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Metal finishing Q&As since 1989
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Non-etch stripping of anodic coatings on aluminum
Q. I'm interested to see what the industry is using for the removal/stripping of anodic coatings. We are currently using a caustic etch solution and are looking for a NON-ETCH strip solution. If you have any experience with a particular product your comments and recommendations would be appreciated
Tim Martinplating shop - Springfield, Massachusetts
1999
A. If stripping anodize coatings from aluminum the following solution can be used:
- 3.5 %/vol phosphoric acid
- 2.0 %/wt chromic acid
- Remaining D.I. water
Bring to boil and strip for 3 - 5 minutes. This solution will strip the anodize coating but will not etch the aluminum substrate.
Greg Haatajahelicopters - Fort Worth, Texas
Q. I have a client using a solution of ~ 3.5% Phosphoric acid and ~ 2.0 Chromic acid to strip anodized materials. It works fine...
The problem is the rock-like solids that build up on the walls of the strip tank. Short of using a jack- hammer he is unable to remove the material. Do you have any suggestions for cleaning out this strip tank?
![Art Kushner](../portraits/art_kushner.jpg)
Art Kushner
Anaheim, California
2000
A. Hi, Art.
The precipitant salts of aluminum (and some other metals) have a way of settling and pushing out the liquids they were not quite floating in. I discovered a few times that if you have one on these aluminum solids settled in a bottle, hard as a rock, with the liquids floating above it, that inverting the bottle a hundred times or so will get all that aluminum back in suspension. From this I am pretty confident that you can "wash" this precipitate back into solution by, for example, filling the tank with water, and pumping that water through a hose sprayed at the solids, and recirculating. Then you have to pump out the liquid and the resuspended solids before they settle and harden again. Good luck.
Regards,
![Ted Mooney, finishing.com](../portraits/ted_mooney_beach.jpg)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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