Injection Molding of Polystyrene with Spiral Test Mold

Abstract

The effects of injection molding conditions spiral flow and molding shrinkage were measured for polystyrene using a spiral test mold in a Meiki injection molding machine with screw type preplasticizer. i) The relation among the spiral flow length X (cm), the melt temperature Tr (°C), the injection pressure P (kg/cm2), the mold temperature Tn, (°C) and the injection rate V (cm8/sec) is represented as follows: X=-21.4+0.00077 (Tr-125)(P+240) +0.058 Tm +0.14 V. ii) The molding shrinkage of spiral moldings along the direction of flow is smaller in the part close to the gate and larger close to the other end of the spiral, and the increasing rate of shrinkage in the former part is larger than in the latter. iii) The smaller shrinkage is obtained with higher melt temperature and higher mold temperature all over the spiral, and the effect of mold temperature is larger than that of melt temperature. The smaller shrinkage under higher injection pressure is obtained close to the gate and the effect is little close to the other end. The effect of injection rate is little.