Crimping of profiled monocomponent PET fibers under directional cooling: Three-dimensional temperature-field analysis and cross-sectional stress reconstruction

Profiled monocomponent fibers can develop self-crimp under directional cooling, but existing melt-spinning models mainly describe radial temperature and stress variations in axisymmetric fibers. A rod–ring-shaped polyethylene terephthalate (PET) cross-section was examined using three-dimensional computational fluid dynamics (CFD) coupled with cross-sectional stress reconstruction. The CFD calculation provided the temperature field along the spinning line and at the equivalent freezing cross-section. The equivalent frozen axial stress was reconstructed over the profiled cross-section, and the residual stress, resultant bending moment, curvature, and radius of curvature were calculated. Directional cooling caused the rodlike tail to cool faster than the ring-shaped region, increasing the cross-sectional stress imbalance and resultant bending moment with effective quench-air velocity. The predicted radius of curvature decreased from 28.213 mm without imposed quench air to 2.193 mm at 0.77 m/s. Continuous winding was achieved at 0, 0.29, and 0.39 m/s, while no visible crimp occurred without imposed quench air. At 0.29 and 0.39 m/s, the predicted radii were 6.347 and 3.515 mm, compared with experimental values of 7.394 ± 0.450 and 3.286 ± 0.162 mm, giving relative deviations of 14.16% and 6.96%, respectively. Higher velocities prevented stable winding. The results connect the resolved cross-sectional temperature and stress fields with the observed cooling-induced crimp.