Flow of polymers with pressure‐dependent viscosity in injection molding dies

Abstract

Considerable effort has been expended recently by a number of researchers to develop methods of simulating the flow of polymers in injection molding dies. The computer models developed by these researchers provide the mold designer with useful quantitative information concerning the predicted effect of design parameters on mold, filling characteristics. This paper will describe some recent work which is aimed at increasing the usefulness of these models by more accurately describing the flow behavior of those polymers, such as polycarbonate resins, which exhibit a strong effect of pressure on viscosity.

On the pressure dependency of the viscosity of molten polymers

“…I t is of interest to try to correlate the viscosity data to the free Volume fraction. In order to compute the free volume fraction the Simha-Somcynsky equations of state were adopted, which for polymeric liquids can be simplified to the following equations (19): (14) and where += l/(yc)-and y = 1 -f, f being the free volume fraction. P = P/P* , = V / V * , and ?…”

“…Karl reports a considerable decrease of the pressure coefficient with increasing pressure. Lord (14) presents data for polycarbonate as measured by Westover, et a l . (15).…”

Dynamic Compression Induced Solidification

“…However, the steady-state conditions which have always been the basis of previous investigations on the dependencies of glass transition do not reflect the real process either in micro injection molding or in CIS, since the material is not influenced statically but dynamically by pressure and temperature gradients. Several investigations on the pressure dependence of viscosity have shown [36][37][38][39][40][41][42][43][44][45][46][47] that the free volume and thus also the relaxation time are influenced by pressure. Therefore, a solidification due to a temporal pressure gradient at a static temperature would also be conceivable, according to the model of solidification explained above.…”

An exact analytical solution for viscoelastic fluids with pressure-dependent viscosity

“…The effect of the pressure on the viscosity becomes important at a pressure 50 atm approximately [1], while for pressures of the order of 1000 atm the viscosity appears to increase more than an order of magnitude [2,3]. Applications which involve a high pressure difference and/or a large pressure range include polymer processing operations such as extrusion and injection molding [1,[4][5][6], food processing, pharmaceutical tablet manufacturing, crude oil and fuel oil pumping [7], fluid film lubrication [8], journal bearing applications [9], microfluidics [10] and geophysics [11]. In order to avoid major errors when modeling these types of processes the dependence of the viscosity on the pressure must be taken into account.…”