Manufacture of insulating firebrick

Claim 1

THE METHOD OF PRODUCING LIGHTWEIGHT INSULATING FIREBRICK PRODUCTS CONSISTING ESSENTIALLY OF THE STEPS OF: (A) PREPARING A DRY BLEND OF LIGHT INSULATING FIREBRICK CONSTITUENTS COMPRISING CLAY, GYPSUM PLASTER AND SAWDUST; (B) ADMIXING THE DRY BLEND WITH WATER FORMING THE SAME INTO A FLOWABLE, CASTABLE PLASTIC MASS AND INCITING HYDRATION OF THE GYPSUM PLASTER; (C) CASTING THE WETTED PLASTIC MASS INTO SHAPED SLABS SIZED TO APPROXIMATE MULTIPLES OF THE DIMENSIONS OF THE DESIRED INSULATING PRODUCTS, AND UPON SUBSTANTIAL HYDRATION OF THE GYPSUM; (D) DRYING AND FIRING THE WET SHAPED SLABS BY SUBJECTING THE SAME IN AN ATMOSPHERE CONSISTING ESSENTIALLY OF AN OXIDIZING ATMOSPHERE TO UNINTERRUPTED AND UNIFORMLY PROGRESSING INCREASED AMBIENT TEMPERATURE CONDITIONS CULMINATING AT FIRING TEMPERATURES, THE SAID DRYING AND FIRING COMPRISING TRANSPORTING THE SHAPED SLABS WHILE WET INTO AND THROUGH A TUNNEL KILN WHEREIN THE INITIAL AMBIENT TEMPERATURES AT THE TUNNEL CHARGING END ARE MAINTAINED AT AT LEAST APPROXIMATELY 1000*F. AND THE AMBIENT TEMPERATURES THEREAFTER INCREASE UNIFORMLY AND PROGRESSIVELY UNTIL ATTAINING FIRING TEMPERATURES OF ABOUT 2350*F. TO APPROXIMATELY 2500*F., THE TRANSPORTATION OF THE SHAPED SLABS THROUGH THE TUNNEL BEING AT A SUBSTANTIALLY UNIFORM RATE PROVIDING THE ATTAINMENT OF THE AREA OF FIRING TEMPERATURES OVER A PERIOD OF ABOUT 2 TO ABOUT 12 HOURS WITH SAID PERIOD OF HEATING VARYING PROPORTIONATELY WITH THE TEMPERATURES AND A DWELL PERIOD AT FIRING TEMPERATURES OF APPROXIMATELY 2 TO APPROXIMATELY 6 HOURS; AND (E) CUTTING AND TRIMMING THE FIRED SLABS INTO INSULATING PRODUCTS.