The Surface Roughness Effect on the Hydrostatic Thrust Spherical Bearings Performance: Part 2 — Clearance Type of Bearings

The clearance type of bearings, where the sphere radius is smaller than that of the seat, provides a great divergence in results compared with the fitted type. The study deals with the surface roughness and the predominant centripetal inertia terms due to the shaft rotation. The solutions are presented for the un-recessed clearance type of bearings, hemispherical and partial hemispherical seats, with capillary tube and orifice restrictors. On the basis of the stochastic theory, Reynolds equation is developed. Unlike the solution of Dowson and Taylor for this type of bearings, the well known Sommerfeld substitution of journal bearings hasn't been used in this study. Expressions for the pressure distribution, load carrying capacity, volume flow rate, frictional torque, friction factor, power losses and stiffness factor are obtained. The research studies the combined effects of the centripetal inertia and the surface roughness on the bearing performance. An optimum design based on the minimum power losses, minimum flow rate and the optimal restrictor dimensions is theoretically examined. The conventional four cases of this type of bearings, dependant on the eccentricity ratio in the previous studies, have been reduced to three cases only. In addition, a unified solution for this type is developed. Finally, a general solution for the hydrostatic thrust spherical bearing is obtained where it could be applied to the, un-recessed hemispherical and partial hemispherical, clearance and fitted types of bearings.