STUDIES ON GAS COUNTER PRESSURE AND LOW-PRESSURE STRUCTURAL FOAM MOLDING .3. EFFECT OF PROCESSING CONDITIONS ON MECHANICAL-PROPERTIES OF MOLDED PARTS

Abstract

For studying the effect of processing conditions on the mechanical properties of structural foam, high impact polystyrene with varying processing conditions was employed in molding the specimens by applying a low pressure structural foam injection molding (LPSF) and gas counter pressure structural foam injection molding (CPSF). The impact energy of the LPSF part was demonstrated to increase under one of the following conditions: lower chemical blowing agent concentration, higher injection speed, higher reduced density, higher mold temperature, or higher melt temperature. The flexural modulus of the LPSF part would also increase under the same condition except for the injection speed. The flexural modulus and impact energy for the CPSF part was furthermore observed to increase under one of the following conditions: higher melt temperature, lower chemical blowing agent concentration, higher reduced density, lower mold temperature, or lower injection speed. The counter pressure falling below a critical level would lead towards the surface roughness of the CPSF parts increasing with its skin layer thickness simultaneously decreasing. A reduction of the flexural modulus and impact energy would consequently arise as a result of this occurrence. With a sufficient amount of gas counter pressure, a more enhanced impact strength and flexural modulus for the CPSF part occurred.