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Author Topic: Electrolysis - for rust removal  (Read 21136 times)
danny stardust
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« on: April 21, 2012, 10:43:43 PM »

I notice there are a few on here that engage in a bit of tinkering around with all things mechanical so thought this might be of interest.
As I refuse to buy anything new and am not into that whole consumerism nonsense, much of what I get my hands on through extensive wombling is past it's best and in need of work to recondition it to a usable standard.
During a recent car conversion I came across using electrolysis to remove rust. Having had to pay for sand blasting in the past I decided to try this alternative way of removing rust.
I was sceptical about what I had seen but it is actually very simple and effective. My setup involved using an old iron car flywheel as the anode (+ve connection), and the item I wanted cleaned which was some vehicle brake calipers in this case as the cathode (-ve connection).
The solution in the bucket is just water with a couple of tablespoons of washing soda.
I had a charger putting 3amps into the 12v battery to keep the battery charge up as the component fizzed gently whilst submerged in the bucket. After a few hours I removed the component and gave it a scrape to remove some of the loosened corrosion, then put it back in for another session, repeated this several times, rotating it's position each time as I believe the process works on line of sight between the anode and cathode.



After a full 12 hours I removed the brake caliper and gave it a final wire brush in some clean water to remove the last of the remaining dirt. By all accounts I was very pleased with the results, and have proceeded to process every part that will fit in the bucket! Here is the before and after picture of a pair of particularly badly corroded brake calipers.



The interesting thing is that any component I have had blast cleaned in the past is usually starting to rust as soon as it is removed from the blast cabinet and the humidity in the atmosphere gets near it, however the components do not seem to start rusting after the electrolysis process.


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ecogeorge
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« Reply #1 on: April 22, 2012, 12:44:00 AM »

Ok , who can remember chemistry ?  Washing soda is Na2CO3 , -----  + Feo2 (rust) + electric -what do we get ?
O level chemistry a long time ago!
rgds George.
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ecogeorge
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« Reply #2 on: April 22, 2012, 12:54:42 AM »

Even wrong on that !  facepalm

Rust is Fe2O3.nH2O +Na2CO3 = what ? Fe2CO4 + CO2 Huh?? who knows?
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desperate
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« Reply #3 on: April 22, 2012, 01:01:12 AM »

Or what about Hydrogen ions liberated at the Cathode reduces the Oxygen of the Fe2O3 to water

Fe2O3 + 3H2 = 2Fe + 3H2O

And the washing soda just acts as an electrolyte but doesn't contribute to the chemistry?

Desp
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camillitech
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« Reply #4 on: April 22, 2012, 07:42:57 AM »

Nice one Danny,

I've read about it but never seen a real world result. Me I have a great big tub of phosphoric acid that seems to do the trick but that didn't cost me anything either  whistlie

Cheers, Paul
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johnrae
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« Reply #5 on: April 22, 2012, 09:21:02 AM »

The electrolysis route wins on the basis that only the rust is removed so once the metal is 'clean" the reaction stops so dimensions are maintained.  Using phosphoric acid actual increases component dimension since the rust is converted to iron phosphate (the black stuff).  I've used this method on very large items (a whole pillar drill for example) with excellent results.  The bigger the item, the longer it takes.
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camillitech
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« Reply #6 on: April 22, 2012, 10:27:44 AM »

The electrolysis route wins on the basis that only the rust is removed so once the metal is 'clean" the reaction stops so dimensions are maintained.  Using phosphoric acid actual increases component dimension since the rust is converted to iron phosphate (the black stuff).  I've used this method on very large items (a whole pillar drill for example) with excellent results.  The bigger the item, the longer it takes.

Interesting JR, I generally use the acid prior to having things galvanized so they're not really dimensionally critical items anyway.

Cheers, Paul
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julian
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« Reply #7 on: April 22, 2012, 11:35:18 AM »

Another quick and dirty option (with the same issues as the phosphoric acid) is to boil in acetic acid.

(which can be purchased at asda for about 16p/ltr in the form of value vinegar!)

Just make sure noone is in the house whilst youre doing it - boiling vinegar creates a bit of a pong.



Im pleased you posted on the electrolysis though - i will give that a go in the future.  A little more involved than boiling in acid, but better for some jobs (and large items!)
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camillitech
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« Reply #8 on: April 22, 2012, 11:56:53 AM »

Another quick and dirty option (with the same issues as the phosphoric acid) is to boil in acetic acid.

(which can be purchased at asda for about 16p/ltr in the form of value vinegar!)

Just make sure noone is in the house whilst youre doing it - boiling vinegar creates a bit of a pong.



Im pleased you posted on the electrolysis though - i will give that a go in the future.  A little more involved than boiling in acid, but better for some jobs (and large items!)

One other thing that vinegar is very useful for is removing verdigris and you don't need to boil it.

Cheers, Paul
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kev
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« Reply #9 on: April 23, 2012, 02:05:28 PM »

I have used the electrolysis method many times, I just use a battery charger and a couple of equally spaced out lumps of scrap metal for the cathode,
Just make absolutely sure you have the negative to your workpiece (part to be cleaned)
Kev
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garethpuk
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« Reply #10 on: April 25, 2012, 10:41:59 PM »

Another thumbs up here for the electrolytic method, I've always found fresh solution for each new bit to be cleaned works best. I could currently do with a tank big enough to get a whole VW camper into  Grin
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Philip R
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« Reply #11 on: April 28, 2012, 01:44:47 AM »

Will the liberated hydrogen contribute to hydrogen embrittlement of the objects being cleaned. Or is this only an issue during welding of high temperature processing?
PhilipR
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Ivan
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« Reply #12 on: May 05, 2012, 10:35:00 PM »

I've tried electrolysis and have mixed feelings. Not to restore  rusty tools, but old artefacts - probably a bit more rust. What I've found is that the iron oxide is restored to iron again, but it is no longer attached to the un-rusted iron, so it's more of a surface deposit rather than solid metal. Also, I've found that the porous nature of the restored iron was very susceptible to re-rusting, presumably because of it's larger surface area.
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Baz
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« Reply #13 on: May 20, 2012, 10:41:41 PM »

My experiments in the past with this have never been as good as 'mechanical' restoration. Perhaps I did it wrong.
As today I was cleaning rusty gutters perhaps I could rig something so it cleans itself when it rains Smiley
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danny stardust
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« Reply #14 on: May 24, 2012, 10:56:48 AM »

That is me well into double figures of de-rusted brake calipers now. I have the process nailed now. Battery charger putting 3amps into the battery and keeping the electrolyte reasonably clean seems to be the way for best results.

This could be a useful application for dump loads.  Roll Eyes

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