Lubrication of orifice-compensated flexible thrust pad bearings

The effects of the interaction between the restrictor design parameter ($\text{C}{}_{\mathrm{S2}}$), the deformation coefficient ($\text{C}{}_{\mathrm{d}}$) and the Poissons ratio (ν), on the performance characteristics of an orifice-compensated hydrostatic circular thrust pad bearing have been studied. The results are presented for various values of $\text{C}{}_{\mathrm{S2}}\text{,}\text{C}{}_{\mathrm{d}}\text{,}\text{and}\text{ν}$ and are compared with those of capillary-compensated bearings     

Thermodynamic analysis of wide thrust bearings operating in laminar inertial flow regimes

Wide thrust bearings operating in laminar inertial flow regimes are studied. Isothermal and thermohydrodynamic performances of the bearing are analysed. Integro-differential equations of motion, continuity and energy equations are solved to yield pressure, mass-mean velocity and temperature distributions. The effects of contraction ratio and film Reynolds number on the pressure field, load bearing capacity, flow rate and frictional resistance force of the bearing are examined. The effect of film temperature variation on the performance of the bearing is studied and the result is compared with the isothermal case. Viscous heating is seen to reduce significantly the load bearing capacity. The effects of including the inertial terms are also considered. The results for inertial and non-inertial cases are plotted and compared. The results show that, with the inclusion of the inertial terms, the load bearing capacity does increase. Comparisons with some experimental data are made and reasonable agreement is observed.     

Orifice-compensated flexible thrust pad bearings of different configurations

Performance characteristics of capillary and orifice-compensated flexible thrust bearings are presented for various values of the restrictor design parameter, C_s2, and the deformation coefficient, C_d. Interactions between C_s2 and C_d are studied for various bearing configurations.     

Static tilt characteristics of aerostatic rectangular double-pad thrust bearings with double row admissions

Aerostatic thrust bearings have been used in linear guideway systems of various precision measuring apparatus by reasons of low friction, non-hysteresis and high accuracy of motion. In such a case that the measuring systems do not satisfy the Abbé principle, the accuracy of linear guideway systems is greatly influenced by the tilt characteristics in pitch, roll and yaw directions of aerostatic thrust bearings. This paper proposes the application of aerostatic rectangular double-pad thrust bearings with double row admissions of compound restrictors to the linear guideway systems subjected to tilt moments in both pitch and roll directions, and investigates, theoretically and experimentally, the static tilt characteristics of these aerostatic thrust bearings.     

Performance analysis of a fully textured hybrid circular thrust pad bearing system operating with non-Newtonian lubricant

The present paper deals with the theoretical investigation of the influence of dimple geometry on fully textured hybrid thrust pad bearing and operating with non-Newtonian lubricant. The modified Reynolds equation which governs the flow of non-Newtonian lubricant in the clearance space has been solved using Finite Element Method. The simulated results indicate that the values of load carrying capacity, frictional power loss, maximum pressure and fluid film stiffness coefficient are significantly affected by the behavior of lubricant. The results presented in the study are expected to aid in determining the optimum value of dimple diameter and depth for the optimum bearing performance.     

Determination of the dynamic coefficients of the coupled journal and thrust bearings by the perturbation method

This paper proposes a method to calculate the stiffness and the damping coefficients of the coupled journal and thrust bearings. Reynolds equations and their perturbation equations of journal and thrust bearings are transformed to the finite element equations by considering the continuity of pressure and flow at the interface between the journal and the thrust bearings. It also includes the Reynolds boundary condition in the numerical analysis to simulate the cavitation phenomenon. The stiffness and damping coefficients of the proposed mathematical method are compared with those of the numerical differentiation of the bearing force with respect to finite displacements and finite velocities of bearing center. It shows that the proposed method can calculate the dynamic coefficients of a coupled journal and thrust bearing more numerically stable and computationally efficient than the differentiation method. It also investigates the coupling effect of the coupled journal and thrust bearing and it shows that the proposed method makes it possible to calculate the cross-coupled dynamic coefficients in the radial–axial direction of the coupled journal and thrust bearing.     

Static and dynamic characteristics of externally pressurized circular step thrust bearings lubricated with couple stress fluids

The combined effects of couple stresses, fluid inertia and recess volume fluid compressibility on the steady-state performance and the dynamic stiffness and damping characteristics of hydrostatic circular step thrust bearings are presented theoretically. Based on the micro-continuum theory, the modified Reynolds equation and the recess flow continuity equation are derived by using the Stokes constitutive equations to account for the couple stress effect resulting from a lubricant blended with various additives. Using a perturbation technique, results in terms of steady-state load-carrying capacity, oil flow rate, stiffness and damping coefficients are presented. A design example is also illustrated for engineering and industrial applications.     

Static tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors

Aerostatic rectangular thrust bearings with compound restrictors have often been used in ultra-precision machine tools and precision measuring equipment because high bearing stiffness is easily achieved. Compound restrictors combine a feed-hole restrictor with a groove compensation restrictor. This paper investigates, theoretically and experimentally, the static tilt characteristics of aerostatic rectangular double-pad thrust bearings with compound restrictors, when coupled loads or offset loads are applied. Furthermore, the usefulness of aerostatic thrust bearings with compound restrictors is clarified by comparison with the characteristics of conventional aerostatic thrust bearing with feedhole restrictors.     

