Stainless Steel Electrochemical Machining "CURRENT DENSITY" - Includes Gift! - Page 1
Forum section: electronics / projects

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 01:23:16 am
content: 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 wordsbut 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/#msg902986But 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.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.htmlAnd 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/cm2with 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/cm2some 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 1cm2for 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/cm2for 2.5 mm deep in 1 minute.Well, 16 amps/cm2for 0.25 mm deep in 1 minute.Machining a small logo of 10 cm2would take 10 minutes. At 30 amps/cm2it 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

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: April 25, 2020, 02:35:06 am
content: ,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.

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 02:41:44 am
content: CNC EDM rig... got it!Already looking at it. Thank you so much for the tip.

author: duak
author_rank: Super Contributor
timestamp: April 25, 2020, 03:52:56 am
content: 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_chromiumAny 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,

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 04:59:41 am
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: April 25, 2020, 06:02:32 am
content: Quote from: Victor Ramon on April 25, 2020, 01:23:16 amApologize if I misread or misunderstood, its just I spotted, CMIIW that you need affordable, quality yet high power DC PSU ?Just sharing my experience, not sure if the situation is similar in Mexico.I love to hunt down cool & rare electronics stuffs, and mostly used of course, and usually for high power PSU, 1st, I did few detective work for local cellular tower installation contractors, they practically exist at every big cities since cellular industry explosions decades ago.While ago I made few calls to them, and gathered few local contractors that do towers upgrade/installation and "decommission"... voila ... there you go, made few calls again, I managed to snag few used but working fine TDK-Lambda PSUs, and "other" cool RF gears & stuffs too.Almost all countries, starting from early GSM era and then 2G so forth 4G and starting 5G cellular trend, usually these towers produced lots of cool stuffs that probably cost arm & leg when new.An example, these beast can be parallel and series "by design", say series you can pump up multiple of 36V, or in parallel I think up to hundreds of Amps.Here last time they cost me about $20/pcs few years ago, and managed to get few of them.A TO-220 chip as reference size to show how big the output connectors size, really2 chunky.Hope this helps.

