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Home anodizing not working correctly - on some aluminum

2003

I am (trying) to anodize parts from my motorcycle, some have worked, but others don't seem to be drawing any/enough current and are coming out an even pink colour, the pieces are 3-4 sq. inch surface area, I am using a 12 V car battery charger ⇦this on eBay or Amazon [affil links] , I believe they are cast, but I am not sure, so I tried to purchase a desmutter under the advice of Ted Mooney (letter 22496), I phoned around but had trouble finding a supplier (Ireland has only a small market of home anodizers), eventually a chemical company told my to make my own, he suggested 20% nitric acid with 15 g of Ammonium Bifluoride per litre for the parts I was trying to do. The parts are coming out of that solution a white-ish colour, but this has only gotten me a pink finished colour? when I connect an ammeter during anodizing it doesn't even register any current flow, I have checked for continuity, all seems to be fine. The acid solution is 10-15% sulfuric acid with 30 g of sodium sulphate per litre. The solution is stone cold after anodizing (8 litre tank).

My procedure is:

1)clean part
2)use ammonium bifluoride/nitric mix for 2-5 min
3)rinse
4)anodize at 12 V for 50 min (I tried 90 min--same pink result)
5)rinse
6)dye bath

Any help would be much appreciated, should I be trying to anodize at a higher voltage. Also will the nitric/ammonium remove old anodizing?

Thanks,

Robert H [last name deleted for privacy by Editor]
- Dublin, Ireland

The colder the solution, the more volts it will take. Anodizing pure (1100) aluminum can be done at 12 volts, but 15-18 would be a lot better. I doubt seriously if 12 V will work on castings. Optimum temp is 65 -70 F.

James Watts
- Navarre, Florida
2003

Robert, in an earlier letter (18282) you were hooking together three computer power supplies, with two in parallel, and a third one in series; now you've apparently got a new battery charger, but you still don't have a real anodizing rectifier/power supply--which is what you really should have. To anodize something you'll have to start at low voltage and gradually increase it as the insulating anodize film builds up. As James Watts notes, 12 volts probably isn't enough either. Another possibility is that your dye needs to be heated though.

Let me be clear, for the hundredth time in this forum, that I would not keep nitric acid or ammonium bifluoride around MY home, and I don't even have any pets or minors. I most certainly don't think you should. Nitric acid is also a severe fire hazard even in storage. So when you say you say that you are trying to buy this stuff "under the advice of Ted Mooney", I'd prefer it be re-worded a bit :-)

No, the desmutter will not strip anodize, but oven cleaner ⇦this on eBay or Amazon [affil links] will.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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I think that nitric -Fluoride will strip anodize. It will do it slower than attacking the parent aluminum, which can lead to a nasty surface finish. A semi safe strip is 1 lb of baking soda [in bulk on eBay or Amazon [affil links] in 1 gal 120 F water. If it strips too slow, add 1 teaspoon of Draino. Do not get in a rush! Keep it safe. Lower temp solution may require the addition of a second teaspoon of Draino. Adding a teaspoon of baby shampoo will help in the rinsing. If you use dish soap, use the cheapest thing you can find. The good stuff has lotions in it.

James Watts
- Navarre, Florida
2003

Ted,

I realize that you can't be giving advice about dangerous chemicals and I understand that, but I think you read my question in the wrong manner. I was not trying to fault you or this site in ANY way, you did say before that you wouldn't have these chemicals at home, so I should purchase a desmutter made by a company who knew what they were doing-because it would be safer, I took your advice on board and started looking for somewhere to buy some, I rang chemical/plating companies near by, none had an answer except that one guy who told me to make up the nitric/fluoride mix, I even tried to get a supplier in the US to ship their desmutter to me, but they told me they wouldn't ship it because it was dangerous. So the nitric/fluoride was a last resource. But even so I am still trying to get it to work, I trying to get a power supply that I can increase voltage during the process, but I am not having much luck.

Thanks for the suggestions.

Robert H [last name deleted for privacy by Editor]
- Dublin, Ireland
2003

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2003

Thanks, Robert, I appreciate that. In the USA we tend to have "strict liability" laws; not being a lawyer, I'll just say that that apparently means a supplier can be found responsible for damage that a buyer does. So nobody will try to make $20 shipping dangerous chemicals to a residence when they could perhaps find themselves sued for $20 million.

James Watts has told you about the stripper. So when you get a higher voltage, adjustable, power supply you should be in business. Good luck!

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

The "pink coloration" you describe is the result of a very thin coating. Ted has it right on the money, go buy yourself a 0-18 or 0-24 V 50-100 Amp rectifier. These are common, and I believe a few of the "hobby plating" places that advertise here do sell them. Without the right tools, you'll never get the job done. You can shoot at the target till you're out of bullets, or you can go buy yourself a new gun and hit the bullseye the first time :-) Your choice in that regard.

Matthew Stiltner
plating company - Toledo, Ohio
2003