Visualization Analysis of Reciprocating Plastication Process by Glass-Inserted Heating Cylinder

Part 3: Modeling for Reciprocating Plastication Process

Abstract

The reciprocating plastication process in injection molding is a cyclical and dynamic phenomenon during which (factor I) the screw moves forward and backward and (factor II) the screw rotates periodically. Analysis separating these two factors is necessary to probe the causes of characteristic phenomena in the reciprocating plastication process. In this study, the reciprocating plastication process and periodic plastication process in which a screw is set at a fixed position and is rotated intermittently were analyzed visually and compared. The results are summarized below:
1) It was clarified from factor I that a solid bed (SB) containing considerable melt phase appears in the feed zone at the beginning of the process, and breaks into fragments in the compression zone in the latter half of the process. This phenomenon may be explained by the following: a low bulk density group of plastic pellets was heated from the surface of each pellet during the waiting time in the feed zone. During the subsequent gathering and compression of pellets, the SB interior melted prior to the exterior regions due to heat conduction effects.
2) It was clarified from factor II that the SB in the screw compression zone increases from the start to the end of the reciprocating plastication process. It was also confirmed that an insufficiently heated SB appeared in the latter half of the charge process as the backward movement of the screw reduced the distance from the pellet feed position to the observation point in the reciprocating plastication process.
3) Based on a summary of these results, a plastication process model of injection molding was proposed.