Mathematical and computational modeling of heat transfer and deformation in film blowing process

Abstract

AbstractThe blown‐film extrusion process was investigated both experimentally and theoretically. In experimental study, nonisothermal experiments were conducted using low‐density polyethylene. Rheological parameters were studied, considering the polymer melt as a power law fluid in nonisothermal conditions. Axial tension, bubble diameter, and film thickness at a variety of film extrusion conditions, that is, different flow rate, pressure difference across the film, and take‐up speeds were measured. In theoretical study, an analysis was employed to simulate the blown‐film extrusion process by setting up the force‐ and energy‐balance equations on the film bubble moving upward. Four nonlinear complex differential equations were integrated numerically, using an iterative backward shooting method and the fifth‐order Runge‐kutta technique. The program written, based on a mathematical model, predicts the bubble shape, temperature profile, and film thickness as a function of the distance along the machine axis. Furthermore, the model evaluates the elongational viscosity of LDPE in biaxial tension in terms of distance from die axis and take‐up speed. In this simulation, the total stress components in machine and the transverse directions were computed from the die exit up to the freeze line, the knowledge of which is necessary for evaluation of the elastic memory build up in heat‐shrinkable films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2115–2123, 2002