Chromite Sand

Acid washing, benefaction and classification create stable resin set times, maximising heat transfer characteristics, mould densities and dimensional accuracy. While minimising resin additions, gas evolution, burn on/penetration and inhibit the formation of double skin effects.

Chromite sand has received increasing attention sine the late 1950's as a very effective moulding material for a variety of different reasons:

• Low thermal expansion.
• High thermal conductivity.
• Good refractoriness.
  

Chromite is FeCr2O4, a natural oxide of ferrous iron and chromium, usually with magnesium and aluminium present. It usually occurs in magnesium and iron-rich igneous rocks. Commercial qualities and quantities are available in the former USSR, South Africa, Zimbabwe, Cuba, Turkey, and Finland. When Chromite and finely divided aluminium and carbon are heated, chromium is reduced. All our Chromite is mined in South Africa.

Chromite spinel sand is the sand size fraction removed from the Chromite ore and because of its grain size is not commercially practical for reducing Ferro-chromium alloys.

Ideally for foundry use the chromium (Cr2O3) content should exceed 46% and iron (Fe2O3) no more than 33% of the percentage of chromium to make smelting attractive. The table below shows a typical chemical analysis as supplied by Rand York.

This is the material commonly used in foundries:

Turbidity (impurities)

Turbidity is a measure of the colloidal particles within the raw Chromite sand. It is measured in ppm and is a reflection of the amount of tramp material present. The lower the turbidity, the cleaner the sand. When turbidity is high (i.e. > 150 ppm) then more fayelite can be formed at the mould-metal interface, giving rise to double skinning or Chromite frit.

Our turbidity is due to our washing techniques on site in South Africa.

We are able to ship world wide from our plant in 50, 1000, and 1500kg bulk bags