Effects of tilt on the characteristics of multirecess hydrostatic thrust bearings under conditions of no rotation

Abstract: Hydrostatic bearing finds wide application in machine tools with various technologies because of their high stiffness and damping characteristic. The environmental conditions, such as low and/or high temperatures, dust and dirt, moisture and unusual mounting conditions, can also affect a bearing's performance adversely. Therefore, both mechanical and environmental factors may affect the choice of a bearing and its performance. For high speed applications it is necessary to have design data including the effect of rotational lubricant inertia.The objective of the study is to design a hydrostatic bearing with following properties such as high stiffness, damping characteristic and lubrication inertia. In the present study Reynolds equation is used and boundary conditions are changed for various parameters such as temperature distribution, viscosity variation and radial load. The simulated results were analyzed in detail and found that increasing the viscosity of hydrostatic thrust bearing under specific conditions when both surfaces are rotated, the wear and tear are minimized and life time has been increased. This will be of great use in high speed applications.

Abstract: Hydrostatic thrust bearings are an integral part of hydroelectric power stations. These bearings are usually designed to work under parallel operation, but tilt is inevitable due to manufacturing errors, assembly errors, structural vibrations and structural deformations. Owing to the advent of latest advancements in manufacturing techniques, any geometric shape of recess can be easily manufactured and the designer has a greater flexibility. The geometric shape of recess significantly affects the performance of a bearing. Therefore, the present study is aimed to numerically analyze the influence of the tilt and recess shape on the static and dynamic performance characteristics of the hydrostatic thrust pad bearing system having Rabinowitsch fluid model lubricant. The lubricant obeying Rabinowitsch fluid model with tilt makes the Reynolds equation highly non-linear therefore, finite element method is used to analyze. Three different types of recess shapes of equal area A ¯ b / A ¯ o c = 4 have been analyzed to model hydrostatic thrust pad compensated by orifice compensator. The numerically simulated results indicate that the tilt angle significantly affects the dynamic and static characteristic parameters. The value of pocket pressure and fluid film reaction of a hydrostatic thrust pad bearing has been found to significantly decrease with tilt whereas the value of lubricant flow, fluid film stiffness coefficient and fluid damping coefficient increase with tilt.

Abstract: The performance characteristics of capillary compensated tilted pad hydrostatic bearing operating with Newtonian lubricant and cubic law lubricant are studied numerically considering the flexibilit...

Abstract: A hybrid fuzzy control scheme was applied to improve the rigidity of hydrostatic thrust bearing. The bearing oil film control was realized by coupling oil film thickness of four controllable chambers. The chamber flow can be regulated by electro hydraulic servo valve-control variable pump according to the surface roughness, load, cutting force, and thermal effects of worktable. The nonlinear hybrid controller developed was composed of a classical PID controller and a fuzzy controller based on self-adjusting modifying factor, and feed-forward compensation was added. A fuzzy switching mode was employed to avoid the undesirable disturbances caused by the switchover between the two control methods. By simulations and experiments on an electro-hydraulic servo test bench the feasibility of the control scheme was validated by comparison with a PID and a conventional fuzzy control. The research results show that the hybrid fuzzy controller exhibit good dynamic and steady quality, eliminate oil film lubrication failure and be broadly applied in high precision heavy machine tool.

Abstract: This paper aims to describe a theoretical and experimental research concerning influence of recess shape on comprehensive lubrication performance of high speed and heavy load hydrostatic thrust bearing with a constant flow.,The lubrication performance of a hydrostatic thrust bearing with different recess shape under the working conditions of high speed and heavy load has been simulated by using computational fluid dynamics and finite volume method.,It is found that the comprehensive lubrication performance of a hydrostatic thrust bearing with circular recess is optimal. The results demonstrate that recess shape has a great influence on the lubrication performance of the hydrostatic thrust bearing.,The simulation results indicate that to get an improved performance from a hydrostatic thrust bearing with constant flow, a proper selection of the recess shape is essential.

Abstract: The majority of hydrostatic thrust bearings are designed on the assumption that the bearing surfaces are parallel but, with the possibility of manufacturing and assembly errors and structural deformations, this condition is rarely, if ever, achieved in practice. With the increasing demands being made in modern machinery, more detailed design information is required.An experimental and theoretical investigation was carried out into the effects of tilt on the operation of circular hydrostatic thrust pads, the results of which show that, for static conditions, the characteristics of a tilted pad can be reliably predicted, assuming the lubricant to be isoviscous. With this information, a thrust pad can be designed to operate in any specified tilted configuration or can be incorporated in a rigorous structural design. In many applications, however, it may be difficult to specify the tilt and in such situations it is more useful for the designer to have some indication of how the operating conditions may be mod...

Abstract: Equations relating the flow of the lubricant and the axial motion of an externally pressurized thrust bearing are developed. The bearing is shown to be stable when the fluid is incompressible. Expressions for local stiffness and damping coefficients, useful in the evaluation of the dynamic response of the bearing, are given. An analog computer solution of the equation of motion is compared with the results of the corresponding, small displacement equation. (auth)