ELASTOHYDROSTATIC PERFORMANCE OF A SLOT-ENTRY- JOURNAL BEARING SYSTEM

Abstract

The slot-entry hydrostatic journal bearings are extensively used now-a- days in machine tool industries due to their improved load carrying capacity over recessed bearings. The slot-entry bearing has the following features, namely, commercial availability, improved hydrostatic performance. over recessed bearings, good hydrodynamic and hybrid performance, lack of directional variations in stiffness, large bearing lands in the event of sit-down operation and there is no need for external restrictors or non-return valves. :. A review of the studies concerning both recessed and non-recessed hydrostatic/hybrid journal bearings has been presented in the literature. It has been observed that in most of the studies, the journal and bearing shell are assumed to be rigid. However; when a bearing operates at heavy loads the bearing performance characteristics are affected due to bearing flexibility. Therefore, the present work includes the study of performance characteristics of a slot-entry journal bearing including bearing shell flexibility. The performance of slot-entry hydrostatic/hybrid journal bearing has been studied for two different_ configurations, i.e. symmetric. and asymmetric and for a range of flexibilities (0.0-1.0). The performance characteristics of the slot-entry journal bearings have also been compared with that of corresponding similar hole-entry journal bearings, compensated by Capillary. Orifice and Constant Flow Valve restrictors for the same operating and geometric parameters. iii • For computing the bearing performance characteristics, . the Reynold's equation governing the flow of lubricant in the clearance space with the equation of flow through the slot restrictor as constraint is used, along with three dimensional elasticity equations satisfying the appropriate boundary conditions. The deformable bearing shell has been discretized using 8 noded three dimensional isoparametric elements. The study indicates that the performance of a slot-entry journal bearing system gets affected significantly due to bearing shell flexibility for both the symmetric and asymmetric configurations operating in hydrostatic/hybrid mode. In order to have an optimum performance of a slot-entry flexible journal bearing, a proper selection of bearing flexibility parameter (Cd )' Speed parameter (c), External load (W0), Concentric pressure ratio (P') and Bearing configuration is essential. 1V