Welding Cast Iron

[JonnyAlpha]

Hi;

Whilst working on my Mini a gentlemen neighbour has asked if I can help fix one of his garden tools.
The piece in question looks like its cast iron.

I only have a Mig Welder, can it be welded by a Mig?

Thanks

 

[Bsmith]

Not really successful with mig, cast iron arc rod or oxy/acet braze.

 

[Tigman]

only with an expensive spool of the appropriate wire !

 

[Bill Edwards]

Test whether it's cast by touching it with a grinder, CI gives dull red sparks.
It might be cast steel in which case how (or if) it welds will depend on the makeup of the steel.

If it's CI then the only practical way to do it is with a stick welder and a cast iron (nickel) rod.

 

[God mode restorations]

Don't you have to heat it to.and gradually cool it after welding.

 

[Bill Edwards]

Don't you have to heat it to.and gradually cool it after welding.

You have two methods available:
1. Use an oven to very slowly heat it, weld and then use the oven again to very slowly cool down afterwards.
2. Weld it cold. Do pretty small bits of weld so it doesn't get hot enough that you can't comfortably keep your hand on it and while it cools tap the weld repeatedly with the chipping hammer (called peening). Works perfectly and requires no equipment apart from the welder, where even the most basic will do.

 

[God mode restorations]

You have two methods available:
1. Use an oven to very slowly heat it, weld and then use the oven again to very slowly cool down afterwards.
2. Weld it cold. Do pretty small bits of weld so it doesn't get hot enough that you can't comfortably keep your hand on it and while it cools tap the weld repeatedly with the chipping hammer (called peening). Works perfectly and requires no equipment apart from the welder, where even the most basic will do.

I did some cast welding ages ago. Had to weld a steel centre in to a cast v belt pulley .had to heat it and weld it then gradually cool. It worked ok. Used z disimalar rod.

 

[Bsmith]

Think I have read on here about someone mig welding cast iron with stainless wire and peening as it cooled. Never tried it myself, used to use square cast iron rods and flux with oxy/acet or braze.

 

[Bill Edwards]

I did some cast welding ages ago. Had to weld a steel centre in to a cast v belt pulley .had to heat it and weld it then gradually cool. It worked ok. Used z disimalar rod.

You do sometimes get away with these things. I think that if not using the proper rods dissimilar would be the next best thing but it's chancing it.
There are the cast iron rods for welding cast to cast and there are also rods for welding cast to steel. TechnicalAL is the expert on these things and has explained the difference but at this moment I can't quite remember the details. But I think that the proper cast rods will do either kind of welding but the cast to steel are cheaper.

What welding cast cold does is save the hassle of heating and cooling which if done too quick cause stresses which will cause cracking. Peening the weld expands it, as the weld and metal cool the weld needs to expand otherwise stress is placed on the CI.
It's a very reliable method which has saved many engine blocks and head from scrap, yet so many shy away from this method.

 

[optima21]

I once mig welded a cast iron exhaust clamp back together after it cracked (think it was cast iron). the weld held but it cracked somewhere else when I tightened it, it ended up being thrown away and and a pressed steel clamp was used instead.

 

[Chris Stevens]

Tig brazing is the most effective and easy way to repair broken cast iron.

 

[TechnicAl]

What is it?
I cant think of any garden tools that would be cast iron, its too brittle

 

[Ginger Beer]

Well my first post on here! I get asked to repair all manner of things, I believe TechnicAL is probably right. Most garden tools through my workshop have been cast steel. Spark test with a grinder will as said before tell you if it is cast iron, rather dull lifeless sparks are the giveaway. Biggest thing with welding cast iron is the preparation, being very crystalline it absorbs a lot of contaminants over time. I have heated parts in my forge for a day or two before now, prior to shot blast and grinding before welding. Latest job is a horse drawn plough body.

 

[arther dailey]

Well you certainly come from the right neck of the woods to be working on that !

 

[Cobbler]

That's a fair old lump of iron there, I think most of us would be interested how it turns out. Keep us posted.

 

[Richard.]

Dissimilar rods are about the worst thing to repair cast iron with if talking stainless steel. They contain high amounts of chromium . Brazing as said by Chris or welding with a nickel/iron consumable. If welding hot you need to get it veeeeeeeeery hot and slow cool and if welding cool you need to keep it as cool as possible. Both methods require peening as a stress relieve after an inch of weld has been laid down.

 

[TechnicAl]

Dissimilar rods are about the worst thing to repair cast iron with if talking stainless steel. They contain high amounts of chromium . Brazing as said by Chris or welding with a nickel/iron consumable. If welding hot you need to get it veeeeeeeeery hot and slow cool and if welding cool you need to keep it as cool as possible. Both methods require peening as a stress relieve after an inch of weld has been laid down.

Thats true 7016 or 7018 are better....but the weld will become hard and brittle like the cast iron itself
Nickel or Nickel Iron are the best. They have been designed for the job and the coating (graphite) allows them to be used on lower amps thus keeping the heat to a minimum..........its science....not the rocket variety just plain old common stuff

 

[Bill Edwards]

It's true that occasionally people have got away with with a MIG cranked up high.

Note it's 'got away with' and not to be used for anything important.

 

[Ginger Beer]

Yes it is rather large isn't it! Just got it back from blasting., what you cannot see is I have drilled and tapped it with 1/4" whit screws to hold it all together. Next stage is grind vee grooves, get it hot with propane burners (300-400C) and a lot of small welds. Peened as we go, and it will take most of a long day. Cooling down will be in my forge over a day or two. Elga Cast nickel rods, not cheap!

 

[Ginger Beer]

Thought you might like to see where bad welding can lead! The picture shows a 'landslide' off a 1920 Ransomes match plough. Previously enjoyed by someone with a stick welder, and wrong rods. It cracked in 3 places and went beyond repair. I ended up making a new one for the guy. Pic shows the original, the pattern I made, and new one I cast in iron. (Brake discs and melted down AGA cooker!)