Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Alternatives to hexavalent Chromium
November 7, 2012
Q. I operate in the aerospace market where we supply hardware for cargo restraint. Our hardware is sourced in China and is generally zinc plated to withstand 96 hours corrosion resistance through salt spray testing.
A major client has ruled that we must eliminate Chromium 6 from our finishing by end 2013. We have no choice in this matter.
I need to find a suitable alternative finish that gives the same if not better perfomance levels and one which is available in Asia and in particular China.
We do use Dacromet for some parts however the thickness of this finish does not lend itself to all parts.
I would appreciate any advice.
Thank you
Procurement Manager - Bridgeport, Dorset, UK
A. Hi Stephen. This need not be a serious issue. It is simply a matter of specifying RoHS-compatible trivalent chromate conversion coating on your zinc plated parts, in lieu of hexavalent chromate conversion coating. These trivalent chromates are proprietary and widely available, in Asia, in China, and throughout the world ... and have been for many years now.
The only problem, which is a risk you undertake when you choose to have parts plated in China, is that just because the shop says they will do trivalent chromating doesn't mean they actually will if you are not looking. I am not bashing anyone or being xenophobic, just recognizing that cultures are different and it is apparently a significant aspect of manufacturing culture in China to get away with what you can get away with. You probably need to send an inspector there, plus regularly check the parts for the presence of hexavalent chrome, or risk a recall that could be costly. Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 7, 2012
November 12, 2012
Ted, thanks for your reply.
Q. Should I worry that trivalent coatings are not as corrosion resistant as hexavalent?
Procurement Manager - Bridgeport, Dorset, UK
A. Hi Stephen. Today's proprietary trivalent chromate conversion coatings are as corrosion resistant as the hexvalent chromates. They can be somewhat less robust if not operated correctly, and they do not offer a "self healing" property yet, but they are almost universally employed today -- for example, by every automobile manufacturer in the world.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 13, 2012
Thanks Ted
- Bridgeport, UK
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