Where theworld gathers for metal finishing
Q&As since 1989
-----
Chemical for easy removal of MIL-C-5541, CL3 ?
June 17, 2008
We are a producer of military airborne radar systems. Some of our dip brazed, 6061 Al housings are finished per
MIL-C-5541, CL3 all over, then externally finished with an epoxy paint system. Internally, there are certain areas of the chassis that require very good electrical bonding with circuit boards, that the chemical conversion coating is preventing. We know that we can abrade the coating off in these areas, but this is very labor intensive and can change surface finish and flatness, so I was curious if anyone knows of a chemical that is commercially available that will etch away the coating easily, without attacking the base aluminum.
Ken
Sr. Mechanical Engineer
radar systems engineer - Huntington, New York
It is cheaper and easier to mask the small area that you need contact with a proper tape that has been burnished with a wood or plastic paddle (stick). This can be removed after the process and you will have bare aluminum. There are several chemicals that will remove the coating, but you do not want that chemical running around on the inside of your part.
PS, this is a time consuming process also, so try the masking. The tape choice is very important, so try several to get the best.
- Navarre, Florida
June 19, 2008
I won't say that James' response is incorrect, however, hand application of tape on internal surfaces is sometimes difficult if not altogether impossible. Furthermore, tapes are reknowned for leaving adhesive residue that would degrade the ability to "electrically" bond to the otherwise bare aluminum surface. One technique that my firm has been particularly successful with is designing mechanical fixtures that prevent chromating on interior, masked off features and chromates only the exterior portions. This is obviously more costly upfront but once the investment is made it's (1) faster, (2) cleaner in that there is no residue on masked surfaces, and (3) less labor per piece required (i.e. cheaper).
Milt Stevenson, Jr.
Syracuse, New York
June 21, 2008
You might try 1:3 aqua ammonia, or a 10% solution of sodium carbonate / washing soda [affil links] in water, along with gentle abrasion. I don't think these would attack the Al basis metal, at least not very quickly...try it on a scrap part first.
Dave Wichern
Consultant - The Bronx, New York
June 28, 2008
You might try application of one of our paintlike peelable maskants. Apply by brush to the surface not requiring processing, then finish, then peel off.
Jim BaldwinMask Coat LLC
West Monroe, Louisiana
July 1, 2008
finishing.com is possible thanks to our supporting advertisers, including:
Q, A, or Comment on THIS thread -or- Start a NEW Thread