Hello MMD readers,  I have answered a couple times on questions people
have and thought I would write some about the repairing of cast iron.

I am a tooling engineer with 48 years of experience in the automotive,
lawn & garden and agricultural world.  I am actually working in China
at this time.  Most of the large dies that produce the body panels for
your cars are made of cast iron or cast steel.  Cast iron is what the
base of the tooling is made from and you add steel inserts where the
cutting or forming takes place.

As with all manufacturing, accidents happen: the tooling is hit too
hard, two parts are hit at one time, or the tools are known to have
been dropped.  We are talking about dies that weigh up to and above
90,000 pounds!

Just last week in our shop we had to weld up a cast iron die that
split.  It was preheated like some have stated and welded with a rod
made just for that type cast iron.  You weld for the length of one rod
and then you use an air hammer or air chisel to peen the material to
expand it to prevent cracks.  After it is all welded you heat the piece
up and let it cool slowly.  Some pack the parts in cast iron shavings
or some use lime to hold in the heat so it will cool slowly.

In the U.S.A., when we broke one of the large dies 8 feet to 15 feet
in length, we would send it to MPD Welding in Michigan.  They make
their living putting broken dies back together.  When it is just gray
cast iron, which is probably what the piano frames are cast from,
they usually braze them back together.  They grind out the crack into
a V shape so that there is more area to work with.

They have the iron sitting on a gas fired heat table and gradually take
the die up to the correct temperature.  They use brazing rod that is
probably 1/2-inch in diameter and start filling in the crack.  There
will be two men; one will braze for a while, then the other will reach
around and take the torch and the rod and keep going while the one that
was brazing rests.  They are working over several hundred degrees of
heat, in a heavy welder's jacket, so they cannot take long periods
without a break.  They do this for hours, even days, on a really bad
crash to repair the tooling.  I have personally operated dies for years
after being repaired in this manner and they are under heavy loads from
the hammering of the press.

So, all this being said, you can both weld and braze cast iron to do
the repair but the correct alloy rods have to be used and the broken
part has to be heated and then stress relieved to prevent cracks.  The
part will most likely warp during the process; I cannot say how much,
but it _will_ warp.

I would try to find a replacement from a junk piano or parts piano if
I could, and repair the original only as a last resort.  I would not
waste time and money trying to use an epoxy material to do the repair;
if the iron broke [due to force] the epoxy will not hold the force.

Have a great day,

David F. Fowler