Electrolytic Rust Removal

As described in this post, electrolysis was used to clean many of the donor parts. A lot of websites described this method as being magical in how rust just falls off. While in my experience it definitely made things a lot easier, there was still a lot of work involved. The biggest benefit was that rust could be removed with a normal kitchen scourer, or a bronze-bristled wire brush. This meant that I was not concerned about removal of good metal.

Diagram of rust-removal setup

What you need:

  • Electrolysis tank
  • Power source (e.g. 6-12V battery charger)
  • Chemical to make solution basic (more on this)
  • Method of suspending article

Some notes upfront:

a) Once you have removed the item and scrubbed off the scale, it will rust EXTREMELY quickly. So you’ll either have to paint it immediately or coat it with a light oil. I used Q20 on everything, as it washes off again fairly easily, and seems to have good covered.

b) Polarity is VITAL. If you get it right, you can leave your delicate bearing surfaces in this corrosive mixture for days with complete confidence that it’s actually safer than being in the air. Get it wrong and in minutes those surfaces will be pitted and destroyed. Don’t cut corners with the wrong colours for wires or clamps, which may cause confusion – you have been warned.

c) The method produces hydrogen and oxygen gas, in the same place. I’m pretty sure that it dissipates long before it can build up to dangerous levels, but I suggest you do this in a well ventilated room.

d) The only things that must go in your tank are non-conductives that don’t dissolve such as plastic and wood, and iron. Ensure no other metals go in the tank (i.e. remove any galvanising, and the clamps connecting the object to the power source must be made of iron only). Do not use stainless steel anywhere – it produces some nasty chemicals.

Solution Chemical

  • What is it?

Many internet articles describe the use of “washing soda”. This is NOT washing powder, it is sodium carbonate or soda ash. I honestly don’t know if you can get it in South Africa. I used caustic soda, described in many articles as “lye“. This is easy to find, and is often used to unblock drains. The downside of this stuff is that it is very aggressive (in case you missed it, it unblocks drains!).

  • The dangers?

The solution does not need to be strong, but you will be dealing with raw crystals of the stuff which will eat through clothes and flesh. It also gets hot when it dissolves in water – VERY hot. If you put a large amount (e.g. a tablespoon full) in a little bit of water (e.g. a glass of water) it could boil the water, quickly, spraying you and everything around you in a boiling, caustic mixture. Don’t do this, and keep little Johnny away while working with this stuff.

Another thing about cautic soda – it is a dessicant. If you leave the lid off your container, it will pull water out of the air until it all liquifies. Make sure you put the lid back on tightly, and keep the stuff somewhere safe.

  • Making up the solution

Start with your electrolysis tank, full of water. Position it where it’s finally staying, since it will be heavy when it is full. My tank was about 45l, and I used about 6 tablespoons of caustic soda. Add the caustic soda, bit by bit, to the full tank of water. DO NOT “pre-dissolve” it in a small cup of water (see dangers above) – you are not making soup, it won’t come out lumpy. You don’t need to stir, it will dissolve fairly quickly.

It’s important to note that the quality of the result does not improve, or go quicker, with a stronger solution.

The Tank and the Anode

Anode made from steel flat bar

My tank was a 45l plastic container. This was big enough for all the parts I did, and I was able to double up many parts. My anode was welded (see, it’s not a kit car, I did some welding) from super-rubbish Builder’s warehouse flat plate. The idea was to “wrap” around the object, providing maximum line of sight between the anode and the object. You can get fancier, for example using braai-grid or steel plate. However, as noted up front, any coatings should be removed first. I used a grinder to expose the surface of the raw iron. Don’t use anything you hope to keep – the anode gets quite abused by the process.

Tank with anode

Power Supply

Battery charger used as power supply

I used a normal battery charger, but it had the ability to charge at either 6V or 12V. I tried to use 6V as much as possible, but in some cases nothing seemed to be happening, so I popped it up to 12V. In retrospect it may be that not seeing anything happening is when it is really working well.

If you do have a variable-voltage power supply (or better, a current limiting power supply) then use that and try to dial in approximately 250mA. Apparently at this level the reaction occurs without breaking down water (forming bubbles) and is likely to produce the best finish in the final article.

Connecting to your object

This is where you have to get quite creative. I had normal crocodile clips coming from my power supply. However, these could not be submerged in the electrolyte without causing issues. So I needed some way to connect to the object that only involved iron. My solution was a couple of old 9″ iron nails. I used a file to remove all sign of galvanising, and the cable-ties (plastic can go in the solution) to firmly attach them to a hole on the object. I found that by putting a small bend near the top of the nails, I could thread two nails through most holes and have them scissor into place. A cable tie held them together, and some nylon string through somewhere else supported the contraption. The whole thing hung from a piece of planking across the top of the tank. The nails then extended above the surface of the electrolyte, and the clip was attached to this.

Make sure your object is completely submerged. I have read that you can do objects in two parts, but I would be concerned about a “tide mark” at the overlap point, and while the second half is being done, the first half will be rusting again. Also you will see what happens to the nails at the interface with the electrolyte. I wouldn’t want that on a surface that is meant to take a bearing.

Uprights ready to go

Preparation of the Object

The most important thing is cleaning all the grease and oil off the object. I did find that the process loosened paint, so I suspect that grease spots that you miss will be dealt with. However, I did not experiment with this much – I cleaned all the parts quite thoroughly with paraffin and then degreaser.

Running the electrolysis

Most items were submerged for 48 hours. I got lazy towards the end, and the front hubs were run for at least 3 days. I think these came out the best, the rust just fell off them and the surface was quite shiny – so perhaps there’s a lesson there. One thing to be careful of is power failures. With trusty Eskom in charge of this bit, you might struggle to get three days of solid power. I had a power cut for several hours during one of my runs, but the part did not seem adversely affected.

As the power is applied, you will slowly see a fine mist of bubbles rising off the part. You will also see the anode (the iron bit connected to the positive) getting very rusty and nasty. By the end of my cleaning the anode looked horrible.

The surface of the electrolyte also gets pretty mucky – a dirty brown scum seems to form. This goes against what my reference says, and implies that I’m using too high a voltage. Unfortunately I was limited in what I had available as a power supply, and the system seemed to work.

Results
Here is a photo of one of the front uprights, after electrolysis and scrubbing. The gold colour is the rust already starting to form. Given that this level of rust removal was achieved with no sandpaper or heavy abrasives, I would say the electrolysis method works well.

Front upright after electrolysis (rust already forming)

References:
http://myweb.tiscali.co.uk/andyspatch/rust.htm

Comments, feedback and suggestions welcome – I’ll update my page appropriately.

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