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Rotors on magnetic bearings rely on external controls to guarantee stability and are designed in case of partial or total failures, when impacts happen and potentially lead to a breakdown. Therefore backup bearings are indispensable. In such rotor-stator interactions the main undesired phenomenon is the backward whirl. The current work investigates the experimental behavior of a horizontal rigid rotor interacting laterally with two types of backup bearings during run up testing. The experimental data is analyzed by orbit analysis, spectrum analyzers, and force magnitudes collected by sensors installed. It is shown experimentally the nonlinear behavior of the rotor-bearing system and the elimination of backward whirl. The advantages and drawbacks of each type of backup bearing are given. [ABSTRACT FROM AUTHOR]

Rotor drops in magnetic bearing and unbalance in rotors have been objective of study for many years. The combination of these two well-known phenomena led to an interesting chaotic response, when the rotor touches the inner race of the back-up bearing. The present work explores the nonlinear rotor backup bearing dynamics both theoretically and experimentally using a fully instrumented test rig, where the position of shaft, its angular velocity and the contact forces between the shaft and the backup bearing are sampled at 25 kHz. The test rig is built by a removable passive magnetic bearing, which allows for simulation of magnetic bearing failure (loss of carrying capacity and rotor fall). The rotor is studied numerically as well as experimentally. A theoretical approach is given beforehand and supplies the basis of the study. Finally the presented results are commented on the point of view of nonlinear dynamics applied to the practical use. The theoretical and numerical analyses are shown through orbit plots, phase plans, Poincaré maps, force response in time and double sided spectrum. The latter is important to characterize the condition at different levels of unbalance between forward and backward whirl. Our preliminary results indicate that for smaller amount of unbalance the rotor swings at the bottom of the bearing, the more the unbalance increases, other dynamical behavior occur and some can be extremely harmful, since the rotor can be lifted from the contact state and return, starting to impact innumerable times without reaching a steady state. [ABSTRACT FROM AUTHOR]

• Demonstration of a theoretical model of a rotor impacting on a backup bearing with a housing. • Two types of backup bearing are investigated: the ball bearing and the pinned bearing. • Application of the Hunt & Crossley impact model to represent the rotor interacting with the backup bearing. • Identification of the test rig parameters and simulation of the mechanical model. • Theoretical-experimental validation for the case of crossing critical speed of the rotor. The magnetic bearing rotors are present nowadays in many industrial applications. However, a damage or a malfunctioning of the magnetic bearing can produce a dangerous high lateral vibration.Backup bearings hold them to protect the machine integrity. The present study investigates the effectiveness of a pinned bearing on a horizontal rotor compared with a conventional rolling bearing. Experimental tests have been conducted; a mathematical model to describe the motion is then developed and validated numerically. It is shown that both the simulation and the test rig are in good agreement with each other and that the pinned bearing is able to reduce the interval of impacting velocities. The experimental set up is able to gather data fast enough to observe the dynamics and the forces acting on the structure. The orbits and the magnitudes of the impact forces are the key elements to assess the validity of the pinned in contrast to the rolling one as a relevant type of backup bearing. [ABSTRACT FROM AUTHOR]