation angle ? and eccentric distance e is applied to describe the effect of rotation strength of circumferential airflow on the untwisting performance. In addition, a high-speed photography was conducted to allow visual analysis of the transient process of filaments during the untwisting process, the results of which were used to verify the simulation results.In the following, a computational domain of a mingling chamber comprising an inlet channel, accelerating channel, rotating channel, and groove channel is established. The renormalization-group k–? turbulence model is adopted to simulate the vortex patterns in the rotating channel under different inlet pressure. And the airflow characteristic of vortex is the dominant in influencing the wrapped effectiveness of untwisted filaments and consequently the splice strength. In order to describe the effects of wrapped force determined by the characteristic of vortex patterns on the strength of spliced yarn, a wrapped model of spliced yarn is presented. A strength tester was then used to acquire the strength of spliced yarn produced under different inlet pressure and interpret the reliability of theoretical analysis.At last, for investigating the motion of filaments and joint forming mechanism in the mingling chamber, the combined methods of visual experiment and numerical simulation is carried out to reveal the mingling process of filaments. Based on a high speed camera, a visualization test bench was established to record the mingling process in the transparent specific splicing device. In addition, a turbulent mathematical model was adopted to describe the airflow field in mingling chamber. The motion and deformation behavior of a large aspect filament was analyzed in detail according to the experimental images and the numerical results of airflow field. Furthermore, the effect of overlapping length and inlet pressure on the splicing process is discussed. Meanwhile, the experiments with varying overlapping length and inlet pressure were conducted to verify the analysis results.