The main difference
between steel and cast iron is its carbon content. Mild
steel contains less than 0.30% carbon, and most high
carbon steel contain less than 1.0% carbon. The maximum
carbon that can be put into steel is 1.7% as this is the
maximum carbon that can be absorbed in solution with iron. When larger amounts of carbon are combined with iron, the
carbon not absorbed by the iron is present in the form of
small flakes of graphite. Grey iron contains up to 4.5%
carbon, usually between 3.0% and 4.0%.
When cast iron is heated,
at a temperature near its melting point, practically all
of the carbon goes into solution with the iron in a
combined form of iron carbide. If the cast iron is allowed
to cool very slowly nearly all of the carbon will pass out
of the combined state and segregate as free flakes of
graphite. If the iron is cooled rapidly a large portion of
the carbon will remain combined with the iron as iron
It is this high carbon
content that makes cast iron so different from steel. If
we could remove the graphite flakes from cast iron and
squeeze what is left together, we would have steel.
Because cast iron has the
flake-graphite structure which prevents it from bending
and causes it to have no elongation, it breaks readily. It
is a common event in factories, construction companies,
farms, and all other industries for cast iron machinery to
fracture. Often a costly casting breaks simply from
vibration. Costly downtime from mishap with cast iron
machinery is common in industry. Also, because cast iron
is soft, it often wears. For example in threaded holes,
the threads wear or strip easily. No one can estimate the
loss to industry by breakage of automobile and truck motor
blocks, exhaust manifolds, transmission housings, and in
factories of such indispensable machines such as pump
housings, punch presses, electric motor housings and the
myriad of other cast iron machinery components.
When a cast iron part
breaks, the cost is enormous to almost any industry. It is
impossible for an industry to carry spare castings in
their store room. Often the machinery is old and obsolete
and the manufacturer cannot provide a spare. To make a new
casting usually involves making a pattern first. This can
take up to four weeks just to make a pattern and often the
pattern can cost thousands of dollars.
It is for these reasons
that industry must be well prepared with Magna
Maintenance Welding Electrodes and Alloys, to enable quick
restoration of the broken machinery to useful service.
Many engineers who have
encountered repeated failures in attempts to repair cast
iron with ordinary cast iron production welding rods.
Some engineers state that
they have been able to weld cast iron, in some cases using
brazing rods or gas welding rods, which require a long
complicated procedure. Usually brazing or gas welding cast
iron involves: Dismantling; building a fireplace around
the casting; preheating, often for as much as 24 hours;
gas welding; burying the casting in lime or other
insulating material; and slow cooling for up to one week.
The answer to successful
welding of cast iron is the development of
Magna 770 which has brought industry a
There are a number of
companies that market production welding cast iron
electrodes. They usually offer from 3 to 7 different cast
iron electrodes, since they readily admit that each
electrode has only a limited range of applications on
which it can be used on.
electrode manufacturers that offer several different
electrodes for cast iron are not capable of serving the
needs of maintenance. Such a variety of cast iron
electrodes, each with a limited scope of usage, is
generally all right for production welding where only a
limited number of applications exist. A production factory
manufacturing, for example, pumps and has only one
analysis and one thickness of cast iron to weld under
perhaps only one condition, can select one of these
production cast iron electrodes for the one application.
In maintenance the
conditions are completely different. In maintenance they
never know what type of cast iron will break, what
thickness it will be or whether or not the weld will have
to be machined or not. Generally they do not know what the
analysis of the casting that may break will be.
MAGNA has solved
this old industrial problem of cast iron failures with
Magna 770, which welds all types of cast iron,
thick or thin, including grey, malleable, meehanite and
nodular iron. It welds in all positions, including
overhead or vertical. It makes porosity-free welds without
undercut. The welds are fully machinable and crack-free.
Magna 770 even welds cast iron to steel.
Magna 770 is the one practical solution
that can help you prevent costly downtime and loss of
profit due to cast iron failure.