Improvements in and relating to the manufacture of cement

摘要

508,736. Cement; calcium sulphate. SOC. ANON. DES CIMENTS DE THIEU, and BLONDIAU, L. April 19, 1938, No. 11790. Convention date, April 17, 1937. Addition to 437,855. [Class 22] [Also in Group III] Cement containing calcium sulphate is obtained by mixing or grinding the constituents of the cement with gypsum which has been calcined in a slightly reducing atmosphere at 900-1200‹ C. Rock gypsum may be calcined in the presence of 0. 5-1 per cent of coal, or calcination be effected in a rotary kiln in a flame containing 0.5 per cent of pulverized coal, or a carbon monoxide flame may be used. A short period of calcination, say 5-15 minutes, is preferred as decomposition of the sulphate is thereby avoided. The invention is particularly applicable in the production of blast furnace slag cements rich in calcium sulphate but may also be used in the production of Portland cements containing only small quantities of sulphate.