Research On New Type Catcher Bearings In Active Magnetic Bearing System

In active magnetic bearing system (AMBs), the catcher bearings (CBs) are indispensable totemporarily support the rotor from directly impact the stators. They prevent damages during themaintenance and destruction of the AMBs. In most cases, traditional catcher bearings cannot bear theultra high speed and the following vibration and impacts after rotor drop. Aiming at the defects oftraditional catcher bearings, double-decker ball bearings (DDBB) are proposed to use as catcherbearings in AMBs, and a series of relevant researches are carried out.The mechanical characteristics of DDBB are analyzed before using them as CBs. The mechanicalmodel of DDBB is established based on the quasi-static method by considering the radial load, axialload, centrifugal force as well as the gyroscopic moment acted on the bearing simultaneously. Thecalculation program is compiled in MATLAB to analyze the influences of various load and structureparameters on the mechanical characteristics of DDBB and single-decker ball bearing (SDBB). A testplatform of rotor-bearing system is established, and the relevant experiments are carried out to verifythe theoretical results. The results show that the relationship between the inner and outer pitchdiameters determines the rotate speed distribution of DDBB. In the same work condition, comparedwith SDBB, DDBB has relatively smaller radial and axial support stiffness. The external loads andworking speed affect the ball contact angles of SDBB and DDBB, and the ball centrifugal force makesthe contact angles between the ball and the corresponding inner and external groove no longer equal.External loads, working speed, ball materials, groove curvature radius and ball initial contact angle allhave certain influence on the axial and radial deformations of both SDBB and DDBB. Radialclearance, working speed and radial load have certain influences on the radial deformation ofsingle-decker and double-decker deep groove ball bearings.Based on the analysis of DDBB, the dynamic responses of rotor drops onto DDBB under the supportof elastic dampers are detailed analyzed. The rotor dynamical modes before and after AMBs failure,support model of active magnetic bearings, impact model between rotor and inner race, ball forcemodel as well as the real-time support force model of DDBB are respectively established. Based onthe established models, the dynamical responses of each part after rotor drop for different parametersare theoretically simulated. And the relevant rotor drop experiments are carried out on a five-degree offreedom (DOF) AMBs test platform. The results indicate that compared with traditional catcherbearing, using DDBB as CB helps to reduce the following collision forces，inner ball contact stress aswell as heat energy. In the actual applications, the inner and outer ball maximum contact stresses canbe regulated by adjusting inner and outer bearing combinations. Rotor work speed and unbalanceshould be in the safe zone to make sure the ball maximum contact stresses do not exceed the allowable stress range after rotor drop. Friction coefficient between rotor and inner ring, suitable protectionclearance and support damping of CBs are beneficial to reducing the collision force after rotor drop. Itis advisable to choose larger ball initial contact angle and smaller pre-tightening force when useface-to-face mounted angular contact bearings as the inner bearing of DDBB used as CB. Largerradial clearance is advisable when the selected DDBB used as CB are composed of deep groove ballbearings. Compared with aluminum, choosing45steel which has larger density as adapter ring of theintermediate ring has better cushion performances. In the guarantee of the maximum ball contactstress in the permission stress range, it is better to choose light and thin series of ball bearings tocombine DDCB. The work performance of tolerance ring in the CB system can be improved bymodulating its thickness, number of waves and some other design parameters. The added metal rubberring can effectively cushion the vibrations after rotor drop. The vibration reduction effects of bothtolerance ring and metal rubber ring are confirmed, but proceed from economy and degree ofassembly difficulties, it is suggested to use tolerance ring. The destructive tests show that DDBBunder the support of suitable elastic damper has longer service life, and all the bearing damage formsduring the destructive tests are cage fragmentation.