| 摘要 |
PROBLEM TO BE SOLVED: To provide a vacuum pump with little possibility of breaking of a rotor, excellent in balancing the rotor, and capable of maintaining the balance for a long period of time. SOLUTION: An annular groove 20 is formed on the inner surface on the lower side of the rotor 9 in the circumferential direction, and a weight 21 is engaged with the annular groove 20 for balancing the rotor 9. Therefore, there is no variation of the cross section of the outer periphery of the rotor 9 in the peripheral direction and there is no notch, so that concentration of stress, etc., will not be generated. As a result, the maximum stress of the rotor 9 is reduced and the rotor 9 is hardly breakable.
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