Page 339 - Injection Molding Advanced Troubleshooting Guide
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34.3 Jetting Troubleshooting 335
Figure 34.4 Jetting on a polycarbonate part: notice the milky appearance around the jetting
Case Study: Gate Thinning
This case study is one that is eye opening. Normally, thinner gates are more
prone to jet but in this case the opposite was true! This polypropylene part
originally had two round 0.110-in cashew gates and was experiencing both jet-
ting and pull sinks at the gates. To try to make a change and determine impact
the gates were modified to 0.050 × 0.110 in. This change to a thinner rec-
tangular gate eliminated the jetting problem but the pull sinks were still occur-
ring. The gates were again modified to 0.025 × 0.110 in, which eliminated all
defects. The change of thickness from 0.050 in down to 0.025 in thick led to
an increase in fill pressure from 10,000 ppsi (plastic pressure) to 13,000 ppsi.
The thinner gate led to a much-improved process in this case, which again
proved that keeping an open mind is critical when troubleshooting.
