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Q&A about electropolishing of stainless steel and aluminum

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A discussion started in 2002 & continuing through 2017 -- add your Q to bring it back to the Hot Topics page.

(2002)

Q. Trying to find the chemical makeup of a solution for electro-polishing of stainless steel, carbon steel, and aluminum.

Merlin Milligan
- Somonauk, Illinois, USA


(2002)

A. Many electropolishing solutions contain phosphoric and sulfuric acids. Various formulas are given in the in the Metal Finishing Guidebook article on Electropolishing

There are many vendors with proprietary solutions; this is a good way to begin as you get the correct solutions and procedures for your particular alloy(s). Also, they will advise as to the most suitable alloys and run sample parts. Click the Chemicals link below, then search for electropolish. At least one of these vendors has a non-environmentally hazardous product.

Ken Vlach
- Goleta, California
contributor of the year

Finishing.com honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.



(2002)

A. I would like to recommend the following formulation to you: Glycolic acid 55%, sulfuric acid 30%, water 15%. The formula is free of phosphate and absolutely environmentally friendly. Of course you can obtain excellent result.

Benlogo G.B. Huang
Benlogo G.B. Huang
- Guangzhou, China


Electropolishing, Anodizing and Electrolytic Pickling of Metals

(2003)

Q. Dear Advisor,

As I could determine from your site, you are interested to support people to find a good and environmental friendly process to electropolish metal parts.

I am a retired Chem. Engineer and am trying to electropolish some machine parts made of stainless steel AISI 304 and AISI 316 to improve surfaces for sanitary use.

I never did electropolishing by myself and want to try it in my garage before to launch any service operation. Could you be of any help giving me some adequate formulation for this task? What also could be a good DC voltage to induce the controlled corrosion of the peaks at metal surface?

Best Regards,

Herbert F. Steffen
- São Paulo, SP, Brasil

----
Ed. note: It is kind of Herbert to address the readers as 'advisor', but we don't want people to be misled. This is NOT a consultation service; it's a public forum where everyone is expected to give as good as they get. Every reader knows something, and a great way to learn is to try to teach ... so we're waiting to hear your answers as well as your questions :-)


(2006)

Q. What could be a good DC voltage be to electropolish stainless steel?

pieter coetzer
active fleet - durdan South Africa


(2006)

A. Things are, I'm sure, different in Brazil than the U.S., Herbert. But the idea of running a process like electropolishing in a garage is a dangerous one. There is a tendency to think that the selection of the exact electropolishing formulation is the key to success, but it's not. So I'd try Benlogo's suggestion.

Pieter, if you don't find the guidance you seek in the previously mentioned article in the Metal Finishing Guidebook, there is a great chapter on electropolishing in the Electroplating Engineering Handbook. Voltage has very little to do with anything at all, but maintaining amperage in the 'polishing range' rather than the 'etching range' is a critical element. Good luck.

Merlin, to my knowledge carbon steel cannot be electropolished.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



Electroolishing of surgical instruments

(2004)

Q. I am a manufacturer of surgical instruments. I am interested in electro polishing my surgical instruments. Can anyone please give me the formula for the chemical composition of the bath as well as machine specifications and requirements? Thanks for your efforts in advance.

Rajesh Shoney
Manufacturer - Pondicherry, India


(2004)

A. There are many different electropolishing solutions for stainless steel. The most extensive conveniently available list is in The Electroplating Engineering Handbook. There are also electropolishing chapters in the Metal Finishing Guidebook and ASM Metals Handbook, Vol. 5, Surface Engineering. The AESF (NASF) has an illustrated lecture on electropolishing. Dozens of formulas have worked, but if you focus on finding the best magical chemical formula, you are misunderstanding the subject and are therefore unlikely to achieve success.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2004)

A. Dear Mr Shoney,

Sorry for not replying after visiting your factory on 6th January.

My concern with suggesting a chemical process for brightening and passivating SS is that your products are used in Surgeries and chromic containing chemistries that are carcinogenic; are not a good idea according to me.

