[TheForge] Welding cast iron

[Bruce Freeman]

I stumbled on this:
http://www.locknstitch.com/CastIronWelding.htm

Bruce
NJ

>>> awashington at ou.edu 12/7/2005 10:40:13 AM >>>
As long as we are talking about welding cast iron, I have a question.  Recently I bought an Acme post drill that looks exactly like one in the 1915 Sears catalog; the one for $7.10 at http://www.anvilfire.com/21centbs/drilling/postdril.htm.  After cleaning off 90 years of ossified grease and dirt and oiling it up, the drill worked great!  I was able to drill a 3/4" hole in 1/8" plate in a couple of minutes.  I was so happy I began gleefully drilling holes in everything I could find.  Then came the problem; I broke my new toy. 
 
The small wheel at the top advances the down-feed of the spindle by means of a pivot arm that works against the eccentric hub of the flywheel.  I broke the pivot arm by continuing to crank after the spindle reached its maximum extension. In my feeble defense, it broke at or near a previous repair.
 
Now here are my questions.  Is this arm likely to be cast iron?  It looks like it might be because the angular shape of it looks like it was designed to release from a mold.  The interior of the break looks grey and grainy.  From this thread I take it the repair could be done by arc welding with nickel rod, brazing, or gas welding with iron.  Bernie points out that expansion is often a big problem in welding cast.  But that should not be much of an issue with this part since it is small and there is no restriction on expansion in the length of the arm.  It would also be easy to pre and post heat.  BTW, if I decide to weld it, I will find someone else to do it since I'm a lousy welder.
 
Is any repair likely to be strong enough for the strain put on this part?  Would I be better off just forging a new arm out of mild or medium carbon steel?
 
Aubrey Washington
Saltfork Craftsmen ABA, ABANA
Rock Creek Forge
Norman, OK
 
 
Date: Wed, 7 Dec 2005 16:26:20 +0900
From: Bisnette SSgt Bernie R <BisnetteBR at 1maw.usmc.mil>
Subject: RE: [TheForge] Welding cast iron
To: "'blacksmith at atlasok.com'" <blacksmith at atlasok.com>,        'Sponsored by
        ABANA' <theforge at mailman.qth.net>
Message-ID:
        <3621DB29C10C214F8D7445C338C5C5F9D913B9 at 1maw01e.1maw.usmc.mil>
Content-Type: text/plain

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.