Development of the vent clogging monitoring methods for injection molding

Abstract

The gas in polymer melt during injection molding includes various chemical substances that leave deposits on the vent, which leads to a clogged vent. The predictive maintenance of the vent is necessary to prevent the sudden generation of defects and the unexpected downtime of the process due to vent clogging. Hence, it is necessary to monitor the state of the vent. In this study, we propose cavity-gas-pressure (CGP) and cavity-gas-temperature (CGT) sensors as monitoring sensors and evaluate the feasibility of the sensors for monitoring vent clogging. The CGP and the CGT sensors measure the pressure and the temperature changes of the cavity gas respectively when the gas is compressed at the end of the filling. To examine the monitoring capability of the sensors, three sets of tests were conducted: a sensitivity test, an influence test of processing conditions, and a reliability test in a long-cycle run. The sensors were installed in a spiral mold with an interchangeable vent block of various depths in the experiments. Although the CGP and the CGT sensors exhibited sufficient sensitivity to detect vent depth differences, the CGP sensor showed higher sensitivity. In the influence test, processing conditions, such as the injection speed, metering value, melt temperature, and cooling time were examined with respect to PE and TE. In the reliability test in a long-cycle run, only the CGP sensor was tested. The CGP sensor produced a reliable result over 550 cycles, which proved that the sensor is a feasible sensor for monitoring vent clogging.