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What Is Contamination in Injection Molding?

Contamination appears as discoloration, streaks, splay, delamination and other types of defects. Because it’s such a broad area with multiple possible culprits, is best to start with the usual suspect: the material brought to the molding machine.

Troubleshooting Contamination

Starting with the material, then working backward from there if necessary, you’re more likely to catch the root cause of the contamination earlier in the process, saving you time and energy and getting things back up and running as soon as you can.

Molding Process Mold Machine Material
Poor changeover Hot runner hang-up Hang-up areas Improper storage
High melt temperature High hot runner temperature Anti-seize Regrind
Wear Surfaces Robot contamination Incoming contamination
Lubricants Mixed Materials
Cleaning

How to Eliminate Contamination in Injection Molding

Start with material storage. If your material is left in an open container, it’s nearly certain you’ll end up with a contaminant. Every molding shop has dust, dirt, cardboard, wood, metal, grease and other potential contaminants in abundance. If your materials aren’t stored properly, any one of those foreign substances can lead to contamination and a rejected part.

Another potential issue with the material is regrind. Make sure no one is grinding the wrong material with other materials (for example, just because one material is the same color as another doesn’t mean it’s the same material). Improper storage of regrind can be an issue if foreign substances can sully the material. The machine itself, if not properly cleaned, can add contaminants to the regrind.

Avoid mixing materials. Not only can putting the wrong materials together lead to contamination, but some—like PVC and acetal—are dangerous when mixed.

If you confirm everything is being done right with your materials, you can move into the process settings, mold and machine to see if any contaminants are being introduced there.

Want to learn more? Check out these other great articles that solve common injection mold issues:

Source: Injection Molding Advanced Troubleshooting Guide: The 4M Approach by Randy Kerkstra and Steve Brammer.