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# Electro-polishing stainless steel

## Electro-polishing stainless steel

(OP)
Hi,

I need to know how much material is removed from stainless steel with electro-polishing. I have some laser drilled holes that are 10 microns (10 millionths of a metre) in diameter and i want to know how much the diameter will increase if they are electro-polished? And how much rounder will the holes get?

Regards,

Antknee.

### RE: Electro-polishing stainless steel

This is a bit like asking " how long is a piece of string." Immersion times for electro polishing can vary from a few minutes to several hours.
Here is a link to somebody with a bit more job knowlege.
B.E.

http://www.neelectropolishing.com/passivation.php

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

### RE: Electro-polishing stainless steel

(OP)
Surely there is a limit to how big the laser drilled holes will become in anything like a practical time? And if for example the holes started out as squares would they ever end up round in a practical amount of time? I realise the question is a bit length of stringish :)

### RE: Electro-polishing stainless steel

A typical process time is 5 to 15 minutes. You can expect material removal of ~ 5 micrometers from the surface.

### RE: Electro-polishing stainless steel

(OP)
That is interesting and more removal than i'd thought likely. It appears I could increase the diameter of these holes by 10 microns to 20 microns.

Does anyone know of a company that can electro-polish specialist parts for research and development? I've attached the job I need doing, it's very specialist.

Regards,

Antknee.

### RE: Electro-polishing stainless steel

So you need to EP one face of a disc?

You must make electrical contact with the part. For this one you might need a contact spring on the back and then seal the edges with wax.
There will also be a working electrode. It will be similar shape to your part.
I don't know of any way to control the EP of half of the edge.
How has the part been prepared? this is the other half of the question on what surface finish do you need?
Contrary to popular perception EP only improves the micro surface finish, not the macro.
The mechanical polish prior to EP is critical to getting a consistent finish.
When we EP we aim to remove about 0.0005" of metal.

Is your hole through the disc? If so and you EP from one side the hole will become tapered.
In order to keep the hole straight and uniform you would need to have an electrode strung through it.
At this size I don't see that happening.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)

#### Quote (EdStainless )

So you need to EP one face of a disc?

You must make electrical contact with the part. For this one you might need a contact spring on the back and then seal the edges with wax.
There will also be a working electrode. It will be similar shape to your part.
I don't know of any way to control the EP of half of the edge.
How has the part been prepared? this is the other half of the question on what surface finish do you need?
Contrary to popular perception EP only improves the micro surface finish, not the macro.
The mechanical polish prior to EP is critical to getting a consistent finish.
When we EP we aim to remove about 0.0005" of metal.

Is your hole through the disc? If so and you EP from one side the hole will become tapered.
In order to keep the hole straight and uniform you would need to have an electrode strung through it.
At this size I don't see that happening.

Hi Ed, yes I need to EP one face of the disc. The drilled holes are completly through the part, all 0.2mm, and the intention of the procedure is to shape the hole, giving the top half a bigger diameter. The surface finish isn't a consideration.

There is a way of doing this, but I'm not sure which companies could do it, or the exact mechanics. It is for R&D so I need just a couple of small parts at a time, and not rack upon rack. Does anyone who can do this spring to mind?

Removing 0.0005" (12 microns) will be too much so I presume I'd just get these EP for a short time?

Thanks,

Antknee.

### RE: Electro-polishing stainless steel

Yes, shorter time, and/or colder or at lower current densities.
You could try this on the bench top.
A glass battery box, some Cu plate and leads, a DC power supply, and EP solution (sulfuric/phosphoric with some additives).
It will take you longer to mount each part then EP it. This is a few minutes each is all.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)
I could try this, I'd have some health and safety concerns though... how concentrated would the acid need to be? And what sort of current? It doesn't look too difficult in theory, I can even remember doing some electroplating at school many years ago!

Regards,

Antknee.

### RE: Electro-polishing stainless steel

You do it in a fume hood, there will be a little acid vapor and some Hydrogen.
Buy the EP solution premixed from a supplier.

Info is out there on current density and such.
I won't try to remember, and risk telling you wrong.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)
The best mixes appear to be 45% sulphuric and 55% phosphoric acid. I couldn't get permission to use that because spillages would result in hospitalisation. I could use some diluted sulphuric, the type that would be used in a school lab etc. I'm guessing that would work? but take longer, probably hours. Thanks, Ant.

### RE: Electro-polishing stainless steel

Antknee,
I have had good results electropolishing stainless steel with just Dilute Phosphoric acid.
Since you are in the UK. I do not know what health and safety would have to say about that.
Are you still working in a test lab situation, or do you have your product into a manufacturing stage yet?
Berkshire.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

### RE: Electro-polishing stainless steel

The ratio is about 45sulfuric/55phosphoric, but the solution is more dilute, there is a lot of water in it.
There are standard commercial sources for it pre-mixed, with additives in it.
You don't want to just use straight acid.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)
I'm working in a test lab, so I will be seeing what works and what doesn't myself. I've spent an hour googling for dilute electropolishing solution suppliers but drawn a blank. Can anyone give me a heads up where to look? (Preferably in the U.K.) I wont be able to use a test hood, probably, but the rest of the kit I either have or can source easily. Thanks Ant.

### RE: Electro-polishing stainless steel

Looks like a few prospects
stainless+electropolishing+solution+UK

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)
I guess I was looking for a retail type shop to sell me 1 Litre or so. I'll have to try industrial companies. Regards, Ant.

