Abstract
Tilting-pad journal bearings are widely used in industry to support rotating shafts due to their high dynamic performance. The operating limits of these bearings are mainly represented by the maximum permissible temperature of the lined materials of the pads and by the minimum thickness of the oil-film under which mixed lubrication can occur. The current trend in bearing development sees the adoption of innovative materials in the production of the pads, that provide higher load capacity, higher temperature capability and greater fatigue resistance. In this paper, the static characteristics of bearings lined with different materials, will be investigated. The temperature distribution in the bearing will be evaluated by means of a full 3D thermal model whereas the deformation of the pads will be evaluated by means of a finite element model. At the end, the permissible operating range in terms of load and speed will be defined for each material by considering the limits on the maximum temperature, permissible mechanical stress and minimum oil-film thickness.
Highlights
Oil-film bearings are widely used in industry to support rotating shafts especially when diameters, loads and operating speeds are not compatible with the use of simple rolling elements bearings
In modern rotating machines such as compressors, gas or steam turbines and large-sized generators, tilting-pad journal bearings (TPJBs) are used in most cases due to their high dynamic performance. Their principle of operation based on hydrodynamic lubrication is very simple, they are still extensively analyzed and studied by many researchers who have developed increasingly sophisticated mathematical models capable of describing the hidden phenomena involved in the effective functioning of the bearings [1,2]
The state of the art of bearing models is represented by thermo-elastohydrodynamic models (TEHD) in which the temperature distribution in the entire bearing is estimated and the geometry of the oil-film is evaluated considering the deformation of the shaft-bearing system due to the mechanical and thermal stresses [5]
Summary
Oil-film bearings are widely used in industry to support rotating shafts especially when diameters, loads and operating speeds are not compatible with the use of simple rolling elements bearings. A thrust bearing with a steel pad with a 2-mm-thick hardpolymer liner was compared with that one using hard-polymer material for entirely pad whose elastic modulus is just 12.5 GPa. A novel TEHD model that considers a 3D thermal energy transport equation in the fluid film, coupled with heat conduction equations in the pads, and a generalized Reynolds equation with cross-film viscosity variation was developed. The bearing with solid hard-polymer was demonstrated to be suitable for operation at a turbulent flow condition It shows a lower power loss and a larger film thickness; it requires too large supply flowrate. The permissible operating range in terms of load and speed will be defined for each material by considering the limits on the maximum temperature, permissible mechanical stress and minimum oil-film thickness
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