| 摘要 |
PURPOSE:To suppress the change of magnetic gaps to the minimum when the rotor is thermally shrunk, and to obtain stable performance by fixing a magnetic bearing on the stationary side to a casing through an internal cylinder consisting of a material having a large coefficient of linear expansion. CONSTITUTION:A casing 2 reaches only halfway of a rotor 5, and an internal cylinder 11 consisting of an aluminum alloy, lead, etc. having a large thermal expansion coefficient and patially provided with a threaded screw which acts as a molecular pump is fixed on the upper surface of a flange 2a which is provided to the upper end of the casing 2. A bearing fixig flange 12 to which a magnetic bearing 6 is fixed is equipped to the upper end of the internal cylinder 11. An upper cover 13 is arranged on the flange 2a so that the internal cylinder 11, etc. may be airtightly overed. Accordingly, when the rotor 5 is expanded due to the heating caused by the windage loss, etc. during the operation, the internal cylinder 11 having the moleuclar pump part is similary expanded. The fluctuation range of the magnetic gaps can be minimized in this way.
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