Page 53 - Injection Molding Advanced Troubleshooting Guide
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36 4 Gating Details
Figure 4.1 Chart comparing various gate areas
Case Study: Gate Differences
One example of this was on a two-cavity mold with sub-gates. This mold had
a right-hand and left-hand part that were exactly mirrored so there was no
difference between cavity size but the cavities were significantly unbalanced.
I was asked to open up the sub-gate orifice on the cavity that was short even
though the gate orifices were the same size (not always a good idea). After
opening the orifice to where it had 50% more volume, I knew something was
not right. I looked closely and found the sub-gate tapers were slightly differ-
ent, but not enough to be noticeable without very close examination. I in-
creased the taper on the cavity that was short to match the taper on the
other cavity. Wow, what a change! The cavity that had been short now filled
way ahead of the other cavity. A D-gate would have eliminated the imbalance
because the taper is not gradual to the orifice.
