To provide a method for preheating and charging ash to a melting furnace, wherein a seal ring made of a material having a high heat resistance is employed and dry compressed air is supplied into a housing to pressurize the housing and minimize the air pollution caused by dust.

In a swirling ring bearing device which can be used in a high temperature atmosphere containing dust, an upper-side seal ring 6f is snugly fitted into a groove formed on an upper portion of the inner periphery of a rotating outer ring 6b. A slight gap is formed between the front brim portion of the upper seal ring 6f and an upper surface of a stationary inner brim 6a. A lower-side seal ring 6f which is snugly fitted into a groove formed on the lower portion of the outer periphery of the stationary inner ring 6a also defines a slight gap between its front brim portion and the lower surface of the rotating outer ring 6b. Furthermore, an annular air tube 10 and a plurality of grease supply holes 6d are connected with each other by means of air blow-off tubes 11. A small amount of dry pressurized air is supplied from the annular air tube 10 into a housing 6e defined between the stationary inner ring 6a and the rotating outer ring 6b so as to pressurize the housing 6e and dry and cool a rolling ball 6c with air and discharge the air only through a gap portion formed in the front brim portion of the seal ring 6f. Due to such a construction, it becomes possible to prevent the infiltration of a floating dust into the housing 6e.