The reciprocating plastication process in injection molding is a dynamic phenomenon during which the relative positions of the screw and the heating cylinder change cyclically. In our previous report, we proposed a visualization analysis method for this process using a glass-inserted heating cylinder. In this study, based on the above proposed method, we carried out an analysis of the reciprocating plastication process using polyethyleneterephthalate, polyamide, polystyrene and polycarbonate. The results are summarized below:
(1) The characteristic plastication processes of the above-mentioned resins in the screw channel could be explained by an extended lamination image of the screw channel and the solid-bed ratio calculated from the image. We were also able to explain the phenomenon of the formation and disappearance of a void (pellet-unfilled area) in the screw channel of the feed zone during the early stages of the charging process for each resin.
(2) The void formed during the initial stages of charging because of a melt-plugging phenomenon occurring in some parts of the screw channel in the feed zone, due to the melting of the resin during the waiting time. This phenomenon resulted in an insufficient supply of resin in the nozzle side of the melt-plugged area, hence forming a void. Moments later, pellets with a wider volumetric space located on the hopper side and compressed by the continued screw rotation would push the melt-plugged area to the nozzle side, causing the void to disappear.
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