Air-jet weaving is a weaving technique with high production rate. However, efficiency decreases if instabilities in the motion of the weft yarn leader occur causing weft insertion failure. A 2D geometrical model was developed for the main nozzle of the air-jet loom and a mathematical model employing the fluid–structure interaction (FSI) technique was used to simulate the air-flow and whipping action of the leader in the air flow at the exit of the main nozzle. With numerical results, the resultant force normal to the yarn determined by the yarn shape and the air-flow field has a significant influence on this whipping action. Starting with an initial gravity-induced drooping leader, a large normal force exerted by the air flow subsequently leads to a strong whipping action. To verify the validity of the numerical analysis, an experimental apparatus with a high-speed camera attached was constructed to observe the leader trajectory under different air supply conditions. The experimental results show that during weft insertion the motion is more stable with an initially straight leader than one initially drooping.
The internal airflow of an untwisting chamber clearly affects the untwisting performance as determined by the appearance of the untwisted yarn end. This study established a geometric model of an untwisting chamber comprising an intake tube and untwisting tube, and adopted the renormalization-group k-" turbulence model to simulate the airflow patterns inside chamber structures having three varying parameters. These were the chamfer angle of the intake nozzle, rotation angle of the intake nozzle, and eccentric distance between the intake nozzle and untwisting tube. The chamber angle of the intake nozzle mainly induces a radial flow from the axial flow in the intake nozzle. The strength of the circumferential airflow in the untwisting tube, which is converted from the radial flow, is affected by the combined effects of the rotation angle of the intake nozzle and the eccentric distance between the intake nozzle and untwisting tube. An experimental bench that employed a high-speed camera to capture yarn movement was designed to verify the numerical results. Comparisons between simulation and experimental data show that the structural parameters of the untwisting chamber affect the airflow patterns and consequently the performance of untwisting the yarn end.Pneumatic yarn splicing used to join two separated yarn ends is a key technology for promoting yarn quality. As a complex process, pneumatic splicing can be obviously divided into an untwisting stage and a mingling stage. Firstly, a high-speed jet generated from compressed air is used to untwist two yarn ends intermingled by fibers in a helical manner, causing the yarn ends to become individual fibers, in an untwisting chamber. The two untwisted yarn ends are then dragged into a mingling chamber in an overlapping relationship using yarn clamps. Finally, another strand of airflow opposed to the rotation of untwisting airflow is applied to join the two separated yarn ends to form a neat strong yarn.There are many factors affecting the performance of the pneumatic splicing of yarn, such as the splicing inlet pressure, splicing duration, overlap length of the two yarn ends, and physical characteristics of the yarn. 1 Owing to the importance of splicing parameters, researchers have investigated the effect of such factors on the quality of twisted yarn normally characterized by strength and diameter, both experimentally and theoretically.Li presented the working principle of the pneumatic splicer and described how the factors affect the performance of splicing yarn. 2 Focusing on the dynamic response characteristic of the pneumatic actuator in the air splicer, Chattopadhyay et al. 3 realized rapidity of splicing by modifying the mechanism parameters.
Pneumatic yarn splicing is a complex process that involves the simultaneous movement of two strands of counterrotating yarn. Depending on the process and structural parameters of the mingling chamber, the airflow field is more dominant in influencing the wrapped effectiveness of untwisted filaments and consequently the splice strength. This study establishes a computational domain of a mingling chamber comprising an inlet channel, accelerating channel, rotating channel, and groove channel. The renormalization-group k-e turbulence model is adopted to simulate the vortex patterns in the rotating channel under different inlet pressure. Furthermore, a transient mass flow test bench based on the isothermal principle is used to verify the numerical simulation results by comparing the mass flow of a pneumatic splicer. A wrapped model of spliced yarn is presented to describe the effects of wrapped force determined by the characteristic of vortex patterns on the strength of spliced yarn. A strength tester is also used to acquire the strength of spliced yarn produced under different inlet pressures and interpret the reliability of theoretical analysis. Comparisons between numerical results and experimental data show that the inlet pressure of the mingling chamber clearly affects the vorticity of the vortex and the strength of spliced yarn. The vorticity of the vortex will be enhanced with increasing inlet pressure and improve splice strength to avoid insufficient twisting of the yarn end. However, excessive twisting of the yarn end, as reflected by splice strength, would occur if the inlet pressure strengthens continually. Keywords pneumatic splicing, numerical simulation, wrapped model, transient mass flowPneumatic technology has found a variety of applications in the textile industry, such as rotor and airflow spinning, air-vortex spinning by Murata Vortex Spinning, air-jet weaving, the pneumatic splicer, and others. 1-3 Among these applications, the pneumatic splicer is a key technology for manufacturing no-knot yarn with two gray yarn ends in two stages, namely the untwisting stage and the twisting stage. 4 During the untwisting stage, two gray yarn ends are converted into parallel filaments and a stem yarn. In the twisting stage, a blast of airflow issued from the air splicer forces the filaments to wrap the stem yarn on each other.With the development of Computational Fluid Dynamics (CFD) technology, the numerical method is increasingly used to analyze the airflow field, which plays a decisive role on yarn or fabric formation. Wu et al. 5 established a geometry model for two different mingling chambers and employed a twoparameter k-e turbulence model to simulate their airflow patterns. Taking Murata Vortex Spinning as a research object, Zou et al. 6 simulated the airflow field in the nozzle block and analyzed the effects of structural parameters and process parameters on the
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