Cathodic cleaning.

[T i m]

Hi all,

As a spinoff of my recent 'Drake drum skimming' trailer restoration thread I'm currently (ouch) giving this 'electrolytic de-rusting' or 'cathodic cleaning' of the brake drums a go (thanks to Peter Parry for the heads up).

can be a 'before' shot of the frictionable surface.

I've got one of those large grey tough-plastic workshop storage tray / bins filled with ~7 gallons of warm water with a mug of washing soda thrown in (should work out to about 1 teaspoonful / pint).

I wired a bit of coat hanger under one of the wheel studs, held in place by a wheel nut put on backwards. The two drums sat in the solution ok with the coat hanger connectors sticking out and touching.

For the anode I initially used a 1m length of 1/2" diameter metal bar I had kicking around laid in the box.

I hooked it up to my 12V / 4A bench PSU and instantly noticed a cloud of bubbles from the outside of the drums nearest the anode. It was drawing about 3A.

I then added another anode into the opposite side and joined the two with a short jump lead and whilst I saw bubble off the drums on that side it was reduced because the PSU was current limiting and the voltage had dropped to about 10V.

I then dug out a spare PC PSU (as per the suggestion in the link), cut all the 12V (Yellow) and similar number of earths (black) and the On wire (green) and earth and stripped and twisted them up in the right groups. Joined the Yellow to my anodes and the black to my drums and shorted the green to the black and away it went (11.8V on my DMMM).

However it seems that (for now anyway) it's mainly reacting with the outside of the drums nearest the anodes and I'm now thinking of creating two rings of iron, sat inside the actual drum and isolated from it with some suitable spacers (some garden hose segments or similar) to try to focus the reaction more on the actual area in question?

Am I on the right track or will it do all over in time in any case?

Cheers, T i m

p.s. And this isn't going to affect the non rusty metal is it? ie, I'm not going to erode anything off my bearing mount surfaces?

[Ian Jackson]

In message , T i m writes

If it might erode the bearing surfaces, could this be minimised by greasing them surfaces well? Or would the alkaline solution tend to remove the grease?

[Thomas Prufer]

Yup, "nearest the anodes" does that, as the current takes the paths of least (or at least lesser) resistance.

I have used aluminum foil to shape and electrode. This will dissolve eventually, leaving a black mess, though, but it's convenient.

Nope, not unless you have misconnected the wires. It reacts away the rust, turning it back to iron. Flaky rust bits turn back to smaller flaky iron bits, not the original surface, though. The iron surface will be microscopically rough and will rust again very quickly, so give it a wipe with an oily rag once you've washed the soda water off.

Thomas Prufer

[T i m]

Good thought and I think you might be right as when I just pulled one of the drums out to check it's progress (it's doing well ) the greasy surfaces seemed to still be greasy.

From what Thomas mentions later is that it should be ok unprotected though (as long as you wire it up right). ;-)

Cheers, T i m

[Fredxx]

The article implies that a thin layer of porous iron is built up. That might not be strong enough to withstand roller bearings without collapsing. I think I would stick with the grease!

[T i m]

Understood.

OK, so it is a valid thought then.

Oh Daaaad. ;-(

Being that it's not an acid concoction as such I've just had a quick peek and it looks like it's already processed the rust all around the outside of the drum across half the width. ;-)

Isn't chemistry clever. It's a bit like a Thermos flask. They keep hot things hot and cold things cold but how do they know what to do?

When I just lifted it out I think it was also stripping the paint that was still present on the face that touches the back of the wheel.

Understood. I'll probably give the outsides a blow over with some red oxide primer and the inside a wipe with an oily rag.

Thinking ahead now I'm considering making a better tank (with a lid / vent holes) so nothing gets in there if it's left outside and keeps the rain out etc. Then I can similarly process the bigger bits like the suspension arms (keeping the actual rubber parts out of it) and brake back plates etc.

I'm thinking a central heating header tank maybe? Waterbut drain near a bottom corner and an upturned square bucket stuck on the end to hold the PC PSU out of the elements? ;-)

Cheers, T i m

[Fredxx]

LOL - I think ventilation is rather important. The lid might become detached rather violently!!

[NT]

Do NOT apply any oil to the inside surface, or your brake shoes will be ruined, and your travel more dangerous. I doubt there's any point applying anything where the brake shoes meet, as all films will be promptly stripped off, or in the case of oil or grease make the brakes fail. If there's spongy iron on there, the first drive should strip it off.

