Procedure for electropolishing stainless steel

A. Hi again Azeez.
Personally, I'd go with a fiberglass tank, but polypropylene is acceptable as long as you are aware of its flammability.
There is no "right" proportion of phosphoric to sulfuric acid, but 2 to 3 parts phosphoric to 1 part sulfuric is a common mix.
Lead is probably the most reliable cathode material although others are used depending on solution composition.
Jigs can be copper.
As for additives there are almost endless available electrolytes.
Etching is not required.

But there are week-long training courses in stainless steel electropolishing, and the introduction to electropolishing in the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] is more than 20 pages. You asked for the "complete process" on this page 3 years ago, and I don't know whether you've done some serious investigation and are now down to these specific questions, or if you're still just starting to learn about it.

I think step 1 is to have an experienced electropolishing shop do some samples for you of both the 201SS and 304SS so you have a good idea of what is achievable; otherwise you may give up on improvement too soon, or expect miracles that no one has yet achieved :-)

Luck & Regards,


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

A. Hi Frank. Your question isn't specific enough to be answerable within the confines of the forum, Frank, because explaining the process takes about 20 pages. Please see the chapter about electropolishing in the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] ; it's excellent and quite complete. But if that text isn't readily available, the Metal Finishing Guidebook, and ASM Metals Handbook Vol. 5 have pretty good introductions. Then please come back here and ask for clarification on anything you're having trouble with. Thanks.

A. If you can give me more information on the specifics of what you are doing we may be able to help.

A. Hello Jim. What you are describing (frosty look, loss of metal) sounds like etching. I believe that the two most common causes are the current density too low and water in the electropolishing solution. But there may be other causes -- unfortunately it's always easier to do one thing wrong than everything right :-)

A. Do not electroclean before electropolish, soak clean only. Look for excessive solution movement, this will break down the "viscous layer"; the magic layer necessary for EP to take place. Also if you are doing wire goods remember SS is a lousy conductor, is the article picture framing?

Hope this is helpful.

A. Hi Mike. Electro-polishing inherently passivates, and obviates the need for separate passivation. I would not passivate wither before or after.

Prepare by alkaline soak cleaning; nitric acid is not an effective cleaner for dirt, oil, and greases.

A. Hi Oswaldo. I don't believe so.

Luck & Regards,

Hi, Dhiresh. Unfortunately, there are about 20 pages of things you must do right, including proper cleaning, proper formulation, proper temperature, proper racking, proper agitation, proper current density, proper procedure to exclude pre-cleaning rinsewater ... which conspire to make it difficult to guess which one or ones were missed. But it seems like you have a pretty good understanding of the process, so my first thought is that the shape, position, and racking of the glasses is causing trouble. Please try your best to electropolish a simple flat shape first and let us know the result. Good luck.

It is always difficult to process anything the shape of a water glass because anything other than exactly horizontal racking either causes excessive process solution carryover, or traps air and thus prevents proper processing.

Regards,

A. Hi Michael. The process sequence is quite easy: soak clean, double rinse, electropolish, double rinse. But it's not easy to do right if you have no prior experience, although the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] will be a big help. There are companies like Metal Coating Process Corp. who specialize in educating people on electropolishing, and other companies like Russamer Lab [a finishing.com supporting advertiser] who license their knowledge and processes. Good luck.

Regards,

A. Hi Herb. One reason for doing so would be to comply with specs; there are some which require it. A second possible reason is improved corrosion resistance. Traditional thought was that electropolishing provides excellent passivation without need for further treatment, but some feel that citric acid passivation after electropolishing improves upon it. We'll wait for someone who advocates for that to make their case.

Regards,

A. Herb,
Lots of folks say that electropolishing passivates stainless, but then we always have to be careful about the word "passivate", because it means a lot of different things depending on what process and what material you are talking about.

Electropolishing (or mechanical polishing for that matter) creates a very smooth surface, which is good for corrosion resistance.

A nitric or citric acid bath removes iron from the surface, which is also good for corrosion resistance.

If you remove the iron from a very smooth surface (i.e. polish followed by acid dip), then it is DOUBLY good for corrosion resistance!

But note that just one or the other may be perfectly sufficient depending on the application.

A. Hi Jon. Pictures can be deceiving, as the world knows from the famous gold & white dress which my son insists is blue & black. But your component looks to me like it has not been plated at all. Are you implying by "chrome finish", and by which thread you posted your inquiry on, that your finisher was supposed to nickel-chrome plate it? Or was he supposed to electropolish, manually polish, or what?

"Stainless steel" is a very broad description of the material of construction, and you should probably try to find out what types of stainless steel the rod and tube are, and to get at least a general description of what the alleged finishing process is. But personally, I'd probably retain a finishing consultant if I was in your situation.

Regards,

A. Hi again Jon. Myself and other readers would like to help, but finishing is like anything else: We might possibly be able to assist your electropolishing shop in a small way if they told us exactly what steps they were doing and if we were 100% sure of the alloys ... but unfortunately it can be impractically difficult to try to guess what went wrong only from a picture of the end result :-(

Was the rod black before you shipped it? Did anyone do any heat treatment after the welding? Why are the parts electropolished -- only for looks, or for corrosion resistance, or for cleanability/hygiene? Can you send one unsuccessfully polished part to another electropolishing shop to see what they say and achieve? You can search the site for "electropolish stainless steel" to learn more. Thanks.

Regards,

A. Hi Azeez. You need to mechanically prepare the component, then properly clean and rinse it, then electropolish it. Unfortunately, I don't know exactly what "new to this field" means; but you're not going to learn to electropolish solely from a response to your question here. You can start with the previous Q&A's on this thread, search the site with the term 'electropolish stainless', and consult the 22-page chapter in the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon] for current density, solution concentration, and some other tips ... but it will still hard to do without knowledgable hands-on instruction.

Luck & Regards,

Try https://www.worldstainless.org/Files/issf/non-image-files/PDF/Euro_Inox/Electropolishing_EN.pdf. There you can find download free booklet on electropolishing of stainless steel...

Hope it helps and good luck!

A. Hi Anders. You can look at Charles Faust's US patent 2,334,698, bath No 5, at patents.google.com, which is a sulfuric acid and phosphoric acid formulation claimed to be satisfactory for both 3xx and 4xx stainless steels.

The process tank should be big enough to allow at least 15" of free space below, 6" above, say 6" or more on each end, and 12" or more on each side (to accommodate clearance, and cathodes).

I don't see a need for an actual nitric acid post treatment, but a dip in dilute nitric acid can often improve rinsing

I assume that this is a hypothetical project, and you're not actually attempting to electropolish a sculpture. But if you are, be warned that it's not as easy as it sounds, so you would want to do significant experimental work with smaller parts first, then with scrap of this size before risking an actual sculpture.

Good Luck!