electrolysis for rust removal- carbon plates

The venerable shopdogsam

from the east coast of Arkansas recommends graphite plates which do appear to be much cleaner. Where can they be obtained in the UK ?.

Edited By capnahab on 11/03/2014 10:59:37

No idea about graphite plates, I imagine they will be expensive. I use stainless steel, a strip cut of an old sink drainer. This can be bent to suit the size of the job, the closer the better. There seems to be some worry about heavy metals but I can't see any great problems, there's probably more in road dust.

Cheers Gordon, good tip about the sink. Does the electrolyte stay clean(ish).

I use a bit of bent welding rod inside a plastic tube with holes cut in it (to prevent shorts), but the biggest thing I've de-rusted is only about 6 ounces.

Neil

Graphite plates never seen anything like them in the UK, I use some old lead flashing to line a bucket and have the item/s hanging from a bit of timber

Electrolyte soon gets dirty, depending on the amount of rust to start with, but settles clear if left overnight after switching off. The liquid can be poured off and reused, add water if needs be. I've just taken out a largish bit, about 7" x 5", after 2 days it's pretty good considering it was encrusted solid ( it is a wire fence tensioner grab ) A quick wash in water and dumped in some diesel should be working tomorrow. There is no sign of any thinning on the s/s.

The process involves (if you get it right) the rusty object being connected to the negative supply - this is the cathode. What happens is that there is hydrogen evolved on its surface, and a smaller amount of oxygen at the other electrode (the anode). Along with the hydrogen is a process of reduction (turning ferric compounds into ferrous, for example) - this turns the red rust black, and it is loosened.(Fe2O3 becomes Fe3O4). I wish this system could do subscript-letters! This is the same black powder you get in the bottom of your central heating radiators, incidentally.

At the anode, there tends to be an oxidation reaction, so in ideal conditions metal might be dissolved. But the solution (the electrolyte) is sodium carbonate, (so if any metal is attacked it might become a carbonate) - except that the process is very fussy - difficult to get to work well - even with more suitable compounds rather than washing soda. That is why nickel and chrome plating are so expensive. Most metals and most solutions (including Na2CO3 - sodium carbonate) just won't play the game.

So, an anode which cannot be attacked is ideal (but not vital) - and carbon would meet this need, if you can find it in big enough sheets. Also good are stainless steel and lead sheet, and lots of other metals. You are, after all, concerned with the object, and you will rinse it off before working on it. You are not going to immerse yourself in the liquid or drink it, so there is little chance of poisoning yourself.

Hope this helps - Tim

Graphite could be had from a spark erosion company, they use it for sparking out steel moulds for injection moulding machines etc, they may have odd bits laying around!
If they don't have any to spare they could point you in the direction of a supplier, I do know one such company, will ask about sources atc next time I'm over there, but may not be for a couple of weeks yet!

If using stainless as an electrode in your electrolytic tank, keep shtum about it, the process 'could' in certain circumstances leave hex-chrome in the fluid, which is illegal to tip down drains and 'could' lead to a serious 'Whigging' by elf & safety if caught! (Please don't shoot me, I'm only the messenger, if you don't believe me, google it!

e.g: **LINK**

**LINK**
(This link includes methods for neutralising said hex-chrome)

John.

I work for a graphite machining company. I could enquire about supplying smaller quantities if you give me an idea of the size of plates you have in mind.

I could also ask about the most suitable grade to use for this application - talking about "graphite" is like like talking about "steel " or "alloy" - there are many different grades with different properties for different applications. We have had some that was so soft & friable that it could be "machined" with a teaspoon & measuring it was a problem - other grades are so hard they can only be machined with diamond tooling.

If you would like me to enquire further, post the sizes you want on this thread & I'll ask.

Nigel B.

@ Tim - and sorry to the OP, not rying to hijack your post

Probably a really dumb question, but if the attack on the anode metal isn't that severe, why don't people use a tin drum as the container and this doubles as the anode - genuine question, not trying to be a smart ass

Cheers,

Paul

Paul, that will be OK until one day all the electrolyte falls out through the holes eaten in the tin drum, unless you keep the drum in a plastic bucket.

I use a block of lead as my electrode, I think its about 6" x 4" x 1/2" (I'v got plenty of lead), every now and then I attack it with a chipping hammer when the scale builds up. I used to use a bit of steel bar, but it got eaten away fairly quickly.

When making parts for vintage machinery for our museum, it is some times worth while reversing the leads, and ageing the part, done carefully, you can't tell the new from the old. Ian S C

Use of metal container, for a one off job, is Ok but you must remember to insulate the part or suspend by insulator. I use an ex supermarket plastic tray with lots of holes in it.

Graphite anode - how about the positive rod from an old zinc/carbon battery?

Russell.

One thing not mentioned is that when the rust Fe2O3, which is much bulkier than the parent metal, becomes Fe3O2 (Magnetite) it has a similar volume to the metal lost (unlike rust it is not friable and does not contain a huge amount of water) and does not all detach. This means that you often end up with hard black stains that resemble a phosphated surface of similar dimensions and surface finish top the pre-rusted item, particlularly when the rust is only superficial.

In this way electrolysis can, to an extent, repair some of the damage caused by rust.

The example below is a 'Seal' crankshaft I was given, which was rusty enough to appear to be a scrapper when I got it..

Neil

Paul asks 'What about a tin drum as anode?' - my response is:

No problem with the theory, really, but in practice I think people with this sort of kit tend to leave it between uses with the electrolyte in the container. Tin (or tin-plated thin sheet steel for clarity) only has a very thin layer on tin, and my guess is that the steel would rust away. And use would only make this worse, as the anode is oxidising - ie promoting rust.

I'm not sure how good any adhesion of the Fe3O4 is, in engineering terms. So, I would be inclined to clean as much as I could off any bearing surfaces, etc. Another factor is that there is a risk of embrittlement* of any high-tensile steel, so an hour or two in a domestic oven should help. Especially for a wide two-bearing crank ...

* this is because hydrogen tends to creep between the crystals of the steel, and this can continue if a tensile load is applied. Plated HT bolts will snap off when tightened or a few minutes later, if de-embrittlement is not done properly.

Cheers, Tim

The carbon from an old telephone battery would be ideal, if you can find one, they are about 5" long, and a bit over 1/2" diameter, with a Fahnstock clip on the top end. these batteries were for real telephones, they had two batteries about 6 1/2" high by 2 1/2" diameter, Eveready no., 6, they weigh 2lb 2oz each (that's the battery, not the telephone, it was screwed to the wall). Ian S C

Thanks guys, very informative. I have a couple of 25l drums made of thin steel/tin that the solvent for the parts washer came in. Plan now is to cut off top and bottom and drop into a plastic drum as the anode. Means the anode will suround the items to be cleaned.

Cheers.

Paul.

I use a 20L plastic paint pot for my container. Ian S C

Just FYI you can get high quality graphite blocks from any EDM workshop or from a mouldmaker who uses EDM. They often have bins full of large chunks of worn out graphite electrodes. Usually these chunks can be bought very cheaply and sometimes they are free for the asking in shops local to me. Some are quite large, being used for automotive part moulds.

EDM shops often also have quantities of worn copper electrodes which can sometimes be bought reasonably depending on copper scrap prices.

Good luck, JD