Electrolytic cleaning/stripping

[Sean Williams]

Hi all,

Just a small tip really - for those of you that come across really grotty things that need cleaning!

I have a quantity of really tarnished, and damaged Plessey military connectors - I use these in various projects relating to amateur radio.

Having used my stock of clean and shiny brass connectors I was left with some "unusable ones".

Anyway, they arent easily dismantled for cleaning without the correct tools, so I set about a way of cleaning them.

I ruled out the use of acids, as I did not want to strip the silver plate off the pins of the connectors - likewise mechanical removal of tarnish and damaged plating would leave a ruined connector.

A while back one of our fourm members pointed me to a site that dealt with derusting chassis by electrolysys - this looked reasonable for my application as well.

So, the basics - what you need:

Plastic container (large enough to hold the items and allow a covering of fluid)

A source of DC current 10-30v @ 2amps

A suitable electrode for the positive side of the supply (I used a brass block, but stainless is better)

Connecting wire

Salt

Water


Method......


Attach a wire to the item you wish to strip (or clean), suspend the item in the plastic container (it must dangle in free space) Connect this to the NEGATIVE terminal of the supply.

Attach your other electrode to the wire and POSITVE side of the supply, then drop the electrode into the container.

Make up a solution of salty water (adjust to taste ) the stronger the solution, the higher the initial current flow....

Fill your container so that all of the item to be processed is covered.

Switch on supply and note current flow (you should see some bubbling around the item you wish to clean - if not then the supply is connected incorrectly!)

For heavy cleaning/ stripping then the full 2 amps will do the job, for a light clean then keep the current low, and inspect frequently.


Final Cleaning

if you have gone for the real heavy clean then brass will come out a little discoloured - just give it a good scrub with a brillo pad to remove this.

You will end up with a tub of fairly grotty mess - this is mainly a mixture of copper sulphate, and in my case Nickel sulphate - these can be disposed of by diluting with plenty of water.

Have Fun!

Cheers
Sean

[GMB]

I would just like to add that using salt (sodium chloride) is perhaps not a good idea for a number of reasons. Some other salt (in the chemical sense of the word) would be better although I'm not sure what to suggest that is easily available. Washing soda might be better although it will attack aluminium and zinc.

The reasons to avoid common salt are:
a) Chloride ions play a powerful role in the rusting process. Having got your nice result they lurk until the humidity gets high and then the rust may break out again much worse.
b) Any remaining sodium chloride will attract water and thus provide the wet conditions necessary to start up the rusting again.
c) You may discharge chlorine gas at your other electrode.

Also, be aware that your other electrode dissolves during this process and it will then start to plate out on the object being cleaned. A carbon rod might be a better electrode, e.g. from an old-style U2.

If you have used salt then I suggest that you boil the object in pure water, or if it won't stand the boiling then soak in cooled boiled pure water, to help remove as much of the salt from micro cracks in the surface.

[Sean Williams]

I would think the very dilute nature of the salt solution we are talking about here would not be an issue - around 5g in 1000ml.

To be completely honest, the salt is only there to make the water conduct electricity a little better.

The other electrode does dissolve to a point (hence the comment regarding stainless), however, I wouldnt think it will migrate to the other electrode, as it is repelling.

Chlorine, yes, possibly, more likeley Hydrogen - but at the size of operation we are using here, the quantities are negligible.

You do have to rinse the object thoroughly after the process is carried out, as there will be some residual crud floating around (see the brillo pad comment)

Cheers
Sean

[Mike Phelan]

If you were concerned about the salt, sodium carbonate (washing soda) or a weak acid like lemon juice or vinegar is good; the two latter will also brighten brass after electrolysis as well.
To really brighten brass, clock cleaner (detergent + ammonia + oleic acid) does an excellent job.