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Removing anodizing from aluminum

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A discussion started in 1998 but continuing through 2020

March 10, 2012

Q. I have a brass-tone anodized finished shower frame. I want to strip it and have a plain aluminum frame. What would you suggest?

Ira Boren
- Los Angeles, California

January 2014

A. Hi Ira. The caustic soda or oven cleaner should work, but just removing the anodizing doesn't necessarily mean it will be attractive -- and it will probably quickly get corrosion volcano/pits. So it's a big job with hazardous chemicals, with little reward. But good luck.


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

January 3, 2014 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I have an Aluminum shallow cup 50 grams. It is already in anodised condition. I have to remove the anodized layer. Please give me a proper process. How to remove hard anodising from aluminum material.

gosai jaydip
heat engineering works - Surat, gujrat, India.

January 22, 2014

A. You can use 70 gpl caustic solution at 60 °C to strip the anodic film. Be careful, as the reaction is exothermic, creating fumes. Then you have to rinse in water and then neutralize the part in 200 gpl sulphuric acid or nitric acid solution, and then rinse in water well.

Timur Ulucak
- Istanbul, Turkiye

June 24, 2015

Q. I have to remove a Type 2 anodize coating off one side of the aluminum but leave the other edge coated with anodize. I can't put the entire part into an immersion tank because I can't strip all the anodize off. Would wiping oven cleaner on this edge with a rag be my best method?

Tom Beine
- Broomall, Pennsylvania

A. Hi Tom. Oven Cleaner is usually considered an amateur rather than a professional approach because it was neither made for that purpose nor do you know quite what is in it -- which leaves you with a lot of 'splanin' to do to your customers about how your quality control system works, and to your employees and the regulators about how your safety program works.

Depending on the particular parts, an alternate and perhaps preferable approach would be to mask the components either for one-side anodizing or for one-side stripping. Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

REACH-compatible removal of anodizing

August 12, 2015

Q. Stripping of anodic coatings is done by either pickling solutions (acidic or alkaline) or with chromic/phosphoric acid solution. The latter having no influence on part tolerances.
In Europe,the REACH legislation will prohibit the use of chromic acid as of 2017.
My question therefore: does anybody know whether there are non hexavalent chrome containing solutions that work the same as the chromic/phosphoric acid stripping solution. i.e. no influence on tolerances?
Or is work being done to find such an alternative stripping solution?

Arnold Langeveld
Fokker Aerostructures - Papendrecht, Netherlands

simultaneous August 17, 2015

A. Hi Arnold,

I have been involved with the Chromium Trioxide Authorization Consortium (CTAC), which has applied for authorization for the use of chromium trioxide in Aerospace. If you visit the ECHA website you can see that it is up for public consultation at the moment. You can check that this use scenario is covered (I am pretty sure it is). Alternatively you can check with your CTAC representative (Fokker were at least originally part of CTAC) to look a the detailed dossier to check that the use scenario is covered.

If the authorization is granted we are hoping to have up to 12 years more to find replacement technologies. The sunset date of September 2017 looms large, but hopefully we will have a little breathing room to find replacement technologies after the sunset date has passed, otherwise I think EU based Aerospace will be crippled.

At the moment I am not aware of a stripping solution that works like chromic/phosphoric, with no loss of dimension and no attack of base material. The only thing I have been looking at is caustic based and this is nowhere near an ideal solution, the danger of attack of the base material is too great for my liking. Hopefully someone out there has the solution to your problem, but I am not hopeful at this stage.

Brian Terry
Aerospace - Yeovil, Somerset, UK

August 19, 2015

I answered this one a few days ago, may have gotten lost in the shuffle while Ted was sipping drinks with umbrellas in them on some beach.

Yes, there is a non hex-chrome anodizing stripper available, at least here in the states. It's sulfuric acid based, and has similar operating parameters as the chrome/phos strippers. We're only in the testing phase of this product, and have not put into production as of yet, but it does work quite well...at least on a small scale.

I do not know how the shipping stuff would work from North America to the Netherlands. Ted generally discourages product links in the forum. So if I can get your email address via Ted, I could give you product and contact info.

Marc Green
Marc Green
anodizer - Boise, Idaho

August 2015

Thanks Brian. Thanks Marc, I sent you Arnold's e-mail address; please contact him privately with your sourcing info.