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 06:36:24 am
content: Wow friend, this is amazing!Yeah, in my town lots of cell towers all around, almost one in every corner and 5G has been indeed already entering my area since a year ago, from what I can remember.The metal surface of the pieces are going to melt like butter and dissolve like sugar in water. All the cool designs are going to show in seconds, I bet.And the best of all it's already outputing the 30 something volts I'm looking for.This is great!Thank you thank you thank you so much... it'll be so much fun gathering these around for pennies on the dollar.Thanks again friend. Take care.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2020, 06:53:07 am
content: Hexavalent chromium is apparent as a yellow to orange coloration of the solution. Clean up all the residues of course, and let the goop settle (the metal will either be present as precipitated hydroxides or salts; at least, I'm not aware offhand that iron, chrome or nickel phosphates are very soluble). If it has a yellow tinge, add a reducing agent like sodium bisulfite to it.I think chromate is most likely in basic solution, where atmospheric oxygen, or electrolytic oxygen from the process I suppose, can oxidize chromium hydroxide in suspension. Solution stored for a long time may turn yellow for this reason.Oxidation occurs at the anode:- In acid solution, this leads to dissolution of the metal. The dissolved metal may remain in solution (in which case it will also plate out on the cathode), or it can precipitate with the electrolyte. Hence the choice of phosphoric acid, as the phosphate salts of these metals are insoluble.- In neutral (salt) solution, the metal is dissolved, but later, hydroxides from the cathode mix with it, precipitating hydroxides.- In basic solution, hydroxides prevent acidic ions attacking the anode (to some extent), and oxygen gas can be produced, without needing specially resistant anode materials. (Or chlorine, which is likely to corrode the anode, too. Another good reason to avoid chlorides in solution.)Chlorides are rather pernicious, forming complexes with transition metals, getting stuck in cracks and between grains, and causing microscopic corrosion and internal stresses. There are stainless alloys resistant to stress-corrosion cracking, chlorides and so forth, but just another reason to keep them away.On a related note, I've had copper pieces corrode even after tinning. The process was thus: metal heated for working; HCl pickle used to clean scale; rosin or acid core solder used to tin; item left to sit in normal ambient air for some years. It seems enough HCl gets stuck in the crevices of the metal (which has a rough, matte surface after being oxidized and etched in this way) that rinsing isn't perfectly effective, and this traps chlorides even under solder (and to add insult to injury, acid core flux is also chloride based). The contaminants probably leave pinholes in the solder, through which corrosion can proceed; or perhaps the trapped crud continues to react (even despite being dried by soldering heat), causing expansion which breaks through the solder layer just the same.Regarding electromachining and current density -- the voltage isn't necessary to drive the current, it's just an unfortunate side effect of circumstances. The electrolyte isn't terrifically conductive, even at such high concentrations. It's just the brute force consequence of an ionic conductor. The electrode reaction itself might be a volt or two; all the rest is dropped across the solution. Keeping a short separation between electrodes helps, but is only so practical, and obviously you need some volume of electrolyte in the gap to take up the removed metal/ions. Electrolyte volume is also significantly reduced by the copious hydrogen (or oxygen when applicable) bubbles generated, and this can lead to uneven material removal.Regarding power supplies: a capacitor is just a store of electricity. A rectifier delivers power intermittently, because the mains is alternating. The capacitor needs to be large enough value to supply the load, given some modest drop in its energy state between charge pulses. We can refer to the capacitor equation:I = C dV/dtwhere I is the capacitor current, C is its value, and dV/dt is the rate of voltage change on the capacitor.If you'd like an analogy, consider a chemical buffer solution. It can absorb some change in acid/base ion concentration, while holding the pH relatively stable; a larger buffer volume resists more change. (pH is a nonlinear transfer function, so this is not intended as a functional analogy.)Say we have a 50Hz source, full wave rectified to give 100Hz charging pulses. Say the charge duty cycle is 30%, so that we spend 7ms between pulses, drawing power from the capacitor alone.* Say our load is 30V 10A, and we want the load voltage to drop no more than 20% (i.e., to 24V) between pulses. Solve for C:C = (10A) (7ms) / (30V - 24V)~= 11.67mFSo, say 10mF (often seen as 10,000uF, for some reason it is conventional to use uF even in ridiculously large values).*This is a design assumption, which depends on the capacitor value; the full interaction between frequency, capacitance, rectifier and load is rather involved to solve by hand, and frankly we don't need anywhere near that level of accuracy. So, we gladly hand-wave assumptions instead, and then check that they remain true.**In practice, the voltage will drop along some kind of curve depending on the load characteristic. In this case, the load is largely resistive, so an exponential decay will be seen. This is another assumption we gladly hand-wave away: when the voltage ripple is small (like 20%), the drop is roughly linear between pulses, so we use the linear relation (assuming dV/dt == ΔV/Δt).All of this of course is taken into account for the SMPS, which typically has a rectifier and filter at its mains input, and a smaller rectifier and filter (because of the high frequency) at its output.Note one hazard with large capacitors: if you short the electrodes together, BLAM, the capacitor discharges into the sudden short circuit, pitting both surfaces (and stressing the capacitor; don't do this very often!). The SMPS likely has less capacitance on its direct output, and likely has current limiting to operate into heavy loads without faulting, making this less problematic.Most SMPSs do however have a "hiccup" current limiting mode: that is, when the output gets pulled below some threshold voltage, the SMPS stops, waits a moment, then retries. It keeps hiccuping into the load until the fault is cleared. This prevents it from dissipating too much power, but wouldn't be so convenient for use here. This would be where the buck converter module comes in handy, offering a continuous current limiting function.Tim

author: BravoV
author_rank: Super Contributor
timestamp: April 25, 2020, 07:03:19 am
content: Quote from: Victor Ramon on April 25, 2020, 06:36:24 amMy pleasure, wish you good luck on your hunt.Abit about the brand, the TDK-Lambda is considered top tier PSU manufacturer, and just don't compare to those popular brand like Meanwell, its not the same league. The above model I bought, brand new is cost about $1300 a pop. ->Example at DigikeyAlso make sure you do lots of homework 1st reading it's datasheet/user manual before purchase, as I did for this particular one with nominal at 36 Volt, that its also adjustable starting from 7.2 Volt up to 43.2 Volt, which is amazing imo.And no, not all PSU have the flexibility and capabilities like setup in series for higher voltage, parallel for more current, wide adjustment range on voltage output, and remote sensing and etc, again do your home work 1st before purchasing it.These below examples on how to do parallel or adjusting the output voltage from the manual as example.

