Externally pressurized air journal bearing is in wide use in high speed rotating machinery and high precision spindle system because of its advantages such as low friction, low heat generating character and averaging effect of the pressure deviation in the air film in bearing. Stability characteristics and rotational accuracy of externally pressurized air journal bearing are studied both theoretically and experimentally to forecast and to prevent the whirl instability and to supply the basic data about the shape tolerance of precision air bearings.
As for the high speed rotating machinery, the instability called 'whirl' occurs when the rotor rotates at a speed more than twice the resonant speed. Once the whirl occurs, rubbing contact between the journal and the bearing occurs mostly and the bearing-rotor system is destroyed ultimately. therefore, the forecasting and prevention of the occurence of whirl instability is a very important subject especially to develop highly efficient high speed machinery. Theoretical method adopting new boundary condition which takes inertia effect around the feeding hole into account is proposed and used to calculate the stability characteristics. The multi-lobe bearing is used for the propose of the prevention of whirl instability. It is shown that the theoretical method proposed in this thesis can forecast the instability threshold more easily and more accurately than conventional methods and that the two-lobe bearing is most stable and useful for the purpose of the prevention of whirl instability.
With respect to the rotational accuracy of precision air bearings. the quantification of the effect of shape error of spindle parts on the rotational accuracy is carried out. The journal and bearing are considered to have sinusoidal lobe profile and the effect of roundness of the journal and bearing on the rotational accuracy is examined. The expression which quantify the maximum amplitude of the locus of the journal center under various operating conditions owing to the error of form of both bearing and journal is presented.
