Turbomolecular pump rotor-bearing system analysis and testing

Abstract

During turbomolecular pump design, it is very critical to know the dynamic behavior of the rotor-bearing system, which is also of great importance to the pump performance. In this study, a typical small size turbomolecular pump was used. Using an inertial coordinate system, the dynamic models of the pump rotor-bearing systems included gyroscopic moments, rotary inertias, and bending and shear deformations. The models were analyzed in order to predict the natural frequencies, to produce critical speed maps, and to estimate the bearing stiffness. These rotor-bearing system analyses were then applied to the turbomolecular pump rotor system applications. Both theoretical and experimental analyses were used to study the rotor-bearing system. Modal testing and dynamic test were used to verify the analytical results, including the critical speed map and the bearing stiffness. Very good agreement was demonstrated between the analysis and the test data. The analysis demonstrated that the rotor operation of 51600rpm is very close to the second critical speed, which may have caused the recent pump bearing failures near the pump bottom. The analysis can also provide guidelines to avoid the second order critical speed mode shape failures.