I would suggest that you continue your mechanical buffing, cleaning operations with its difficulties and conclude the process with an Ultrasonic Cleaner. Maybe anyone else here may suggest a safe process.

khozema
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


(2004)

adv.
There is an alternative to chromic-acid-based electropolishing. Non-acid saline based electropolishing will polish to mirror finish 300- and 400-series stainless steel. There will be no need for additional passivation step.

anna_berkovich
Anna Berkovich
Russamer Labs
 
Pittsburgh, Pennsylvania




(2005) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Does anybody know preparation of stainless steel electropolishing mixture? We want to prepare it in our laboratory. Is this possible?

There are alternatives. For example: phosphoric acid, sulphuric acid, chromic acid etc.

We are not sure about the percentages. What might be?

Which one is the best for following issues: performance, economical, environmental, occupational health, easy to applicate & prepare.

Regards

Ayca CAKIR
healthcare products - Turkey


(2007)

Q. Looking for the chemical composition and metals in electropolishing solution for electropolishing 300 and 400 stainless steel. Also the specific gravity, percent of the acids, water content, metals.
Thank you,

Joseph Clyde Smith
metal finishing - Vicksburg, Michigan, USA



ElectroPolishing of Stainless Steel -- Chemical Formulations

(2006)

Q. I would like to know what percentages of sulphuric acid and phosphoric acid and any other chemicals required to carry out electropolishing of stainless steel.

Oliver Hollard
Bathroom accessory manufacture - Nelspruit, South Africa


(2006)

A. 40% sulfuric acid, 60% phosphoric acid
So 11 Volts
The object to electropolishing is anodic-- For cathode use Stainless steel 316L 1:1
Distance between electrodes 2 inches.
For hanger use copper.

Time 7 minutes or by the quality of electropolishing.

Best regards

Juan Moreno Arenas
- Santiago, Chili


(2006)

This formulation comes from the excellent book Metal Finishing Guidebook and Directory.
Phosphoric acid 40%
Lactic acid 46.5%
Sulphuric acid 13.5%
The cold phosphoric and lactic acids are put into the tank first and then stirred to mix. Lastly the sulphuric acid is added and stirred. Heat is generated and the temperature will rise to about 65 °C.
Sulphuric acid and lactic acid must not be mixed first because there is a chemical reaction which destroys the lactic acid and generates too much heat. 10% water is acceptable and reduces the tendency for the mixture to char and become black.
60 - 90 °C operating temperature is suitable. About 9 volts is typical.
The reason for using this formulation rather than the sulphuric phosphoric mixture is that I found that the high sulphur content of free machining stainless steels is less liable to be pitted. Metal removal rates are low and the polish is excellent. Maintenance does not require chemical analysis of the composition, just replace drag out with new solution.

Nick Clatworthy
- Whitstable, Kent, UK


(2006)

A. For optimum, it is going to depend on the alloy and exactly what you need. Several books have good suggestions.

James Watts
- Navarre, Florida


Electroplating Engineering Handbook

I agree with James completely. I have seen straight sulfuric acid used in a very capable high production shop although a substantial mix of phosphoric acid is more common, and there are dozens of mixes. But a starting point is to really understand what electropolishing is about, and a great article on the subject is in the Electroplating Engineering Handbook =>

It is problematic to try to learn the 'right' formula and the 'right' operating conditions, without much knowledge of things practitioners should probably understand about it, like the need for a clean surface, the problems of water accumulation, getting from the 'etch' range to the bright polishing range, why the parts probably won't get as bright as mechanically polished parts, etc.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2006) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. We want to know the process of electro polishing of SS 316/SS316L. What is the composition of the electrolytic bath, what voltages are to applied and the temperature of the bath and time to keep the component inside the bath for best results?

Girish Anantha Iyer
- Coimbatore, Tamilnadu, INDIA



To minimize searching and offer multiple viewpoints, we combined multiple threads into the dialog you're viewing. Please forgive any resultant repetition.



Stainless steel electropolish chemical composition

June 2, 2008

Q. I'm developing electropolish for stainless steel in India. So, I'd like to know if someone can help me giving the chemical composition of the liquid used in the bath.

sudarsan avinash
Sudarsan Avinash
partner - Chennai, Tamilnadu, India


March 4, 2015

A. Read this...
http://www.euro-inox.org/pdf/map/Electropolishing_EN.pdf

This was of immense help when I was finding out the requirements for an electropolishing plant

Abhishek Gour
- Mumbai, Maharashtra, India


March 2015

A. Hi folks. There's a lot of good info on this page, but there has also been great progress in the last several years on "no dump" extended life electropolishing chemistry, and processes which use less toxic chemistry. Read the suggested books, articles, and websites, etc. ... but make contact with the proprietary vendors to learn about what's new before making final commitments.

adv.   Russamer Labs

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



February 4, 2016

Q. Does anyone know the life of electropolishing solution?

puneet_singh
puneet singh
- Ludhiana, punjab, india


February 2016

? Hi Puneet. What material are you electropolishing and what solution are you using? With that information, a guess might be possible. But these days there are "never dump" solutions, and a number of proprietary approaches as well.