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 08:20:39 am
content: Quote from: T3sl4co1l on April 25, 2020, 06:53:07 amYou've touched on so many of the most important aspects. It's obvious to me you've been working on electrochemistry at a very deep level. And I admire that. By the way you exposed your arguments so clean and clear, I couldn't tell if you're a chemist who is into power electronics, or an EE who is into electrochemistry. It'd be nice to know.As you very well pointed out, the reason for higher power requirements is due not to the reaction itself, but the separation of the electrodes, which in an ideal world the'd be nanometers apart from each other, but this is not practical for so many reasons, safety being one of the main ones and the many other side effects that you flawlessly already pointed out. Hence the separation and the ohmic resistance, which then demands more power due to the voltage drop. Most of the power goes into pushing the electrolytes from one place to the other, yes.A while ago I found a littla piece of data in several research papers that caught my attention: when the current feed is continous, steady and uninterrupted, the yield goes down in several devices, ozone-in-water generators for disinfection purposes being one the most notorious. But when a PWM at low frequencies, say 100Hz is applied at a duty cycle of about 70%, the yield goes up. From what I can gather, this happens in many many reactions for different applications. Take the duty cycle above 85% and the yiedl goes down, take it below 55% and there it goes down again. It seems in the 70% region is where the sweet spot which translates as higher reaction yields. It sure looks like an empirical finding but I'm sure you know better. Some crazy thermodinamics going on there.Which takes me back to the buck converter issue at hand.With a little SMPS and a small buck converter is easy to kook up a PWM modulator and establish the 70% duty cycle I was talking about. For now it's been simple and easy to operate at about 150 watts, (24 VDC at 6 or so amps) which is something.And there are only two options left to reduce oxidation time:1. Reduce the distance between the two plates.2. Increase the power.With some rheology modifiers, conductive gels are quick and easy to make so that way I can forget about high electrolyte volumes, which reduces distance and waste volume.All that's left is the power.I was thinking, naively, perhaps a half H bridge inverter with an IR2110 driver with 2 overkill mosfets in parallel could possibly work to chop the input current coming from a higher SMPS. Something like this:http://1.bp.blogspot.com/-J9Yq35bgrE0/UPvoC1fe2XI/AAAAAAAAAaU/vqhm1HpkK0I/s1600/IR2110+-+6.pngIt will not be as nice and clean as a buck converter, but I'm assuming that could offer some kind of control? But I don't know. I'm just assuming that in a classical way, maybe a frequency/duty cycle IC connected to some logic gate and then to the inverter driver and then to the mosfets which control the SMPS input to the electrolytical cell?After all, highly resistive loads demand higher power sources. This IR2110 setup is the best one my electronics-ignorant mind could think of so far.Is it correct to think this way? Or am I brutally suggesting the violation of a well established electronics design law? Is it a good idea? Or is it just a stupid one?What do you think, Tim?Guys?

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 08:24:41 am
content: Understood.I will comply.And thank you for the heads up on the Meanwell and TKD-Lambda. As an outsider, I did not know and so I thank you.Ii will do as you say.Much obliged.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2020, 01:37:03 pm
content: Quote from: Victor Ramon on April 25, 2020, 08:20:39 amOne of those rare times when an inclusive-or "yes" answer is appropriate.Professional EE, amateur chemist. Haven't had a place to practice chemistry in quite some years, but I remember much.I'm sure there are theoretical bases for what waveforms, additives and electrodes accomplish, but I'm quite happy waving my hand at "surface chemistry" and leaving it at that... the professionals and academics can handle it.Have also heard that "high throw" copper plating (e.g. for PCBs) can be done with a partial reversal waveform, which apparently works by etching the peaks more rapidly (electropolishing). Meanwhile, levelers and other additives encourage uniform deposition, even into narrow or blind holes.A typical PCB is 1.6mm thick, and is drilled with 0.3mm holes -- a 5.3:1 aspect ratio -- which get plated with 35µm or so of copper. The glass-epoxy laminate is treated with an activator, then electroless copper plated for initial coverage, then electroplated to finished thickness. This is how they plate holes, edges, anywhere that isn't covered in copper foil to begin with.(I've etched my own boards, once upon a time; never had the things together to try plated through holes (PTH) though.)QuoteWell, two things --0. If straight on-off is all you need, a single switch will do. Simple!1. If the buck converter is controllable, why not program its setpoint in the first place? This gets you a multi-level, unipolar (always positive) waveform.1a. If it's not controllable, it may be worth seeing if it can be hacked to do so. Example: adjustable regulators have a feedback/sense pin, which connects to a resistor divider which senses the output voltage. You can bleed in a small current (directly, or through a resistor from another voltage source) to offset the default value. In this way, the regulator never loses control -- it's always in control of the load, no danger of confusing or destabilizing the control loop -- and the voltage can be controlled arbitrarily. (Control might be from an Arduino with DAC shield, for instance. DACs produce a digitally controlled output voltage.)2. If the waveform should be bipolar (reversing), you can't use a half bridge anyway, but need a full bridge. Which isn't to say you're on the wrong track -- a full bridge is just two put together, driven oppositely.IR2110 style drivers have the downside that they must always be switching -- the high side driver is only powered when the low side turns on. The rest of the time, a capacitor supplies its power, and this can only go for so long (milliseconds, seconds?), depending on its value of course.So if you're driving a full on/full off waveform, or full on/full reverse, and it's switching at some minimum frequency or higher, a bridge will do fine, and bootstrap gate drivers will also do fine.I would suggest opting for an off-the-shelf development board, as there are some details in bridge layout that would take some time to explain.Also if you combine these approaches, you can do an asymmetrical reversing waveform, for example. I don't know that that's helpful here, but it's apparently the kind of thing that's helpful for copper plating, so who knows.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: April 25, 2020, 01:49:37 pm
content: I don't have anything specific to add but if you are dealing with bare PSU modules keep in mind the chassis. You don't need EMI for this but it would help if they are splash proof and stuff. If you are making your own from the bricks and you are doing chassis you might want to make it a bit non standard with more complicated ventilation/splash control, i.e. blower fan with bends, mesh filters (not just perforations), etc.The design of something for working around chemicals is different then a bench top lab power supply IMO. Also corrosion, it might make sense to use potted electronics or to use conformal coat. Also use switches with coverings if you can afford them, in case you need to turn it off while wearing gloves (preferably add a EMO switch that you can slam)good design around fluids will increase cost significantly. For low currents you might want to consider using batteries.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 25, 2020, 02:18:01 pm
content: Speaking of chassis and ground, mind that a cell driven by full-bridge either needs to be isolated by itself (ungrounded), or the power supply does, or both.Shouldn't be hard to get power supplies with non-grounded outputs, but keep this in mind if you're going to connect anything else to it as well (e.g., programming cable to Arduino board).Tim

