Fire-Clay Bricks Or Refractory Bricks
Fire-clay bricks are made from fire-clay. The process of manufacturing is as of an ordinary brick, burnt at very high temperatures in special kilns (Hoffman's kiln). The raw materials used for the manufacture of fire bricks consist of flint clay and grog (burnt fire clay) as non-plastic materials and soft fire clay as plastic material. Fire clay mortar is used to clay rerfractory bricks.
1.The colour is whitish yellow or light brown.
2.The water absorption of fire-clay bricks varies from 4-10%
3.The minimum average compressive strength of the bricks should be 3.5 N/mm2.
Uses These are used for lining blast furnances, ovens, kilns, boilers and chimneys. The principal varieties of fire-clay bricks are as follows:
Acid Refractory Bricks consist of silica bricks (95-97% silica and 1-2% lime) and ganister bricks (ganister-a hard coloured sand stone containing 10 per cent clay and 2 per cent of lime), used in lining furnaces having siliceous and acidic slag, steel industry and coke oven. The softening temperature ranges from 1700 o to 1800 o C. Silica bricks are hard and also possess good refractoriness under load. But they have tendency to spall during rapid temperature change therefore, these can not be used for lining of furnaces which have to be cooled and reheated frequently.
Basic Refractory Bricks consist of magnesia bricks (magnesia minimum 85 per cent, calcium oxide maximum 25 per cent and silica maximum 5.5 per cent) and bauxite bricks (minimum 85 per cent aluminium oxide and maximum 20 per cent clay). These are highly resistant to corrosion and are used for lining furnances having basic slag. Due to high thermal expansion and consequent poor resistance to spalling the use of these bricks is retricted to copper metallurgy and basic open hearth testing machine. A 75 × 100 × 300 mm block is placed over the ridge of the tile and a load of 2.7 kN/min is applied on the block. The breaking load of individual tile is noted. It is divided by the length of tile. The results are reported in N/mm.