Electronics > Projects, Designs, and Technical Stuff
Stainless Steel Electrochemical Machining "CURRENT DENSITY" - Includes Gift!
Victor Ramon:
I am new to the forum. Not an EE, but a chemist playing with electronics.
Anodizing, electropolishing, electrocleaning, hydrogen fuel cells sandwiched with Nafion polymer membranes from Dupont, soluble ozone in water generator and many many other applications of the combination of chemistry and electronics. The list is endless. It's all fun until you need more power with the sole intention of producing more and faster of whatever yoy're doing with chemicals and a power source.
Sorry for the excess of words :blah: :blah: :blah: but it's to provide you with some context at the cost of your attention, in exchange for the formal source where these ideas are from.
Someone else has already touched on the subject:
https://www.eevblog.com/forum/projects/decorative-electrolytic-metal-etching-plating-and-marking/msg902986/#msg902986
But I feel many things were left out and the thread wasn't solved. Hence, I've decided to rescue the subject, but from another perspective.
But before I go into my question about stainless steel electrochemical machining (ECM) and how it relates to power requirements, let me just say that your most humble servant is sufficiently aware that in a modular easy fashion:
12 volts and 5 amps can be considered child's play. A cheap SMPS and a $ 10 dlls buck converter is all you need for weekend electrochemical projects.
24 volts and 3.5 amps is a little more serious. A Meanwell SMPS and a $ 40 dlls buck converter (and some alkaline gel) gets you something like the video at the bottom.
I call it the "Speedy Decarbonizer", one of my many inventions. (I made it because Easy Off and other harsh chemicals just don't work against aged carbon deposits on metal. You can use solvents, sure, but if your removing carbon deposits at food joints and other charbroiled cookware, perchloroethylene asnd xylene are out of the question).
Once you are done with the safe electrochemical decarbonization procedure, then you can switch the alkaline gel for some phosphoric acid at 50-70% along with other additives and now hook the stainless as the anode, you turn the device into an electropolisher. It will shine just as new.
In my experience, I've found that for electropolishing and electrodecarbonizing, 24 volts DC at around 2-5 amps is more than enough so you can use the anode as a brush-tool and be done with it in a matter minutes, 15 tops if it's too grimy.
And so on and so forth.
(BTW, I shot the FB video down below.)
Now I've decided I'm after 30 VDC and at least 12 A. And there is a scientific reason for that. (More on that later.)
We industrial chemists with an interest in power sources, struggle with electronics, but we don't give up that easily. :box:
Most chemical reactions need heat in order for the reaction to occur fast and at high yields. But the most interesting, at least for me, are the ones that require high electric power. Productivity is the name of the game.
So... after a rabbit hole experience, and unless I'm mistaken (which I am sure I am), I've already learned there's no cheap buck converter to comfortably adjust the raw power I'm after, coming from a suitable SMPS or an old school transformer/variac/rectifier/inrush current device/large capacitors arrangement for that matter, with the inductor of a buck converter being the "Achilles heal" of the process, so to speak.
Sure, I will purchase an already made regulated power supply like this beauty:
http://www.volteq.com/volteq-power-supply-hy3030ex-30v-30a-over-voltage-over-current-protection.html
And at $ 300 dlls it's a no brainer. It will easily give me the 30V/12A I'm after and with warranty and all the customer service a manufacturer can offer.
That's the responsible and professional thing to do.
So why do I insist on asking, when I can carry on with my life?
Because this is my life.
Because I want to understand what's going on between the electrolytic power caps after rectificacion and my jazz electrodes, when no buck converter is available... that's it.
How do they do it? :-//
The ignorance is bugging me, I can't sleep and there's no one around to ask.
So, at the risk of being expelled from such a respected electronics forum for a low-level question, here I am. That's why I've decided it was appropriate to offer something valuable in return.
And just for the record: it is NOT my intention to build a 30VDC/12A power supply... no no no... I would not dare to usurp the place of an specialist.
Knowledge and understanding, to explain what is happening, when steady and clean 30, 40 50, 60 100 VDC at 10, 20, 40, 50 100 A are what is required. That's all I'm asking for.
Now for the gift.
When we chemists come upon something "new" we have never ever even heard of, there is a moral obligation to go to "The Source".
That is the Ullman's Industrial Chemistry Encyclopaedia. Thousands of pages on almost every chemical subject you can think of.
Every applied chemist and chemical technologist should have theirs.
For today, I brought you "Electrochemistry 2 - Inorganic Electrochemical Processes".
From page 307 to 311 in volume 12 you will find out about the most power consumig industrial electrochemical process of all, known to man: ELECTROCHEMICAL MACHINING.
We've already touched on electrocleaning, electropolishing and so on. At the most you're looking at 24 VDC.
