Abstract
In this study, we developed a thin-walled bar-flow cavity mold (cavity thickness: 0.5mm) in order to understand the influence of residual gas inside the cavity on the flow length and appearance during ultra high-speed injection molding of polypropylene (PP) and liquid crystal polymer (LCP). Both the resin flow and the internal gas pressure were simultaneously measured. The results of the effects of gas-venting on the flow length and blister generation of the LCP and PP molded part are summarized as follows:1) The flow length of PP and LCP molded samples increased with increasing screw injection speed (injection rate), but the flow length did not differ between natural exhaust (with gasvent) and forced exhaust (with vacuum-pumping).2) After heat treatment, numerous blisters were found in the LCP molded samples during high injection rates under natural exhaust, but not under forced exhaust even at ultra high-speed.3) The results suggested that blisters generated from residual gases trapped in the resin due to the jetting phenomenon inside the sprue during ultra high-speed filling.
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