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Is trivalent chromating a billion
dollar farce?
by Ted Mooney
Drop whatever you are doing and read "Unexpected Results from
Corrosion Testing of Trivalent Passivates" by Tom Rochester and
Zachary W. Kennedy in the Oct. 2007 issue of Plating & Surface
Finishing.
This may be the most important surface finishing paper of the
decade. -- Ted
Mukund Shinde
Shinde Chemicals Pvt Ltd - Mumbai, Maharashtra, India
Mr.Mooney,
I think you are one of the few people in the industry who understands
the surface finishing aspect of chromate conversion coatings. In
terms of trivalent coatings most of them do not provide adequate
corrosion resistance to zinc plated surfaces which may be virtually a
known and accepted fact throughout the plating industry. We have been
in the industry for 30+ years, my personal experince being 15 years
(I started at a early age of 17 in the industry) and know the
importance of a good chromate passivation.
Though there are claims from various formulators to provide
trivalent chromates which provide 100+ hours of corrosion resistance
we desist from making such a claim. The best life we have observed
from testing all the materials available is about 80+ hours, that too
with a good organic top coat. I tend to agree with your point of
view. For me on a personal front, although I agree it's toxic and
environmentally hazardous when introduced in the environment, hexa
chrome remains plated zinc's best friend. Parting note is that
untreated trivalent chromium is almost as hazardous as hexa chrome.
Thank you for beginning of a worthwhile discussion. -- Mukund, Nov. 11, 2007
Thank you, Mukund, but I am not a chemist , and do not actually have the deep understanding of trivalent chromating that you credit me with, just an ear to the ground. Please listen to our Podcast Interview with Tom Rochester on the subject. -- Ted
Update
by Ted Mooney
Please see letter 47049, which includes a reply by Eric Olander of EPI, with details about a Sur/Fin paper/session addressing the issue (I infer that this paper will rebut the theory of spontaneous conversion to hexavalent), The same letter also mentions an article by John Bibber of Sanchem which includes photos and test results supporting the conversion to hexavalent -- Ted
Frank Zemo
Polaris Plating Inc. - Paterson, NJ
How many platers or their customers actually test for tri versus
hex chromate in production parts anyway? The whole system of PPAP
testing is flawed and open to misinformation. It seems to me that
quality systems and the elegant documentation they generate have
replaced actual "fitness for use" . But guys sure do feel "cool"
flashing their black and green belts around the office don't
they!
( Forgive the cynicism. Guess I'm getting old!)
Reply
The principal hubris that permeates industrial management systems and society as a whole is the belief that every generation before us was dirt stupid, but we've finally got it right. 40+ years in business and 60+ on earth tells me that 10 years from now most of today's practice will be completely discredited 🙂
Regulations, on the other hand, tend to stay on the books long beyond their useful life. So their intended benefits quickly evaporate, while their unintended consequences plague us for additional decades 🙂 -- Ted Mooney
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