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Anodizing stains

2006

We supply thresholds/ carpet bars to the transit industries and having a problem with stains appearing on the aluminum carpet bars after anodizing. We anodize to MIL-A-8625 / MIL-PRF-8625 [on DLA] E, Type II Class 1 .0007 Minimum thickness. The aluminum is #319. The discoloration is minimal but very evident and no pattern to its location on the carpet bar.

This is a critical item to our customer building transit cars for ALSTOM.

Dick LaPaglia
- Syracuse, New York

It is very difficult to prevent bleed out from castings. Even though you may "seal" the anodic pores, the porosity in the 316 casting can entrap and later bleed out all the solution from the process line. After sealing the anodizing, then do a hot-cold-hot-cold-hot-cold flushing to try to pump out the salts entrapped in the casting pores. Impregnating may be a fix, off line I can refer you to such a place.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2006

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