In addition to its use in foundry casting moulds, chrome ore sand is used in the steel industry to protect tap holes in steelmaking ladles. The chrome ore sand used in this application is known as nozzle sand base.
After it has been decarburised in a basic oxygen furnace (BOF) or an electric arc furnace (EAF), molten steel is transferred to a ladle, where the chemistry of the steel is adjusted exactly to the required specifications. Unwanted impurities form a slag which floats to the top of the ladle, with pure molten steel sinking to the bottom. At the bottom of the ladle is a taphole, through which the molten steel is removed once the correct chemical specification has been attained. The taphole is usually covered from the outside by a sliding gate. If molten steel gets into the taphole it can often begin to solidify and block up the hole, therefore it is necessary to fill up the taphole with sand prior to molten steel being placed into the ladle. Sand used to fill steelmaking ladle tapholes is known as "nozzle sand". When it is time to remove ("tap") the molten steel from the ladle, the slide gate over the taphole is opened and the nozzle sand falls out, followed by the liquid steel.
The physical properties of chrome ore sand – its high melting point, good thermal conductivity, and resistance to thermal shock, burn-on and slag attack – make it an excellent material for use in nozzle sand, ensuring a wide taphole opening even when the temperature of the molten steel is high and the processing time in the ladle is long. For maximum performance, chrome ore nozzle sand is often blended with silica sand and/or graphite.
Clover Alloys produces nozzle sand, in addition to foundry sand and metallurgical chrome ore, at its Benoni plant in South Africa.
Typical specifications for Clover Alloys nozzle sand are as follows: