Special sands

Chromite sand is used for its high thermal resistance, fast chilling capacity and resistance to liquid metal penetration. Its thermal expansion is uniform and clearly lower than that of silica sand thus finning problems are minimised. Chromite sand is provided with a size of 45 - 65 AFA and a typical composition of Cr₂O₃: 46%, FeO: 27%, Al₂O₃: 15% and MgO:10%.

It is compatible with all binding systems and steel castings, being specially appropriate for chromium, chromium-nickel and manganese steel casting. When compared to silica sand, it is less reactive with MnO thus calcination problems are reduced.

Olivine special sand is available in different sizes and is particularly appropriate for mould and coremaking. Its inherent alkalinity makes it applicable in manganese steel casting, being less reactive with MnO than silica sand. Olivine sand thermal expansion is lower than that of silica sand and its high thermal shock resistance furthermore reduces sand expansion problems. Foundry quality is supplied with 50–60 AFA size and typical composition is MgO: 48%, SiO₂: 41% and Fe₂O₃: 8%. Granulated olivine of 2-6 mm is used in the iron and steel industry as taphole filler in bottom (EBT and OBT) and lateral electric furnaces. SiO₂ in sand is not free but combined as magnesium orthosilicate (Mg₂SiO₄) which ensures minimal steel silicon uptake.

Olivine sand with 100–120 AFA size is used as raw material in the refractory industry for gunite manufacturing ultimately applied in the iron and steel industry.

Zirconium sand presents excellent refractory properties, low thermal expansion and high thermal conductivity. It is made of zirconium silicate (ZrSiO₄) and has a bulk density of 2,7 g/cm³. Zirconium sand is used in manufacturing moulds and cores subject to high thermal stress like those used in steel or mass iron castings. Its inherent properties eliminate or minimise veining problems, avoid metal-mould cross reactions and increase metal cooling speed.

Cerabeads is a synthetic sand composed of aluminium silicate (3Al₂O₃2SiO₂) with excellent refractory properties, high permeability and thermal expansion similar to that of zirconium sand. It is supplied as highly-fluid round 65 AFA size particles with 1,7 g/cm³ bulk density. Cerabeads is compatible with all binders and is especially recommended for steel alloys or cores subject to high thermal stress conditions such as oil inlets in combustion engines.

Bauxite sand is mainly (75%) composed of aluminium oxide (Al₂O₃). This synthetic sand presents excellent refractory properties and a thermal expansion similar to Chromite sand. It is marketed in different sizes though normally supplied with 65 AFA size and 2 g/cm³ bulk density. Its magnetic properties enable its separation from silica sand. Furthermore, Bauxite sand gives high mechanical strength to moulds in Cold Box, Hot Box and No-bake furan systems. It is often used as Zirconium sand substitute in steel applications.

Sand grade	Linear thermal expansion [10-6·K-1]
	20 – 300ºC	20 – 600ºC	20 – 800ºC
Silica	14.0	23.0	17.0
Chromite	7.1	7.5	7.5
Zirconium	3.4	4.1	4.5
Cerabeads	3.5	4.0	4.3
Bauxite	7.1	7.3	7.2