Alodining to MIL-C-5541
One of my clients is a small civilian repair shop. I'm setting up a process for them to perform 'alodining' to Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil]. The application is non-critical - basically the surface preparation is for painting. The QA provisions for MIL-C-5541 are fairly onerous for a small shop so I was going to allow some exemptions from testing (i.e., para 4.5.1 and 4.5.2). Does anyone have comments or suggestions for this type of situation?John Roberts
- Richmond, BC, Canada
First of two simultaneous responses -- 2002
Paragraph 4.5.1 probably will not be necessary if corrosion resistance isn't an issue (i.e., entire component being painted). However, 4.5.2 verifies paint adhesion and, in my opinion, should not be waived. If it is not possible to do either test, than a simple paint adhesion test on the component itself may be enough process verification for you since the application is not critical. Alodine solution should be analyzed however for pH, temperature and concentration.John Wickersham
aircraft products - Ravenna, Ohio
Second of two simultaneous responses -- 2002
John, if you're not going to do the corrosion resistance or the wet tape adhesion tests, how do you show process control as required in 4.3? These test are monthly anyway, and can be done by sending the panels out to a test lab, should your client not want to muck about with it.
My company would have serious heartburn with you skipping parts of the specification. If all you are doing is a paint base application, maybe your client should "Alodine per Henkel instructions" rather than "chemical conversion coat per Mil-C-5541".Lee Gearhart
metallurgist - E. Aurora, New York
I agree with Lee, If you are stating to customers that the conversion coatings are to MIL-C-5541 then all aspects of the spec should be adhered to. Allowing exceptions simply means that the coatings are in fact not to specification.Rich Mosley
metalsmiths - UK
I may prove myself ignorant, but I have to disagree with Lee and Rich this time. Specifying "Mil-C-5541 except blah, blah" is much better than not referencing a spec. Again and again over the years I have watched as buyer and job shop got into nasty and costly contract disputes because the only spec anyone was working to was "commercial zinc plating with yellow chromate"--or something equally vague and ultimately meaningless.
I think you are much better off clearly stating what you are doing and not doing than relying on generalities like "chromate conversion coat" because everyone will not agree on what that should include.
So I see nothing wrong with writing: "Chromate conversion coating per Mil-C-5541 except blah, blah".
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha