How Fusion Welding Cast Iron Works
from Automotive Builder
. .Fusion welding cast iron is called the "black art"'
of crack repair because it involves a lot of heat and requires
a highly skilled welder. Learning how to "recast"
damaged heads is not something an inexperienced welder can
pick up overnight. . .
"If furnace welding was easy, everybody would be doing
it." said Rick Geertsema of *A&C Casting Rebuilders,
formerly of Excelsweld USA.. "It's a hot job that doesn't
exactly appeal to a lot of people."
Today, most of the work he does is specialty restoration work
on older heads from classic cars and antiques. Examples of Rick's fusion welding experience.
Geertsema says he may use either *fusion or powder welding
to repair a crack depending on the application. Either way,
the first step is to fully identify the cracks, then grind
them out with a hand-grinder.
If a crack is being repaired by *fusion welding, Geertsema
first preheats the head to 1300 degrees F (cherry red) in
an oven. . .Preheating is absolutely essential to minimize
thermal shock, and to relax the metal so it won't distort
when the torch is applied to the casting.
When the head preheat temperature has stabilized (it takes
about an hour), a "neutral flame" oxyacetylene torch
with slightly more oxygen than acetylene is used to melt the
cast iron (which melts at approximately 2700 degrees F). Geertsema
says he uses a several varieties of cast iron filler rod and
borax flux. The trick here is to keep the weld clean by adding
a little flux so the impurities will rise to the top. The
impurities can then be floated out of the repair area with
we're building up a valve seat, we'll make a carbon graphite
plug to fill the hole, then weld up around it," said
Geertsema, "The puddle will be about half-an-inch deep
and maybe two-inches in diameter. It takes a lot of heat to
do this, about 5000 degrees F.
the crack has been filled, a long, slow cool-down follows.
This step is also important to prevent the head from recracking.
If cast iron cools too quickly, one of two things can happen.
The surrounding metal can shrink away from the weld causing
new cracks to open, and/or the carbon in the iron can turn
into carbide making the metal too hard and brittle to machine.
*Geertsema said, therefore, the casting must be cooled very
slowly to prevent these undesirable metallurgical changes.
says he wraps the heads in an insulating blanket and keeps
the head in a hot box so the head will cool at a rate of no
more than 200 degrees F per hour.
these rates, it can take quite awhile for the head to cool
down to ambient temperature: 8 hours to overnight. So one
can't be in a hurry when *fusion welding cast iron heads.
Geertsema says once the head has cooled, it is cleaned to
remove the scale, then rough machined and submersion pressure
tested in hot water at 100 psi for leaks. . ."
words have been changed from the original document.
Rick Geertsema for quotes and shipping information.
3560 Big Valley Road
Kelseyville, CA 95451
A&C Casting Rebuilders All Rights Reserved