Effects Of Non-uniform Magnetization On The Performance Of Permanent Magnetic-thrust Bearings And The Rotor System

Permanent-magnetic bearings are a kind of magnetic force bearings that usemagnetic-field force to suspend a rotor. The magnetic bearings are simple inthe structure, reliability in work, without the wear, and cheaper in cost. Themagnetic bearings have a lot application in various fields. Many scholarshave studied properties of the magnetic bearings. But the studies werefinished under the assumption that permanent material is in uniformmagnetization and effect of the soft magnetic material magnetized is notconsidered. However, non-uniform magnetization of the magnetic rings andthe soft magnetic material magnetized affect evidently properties of themagnetic bearings since the bearings consist of the magnetic rings and thesoft magnetic material. Therefore, studying the effects of non-uniformmagnetization and the soft magnetic material magnetized is important inimproving properties of the magnetic bearings, the bearing-rotor system andthe machine. This paper carries out researches in following fields:1. Distribution of the magnetic induction intensity on the magnetic ringsurfaces is measured along the circumferential direction from analyzingreasons of the non-uniform magnetization of the magnetic rings.Bearing-load model of the permanent magnetic-thrust bearings with thenon-uniform magnetization is established from the equivalent magneticcharge theory. The model contains the effects of the non-uniformmagnetization of the rings, the soft magnetic material magnetized andthe fringe action of the magnetic material. Bearing load and stiffness ofthe magnetic bearings are analyzed from the model. The analysis showsthat the non-uniform magnetization causes the bearing load and thestiffness to fluctuate during the magnetic bearing working and that thesoft magnetic material magnetized increases the bearing load.2. An experimental rig for the magnetic bearings is designed andmanufactured in this work. The bearing load of the magnetic bearings ismeasured and analyzed using the rig. The experiment shows that theestablished model is correct in predicating the bearing load. The bearingload of the magnetic bearings fluctuates during the rotor turning sincethe magnetization of the magnetic rings is not uniform. This causes themagnetic bearing-rotor system to vibration. Therefore, accelerationresponses of the axial vibration of the rotor system are measured underdifferent turning speeds. This is an experimental foundation to studyfactors of affecting the rotor system vibration.3. A dynamic model of the system vibration is established from analyzingthe bearing load and stiffness of the magnetic bearings. The dynamicmodel is calculated numerically and analyzed theoretically, and therelation is studied of resonance turn speeds of the rotor system with thenumber of the magnetic material pieces of consisting of the magneticrings, the average stiffness and mass of the rotor system. The dynamicmodel and the analysis calculation are verified using the measuring dataof the acceleration response of the rotor system. Displacement andacceleration of the system with the magnetic bearing of the non-uniformmagnetization are analyzed using the dynamic model. The analysisshows that the system has a lot order of resonance speeds. Andamplitudes of the displacement and acceleration of the first order speedare the maximum among various resonance speeds. The system vibratesevidently under the first order resonance speed. Smaller is the magneticgap of the magnetic bearing and less is the number of the magneticmaterial pieces, higher is the first order resonance speed of the system.The first order resonance speed of the magnetic bearings is low since themagnetic ring consists of several pieces of the magnetic material.Therefore, the magnetic bearings are not suitable for working at lowspeeds. Work in this paper supplies theoretical and experimentalfoundation for developing permanence magnetic bearings with highproperties.This paper will study effects of non-uniform magnetization along the radialdirection of the magnetic rings and the soft magnetic material non-uniformmagnetized on the properties of the magnetic bearings to improve thebearing.