Viscoelastic Multi-mode Simulations of Wire-coating

A time-stepping nite element method is used to predict the viscoelastic stresses that arise in a tube-tooling wire-coating problem. The polymer melt HDPE is modelled by a multi-mode Phan-Thien/Tanner constitutive equation. Di erent ow geometries are considered to address optimisation of the process with respect to minimising the stress induced within the coating produced. The in uence of the die itself and the various modes are considered. Relaxation times range for a three-mode model from 10 2 to 10s and for a seven-mode model from 10 3 to 10s. Typical Weissenberg numbers may range up to 10. Three modes are su cient to adequately describe the ow, and shorter/narrower draw-down regions are identi ed as being preferable. Once an adequate land length has been gathered, that has relaxed the ow stresses prior to draw-down, the actual details of die design are found to be inconsequential to the induced stresses in the delivered coatings.