Electro-polishing stainless steel 1

[antknee]

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.

 

[berkshire]

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

 

[antknee]

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.

 

[antknee]

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/electropolishing.html

[li]Do the cathodes need to be lead or copper? I have plenty of stainless and it would be easier to use that. [/li]
[li]Do I have to have cathode strips of a particular width? I mean why can't I just drop the wire into the solution?[/li]
[li]How important is heating the bath? I'd need to get some kind of bunsen burner.[/li]
[li]How important is agitating the solution? That would be awkward, I could put a fan on it[/li]
[li]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![/li]
[li]The solution will be sulphuric acid that is about 5%, with no additives, how important are the additives[/li]

Thanks,

Ant.

 

[berkshire]

Ant Knee,
Please re-read Ed from Plymouth tubes posts to you, he has already covered that.
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

 

[antknee]

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.

 

[antknee]

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?

 

[EdStainless]

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

 

[antknee]

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.

 

[antknee]

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.