On the hydrodynamic lubrication in tilting pad thrust bearings

Abstract: The primarily objective of this work was to investigate the performance of environmentally adapted synthetic oils in the hydrodynamic lubrication regime. A special test facility has been designed and manufactured for this purpose. The facility contains two equalising tilting pad thrust bearings typical of design in general use. One of the bearings is instrumented with thermocouples, pressure and oil film thickness sensors. Three thermistors and two pressure sensors are installed in one of the shaft collars. Power losses are measured by monitoring bearing friction torque and by the calorimetric technique. All sensors are connected to a PC based high-speed data acquisition system. The facility allows a complete set of bearing operating parameters to be obtained. Bearing characteristics in steady state and transient operating conditions were investigated at different load-speed combinations as well as at various supplied oil temperatures and flow rates. Steady state results were compared with the outputs of THD and TEHD theoretical models. The agreement was found to be good. Tests were run to find a possible replacement of ISO VG68 mineral oil currently used in thrust bearing units of hydroelectric power stations. Oils tested included mineral base ISO VG68 and ISO VG46 oils, PAO and ester base ISO VG46 oils. Tests showed that a change from VG68 oil to the lower viscosity grade oil reduces bearing peak temperatures. It is also shown that the energy savings associated with the use of VG46 oil in place of VG68 are significant. However, such a change may only be justified for the ester base oil since it gives as thick oil films as mineral oil ISO VG68 does. Alternatively, if the ester base oil is used instead of a mineral oil of the same viscosity grade bearing reliability is increased due to the increased oil film.