Abstract:

Objective The design of the double fiber channels in dual-feed-opening (DFO) rotor spinning technology broadens the range of materials for spinning. The fiber channel is a key component that connects the opening roller and the rotor in the rotor spinning unit. However, studies on the airflow field and yarn characteristics of DFO rotor spinning when the spatial positions of the two fibers channels are not symmetrically distributed have not been reported to date.

Method Building upon previous research on DFO rotor spinning with a fiber channel angle of 180°, this study constructed a control equation system for the airflow problem inside a DFO rotor spinning unit based on the Realizable k-ε turbulence model, and discretized and solved the control equation system for unstructured grids using the finite volume method and SIMPLE algorithm. Based on the established numerical model, this study delved into the impact of the symmetry of the two fiber channels on the internal airflow field distribution within the DFO rotor spinning unit. Additionally, image processing techniques and experimental testing were utilized to compare and analyze the specific effects of the symmetry of the fiber channels on yarn characteristics.

Results The fluent module in Ansys 19.0 software was used to simulate the internal flow field of DFO rotor spinning units with fiber transport channel angles of 180° and 110°, respectively. The convergence residual was set to 0.000 1.Simulation results indicated that the tapered structure of the fiber channels caused the external airflow to accelerate continuously as it enters the two channels, reaching a maximum velocity of over 100 m/s at the channel outlets. When the two fiber channels were asymmetric, the outlets were in close proximity, and collision of the two high-speed airflow exiting the channels were observed,which resulted in a noticeable low-velocity airflow zone between the outlets. The airflow underwent significant energy transformation within the fiber channels, with a decrease in pressure potential energy and an increase in kinetic potential energy. The high-speed airflow exiting the channels impacted the rotor's sliding surface, creating a localized high negative pressure area. The asymmetry of the two fiber channels caused the airflow, upon entering the rotor, to concentrate more in the areas near the two fiber outlets, leading to a pronounced negative pressure high-pressure zone. When the centers of the fiber channels were symmetric, the two types of fibers entered the rotor condensing trough in a 1∶1 ratio, and their movement and arrangement were relatively orderly and uniform, so the area occupied by the two types of fibers on the yarn surface was very close to the theoretical value of 1. After the fiber exchanged feeding method, the curves of the two samples showed little difference. When the two fiber outlets were not centrally symmetrically distributed, the distance between the two channel outlets was very close. During the process of two types of fibers flowing out from the two outlets and entering the rotor, the high-speed rotation of the rotor caused a covering phenomenon between the fibers flowing out from the two outlets. According to the image processing results of the yarn appearance, the fibers flowing out from outlet 2 were more likely to cover the fibers in outlet 1, resulting in a distinctive yarn appearance. The tensile properties, evenness, hairiness index, and number of defects of DFO rotor spun yarns with symmetric fiber channels were superior. When the angles of the fiber channels are the same, changing the fiber feeding method had little effect on the yarn performance.

Conclusion The internal airflow velocity and static pressure distribution in the fiber channels in the two types of rotor spinning units showed certain similarities. However, when the fiber channels were not centrally symmetric, the airflow distribution within the rotor became unstable and uneven. Due to the close proximity of the two channel outlets, high-speed airflows were prone to collision, leading to the formation of local negative high-pressure zones, which could cause fiber entanglement and affect the orderly arrangement of fibers in the yarn. A balanced flow field distribution is conducive to the orderly arrangement of fibers, reducing fiber entanglement, and improving yarn quality. In the rotor spinning device with a 110° channel angle, fibers entering from channel 2 tend to be distributed more on the yarn surface, and there was a difference in the area occupied by the two types of fibers, which was related to the uneven distribution of the airflow field within the rotor. The study confirmed the feasibility of DFO rotor spinning with non-centrally symmetric fibers transfer channels, providing a theoretical basis for the development of new types of rotor yarns with unique appearance characteristics.

Key words: dual-feed-opening rotor spinning, fiber transfer channel angle, numerical simulation, airflow field distribution, yarn characteristic