Using a welder for electroplating

Is it possible to use a constant current DC welding machine for electroplating or derusting?

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Ignoramus15120 wrote:

I've heard of guys using MIG machines (CV) to do electrolytic derusting. In that process, the variables you have are strength of solution (i.e. 1/4 cup washing soda or the whole box?) also distance to the electrodes and to some extent electrode topology. In my most-used setup, I use a square 5-gallon bucket that once contained laundry detergent (itself mostly cut with washing soda) and two railroad track ties with 10 ga. wires soldered to the track ties. The track ties lean in the bucket against the sides, leaving a nice volume for workpieces, which I suspend via a wire/clamp through a stick over the top of the bucket. The problem with this setup is that it's a real hassle when your current isn't enough, or is too much. All I can do with a buzzbox car battery charger is toggle 6V/12V. With a MIG welder, however, I can crank the voltage wherever it needs to be to get the desired level of bubbling, and after the electrodes "load up" I can crank it up a little more to overcome the resistance.
That's a MIG welder, though. A CC source would be really great as long as you can really control the current. Most of the time I'm shooting for 3-15 amps (I'm sure what you really want is some value of amps per unit workpiece area, don't know what that is) and if you can hit that easily and controllably with a CC welder, why sure it will work.
I don't see you have much to lose. I suggest you give it a try and report back.
GWE
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you mean tie plates (steel), right?

Makes sense.

Yes, I have a 100% duty cycle CC welder, where I can set amps to whatever I want. It can run for hours.

I will. Right now I want to do nothing big that would take my time away from the tig inverter project, but it will definitely be on my list of things to try.
i
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replying to Grant Erwin, S G wrote: carbon crucible blocks work better, no sludge
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Constant current is ideal for plating, anodizing and derusting -- if you can get the current low enough to be suitable for the job.
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Thanks Don. I will try it later, after I am done with my current inverter project.
i
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replying to Don Foreman, S G wrote: A friend uses 1000amp 6volt rectifier but that unit costs $7500 bucks, 3 phase 280v
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On Wed, 16 Nov 2005 01:44:26 GMT, Ignoramus15120

It's not a sensible thing to do. The voltage is too high and the overall output is enormous for any reasonable "rec.crafts" process.
Electronics is cheap these days. Do it right,
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Andy, I will check my welder for what the minimum amperage of its output could be. My welding machine has digitally settable output current, although I do not know how low it goes. My guess is that I could get under 20 amps, maybe a lot less (like 10 amps).
The voltage on this constant current welder is automaticaly adjusted to provide desired current.
http://igor.chudov.com/projects/Welding/00-Hobart-CyberTig-Welder/
Assuming that it is the case, do you still have objections to this use?
thanks
i
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On Wed, 16 Nov 2005 14:56:39 GMT, Ignoramus7434

The _voltage_ will be too high. You don't have any way of reducing this (for any welder I've seen) down to the low voltages required.
Besides which, electroplating is a foul process. If you're into the region where you need kW of power, then it's a serious chemical waste handling problem. For "backyard" scale work you can just lash something up from the junk pile.
Here's a piece of electroformed copper (the underlying skeleton is plastic) about 12" across - work by a friend of mine. Nothing more obscure electrically than scrap-box transformers. http://www.jarkman.co.uk/catalog/random/butterfly.htm
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You misunderstand the concept of constant current welders, such as my Hobart Cyber TIG welding machine.
The constant current welder adjusts the voltage, up to a certain amount, and down to almost zero, to produce desired current.
If I short the leads of the welding machine, the voltage drops to almost zero.
Similarly, if I was derusting and resistance of the setup was low, the voltage would drop to a very low value, so that the produced current does not exceed the current that I dialed on the welder's control.

Right. Right now I am mainly interested in derusting, using steel electrodes, which is environmentally safe.

That's very nice and artistic...
i
--


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On Wed, 16 Nov 2005 17:41:50 GMT, Ignoramus7434

Plating wants a voltage of around 6-7V, with good control of current. This isn't a "constant current" source, because if it does vary (owing to workpiece conditions changing) then it's better if the source behaves as a constant voltage source, once set. Current needs good manual control though and is a crucial adjustment for plating.
Some processes want higher voltages: 12V for hard chrome, 16V+ for anodising and some quite high voltages for anodising titanium.
I've also not seen a welder that went down to this 6V level.

I'm pretty certain that it _is_ zero. The welder will detect this as a specific case and go into a "shutdown" condition.
We live in a world full of cheap scrap electronics. I just wouldn't use a welder for this, when I have any number of small compact 5V and 12V high-current PSUs just looking for new homes.

Car battery charger (old non-auto one). You only need maybe 5A tops at 12V for anything that fits in a dustbin. I've done boat hulls where I used an old computer PSU and about 60A.
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I have seen this happen to my welder.

Nope. It continues to happily produce current, as evidenced by the DC ammeter on the welder. I tried this, a dead short as well as a short with a copper bar that had about 2 volts or so of voltage across it.
This is real, my welder is a constant current source that does produce required current and drops voltage to where is has to be for that.

But why would i buy anything else if my welder can do what I want.

That's interesting to know...
i
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On Thu, 17 Nov 2005 14:07:19 GMT, Ignoramus24428

You can't have "a copper bar" with "about 2V across it". The power required to maintain such a voltage would be enormous.
There are no true "constant current" sources, outside of Norton and Thevenin - when you get to the limits, something has to give.
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that was a 6mm by 1.6 mm by 180 cm copper bar, more properly called copper strip.

I thikn that this discussion became sidetracked. I have a constant current source that really is a constant current source within the relevant limits. That's not questionable.
i
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On Thu, 17 Nov 2005 15:46:39 GMT, Ignoramus24428

That's more like "two yards of thin cable" rather than "a copper bar".
2m of 10mm^2 cable, and copper has a resistivity of 2e-8/m is a resistance of about 4m ohms With 2V across it is a power of 1kW, which is certainly practical for a welder.
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Andy Dingley wrote:

You most certainly can, it's essentially a current shunt. With a welder happily pumping 200A+ through the bar, you will develop a voltage across it based on it's resistance.
You've clearly never had any experience with a quality TIG welder before.
Pete C.
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2V at 200A is just 400 watt, not too much.
i
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Of course you will. And for 200A current, that's about 8kW of power and a voltage of 40mV (for a nominal "copper bar" shorting link of 0.0002ohms). To develop 2V across this sort of resistance needs 10kA, not 200A - just how powerful a welder are we talking about here?.
You just can't get 2V across a "copper bar" - it would melt almost instantly.

Nope, my experience is all with Ohm's law. Good on electrons, bad on bogons.
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Andy Dingley wrote:

If he's going by the volt meter on the welder it most likely represents the voltage across not only the copper bar, but also the welding leads.
Pete C.
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