Chrome sand is used in the production of chrome magnesite refractory bricks, which are used in the construction of certain furnaces and kilns. Due to its highly corrosion-resistant nature, chrome sand is also used to produce magnesia chrome refractories that are used in non-ferrous metals like copper, lead, and zinc.
In stainless steel production, filler sand made with chrome sand prevents molten steel from settling inside tap holes and solidifying. The chrome sand allows this solution to be effective at high temperatures with long processing times.
- Stable at high temperatures
- Thermal-shock resistant
- Resistant to corrosive slags and gasses
- High refractoriness/heat resistance
- Cr203 of typically 44%
- Al2O3 of 15%
- Chrome content between 15% and 35% Cr203 (Magnesite chrome refractory bricks require 8% to 18% Cr203)
Refractory bricks made with chrome sand are suitable for use in:
- Open earth furnaces
- Electric arc furnaces
- Metallurgy furnaces
- Cement rotary kilns
- Glass kilns
- High-temp industrial furnaces
African Pegmatites chrome is trivalent chromium (Chrome III), not hexavalent (Chrome VI). Hexavalent chrome is a hazardous carcinogen that is heavily regulated. African Pegmatite’s chrome is environmentally friendly and safe when precautions are taken to avoid oxidation, which can produce Chrome VI.
Ladle Filler Sand
Ladle filler sand is a combination of raw materials that prevent molten metal from coming into contact with the slide-gate system or solidifying in the taps of certain moulds. Continuous casting requires the opening of a slide gate system. If this becomes blocked by solidified steel, productivity comes to a halt and there’s a risk of a violent expulsion when the tap is freed again. To free the tap it becomes necessary to use an oxygen lance, which is slow and damages the refractory materials. When all is said and done, the solidification of metal against the slide-gate system or inside the taps is a costly malfunction.
Molten steel is kept away from the slide gate system and taps by filler sand made with chrome sand. Effective filler sand will have high heat resistance, consistent particle-size distribution, consistent density, low thermal expansion, good flowability, and the ability to form a thin, sintered crust when in contact with molten metal. Rapid sintering is preferred because it inhibits the permeation of steel into the nozzle.
Difficulties in removing the sand are often caused by imperfect sintering. If sand blocks the nozzle, oxygen burning must be used to clear it. This process lowers the quality of the steel and generally makes the entire process more difficult. The sintered layer cannot be too thick or high pressure will be needed to open the ladle. If it’s too thin, the nozzle will become clogged.
Placing filler sand into the nozzle is either done by separating the sand into several bags and throwing it into the centre of the tap or placing a metal tube over the tap hole and pouring the sand in to cover the sliding gate system.
Filler sand made primarily with chrome ore is called chromite-based sand. Its advantages include good fluidity, high density, high melting point, and resistance to over-sintering. At high temperatures, the FeO component of chrome sand forms a secondary spinel that changes the volume of the sintered layer. This can cause cracking when the slide gate is opened.
Upon opening the slide gate, the unsintered chrome sand in the lower part of the nozzle should easily fall out. This should form cracks on the sintered layer, which should then break under the static pressure of the steel. Most steel plants today are using chrome sand in their nozzle sand because of its superior performance when compared to other options.
Magnesite chrome refractory bricks usually contain at least 33% chromium III oxide. Magnesite chrome refractory bricks are used in the electric furnaces, open-hearth furnaces, finery forges, and other furnaces for non-ferrous metals. Fused cast magnesite chrome brick is used inside the walls of electric arc furnaces, in the burning zones of rotary cement kilns, and the regenerative chamber of glass furnaces.
If significant erosion is likely to occur in non-ferrous metals inside a flash smelting furnace, magnesite chrome brick of synthetic compost and fused cast magnesite chrome brick can be used to counteract it. The same is true of potential erosion within a finery forge.
Chrome sand is used in another type of refractory brick known as a chrome conundrum refractory brick. This type of brick is most often used in electric furnaces and volatising kilns for zinc smelting, for copper smelting furnaces, and in certain areas inside metallurgical furnaces where there is a likelihood of abrasion.
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