Whirling instability of a rotor supported by aerostatic porous journal bearings with a surface-restricted layer

Recently, aerostatic porous bearings have been used in ultra precision machine tools and precision-measuring equipment because they have higher stiffness and larger damping coefficients than other types of aerostatic bearings. However, an aerostatic porous bearing has a disadvantage in that it is prone to cause pneumatic hammer instability. Therefore, it is considered that reducing the permeability of the porous material only near the bearing surface in an aerostatic porous bearing is a very effective means of avoiding pneumatic hammer instability. In this article, the whirling instability of a rotor supported by aerostatic porous journal bearings with a surface-restricted layer is investigated theoretically and experimentally. It is found that a surface-restricted layer can greatly improve the static stiffness and the whirling stability of a rotor at high speeds.