Chrome Sand

General Information

African Pegmatites chrome is trivalent chromium (Chrome III), not hexavalent (Chrome VI). Hexavalent chrome is a hazardous carcinogen that is heavily regulated. African Pegmatite’s chrome is environmentally friendly and safe when precautions are taken to avoid oxidation (see below).

Casting Moulds

Chrome sand is a naturally-occurring mineral that consists of iron and chromium oxides. Due to its high stability in extreme conditions, it is suitable for use in iron and steel foundries. Chrome sand is mixed with a binder to make casting moulds that are used in the manufacturing processes of metal products. The high thermal conductivity of chrome refractory sand allows it to perform well in specialized castings like automotive engine blocks.

The thermal conductivity also helps the castings cool quickly, which reduces the risk of penetration of the mould’s surface. Low thermal expansion is vital to the required stability of casting moulds. The basicity of chrome sand is close to neutral, so resin bonding materials and inorganic binders are often used.

Chrome Sand Foundry Application

The properties of chrome sand allow it to be used effectively in grey iron and steel foundries both as a core and a mould-making sand.

Green Sand

Green sand is not green in colour. It gets its name from that of green wood because, like green wood, it contains moisture. When the molten metal is poured into the mould, the moisture in the green sand is dried.

Green sand consists of chrome sand and a mixture of other ingredients. Depending on the application, the other ingredients may include silica sand, zircon sand, anthracite or coal dust, inert sludge, water, clay, graphite, staurolite, or olivine.

Silica tends to be the least desirable option because its grains are prone to explosion. The microscopic particles that are formed by these explosions place workers at risk of health risks like silicosis. Chrome sand doesn’t explode and so does not pose the health risks associated with microscopic particles. Chrome sand will also cool the metal faster than silica, which helps in avoiding certain casting defects.

The type of sand used in a mould is highly dependent on the temperature to be applied.

Ladle/Nozzle/Filler Sand

During the continuous casting of steel and some other metal casting processes, it is necessary to employ a refractory sand to prevent the molten metal from coming into contact with the taps and slide-gate systems.

The slide-gate system controls the flow of the molten steel or metal from the teeming ladle to the turn dish. If the slide-gate or taps become blocked, an oxygen lance must be used to free them. This can result in a dangerous expulsion of pressure and will certainly delay production.

Chrome sands are the most widely-used type of filler, ladle, or nozzle sands. These sands must be refractory and have a particular particle-size distribution, density, thermal expansion, and flowability.

Another crucial factor is the sintering ability of the sand. Sintering is the forming of a solid mass without liquification. The sintered layer of the sand has to be a particular thickness so that the pressure of the cast metal will easily break through it when the filler sand is released from the tap.

Refractory Bricks for Foundry

Chrome sand is a major component in refractory bricks that are used in the foundry industry to line furnaces, fireplaces, kilns, ovens, and other high-heat environments. The bricks must be able to withstand temperatures over 1700° C, have excellent thermal shock resistance, and have both acid and basic slag erosion resistance.

Specific applications of magnesite chrome refractory bricks include electric furnace tops, open-hearth furnace tops, finery forges, inside walls of electric arc furnaces, burning zones of rotary cement kilns, regenerative chambers of glass furnaces, erosion areas of flash smelting furnaces, erosion areas of finery forges, other furnaces for non-ferrous metals.

Another type of brick made with chrome sand is the chrome conundrum refractory brick. This type of brick has the same properties as the magnesite chrome bricks. Applications include electric arc furnaces and volatising kilns for smelting zinc, copper smelting furnaces, metallurgy furnaces prone to abrasion and high temperatures.