The quality of cast iron is dependent on the care taken while pouring the molten material, coupled with how complicated the mould is. The moulds can be expendable moulds (sand) or non-expendable molds (metal). The pouring can happen via gravity, low-pressure or vacuum. Gray cast iron components are cast by pouring the molten iron in to the mould, which gives it the desired shape. It is this graphite that is the characteristic of gray iron as it gives it a ‘flaky’ appearance. Once it is molten and the impurities removed, a small amount of silicon is added to convert the carbon into graphite. Often times, scrap iron and even steel is used in the manufacturing of gray iron. The process of manufacturing gray cast iron in a foundry starts with the pig iron being melted, purified to remove contaminants and then poured into a mould to solidify. Additionally, this type of cast iron is cost-efficient and has an excellent ability to withstand thermal cycling. It has high thermal conductivity, superior vibration damping capability, and acceptable tensile strength. The low degree of shrinkage in gray cast iron makes it favourable for industrial engineering applications since it has a varied tensile strength range from less than 20,000 psi to over 60,000 psi, and hardness from 100 to 300 BHN (Brinell hardness number). While gray cast iron is not as strong as ductile cast iron or steel, it has reasonable amount of tensile strength, hardness, and other properties that make gray cast iron ideal for most cast iron components that come out of the foundry. In other words, the properties of the grey iron will depend upon how the melt is prepared as well as how it is cooled. While the flakes cause fracture in the melt, it also imparts other properties to the gray iron. With a strong enough microscope, it is possible to visually see the graphite microstructure that is present as flakes. And what makes grey iron 'grey' is the crystalline carbon found as flakes when the molten metal is cooled. It is characterized by a random flake graphite pattern in the metal. Gray cast iron is suitable for lightweight castings (usually up to 200 kg), medium weight castings (usually from above 200 up to 1000 kg) and heavy castings (usually over 1000 kg). In this article, we will use both ‘gray’ and ‘grey’ interchangeably. Gray cast iron (‘grey’ cast iron in the British Englsih) is also known as flake graphite cast iron is an iron-carbon casting material in which the carbon in the form of graphite is predominantly present as flakes. However, steel and iron offer excellent mechanical properties for a wide range of applications. Apart from cast iron of all types (ductile, gray, white, white, S.G., etc.), the casting process can also work on aluminium, ceramics and even synthetic material. What makes casting popular is that it can eliminate the requirement for added assembly and fabrication. Casting offers exceptional capability for design details and customization. It uses moulds to shape the molten metal in the desired shape. Casting is a procedure to manufacture finished steel and iron products and components in a foundry.
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