Flow and Solidification During the Filling of Cold Cavities with Crystallizing Viscoelastic Polymers

This article presents a model for the filling of cold cavities with solidifying, semi-crystalline viscoelastic polymers. Based on this model, prediction on the extent of wall solidification, skin crystallization and pressure drop as functions of processing conditions during filling are presented. The mathematical model considers two-dimensional creeping flow and three-dimenslonal transient heat transfer, coupled with the White-Metzner viscoelastic constitutive model and the Nakamura nonisothermal crystallization kinetics model. The resulting set of partial differential equation is non-linear, since the material properties are function of processing conditions. Geometry-adaptive body fitted curvilinear coordinates are used for the discretization of the flow field and the resulting set of finite difference equations is solved using iterative methods on curvilinear structured meshes. The numerical model Is presented in some detail and the obtained solutions are extensively validated by comparison with analytical results and by mesh refinement. Simulation results show that wall solidification during filling is mainly affected by conductive cooling to the mold walls and, to a lesser extent, by convective heating due to polymer matt flow. The level of surface crystallinity at the end of the filling stage depends on the prevailing heat flux conditions. The temperatures at the surface of the cavity during filling are largely unaffected by the fountain flow effect