2019 Volume 31 Issue 8 Pages 317-327
Homogeneous plastication using the appropriate screw is crucial for precise molding. In this study, to investigate the influence of the screw's shape on the plastication process, visualization analysis and measurement of melt temperature distribution inside the nozzle with an integrated thermocouple ceramics sensor were conducted using three screw type (hsaving same outer diameter D) with different screw pitches (P). The following results were observed.
(1) In continuous plastication experiments, the plastication capacity increased with increasing P/D at low screw rotation rates. In contrast, at high screw rotation rates, the plastication capacity was the highest at the minimum P/D. Furthermore, as P/D increased, the starting point of the plastication process and that of the solid bed break-up shifted downstream.
(2) In reciprocating plastication experiments, the plastication capacity increased with increasing screw rotation rate or P/D. In addition, similar to the continuous process, the larger the P/D, the more the plastication process shifted downstream and became delayed. Calculating and comparing the solid bed ratio in the compression zone showed that melting was significantly delayed with the maximum P/D screw and that the solid bed ratio increased with increasing screw rotation rate at any P/D, becoming constant at 150 rpm and above.
(3) The melt temperature distribution inside the nozzle was affected by the screw pitch and rotation rate, and a negative correlation between the average temperature and the standard deviation of each measurement point was observed. In reciprocating plastication, the decrease rate in the melt temperature using the minimum P/D screw and its standard deviation was small.
