Sand molded casting, popularly known as sand casting, is a metal casting process in which sand is used as the mold material. A factory where sand casting is carried out is known as a sand casting foundry. Sand casting has been used for a long time and different foundries use different base sands for the process. Each one of the base sands has its own characteristics and benefits.
Here are the different types of base sands used for sand casting:
Silica: One of the most commonly used base sands is silica sand. This sand can be easily found at the beach or river beds. Depending on the metals used, the foundries need sand of varying purity levels. For instance, they need minimum 98% pure silica sand for steel while for cast iron and non-ferrous metals, they can use silica with a purity of 94 to 98%. Being one of the most commonly found base sands, it is the most cost-effective to be used in sand casting.
Chamotte: The second most affordable base sands, Chamotte is made by calcining fireclay. Because of its coarse grains, Chamotte sand can only be used in dry sand casting. It has a high fusion point and low thermal expansion. Foundries that use chamotte for sand casting use a mold wash to improve the surface finish. Since it is relatively safer to use than silica and cost-effective than other types of base sands, it is widely used for casting large steel work pieces.
Olivine: Olivine sand is a mixture of magnesium and iron orthosilicates from the mineral dunite. One of the main reasons behind the popularity of Olivine sand in sand foundries is that it is free from silica and, therefore, safer to use. It offers high thermal conductivity and fusion points, and a low thermal expansion. Olivine sand is quite popular in Europe-based sand foundries.
Chromite: One of the expensive base sands used in foundries, Chromite sand is a solid solution of spinel, a group of minerals. It has a very high fusion point and thermal conductivity and can be easily used for alloy steel casting. It has a low percentage of silica. The only disadvantage is that Chromite sand is expensive. Many sand foundries still choose to use Chromite sand for metal casting.
Zircon: Two-third zircon oxide and one-third silica make Zircon sand one of the best casting sands for foundries. It has an extremely high fusion point, high thermal conductivity, and low thermal expansion. Zircon sand is really expensive and hard to find but it is still frequently used for casting expensive alloys because of its inherent qualities.
