Compacted Graphite Iron was first patented at about the same time as
ductile iron in the late 1940's. At the time it was viewed
more as a curiosity rather than a production material, but its
unique properties has led it to be used in many applications which
are unsuitable for grey or ductile iron. Compacted Graphite Iron,
which is also known as CGI or Vermicular Graphite Iron, is a form of
cast iron in which the shape of the graphite particles is between
that of conventional grey iron flakes and ductile iron where the
graphite is in spheres. The worm-like compacted-graphite shape
provides physical properties that mirror the most beneficial
properties of grey and ductile irons. CGI has twice the strength of
grey iron and costs no more to produce than ductile iron. Grey iron
is particularly easy to cast and machine and it has good damping and
thermal conductivity, but its flaky structure makes it brittle, as
reflected by its low tensile strength. At the other end of the
spectrum, ductile iron has a high tensile strength but relatively
poor thermal conductivity and damping properties. Compared with
these two extremes, CGI has thermal conductivity and damping
properties roughly the same as grey iron and tensile strengths and
stiffness comparable to those of ductile iron.
At The Foundry we have been producing compacted graphite iron
castings for the last 20 years. As well as compacted graphite iron
castings, our customer base also covers grey, ductile and alloyed
irons for the engineering, decorative, architectural and artistic
sectors and we can supply castings from one off up to small to
medium batch production using Alkali Phenolic resin bonded sands.
Our workforce of highly skilled moulders can work from complex loose
pattern equipment, particularly where low volumes are required,
whilst our moulding line is suited for batch production. Our long
trading history, coupled with an investment programme that has
enabled us to keep up with modern production methods and
environmental legislation has meant that we have been involved with
many projects requiring compacted graphite iron castings and
continue to be so. All our compacted graphite iron castings are
produced to the current ISO material specification, ISO 16112, along
with any further certification which a customer may require. Our
diverse customer base has also given us experience in a wide range
of applications for compacted graphite iron castings , including
pumps and valves, forges, foundries and rolling mills, automotive
and aerospace, a wide range of OEMs, quarries and mines, railways
and rolling stock, local authorities and artists and sculptors. We
also have long term trading relationships with local pattern makers,
machine shops and surface finishers which enable us to quote for the
complete supply of the finished casting.
CGI
is produced by treating the melt as if ductile cast iron was being
made, but the reaction is 'killed' before it has time to complete,
resulting in a graphite shape between that of flakes and spheres. A
special type of ladle addition known as Compact Mag is used to
achieve the desired reaction.
The first commercial CGI applications were the high-speed rail
trains (175+ mph) in Europe. Initially, they had cast iron disc
brakes that were simply not up to the task. They suffered severe
heat-checking and cracks, which were potentially catastrophic. CGI
cured all that, and it has been widely reported that several engine
builders and automotive manufacturers are beginning to rely on CGI
to meet efficiency and strength requirements.
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