Page 195 - Injection Molding Advanced Troubleshooting Guide

20.3 Burns Troubleshooting 185

Figure 20.2 Classic example of burning from lack of venting at knit line

When a mold is dirty venting will be compromised. One of the first things to do if a
burning problem appears after a mold has been running good parts is to clean the
mold. If cleaning the vents of the mold (make sure to check for venting on slides
and lifters) solves the problem then the problem is definitely a venting-related is-
sue. To completely eliminate this problem, it may be necessary to add additional
venting or plan for more frequent mold cleaning during production runs. If the
mold is requiring frequent cleaning of the parting line and vents it is a good
indication that the mold needs additional venting.
If a mold is prone to burning there is a high risk that the steel in the burn area will
start to erode over time. This erosion of steel can lead to many issues including
sticking parts, poor appearance, and parting line flash. It is better to address the
burning problem than to repair the mold for erosion-related issues.

20.3.2.2„ Mold: Contaminants
If a mold has surface contaminants such as grease from moving components or oil
from cylinders it is possible that this contaminant may trap in locations of the
mold including vents. If this contamination is an ongoing issue determine what
the cause of the contamination is and have it fixed.