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Masking During a Zinc Phosphating and Powder Coating Process

Q. Hi,

I have a component that is given a zinc phosphate coating prior to powder coat on an automated line in which it is not removed from the hanger until after the entire process in completed.

The issue I have is that the top edge of the component is cold rolled after the powder coat is applied to seal an assembly.

Currently our supplier is milling that edge to remove the powder coat so that there is no cracked and flaking paint on the rolled edge, but this allows for the exposed steel to corrode.

I am looking for a way to prevent corrosion on that section without changing to a more expensive stainless steel.

My original thought was to mask the top edge of the component so that zinc phosphate coating would be exposed and there would be no powder coat to machine off the part.

Since it is an automated process, I have not been able to figure out how to mask the component without removing it from the hanger after the zinc phosphate coating and before powder coat.

Has anyone encountered a similar problem? I was thinking maybe using a silicon cap that could be pushed down on the part after the zinc phosphate coating has dried and before the component gets powder coated but am not sure about the feasibility.

Noah Rehman
- Toronto Ontario
July 18, 2025

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