Cast iron rust removal best method?

[olly_k]

Hi Folks, I have got a 1950's cast iron telephone that I would like to restore. I plan to start on the casing and work my way inwards, and hopefully end up with a clean working example!

I am wondering what best method I can use to clean the rust up though? I thought about chemical, sandblasting etc. but think perhaps the only thing that is going to remove the bubbles of rust is an angle grinder with appropriate attachment?? I think I might have to clean lines up with an epoxy filler afterwards but I obviously want to cause minimal damage to the original surface!

Couple of piccies of the rust areas...

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[JohnD]

If you can immerse it in a non-conductive container such as a plastic tub, the Electrolysis method of rust removal would be best. it is non-abrasive and non-destructive, it only removes the rust.

I can't find my link, but there are lots of descriptive websites on engineering forums if you do a search.

You immerse it in a solution of washing soda in water and use a DC current with a sacrificial iron anode (not stainless steel). A 12v battery charger will do.

edit
this link is quite clear
http://myweb.tiscali.co.uk/andyspatch/rust.htm

By the look of your pic, that thing has been in the sea, and has concretions on it. I don't know how to remove them. An acid bath might do it but might damage the steel. Try de-rusting it first by electrolysis and then see. Try http://nautarch.tamu.edu/CRL/conservationmanual/

 

[Norcon]

I'd blast it with sand or beads.

 

[Burnerman]

Thats heavy duty corrosion - I'd be looking to have it professionally bead blasted, if the metal is sound enough.
Rust removal products such as Bilt-Hamber Deox concentrate are good for light duty stuff.
It looks like the thing has been submerged for a while?
John

 

[JohnD]

go on, use Electrolysis!

It is ideal for restoring historical artifacts while retaining as much of the original surface detail as remains under the rust

 

[olly_k]

Thanks for the ideas folks, john i like the idea of electrolisys so will try that method first, and then if this does not work will have it blasted. I can only assume it has come from a very corrosive environment as it was originally designed for mining use!

 

[maltaron]

Some follow up pictures would be nice if you succeed.

 

[olly_k]

Yep no problem I will do that I am going to take it slow I don't want to damage this thing, but I think once I get going with the rust treatment hopefully things will loosed so it won't be so difficult to pull apart!

 

[olly_k]

Progress is slow, but getting there!

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getting there

Ideally I would have the bits lightly blasted and then powder coated but I am skint so will probably spray with primer, fill in the pitting that shows up then eventually get a mate to give it a couple of coats at a body shop - it can always be done properly at a later stage!

 

[JohnD]

that final pic looks very good. What method did you use?

does it come from a mine or ship or something?

 

[olly_k]

that final pic looks very good. What method did you use?

does it come from a mine or ship or something?

Yes John it is a mining telephone, lost rotting and long forgotten in a mine that will not be accessible for much longer!

I am using reverse electrolysis to remove the rust.

 

[olly_k]

A couple more pictures of the front cover shown at the beginning of the thread..

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as you can see they have come up as good as I could ever have expected, only some areas of minor pitting so I need to find a fairly easy method to fill in.

I don't think anything available from the local shed is going to touch the enameled paint that is still adhered to the metal (I tried burning off and it isn't touched) so when I can afford to I will take the pieces and have them professionally sand blasted then powder coated I think. At least it will not cost as much and one thing I can say for sure after my experiences - so long as there is base metal left, and the item is not too large, this method of removing rust is without doubt one of the best!

Thanks to JohnD for the original suggestion

 

[joe-90]

It's amazing. Never heard of the idea myself. JohnD is the daddy.

Did you use a battery charger? What did you use as the sacrificial anode?

I'll re-read the thread to see if you said.

 

[olly_k]

I used a bench power supply (I am electronics tech so no expense) but I think it is important to understand that the current must be limited especially with delicate items! I go for about 2 - 5mA per cm2. For the front above that equated to about 2 amps. Set the power supply for 20V 2A maximum. Lower the anode into the electrolyte and the voltage will drop to about 3v but slowly rise as the anode builds up with crud as resistance increases to maintain the same current. When the current starts to drop it is time to clean the anode and check progress.

There is a bit of manual work involved as the rust doesn't literally fall off (well most of it does) you still have to scrape but it doesn't take a lot of work - and of course the black rust is converted back to base metal!

Regards the Anode material I used the base of an old hifi stripped of paint again it is important to use plain steel / iron as you do not want alloys (stainless) or other impurities like chrome etc. messing things up and besides the water could turn quite toxic! I believe carbon stirring rods are a good material as they will last and not rust unlike iron / steel!

 

[Norcon]

Soda blasting.
Only learnt about it today. Sealey even make the blaster.
The vintage guys use them as it causes no damage.
And protects against rust for up to three weeks after if no paint applied.
http://www.youtube.com/watch?v=Hsxy06y1_hg