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topic 27078

Electropolishing 304 stainless steel, or alternative to it

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2004

Q. I happened onto this site today while trying to find information regarding the finishing of 304 ss. I manufacture a piece of equipment that is used in meat processing. We manufacture an average of 30 units per year. Made of 304 ss mill finish, 7 ga. and 10 ga. sheet, 14 ga. tubing, 1/4"plate. The basic footprint is 5' long, 4' tall and 2' wide. I had inquired about having the frame (welded complete) electropolished. I have a source with a tank sufficient to submerge the entire machine but I was told that the finish would not be uniform because of the bends, angles and shape. It was suggested that welded and non-welded sub-components be electropolished and then final assembly welded. It was recommended that a gel(?) be used to clean those welds. It seems to me that it would defeat part of the purpose of electropolishing and that is to have a uniform shiny/clean appearance. My objective is to find a finishing/polishing process that seals the pores of the material the way electropolishing would, is economical, not entirely labor intensive and suitable for food contact and can withstand a harsh cleaning environment. Plating or surface coating is not an option.

I hope this is sufficient information to form a conclusion. Thanks in advance.

Judy Godfrey
metal fabrication,food processing equipment - Canton, Georgia, USA


2003

A. Hi Judy. I believe you need an electropolishing shop with larger tanks and the time to give attention to the jigging of this part with auxiliary cathodes, special agitation, and whatever is required to electropolish it despite its peculiarities. There is no real substitute for electropolishing, and huge parts have been electropolished.

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


2004

A. Large electropolishing tanks can handle your size part. Ted is correct in saying that proper cathoding can produce a uniform appearance on a complex shaped part.

Dan Weaver
- Toccoa, Georgia


2004

The simplest and easiest way is to get it electropolished by someone who knows what he is doing. If that is not possible, there is one other way that is not very labor intensive and will give you what you need. You can rig an electric wand using the right chemistry and equipment with enough power to give you the speed you need. This is being done quite effectively to welds by a number of companies.

lee kremer
kremer signature
Lee Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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May 8, 2013

Q. I'm hoping someone can give me some insight, for I am at a loss. We are electropolishing 304ss and we just started getting corrosion on the parts. These are parts that we have done for years, using the same process. The parts are stamped, cleaned in CIP 100, rinsed 2x, partially electropolished (meaning only a section of the part is EP'd), rinsed 2x and then hot rinsed. We changed out the baths and the rinse tanks and we're still having this issue. The EP rinse baths are part of a closed loop filtration system that go through carbon and mixed bed tanks. We use DI water. We thought maybe the EP rinse water was too acidic, but even after the change out... we're still having this issue. Any thoughts or input is certainly welcome.

corrosion on electropolished 304ss

Thank you
-Dana

Dana Herring
- Freeport, Pennsylvania, USA


May 10, 2013

A. Dana,

adv.
If you switch to the Universal Electrolyte (the one I supply to you for 420 stainless steel electropolishing), then there will be no rusting areas. 304 steel polishes well in this electrolyte (but in different regimes). I am in town right now and can deliver electrolyte if you need.

anna_berkovich
Anna Berkovich
Russamer Labs
supporting advertiser 
Pittsburgh, Pennsylvania
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May 13, 2013

A. It's funny, 1 stain is above the EP line, means this part did not enter your electrolyte, still you are in no doubt, that your process is to blame?

To make sure the problem is in your polishing line, try to take some parts, degrease those parts and leave the parts to dry, see if they get stains also.

Bo Koenig
- Aalborg, Denmark


May 14, 2013

A. If somebody uses conventional electropolishing solution, fumes from the electrolyte can contact the metal surface above the electrolyte level surface and impact the metal above the polishing line. Do not forget that the whole metal part is under the current.

adv.
Our electrolyte does not have this problem. That is why we successfully use it for partial polishing or for reel-to reel continuous electropolishing, when wire or tape or conveyor exit the electrolyte tank while under electrical current, and enters the rinsing tank.

anna_berkovich
Anna Berkovich
Russamer Labs
Pittsburgh, Pennsylvania


May 15, 2013

thumbs up signThank you, everyone, for your responses. I actually was able to find the problem. We run these parts through CIP 100 w/ an ultrasonic, and somehow the sweep on the ultrasonic got moved from its standard position and the parts weren't being cleaned properly. We had to scrap out a bunch of parts, but at least we found the problem and got it resolved.

Dana Herring
- Freeport, Pennsylvania, USA


May 16, 2013

A. You've got a point, but conventional electrolyte consists of sulfuric and phosphoric acid; neither tend to evaporate at normal operation temperature, but splashes from hydrogen bubbles might be an opportunity. Still, my first shot would be would look for iron contamination of the work piece.

Bo Koenig
- Aalborg Denmark



July 28, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I'm researching nontoxic replacements for corrosive acids for electropolishing solutions.

Can you tell me what problems are commonly associated with electropolishing solutions and the electro polishing process.

I'm focusing on stuff like contamination of metal surfaces with acids from the bath. Minor and major imperfections caused by acid ingredients. Please tell where I can get info also.

Neil Frabstein
nanobiotech - Woodbury, New York, USA


July 30, 2013

A. Hi Neil. Is the objective to buy and use them or to formulate them? What substrate do you wish to electropolish -- stainless steel?

Regards,

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



July 23, 2018

Q. Hi everyone. Thanks for all the great info from this community; I'm having a crash course and cramming hard to try and pass through the eye of needle with a current situation we are experiencing.

Part:
Material: SS304
MFG: Casted
Parts size: 40cm x 18cm x 12cm

The required finish is for the pocket (visible surface) to be cosmetic electropolished (clean, shiny and consistent)

1st try -- the part was, the supplier said, tumbled and then electropolished it; I was to see the EP step.

27078-2a
Results- it looks as if the part is oxidizing/rusting

The 2nd attempt --
The caster bead blasted the parts with SS beads which looked good when they came out of the machine. I then said we need to clean it as it had dust on it from the bead/shot blast. So we cleaned it with hot water (it looked better 2 days ago when we cleaned it with water but it started to oxidize within 10-20 min; now 2 days later it looks like this)

27078-2b1

The other part was bead blasted, same batch as previous part, and Electropolished. The part looks 100 times better after bead blasting and then electropolishing, however the electropolish is not consistent on the floor of the part; we are adding a permanent gating to the mold to eliminate the non-surface treatment issues.

27078-2b2

Conclusion: the shot blasted part then EP, came out much better.
So my question is: Is it possible to get (cosmetic finish): consistent, shiny polish inside here? If So any recommendations would be great. I was thinking to an extra cathode might help and make sure the part is facing it (front and back side). 2nd after shot blasting does the part need to be cleaned? If yes with what?

Thanks for any tips if anyone has any.
Scott.

scott stefan
Project - fort pierce, Florida, USA



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