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How to: clean your rusty bits with electrolysis! (cheap and easy)

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TBJ
Posts: 4
Joined: Tue Dec 13, 2016 11:43 pm

How to: clean your rusty bits with electrolysis! (cheap and easy)

Postby TBJ » Mon May 01, 2017 9:31 pm

There was some interest for this when I posted about it on the Facebook group, so without further ado, here's the write-up as promised!

Electrolysis - what's that, then?

Simply put, electrolysis is a chemical reaction driven by electricity. Electrolysis isn't only used for rust removal - it's commonly used for splitting chemical solutions into their component elements (for instance, splitting water into hydrogen and oxygen), and for electroplating parts - i.e zinc or copper coating. However, the reaction we're looking at is very useful for removing rust from parts.

I don't want to get too deep into the chemistry of the process (and besides, Walter White I am not - if I had to choose, I'm more of a physics guy than chemistry), but essentially the electric charge is breaking down the bonds between the iron and oxygen on the rusty part, converting the iron oxide back to iron and loosening surface rust at the same time.

Dangers

This is a relatively safe process but there are still a few things you need to be aware of.

1) The process creates hydrogen gas - which is explosive - so put your electrolysis tank(s) outside!
2) Contrary to the above, electricity and water doesn't mix, so keep your power supply well away from water - I keep mine inside and run wires through the window to the tank.
3) If you use soda crystals as the electrolyte, it's relatively safe, but it's still an alkaline solution, so don't get it in your eyes and wash it off your skin if you do get any on you. Caustic soda, if you choose to use this instead, will burn you and will ruin your eyes, so be REALLY careful if you do this!
4) Don't use stainless steel anywhere in the tank (it forms hexavalent chromium which is quite bad for you - it's a carcinogen).
5) The process as described here only works on rusty mild steel parts - the alkaline electrolyte will damage aluminium and other alloys, so just be mindful of what you're putting in the tank.
6) While the process shouldn't harm stuff like rubber bushings, it will wash the grease out of bearings. If you put parts containing bearings in, I'd recommend to remove the bearings first, or at least repack them when you're done.


What you need

OK. To make this work, you need a few things, most of them are not that hard to come by.

1) A watertight container - one of those plastic storage boxes works quite nicely.

Image


2) An alkaline chemical to use as electrolyte. Soda crystals (NOT baking soda - you want sodium CARBONATE, not sodium bicarbonate) from the supermarket are what I use, you can also use caustic soda but it's highly corrosive so I wouldn't recommend it! You only need enough to make the solution electricially conductive, I use roughly a full 1kg bag for my big 85 litre container.

Image


3) Wire.

Image

Just bog-standard insulated copper wire will be fine. You should only be running about 2-3 amps or so unless you're using a very high voltage, so use whatever you have around. A bit of flex, speaker wire, whatever.


4) the hard bit: a low voltage DC power supply, around 12 volts, and capable of 2-3 amps. I use a proper regulated bench power supply because I'm an electronics nerd and I have one - this is useful because I can set the current limit to 2 amps and it will adjust its output voltage automatically to maintain the current at 2A.

Many people use a car battery charger (but if you're unlucky enough to have a modern 'smart' one, it might be too clever for its own good and not work), or you can even use a car battery (but if you do this, be VERY CAREFUL and put a 5 amp fuse inline because car batteries are capable of insane amounts of current and will set your wiring on fire if there is a short.)

Be careful - some cheap mains powered supplies don't have very good isolation; you definitely don't want a supply that puts mains voltage on either of the output terminals, especially when there's water around.


5) Sacrificial anode. This is a fancy way of saying "whatever random lump of mild steel you have laying around". Generally, the more surface area the better, so a bit of mild steel plate is best, but flat bar, box section, or most other things will work. Don't use stainless steel - see the warning above, galvanised is also bad as apparently it will try and zinc plate your workpiece, so just use mild.



Time to set it up

OK, let's get started. First, have a look at this (rather poor) diagram.

Image

Note that the negative goes to the part being cleaned.

I'll say it again. The negative goes to the part being cleaned. Don't get them the wrong way round.

Nothing dangerous will happen if you do, it'll just make the reaction run in reverse - in other words, the thing you're trying to derust will actually get rustier. So don't do that.


