Characteristics Of Hydrostatic Thrust Bearings Research Articles

Investigation of the Static Performance of Hydrostatic Thrust Bearings Considering Non-Gaussian Surface Topography

The dynamic and static characteristics of hydrostatic thrust bearings are significantly affected by the bearing surface topography. Previous studies on hydrostatic thrust bearings have focused on Gaussian distribution models of bearing surface topography. However, based on actual measurements, the non-Gaussianity of the distribution characteristics of bearing surface topography is clear. To accurately characterize the non-Gaussian distribution of bearing surface topography, the traditional probability density function of Gaussian distribution was modified by introducing Edgeworth expansion. The non-Gaussian surface was then reflected by two parameters: kurtosis and skewness. This had an effect on the static characteristics of hydrostatic thrust bearings with both circumferential and radial surface topographies. The comparison between the Gaussian distribution results and those of the non-Gaussian model showed that errors between the two models could reach more than 10%. Therefore, it is important to take into account the non-Gaussianity of bearing surface when discussing static characteristics of hydrostatic thrust bearings considering the surface topography.

Difference Between SFMR and SITMR Compensation for Hydrostatic Thrust Bearing

Abstract Both flat and island type membranes are used in single-action membrane restrictors. But the difference between the single-action flat membrane restrictor (SFMR) and the single-action island type membrane restrictor (SITMR) has rarely been reported in the literature. In this study, we first compared the static and dynamic characteristics of SFMR and SITMR and found that there is a little difference between them when the difference between supply pressure ps and outlet pressure pr is not large. Then, we investigated the dynamic characteristics of hydrostatic thrust bearings using both SFMR and SITMR compensation and found SITMR having a better dynamic bearing performance. The reason for this phenomenon is that the mass of the membrane in SITMR is smaller than that of the membrane in SFMR. When the difference between supply pressure ps and outlet pressure pr becomes large, SFMR reduces the static flowrate of the lubricant of bearing systems more significantly than SITMR.

Static characteristics of hydrostatic thrust bearing considering the inertia effect on the region of supply hole

In the previous studies on the hydrostatic thrust bearing, the differences between the theoretical results and experimental results are obvious when the inertia parameter S and the ratio of supply hole radius to bearing radius r0/ R become large enough. To explain the differences, in this study, the inertia effect on the region of supply hole is considered in discussing the static characteristics of hydrostatic thrust bearing, and then new expressions of pressure, load capacity, and flow rate are given. For the continuous parallel bearing, the results of this study agree well with experiments, thus there is no need for the extra modified inertia theory. For the step bearing with a large inertia parameter (e.g., S = 2), the results of this study agree with experiments on the recess region, and are closer to the experimental results than those of old method on the region of bearing land. So when the inertia parameter S and the ratio of supply hole radius to bearing radius r0/ R are large enough, the inertia effect on the region of supply hole cannot be ignored in discussing the static characteristics of hydrostatic thrust bearing.

Influences of Lubricant Viscosity Ratio on Static Characteristics of Hydrostatic Thrust Bearing

This paper uses numerical simulation to study the influences of viscosity ratio on the static characteristics of hydrostatic thrust bearing compensated by various restrictors. The design parameters of open type hydrostatic bearing include: effective area, supply pressure, restriction constants of restrictor and bearing pad, and specific value of average viscosity of the lubricant passing through restrictor and bearing pad film. The optimal design requirements of restrictors and hydrostatic bearing and the corresponding range of design parameters for excellent bearing characteristics can be obtained from the relationships between these design parameters together with their composed parameters and ratios, and the static load capacity and film stiffness and worktable displacement of hydrostatic bearing. Fixing the other design parameters and changing viscosity ratio, the simulation results depict that the lubricant viscosity during restrictor being greater than that in bearing pad film will make the load capacity decrease, but will improve the film static stiffness.

Modeling and Experimental Investigation of Micro-hydrostatic Gas Thrust Bearings for Micro-turbomachines

One major challenge for the successful operation of high-power-density micro-devices lies in the stable operation of the bearings supporting the high-speed rotating turbomachinery. Previous modeling efforts by Piekos (2000, “Numerical Simulation of Gas-Lubricated Journal Bearings for Microfabricated Machines,” Ph.D. thesis, Department of Aeronautics and Astronautics, MIT), Liu et al. (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbo Machinery,” ASME J. Vib. Acoust., 127, pp. 157–164), and Spakovszky and Liu (2005, “Scaling Laws for Ultra-Short Hydrostatic Gas Journal Bearings,” ASME J. Vib. Acoust. 127, pp. 254–261) have focused on the operation and stability of journal bearings. Thrust bearings play a vital role in providing axial support and stiffness, and there is a need to improve the understanding of their dynamic behavior. In this work, a rigorous theory is presented to analyze the effects of compressibility in micro-flows (characterized by low Reynolds numbers and high Mach numbers) through hydrostatic thrust bearings for application to micro-turbomachines. The analytical model, which combines a one-dimensional compressible flow model with finite-element analysis, serves as a useful tool for establishing operating protocols and assessing the stability characteristics of hydrostatic thrust bearings. The model is capable of predicting key steady-state performance indicators, such as bearing mass flow, axial stiffness, and natural frequency as a function of the hydrostatic supply pressure and thrust-bearing geometry. The model has been applied to investigate the static stability of hydrostatic thrust bearings in micro-turbine generators, where the electrostatic attraction between the stator and rotor gives rise to a negative axial stiffness contribution and may lead to device failure. Thrust-bearing operating protocols have been established for a micro-turbopump, where the bearings also serve as an annular seal preventing the leakage of pressurized liquid from the pump to the gaseous flow in the turbine. The dual role of the annular pad poses challenges in the operation of both the device and the thrust bearing. The operating protocols provide essential information on the required thrust-bearing supply pressures and axial gaps required to prevent the leakage of water into the thrust bearings. Good agreement is observed between the model predictions and experimental results. A dynamic stability analysis has been conducted, which indicates the occurrence of instabilities due to flow choking effects in both forward and aft thrust bearings. A simple criterion for the onset of axial rotor oscillations has been established and subsequently verified in a micro-turbocharger experiment. The predicted frequencies of the unstable axial oscillations compare well with the experimental measurements.

