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Simple test for presence of clear chromate
(2002)
We are trying to confirm the presence of a clear chromate conversion on an aluminum extrusion. Is there a simple chemical (or other) test that can confirm that the chromate is there? Specifically, the coating is per Mil-C-5541 [link is to spec at TechStreet]E Class 3, and the base metal is 6063-T5 aluminum. Is it possible to determine that it meets the class 3 thickness? We are trying to avoid the costs of outside material testing.
Thanks,
Mark Mozgowiec- Cambridge, Massachusetts
(2002)
My shop does chromating both clear and yellow.
Our testing indicates that we can not meet the mil-spec with a clear coating.
At our shop we offer the customer the choice:
- they can have clear chromate, not certed to a spec or they can have yellow chromate with a cert
I know of no test you can do, BUT, I do know to get a truly clear coating you need to put on very light coating.
I would be interested in hearing if you find a test & if so, if your parts meet the mil-spec. I have posted this question here many times re: meeting mil spec with clear chromate & some finishers respond that they do clear chromate & it does meet the spec - but no one referenced a specific QPL approved chemical to do this.
David A. Kraft- Long Island City, New York
+++++
Gentlemen,
I am an engineering student at a company that offers in house chromating. Recently we've switched to a trivalent chromium to meet a new European directive that limits the use of hex chrome (among other heavy metals).
The problem I was facing with this new tri chromate is that the finish is practically invisible if no zinc plating is done previously. I was asked to find a simple test for the presence of chrome. Upon searching I found your site.
Our base alloy is 99% zinc so this might not work for aluminium. The process is as follows.
Lead Acetate Tri Hydrate
[Pb(C2O3H2)2*3H2O]
Mix 50 g in about 1 litre of water. Filter for white precipitate or use acetic acid to dissolve. The solution should have a pH of 5.5 -
6.8
Place a drop of this solution on the part and wait 5 seconds. With a cotton swab, gently blot.
A dark deposit or black stain equates NO COATING.
The Spec for this test is:
ASTM B201-80 [link is to spec at TechStreet]
I suggest reading that first and also obtaining a proper MSDS for Lead Acetate.
This test is for Zinc and Cadmium surfaces... Perhaps it is worth an experiment.
Cheers,
JG
- Peterborough, Ontario, Canada
July 28, 2009
There is a newly developed trivalent chromium conversion coating two drop test kit on the market yo detect the presence of Trivalent Chromium on aluminum substrates, Trivalent Tester LLC.
James Savoy- Columbia, Maryland
November 21, 2011
Dear Gentlemen,
Just make sure that your chromating solution is acidified to ensure that it is zinc chromate you are seeing on the galvanized material and not the aluminum oxide layer.
Regards.
| Barlow Campano galvanizing chemist - Jeddah, KSA |