electrolytic rust removal again (black stuff)

[Henrik]

So as per previous thread (http://www.mig-welding.co.uk/forum/threads/electrolytic-rust-removal-setup.49935), I've been playing around with electrolytic rust removal for a while, and it's great at restoring metal.

However, I'm having problems getting the "black stuff" off that forms on top of the metal being cleaned. Basically, this seems to be some thick tar like substance (pain to get off hands etc), and I'm currently resorting to soapy water and a wire brush, but I keep pricking my delicate little hands

Does anyone know what this gunk is, and what might shift it easier? It might be because I'm leaving my stuff in the tank for too long, I suppose (I only really get time to go out to the shed very occasionally, so sometimes the metal sits in the tank for up to a week being derusted).

I'm using normal soda crystals (not loads, it has to be said. About 50ml of crystals for 15 litres of water), and I've just started a new batch but also poured some fairy liquid into the solution to see if that'll make any difference to the stickyness.

I don't hold much hope for the fairy experiment, so has anyone got any other tips? I'm half tempted trying some of the following after running through the electrolysis bath:

* rust removal gels (e.g. the hammerite)
* Vinegar
* Some weak acid (Can you get hydrochloric acid from the paint shop still?)

Any other "bright" ideas to bring my steel up to a good shine again?

 

[Henrik]

Mr Muscle oven cleaner?

 

[mike 109444]

Don't use washing up liquid as it contains LOTS of salt!! (why you should not use it in your screen wash = rusty area around wiper arm mounts) The black stuff is better washed off as you go along rather than leaving it to build up. You can get hydrochloric acid as "brick acid" (<£10 if I recall) from toolstation. but it may cause you more problems as any thing not submerged in the bath will corrode like crazy from the mixture of fumes from acid and air

 

[MattF]

How you're doing it already is pretty much the best method. With the wire brush though, go with a fine bristle brass else stainless brush. It'll be a lot easier on your fingers, and they work just as well as a coarse brush. Depending on what you're doing with the piece, you don't need to be anal in cleaning that stuff off. It's bonded well enough to the surface to be of no detriment if you're painting it or suchlike, once you've got the really loose stuff off.

 

[Henrik]

Mike, oops, shame about the salt! Luckily I've only got a little handwheel in there at the moment.

MattF, hmm, good call on the brass brush! Might also get some wire wool and give that a try, and i suppose you're right about the black stuff being bonded on enough, seeing as it's so hard to get off in the first place

 

[fizzy]

Apparently most household washing up liquids contain about 0.8% NaCl. So basically by the time you mix it with water to wash your car or bit of metal the salt content is very tiny indeed - some houses have water softeners fitted - I would worry far more about that!

 

[PSweeney]

try jet washing it off

 

[julianf]

Ive read of people using NaOH as the electrolyte (sodium hydroxide / caustic soda)

Im wondering if changing to a more hostile electrolyte would change the black stuff?

 

[JohnH]

The black stuff is good. It shows that its working. Just wash it off with running water and a nylon brush.

 

[wristpin]

Hot water and a scrubbing brush is usually good enough.
Note th comment re water softeners - they don't add salt to the supply but use it in the ion exchange process that removes the calcium from the medim that extracts it from the supply - regeneration .

 

[MattF]

Ive read of people using NaOH as the electrolyte (sodium hydroxide / caustic soda)

Im wondering if changing to a more hostile electrolyte would change the black stuff?

Doesn't make a jot of difference. It's still there and just as tenacious. I currently have caustic in mine.

 

[julianf]

Ive got to get around to doing this myself.

I have -

caustic
stainless chip pan 'sieve' thing
bucket
scrap iron

but its the psu that i cant find at the moment.

 

[mike 109444]

Ive got to get around to doing this myself.

I have -

caustic
stainless chip pan 'sieve' thing
bucket
scrap iron

but its the psu that i cant find at the moment.

Old Car batter charger ?

 

[bigegg]

Ive got to get around to doing this myself.

I have -

caustic
stainless chip pan 'sieve' thing
bucket
scrap iron

but its the psu that i cant find at the moment.

mobile phone wall wart?

 

[Henrik]

Just to give an update on this, I've figured out why my black stuff was so hard to get off...

Basically, I think I've been using too weak a mixture. Last week I de-rusted a lathe bed, and I went a bit overboard with the soda crystals, and the black sludge literally wipes off.