| 摘要 |
PURPOSE:To improve durability and to prevent lowering of cooling performance due to leakage of cooling water by providing an air feed port between the inner peripheral surface of a rotary joint and the outer periphery of the rear end of a shaft and a cooling water feed port, communicated of a shaft water flow hole, in the rear end of the rotary joint. CONSTITUTION:With a shaft 14 rotated with the aid of a motor 15, a rotary grinding stone 13 is rotated at a high speed to perform grinding. During the operation, a cooling water having a specified temperature flows to an empty chamber 17b of a rotary joint 17 through a cooling water feed port 18 by means of a cooling water feed pipe 19. Further, after the cooling water flows through a water flow through-hole 16 of the shaft 14 to cool the shaft 14 and the rotary grinding stone 13, it is discharged to the outside. Simultaneously, an annular groove 20a is filled with compressed air fed through an air feed pipe 21 after the compressed air flows through a communicating hole 20b of an air feed port 20. Since an air seal layer is formed between the annular groove 20a and the outer periphery of the shaft 14 to shut off inflow of cooling water to a housing 11, failure in operation due to leakage of cooling water of to the motor 15 and a pneumatic bearing part 12 can be reliably prevented from occurring. |
