If the air can’t escape, it will be compressed by the melt.
This leads to an increase in temperature and builds burn marks (black marks on the polymer).
A better venting or slower injection at lower temperatures can solve this issue in most cases.
![Burn Mark in Plastic Industry Burn Mark in Plastic Industry](https://www.plexpert.ca/wp-content/uploads/2018/12/Burn_Mark.jpg)
Injection Molding Error: A burn mark at the end of the flow front
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This glossary of plastic industry is provided by PLEXPERT Canada Inc.