Black Stains on Zinc-Plated Parts

Our rack alkaline-zinc-plated parts occasionally exhibit black or caustic stains that don’t show up for 24 hours. Can we add anything to our plating solution or rinses to eliminate this condition?


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Q. Our rack alkaline-zinc-plated parts occasionally exhibit black or caustic stains that don’t show up for 24 hours. Can we add anything to our plating solution or rinses to eliminate this condition? —W. L.

A. I suspect that your problem is with rinsing after the plating step. The simplest solution is to investigate your rinsing procedures. Consider such things as improved agitation, adding a warm water rinse and perhaps increasing the flow rate in your rinse tanks. I am not a big believer in adding materials to process tanks unless they are absolutely necessary.

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