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Colour variation with trivalent dips after zinc plating

Hi, I run a electroplating plant on the Central Coast of New South Wales. Australia. We electroplate our own "in house" products nickel on a automatic line, we also do zinc plating for external customers. We have recently converted to trivalent"yellow" and "silver/blue" dips after our zinc plating (acid-chloride). We have encountered two problems. Firstly colour variation with the yellow dip on a single component. And secondly the trivalent yellow gives an extremely light yellow colour, one customer called it "champagne" or "chardonnay" that's how light it really looks. Can you please give me some advice on these problems? Thank you..... Pete

Peter Hordern
Plating Supervisor, Metallurgist. - Gosford N.S.W. Australia
June 4, 2010

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Hi, Peter. Trivalent chromating is completely proprietary and based on several different approaches. It is claimed that the "thick film" trivalent chromates can give a rich yellow color. However, if I were you, I would lobby for getting the customer to accept "champagne" by explaining that the origin of the deep yellow color that he is familiar with is the toxic, carcinogenic, hexavalent chromium slathered onto the parts :-)

The dark yellow color IS hexavalent chromate and there could be future value for him in making sure his parts aren't that color. You never know when the Sierra Club, or Audobon, or PIRG, or EPA might start calling public attention to the presence of hexavalent chromium compounds on articles that people touch.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
June 4, 2010

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