Page 52 - Injection Molding Advanced Troubleshooting Guide
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4.2 Gate Size, Shape, and Taper 35
defect? Because the first change had no impact on fill pressures we thought
it was worth a shot. We welded the gate orifice and reduced it from 0.050 ×
0.110 to 0.025 × 0.110 in.
This time around our fill pressures did increase from around 10,000 psi to
13,000 psi but the pulls were eliminated and the process window drastically
improved, with less jetting and thousands of dollars in scrap savings.
We worked on a program of PP parts that were having high-gate issues. In
this case the cashew gates had a 0.040-in diameter. We went to 0.020 ×
0.080 in, and the high gates were eliminated, and there was no increase in
fill pressures.
4.2 Gate Size, Shape, and Taper
Figure 4.1 and Figure 4.2 show geometry alternatives to the industry standards.
The D-gate style sub-gate versus the standard sub/tunnel gate simulates the thin/
wide concept and will provide much cleaner gate breaks than the standard sub-
gate. And with this style in one case we were able to reduce gate-seal time by
5 seconds, saving an equal amount in overall cycle time. With the D-style sub-gate
the taper is taken out of the equation for flow restrictions because there is not a
gradual taper of mass like the standard sub-gate. You can also sub-gate into angled
walls, where when using a standard sub-gate you would end up with a gate vestige.
Also, you can gate into shorter walls than with a standard sub-gate. We have gated
into cavity walls that were 0.125 in tall. You have endless opportunities with D-gate
orifices. You can increase the tip of the cone on the D-gate to create a wider orifice.
It is important to understand the volume of the gate orifice. You can use a much
thinner gate orifice because you are increasing volume with the extra width.
