A group of refractory clays which can stand temperatures above Pyrometric Cone Equivalent (PCE) 19 are called fireclay. Fireclay is essentially of kaolinite group and has a composition similar to that of china-clay. In nature it is usually found to contain 24-32 per cent Al2O3, 50-60% SiO2 and LOI between 9 to 12% and is white, grey and black in colour.
A good fireclay should have 24-26% plasticity and shrinkage after firing should be within 6-8% maximum. It should also not contain more than 25% Fe2O3.
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Industrial Applications
Because of the abundant supply of fireclay and its comparative cheapness, the refractory bricks made out of it are the most common and extensively used in all places of heat generation, like:
in boiler furnaces
glass melting furnaces
chimney linings
pottery kilnsblast furnaces
reheating furnaces
Fireclay is classified under acid refractories as they are unhurted by acid slag. In blast furnaces, the lining is done almost entirely with fireclay bricks. Pouring refractories like sleeves, nozzles, stoppers and tyres are made of fireclay.
