Refractories

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RefractoriesCeramic materials that are capable of withstanding high temperatures, resistant to thermal shock, chemically inert, and have low thermal conductivities and coefficients of expansionUsed to line furnaces and keep heat within the furnace heart (metal smelting, glass production, ceramic component manufacture)

Requisites of a good refractory materialDependent on operating factors such as:-Temperature-Atmosphere-Materials to be in contact with

Type of Material to be in contact withType of material the a refractory come into contact with can also dictate which materials are suitablesteel making-uses basic refractory-acidic refractory (silica) will be eroded quickly by the basic slag forming low melting point compoundsRaw materials usedOxide refractories:SiliconAluminumMagnesiumCalciumZirconium

Non-oxide refractories:CarbidesNitridesBoridesGraphites

Properties of RefractoriesAny refractory should withstand very high temperature with any deformation or softeningCan withstand adequate load during working in kilns or furnacesAble to withstand abrading action of furnace charge

4. Should withstand spalling during any process5. Dimensional stability and chemical inertness6. Have either low or high thermal conductivities7. Comes in range of different densities and porosities8. Materials of low electrical conductivity are generally used for lining in furnaces

Classification of RefractoriesAcid -Silica Bricks, Fire clay bricksBasic Magnesia Bricks, Bauxite BricksNeutral Chromite, silicon carbide, graphite, mullite

Acid RefractorySilica Most abundant material in earths crustRaw material for manufacture of glass and ceramicsSources: sandstone, silica sand or quartziteGood abrasion resistanceElectrical insulation High thermal stability (Behaves like an acid when reacted to base at high temperatures) Insoluble in majority of acidsBasic RefractoryProperties:-good corrosion resistance-high thermal conductivity-low electrical conductivity-transparency to infraredApplication:-Steel industry as a refractory brick impregnated with carbon-In Glass cement industries in combination with spinel or chrome-Castables and sprayables based on magnesia used for basic refractory for steel transfer applicationsManufacture of RefractoriesCrushing and Grinding the material in crushed and grounded well to a proper size and sieved to a particular uniform size

2. Screening -the materials are subjected to different physical, chemical and magnetic methods to free from unwanted impurities

3. Mixing it is subjected to mixing for equal distribution of plastic materials throughout the mass so that molding would be easy

4. MoldingHand Moldinghand molding gives low density and strengthMechanical MoldingProduces refractories of high strength and density-de-airing is desired to increase the density and strength

5.Dryingthe removal of water/moisture -carried out at very slow and in particular set of conditions of humidity and temperature

Manufacture of Fireclay/kaolinStorage of procured clay to weather for a yearGrinding the weathered clay is mixed with grog and sent to the grinding millMilling a suitable water is added to give proper elasticityMoldingmold is supplied to different mahicines for making standard brick or shapes-intricate shapes are made by hand5. Drying in hot floor driers6. Firing of the clay in kilns7. Cooling kilns are allowed to be cooled8. Unloading of the bricks