PREDICTING FLOW LENGTH OF SPIRAL MELT FLOWS IN INJECTION MOLDS BY A SEMI- EMPIRICAL MODEL

摘要

A spiral-shaped mold of nearly rectangular cross-section with height and width in the order of a few millimeters is often used to classify injection molding materials according to their flowability. The length of the solidified plastic in the spiral, known as flow length, is taken as a measure of the flowability of the resin concerned. The parameters involved in the flow process are, mainly, resin viscosity, melt temperature, mold wall temperature, axial screw speed, injection pressure and geometry of the mold. To minimize the number of experiments required to determine the flow length, a semi-empirical model based on dimensional analysis has been developed. The modified dimensionless numbers used in this model taking non-Newtonian melt flow into account are Graetz number, Reynolds number, Prandtl number, Brinkman number and Euler number. Comparison between experimental data obtained with different thermoplastic resins and the model predictions showed good agreement, confirming the applicability of the approach for any injection molding resin.