What is foundry sand?
Foundry grade chromite sand is a complex compound of various elements; chromium (Cr2O3), aluminium (Al2O3), silica (SiO2), and magnesium oxide (MgO).
High melting point
Low thermal expansion
Not wetted by molten metals
Resistance to metal penetration
High heat tolerance
Resistant to thermal shock
Increased dimensional stability
Resistance to acid slag
Foundry sand applications
Chrome sand is the perfect material for hot metal casting, it is also an excellent ladle filler preventing contact between the molten steel and the ladle slide gate system. Chrome sand is also used in the production of magnesite chrome refractory bricks which usually contain over 33% of chromium and in the manufacture of chrome conundrum refractory bricks, providing resistance to abrasion and high temperature.
Chrome sand is extensively used in casting molds given its high thermal conductivity and low thermal expansion properties.
Chrome foundry sands used as a ladle filler
Chrome flour and chrome sand, as refractories, are a crucial part of ladle sand.
Continuous casting relies upon ladles to move molten metal from the furnace to where they are to be casted, such ladles (often referred to as pots) are large pieces of equipment that are lined with refractory materials so as to avoid solidification of the metal. A key feature of the ladle is the slide gate, which allows the molten metals to be released from the ladle into its next process.
The slide gate can become blocked by solidified metal, which causes a backing up of production and a potential explosion once the gate/tap is freed and opened again. To prevent this, filler sand (also commonly referred to as ladle sand) is used to keep the molten metal away from the slide gate, thereby preventing blockages. The slide gate leads to the nozzle, through which the molten metal leaves.
Ladle sand is a type of compound sand used to protect the tap/slide gate at the egress point of the ladle, and at other points throughout the pot. As a refractory material, often containing quartz and other high performing refractories such as chrome sand, filler sand has an excellent tolerance for temperature and a low reactivity with the molten metal.
Usually ladle sands are made with high quality chrome sand and flour and refined quarts sands. The addition of chrome refractories enhances the performance of the overall sand.
A ladle is used in the foundries to receive molten metal or steel and to move it between the furnace and where it is to be casted into a mould. The metal is at extremely high temperatures and is liquid. At the opening of the slide gate, most of the casting ladle sand will flow out from both the nozzle and the area around the gate, while the ferrostatic pressure in the ladle which is being exerted by the steel will cause the sintered layer to break, thereby releasing the molten metal.
Chromate has a high melting point and high thermal conductivity which gives it the ability to better distribute temperature through the sand. It is known for its high refractoriness and broad tolerance to thermal and mechanical shock, in addition to a resistance to chemical attack.
As a premium refractory, chrome sand and chrome flour are known for their ability to withstand high temperatures for lengthy periods of time. Filler sands containing chrome type refractories are known for their appropriate fluidity, high density and a resistance to over sintering.
Chrome flour and chrome sand are often regarded as some of the best refractories for ladle sand owing to their wide-ranging performance.
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Included in this section
Chrome’s colourful history
Photo credits: Rand York Minerals (Pty) Ltd.