Influence of fiber length on the yarn-forming process of rotor spinning

Recycling textiles into yarns and various textile products is an effective method for high-value utilization. However, the length of recycled fibers is much shorter than raw cotton fibers, making the spinning process challenging. In this study, we numerically simulated the motion characteristics of multiple recycled fibers with different lengths (9.5 and 16 mm) as well as raw cotton fibers (28 mm) in a rotor spinning unit using Rocky DEM 2022R1 and ANSYS Fluent 2022R1. The results indicated that both recycled fiber and raw cotton fiber exhibited similar speed trends in the spinning unit. However, the 9.5 mm fiber was more susceptible to high-speed fiber-flow influence. In both the fiber transport channel and rotor, single fiber speeds and fiber-flow speeds were higher compared with other types of fibers. Fibers of varying lengths coalesced in the collection groove to form a fiber ring, with most fibers tightly attached to the collection groove in an extended state while some formed different shapes of loops. Although loops existed in both recycled and raw cotton fibers, their number and aggregation degree were lower in raw cotton fiber rings, resulting in better uniformity of fiber movement within them. Consequently, it is challenging to spin yarn using 100% recycled short fibers; therefore, it is recommended to blend recycled fibers with raw cotton or cotton-type chemical fibers for improved spinning performance.