Editing Sand casting (section)

====Types of base sands====
''Base sand'' is the type used to make the mold or core without any binder. Because it does not have a binder it will not bond together and is not usable in this state.<ref name="rao19"/>

=====Silica sand=====
[[File:Silica Sand.jpg|thumb|150px|Silica sand at [[Panavally]]]]
[[Silica]] (SiO<sub>2</sub>) sand is the sand found on a beach and is also the most commonly used sand. It is either made by crushing [[sandstone]] or taken from natural occurring locations, such as beaches and river beds. The [[fusion point]] of pure silica is {{convert|1760|C|F}}, however the sands used have a lower melting point due to impurities. For high melting point casting, such as steels, a minimum of 98% pure silica sand must be used; however for lower melting point metals, such as [[cast iron]] and [[non-ferrous]] metals, a lower purity sand can be used (between 94 and 98% pure).<ref name="rao19"/>

Silica sand is the most commonly used sand because of its great abundance, and, thus, low cost (therein being its greatest advantage). Its disadvantages are high [[thermal expansion]], which can cause casting defects with high melting point metals, and low [[thermal conductivity]], which can lead to unsound casting. It also cannot be used with certain [[base (chemistry)|basic]] metals because it will chemically interact with the metal, forming surface defects. Finally, it releases silica particulates during the pour, risking [[silicosis]] in foundry workers.<ref name="rao20">{{harvnb|Rao|2003|p=20}}.</ref>

=====Olivine sand=====
[[Olivine]] is a mixture of [[orthosilicate]]s of iron and magnesium from the mineral [[dunite]]. Its main advantage is that it is free from silica, therefore it can be used with basic metals, such as manganese steels. Other advantages include a low thermal expansion, high thermal conductivity, and high fusion point. Finally, it is safer to use than silica, therefore it is popular in Europe.<ref name="rao20"/>

=====Chromite sand=====
[[Chromite]] sand is a [[solid solution]] of [[spinel]]s. Its advantages are a low percentage of silica, a very high fusion point ({{convert|1850|C|F}}), and a very high thermal conductivity. Its disadvantage is its costliness, therefore it is only used with expensive [[alloy steel]] casting and to make cores.<ref name="rao20"/>

=====Zircon sand=====
[[Zircon]] sand is a compound of approximately two-thirds [[zirconium oxide]] (ZrO<sub>2</sub>) and one-third silica. It has the highest fusion point of all the base sands at {{convert|2600|C|F}}, a very low thermal expansion, and a high thermal conductivity. Because of these good properties it is commonly used when casting alloy steels and other expensive alloys. It is also used as a [[mold wash]] (a coating applied to the molding cavity) to improve surface finish. However, it is expensive and not readily available.<ref name="rao20"/>

=====Chamotte sand=====
[[Chamotte]] is made by [[calcining]] [[fire clay]] (Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub>) above {{convert|1100|C|F}}. Its fusion point is {{convert|1750|C|F}} and has low thermal expansion. It is the second cheapest sand, however it is still twice as expensive as silica. Its disadvantages are very coarse grains, which result in a poor surface finish, and it is limited to [[#dry sand molding|dry sand molding]]. Mold washes are used to overcome the surface finish problems. This sand is usually used when casting large steel workpieces.<ref name="rao20"/><ref>{{harvnb|Rao|2003|p=21}}.</ref>