### RE: Electro-polishing stainless steel

This may be a dumb answer and not what you want - but how about polishing before drilling the holes??

### RE: Electro-polishing stainless steel

It sounds like you are not really electropolishing for polishing. You want to electrochemical machining or forming. There are probably better ways to make your small tapped hole in the precision you are after.

### RE: Electro-polishing stainless steel

(OP)
I'm not going to be able to get any EP solution that is safe or in smallish quantities. I think I'll get some sulphuric that is 1-5% concentrated, so safe and experiment with that. For Mike and HDS, you've skipped to the end of the conversation while missing my third post which gives more info. Regards, Ant.

### RE: Electro-polishing stainless steel

Go figure - I don't listen to my wife either.

You can buy sulfuric acid at Lowe's - here in the states. - a big box hardware store. Used to clean driveways, etc...

### RE: Electro-polishing stainless steel

Ant Knee,
Try asking these people for a sample.
B.E.

http://www.kiloltd.co.uk/item/phosphoric-acid

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

### RE: Electro-polishing stainless steel

(OP)
I've ordered some acid, it is weak stuff, I will reorder some stronger acid when I'm more familiar with the process. I'm wondering what sort of container I should use, probably not a coffee mug! As the parts are small (15mm diameter) I might be able to get away with a DC current that is quite low. A small container and not much acid might help. Any hints or tips?

Regards,

Ant.

### RE: Electro-polishing stainless steel

(OP)
Hi, I'm working with the web link below for some guidance. I have a few questions though. Generally I'll need to buy equipment which let me get it done so I think it is best to ask. I have no problem providing the current and have enough transformers and power supplies to not to need to think about that. It's more about the practicalities.

http://www.surfinetek.com/electropolishing/electro...

• Do the cathodes need to be lead or copper? I have plenty of stainless and it would be easier to use that.
• Do I have to have cathode strips of a particular width? I mean why can't I just drop the wire into the solution?
• How important is heating the bath? I'd need to get some kind of bunsen burner.
• How important is agitating the solution? That would be awkward, I could put a fan on it
• The anodic current density needs to be 16-45amp/dm2. My part is 1.5cm2 in area so that means I need 0.25-0.75amps? It doesn't look much, wondering if I've done the calc wrong!
• The solution will be sulphuric acid that is about 5%, with no additives, how important are the additives

• Thanks,

Ant.

### RE: Electro-polishing stainless steel

Ant Knee,
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

### RE: Electro-polishing stainless steel

(OP)

#### Quote (Ed)

You must make electrical contact with the part. For this one you might need a contact spring on the back and then seal the edges with wax.
There will also be a working electrode. It will be similar shape to your part.
I don't know of any way to control the EP of half of the edge.
How has the part been prepared? this is the other half of the question on what surface finish do you need?
Contrary to popular perception EP only improves the micro surface finish, not the macro.
The mechanical polish prior to EP is critical to getting a consistent finish.
When we EP we aim to remove about 0.0005" of metal.

Yes, shorter time, and/or colder or at lower current densities.
You could try this on the bench top.
A glass battery box, some Cu plate and leads, a DC power supply, and EP solution (sulfuric/phosphoric with some additives).
It will take you longer to mount each part then EP it. This is a few minutes each is all.

Yes there was a fair bit of info here that I read and passed over.

A spring and wax is a good way of connecting the part/anode. Cathode has to be at least as big as the part/anode.

I've done a bit of reading myself and a stainless steel cathode should be fine. I guess I'd better start looking for a glass box of some kind and get on with it.

Regards,

Ant.

### RE: Electro-polishing stainless steel

(OP)
I had a go using salt, hot tap water and a 12VDC 1amp power adapter. There were lots of bubbles so it worked. The part is small (a 15mm diameter disc) so not much fumes, but a little, is that much to worry about?

### RE: Electro-polishing stainless steel

You want good air circulation, you will be generating hydrogen and you don't want ti collecting.
We always use Cu for the cathode to minimize the voltage drop, at your low power SS should work fine.
It really should be about the same size(just a bit larger) than your work piece. You will need to keep them very parallel. Otherwise you will remove more metal where they are closer. Maybe use three small plastic beads glued to the cathode so that your work piece can sit at a uniform height.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

### RE: Electro-polishing stainless steel

(OP)
Hi Ed, I tried the sulphuric acid but it is weak, I was too cautious when I bought it, so it works but not aswell as the salt and hot water. The salt and hot water also ate away at the cathode leaving not much cathode but plenty of green sludge in the bath. I moved on to caustic soda, it works cold and there is no green sludge but it is giving off a lot of hydrogen so i can't do that for long as I have no fume hood. I think I'll stick with the caustic soda because i can keep adding flakes to make it more concentrated and it can be added to hot water easily, I'll have to do this outside.

I'm now seeing why earlier in the thread you mentioned it would take longer to set the jig than do the polishing. I have to make a bath/jig that will allow me to polish half of the thickness of my part (0.1mm) and be kept firmly in place and allow the cathode to be close and parallel to the part. This would be easier if I didn't have to get half of the part out of the water - I can't even see 0.1mm. I'm currently sat with the part and prospective cathode thinking about using beads and springs. Thanks, Ant.

### RE: Electro-polishing stainless steel

(OP)
Well i've been working with a setup that I thought would work, it used duct tape, aluminium tape and a plastic holder. I thought that will work no problem. And then it didn't. I realised that the bubbles were collecting under the part and stopping the polishing altogether. It'll need some strong agitation or a different type of holder.

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