Instability of Aerostatic Journal Bearings with Porous Floating Bush at High Speeds

Abstract

Recently, demands of higher rotational speeds and rotational accuracy to aerostatic spindles used in machine tools such as a drilling machine for printed circuit board and a milling machine for manufacturing very small precise parts have been remarkably increasing. In this paper, to achieve higher rotational speed and accuracy, a new design of an aerostatic journal bearing with a porous floating bush was proposed and the instability of the proposed bearing at high speeds was investigated experimentally and theoretically. The optimum design parameters of the proposed aerostatic journal bearing with a porous floating bush were obtained by theoretical calculation and a test spindle of a 12 mm diameter rotor supported by proposed porous floating bush was constructed for experimental investigation of the instability. It was consequently found that the proposed porous floating bush journal bearings could greatly improve the whirling stability of a rotor at high speeds than the conventional externally pressurized porous journal bearings.