Optimisation of multi layer extrusion Die Flow by varying Slip, using Visco-elastic Simulations, 2008 PLACE Conference

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During the extrusion of a PET (polyethylene terephthalate) coating, the thickness of each layer can vary across the width of the film. To investigate the parameters governing layer-thickness differences during the co-extrusion of an asymmetric coating, a typical extrusion die was modelled using Polyflow. Previously, non-Newtonian simulations were made without including visco-elastic effects. In this study, the extrusion die was simulated visco-elastically to identify instabilities. The coat hanger and preland were simulated separately to investigate the flow stability in each part. From practice, it was established that some wall slip must be applied to obtain realistic results from the simulations. Based on literature and rheometer data, a slip model was selected and incorporated into the experimental data.