|
Letter 17722
Simple test for presence of clear
chromate [Massachusetts]
++
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, MA, USA
++
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.
+++++
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 50g 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
Jeff Gilchrist
- Peterborough, Ontario, Canada
Dear Reader: please choose what you want to do.
- I want to post a
question or inquiry of my
own.
-
- I want to answer or follow-up on this question
publicly (in non-commercial
fashion).
-
- I am a supporting advertiser and want to
reach
the inquirer privately.
 |