Firing of lime and dolomite shapes

摘要

Burned refractory shapes are prepared from a refractory grain consisting essentially of MgO and at least 50% CaO (e.g. dead burred dolomite) by first heating to a temperature of at least 1000 DEG F. in a moisture-free atmosphere at a slow rate (e.g. 200 DEG F. per hour) to prevent hydration and cracking of the shape. The heated shapes are subjected to a second firing to a temperature of at least 2700 DEG F. for 48 to 100 hours. The shapes must not be in contact throughout the process. They may be separated by sanding with a particulate material which is physically inert to the firing and chemically inert to the shapes (e.g. dead burred periclase). Hydration of the grain may be prevented during formation of the shapes by maintaining a temperature of at least 212 DEG F. A non-aqueous binder (e.g. pitch or tar) may be used in forming the shapes prior to firing. The shapes may be coated with a water repellent material after firing. The firing may take palce in kilns and the shapes may be conveyed to the kilns on movable kiln cars. In a review of the prior art a number of British and U.S. Specifications are referred to.