MAGNESIA-SPINEL BRICKS FOR THE CEMENT INDUSTRY

Over the past 10 years magnesia-spinel bricks have replaced magnesia-chrome bricks as the lining for the basic zone in the majority of rotary cement kilns. With the varied range of magnesia-spinel bricks now used it is possible to differentiate, on the basis of the type of sintered magnesia employed, between bricks based on synthetic sintered magnesia for very severe stresses and less expensive bricks based on natural sintered magnesia. During the development of new types or improvement of existing ones particular attention is given to the thermomechanical properties (deformation behaviour, alternating load, flexibility of microstructure). Tests are carried out in a laboratory rotary kiln under conditions resembling those found in practice to check the chemical resistance. An evaluation of investigations carried out on used bricks shows that the critical zone in the basic region is the lower transition zone. The most important wear factors (clinker melt infiltration, alkali sulphate and chloride attack, mechanical overloading) are described using examples taken from practice. Lining schemes suited to the particular stresses are then described and the direction of current developments is discussed.