Numerical simulation and experimental verification of fiber motion in the convergence zone of lattice-apron compact spinning

In lattice-apron compact spinning, the convergence behavior of fibers in the condensing zone strongly influences yarn compactness, hairiness, evenness, and strength. However, experimental observation alone is insufficient to reveal the force interactions and deformation mechanisms of individual fibers during dynamic convergence. In this study, a three-dimensional fiber dynamics model based on the elastic rod finite-element method was developed to simulate fiber motion in the convergence zone. The model incorporates large deformation, nodal inertia, fiber flexibility, airflow drag, fiber–fiber contact, and fiber–lattice-apron contact and friction. The simulation results show that increasing negative pressure generally enhances fiber convergence and reduces the final bundle width, while the response depends on yarn linear density. The model also reproduces the characteristic motion of marginal fibers, which first incline to the right and then flip leftward under the coupled effects of airflow force, contact force, and friction force. High-speed imaging experiments were conducted to validate the simulation results under three yarn linear densities and three negative pressures. The simulated bundle widths showed good agreement with experimental measurements, with a mean absolute error of 0.018 mm and a mean relative error of 3.79%. Statistical analysis further confirmed that linear density and negative pressure are the dominant factors affecting bundle width. The proposed model provides a useful predictive tool for revealing fiber-level dynamic convergence mechanisms in lattice-apron compact spinning and offers a theoretical basis for optimizing negative pressure and related compact-spinning process parameters.