Abstract
The solid bed (SB) break-up (BUP) phenomenon seen in the single-screw plastication system causes instability in the plasticating process, and clarification of the generation mechanism is required. In our previous reports, we proposed two kinds of BUP generation models by a dynamic visualization method using a glass-inserted visual heating cylinder. In this study, visual analyses of the plastication process with the standard screw and long feed screw were carried out, and the influence of screw feed-zone length on BUP phenomenon was clarified. The results are summarized below:1) The SB structure when BUP occurs was clarified by static visualization in cooling and screw extraction experiments, and the validity of the two BUP generation models was confirmed.2) The polyamide plastication process of the long feed screw was visualized, and it was clarified that BUP of SB occurs in the long feed zone. BUP was assumed to occur in the feed zone where the SB structure changed from the Tadmor type to the melt invading type.3) This generation process is considered different from the two BUP generation models proposed so far, and the following new model was presented:The invading type SB is pushed up to the cylinder wall by the pressure of the invaded melting layer between SB and the screw wall. This increases the shearing force between SB and the cylinder wall to generate a large tension in SB, resulting in BUP of SB.
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