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topic 11466

Ductile Iron Zinc Plating


 

Our shop is trying to switch from a malleable to a ductile iron base metal and then zinc plate. When the ductile iron parts are plated using the same chemistry we use to plate the malleable parts the recessed crevices have a black soot that I suspect is graphite. Any ideas on how to address this. I think a more aggressive electroclean will solve part of the problem, but do I need to change anything on the HCl acid etch/pickle?

David A. McWilliams
- Columbus, Nebraska, USA


 

You didn't mention whether you use acid zinc or alkaline zinc. The bad news is that alkaline zinc is probably unsuitable for these parts. It has to do with a fairly complex phenomenon called 'hydrogen overvoltage', but in brief, zinc will not deposit on carbon-rich areas.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


 

We had the same problem. I switched the pickle to 5% sulfuric acid, and the problem was solved.

Michael Brewington
- Salisbury, Maryland, USA


 

Our shop uses an acid zinc process. Ammonium Chloride Zinc bath.

David A. McWilliams
- Columbus, Nebraska, USA



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