Automatic hot pressing of refractory compounds

The feasibility of the automatic hot pressing of refractory materials, particularly of boron carbide, is considerd. In order to consider automation, the kinetics of hot pressing must be considered, which is dependent on: 1) starting material, the consideration of which comprises particle size distribution, purity, and additives, 2) the temperature of hot pressing, 3) pressure and pressure application, and 4) time as it relates to the rate of temperature rise and dwell time at temperature. In advance of considering the material preparation and processes for boron carbide, study was made on titanium diboride and zirconium diboride to define those parameters leading to property optimization, and was used as a guide. Several prototype hot pressing units were designed and built to closely define hot pressing parameters, before a fully automatic production unit was contemplated. Two units were finally designed, engineered, built and debugged; a counter-current unit capable of producing 24-28 - 6x6inch tiles per hour, and the second a larger unit with capacity for producing 6-12 - 9x9inch tiles per hour. The counter-current unit reflected the basic design features of the prototype furnaces previously built, but incorporated automatic features for temperature control, pressure regulation, and indexing. The production units built clearly demonstrated that automatic hot pressing is feasible when hot pressing kinetics is incorporated into equipment design. (Iwakiri, K.)