An electrode above or inside would prioritise interior cleaning.

NT

[Mark Bluemel]

"What have you got in it?"

"Two cups of coffee and a Choc ice"

[The Natural Philosopher]

+1

[T i m]

Quite and hence why I was continuing the 'this needs to stay outside' theme. ;-)

As I have quite a few PC PSU's kicking about and soda being cheap I'm thinking I can easily have a couple of these things on the go at once if I have a particular project in hand.

I was even thinking of having a 'bus bar' along the top of my tank where I could make up some coat hanger hangers to support the smaller bits whilst giving them an electric connection?

Even the 'kids' (21/20) are fascinated watching it all bubbling away. ;-)

Cheers, T i m

[Nightjar]

On 13/07/2011 12:14, T i m wrote: ...

That is the shadow effect. Any bits in an electrical shadow, as seen from the electrodes, will be done slowly, if at all.

It is the way I would go about it.

Colin Bignell

[Thomas Prufer]

The hydrogen bubbles it off, as it were.

Yup. I wouldn't worry about ruining brake shoes -- I said wipe it with oily rag, not "oil" it or "apply coat of grease".

Naah. The solution turns pretty foul quickly, and it's not as if there's any money tied up in it. I wouldn't drain it into the grouang, as it'll be a witches' brew of oil, paint, rust, dissolved aluminum, and dirt. And venting the hydrogen is a good idea, too.

Thomas Prufer

[T i m]

Even if wiped off beforehand with panel wipe, brake cleaner or acetone (they are my usual solvents for such tasks).

I think we were talking about more when the drum was in store / off the actual trailer as such but your points are welcomed and noted.

I've, just made up one from a opened out coat hanger and spaced off the drum with 4 rings of 15mm foam pipe insulation plus cable ties and held submerged with some strips of wood. It does seem to be more chemically active in the drum with the added ring. ;-)

I'm guessing all these extra electrodes all add to the general current load?

Cheers, T i m

p.s. I just spoke to our local Jewsons and a 6m length of 12mm Rebar is about 12 quid. You could make quite a few anodes with that. ;-)

[T i m]

Cheers, T i m

[T i m]

I know. Did you know many new iron brake discs come covered in a layer or oil / grease?

Ok, what I was thinking is that once this electro cleaning is finished is washing the stuff off with plenty of water, seeing if the wire brush / electric drill would improve it further and see if I can at least get down to some consistency on the frictional part (possibly some coarse wet n dry etc). Once done the best I can I would wipe it all over with some panel wipe and once warmed in the sun, give it all a blow over with some primer to stop it rusting again. I would try to avoid the frictional area but wouldn't be too bothered if any paint went on there. I would then refit it all to the suspension unit /if/ I had all the other stuff ready. If I didn't then I might be inclined to wipe the inside of the drum over with a bit of oil or WD40 knowing I would ensure it was all washed off before refitting it.

True.

So how should I dispose of it out of interest?

I know. ;-)

Cheers, T i m

[T i m]

Ok (logical name for it).

Is the 'fizzing' an indication of the process in action so if it stops it's either complete or the solution is exhausted?

Ok and again makes sense if you consider how it works etc. I've got a couple of turns of wire coat hanger in one drum as well now but as it doesn't really matter about the outside of the drums (other than for aesthetic reasons) I think I'll look to put something 'chunkier' in there (larger surface area = greater effect?)

Cheers, T i m

[Fredxx]

Don't forget any insulator will effectively cast a shadow on the drum.

[Andy Dingley]

I've never heard of "cathodic cleaning". There are two processes used here: one is a cathodic workpiece and used for de-rusting, not cleaning. The other is an anode workpiece and is used for electro- polishing and anodic cleaning.

The big difference is that a cathode workpiece is self-limiting and can be left unwatched. OTOH, an anodic brightening (a fine process) needs very careful control and continuous monitoring, otherwise it will not only damage the surface, it will eat great big holes through.

So when making your cathodic de-rusting rig, make sure the croc clips are obvious. My rig uses pluggable cables to a front panel (cables have a short service life), but the panel is clearly labelled and the plugs & sockets are two different types to avoid mis-pluggings.

[fred]

In article , T i m writes

Primer is porous so this might do better in the long term (heat resistant spray paint, no primer reqd):