Regards,

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



How to do electropolishing in my garage?

April 11, 2016

Q. I would like to try to do electropolishing in my garage. Questions:
What stuff do I need?
How long to process?
What chemical do I have to buy?

The object I want to electro polish is:
1. metal
2. aluminum

Almost the object was part of machine of motorcycle.

This is first time I want to try. And I want to do it safely. Thanks.

muliana tresnayana
hobby - indonesia, Bandung


April 2016

A. Hi Muliana. Electropolishing of aluminum is probably not a good hobby, and electropolishing of "metal" might not even be possible, depending on the kind of metal. You can read about the topic in textbooks and get a general introduction to it, but for motorcycle parts it will probably be cheaper, safer, faster, and much less to learn if you simply mechanically polish them, which is what "everybody" does. Please start with letter 800, "Aluminum motorcycle polishing -- rims, wheels, swingarm, frame". Good luck.

Regards,

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


June 14, 2016

Q. FOR ELECTROPOLISHING OF BALL BEARING STEEL WHAT TYPE OF SOLUTION WE CAN USE? AND WHAT WILL BE THE COMPOSITION?

manisha baby
- bangalore, karnataka, india


August 26, 2016

Q. Hi all
We are anodizers of aluminium in bangalore. Polishing aluminium has been very difficult.
I used 60% Sulphuric and 40% phosphoric acid
Temperature 60 degrees
I got excellent shine but metal removal rate is very high and pit formation in some places, and non-uniform shine in contours of parts.
Can anyone help me as to how to reduce metal removal rates and increase uniformity?
I guess we have to do something about throwing power!
Please suggest to me in this regard.

Arun kumar
- Bangalore karnataka, India


August 27, 2016

Q. I want to reduce the cost of electropolishing SS202. My workshop manufactures SS baskets. Is there any effective way?
Also how can I analyse the solution?
Currently I use 33 percent sulphuric and 66 percent sulphuric^phosphoric. And simply add sulphuric or phosphoric without calculations.

Manas Kundu
- Luncknow, India



Electropolish 304V Stainless

September 20, 2016

Q. Hello everyone,
I am using following formula for electropolish of SS 304V, but can't get shining surface ... any suggestion? Please help.

Formula:

#1 sulphuric acid 41% = 543.25
#2 phosphoric acid 45% = 596.25
water 14% = 185.5
operating temp: 140 °F

Kind regards,

Adnan minhas
- karachi, sindh, Pakistan


September 2016

A. Hi Adnan. I'm not familiar with that particular formulation, but dozens of different formulations have been successfully used, and I have no reason to think that your formulation would be unworkable when so many similar ones work. Where did you get the formula?

No part of your item polishes? Does it etch or does nothing happen? What current density are you using? Have you been electropolishing successfully and it suddenly stopped working, or are you just beginning your research and have never successfully electropolished anything before? Are you sure the surface is clean to the point of waterbreak-free?

If you can get access to the previously suggested Electroplating Engineering Handbook, it has an excellent chapter on electropolishing. We'd like to help, but if our response is limited to just suggesting a different formulation, odds are strong that it won't help much.

Regards,

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


September 20, 2016

Q. Hello Sir,
Thanks for your kind reply. Following are the answers to your questions:

Where did you get the formula? I got this formula from the net I think it's made by ESMA.
No part of your item polishes? No sir, when I polish the SS 302 & 303 it was done very well but PH-17 & 304V SS polishes but not like SS slightly gray color try to a lot of times but can't get results.
Does it etch or does nothing happen? Yes it etches but color is slightly gray.
What current density are you using? 7 amps, per square inch, per minute (7 AMSI) at 140 °F.
Have you been electropolishing successfully and it suddenly stopped working? Yes, but you can say a beginner.
Are you sure the surface is clean to the point of water break-free? Yes
If you can get access to the previously suggested Electroplating Engineering Handbook? No, need your suggestion. Different formulation? You know the best one for said SS?

