Electrolytic Rust Removal

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If you're looking for a effective, relatively safe, and (best of all) cheap method for removing rust give electrolytic rust removal a try. I know that it sounds intimidating but it is actually very simple and won't damage the underlying material. This method basically consists of submerging the rusty metal in an electrically conducting solution of washing soda (also known as sodium carbonate). I've been told that baking soda (sodium bicarbonate) also works but I have no personal knowledge of this. The positive lead from an automotive battery charger is connected to a steel electrode and the negative lead is connected to the piece to be cleaned. When the charger is turned on a reaction occurs at the metal/rust interface on the object. this loosens the rust so it may be easily brushed off. This method does not appear to damage the underlying metal in any way, it seems to only remove the rust. Of course it will not improve the finish of the metal under the rust so any pitting on the metal will remain, just the rust will be removed from it. The cleaning solution should last almost indefinitely, only add water to replace that lost by electrolysis and evaporation.

Important Safety Precautions

  • The cleaning solution is alkaline and will irritate the skin and your eyes. Always use eye protection and rubber gloves when working with the solution and rinse off any spills.
  • The battery charger must be completely shielded from the cleaning solution. Make sure the battery charger is in a location where you won't accidentally spill any water or cleaning solution on it. The 6/12 volt leads from the charger are relatively safe but it is still possible to get a shock if you put your hands in the cleaning solution or touch the electrodes while the power is on. Turning off the power to the charger will eliminate that risk.
  • One of the side effects of the electrolysis is that the water will break down into its components, hydrogen and oxygen. For this reason you should work in a well ventilated area and avoid any sources of ignition, ie. cigarettes, or sparks from shorting out the battery leads.

What do you need to start?

  • water
  • washing soda (sodium carbonate)
  • a battery charger (with a current meter if possible) or a car battery
  • steel or iron electrode (I use rebar as it's cheap and the anode will eventually be eaten away)
  • a plastic tub (slightly larger than the part to be cleaned, although it is possible to clean a part with some of it sticking above the solution and then rotating it to clean the rest it may leave a small mark or discoloration which is undesirable)
wiring diagram for electrolytic rust removal

The Procedure

The first step in the process is to prepare the cleaning solution. dissolve roughly 1 tablespoon/gallon of washing soda in water. Ensure that all the crystals are dissolved.

Roughly clean the steel anode. It doesn't have to be perfect just good enough that you can get good electrical contact. Attach the positive lead (red) from the battery charger to the steel anode. Submerge the anode in the cleaning solution, ensure that the clamp from the battery lead isn't submerged. If it is it will be eaten away with this process. The steel electrode will also be eaten away but very slowly. If you are trying to clean a large piece you will likely need more than one anode as this process almost works "line of sight". In other words the anode and part to be cleaned shouldn't be hidden from each other, for example if you are cleaning a large piece and only have one anode the side facing the anode will clean better than the side facing away from the anode. You can use multiple anodes so that the piece to be cleaned is surrounded, just connect them together with wire.

Attach the negative lead from the battery charger to the piece to be cleaned. Submerge this piece, it doesn't matter if this clamp is submerged as it won't be eaten away. Ensure that this piece and the anode don't contact each other as this will cause a short circuit. They should be separated by several inches.

Turn on the battery charger. If the current is too high on the battery chargers current meter there are a number of things you can do to reduce it;

  • increase the distance between the part and the anode
  • dilute the solution by adding more water
  • if you have a 6/12 volt charger set it to the 6 volt setting

In the picture below you can see the plastic drum I use for cleaning large parts. The electrodes around the side are pieces of rebar connected with the black wire on the outside of the drum. If necessary I can have all the electrodes connected or only some of them. The piece that is in there has been connected for a few hours and you can see the rust colored scum now floating on the top of the solution. It's not visibel in this picture but the negative (black) lead from the battery charge is connected to the bar from which the part is hung.

rust removal in progress

Once it is set up and working you should see small bubbles of hydrogen and oxygen coming of the electrodes. Now you just have to wait. the time required to clean a part will depend on many variables:

  • size of the part
  • current used
  • how badly rusted the part is

If necessary it is acceptable to leave the operation on overnight so long as it is not in an enclosed space (see the safety precautions above). You may have to move the piece occasionally for better cleaning as the best cleaning is done on the part that is in direct view of the anode (line of sight). If a piece is too large to fit in the bath you will obviously have to rotate it at some point. It may also be necessary to take the part out of the bath and clean it with a wire brush to remove some of the now loose scale which will look like a dark sludge.

You can use a plastic scrub brush an water to remove the sludge, if it looks like you took the piece out too soon simply put it back in the cleaning solution. Once the piece is finished it will be a grey color. If it is an antique this may be an acceptable finish, otherwise use a wire brush to remove the grey oxide coating. Now you have to make sure the piece is dry so that it won't start rusting again and put some sort of rust inhibitor, wax, or oil coating.

Below are some pics of a test I did. As usual I forgot to take the before picture so the first picture is a different disc blade that was rusted the same as the ones that I had done. The second picture is what the disc looks like after being removed from the cleaning solution. The black stuff on it is quite loose and came off easily with a wire brush. The final picture is of the completed disc blade after wire brushing.

disc blade before cleaning disc blade just out of cleaning solution cleaned disc blade

NOTES

  • Sound plating should not be affected by this process but if it is loose for any reason it will likely flake off.
  • The cleaning solution may soften some paints.
  • Remove wooden parts/handles before cleaning if you plan to submerge the whole part.
  • The cleaning process relies on electrical contact for the cleaning. If you are cleaning a piece with more than one part (such as a pair of scissors) you must make sure that both parts have good electrical contact with the negative lead from the charger.
  • If you want to clean a piece that can't be submerged you can use a sponge soaked in the cleaning solution. Place it on the piece then an anode on top of it and make the electrical connections as before. You will have to rewet the sponge to ensure it doesn't dry out.
  • Use your imagination for the containers. You can use whatever will safely hold your parts, such as tupperware containers, plastic drums, vinyl eaves trough, wooden container lined with plastic, or whatever works for your piece.
  • This method may also help remove rusted screws or other fasteners.
  • While I have not concerned myself with it yet there is a chance that metal cleaned this way may be subject to hydrogen embrittlement. This can happen in many processes such as electroplating or welding. It should not be a problem unless you are cleaning hardened steel such as saw blades, knives, or chisels. If you are and you intend to use the item (rather than simply displaying it) you may want to try baking the part in an oven, I've heard of using temperatures from 300F to 440F (150C to 225C) for several hours. ASTM-B633 is a standard relating to zinc plating of parts and it specifies baking at 375F (190C) for 3 hours within 4 hours of plating. As I haven't done this myself I can't provide any more information on the process other than to say that you will have to watch the temperature to ensure that you don't affect the temper of the piece.



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