Anodizing Aluminum

[Bob Gross]

It seems to me that any inside lining out to bake out with excess heat.

Then there is the problem of optional color dyes. There are acid dyes and vegetable dyes for fabric. Apparently those can be used _before_ the anodized surface is sealed. Maybe that would be gilding the lily.

I was going to do this outside on Monday (outside for ventilation). Then it rained. I'll get around to it. Maybe I should empty some more containers first.

–B.G.–

[Bob Gross]

We have identified several commercial food or beverage containers that are made from aluminum, and they are candidates for this treatment. This includes aluminum beer bottles, plus maybe soft drink cans and others. Note that all of these are rather tall and skinny.

What recyclable aluminum containers are there that are short and fat? The only one I can think of right now is a Sterno can. Hmmm. It's a lot easier to empty the aluminum beer bottles.

–B.G.–

[Kevin Beeden]

> "Miller Lite" is not a desired color to me.

Okay, your concern is cosmetic. That's fine.

The difficulty of removing the 'paint' is one reason why I'm not sure what the surface treatment is. It may be a printed dye that is taken up by the anodizing, or it may be a conventional paint that is then lacquered with a thin coating of the epoxy-phenolic that's used for the inner surface.

The White Box Stove seems to have the surface finish removed, but it doesn't look like this has been done abrasively (comparing the WBS with a raw Budweiser bottle). Maybe the guy who makes them could advise?

Having made a number of chimney stoves, I've found that the inner coating does tend to char and come off in use. In fact, it's probably wise to try to remove most of the coating from the can dimple that forms the chimney opening before doing the first few runs outside; the fumes coming off smell quite unpleasant (and that's with my somewhat relaxed approach to chemical ingestion…). You have to expose it to quite a flame to get it to come off, and it's pretty hard to remove with abrasive.

I'd be tempted to leave the internal coating in place, unless you intend to heat the bottle above 100C. After all, the coating is intended to resist attack by dilute phosphoric acid (cola), and fruit acids (fruit-based drinks).

[Bob Gross]

Well, that was an interesting experiment. The electrolyte was 2 gallons of Exide battery fluid. The acid vat was a 2-gallon bucket, and the cathode was a length of heavy gauge aluminum wire. The power supply was a 12VDC 5A car battery charger. The first bottle became the anode. It ran for 3-4 hours and slowly bubbled away. I extracted it, rinsed it, and then attempted to put a hot color dye on it. The anodized finish looked OK, but the dye would not stick. I ran my second bottle for 3-4 hours and it slowly bubbled away. I extracted it, rinsed it, and stopped. Somehow the aluminum wall had been etched to be thinner than what I started with. Just touching it with a finger, and it would bend.

Neither went exactly as I planned. I expected to get aluminum that was slightly harder than what I started with.

Nothing ventured, nothing gained.

Any suggestions on what I did wrong?

–B.G.–

[Josh Leavitt]

Bob

You need a lead cathode. For doing beer cans you wont need much, a couple of battery clamps with anything that is not lead removed will work. Make sure you have a good conection between your heavy gauge aluminum wire and cathode. Zip lock bags of ice, you want the acid solution to be ~65*. 45 mins to an hour is all you should need in the acid. Mix up RIT fabric dye, on the strong side, in a stainless pot, and heat to ~140. Pull the beer can out of the acid bath, leave it on the aluminum wire, rinse with cool clean water, do not touch it with your hands. After rinsing, place it in the dye bath for about 10-15 mins. pull it out of the dye bath, rinse, and place it in boiling water for ~5 min. The boiling water seals the "anodized" surface and locks in the dye. The big one, is to make sure your conection between you aluminum wire and your beer can is very very good and tight. If that connection fails, its all over, and nothing will happen. Its been years since I've done this, but I think thats about it.

[Bob Gross]

Why do you need a lead cathode? What is wrong with a heavy gauge aluminum wire for a cathode (maybe 18" immersed)? As soon as I turned the power on, I had bubbling from the entire length of it. If the electrical connections had failed, the current meter on the charger would have dropped to zero.

