Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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How to set up a DIY Electropolishing system for stainless steel
Q. I am the owner of a stainless steel fabrication shop in the marine industry. I would like information on setting up a small electropolishing and/ or passivating system. I can start with a small 5 gallon bucket type system until I learn the process better. I can then fabricate my own tank to the size I can control. Please give me some suggestions on startup. I am a small shop, and will be using this only on occasion for some projects. I use 304 and 316 grade only. Some material is highly polished and some is in the mill finish form. (ex.3"x 3/8"x 16" long flat bar).
Thanks for any comments,
Jackie
Jackie D. HartCustom Rails and Fabrication - Texas City, Texas, USA
2000
2000
A. Jackie:
It is easy and safe to set up a citric acid based system for passivation, that can grow with your business. Because you do not have the hazards of nitric acid, it can be done in a very simple and economical way.
There are a lot of questions that need to be answered in order to determine the exact setup you want to use, but you can easily start up with just some 5 gallon plastic pails or simple poly tubs, if you want to. The formulation you use depends on exactly what you are doing. It is important to get the right product to do the job, not just throw some citric acid in a bath.
There are some improved electropolishing systems available that are safer to use than the old systems, also. It is important to remember that you should passivate even after electropolishing to get the optimum performance.
adv.
We would be happy to work with anyone on this.
Regards, Lee
Lee Kremer
Stellar Solutions, Inc.
McHenry, Illinois
Q. Can anyone please tell me the recipe to electropolish a 316 SS rod
1/8" x 2" ( 0.7 sq. in area) and how to set this up? DC voltage? Current?, electrolytic solution, concentration and volume, time duration, etc.
I am doing some research on this approach to improve the life a Teflon seal through which this rod passes on a continuous cycle basis. Currently the best life we have achieved is about 500 cycles. The current rod finish is about 35 µinches. We polish the rod with 1000 grit emery paper.
- Edmonton, Alberta, Canada
2005
Q. Hi there,
Have you had any responses to your request?
Cheers
- Gauteng, South Africa
December 15, 2008
A. Hi, folks. There are several different solutions for electropolishing stainless steel. Most are based on sulfuric acid or phosphoric acid or a mixture of both, and some formulas include some additives. The most readily accessible source of info is the Electroplating Engineering Handbook.
You need well over 100 ASF and must take pains to insure that your solutions remain water-free because low current or excess water will cause etching.
Electropolishing does take experience, but it's obviously not impossible. However, it also may not solve your problem. I think you'd be better off having an electropolishing shop do a sample part for you than to invest weeks of effort and who knows how much money, only to find that it didn't help.
Generally electropolishing is not about smoother finishes, it's about cleaner finishes -- and it may not increase the life of your seals. Now if you were to chrome plate and lap those rods . . .
Good luck.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 16, 2008
A. I agree with Ted and that is to send the components out for electropolishing. You don't want to mess with acids unless you have a lab facility with adequate ventilation. But, having over a dozen years worth of experience in the area you are endeavoring into I would like to make the following recommendation: Prepare surface of rod to a 32 - 64 ra finish first; electropolish "to clean" second and roller burnish the O.D. third. You will be burnishing to achieve a 4-8 microinch finish which is ideal for a PTFE seal. Burnishing tools can be obtained from Cogsdill or Sugino just to mention a few. I have used both with excellent success. Good luck.
Bill Vernisie- Yaphank, New York
February 27, 2009
Q. WHAT IS THE IDEAL VOLTAGE REQUIRED TO POLISH S/STEEL AND HOW SMOOTH SHOULD THE DC CURRENT BE?
ALEC UPFOLDHOBBYIST - PIETERMARITZBURG , SOUTH AFRICA
2007
A. The controlled variable should be amperage rather than voltage, Alec. The current must be high enough to get out of the "etching" range and into the "brightening range". The voltage depends on rack to cathode spacing, conductivity of the solution, etc. A standard 3-phase rectifier with probably 5 percent ripple should be fine. While most plating books have a chapter on electropolishing, I think the chapter in the Electroplating Engineering Handbook [on AbeBooks or eBay or Amazon affil links] is the best. Good luck.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007
A. Ted's right, amperage means everything, voltage means nothing since it will vary according to spacing and other resistances. Best polishing will require, at absolute minimum, about 50 ASF, but the higher the better. As to ripple, it makes no difference. You can do good electropolishing with a half-wave rectifier, ie. 100% ripple.
Jeffrey Holmes, CEF
Spartanburg, South Carolina
2007
April 20, 2011
Hi Ted and Jeff
It's been a while, however, here is my delayed response.
Thank you for the info, it really proved invaluable.
The result of the last communication ended up with me having built a purpose made transformer with an output of 8.5vdc ( half wave) which was only good for 100 amp.My bath was only 40 lt of Electropol so the jobs I could do were small - but what magnificent finishes I could get in just 9 minutes!
In the end I gave the whole setup to a trusty good friend of mine as I now live in New Zealand.
3 months ago I decided to venture back into electropolishing with the idea of starting small but not as small as previously. I have just completed winding a transformer which is again 8.5v but with an output of 350 amp, perhaps a little more if I oil cool it. It also has an unused 250000 uf cap just for good measure which I got for $6 on eBay .
As far as the acid tank goes, well I am still on the scrounge for one and I would like it lead lined (NZD$600/ half a square meter) if I can find some at no charge.
I'm thinking of making up my own acid mix and if at all, this is where I could be going wrong. I can get the acids (at the correct concentrations) quite cheap and that is why I want to give it a go. If all fails then it's back to Electropol (it's the only brand name I know of).
No photos at the stage - all looks as rough as guts anyway until the job is done.
Longer term plans - I will need a proper rectifier if I decide to grow this interest.
Cheers,
- Napier New Zealand
Tank setup for electropolishing
Q. Hi my name is Alf; I am from South Africa. I manufacture steam autoclaves up to 400 liter chamber size. Is there anybody who can help me to set up a plant to electroplate my chambers? My chambers are 304 stainless steel. I want to know what size of tank and material of the tank, what size rectifier, and what chemicals I must use.
Alf Booysensautoclaves - Pretoria.gauteng.South Africa
August 13, 2017
Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)
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