Abstract
The effects of injection molding conditions on spiral flow and molding shrinkage were studied for high density polyethylene 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 injection pressure P (kg/cm2), the melt temperature T r (°C), the mold temperature T m (°C) and the injection rate V (cm3/sec) is represented as follows: X=-33.27+0.0002 (T r+95)(P+425) +0.206Tm+0.046V. ii) The molding shrinkage of spiral molding along the direction of flow is smaller in the part close to the gate and larger in the part close to the other end, and the rate of increase in shrinkage in the latter part is larger than in the former. iii) The smaller molding shrinkage is obtained at lower mold temperature in the part close to the gate, and at higher melting temperature close to the other end, but the after shrinkage by annealing becomes greater at lower mold temperature. The smaller molding shrinkage is obtained under higher injection pressure over the whole length of the moldings. The injection rate has little effect on molding shrinkage.
