Eletrolytic Rust Removal Question

Andy Dingley wrote:


Is electrolytic rust reduction the same process as plating removal ? I have a bunch of landrover parts that are zinced and damaged that I'd like to strip and replate.
Steve
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wrote:

No, pretty much the opposite.
Electrolyting de-rusting is the reduction of iron oxides by a cathodic process. It's basically electroplating, but with no metal in solution to plate out.
Electro-polishing is an anodic process. Although it will certainly remove rust, it also removes steel even more effectively. This is a short-term process (a couple of minutes) and needs careful monitoring. Cathodic de-rusting has the great advantage that it's self-limiting and can be left in operation for days until it stops by itself.

Easiest way to take zinc off is to immerse it in hydrochloric acid (any builders' merchant)
For electrolytically stripping zinc from steel, make it the anode with a large steel cathode (sometimes the whole tank), a voltage of 6V and an electrolyte of 1lb/gallon caustic soda. This is moderately benign on steel, but keep an eye on it - when the zinc is gone, it'll start attacking the steel.
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With the Caustic soda any paint will be gone soon as well.
When working for GM as plant protection just after getting my degree and before the time my job started - I saw a tank used for whole car bodies, fenders... they would route the line to the tank and extract the bad one - drag it through getting fire and sparks - out the other side and back into the paint line. Drips didn't have a chance in that place. That was dangerous stuff.
Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder
Andy Dingley wrote:

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Andy Dingley wrote:

Thanks for that Andy,
I thought the chemistry would be very simple. Frost automotive ( http://www.frost.co.uk , amongst other neat toys sell a "plating removal kit" , but I figure the price for what you get is a bit much.
Steve
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wrote:

It is. If you're just doing zinc, then stick with hydrochloric ("brick acid" will work fine). You only need complicated chemistry if you want to strip chrome or a few other metals.
Plating chemistry is very sensitive to combinations of base metal and plating material. These "one size fits all" kits have to be very complicated (i.e. expensive) to work, and don't actually work that well compared to a more job-specific approach. Fortunately for zinc you've got the easy one.
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Andy Dingley wrote:

Hi Andy, I've got their nickel plating kit at work, and its been great for flashing brass and MS parts. I hope it will work on some of these zinced bits too. Be a very flash looking 200Tdi engine when I've finished ;-)
Steve
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Andy Dingley wrote:

Why use acid to strip zinc off of steel? Why not use caustic soda (lye) instead? The lye dissolves the zinc quickly, faster if you heat it, the lye doesn't attack the steel, and further, if there is any oxidation (rust) the zinc ions will reduce the iron oxide and so the part will come out shiny clean, not dull grey, and won't have any issues with hydrogen embrittlement either.
If there is a little oil or paint on the galvanized part, the lye won't care, it will eat those too.
GWE
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On Fri, 25 Nov 2005 14:29:07 GMT, John Redmond

Maybe you need to use an adapter that was built to supply more "juice"? DC output from a AC/DC stick welder comes to mind.
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Check out some of the sites where thy talk about anodizing aluminum. They have had a lot of discussion about car battery chargers and how to modify them. Same tech difficulties for both processes.
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Diamond Jim wrote:

Try anodising101 on Yahoo groups.
Steve
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Sorry for the delay in getting back on this. After upping the electrolyte in my solution, I fried a couple of more wall warts. Then I went to the auto parts store and bought a basic 6-12 Volt,1 amp car battery "trickle" charger for $17 new. I plugged it in and it works like a charm! Thanks for everyone's advice.
All the red rust is gone now on my work piece. Is it removed or converted to black rust? I'd guess both. Loose rust flaked away and at the surface of the metal, black rust was created. Is that right? What is a good way to remove the remaining black rust without scratching the finish, aside from a wire brush and elbow grease? Thanks again.
--
John Redmond

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John Redmond wrote:

The black should come right off under warm running water with light rubbing with a 3M pad - I use the maroon ones because I have a lifetime supply. If it's tight don't worry about it, it's just black oxide.
GWE
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Most of it does rinse/wipe off easily, but there is still a thin coating of black oxide. Diluted vinegar does a good job getting most of what remains off and down to the bare metal.
--
John Redmond

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On Fri, 25 Nov 2005 14:29:07 GMT, John Redmond

As you scale up your electrolytic cleaning you need to scale up size of your power supply. Your amps drawn is exceeding power capacity. Battery charger might work better. Get one with amp meter and circuit braker or fuse the protect the battery charger.
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