弾性変形を伴う静圧スラスト軸受のトライボロジー特性に関する解析(S52-2 機素潤滑設計部門第10回卒業研究コンテスト(2),S52 機素潤滑設計部門第10回卒業研究コンテスト)

弾性変形を伴う静圧スラスト軸受のトライボロジー特性に関する解析(S52-2 機素潤滑設計部門第10回卒業研究コンテスト(2),S52 機素潤滑設計部門第10回卒業研究コンテスト)

Experimental assessment of hydrostatic thrust bearing performance

This work presents an experimental study to assess the performance characteristics of hydrostatic thrust bearings. A test rig is designed for testing two configurations of hydrostatic bearings compensated by a capillary tube, one with a mid-circular recess and the other with multi-sectors (four recesses of different recess radii ratios). The performance characteristics have been measured, namely, oil film thickness, recess pressure, pressure distribution and oil flow rate. A specially devised computer program using an iterative technique has been adopted to compute numerically the pressure distribution and predict other performance characteristics. Good agreement has been obtained between predicted theoretical performance and that experimentally measured. The results demonstrate that the bearing recess size and location have a great influence on the performance of the hydrostatic thrust bearing.

Experiment on Mixed Lubrication of Hydrostatic Thrust Bearings for Hydraulic Equipment

Mixed lubrication characteristics of hydrostatic thrust bearings are examined experimentally. The effects of the surface roughness, supply pressure, loads, speed of rotation and size of restrictors on the frictional force, leakage-flow rate and power losses are clarified. Introducing the concept of mean pressure based on load-carrying capacity due to asperities, and the ratios of hydrostatic balance and leakage-flow rate, the experimental data can be normalized. Also good agreement is found between theoretical results based on a mixed lubrication model presented in a previous paper and the experiment.

Turbulent lubrication for hydrostatic thrust bearing with a circular recess.

This paper is concerned with the characteristics of hydrostatic thrust bearings operating in the turbulent regime. Using the calculated results of the three-dimensional turbulent mean velocity between a rotating disk and a fixed wall as already proposed, the pressure distribution, the load capacity and the oil flow rate of the hydrostatic thrust bearing with a circular recess are presented. Comparing the calculated results with the experimental ones, it has been found that the characteristics of the above bearing are little influenced by the transition to turbulence of the lubricant flow in the recess, but that the transition in the land produces an extreme change to the bearing characteristics such as the load capacity and the lubricant flow rate.

Turbulent lubrication for a hydrostatic thrust bearing with a circular recess.

The paper is concerned with the characteristics of hydrostatic thrust bearings operating in the turbulent regime. Using the calculated results of the three-dimensional turbulent mean velocity between a rotating disk and a fixed wall, as already proposed, the pressure distribution, the load capacity and the oil flow rate of the hydrostatic thrust bearing with a circular recess are presented. Comparing the calculated results with the experimental ones, it has been found that the characteristics of the above bearing are little influenced by the transition to turbulence of the lubricant flow in the recess, but the transition in the land produces an extreme change in the bearing characteristics such as the load capacity and the lubricant flow rate.

Floating and Bouncing on Oil

IN A HYDROSTATIC thrust bearing the two flat metal bearing surfaces are held apart by a film of oil two or three thousandths of an inch thick, the oil film being maintained from a pressurized supply. In this way coefficients of friction between the bearing surfaces can be reduced to very low values, usually less than 0.00005. The Mount Palomar telescope weighing nearly 500 tons is supported on three hydrostatic pads and the whole system can be rotated by a 1/12 h.p. clock motor. In machine tool practice the use of hydrostatic slideways enables the moving member to move along straight lines to a tolerance of a few millionths of an inch. The author has been concerned with the design of hydrostatic thrust bearings for machine tool applications. In this case it is not enough to design a bearing merely to lift a given weight, but the bearing must be designed so that its stiffness (i.e. load per unit deflection, as for a simple spring) is adequate and so that the damping ratio of the oil film is nearly critical. The Mount Palomar bearings have theoretically no stiffness at all, and would be quite unsuitable for machine tool applications, or for any other application where the amount of deflection under load is important or where there is a possibility of vibrattion occurring. In this article the author will show how the stiffness and damping characteristics of hydrostatic thrust bearings can easily be found.