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topic 47037

Chromate conversion on cadmium not adhering

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A discussion started in 2007 & continuing through 2017


Q. We have a steel stamping that is cad plated with chromate conversion- it is then painted

We have problems with the paint coming off and it appears to take the yellow conversion coating with it. Any ideas what could be causing this? It appears the conversion is not adhering to the base cad metal.

Joe Arnold
machine shop - Falconer, New York


A. I don't think you can troubleshoot this problem from your position or we from ours, Joe. You need to make contact with the plating shop and have them figure out what's wrong. It could be excessive brightener, and the next batch could be fine; it could be an unsatisfactory attempt to substitute trivalent chromating. Too many possibilities, I think :-)

Ted Mooney, amadeya42.com Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

simultaneous (2007)

A. I've seen problems like this arise both from excessive brightener, as Ted suggests, and from poor post plate rinsing.

If it's the latter, a dip in 1 - 2% nitric acid before the part goes in the chromate might help. And, of course, using cleaner water.

dave wichern
Dave Wichern
Consultant - The Bronx, New York


A. Joe - Falconer isn't all the far from Syracuse where my shop is located. It would be a whole lot easier to see the actual hardware that is exhibiting the problem (if at all possible before and after painting). I'd be willing to do so if you're willing to send in a couple of parts to review. People like to point their finger at the plater, but contamination post-plating is a likely cause as well. Have you gotten good parts in the past? Have you changed painting houses? How long was the lag between plating and painting? Do the parts require embrittlement baking between plating and chromating? There's a lot more to solving this issue than "why is the paint coming off?"

milt stevenson jr.
Milt Stevenson, Jr.
Anoplate Corporation
supporting advertiser
Syracuse, New York

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A. Ted,
Trivalent chromate on cad? I am yet to hear of such a product. I have had several people asking about one but know of none. Part of the reason is economics, a small market.

That being said, Joe make sure the plater is actually plating the cadmium you have specified and not substituting zinc. There are not too many platers who still plate cadmium due to lessened demand and the toxicity of the bath components

Gene Packman
process supplier - Great Neck, New York


thumbs up sign No, I haven't heard of a trivalent chromate designed for cadmium, Gene; but perhaps the plating shop is trying to apply a trivalent chromate to cadmium that wasn't meant for cad and that's why it's not adhering? :-)

Ted Mooney, amadeya42.com
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. I think there is no need to chromate at all if a topcoat of powder or paint is being used. Cadmium is used because it forms its own oxide topcoat which retards further corrosion, unlike zinc that corrodes away.

It might be worthwhile to see if a light phosphate over the cadmium would work better.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

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June 13, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. The passivation done after cadmium plating is coming off on simply rubbing with cloth.
Can somebody please suggest remedial measures?

Thanks & Regards

sahil arora
- kanpur, india

August 8, 2017

A. Hello Sahil!

Usually if you can remove the chromate with your fingers or a cloth, there are two big possibilities:

-Organics in your cadmium/zinc bath are too high.
-Concentration of the chromate bath is too high.

This two possibilities have a relative probability that depends on each facility and methods, so please explore them and let us know what you find!

Best regards!

Daniel Montanes
TEL - N FERRARIS - Canuelas, Buenos Aires, Argentina

November 26, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hello all,

I have a small cad plating tank for doing small parts. Everything was working very well until I lost my finish gold dip bucket; it cracked and leaked out.

After getting more gold dip and mixing according to the recommended ratios, same as before, I cannot get the gold to stick.

It will coat evenly but wash off.

The cad seems to be coming out nice and bright; just cannot get the gold dip to adhere.

Chip Woods
- Memphis, Tennessee USA

November 2017

A. Hi Chip. I am guessing that when you talk about 'gold dip' you are referring to a yellow or gold colored chromate conversion coating designed for cadmium plating. So we appended your inquiry to a thread about that problem.

Daniel has given you two good possibilities, and your statement that "the cad seems to be coming out nice and bright" might be a clue that you have too much brightener (organics). But it is not quite clear to me whether you are attempting to chromate conversion coat freshly plated parts and it no longer works, or whether the problem might be that after you got a replacement container and replacement solution and made up the process, you are now attempting to chromate conversion coat cadmium plated parts which you plated some time ago (before the leak); if that is the case, the surface may no longer be active enough for reliable chromating anymore.

(It's not clear whether you are a small industrial plater or a hobbyist. Since you didn't mention catching the leaked solution in a secondary containment vessel, perhaps it's the latter. If so, I hope you have researched the toxicity of cadmium and hexavalent chromium; they're bad ones).

Luck and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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