Browsing by Author "LEE, MJ"

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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
(1994)
WU, JS
;
LEE, MJ
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
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.
STUDIES ON GAS COUNTER PRESSURE AND LOW-PRESSURE STRUCTURAL FOAM MOLDING .2. EFFECT OF PROCESSING CONDITIONS ON STRUCTURE OF MOLDED PARTS
(1994)
WU, JS
;
LEE, MJ
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
Studies involving the structure of the parts molded from the low pressure structural foam injection molding (LPSF) and the gas counter pressure structural foam injection molding (CPSF) were conducted via varying processing conditions. The bubbles near the skin layer were observed to be less uniform in size and more elongated for the LPSF parts than for the CPSF parts. The CPSF parts, however, exhibited a more uniform cellar core. The skin layer thickness from both processes increased under one of the following conditions: higher melt temperature, higher reduced density, lower injection speed, or lower blowing agent concentration. As regards the effect of mold temperature, a higher mold temperature resulted in an increase of the skin layer thickness for the LPSF parts but a decrease for the CPSF parts. The skin layer of the CPSF part would, become thin if the gas counter pressure was not high enough to prevent foaming during melt injection. With a sufficient amount of gas counter pressure, the CPSF parts were observed under the same processing conditions to become superior to the corresponding LPSF parts owing to a thicker skin layer with a greater integrity and smoother surface.
STUDIES ON GAS COUNTER PRESSURE AND LOW-PRESSURE STRUCTURAL FOAM MOLDING .3. EFFECT OF PROCESSING CONDITIONS ON MECHANICAL-PROPERTIES OF MOLDED PARTS
(1994)
WU, JS
;
LEE, MJ
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
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.