mobile?Metal finishing Q&As since 1989
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Adding more anodize to an anodized surface
Q. Can you add to anodizing once the part has been completed. We have some very close toleranced parts that were Type II anodized. We allowed for a total build-up of .0003/.0005 on diameter. When we received the parts they were .0001/.0002 undersize to the finish dimension. I'm afraid to have them stripped because the diameter is only a .0005" tolerance and stripping may remove base metal. Can I add to the already anodized surface?
Don TanskiManufacturer - Chesterland, Ohio, USA
2004
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A. If you have .2 mils anodic coating, after stripping you'll lose only 0.1 mils of your original dimension. If you anodized your part for .5 mils you'll add .25 mils approx. to your original dim. (by experience, at room temp). Anodizing requires more than 24 hours to close the pores, but I never tried re-anodizing. If you have sealed your coating, I don't believe that it is possible.  Khair Shishani aircraft maintenance - Al Ain, UAE 2004 A. No. Sealed anodizing (hydrated aluminum oxide) cannot be added to. Even if the anodizer skipped the sealing, then after a few hours in the air enough hydration (sealing) will take place to prevent additional anodizing.  Robert H Probert Robert H Probert Technical Services  Garner, North Carolina  2004 |
A. Once the coating is sealed, I'm afraid not. Work closely with your coater on tight-tolerance parts like this. I'd even provide them with a few "dummy" parts to coat, so all can be sure how the dimensions will change after coating. You didn't say whether it was an ID or OD, but remember, that unless your coater makes a special cathode to go into an ID, typically you will get less coating thickness on an ID.
Marc Green
anodizer - Boise, Idaho
2004
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