Abstract:

Objective Rotor spinning is based on the transportation of fibers using airflow as a carrier. However, the core spinning assembly is a closed entity, and the spinning process cannot be directly observed. With the help of numerical simulation, the movement behavior of fibers in the spinning machine can be observed and analyzed in order to address the instability of the spinning process and provide optimization solutions, and to reduce fiber waste in production. This study is also an effort yo enhance the understanding of the theoretical basis for rotor spinning of yarns.

Method The fiber motion trajectory was modelled using the Lagrangian-Euler method by considering the airflow as a continuous phase and the fibers as discrete phases. 3D modeling software SolidWorks 2021 was used to establish a model for the rotor spinning assembly, and the numerical analysis was carried out using Rocky DEM 2022R1 and ANSYS Fluent 2022R1. The airflow field was selected using the Standard k-epsilon turbulence model, Standard Wall Function (SWF), and SIMPLE algorithm. The fiber model was modelled a rod-chain structure, made of cotton fiber with a length of 28 mm.

Results The velocity of the fiber in the fiber transport channel was chosed to be (22-27.4) m/s, with a small increase in velocity and acceleration. The velocity and acceleration were gradually increased along the fiber movement direction. The velocity of the fiber on the slip surface of the rotor was set in the range of (27.4-61.1) m/s. After the fiber tip contacts the slip surface of the rotor, the velocity was increased rapidly. The increase in normal contact force was found to be the main reason for the increase in fiber acceleration. After entering the coagulation tank, the velocity of the fibers was further increased as indicated by the fiber acceleration. After reaching the maximum value of 115.5 m/s, the velocity remained stable.

When the fibers were located in the fiber transport channel, they basically maintained their morphology at the entrance and did not undergo significant morphological changes. After the fiber contacts the sliding surface of the rotor, it moved at a certain angle on the sliding surface and gradually slided towards the condensation groove. When the fiber first entered the condensation tank, it exhibited a multi segment small amplitude bending shape. The small segment bending tended to converge into a large amplitude bending, and was gradually straightened and pressed against the wall of the condensation tank.

Conclusion Numerical simulation software Rocky DEM 2022R1 and ANSYA Fluent 2022R1 were used to simulate rotor spun yarn formation from fibers with cotton fibers of 28 mm in length and 20 μm in fineness. The movement of the straightened cotton fibers in the channel of the rotor spinner was studied, and the velocity distribution, motion trajectory, and morphology of a single fiber at different positions were obtained. Combining theoretical formulae, the reasons for the velocity change of a single fiber were revealed, and the motion and morphology changes of the fibers in the rotor spinner were deeply explored. The results of this study provides some theoretical guidance for design and optimization of rotor spinning production, and has certain reference significance for the design of key components such as the fiber conveying channel and rotor in rotor spinning.

Key words: rotor spinning, motion of fiber, fluid solid coupling, fibre model, force analysis