White cast iron and wear/abrasion resistant castings
White cast iron displays white fractured surfaces due to the presence of an iron carbide precipitate called cementite. It is too brittle for use in many structural components, but with good hardness and abrasion resistance and relatively low cost,
White cast iron castings possess high strength and excellent wear resistance. They are used in wear resistant applications such as grinding balls and grinding rings in coal pulverizers and grinding table segments, grinding roller liners, grinding table liners in vertical roller mills, teeth of a backhoe’s digging buckets, shell liners and lifter bars in grinding mills.
Wear/abrasion-resistant irons can be classified into five groups but the majority of castings used today are in two groups. One is the nickel containing alloys, known as Ni-Hard. The second white iron group contains high levels of chrome and is commonly referred to as Hi-Chrome iron. When toughness, abrasion-resistance and possibly corrosion resistance are required, the Hi-Chrome group of white irons is superior to Ni-Hard.
15% and 25% Hi-Chrome alloy iron is typically used in applications of wear resistance and long term heat resistance, such as impellers, turbines, and grinding applications. The iron expresses a very hard surface. These high-chromium alloys attribute their superior hardness to the presence of chromium carbides. The main form of these carbides are the eutectic or primary M 7 C 3 carbides. The eutectic carbides form as bundles of hollow hexagonal rods and grow perpendicular to the hexagonal basal plane. The hardness of these carbides is in the range of 1500-1800 HV.
Ni-Hard is a white cast iron, alloyed with nickel and chromium suitable for low impact, sliding abrasion for both wet and dry applications. Ni-Hard is an extremely wear resistant material, cast in forms and shapes which are ideal for use in abrasive and wear environments and applications.
Ni-Hard castings are produced with a minimum of 550 Brinell hardness. Hard white cast iron containing 4% Ni and 2% chrome, used for abrasive resistant and wear resistant applications in the industries of mining, earth handling, asphalt, manufacturing, and so on. Ni-Hard parts and components extend the life of products when compared to other cast iron or mild steel cast components. Ni-Hard castings are typically used in power generation, brick, asphalt, cement, concrete, rock, sand and gravel industries.
The grinding parts, grinding roller tyres and grinding table segments, are made from white cast iron (nickel chromium alloy). The grinding surface of the grinding roller tyres and of the grinding table segments are subject to wear due to the grinding operation. Because the material is very hard and sensitive to thermal shock, therefore, these grinding parts must prevent from collision, impact and heated.
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