[TheForge] Welding cast iron

[Bisnette SSgt Bernie R]

I've been following this thread and here's what I can throw in the mix:

Gray cast iron is 94% pure iron and varying portions of carbon, manganese,
phosphorus, silicon and sulfur.  Engine blocks, pulleys, and pump bodies use
this.  A torch test will show a heavy tough film that forms on the surface
as it melts. Spark test will reveal a small volume of dull red sparks that
follows a straight line will form close to the wheel.  These break up into
fine, repeated spurts, which change to straw color.

White cast iron is produced by casting against metal chills.  This causes
the free carbon in the gray cast iron to combine with the iron.  Recommend
NOT to be welded.  It is very hard and brittle.

Malleable cast iron.  Created by heating white cast iron to about 1,659 deg
F and holding it here for several hours or even days and cooling it slowly.
Can be bent without breaking and it will withstand shock.  Hard wearing hand
tools, pipe fittings and automotive parts are usually made with this.  Spark
testing will show the outer bright layer gives bright sparks like steel.
When the interior is reached the sparks quickly change to dull read color
near the wheel.  A little longer spark than that from gray cast.

I was taught that the big problem with welding cast is the expansion.

-----Original Message-----
From: Tod Estes [mailto:blacksmith at atlasok.com] 
Sent: Wednesday, December 07, 2005 2:30 PM
To: Sponsored by ABANA
Subject: Re: [TheForge] Welding cast iron

There was a Thermit mix for welding Cast iron. It used the basic Thermit
mix of aluminum and iron oxide with the addition of ferro-silicon and mild
steel punchings. From what I understand the success still rested on prep
of the weld area and the preheat / post heat. Still was not really
reliable.

 Gas welding is an option but you have to really raise the preheat temp of
the entire casting somewhere tween 750 to 900 deg. F.  Cast iron rod
recommended.

> Okay, idea time:
>
> I've long wondered (having no practical experience in the matter AT ALL)
> whether the problems in welding cast iron were due to the graphite
> (carbon).  Folks sometimes say that the stuff has absorbed oil or grease.
> Well, castings CAN be porous, but it strikes me that if grease were the
> problem with welding cast iron, then it would be more of a problem in
> welding steel.  (You don't want a lot of junk on steel, but you don't need
> perfect cleanliness - the grease will burn off.)
>
> But graphite would burn off less readily, and more would be exposed as you
> melted the mother metal.
>
> So if graphite is the problem, how can you get rid of it?
>
> So I looked up graphite on the web and found that it's soluble in
> something * molten iron!    This suggests that a pure iron electrode might
> be a good candidate for welding cast iron.
>
> This is all by guess and by golly.  I'd be interested if anyone has ever
> tried it.
>
> Bruce
> NJ
>
>>>> gladish at cnw.com 12/4/2005 11:29:16 AM >>>
> One tip that has helped me in the past is to use a file rather than a
> grinder to clean the mating edges. The explanation given to me is that
> the grinder smears the carbon that is in the cast iron (high percentage)
> and makes a dirty surface, though it's not apparent to the eye.<snip>
> Andy G.\
>
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Tod Estes
Oologah Smithy
Oologah,Oklahoma. (Home of Will Rogers.)
Saltfork Craftsmen ABA, ABANA
Time enough for sleep in the grave.

"Prometheus: I took from man expectancy of death.
Chorus: What medicine found'st thou for this
        malady?
Prometheus: I planted blind hope in the heart of
           him.
Chorus: A mighty boon thou gavest there to man.
Prometheus: Moreover, I conferred the gift of fire
Chorus: And have frail mortals now the flame-
        bright fire.
Prometheus: yes, and shall master many arts
            thereby."

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