letter 32013

Alternatives to Chrome Conversion Coatings over Zinc  

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We are a contract manufacturer for the DoD of Cartridge Cases. The US Army prefers the cases Zinc Plated with an OLIVE DRAB chrome conversion coating. The only OLIVE DRAB color attainable over Zinc Electroplating is in the HEXAVALENT form. We are trying to get away from this HEXAVALENT chrome conversion coating for its toxicity. Is there a TRIVALENT chrome conversion coating being developed? I got information for Bright Blue and Yellow and even a Black color, but no Olive Drab. Does anyone have any information on any new developments in this area? Perhaps any spec changes on alternative coatings for cartridge cases from the Army?

Jesus Quinonez
Riverbank Army Ammunition Plant - Riverbank, CA, USA

The latest generation "thick film" complex trivalent chromates can be dyed, although for reasons that I don't claim to really understand, the dyeing seems to take a serious toll on the corrosion resistance. Stay in touch with the vendors, as I'm sure things will change.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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