Metal finishing Q&As since 1989

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Selectively stripping hard anodize

How we can remove hard black anodize?
We have some parts that their thickness is more than our request so we must remove it in some places of that parts.

Farhad Mahshari
product designer - Tabriz, Iran
May 12, 2010

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May 17, 2010

Farhad,

Stripping Hard Anodic coating is quite difficult

1. You can dip in etch bath / 5-10% NaOH solution, the problem here is the base aluminum surface also gets stripped off

2. Non-etch type strip: which removes only the oxide layer is Chromic Sulfuric mixture: in water say 150 g/L Chromic acid and 50 g/L sulfuric Acid, at a little elevated temp. The problem here is Cr6+ / effluent treatment

3. Some "non etch" strippers are available commercially too.

4. Some times you can't get strip it off uniformly, when your sealing is stronger...what we do is immerse the component to be stripped in desmut bath (Nitric acid 10-15%) for about an hour and then rinse and strip..

Hope this helps...

Keshava Prasad M
- Chennai, India