Abstract:

Objective Optimization of rotor spinning technology has long relied on traditional means of high-speed photographic observation and experimental testing. However, this means can not provide fiber or flow field data during the spinning process. This is not conducive to the understanding of the yarn formation mechanism, and is very costly in terms of manpower, material and financial resources. This paper report a study on development of numerical simulation technology which provides a new path for the study of the dynamic process of rotor spinning.

Method The rotor spinner was modeled by 3-D modeling software SolidWorks 2024 and meshed by ICEM software. Using ANSYS Fluent 2024R1 software, the standard k-epsilon turbulence model and SIMPLE algorithm solution were selected to simulate the airflow field inside the spinner. The rod and chain fiber model was adopted and the airflow was imported into Rocky 2024 R1.1 software for simulation numerical simulation, where the fibers were defined as cotton with a length of 28 mm. Based on the numerical modeling framework of multiphase flow coupled with computational fluid dynamics and discrete element method, the yarn formation process of 73 tex rotor-spun cotton yarn at rotor speed of 60 000 r/min and negative pressure of 5 000 Pa was simulated.

Results The simulation of multiple fibers coalescing, twisting and yarn formation in the rotor and leading out of the rotor was ahieved, revealing the three-dimensional movement of fibers in the rotor. The surface characteristics of the simulated yarn were highly consistent with the actual yarn condition. The arrangement structure of fibers, the twist transfer process, the formation process of wrapped fibers and the yarn splice status were made clearly visible. For setting up the simulation, the rotor spinning process was divided into three stages, i.e., preparation, yarn settling, and yarn piecing. During the preparation stage, the simulation indicated that the fibers migrated into the rotor's condensing groove, where the average normal contact force built up 5.3 times faster than the tangential contact force, building fiber reserves for subsequent yarn formation. In the yarn settling stage, the wrapping length between fibers and the seed yarn grew from 0% to 68.2%, accompanied by a sharp rise in entanglement density. Such simulation results enhances the understanding of yarn splice section formation. During yarn piecing simulations, the contact force fiber-seed yarn surpassed the condensing groove's frictional resistance, meeting the pre-stripping conditions required for continuous yarn separation and production.

Conclusion A coupled modeling approach based on Computational Fluid Dynamics (CFD) and Discrete Element Method(DEM) was adopted in this research. Through the co-simulation platform of Rocky DEM and ANSYS Fluent, the dynamic mechanism of rotor spinning fiber transport, coalescence and twist formation is explored. The simulation enables the observation of the fiber arrangement structure, twist transfer process, winding fiber formation process and yarn splice status. The generation of contact forces is directly related to rotor spinning dynamics. Compared to straight fibers, hooked fibers significantly enhance the mechanical interaction between the seed yarn and the fibers, improving the strength of the joint. It is easier to form multi-point contact with the coalescing groove, and the normal contact force accumulates faster and forms stable contact with the rotor coalescing groove first. The fiber speed change and force situation were analyzed and discussed. The scientificity of the theory related to rotor spinning is effectively verified.

Key words: rotor spinning, yarn formation process, numerical simulation, rotor spun cotton yarn, fiber cohesion, twisting, yarn splice, yarn structure