Effect of Bolted Joints on the Vibration Characteristics of a Hydrostatic Air Bearing Spindle Rotor.

Abstract

This paper investigates the effects of bolted joints on the vibration characteristics of the hydrostatic air bearing spindle rotor by using the Finite Element Method and experimental modal analysis. The test rotor is composed of a journal part and two thrust plates bound with bolts. First, it is shown that the measured natural frequencies increase and modal damping ratios decrease as the clamping torques of each bolt increase. The calculated natural frequencies of a modeled rotor without bolted joints are shown to be always larger than the measured ones. Next, it is found that this discrepancy can be eliminated if the joint layer between the journal part and thrust plates are modeled as distributed normal springs with stiffness Kz and tangenial springs with stiffness Kr, which are identified by the two experimental natural frequencies. The modal dampings mainly depend on the normal spring, and increase in inverse proportion to Kz.