STUDIES ON GAS COUNTER PRESSURE AND LOW-PRESSURE STRUCTURAL FOAM MOLDING .1. PROCESS DESIGN AND EFFECT OF PROCESSING CONDITIONS ON SURFACE QUALITY OF MOLDED PARTS

Abstract

Gas counter pressure structural foam injection molding (CPSF) with hot runner mold was successfully developed in this study. The process has overcome the disadvantages of the low pressure structural foam injection molding (LPSF). Having a sufficient short-shot weight, a critical timing for the counter pressure to release, and a sufficient amount of counter pressure to prevent foaming during melt injection were deemed necessary for the sake of achieving a part free from surface defects through application of this developed CPSF process. The surface smoothness of the CPSF part was observed under these conditions to be substantially better than that of the LPSF parts molded under the same processing conditions. For the LPSF part, the surface roughness was indicated to increase progressively in the direction of melt flow from the cold sprue towards the end of the part. The processing conditions found to enhance the surface smoothness of the LPSF part were a higher melt temperature, higher mold temperatures, higher short-shot weight, higher injection speed, and lower blowing agent concentration.