What Causes Buildup In Plastic Injection Molding

Update: 17-06-2020

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.


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.

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