Uncovering Molding Defects and How To Troubleshoot Part II

In last month’s blog, Uncovering Molding Defects And How To Troubleshoot, we discussed the importance of technical expertise and attention to detail to prevent molding defects. There are several common molding defects that our experts at Midstate already know how to troubleshoot. Last month’s blog only highlighted three defects, and we believe it is important for our readers to be informed of additional problems that may arise and how our experts are able to provide precise solutions.

Delamination

Delamination is a condition where the finished part has a flaky surface layer due to a contaminated or foreign material. The foreign material finds a way into the molten plastic, and it ends up separating from the finished product because the contaminant and the plastic cannot bond. They appear like coatings and can usually be peeled off. This affects not only the appearance of the product but the overall strength. The main culprit is usually due to excess moisture.

Two Solutions for Delamination Defects

1. Pre-dry: If the defect is due to moisture, pre-drying the resin pellets or increase the mold temperature.
2. Mold release agents: Focus more on the ejection mechanism in the mold design to reduce or eliminate the dependence on mold release.

Discoloration

When a finished part ends up being a different color than intended. It is similar to burn marks or brown streaks, but generally not as dark or severe. This defect is usually caused by overheating, excess pellets in the hopper, mechanical shearing, or contamination. When barrel temperatures are too high, the material will overheat and undergo thermal degradation—the more it degrades, the darker it becomes.

Two Solutions for Discoloration Defects

1. Barrel temperature: If the defect is due to high temperature, decrease the barrel temperature to the correct range and make sure the material heats progressively from the rear to the front of the barrel.
2. Excess pellets and resin: The problem can be addressed by thoroughly flushing the hopper and the feed zone of the machine in between processes.

Flash

This is the occurrence of thin, wafer-like layers of plastic that flows outside of the cavity where two halves of the injection mold meet. It can appear on the part’s edge along the parting line of the mold, or any place where the mold has metal meeting to form a boundary. It can be caused by the mold not being clamped together with enough force or if the mold has exceeded its lifespan.

Two Solutions for Flash Defects

1. Clamp pressure: Focus on increasing the clamp pressure to ensure that the mold parts remain shut during shots.
2. Mold Lifespan: Make sure that the mold is properly maintained, cleaned, or replaced when it has reached the end of its useful lifespan.

Midstate Mold is committed to the success of your project from concept, to prototype, to completed product. Our experience, dependability, and workmanship have put us in a great regard with our customers. If you have a design you are looking to produce, make sure to contact us so we can get started on your project today!