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Spots in the anodic film

I have been anodising aluminium since 1977 but over the last 2 years I have had a problem that I can't solve. We have spots which appear on the surface and sometimes you can feel a center sometimes you can see a center of the spot. It would appear that a particle has burnt out and caused a flare but we get this on different material, not usually on machined parts. On a clear anodic film it is possible to see almost a dust on an edge which is slightly rough to touch. We have 2 anodising vats, 1 with aluminium cathodes the other with lead. The solution is 10.5% and 12%, both run at 21.0 Centigrade. The dissolved aluminium is 6 and 9 g/lt

Nicholas Rogers
Director - United Kingdom
May 17, 2010

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Do you find them in your lead-cathode bath, or in both?
It would be better if you can paste a photograph of the defect, because there are so many varieties of spot defects for various reasons. Your anodising parameters appear to be ok.

Thanks

Srimay Basu
- Dubai, U.A.E.
June 6, 2010

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Yes, we are seeing more and more of this kind of problem as 3rd world countries get into the smelting business and send their inferior metal into our shops. Go back to one of the original "big-4" reputable suppliers and see if the problems go away.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

June 8, 2010