Cast iron is an iron, carbon and silicon alloy that has been melted and poured into a mould to form a shape. The Chinese developed furnaces for making cast iron around 500 BC. These furnaces were hot enough to melt cast iron so that it could be poured into moulds to make many products including weapons, jewellery and cast iron cookware.
An example of the early use of cast iron for jewellery
A current example of cast iron used in valves for a coking plant
An example of a pattern suitable for use with a modern sand moulding system
European development of the cast iron process did not occur until the middle of the 12th century. Due to the lack of technical knowledge of the material and rudimentary production methods, its uses were limited. Primarily at this time domestic items were being made such as pots and cauldrons. These were often very brittle resulting in thick castings to withstand the usage. As more experience was gained with the production process more advanced uses were found for it. One of these applications was in the production of cannon barrels in the 16th and 17th centuries, whilst the 18th century saw extensive usage in domestic areas such as fire places. The surge in uses really came during the early industrial revolution when further improved production methods led to iron that was reliable enough to be used in engineering applications in areas such as bridge, locomotive and ship construction coupled with the vision of engineers like Isambard Kingdom Brunell.
The Victorian era saw an explosion in the use of cast iron and that has continued to this day due to the combination of the ability to cast complex shapes at low cost compared to other production methods and materials.
Modern cast irons are a far cry from the metal produced by our Georgian and Victorian forefathers. Much improved quality control coupled with highly advanced analytical methods have led to the development of production standards that give consistent, reliable metallurgical properties leading to its use in demanding applications covering a wide range of end users.
As the metallurgy of cast iron and the melting processes have improved over the years, so has the technology for the moulds into which the metal is cast. The earliest material used was probably clay which was formed round a wax model of the required casting. The earliest material used was probably clay which was formed round a wax model of the required casting. The clay was then fired which melted the wax out and the molten iron was then poured into the void As larger and more complex shapes were attempted.
Clay became impractical to use and different materials were used including clay/loam mixes and even horse dung. One problem with all of these early moulding systems was that they were only suitable for small scale production, being generally very time consuming. As the Victorian age came and mass production began, a moulding system was required that could keep pace with demand. This system was based round sand. The earliest type of sand system was Greensand, which is a combination of silica sand, clay and water. Naturally occurring sand which contains clay is used as the basis for the system. This sand is usually red in colour, although after use in a foundry the sand takes on a dark grey/brown colour. This can cause confusion when foundrymen talk about "green" sand. The term green is used to denote that the sand is wet, having about 2% water in it. If greensand is compacted around a pattern, the sand will retain its shape after the pattern is removed, which occurs because the clay in the sand provides an electrostatic bond between the clay and the sand grains. This can cause confusion when foundrymen talk about "green" sand. The more the sand is worked or rammed the greater the electrostatic charge that builds up and the stronger the final mould will be. Small additions of dextrose can be added to improve the bond and similar additions of powdered graphite or flour can be used to improve the permeability of the mould.
Although greensand moulding could produce the higher volumes required during the Victorian period, it is a highly skilled job and requires long periods of training to become proficient. Because of this and other cost considerations, sand systems that were simpler to use were developed in the late 50's and early 60's which were based around dry silica sand without any clay addition. The bond was achieved by the addition of a resin and a method of hardening the resin. There are two basic systems.
Firstly a resin can be mixed into the sand that can be set off, or cured, by passing a gas through the sand. An example of this is the Sodium Silicate system. Sodium Silicate is mixed with the sand, the mould is made and CO² gas is then passed through the sand around the pattern. The CO² causes the silicate to harden through a combined action of dehydration and gelling of the silicate, which results in a stable mould from which the pattern can be removed.
The second system is based on a resin and a catalyst. These are mixed into the sand in metered amounts and the sand hardens by a chemical reaction between the resin and the catalyst. One draw back to this system is that once the sand is mixed, there is a finite time that the sand can be used for. Greensand does not have that problem and for very high volume production using mechanised moulding systems, greensand is still the preferred sand system. Durham Foundry currently uses one of the resin/catalyst systems for all its mould and core making, specifically an Alkali Phenolic system. Other systems exist that are suitable for iron castings such a shell moulding and investment casting but these are outside the scope of Durham Foundry. Please browse our website for more information about Cast Iron Castings from Durham Foundry and our ability to manufacture Engineering Cast Iron Castings then contact us on 0114 249 4977 or e-mail us on firstname.lastname@example.org to homepage...