The present relates generally to bearings. More particularly, the present invention concerns segmental bearings of the type used with a rotating machine of substantial size.
Stringent requirements are placed on shaft bearings of power plant turbosets and power plant generators as a result of the great rotating weight associated with rotors, shafts and the components supported thereby. By virtue of the high static and dynamic force loads and the external effects generated by the working medium, these shafts bearings are subjected to high specific bearing surface compressions (20-60 bar) and journal circumferential velocities which substantially exceed 100 m/sec.
A hydrodynamic bearing is used exclusively for supporting such shafts has proven to be thoroughly satisfactory for the operating conditions. In addition, the hydrodynamic bearing has attained a high state of development. With a hydrodynamic bearing it is possible to produce a sufficiently thick lubricating film by self-lubrication. The required thickness for such a lubricating film is determined by the magnitude of the deflection under load that is experienced by the guide block in the case of an axial bearing such as used in a hydroelectric generator or by deflection of a bearing box segment in a radial bearing of a power plant turboset. In these hydrodynamic bearings, deflection of the bearing surface of the guide block on bearing box segment is caused by hydrostatic pressure in the oil lubricant film created during rotation of the shaft. Such an hydrostatic pressure acts as a stress nonuniformly distributed over the entire bearing surface with the stress decreasing toward the edges of the respective guide block or bearing box segment and causes a bending to occur in the bearing surface.
This mechanical deflection caused by hydrostatic pressure has superimposed thereon deflections which result from the heating of the guide block or bearing box segments and the associated supporting elements. It is to be understood that supporting plates are exposed to this thermally-induced deflection in the case of axial bearings whereas supporting segments are exposed to the thermally-induced deflection in the case of radial bearings.
In order to avoid removal of the lubricant film and subsequent metallic contact of the bearing surfaces, sometimes referred to as mixed friction, the thickness of the lubricating film which occurs during operation must always be greater than the resulting deflection produced by the combined stresses: i.e., induced by the hydrostatic pressure and the thermally induced deflection. It is only when such a thickness condition is satisfied that the bearing surface and the cooperating shaft surface will remain separated from one another by the lubricating film. Without such separation, damage can occur which can eventially lead to destruction of bearing surface and adjacent shaft.
One object of the present invention consists of providing a bearing of the type suitable for use with large rotating machines in which the bearing surfaces deflect in such a manner that the bearing surface remains essentially planar and moves essentially parallel to the original undeflected position. These deflections are caused by the mechanical and thermal stresses noted above. Moreover, it is an object of the present invention to confine the geometrical deviations of the deflected bearing surfaces so that those deviations lie within very narrow limits from their unstressed configuration and so that the deviations are less than the lubricating film thicknesses conventionally occurring during operation. Accordingly, liquid friction is guaranteed under all operating conditions.