Letter 15066

Cad Plate Neutralization  

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We do cyanide cad plating for the aerospace industry. I am new the the cad plating process. Have done cyanide and non-cyanide zinc plating for many years.

My question concerns the neutralize step after cad plate and before chromate conversion coat. With zinc plate we would neutralize in a 0.25 - 1 % solution of nitric acid. Here, the neutralize step after cad plate is in a solution of chromic acid and sulfuric acid ( 10 % (w/w) chromic acid and 1% (v/v) sulfuric acid ).

Is there any special reason for neutralization in the chromic/sulfuric solution for the cad plate? Can cad plate be neutralized using nitric acid?

Thanks,

Lee Blanton
- Denton, Texas, USA

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I am not familiar with such a neutralization process, and admit that it sounds a bit strange to me. Is your cad plating cyanide based or is it a sulfate or fluoborate? May we assume that the chromate conversion coat is yellow?

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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