Page 75 - Injection Molding Advanced Troubleshooting Guide
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7.2 Alternate Venting 59
Another way of maximized venting is to actually create an overflow where the
plastic will come together at a weld line and flow through a thick vent into an over-
flow tab. This method can be very effective at improving weld lines on glass-filled
materials. Figure 7.8 shows an example of overflow venting. Think of this overflow
as a reverse gate, and in fact using a sub gate design at the end of fill weld line can
create a nice overflow that automatically separates during ejection.
Figure 7.8 Overflow venting
Actuated vent pins can be used where an output signal from the molding machine
opens and closes a vent within the mold. These signals can be configured in nu-
merous ways such as using configurable I/O or even valve gate outputs. Cavity
pressure instrumentation could be used to determine when to trigger the vent to
close to prevent flash.