Step 1. Strip the insulation back and connect the positive lead to the sacrificial anode (the random bit of metal you found earlier). You can just clean up a bit of the metal using a flap wheel so it makes a good electrical connection, then tightly twist the wire around the piece so it makes a sound electrical and mechanical connection. You can get fancy and use bolts and crimp lugs if you want, but this is what I do, it takes 5 seconds and it works.

Image
Why waste that single-use tool you made to undo the cam pulleys on a ford focus?

One thing I need to mention here. If you have bare copper in the solution, it will eventually corrode away and the wire will fall off. This may take a few goes but it will eventually happen. I reterminate the connection to the sacrificial piece everytime I set the tank up for a part.

Image
This slightly more fancy anode is in my bigger tank and is a bit of 3mm plate suspended on a bit of copper brake line. The positive wire is then wrapped around the brake line. There are a million and one ways to make this work, use your imagination :D





Step 2 Connect the negative lead to the workpiece. This is the bit you want to derust. Again, flapwheel the bit you're going to connect back to clean, bright metal then wrap the wire around tightly, just to make sure you have a good connection. Don't worry about cleaning the rest of the surface of the part, the electrolysis blasts right through the surface rust, dirt and grease, you just want a sound electrical connection.

Here's an anti roll bar mounting bracket being connected up.

Image



Step 3 Make up the electrolyte solution. Fill the box with enough water to cover the part (plus a bit more) and then add the washing soda. As I said, a full bag in an 85 litre tank works well for me when it's about half full. I don't know exact quantities here, what I do is just watch the current on my power supply and keep adding the soda crystals until it reaches the 2 amps or so that I want, but this may not be an option for you, so just chuck a full bag in - it's not that critical, it's just there to make the solution conductive.

Now plonk both parts in the solution, making sure they're not touching. This solution is one I've used before so that's why it's a bit murky. You can use it again and again if you don't mind the ming.

Image

Check polarity one last time (negative to the workpiece, remember) then turn on the power. If you have an ammeter, you should see the current start at an amp or so, and slowly rise over the course of about half an hour to 2-3 amps. It should stabilise at around 2-3 amps and 12 volts. Exact current or voltage is unimportant.

If you don't have an ammeter, you can tell the process is working as the workpiece and the sacrificial anode will start to emit bubbles. Don't smoke - this is hydrogen and oxygen!

Image


Step 4 Leave it running (outside!) for 24 hours. When time is up, turn the power off, take your part out, and wash it off with a hose. You should end up with something like this (this was a hub knuckle which was previously very rusty).

Straight out of the tank:

Image

After washing:

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Final Steps

After the initial wash-off to remove the flaked-off rust and the electrolyte, you want to try and dry the part quite quickly. I stick it on top of a radiator for this. For a lot of very boring chemistry-based reasons, the fresh-out-of-the-tank part has a tendancy to flash rust so you do want to dry it as soon as possible.

Once dry, any rust still left on the part should fall off very easily. A quick wire-brushing by hand helps here - the rust is no longer adhered to the part so will come off super-easy with minimal work. I found that once electrolysis was complete in a lot of cases the factory paint was still in reasonable nick underneath, except for a few spots where it had flaked off. What I do here is give it a final degrease and rub down, then lay on a coat of black enamel - obviously you can go further and use paint stripper to get it back to bare metal if you want.




Connecting two tanks in series

One last trick. If you have a nice bench power supply capable of higher voltages, you can connect your electrolysis tanks in series to do more parts while using the same current. Obviously your overall power consumption is higher as the voltage will be higher, but if your supply is limited to 2 amps but will do up to 30 volts, like mine, this is a great way to get more bang for your buck. If you want to do this, connect the tanks like so:

Image



Hope this is useful to someone. It's not a complete alternative to powdercoating as it doesn't clean the parts back to bare metal but, in my opinion, is more than good enough for sprucing up suspension parts with a severe case of surface crust.


Cheers! :handgestures-thumbup:
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blackyb
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Re: How to: clean your rusty bits with electrolysis! (cheap and easy)

Postby blackyb » Mon May 01, 2017 10:38 pm

Good write up.

Took me back to my school days when we did this in chemistry .

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