But, Marc! I most certainly WAS NOT sipping girlie drinks on some beach! I was washing down fried bologna sandwiches with draft beer at Robert's Western World in Nashville -- arguably the very best bar in the whole world, especially when Eileen Rose is So Lonesome She Could Cry and Rich Gilbert is shredding Ghostriders ...

You DO see why I couldn't hurry home, right?


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

March 12, 2016

Q. Where do I put the stripping tank for cleaning the Color anodize profile in Aluminum anodizing plant -- before the caustic tank or after the caustic tank? How to manage low Aluminum content in stripping tank.

Manauwar Azam
- Kuwait Salmiya

June 10, 2016 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Dear All,
How can you strip your anodized re-works (6063-6463 series)?
Do you use normal weak NaOH (60-65 gr/lt NaOH at 50-60 °C) or chromic-phosphoric acid mix? Which is better? We use the first but want to try second. Is there a use for the second one?

alaattin tuna
- sakarya,turkey

June 23, 2016

A. Hi Alaattin,
A Sodium hydroxide solution will indeed strip off the anodising from the aluminium parts.
But, with Aluminium being amphoteric, i.e., it reacts with acid and alkali, the sodium hydroxide will carry on dissolving the aluminium under the anodic layer once that has gone. This will be a fast and violent reaction at the temperature and concentration you have stated.
Therefore you will have no control over the amount of metal that is removed. It would not take long to completely dissolve the components.
So the chromic acid and phosphoric acid solution is the best option. This solution will only remove the anodic layer. It takes about 30 to 45 minutes to remove the anodic layer and there is no violent reaction during the process. The aluminium underneath will be unaffected by the acidic solution. The concentration should be phosphoric acid at 35 ml/l, and chromic acid at 20 g/l, heated to boiling, It will not work even if only a few degrees cooler than that. But it does work well when performed as described.
Good Luck

Mark Lees
- Fog encircled rock in the irish sea

January 9, 2017

Q. I found Marc Green mentioned a non hex-chrome anodizing stripper which also will not attack the base material. Can I get more information on it?

Actually I also have a additive formula of de-oxidizer (or De-smut) with contains HNO3 and H3PO4. If I place my sample with ~10-12µm Al2O3 thickness can the de-oxidizer remove the anodized layer with a prolonged time without attacking Al base? The solution contains 250 cc/L 65% HNO3 and 500 cc/L 85% H3PO4.

Andrew Wong
- Hong Kong

January 15, 2017

A. My ears must have been ringing. It's Sunday, so I'm not at work. I'll try to remember to get the name of the stuff tomorrow. We have used it with success, but not extensively enough to be able to completely recommend it. But it does work. Due to the nature of my customers, changing an existing process can be quite a challenge.

That being said, the manufacturer is not a supporting advertiser on this site, so I'm not sure if I'll be able to post the product name.

Marc Green
Marc Green
anodizer - Boise, Idaho

Ed. note: Please post it Marc, it's no problem! We don't want to interfere with learning, just to discourage spam and avoid opinions which lead to heat rather than light: "Iridite is better than Alodine" (or vice versa), "Atotech is better than Enthone" (or v/v), and to discourage those people who aren't really looking for camaraderie or offering help, but just constantly prowling the site for topics where they feel justified trying to advertise their products for free :-)

As my always insightful partner Tom observed at the dawn of the internet: "The Price/Demand curve for Internet Advertising: Infinite demand at zero cost / zero demand at infinitesimal cost" -- Thomas J. Pullizzi, 1995 :-)

Less Damaging Stripper for Anodizing Racks?

May 19, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am looking for an alternative parts, racks and clips stripper. Have been using Etch and it's just eating the metal more than we would like. Was told about a proprietary rack stripper (AN775 by Stone Chemical).
Does anyone have any experience with them? Does anyone have other ideas or solutions? any input would be greatly appreciated.

