Effect of bolted joint layer on the vibration characteristics of high accurate spindle rotor

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The effect of joint layer on the vibration characteristics of the hydrostatic gas bearing spindle rotor is investigated. The test rotor is composed of a journal part and two thrust plates bound with bolts. The each surface of bolted joints is processed by two methods in order to change the roughness and the roundness of surface. In all conditions of joint layer, natural frequencies increase and damping ratios decrease as the clamping torque of each bolt increases. On the other hands, in all condition of clamping torque, natural frequencies increase and damping ratios decrease as the roughness and the roundness of surface decreases.By fabricating the optimum diameter's countersunk hole near the clamping bolt screw hole, the maximum amplitude of the spindle rotor can be decreased because the stiffness and the damping of the joint layer can be increased.We propose the contact stiffness and damping model of the bolted joint layer of a spindle rotor and the identification procedure of the contact stiffness and damping of the normal and the tangential directions. The contact stiffness in both directions and damping in the normal direction increase as the clamping torque of each bolt increases.