Kind regards,

Adnan minhas [returning]
- karachi, sindh, Pakistan


Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.
September 2016

A. Hi again cousin. I run this site and am somewhat familiar with most of the technologies we discuss; but I do not pretend to be heavily versed in all of them. Thus, I think 304V stainless steel is simply 304 which has undergone an extra vacuum purification, so I don't think it should electropolish any differently ... but I don't actually have any experience to make that claim with confidence. PH-17 is a precipitation hardened stainless, and my understanding is that it therefore requires blasting with glass beads or aluminum oxide before electropolishing.

As I've said countless times on this page, numerous solutions have been successfully used, and I don't feel there is a "best", but this letter includes many postings with formulations, and letter 46041 includes another which the people posting them felt were best or at least good. As mentioned, the Electroplating Engineering Handbook and the Metal Finishing Guidebook have additional formulations. Books may be hard to come by in your area, but simply dismissing the need for books is no good at all. You can find still more in patent databases, such as www.google.com/patents/US2334698
Do not consider perchloric acid in any electropolishing formulation; it is tragically explosive.

"Etching" is undesirable in the sense I was using it, and often indicates that the current is too low or the water content too high.

I don't know what you mean by '7 AMSI'. Maybe you mean 1 Amp/ sq. in. for 7 minutes? The current density must be high enough, probably need at least 1 Amp/ sq. in., maybe twice that, or you will get etching.

It is difficult to function without a good library of metal finishing books and without a proprietary solution vendor to assist you, but at least download the Metal Finishing Guidebook. Good luck.

Regards,

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


September 27, 2016

A. Adman

I would try lowering the current density. Maybe even as low as 2 amps per square inch.

Willie Alexander
- Green Mountain Falls, Colorado


September 28, 2016

Q. Hello Willie Alexander,
You mean I will try 2 amps per square inch -- and what time?

adnan minhas [returning]
- karachi,sindh, Pakistan


September 29, 2016

A. Adnan

Yes, try electro polishing at 2 amps per square inch (290 asf) or even a little lower. Your 7 amps per square inch could be near the upper limits. Then try in between to find what works best. Time will depend on the starting condition of the surface. Rougher surfaces will take longer than smoother but you will still get a shiny finish first. Smoothing requires longer times for more metal removal.

Willie Alexander
- Green Mountain Falls, Colorado



September 28, 2016

Q. Can anyone help me how to electropolish stainless steel and aluminum using sulfuric, phosphoric and chromic? What is the concentration for each?

luvex vilia
- Cebu, Philippines


Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.
September 2016

Hi Luvex. At least 4 electropolishing formulations are already printed on this one page, with references to authoritative sources for additional information, and suggestions that you consider proprietary formulations, and that you skip chromic acid. Is there a particular reason that you want to use a mix of sulfuric, phosphoric, and chromic acids even though you don't know a suitable ratio?

There is a lot to the topic, and I suggest you do some preliminary research into it before falling into an assumption that an exact ratio of three acids is the key to electropolishing--dozens of different formulations have been used, and I've already mentioned that 100% sulfuric - 0% phosphoric - 0% chromic is one such workable possibility. If you don't have books on hand yet, you can start with the on-line version of the Metal Finishing Guidebook. Best of luck!

Regards,

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


October 12, 2016

adv.
I would like you to inform that we have managed to electropolish to mirror finish (no burrs whatsoever) on small pieces of aluminum alloy. So far we do not see any limitations on what aluminum type we cannot electropolish. We are still in the test mode, and are experimenting only on small parts so far.

18495-1a  18495-1b

I think this electropolishing method is suited mostly for high-value parts, for example in electronic industry or airspace, where the level of deburring is extremely important.

anna_berkovich
Anna Berkovich
Russamer Labs
 
Pittsburgh, Pennsylvania




February 26, 2017

Q. I used to electropolish SS 202 with 50% phosphoric and 50% sulphuric. Is it possible to change the chemical ratio to give SS a mirror shine finish in non polished wire and non polished pipe? And what would be exact time to be in the tank?

Sumit Poddar
- Ludhiana india

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