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.
Properties
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.
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