GB755514A - Improvements in or relating to the preparation of silica suitable for use as a refractory and refractory bricks, shapes, and blocks made therefrom - Google Patents

Abstract

Silica for use in refractories is prepared by calcining flint containing on analysis after ignition at least 98.5 per cent silica, preferably more than 99 per cent, at a rate of temperature rise of 40 DEG -80 DEG C. per hour maintained within limits of \sB5 DEG C., until a temperature of 700-950 DEG C., preferably 800 DEG C., is reached, which temperature is maintained within limits of \sB25 DEG C. until at least three-quarters of the combined water has been removed. As a modification when grey flint is calcined, the maintained temperature may be 500-700 DEG C., preferably 600 DEG C. The rate of temperature rise for grey flint is 60-80 DEG C. and for black flint 40-60 DEG C. The calcining may be effected as a continuous moving bed in a bogie type kiln. The calcined material is crushed, ground and screened. Coarse grain (3.5-0.5 mm.), medium grain (0.5 mm. and less), and fine flour (at least 70 per cent 0.1 mm. size) of the calcined flint is kneaded with lime (hydrated, putty, or milk) and sulphite lye temporary binder, and moulded into bricks. The bricks are fired on the following schedule:-Up to 500 DEG C., 10-15 DEG C. per hour; 500-650 DEG C., 5-7 DEG C. per hour; 650-1000 DEG C; 10-15 DEG C. per hour; 1000-1100 DEG C.; 5-7 1/2 DEG C. per hour; 1100-1310 to 1330 DEG C., 3-5 DEG C. per hour; and soak for some time at the maximum temperature to effect complete conversion to cristobalite. A metal oxide, e.g. 0.6 per cent Fe2O3, may be added to the kneaded material to increase the strength, or preferably an oxide may be precipitated by the lime by adding a metal salt solution, e.g. ferrous sulphate, as described in Specification 755,515.ALSO:Silica for use in refractories is prepared by calcining flint containing on analysis after ignition at least 98.5 per cent silica, preferably more than 99 per cent, at a rate of temperature rise of 40 DEG -80 DEG C. per hour maintained with limits of \sB5 DEG C., until a temperature of 700 DEG -950 DEG C., preferably 800 DEG C., is reached, which temperature is maintained with limits of \sB25 DEG C. until at least three-quarters of the combined water has been removed. As a modification, when grey flint is calcined the maintained temperature may be 500 DEG -700 DEG C., preferably 600 DEG C. The rate of temperature rise for grey flint is 60 DEG -80 DEG C. and for black flint 40 DEG -60 DEG C. The calcining may be effected as a continuous moving bed in a bogie-type kiln. The calcined material is crushed, ground and screened. Coarse grain (3.5-0.5 mm.) medium grain (0.5 mm. and less), and fine flour (at least 70 per cent 0.1 mm. size) of the calcined flint is kneaded with lime (hydrated, putty, or milk) and sulphite lye temporary binder, and moulded into bricks. The bricks are fired on the following schedule: Up to 500 DEG C., 10 DEG -15 DEG C. per hour; 500 DEG -650 DEG C., 5 DEG -7 DEG C. per hour; 650 DEG -1000 DEG C., 10 DEG -15 DEG C. per hour; 1000 DEG -1100 DEG C., 5 DEG -7 1/2 DEG C. per hour; 1100 DEG -1310 DEG C. to 1330 DEG C., 3 DEG -5 DEG C. per hour; and soak for some time at the maximum temperature to effect complete conversion to cristobalite. A metal oxide, e.g. 0.6 per cent Fe2O3, may be added to the kneaded material to increase the strength, or preferably an oxide may be precipitated by the lime by adding a metal salt solution, e.g. ferrous sulphate, as described in p Specification 755,515.