Subject: "Best" way to fix broken cast iron

From: James Foster x2912 <[email-masked]>
Date: Fri, 07 Jun 1996 12:17:49 -0500

I don't have many references in this area (my Metals Handbook is missing
the Welding/Forging volumn B^( anyone have an older copy for sale
cheap?), so I wanted to try to get a discussion
going about cast iron repair. Kind of a "if this were you, how'd you do
it?"  These are based
on a couple of real life jobs that I want to try.

Two scenarios: A larger casting, part of it cracked off cleanly, another
part that
is missing a small piece (it's a big machinists vise). Neither are high
stress areas.

Second, a smaller, more delicate casting (a woodworking hand plane
body). One broken off
and rather poorly rebrazed. Another with a partial crack that I'd like
to stabilize. Also
consider a clean break with no brazing.

What are the limitation for tools/techniques? Well, first assume you
have anything you need
to do the "ideal" job and make suggestions for that. Second, to bring it
down to a more
home shop level, assume you have oxy/acetylene, AC Arc, AC TIG, oh, all
right assume DC on
the TIG though I don't have the DC converter done yet! B^)

I'll start the ball rolling with what I've come up with: 
   
     1. Back up the missing area with carbon blocks. Preheat to dull
red. Fill in
        with cast iron rod with AC welder. Deep vee grind the cracked
area. Preheat to
        dull red. Weld with oxy/acetylene and cast iron filler rod.

     2. Cut/grind off brazed on section to be able to better align the
parts. Preheat and
        rebraze. How much preheat do you need here? Drill the end of the
partial crack to
        help stabilize it. Vee grind crack, preheat, and oxy/acetylene
weld. If it were a 
        clean break then I'd basically do the same. 

Since I've got pretty good references on how to do the oxy/acetylene
work I lean toward that.
But TIG might be a better alternative though I have no references.

One thing I wanted opinions on was the degree of preheat. Dull red using
an improvised oven from
firebrick and asbestos, fired with charcoal, followed by slow cooldown
in lime or ashes is what
I've read. Can I get away with less temp, or is this about the minimum
I'll need?

TIA!

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From: [email-masked] (Bart Smaalders)
Date: 7 Jun 1996 21:04:07 GMT

I had good luck fixing a Renault flywheel w/ a piece broken out & missing
using a oxy-acetylene torch and brazing rod... I heated the flywheel to 
black heat all over and then built up the missing area with brass.  After
slow cooling in air (surrounded by whatever firebrick was around) I 
machined the section smooth.  One of the bolts holding the clutch cover on 
was in the broken section; I drilled that anew (into the cast iron) and
used a long bolt in that hole....

Ran just fine, though it was probably rather out of balance....

- Bart

---
Bart Smaalders			Solaris Clustering	SunSoft
[email-masked]		(415) 786-5335		MS UMPK17-301
http://playground.sun.com/~barts			2550 Garcia Ave
							Mt View, CA 94043-1100

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From: [email-masked] (Clhuprich)
Date: 10 Jun 1996 15:32:18 -0400

Large castings are often repaired with thermite.
Cliff Huprich