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View Full Version : What you should know about Cast Iron before welding



Grahame Collins
9th Dec 2007, 01:14 PM
Hi Everyone,

I really tried to to avoid coming into this one,but I could not help myself. I was going to post this on another thread, but thought it might high jack the thread.I have not come here to tell any one how to suck eggs.

What I do wish to point out that the repair welding of this metal is complex and there is more to it than meets the eye of a DIY welder.

Those comments I saw are based on some contributors experiences. What it will work for some it won't for others.
I do not seek to criticize anyone but I do urge caution to all.

Cast iron can be an extremely difficult metal to weld because of differing reasons.



Cast irons vary in type and in composition. They are several base types.Unless you know the type and its composition its just a guessing game and your chance of success is diminished if you don't know what you are working with.


Cast iron has a very different modulus of elasticity to steel which unfortunately many welders unwittingly compare it to. Cast iron in general will compress well, but does not tolerate tensile or torque loads well.


Cast iron disperses heat held in thick and thin sections at a different rate. It is this uneven cooling that causes much grief among those attempting to weld it. Cracking is the result of stress built up by uneven cooling between thick and thin sections.


Cast iron has the ability to draw in compounds used around it. Oil and carbon from exhaust manifolds come to mind readily.Welding of cast iron is greatly affected by contaminants.


Cast iron contains a super saturation of carbon -up to 4% (yes its is 4% its not my typo) in some cases.Excess carbon is the cause of hardness brittleness and in combination with cooling differentials - cracking.


The above very much determines what process and techniques should be employed to successfully undertake a reliable welding repair on cast iron material.



For those in Brisbane look up the phone and check out Accurate Welding Works at Lytonn. Note that they seem to be the only ones in the book to take on cast iron repair in a big way.

They are also the company I started my apprenticeship with, so I do understand a bit of the subject 40 years down the track. You might ask yourself why there are not a lot of welding works around that do cast iron.

Just some things to think about off the top of my head.
Grahame

specialist
9th Dec 2007, 07:24 PM
You might ask yourself why there are not a lot of welding works around that do cast iron.

I agree totally. I have spent almost all my working life repairing things that other people have broken and have come to have a love/hate relationship with cast iron. In 20+ years of trying to repair it, it still comes down to trial and error.

Robert

Grahame Collins
9th Dec 2007, 11:21 PM
Hi Robert,
You and I know that every cast iron welding job is different to the last. The home welder who tackles this stuff once or twice lifetime has little hope of understanding or controlling any of the many variables that act upon the repair process.

Cost and availability of a welding process in a home situation, prevail more often than not and this is the prime cause of a failure.
A lot of what is written by is either plain incorrect and does not apply to particular or specific situations. Even the electrode and consumable manufacturers can only advise in a general way on repair.

I plan to set up a one man small niche welding business when I retire in a few years time .It will concentrate on the repair of small items capable of being carried by one person.
It will be for a specialized market with customers from specific areas of use or application. More to do with one offs or irreplaceable items or expensive replacement.

To do this I am slowly assembling a range of equipment for machining prep, welding and heat treatment necessary to weld cast iron among other materials.This probably involves expenditure on up to $20,000 .
Its basically out of the league of anyone wishing to do a home repair.

Quite often it is possible to think outside the box when a cast iron repair is involved..In many cases a cheaper fabrication that can perform the same function is possible.

Grahame

simso
10th Dec 2007, 12:14 AM
Hi guys, throwing my 5 cents worth in, having done a bit of cast iron welding, may I make the following recommendations.
Dont weld cast iron cold, you gotta heat it up, 400 plus will work a treat, if you weld it cold its just gonna crack or be as brittle as, cast iron has almost no ductibilty in it which is why it fractures so easy when you try and weld it.
Another helpful thing is to increase the carbon content at the surface, you can buy carbon dust for this purpose and just splash it on whilst youve got the steel hot.
Tig mig oxy they all will work if you do the prep, but still no guarantee, could be really grey steel and then you got next to no chance

yogie
13th Dec 2007, 11:05 AM
Hi guys, throwing my 5 cents worth in, having done a bit of cast iron welding, may I make the following recommendations.
Dont weld cast iron cold, you gotta heat it up, 400 plus will work a treat, if you weld it cold its just gonna crack or be as brittle as, cast iron has almost no ductibilty in it which is why it fractures so easy when you try and weld it.
Another helpful thing is to increase the carbon content at the surface, you can buy carbon dust for this purpose and just splash it on whilst youve got the steel hot.
Tig mig oxy they all will work if you do the prep, but still no guarantee, could be really grey steel and then you got next to no chance

spot on chap, I used to work at Schots in Melb years ago doing thier castiron fire surronds, to much cast today is chinese rubbish, so heat it up heap, use carbon dust and pay good dollars for decent quality rods. :rolleyes: