Chemically stripping anodizing

[Swede]

???

Fellas - Anyone know how to do this? I'd rather not attack a particular aluminum part with abrasives, but the current anodizing must come off. It's not hard-coat, just regular black anodize on what I am guessing is either 7075 or 6061.

I have a pretty-much full chemistry lab at my disposal, plus power supplies if necessary. Any hints and/or guidance would be appreciated.

 

[rleete]

Sodium hydroxide will take it off. It will also disolve the part if you're not careful.

Depending on strength of solution, it can take from 30 seconds to an hour.

 

[Sic Semper Tyrannis]

ez off oven cleaner I think will work.

 

[Tin Falcon]

drano crystals
Tin

 

[Swede]

OK, sodium hydroxide it is, then. Thanks, I'll give it a try.

 

[John Rudd]

I'm sure cellulose thinners works... ???

Mind its a long time since I tried....But I'm sure I used it take off the black coating on my bike casings which were alloy and supposed to be anodised( English spelling ;D )

 

[rleete]

drano crystals

Drano (and other drain cleaners) are sodium hydroxide. I happen to be able to get industrial strength liquid here at work, but almost any off the shelf brand will do. Sodium Hydroxide is commonly called lye. I believe it is also the main ingredient in most oven cleaners.

Take care with this stuff. It will cause burns, and can blind you.

 

[Swede]

I mixed a 10% NaOH solution and immersed the anodized part in it from a stainless wire. The anodize came off after maybe 4 to 6 minutes. It worked very well. The trick is, one must cease after the anodize is gone, or you will lose virgin aluminum. I stopped when there were still traces of andize, and these were smut and came off with a cloth.

What's left behind is a kind of matte finish.

Professional shops use a chromic acid mix that won't attack aluminum, just the oxide, but chromic acid is hideously toxic and it is not something I'd mess with.

 

[rleete]

but chromic acid is hideously toxic and it is not something I'd mess with.

You got that right. We're an electroforming shop, and we won't have the stuff in-house. That should give you some idea how nasty it is.