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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