OT: welding query - cast iron

On Mon, 20 Nov 2006 20:37:15 -0000, "Richard Brookman" scribbled the following nonsense:

I managed to chip a triangular chunk 2" by 1" out of my cast iron fireplace after I had spent 3 weeks with toothbrushes and nitromors getting it back to bare metal. grr

Managed to repair it by clamping the chip in place and turning the current low on the welder and welding it by tacking it initially at different points to prevent one point from becoming too hot and cracking further. Once I had done this I filled in the gaps 5mm at a time, again switching sides to prevent too much heat. About 20 mins later it was finished and now can't be seen.

I did the welding on the hidden side and had ensured that the chip was fitted very tightly in place before starting. Also helps to turn the welder to the lowest setting and then bringing the current back up.

On Mon, 20 Nov 2006 20:37:15 +0000, Richard Brookman wrote (in article ):

Welding cast iron is perfectly possible but it's one of the more difficult materials to weld since it is fairly brittle and so the stresses caused by differential heating can cause it to crack as it cools. Gentle heating and a very slow cooling are required (one solution is to bury the part in hot sand which is then allowed to cool slowly.

Try the 'knowledge' sections of the Miller Welding

Have you considered making the hole bigger and putting a replaceable bush made out of steel or brass and held in place with screws or a nut in ? - no risk of cracking, and easier to fix next time around.

Nick.

permanent

You are supposed to pre heat cast iron before welding, I think probably to a dull red, that's assuming you can get the bit on the Missus' cooker. :-)

Martin

permanent

What about finding a way of lighting it without the rod in place, then weld the hole up with the fire at full temp, let it go out and cool down, then drill the hole? Badger.

||| Have you considered making the hole bigger and putting a ||| replaceable bush made out of steel or brass and held in place with ||| screws or a nut in ? - no risk of cracking, and easier to fix next ||| time around. ||| || || What about finding a way of lighting it without the rod in place, || then weld the hole up with the fire at full temp, let it go out and || cool down, then drill the hole? || Badger.

Thanks for all the suggestions chaps. My understanding now is that cast iron *can* be welded, but only with some care and a bit of expertise (which in our case we have not got - would have to be bought in). I'm rather taken with the idea of a replaceable bush - sounds to be within my capabilities and infinitely repairable, whereas the welding route would mean doing it all over again in another ten years!

Cheers

Why not just bush the hole, so it won´t wear out again ?

Steve

If this is a smokeless fuel stove "idling" is fairy nuff but think twice about doing the same with a freshly stoked supply of wood.

Funnily enough I've just attempted to repair the grate from a Redfyre back boiler by nickel welding in some new bars, it looked grand but as I fitted it the thing broke in two from the stress. As others say you need to keep the casting in a plastic state (red heat) and cool it very slowly to anneal the stresses out of it.

Best bet I reckon but stick it in with some exhaust goo.

AJH

|||| original size, and the air that bleeds in through here means it |||| won't idle any more (like overnight) and uses about 50% more fuel |||| than it did when it was new. || || If this is a smokeless fuel stove "idling" is fairy nuff but think || twice about doing the same with a freshly stoked supply of wood.

Anthracite overnight, and mixed with whatever wood I can get at other times. No probs in the last 10+ years. Funnily enough, I turned it right down last night and this morning it was almost out (through lack of O2, not lack of fuel). Before the repair it used to be glowing merrily at 7 am. The repair works well from an air supply point of view. I think a replaceable bush is the way to go for long-term durability.

You should be able to sort it out with the gas welding set and some wearbraze if you want a simple solution.

Beyond what the others have said about arc welding it, not only does it need preheating but it should be cooled slowly (over several hours) by packing it in insulating material (or even dry sand).

It would almost certainly repair ok with a MIG, argoshield (or whatever the argon mix gas is called in the UK) and ordinary mild steel wire. Just keep running a small bead at a time and letting it cool between attempts - I've welded a lot of exhaust manifolds this way without preheating and the results have been fine.

|| Richard Brookman wrote: || ||| ||| Which is a long way round to asking: would it be feasible to weld ||| in a plug of , which I could drill out the same way to ||| make a more permanent repair? Can normal welding be done to cast ||| iron? The size of the plug would be about 10mm wide by about 5mm ||| deep. || || || You should be able to sort it out with the gas welding set and some || wearbraze if you want a simple solution. || || Beyond what the others have said about arc welding it, not only does || it need preheating but it should be cooled slowly (over several || hours) by packing it in insulating material (or even dry sand). || || It would almost certainly repair ok with a MIG, argoshield (or || whatever the argon mix gas is called in the UK) and ordinary mild || steel wire. Just keep running a small bead at a time and letting it || cool between attempts - I've welded a lot of exhaust manifolds this || way without preheating and the results have been fine.

Thanks for that.