James Dunne
Coatings - Kalispell Montana USA
  ^- Privately contact this inquirer -^

May 2017

A. Hi James, even such authoritative tomes as the previously-mentioned 1200+ page Wernick, Penner, & Sheasby tell us to either use titanium or titanium-clad racks, or suffer the wear & maintenance of caustic stripping of aluminum :-(

But we appended your inquiry to a thread which addresses a chromic-phosphoric anodize stripper which is non-etching. Whether it does a good job on rack stripping hasn't been discussed on this site yet, but maybe now it will be :-)

I am not an anodizer, but my suspicion is that consumption of raw aluminum rack components by the caustic is a smaller issue than their consumption by the anodizing process, such that improved rack strippers may address the round off error rather than the heart of the problem; even if the stripping removed no aluminum, the next anodizing cycle consumes raw aluminum to build the anodic film which you then remove, and "rinse and repeat". Good luck.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

May 23, 2017

A. Chrome/phosphoric strip will minimize the loss of aluminum but may be an environmental issue. This can also be accomplished by removing the racks from the caustic strip as soon as they are bare. Of course that takes some babysitting. Leaving them too long or forgetting them in the caustic will result significant loss.

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.
supporting advertiser
Wadsworth, Ohio
luke banner

May 25, 2017

Well, it only took me 4 1/2 months (sorry guys, I spaced this off), but the product I was referring to earlier is Stripper 5275, from SIC Technologies (http://www.sictechnologies.com/Misc.html).

It's a non-chrome stripper. I played around a bit with it on a small scale, and it does work as advertised. That being said, we decided not to facilitate it (limited space for an additional tank and ventilation), so my experience with it is limited. I do not know how long the bath will last. It seemed to take a long time to remove the anodizing, however with increased heat and concentration, the time shortened up. We never spent enough time to optimize the process.

It was pretty viscous, and had a sweet smell, I would guess it was a phosphoric/sulfuric acid based chemistry.

Marc Green
Marc Green
anodizer - Boise, Idaho

May 30, 2017

A. We used caustic-based formula for stripping anodizing racks for 3-4 years; later we gave it up. But we did not try either phosphoric/sulfuric acid or chrome/phosphoric based formula because of environmental issues.

At first we viewed stripping with a hand grinding machine (pneumatic) suspiciously. But we saw it as easier, faster, and faultless. So, we have used this method for 2 years now ... if I were you I would at least try this method, I advise everyone.


alaattin tuna
- TURKEY, sakarya

December 23, 2017 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Please let me know the method to clean the surface of aluminium sheet of thickness of 0.28 mm [0.011 inch].
Here cleaning means removing dirt or oil or grease or ink and as well the top layer which is anodized.


Parthi sethu

December 2017

A. Hi Parthi. We appended your inquiry to a thread which offers at least 4 methods: oven cleaner, caustic, chromic-phosphoric acid, or sanding. Please introduce yourself and your situation so people can advise you which is most appropriate, least dangerous for you, and most environmentally friendly. Telling us that the sheet is this thin is of some help, thanks, but it doesn't tell us whether you are a hobbyist with one old piece of dirty aluminum, or a process planner with acres of aluminum sheet to strip the anodize from every day, and the best stripping method also depends on what you intend to do with the aluminum next -- re-anodize it, paint it, clearcoat it, etc. :-)

Good luck, and Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

March 7, 2018

A. To remove anodized coating from automobile parts, build some troughs using 10 inch pvc pipe about 8 feet long. Cut an open slot about 90 inches long, and about 8 inches wide out of one side put a drain in the end, also close off both ends with a cap.
Using a 5 gallon bucket of water, add about 8 ounces of caustic soda slowly while stirring.
Pour this solution into your trough, then place your parts inside. After a few minutes it will look like it is boiling as it removes the coating. Most parts need about 20-30 minutes, but some take longer. KEEP A CLOSE WATCH ON THEM, IF LEFT TOO LONG IT WILL EAT INTO THE PARTS.
When finished, remove parts, rinse quickly with water, then brush off immediately, this will remove the black coating. Then buff to a new looking finish. Drain liquid into bucket, and re-use at any time. More acid^caustic will be needed if used several times. I DO THIS ALL THE TIME -- IT WORKS PERFECT.

Dean Lawson
- Mooresburg Tennessee usa

February 22, 2020

Q. Will not lye in the dry form added to warm water work to remove the anodizing

Shawn Marshall
- Nanaimo bc Canada

February 2020

A. Hi Shawn. Yes it will, and that's what most shops use to strip anodizing. Without too much simplification:
'lye' = 'caustic soda' = 'sodium hydroxide'.
However, it also dissolves the underlying raw aluminum, so babysitting and some experience regarding the timing is helpful.


pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey

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