Welcome to our Plastic Injection Molding Defects series, where we will explain some common defects seen by injection molders and present ways to fix or prevent them.
What is an Ejector in Injection Molding?
The ejector is the part of the molding process that pushes the part out of the mold when it’s time to do so. Because of the ejector itself and the ejector pins, there are several areas that could result in the mold sticking to the ejector.
What Causes Parts to Stick on the Ejector?
This is one of the most difficult injection-molding defects to diagnose because there are so many possible reasons a part would stick to the ejector. In the molding process itself, multiple settings could be off one way or another. Second-stage pressure, mold temperature, cooling time, melt temperature, and possibly a fast injection speed.
When you’re looking at the molding process as the culprit, you’ll likely end up with a tight processing window. At that point, you should look into improving the mold itself for the best results.
Table 36.1 Part Sticking on Ejector Troubleshooting Chart, found in Injection Molding Advanced Troubleshooting Guide: The 4M Approach (p. 345)
| Molding Process | Mold | Machine | Material |
| Low or high second-stage pressure | Surface finish | Machine performance | Material type |
| Low or high mold temperature | Lack of ejection | Ejector Plate | Moisture content |
| Long or short cooling time | Lack of draft | Robot handling | Release agents |
| Fast ejection speed | Buildup | ||
| Low or high melt temperature | Slides or lifters | ||
| Damage, erosion, or burrs |
How to Prevent Parts from Sticking on the Ejector
When you use our Heat Cure™ and Quick Cure coatings—which are also ideal for preventing pin push—you get extraordinary release characteristics, preventing the ejector pins from sticking in the plastic.
Because injection mold buildup could also be an issue with sticking parts, you could also try one of our mold cleaners like Clean-N-Run, Mold Brite, Power Clean, Kleen All, and Zap-Ox.
Feel free to contact us if you have questions about our products and how they might solve your injection-molding problems.
Stay tuned for future installments of our plastic injection molding defects series.
Source: Injection Molding Advanced Troubleshooting Guide: The 4M Approach by Randy Kerkstra and Steve Brammer.
