A test bench on rotors supported on air bearings floating on O-rings has been designed in order to study the whirling phenomenon and individuate the stability threshold with the presence of damping elements mounted on the bearings. The work contains description of the test bench and the first experimental results. A rotor of 1 kg mass and 37 mm diameter is rotated up to 75000 rpm by an air turbine manufactured on the rotor. Capacitance probes, placed in two radial planes, allow to scan the orbits of both the rotor and the bushing at different rotating speeds and proper load devices make it possible to measure the static and dynamic stiffness of the rotor-bearing system. Diagrams on the rotating response using different kinds of rubber O-rings are presented and compared, with also indications on the Fourier spectra of the signals relative to the rotor displacement. The phenomenon of whirling instability is showed, with considerations on the whirling frequency and on the orbit amplitudes of the rotor and the bearings. The effect of both supply pressure and angular velocity on the stability threshold is showed.

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