Method of compressing ceramic refractory bodies

The method of compressing a porous block of ceramic refractory material to decrease its porosity and increase its strength, said compressing being carried out in a mold having inwardly movable side means to exert the compressing force on the block, said porous ceramic block being at a pyroplastic temperature in the range of about 1100.degree. to 1500.degree. C. during said compressing, wherein the improvement comprises:

• a. utilizing as said mold a breakaway mold providing oppositely-disposed separable die members defining the walls of the mold, said die members having their inner surfaces which contact said body during said compression formed of hardened tool steel, and said die members being provided with passage means in heat exchange relation with said die inner surfaces;
• b. compressing said porous ceramic pyroplastic block within said breakaway mold under pressures of the order of 2000 to 10,000 psi while circulating a cooling fluid through said die passage means to cool said inner die surfaces, said compressing being carried out so rapidly that a temperature gradient of the order of 1000.degree. C. is maintained from the die-contacted outer surfaces of said die surfaces block to a depth of about 5 millimeters or less into said block from said outer surfaces, whereby a thin porous skin is formed around said block which is limited in thickness to said depth;
• and
• c. releasing the pressure on said body and opening said mold by separating said oppositely-disposed die members in directions perpendicular to the respective contacted sides of said block, so as to limit sliding friction between said body and said mold as it is released therefrom.