| 摘要 |
1,084,675. Bearings. MINNESOTA MINING & MANUFACTURING CO. May 31, 1965 [June 8, 1964], No. 23091/65. Heading F2A. A gas bearing is made of ceramic material and has highly polished " bearing " surfaces. In an embodiment, a sleeve 10 of ceramic material is mounted with clearance on a shaft 11 of ceramic material. The sleeve 10 carries an armature 14 of an electric motor, an extension 15 of which is provided for a pulley &c. to be affixed thereto. A housing 12 of the electric motor carries field windings 13 and is supported by the shaft 11. Axial movement of the sleeve 10 is restricted by retaining end thrust-washers 17, 18, which are attached to one end of the shaft 11 by a bolt 16; and by a thrust-washer 19 located between the other end of the sleeve 10 and the housing 12. The thrust-washers are made of ceramic material. The " bearing " surfaces are extremely smooth, the finish being no greater than twenty R.M.S. micro-inches; and are free from flaws of more than 0À01 inch in cross-section. The ceramic composition consists of 91 to 98% by weight of alpha alumina crystals and at least 2 to 6% by weight of a refractory glassy matrix. The alumina crystals are no greater than 150 microns in any dimension and 98% of the crystals are within the range of 0À5 to 40 microns. The glassy matrix consists of silica with alumina and magnesia distributed randomly therethrough. The ceramic material is compacted to a density of at least 89% of the theoretical maximum density. |