I'm not sure that ice would have done much since the air temperature outdoors was about 65 F, and the acid vat was not getting warm.

The Rit dye was mixed up strong into near-boiling water, and the cold rinsed bottle went directly into the dye bath. Almost zero dye stuck.

The one where the aluminum was etched thin kind of surprised me.

–B.G.–

[Josh Leavitt]

Bob

I honestly dont know why, but we always used lead cathodes for anodizing. And I've built allot lead cathodes for hard crome plating operations.

Temp doesn't sound like an issue.

The connection between the aluminum wire, and the beer can needs to be tight though. You cant just hang the can from the wire. The can needs to be the anode. You wont be able to tell if that conection goes bad from the meter, because the hang wire will still make a circuit.

[Colin Krusor]

Bob, I tried sending you a PM but it isn't enabled, evidently. Did you pursue anodizing aluminum cans any more in the 18 months since the last posts to this thread?

I tried it recently and got mixed results. The photo below is one I did today. It anodized, dyed, and sealed fine, but it also got a few corrosion pinholes in the anodizing bath. Have you made any progress since this thread was last updated?

[David Thomas]

One advantage to lead as an anode is that it is very resistant to corrosion and plating solutions have to very acidic, basic, or salty to carry the current.

I'd think if you had a good connection and the whole can was an anode, you could easily detect a higher current.

[Bob Gross]

"Have you made any progress since this thread was last updated?"

Nope. The cans got thinner and more fragile as I went farther along.

–B.G.–

[Tyler T]

You want to use a lead anode, as an aluminum anode might get anodized (and anodization is not conductive, so the process stops prematurely).

Similarly, you want a strong physical connection to your parts being anodized. If the connection is weak, anodizing creeps into the joint, current stops flowing, and anodizing ceases early.

If you're getting corrosion pinholes in the ano bath, I'd increase the current and decrease the time spend in the bath.

[steven franchuk]

"Have you made any progress since this thread was last updated?"

"Nope. The cans got thinner and more fragile as I went farther along."

the Anodizing process does nothing more than converting aluminum to aluminum oxide. It's a controlled corrosion process. Most anodized pots and pans you see in the stores have 2 to 3 thousandths of an inch of of aluminum oxide. So if you start out with a thin aluminum can you will end up with a very thin aluminum foil with a thick aluminum oxide coating which has no strength. So it is not practical for thin aluminum cans.

You don't need to use a dye in the anodization process. Also I would not use lead if the part to be anodized is going to be in contact with food. Lead is toxic.

[Bob Gross]

"You don't need to use a dye in the anodization process."

The dye is part of the dye process for color.

–B.G.–

[Colin Krusor]

Tyler, the aluminum workpiece is the anode. The cathode doesn’t need to be lead. I’ve used a 6061 aluminum cathode to successfully anodize a handful of articles of several different (3000 and 6000 series) alloys. I've read that stainless steel and titanium also work as cathode materials. Thanks, though, for the tip about increasing the current and decreasing the anodizing time to reduce pitting and pinholes.

Steven, I think anodizing results in a part having a layer of aluminum hydroxide monohydrate on the surface, not aluminum oxide. The aluminum oxide that forms on the part in the anodizing bath grows into and out of the metallic surface of the part as irregular dendrites. The dye intercalates between these and is trapped when steam sealing converts the superficial parts of the aluminum oxide layer to aluminum hydroxide monohydrate.

The purpose of the dye, in my view, is to confirm that a uniformly anodized surface has been achieved. If some of the epoxy lining of the can wasn’t removed, for example, so a spot wasn’t anodized, I wouldn’t know it unless I used dye. I elected to use food coloring instead of special anodizing dye, and it worked fine.

[M B]

Have you tried ordering it from Autozone and having it shipped to store for pickup?

I think they stock it at the stores anyway, $4 qt
You shouldnt be hit with any hazardous shipping charges for store pickup.

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