GB790366A - Improvements in or relating to refractory bricks, shapes and blocks - Google Patents

Abstract

Flint containing 98 per cent silica on analysis after ignition is calcined to yield silica suitable for use in pottery, the calcined flint is crushed to less than 20 mm. size, and screened to remove the finer and softer material from the residue exceeding a predetermined minimum size (selected in the range 3.5 mm. to 8 mm.) up to the maximum size, and the residue is used to provide at least the coarse and medium grain silica in the manufacture of refractory bricks. Flint is calcined in a shaft kiln with coal at 600-1200 DEG C., or in a gas-fired kiln at 750 DEG C., such kilns being those normally used for calcining flint for pottery. The calcined product, after removal of coal ash by forking or riddling, and after picking out uncalcined flint and unburnt fuel, is crushed and the separated preponderating proportion of finer and softer material is further crushed for use in pottery. The selected material is crushed to produce coarse grain (3.5 mm.-0.5 mm.) medium grain (minus 0.5 mm.) and fine flour (at least 70 per cent minus 0.1 mm.). The proportions of coarse and medium grain, and fine flour are adjusted as necessary for refractory bricks, by further crushing and/or screening and blending. Thus part of the selected material may be further crushed to make up fines deficiency. Alternatively, the fines used may be wholly or in part raw (uncalcined) flint fines with consequent saving of coarse and medium grain selected material. The coarse and medium grain and fines are kneaded, and lime (hydrated, putty, or milk) and sulphite lye temporary binder are added. The resulting mixture is moulded, dried, and fired to cause inversion to cristobalite on the following schedule: up to 500 DEG C. at 10-15 DEG C. per hr., 500-650 DEG C. at 5-7 DEG C. per hr., 650-1000 DEG C. at 10-15 DEG C. per hr. 1000-1100 DEG C. at 5-7 1/2 DEG C. per hr. and 1100 DEG C.-maximum at 3-5 DEG C. per hr. The maximum temperature is 1310-1330 DEG C. Ferric oxide may be added to the mixture before moulding, or a solution of ferrous sulphate, ferric chloride or nitrate, or manganous sulphate may be added from which the oxide is precipitated by the lime present. Specification 755,515 is referred to.ALSO:Flint containing 98 per cent silica on analysis after ignition is calcined to yield silica suitable for use in pottery, the calcined flint is crushed to less than 20 mm. size, and screened to remove the finer and softer material from the residue exceeding a predetermined minimum size (selected in the range 3,5 mm. to 8 mm.) up to the maximum size, and the residue is used to provide at least the coarse and medium grain silica in the manufacture of refractory bricks. The calcined product, after removal of coal ash by forking or riddling, and after picking out uncalcined flint and unburnt fuel, is crushed and the separated preponderating proportion of finer and softer material is further crushed for use in pottery. The selected material is crushed to produce coarse grain (3,5 mm.-0,5 mm.) medium grain (minus 0,5 mm.) and fine flour (at least 70 per cent minus 0,1 mm.). The proportions of coarse and medium grain, and fine flour are adjusted as necessary for refractory bricks, by further crushing and/or screening and blending. Thus part of the selected material may be further crushed to make up fines deficiency. Alternatively, the fines used may be wholly or in part raw (uncalcined) flint fines with consequent saving of coarse and medium grain selected material. The coarse and medium grain and fines are kneaded, and lime (hydrated, putty, or milk) and sulphite lye temporary binder are added. The resulting mixture is moulded, dried, and fired to cause inversion to cristobalite on the following schedule: up to 500 DEG C. at 10 DEG -15 DEG C. per hour, 500 DEG -650 DEG C. at 5 DEG -7 DEG C. per hour, 650 DEG -1000 DEG C. at 10 DEG -15 DEG C. per hour, 1000 DEG -1100 DEG C. at 5 DEG -7 1/2 DEG C. per hour and 1100 DEG C.-maximum at 3 DEG -5 DEG C. per hour. The maximum temperature is 1310 DEG -1330 DEG C. Ferric oxide may be added to the mixture before p moulding, or a solution of ferrous sulphate, ferric chloride or nitrate, or manganous sulphate may be added from which the oxide is precipitated by the lime present.