Theoretical Research About the Dynamics of a Rotor With a Decreasing Length Suspended by Active Magnetic Bearing

The Active Magnetic Bearing (AMB) will be used in the High Temperature Reactor being constructed in Shandong Province, China. The calculation of rotor dynamics is very important for design of the AMB, and is difficult when the AMB is used in the Plasma Rotation Electrode Process (PREP). In this process, the length of the rotor, which is a rotating titanium stick, is decreasing gradually. In a PREP project, a new device supported by the AMBs was used to replace an old device supported by rolling bearings to fit higher working speed. Based on this project, the rotor dynamics of a “length-decreasing” rotor suspended by the AMBs was analyzed. Firstly, the critical speed and the unbalance response of the titanium stick were calculated for the two devices respectively. It’s found that, for the new device, the third order critical speed at the beginning of the process should be larger than the working speed, and the second order critical speed at the end of the process should be smaller than the working speed. Secondly, the influencing factors of the critical speed were studied. It’s found that, with the increasing of the brush’s diameter and length, all critical speeds decrease, especially for higher order critical speed. And with the increasing of the stick’s length, all critical speeds decrease, especially for higher order critical speed. At last, a design for the replacement of the device was present.