When the workpiece is the cathode the connection at 24 VDC at "2 amps/cm2" with an alkaline formula, it is for cleaning. When it is hooked as the anode, at 24VDC at the same 2 amps/cm2 with an acidic formula, it is for polishing.
Make sure your electrolytes don't contain chlorides/halides in it, as it will generate important quantities of chlorine/halide gases and you know what that means.
The water should contain electrolytes, yes, but make sure they're the ones the electrochemical manuals recommend for each metal/alloy surface. Sodium nitrate is specifically for stainless. If you can't find it, then you can make some with lye and nitric acid. Both solutions have to be concentrated so the final "titration" gives you at least 20% sodium nitrate. 30% is ok. 40% is perfect. 50% is too much. Alligation techniques are what tell you how much of which reactants you need to dissolve in pure water, in order to achieve the desired concentration for your proposed electrolyte. Lye is super alkaline. Nitric acid is super acidic. When concentrated, both are super corrosive. They're also cheap and easy to get (at least in my village). You have to mix them slowly and carefully, with patience until you reach neutrality. That's when there's no more extreme alkalinty nor acidity. Now it's only water and a special salt. In this case sodium nitrate. Check for a neutral pH, it should be around 7 with a calibrated pH meter or pH strips and you're set. Anything from 6.9 to 7.1 is safe for the process. Remember: you have to do all this work when there's no commercial sodium nitrate already available.
Onwards.
So for electrochemical machining you have your anode workpiece, your cathode, your electrolyte solution and your power supply.
What now?
The logic is this:
For electrocleaning, electropolishing, electrolysis in general when it is supossed to modify the surface of the workpiece in a short time period with productivity in mind, 12 volts just don't cut it. It does work, yes, but it will take forever.
Crank it up to 24 volts and many reactions and other special effects will happen instantly in front of your eyes. Don't forget your ballast resistance.
Chemically, what you're doing is DISSOLVING the metal. Like dissolving salt or sugar, but it's the metal. We're talking corrosion, but a controlled one. When this happens the electrolyte becomes contaminated/saturated with lots of sludges and residues, so you get rid of them by rinsing with tap water (yes, tap water is ok for rinsing on the fly) and replacing the electrolyte with new solution. You keep doing this until you're satisfied with your results.
Easily oxidizable/reactive metals react faster at lower power ratings. As for the less reactive ones, like stainless steel in all of its varieties, to dissolve them in the same amount of time, you need more power and more solution. So you work more. Hence, more power. But folks on YT and other social media groups and such are using 12 volts SMPS and car batteries and AC adaptors, etc. That's why people on the web say things like "stainless steel is difficult to etch" and "it doesn't work"and such.
To begin with, they are not "etching" stainless... technically, what they're trying to achieve is to ELECTROCHEMICALLY MACHINE stainless... a very stable quasi-unreactive alloy. We take it for granted, but SS is a marvel of alloy technology.
The pdf I've attached down below in page 36 (307 in volume 12) makes it quite clear.
Sure, at 12 volts, 24 volts and a couple of amperes they're dissolving SOME stainless. It's just that the dissolution rate, measured as distance/time from the outer surface to the inner surface, is in the nanometer/hour range. That's perfect for cleaning and polishing purposes. After all, you don't want your equipment to etch the metal away when your sole purpose is to clean some dirty workpieces.
It is when you want to not only clean and polish by dissolving a little metal, but to penetrate the surface 1 million more times deep, from nanometers to milimeters,
not in a matter of hours but in a matter seconds... that's when things get interesting.
It's not cleaning/polishing anymore. Not even "etching". I hate that word.
It's machining. You're cutting metal and trying to do it without carbide bits nor CNC gear, not even an old school lathe, etc. Those who believe they can achieve such a thing and get away with a car battery and some table salt, have no respect for the trade.
Want to carve out some stainless with fancy desgins in the blink of an eye? Welll... you are actually trying to literally drill the metal with household chemicals and a toy power supply. Good luck with that.
ECM is a very well known process in the industry, decades old.
It's similar to CNC.
What's the difference?
CNC is for "normal metals" and ECM (electrochemical machining) is for "crazy metals" like for pieces for space rockets and satellites and moon rovers etc. Specialty alloys a CNC would never be able to cut.
So what do you do?
You apply some chemicals and some serious power, with the"current density", j, in mind.
It is not "i" anymore.
Now it is "j".
And you need lots of it.
Anything above 28 VDC but below 40 perhaps 50 VDC. I'd go with 32 VDC.
As for "j", for industrial ECM purposes, anything less than 160 A/cm2 some would say is too slow.
Yeah, you read that right... 160 amperes per squared centimeter. That would drill 1/10th of an inch of stainless surface, in one minute. That's 2.5 milimeters deep of stainless dissolved in one minute, for an area of 1 cm2... for that you need 160 amps just for that area at that depth in such short time.
