Page 190 - Injection Molding Advanced Troubleshooting Guide

180 19 Buildup

used in a material there is a good chance that byproducts from the additive will
plate out during the molding process.
There will be buildup cases where the material supplier should be consulted. The
material supplier will sometimes ask for a sterile swab of the buildup material. The
swab will then be sent to the lab for analytical studies to determine what the chem-
ical composition of the buildup is.

Case Study: Buildup
A two-cavity mold was running a super-tough nylon and experiencing severe
buildup problems. The mold had to be stopped and cleaned every 2 hours to
avoid complete buildup of the vents which in turn led to burning of the part.
This problem was relieved by adding additional parting line venting; this
allowed the mold cleaning interval to go to once a shift (instead of four times
per shift). The nature of this material required additional venting surface area
to improve the buildup of byproducts in the vents. As the material was a
nylon the vent depth had to be kept shallow to avoid flashing, so extra vent
width was added to allow better venting.
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