High-speed stability of a rigid rotor supported by aerostatic journal bearings with compound restrictors

► Compound restrictors are formed by inherently compensated restrictors with a circumferential groove and the structure is very simple. However, it was found that the circumferential groove could greatly improve the high-speed stability of aerostatic journal bearings. For example, the rotational speed of compound restrictors reaches around 300,000 rpm for the supply pressure=0.4 MPa at the bearing clearance=20 μm, whereas the threshold speed of instability of conventional inherently compensated restrictors under the same conditions was observed at Nmax=120,000 rpm. ► In calculations, the inertia effect of air flow in the bearing clearance was taken into account, and it was numerically and experimentally shown that the influence of the inertia effect on the stability was very large in this kind of bearings. The whirl ratio reached more than ten by considering the inertia effect, whereas the whirl ratio without the inertia effect is always two. ► It can be said from this work that by using the aerostatic journal bearings with compound restrictors, it will be possible to develop a 300,000 rpm high-speed spindle for precision machine tools.