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Trying to eliminate chromate in zinc plating line

My organization makes electrical control boxes. Many of our parts (small to mid sized) are plated in a zinc process. This process has a yellow dichromate dip as well. We use the chromate to prevent corrosion and also to give our product a yellow color. As a result of this process we have hex-chrome that is reduced in our wastewater treatment to tri-chrome. Our permit requirement on tri-chrome in disharge water is pretty strict and we also want to meet European standards for international business. Is there a method or chromate alternative that will give us the same/better product quality? We have tried tri-chrome solutions but with little success. I have also looked into HVOF/thermal spray but I'm not sure the company supports complete process change. Any help would be appreciated!

Jessica Siron
Industrial Intern - Bloomington, Illinois, USA
May 28, 2008

Hi, Jessica. Traditional hex chromating is simpler, cheaper, and more reliable than tri-chromating or chrome-free post treatment. That's why it was hard to replace. But the whole world is moving in the tri-chrome or chrome-free direction you are moving, and thousands of installations have enjoyed success with these alternatives. You simply must find a reputable supplier who can send in a technical service person to work with you until the reliability problems are resolved; there is no alternative to that except possibly hiring an independent consultant to work you through the problems.

Zinc plating is the least expensive metallic finish and it also offers cathodic protection, which many more expensive finishes do not. You will be doing yourself a disservice spending time on HVOF/thermal spray for a commodity like electrical boxes unless your product is very different from what I picture when I hear that term. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 28, 2008

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May 30, 2008

Thermal spray (HVOF) is very difficult to get into inside corners, even worse than spray paint in corners.

One alternative might be to go to a zinc alloy plating process. Zn-Ni is far superior to plain zinc, but it is more expensive and is a lot more picky than plain zinc. Its color is mottled which some do not like. Your customer will be the deciding factor on what you can "sell".

Ted's comments are very valid.

James Watts
- Navarre, Florida