Externally pressurized journal gas bearings: John H. Laub. ASLE Trans., 4 (1) (1961) 156–171; 34 figs., 30 refs.

Abstract

The following elaboration discusses the analytically complete layout of a self-acting gas-lubricated high-speed conically shaped spiral-groove bearing as well as suggestions for practical realization. The simple conically shaped bearing is separated into two conical main bearings, which are situated at the ends of the cone-stump. Both have an identical angle size, but otherwise differ with regard to their bearing geometries and bearing gap sizes. The isotropic layout of the two bearings in radial direction, i.e. the determination of the bearing geometries for the same load angle, the same load capacity and the same stiffness at the same nominal operating conditions, is determined analytically in an iterative way and has the goal of providing dynamically benign behavior. The radial expansion of the rotor which occurs at the nominal rotation, and therefore the occurrence of distortions of the bearing gaps due to enormous centrifugal forces that affect the rotor masses, is rendered ineffective by means of a centrifugal force invariant inner outline of the rotor. For this purpose, the outer contour of the rotor is designed in such a manner that the conically shaped inner contour expands congruently to itself and therefore causes a parallel increase in the bearing gap. The autonomous regulation of the bearing following the gap increase subject to the decrease in load capacity as a result of the decrease of the expanded rotor to the nominal bearing gap sizes restores the nominal state independent of the rotor speed. The half-frequency whirl which is dependent on natural frequencies and detrimental to self-acting, gas-lubricated bearings requires an investigation of the dynamic behavior of the bearing system. It will be shown that natural frequencies will be reached while passing through the turning frequency range. However, the suspension of the “rotor–stator” system in defined additional stiffnesses will show that the natural frequencies of the original system can be displaced upwards so that the turning frequency will no longer reach a natural frequency at any operating point. This prevents the occurrence of the half-frequency whirl. The realization of the described bearing system is supported by suggestions for a non-self-acting start-up assistance at low rotation speeds as well as by suggestions for actuation, pre-stressing, sensor and measurement devices as well as system regulation. It lays the foundation for high-speed bearings in spindle construction, laser and dental technology as well as for precision gyroscopes.