Refractories are materials which withstand high temperature and do not fuse even at very high temperature. The refractories may be classified depending upon their chemical properties. These are acidic refractory, basic refractory and neutral refractory. Acidic refractories react with basic chemicals and are used for acidic composition of slag. Basic refractories react with acidic materials and used for basic slag condition. Neutral refractories may be used for all types of slag conditions. Fire clay, quartz, sand stone and riverbed silica sands are used for production of acidic refractories. Acidic refractories are used when the iron ore is free from phosphorus and sulphur content. The basic refractories are manufactured using bauxite, limestone, dolomite and magnesite. Neutral refractories are manufactured by using chromite, graphite and asbestos minerals like silimanite and kyanite
Good quality refractories are to be chosen for the blast furnace and steel making furnace. The refractories should be able to withstand high temperature conditions. It should be resistant to corrosion of slag, flu gases and flames. It should be able to withstand stress and strain conditions inside the furnace. A good quality refractory may be able to check the heat loss and promote heat transfer in the furnace. No single refractory material can meet all these requirements. So, the selection of refractories for any particular application is made with a view to achieve the best performance. The nature and quality of the refractories has to be decided on the service conditions of the plant. The user has to consider the natures of the refractories before selection for use. The area of application, working temperature and nature of abrasion are to taken into consideration. The structural load of the furnace, heat transfer, heat conservation, temperature fluctuations and temperature gradient are to be considered before consideration of any refractories. The chemical compatibility to the furnace environment is also very important for consideration. Further, the cost and longevity of the refractories are to be considered before selection of the refractories. Fuel conservation, insulation and faster firing also influence the selection process of the refractories.
The refractories are manufactured for specific uses. But the general process of manufacturing is similar for all the refractories. The refractories materials are to be pretreated and properly dried. These materials are crushed and mixed with water and other chemicals. Molding of refractory bricks is carried out and shifted to drying areas. After proper drying, the bricks are fired and cooled. Good quality refractory bricks are picked for use in the furnace.