Abstract
The hydrodynamic lubrication and thermal analysis of tilting pad thrust bearings has been a major subject for many studies in the field of tribology. There is only a limited number of studies regarding thrust bearings with coated surfaces. The purpose of this study is to build a parametric, iterative algorithm in order to perform a complete thermal and hydrodynamic lubrication analysis for pivoted pad thrust bearings with coatings. The analytical model is mainly based on the energy, continuity and Navier–Stokes equations, which are solved numerically with the Semi-Implicit Method for Pressure Linked Equations Consistent (SIMPLEC) method. The analysis focuses on a single pivoted pad of the thrust bearing. The thermal properties of the coating material are taken into account and the resulting thermal and flow fields are solved. The basic hydrodynamic and tribological characteristics are calculated for an uncoated, a Babbitt coated, a PTFE coated and a diamond like carbon (DLC) coated pivoted pad thrust bearing. The pressure and the film thickness distribution, as well as the load capacity and the frictional forces, are determined for several pad positions and velocities of the rotor. A mineral oil lubricant is used to estimate the shear thinning or thickening effects on the pad tribological performance. The results indicate that pads coated with PTFE and DLC show lower friction forces compared to the common steel and Babbitt applications. At the same time, the DLC coating seems to affect the bearing’s flow and thermal fields less than the PTFE, making it more suitable for thrust bearings applications.
Highlights
Hydrodynamic thrust bearings are commonly used in rotating machinery
The results show that the (H-diamond like carbon (DLC)) coatings provide excellent wear resistance and low friction for bearing applications
Results have been recorded for five rotor velocities—1000, 3000, 5000, 7000, 9000 rpm—three pad angles that correspond to three values of the coefficient—k = 0.25, 0.67, 1.54—and three coatings—Babbitt, PTFE and DLC
Summary
Hydrodynamic thrust bearings are commonly used in rotating machinery. An oil film between two sliding surfaces is essential to limit wear and to enhance bearing performance. Hydrodynamic lubrication relies on the convergent wedge and the relative motion of the two surfaces together with the viscous nature of the lubricating oil. Due to technological progress, pad thrust bearings are one of the most essential components of many industrial, commercial and naval applications determining the reliability of the whole operation. Environmental and economic concerns require that pad thrust bearings must operate with minimum power loss. Various design improvements such as different surface profiles, texturing and coatings over pads’ surfaces are carried out in order to enhance the bearing performance.
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