Plastic Injection Molding Defects: Buildup

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 Buildup?

Sometimes called gas buildup or plate out, buildup in injection molding is easy to see on the cosmetic surfaces of the part, appearing rough. You’ll know buildup when you see it as it’s not confused with any other injection molding defects.

Buildup can cause further problems when it occurs in the mold venting, as it makes it harder for the mold to vent gas out of the cavity, which can lead to issues like splay.

What Causes Buildup?

In most cases, buildup forms when volatiles leave the plastic and collect on the surface of the mold. There are several reasons this could be happening, but most of the time, you’ll be able to solve your buildup problem if you can figure out what’s causing the excess volatiles and whether or not those volatiles can be better vented.

If the melt temperature is too high, excess gas can be generated and degrade the materials. Along these lines, too much shear can lead to too high of a melt temperature, which can lead to the gas buildup.

Most of the time, buildup is caused by poor venting. If the mold isn’t vented well enough, the volatiles from the plastic get trapped, directly leading to buildup problems.

Table 19.1 Buildup Trouble Shooting Chart, found in Injection Molding Advanced Troubleshooting Guide: The 4M Approach (p. 174)

Molding Process Mold Machine Material
high melt temperature vents machine performance regrind
excess shear moisture content
 material type

How to Prevent Plate Out in Injection Molding

If you’ve determined your buildup is caused by a venting issue, make sure all vents are open and are deep enough with a large enough land length.

Nanoplas mold-release sprays, coatings, and cleaners are essential to preventing buildup. Our mold-release sprays and coatings work against buildup the same way they work against pin push: exceptional release characteristics allow the mold to eject without sticking, preventing buildup in the process.

Some competing sprays go on heavy and make it difficult to run the mold effectively, but our sprays and coatings eliminate excess mold release without leaving any residue.

To eliminate buildup, Mold Brite, Power Clean, and Kleen All are excellent choices in mold cleaners. The ultimate cleaner: Zap-Ox, which will clean buildup even when you thought there may not be a solution.

Feel free to contact us if you have questions about our products and how they might solve your injection-molding problems.

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.