Shear Heating Effect at Narrow Gate in Ultra-High Speed Injection Molding
Hidetoshi Yokoi, Wookyu Kim, Yasuhiko Murata
Center for Collaborative Research,The University of Tokyo
JAPAN

Keywords: Shear heating efffect, Ultra-high speed injection , Temperature rise

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Ultra high-speed injection molding is a new technology for realizing very thin-wall molded products. Screw injection speed applied for this technology is generally more than 1000 mm/s, which enables a quite short cavity filling time, e.g. less than 30 ms.

Under such an extraordinary injection speed, the temperature of melt should greatly rise at the gate due to shear heating effect, however there are no measuring data about the temperature rise at the gate because the measuring method has not been established so far.

In this report, for the first time we have tried to measure how the temperature of flowing melt rises during passing through the gate under ultra-high injection rates. Two sets of infrared thermometer were set at the location before and after a changeable gate block around the center of the runner-shaped cavity. Then, the temperature change was evaluated comparing with both two-sensor outputs. Materials used were two kinds of polypropylene with different viscosities, and the gate diameter was changed from 0.6mm to 1.2mm. Temperature rise caused by shear heating effect was measured to reach about 100 degrees in the case of narrow gate, which should affect on the promotion of completely filling into a quite thin wall cavity under ultra-high speed injection conditions.