All that's like the rule of thumb.
I get it. 160 amps per 1cm2 for machining 2.5 mm in 1 minute is NASA level.
But what about 16 amps?
Perhaps, if algebraically we assume a "j" linear behaviour with a slope of +1 when compared against machining depth with time as a constant, then electrochemically machining 2.5 mm at 16 amps at a "enough given voltage", (in theory say 30VDC give or take) it should take 10 minutes.
But then again, machining 2.5 mm for a piece of stainless we're talking about a thick piece.
If we're going to machine a cheap sheet of stainless for tinsmith purposes, those are 0.75 mm (1/32 in) thick, say we'd go for 0.25 mm deep, at 16 amps, the task would be over in 1 minute.
160 amps/cm2 for 2.5 mm deep in 1 minute.
Well, 16 amps/cm2 for 0.25 mm deep in 1 minute.
Machining a small logo of 10 cm2 would take 10 minutes. At 30 amps/cm2 it would take 5 minutes and so on an so forth.
A setup like that would be the prototype of a competitive commercial product for small workshop operations and as you can see, I am already working on it.
As I said, I'm assuming a linear relationship with a +1 slope but naturally, experimenting and trial and error are the basis.
All this setup ought to be verified through a formal "design of experiments" exercise to explore the behavior of as many variables as posible in the least amount of time.
So there you have it gentlemen.
All these ideas are presented to you, to explore the possibility of "Carving stainless steel, almost as if it was wood".
Look at it this way: if there is no CNC available for "etching" a piece of stainless steel, perhaps a humble portable ECM device could be a viable choice.
I hope my presentation wasn't so painful and that my offerings live up to your standards.
Also, I offer my apologies in advanced for interrupting your forum with such an "outsider" subject.
Please receive my best from Tijuana, Baja California, in Mexico.
VR
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Ground_Loop:
,and I thought alumina reduction was he most power hungry electrochemical process. Anyway, if you want to carve stainless with electricity how about a good CNC EDM rig? Wire or plunge, they both work well and are great fun to work with.
Victor Ramon:
CNC EDM rig... got it!
Already looking at it. Thank you so much for the tip.
duak:
Victor, I've been using electrolysis to remove rust from various iron & steel items for years and looked into using stainless as an anode. I'm not a chemist, but I understand that it's not a good idea to erode stainless as hazardous hexavalent chromium is generated: https://en.wikipedia.org/wiki/Hexavalent_chromium Any thoughts on or insights into this?
I remember one research project that went on where I worked was to make gravure printing plates by electro chemical erosion. We didn't make a product of it though, I googled "electro gravure" and got a number of hits, mostly in French.
Cheers,
Victor Ramon:
Oh yes, in chemical work there are side effects everywhere. You already know that for stainless steel to be considered "stainless" is should include at least 11-12% Cr and some nickel an a little carbon as well. That's what makes it stainless. Other manufacturers have their own recipes.
Rest assured: eroding stainless will dissolve the other elements into the solution as well as in the sludge that will precipitate.
About being a good or bad idea: I think it depends mostly on the person doing the work. It's a good thing almost no one can do this kind of job so easily and if anyone is interested in doing this work they should know it includes environmental responsabilities. The rinse water and the sluge, which if done effciently, it will be low on both wastes. It's not forbidden. It just means it should be done responsibly according to local laws.
You worked at a gravure plates facility? Those pieces are beautiful.
On the electrochemical behaviour of stainless:
1. When connected to the power supply onto the negative as a cathode, the surface will not be eroded, unless you're operating it as an arc in which case everything gets eroded. But under "moderate voltages" (like in an electrochemical controlled setup) it will remain inert. This is mostly for cleaning/removal activities.
2. When connected to the power supply onto the positive as an anode, IT WILL GET ERODED. The chemistry changes completely in reverse. That's the whole point.
Electropolishing, so called "etching", machining, forming, etc, the base metal and its alloy constituents from the outermost part of the surface will dissolve away.
If the surface is covered in some contaminant, in both cases the cleaning will happen, the difference being that while connected as a cathode it will not erode, whereas an anode it will, the intensity/rate of erosion depending on the power conditions as I've already discused above.
For electrocleaning rusty pieces, I'd recommend connecting the piece to the negative, and for the postive get some graphite electrodes. They're like $ 12 dlls for a set of 5. The graphite will erode as well, even faster than stainless but it is just carbon so the Earth will be ok. Anything connected to the postive will eventually erode. For environmental purposes while doing electrochemical work, there's no other anode material like conductive carbon: glassy carbon, conductive carbon, graphite, nanotubes, graphene, even nitrogen-doped diamond/carbon electrodes... these last ones are intended for research purposes but some people use them for commercial projects.
It was my pleasure.
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