author: duak
author_rank: Super Contributor
timestamp: April 25, 2020, 05:57:27 pm
content: Victor, no, I didn't work in a plate making facility. I'm an EE that worked in various R&D projects that often involved electro-optics. My first major project there was in data storage. Some of the technology we developed was later used to expose silver halide film for printed circuit board fabrication and then for graphic arts, ie. lithographic printing plates. We were one of the first companies to come up with Computer to Plate systems that bypassed silver halide and exposed the plates directly. Early plates were sensitive to green wavelengths but we pushed thermal ie., IR sensitive. Film and darkrooms were no longer needed although some plates still needed processing for longevity. We did not develop or manufacture the plates ourselves but worked with plate media manufacturers like Kodak, 3M, etc. to improve and optimize their products.I remember a lecture by one of the chemists from one of our large customers. The chemistry of ink is complex and interesting - so many conflicting requirements like viscosity, miscibility, drying time, toxicity, etc.Since gravure was a photo and chemical process, our Technology guru thought we we should look into some form of electro-erosion to make gravure plates. I think it was a more difficult problem than expected as well as a market that was too small for us to continue.

author: Victor Ramon
author_rank: Newbie
timestamp: April 25, 2020, 06:32:29 pm
content: Quote from: duak on April 25, 2020, 05:57:27 pmOh yes, I remember my days when working with printing inks. The formulations are very sophisticated. Paint and ink are definitely not the same. One takes hours to dry while the other dries in a matter of seconds. Why??!!!!!That's what got me into ink formulations way back. The photo is from the legendary "The Printing Ink Manual", the chapter about gravure inks and its sophisticated priting rollers. Right off the bat gravure is one of the most difficult and elegant and beautiful quality printing technologies. It's what money paper is printed with in the first place. Offset and flexography are for packaging, magazines, advertising and other garbage.Cheers

author: duak
author_rank: Super Contributor
timestamp: April 26, 2020, 03:59:22 am
content: Victor, I think the reason for the ink to dry quickly is to prevent smearing as the paper web passes through the remainder of the printing press and the next colors are added. In the halftone process, the ink is applied in small dots of varying sizes to change the density. The different ink colors must not mix otherwise the color tint will change. Lithography printing works at certain speeds - not too fast or too slow. I remember about one or two meters per second. It is a miracle to me that it works as well as it does.Best Wishes,

author: StuartA
author_rank: Regular Contributor
timestamp: April 26, 2020, 09:52:40 pm
content: Quote from: Ground_Loop on April 25, 2020, 02:35:06 amI recall taking a component to be sectioned for failure analysis to a local EDM specialist and watching the work being done - really impressive! You have this very powerful spark going on to the work piece, which is completely immersed in paraffin. This was over 20 years ago, and I cannot recall the make of the machine which was used.I did a little bit or work on electropolishing stainless; it greatly reduces the surface roughness and improves the passivity. At the time I worked on that it really seemed to be a "Black Art", but these days they seem to able to polish even internal surfaces of tanks and pipes quite routinely.