Page 388 - Injection Molding Advanced Troubleshooting Guide

386 40 Short Shot

Figure 40.6 Typical eight-cavity shear-induced imbalance

40.3.2.3„ Mold: Plugged Gate or Hot Tip
If foreign material becomes plugged in a gate or hot tip the flow to the cavity will
be restricted. The result of a plugged gate or hot tip is often a short shot due to lack
of material flow. Metal is the most common material that ends up plugging tips;
however, contamination from carbon buildup or a higher melt temperature mate-
rial can also lead to plugged tips.
On a mold with multiple tips either for multiple cavities or multiple gates on a
single part a good check is to run a fill only shot and evaluate if all drops/tips are
providing similar flow. If one drop/tip is lagging in volume flowing through it a
plugged tip may be the root cause.
If a plugged tip is suspected a qualified mold repair technician should clean out the
drop and tip combination. Beware of technicians on the floor trying to clear out a
tip especially if it is a low vestige tip. The low vestige tip has a metal spreader in-
side the tip and there have been cases where a process technician tried to remove
the metal in the tip, which caused damage to the spreader.