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Gas Pitting in Hard Chrome

June 3, 2011

We use a standard chrome plating bath and have been having pitting problems, inspection of the pits shows rounded pits with chrome in the bottom. Also, pitting is worst on the top of a part where the flow is the slowest. To me, this looks like gas bubbles causing the pitting (feel free to offer other suggestions).

According to the ASM Surface Finishing Handbook Vol. 5, gas pitting can be fixed by either agitating the part or having a better surface finish. We bubble air past the surface when we can which has helped, but for many parts it just can't be done.

We grit blast the surfaces prior to plating with 80 grit garnet, do you think using 180 grit would make a difference with the gas pitting?

Any other suggestions?

Mark Robison
Process Engineer - Ogden, Utah

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Hi Mark,

Assume pitting really due to micro bubbles (metallic impurities or organic contamination can cause pitting as well), you may add some wetting agent to reduce bath solution surface tension so as to get rid of bubbles and wet the plating surface easier, or install vibrator/bumping system to remove bubbles besides increase solution agitation or grit blast plating surface.

Regards,
David

David Shiu
- Singapore
June 9, 2011