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Must I do salt spray testing of chem film if it will be powder coated?
2007
Q. Hello,
The company I work for is developing the needs for a new paint line to process aluminum alloy products based on the following customer requirements:
1.) Clean per TT-C-490
[from DLA]
2.) Pretreat per MIL-C-8514
[from DLA]
, or
MIL-A-8625 / MIL-PRF-8625
[on DLA], or
MIL-DTL-5541
[on DLA].
3.) Apply a TGIC powder coat that will pass several tests, including a 500 hr. salt spray test.
We believe that chem film would be the cheapest choice for our paint line but we're really wondering why we have to pass a 186 hr. salt spray test on the chem film panels when powder coated panels will have to pass their own test 500 hr. test. Isn't the chem film salt spray test redundant? Shouldn't the chem film panel salt spray test only apply if we weren't going to powder coat?
Thanks.
- Los Angeles, California
A. Yes, that would be my feeling, too, Dave. But you can't say you will comply with a spec and then just ignore some provisions because you feel them to be inapplicable. Rather you must take explicit exception to specific provisions in the specs. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007
Thank you very much, Mr. Mooney.
- Los Angeles, California
2007
2007
A. Dear Dave,
Having made your choice of the three pre-treatment options given to you by your customer (Chromate Conversion Coating
MIL-DTL-5541
[on DLA]) I think that you have not understood the options that this particular material offers the end user:
a) Stand alone pre-treatment including final finish.
b) Used as a pre-treatment to be followed by a surface coating. This would be powder coating in your particular case.
Evaluation requirements
Anyone providing application "a" would have to carry out 186 hour resistance evaluation.
Anyone providing application "b" would only carry out evaluation on the component after powder coating.
An article covering this subject is available at:
Chromate conversion treatment
www.pioneermetal.com/tech_bulletins/pdfs/conversion_coatings.pdf
Hope this clarifies things for you.
Birmingham, United Kingdom
2007
A. We're saying almost the same thing, Terry, but you can't decide that a provision in a spec is inapplicable based on intending to do "b" -- rather you must take exception explicitly.
"Intentions Change" -- a short non-fiction play involving Ted, and illustrating a point of law ...
- Attorney for the shop that Ted was helping defend: "And Mr. Mooney, did you have occasion to examine the electric bills for that chrome plating shop?"
- Me: "Yes sir, I did."
- Opposing council jumps to his feet: "Objection! Mr. Mooney states on page 23 of his deposition that he does not intend to examine the electric bills!".
- Judge: "Intentions change. Overruled. Move on ..."
- Me: "Yes sir, I did."
"Intentions Change -- Reprise " -- a short fictional play involving Dave ...
- Act 1 -- Customer to Dave: "Your chem-filming and powder coating is great, Dave, but we need a few parts in RAL 9999 color, which we know that you don't do -- so we're asking you to do all of the chem-filming, but to pull a small slip stream out to be sent to Company X for the RAL 9999 powder coating. They'll do the certifying for the RAL 9999 parts.
- Act 2 -- Customer to team members some weeks later: "Geez, Company X raised their price way to the roof, folks! We'll just ship this lot with the bare chromate. Per Mil-DTL-5541 Dave has tested them and certified that they pass 168 hours and that's all we really need".
Dave is much better off if he has previously said: "Exception to Mil-DTL-5541: Because the parts will be powder coated and certified accordingly, we take exception to salt spray testing the bare chromate or certifying its salt spray resistance".
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted,
I agree with your argument and we will state an exception to the customer exactly as you worded it. Thanks again.
- Los Angeles, California
2007
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