Can you remove anodizing color from aluminum?

[wce4]

I dislike the color of the base frame of the USS Monitor side-lever engine that I'm in the process of machining / building. Does anyone know of a easy way of removing anodized coating that will not distort the aluminum ?
I would like to powder coat the frame in a gray that I have instead of the anodized gray that looks dark blue to me.

 

[ChazzC]

No where near an expert, but since anodizing is basically dying the Aluminum with the color adsorbed into the surface (or the oxide surface) removing it may not be possible.

Maybe you can powder coat over the anodized surface?

 

[ChazzC]

Duplicate Post

 

[wce4]

No where near an expert, but since anodizing is basically dying the Aluminum with the color adsorbed into the surface (or the oxide surface) removing it may not be possible.

Maybe you can powder coat over the anodized surface?

ChazzC thanks for the fast reply
"Maybe you can powder coat over the anodized surface?"

That may be a solution but, when anodizing the aluminum it decrease its conductivity and when powder coating you need to introduce a electrostatic charge. An electrostatic charge holds the coating onto the surface.
Does anyone out there know if this is possible?

 

[GreenTwin]

A quick search shows one method involves soaking the part(s) in a caustic compound, using diluted hydrochloric or sulfamic acid.

.

 

[ignator]

That may be a solution but, when anodizing the aluminum it decrease its conductivity and when powder coating you need to introduce a electrostatic charge. An electrostatic charge holds the coating onto the surface.
Does anyone out there know if this is possible?

You may have to remove some of the anodizing to get the ground clip to energize the main part you want to put the powder coat on. But that anodizing will not affect the ability for the powder to adhere via the static attraction.
A bigger problem is the machined holes and tight tolerance items will need to be remachined if you have them on the base. Threaded holes, same issue to prevent the powder coating from getting into them. Or run the tap in them again to clean them up.

 

[GreenTwin]

So why not just powder coat over the existing surface finish ?
You can always remove a thin surface finish with a fine sanding sponge in a rotary tool.

.

 

[wce4]

You may have to remove some of the anodizing to get the ground clip to energize the main part you want to put the powder coat on. But that anodizing will not affect the ability for the powder to adhere via the static attraction.
A bigger problem is the machined holes and tight tolerance items will need to be remachined if you have them on the base. Threaded holes, same issue to prevent the powder coating from getting into them. Or run the tap in them again to clean them up.

So why not just powder coat over the existing surface finish ?
You can always remove a thin surface finish with a fine sanding sponge in a rotary tool.

.

It seems to me also that is my best option is to powder coat over the anodized surface. I am going to give it a try and hope for the best. Thanks ignator and GreenTwin.
Will keep you posted on the outcomes?

 

[Weldsol]

just a thought you could also try shot blasting with a fine medium but you would have to plug the bores of any machined hole and mask any other machined surfaces
paul

 

[toolsrul]

I dislike the color of the base frame of the USS Monitor side-lever engine that I'm in the process of machining / building. Does anyone know of a easy way of removing anodized coating that will not distort the aluminum ?
I would like to powder coat the frame in a gray that I have instead of the anodized gray that looks dark blue to me.
View attachment 159131

Contact a plating shop that’s familiar with plating aluminum

 

[L98fiero]

Apparently it can be stripped with a mix of antimony trioxide and sulfuric acid 40% at 80 °C that will leave an antimony deposit, then to remove the antimony, a dip in nitric acid 30% at room temperature. Nitric acid is nasty and heavily regulated, so probably not a great solution. In the past I've just used sodium hydroxide/caustic soda in a heated solution, a teaspoon or two per gallon @ 130°F, I had a much larger tank and many years ago but those should be workable numbers. You have to pay attention as, depending on concentration and temperature, it acts quickly and will dissolve the aluminum as well. It will leave a black 'smut' that we removed with a nitric acid dip but after a rinse, it could be wiped of as well. Hot caustic soda baths will not kill you just for looking at them, or being in the general vicinity, but do require suitable safety precautions, after all, it's just lye that has been used as a drain cleaner for decades.

 

[creast]

Caustic soda has been my go to for stripping anodising.
It is often used before anodising too to condition the surface and clean but has to be used with care as it will eat away the aluminium.

 

[dsage]

Not sure if you have a household cleaning solution called Spray Nine in your area. At work we had many aodized black aluminum parts and inadvertently put them in an ultrasonic cleaner with Spray Nine to remove the grease and they came out free of anodizing. No harm to the parts other than that.
As was mentioned above it is slightly caustic according to the label. Probably the reason.

 

[Jens Eirik Skogstad]

Use ultrasonic cleaner, very effective to remove color from aluminium.

 

[Richard Hed]

I dislike the color of the base frame of the USS Monitor side-lever engine that I'm in the process of machining / building. Does anyone know of a easy way of removing anodized coating that will not distort the aluminum ?
I would like to powder coat the frame in a gray that I have instead of the anodized gray that looks dark blue to me.
View attachment 159131

Huh! I likes the color. Can you maybe give it a light sanding? I know that coating is REALLY tough, but maybe just paint over it.

 

[Richard Hed]

Apparently it can be stripped with a mix of antimony trioxide and sulfuric acid 40% at 80 °C that will leave an antimony deposit, then to remove the antimony, a dip in nitric acid 30% at room temperature. Nitric acid is nasty and heavily regulated, so probably not a great solution. In the past I've just used sodium hydroxide/caustic soda in a heated solution, a teaspoon or two per gallon @ 130°F, I had a much larger tank and many years ago but those should be workable numbers. You have to pay attention as, depending on concentration and temperature, it acts quickly and will dissolve the aluminum as well. It will leave a black 'smut' that we removed with a nitric acid dip but after a rinse, it could be wiped of as well. Hot caustic soda baths will not kill you just for looking at them, or being in the general vicinity, but do require suitable safety precautions, after all, it's just lye that has been used as a drain cleaner for decades.

I didn't know nitric was heavily regulated. I thimpfks I can use it in silvering telescope mirrors.

 

[swst]

Alkaline etching is usually more thorough in removing the colors. In the case of unsealed anodized parts, you can consider 10-15% nitric acid to help eradicate the dyes.

 

[The Ignoble Troll]

I didn't know nitric was heavily regulated. I thimpfks I can use it in silvering telescope mirrors.

Depends on where you live. In many places it is regulated above a certain %.

Your friendly neighborhood hydroponic shop probably carries it in the 10%-15% range as "pH down". Thats where I bought it, in my youth, to give HCl some kick when analyzing samples of stainless steel I made from raw oxides.

Re mirrors; Silver Nitrate is usually easy to get. Last time I bought some was either from Amazon or Ebay. I forget which.

 

[L98fiero]

I didn't know nitric was heavily regulated. I thimpfks I can use it in silvering telescope mirrors.

I found that, in Canada anyway, though our regs are pretty much dictated by the US, only 75%+ is regulated as an explosives precursor

 

[Richard Hed]

I found that, in Canada anyway, though our regs are pretty much dictated by the US, only 75%+ is regulated as an explosives precursor

I thimpfks it is used in making gun cotton