Twice-Running-Speed Resonances of a Paper Machine Tube Roll Supported by Spherical Roller Bearings: Analysis and Comparison With Experiments

Imperfections in a rotor-bearing system may cause undesirable subcritical resonances occurring when the rotating speed of the rotor is a fraction of the natural frequency of the system. These resonances arise partly from rotor imperfections and partly from bearing imperfections. This study demonstrates that the subcritical twice-running-speed vibrations originating from bearing waviness may be investigated by combining a simplified rotor model with a detailed bearing model, using a finite element method. The rotor-bearing system under investigation is a roller test rig consisting of the tube roll of a paper machine supported by spherical roller bearings. The bearing waviness from the second to the fourth orders is emulated as accurately as possible in the finite element model. This is achieved by measuring the waviness of the real bearings and then incorporating the measurement results into a simulation model. The tube roll of the test rig is modeled as a symmetric tube, neglecting the effects of the uneven mass and stiffness distribution of the roll. The contact between the rotor and the bearings is described using nonlinear Hertzian contact theory. The subcritical responses of the system are studied by means of time integration, and the results are converted into the frequency domain using fast Fourier transformation. The results of the analysis are compared with the measurement results for the subcritical responses of the roll. The agreement between the simulation and experimental results of the studied system can be observed even though rotor imperfections are not considered.