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:
- Fix Ejector Pin Marks in Your Injection Mold
- Eliminate Parts Sticking On Ejectors
- Injection Molding Buildup: Causes and Solutions
- How to Eliminate Plastic Delamination
Source: Injection Molding Advanced Troubleshooting Guide: The 4M Approach by Randy Kerkstra and Steve Brammer.
