The Designer's Edge: Maintaining Mold Component Wear Surfaces

Randy discusses maintaining the parting line shut-offs, vents, cavities and wear surfaces on mold components in the molding machine.


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Plastic flakes on the parting line can contribute to mold damage.

Everyone should have a procedure for maintaining the parting line shut-offs, vents, cavities and wear surfaces on mold components in the molding machine. This will vary from tool to tool depending on complexity and the material being molded. For example, gassy materials require the vents and parting lines to be cleaned more often than other materials. If you have vents that continually need to be cleaned, I recommend evaluating the venting itself.

Buildup on the cavity surface can cause gloss and sticking issues. This can be difficult to clean in the press with standard cleaners. Give Zap-Ox a try when needing to remove buildup, stains and rust. 

Another issue that can frustrate toolmakers is damage caused by plastic flakes building up on the parting line shut-offs (see image). Typically, this results from bad gating that leaves flakes behind, undercuts on sprue puller pins or stringers from the sprue or hot drop. The flaking or stringer issues should be resolved to prevent mold damage.

Varying mold temperatures between the mold halves can also contribute to wear, flash, galling and contamination. When running different temperatures, the half that is hotter will thermally expand, so it will be larger dimensionally, which can affect wear and galling with pins/bushings, lock angles/corner locks and shut-offs, causing flash or galling (depending on the direction the one half is expanding).

I have experienced cases in which wear on the corner locks have created contamination on the part as debris falls into the cavity. When it comes to pins and bushings, I prefer to use solid bronze bushings, especially on larger tools. This prevents galling between the pin and bushing. Solid bronze holds up better than bronze-plated bushings. Since implementing this standard years ago galling with pins and bushings has no longer been an issue.