NONISOTHERMAL FILM CASTING OF A VISCOUS FLUID

Abstract

Finite element models were developed for simulating one-dimensional (ID) and two-dimensional (2D) nonisothermal film casting of a viscous polymer. These models accommodate inertia and gravity, allow the thickness to vary across the width ofthe film (in the 2D case), but exclude die swell and sag. The numerical algorithm is based on a Newton-Raphson approach to solve simultaneously for the velocity, thickness, temperature and the width ofthe film. Numerical simulations using the finite element model found the following: i) upwinding is unnecessary for predicting the temperature distribution; ii) the average temperature distribution in the air gap is well approximated by a linear function; iii) once the film contacts the chill roll the geometry remains essentially unchanged; iv) for low viscosity polymers, the self-weight ofthe material can aid in reducing neck-in and in promoting a uniform thickness; v) nonconstant thickness and/or velocity profiles at the die could potentially lead to less neck-in and a more uniform thickness for the finished product; and vi) cooling ofthe film, especially when localized cooling jets are employed, reduces neck-in and promotes a uniform thickness.