Relationship between geometric errors of thrust plates and error motions of hydrostatic thrust bearings under quasi-static condition

A new model using approximate formulas is established to predict the error motions of hydrostatic thrust bearings. Three different types of geometric errors of thrust plates are listed in this paper including tilt errors, saddle shaped errors and petal shaped errors. The influences of them on lateral tilt error motion, longitudinal tilt error motion and axial error motion are discussed. Definitions of averaging coefficients are made based on the approximate formulas. It is found that the time-varying tilt errors are the main reason for the error motions of hydrostatic thrust bearings. The thrust bearings with six pairs of recesses have priority over the thrust bearings with four and three pairs of recesses in the view of rotation accuracy. Experiments are done using a hydrostatic rotary table with an outer diameter of 2 m. It is found that the second harmonic errors are the main component of the radial run-out and the results agree well with the results calculated from the approximate formulas.     

Lubrication of infinitely long thrust bearings with micropolar fluids

The characteristics of conventional infinitely long thrust bearings were obtained by solving numerically the modified Reynolds equation for the steady laminar flow of an incompressible micropolar fluid that has an increased effective viscosity, especially in thin films. The micropolar fluid pressure and the overall bearing characteristics, as compared with those obtained with a newtonian lubricant, are shown to depend on two groups of micropolar parameters. The bearing performance, in general, is improved by micropolar lubricants.     

Free boundary of lubricant film in ferrofluid journal bearings

The growing interest in ferrofluid bearings is caused by their excellent self-sealing ability. The understanding of behaviour of ferrofluid film boundary adjacent to ambient air is crucial for the proper design of the sealing unit of ferrofluid bearings. This paper is the first attempt to predict the shape of a ferrofluid free boundary in the presence of a static load and magnetic field. Analysis involves simultaneous integration of the Reynolds equation and the free boundary equation using perturbation technique with respect to shaft eccentricity. Magnetic field is shown to flatten ferrofluid free boundaries as well as to reduce cavitation region; both effects diminishing lubricant leakage.     

Experimental investigation into the performance of an aerostatic industrial thrust bearing

Load and flow versus air-gap curves and stability maps have been obtained for an industrial externally-pressurized air-lubricated thrust bearing with a central restrictor. Supply pressure and pocket depth were treated as parameters. Bearing stiffness was estimated by using a computer to fit a polynomial type curve to the test data. The results show that whereas the effect of inserting a pocket into the bearing improves its load capacity, there is no significant improvement in film stiffness at design conditions. The suggestion is made that the diameter of the orifice in the restrictor should be increased. As pocket depth is increased beyond the design value the bearing becomes prone to pneumatic hammer.     

Best steady state performance of a thrust supporting system

An optimization method to reach the best steady state performance of a double-recess circular thrust bearing with variable area orifices in its compensation circuit is discussed. Guidelines for the range for each design variable are established. Pocket size should be maximized for maximum bearing load carrying capacity, but minimized for maximum static film stiffness. Annular groove width recommendations are recess-pressure dependent. Variable area orifices in the supply circuit for bearings having either single or double recess can give improved static performance. A discussion of the practical applications of the supporting system proposed is included.     

Thrust bearing using a magnetic fluid lubricant under magnetic fields

This paper describes a thrust bearing using a magnetic fluid lubricant under a magnetic field. The critical pressures of the bearing versus the magnitude of the magnetic flux densities have been investigated experimentally. It is shown that the critical pressures of the proposed bearing are larger than those of the normal lubricated bearing under high speeds.     

Numerical and experimental analysis of aerostatic thrust bearings with porous restrictors

The finite element method is used to predict the performance of aerostatic thrust bearings with a complete porous surface. Results obtained by a 1D and 3D source flow model derived from D’Arcy’s law are compared for rectangular porous bearings having an infinite width. It turns out that the 1D source flow model is adequate for practical design parameters. For a circular aerostatic porous thrust bearing results calculated with several mathematical models for the source flow and slip flow are compared with experimental results. A relatively simple model incorporating unflatness and deformation of the bearing surface correlates well with the experimentally determined bearing performance.     

涡旋式制冷压缩机止推轴承润滑性能研究的最新进展

在涡旋式制冷压缩机运行过程中,止推轴承动止推盘两端的压力差对轴承的润滑性能有显著的影响;止推轴承本身的结构特点,如键槽的存在,也会影响止推间隙的压力分布以及倾斜角,从而影响止推轴承的润滑性能.对止推轴承动止推盘两端的压力差、止推轴承本身结构等影响因素从理论或试验等方面进行探讨,并对将来涡旋式制冷压缩机止推轴承润滑性能的研究进行展望.     

Analyses of thrust bearings in scroll compressors considering keyways

This work is an attempt to calculate the lubricating characteristics of thrust bearings in scroll compressors, which have non-circular shapes due to the keyways cut for the Oldham's coupling. The outer shapes of these bearings are not circular because the keyways intrude the bearing boundaries. A boundary fitted coordinate technique for hydrodynamic lubrication is modified to handle this non-circularity. The pressure distributions, resultant forces and moments are calculated, which are in equilibrium to the typical conditions generated in the compressing processes. The changes of nominal clearance and tilting angles are obtained during one cycle under the assumption of rigid-body motions.     

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.     

Friction torque of thrust ball bearings lubricated with wind turbine gear oils

Planetary gearboxes used in wind turbines very often have premature bearing and gear failures, some of them related to the lubricants used. Five fully formulated wind turbine gear oils with the same viscosity grade and different formulations were selected and their physical characterization was performed. The lubricant tribological behaviour in a thrust ball bearing was analyzed. A modified Four-Ball Machine was used to assemble the bearings. They were submitted to an axial load and the tests were performed at velocities ranging between 150 and 1500 rpm. Experimental results for the operating temperatures and for the internal friction torque are presented.     

The combined effects of the centripetal inertia and the surface roughness on the hydrostatic thrust spherical bearings performance

This paper deals with the surface roughness and the predominant centripetal inertia terms due to the shaft rotation of the externally pressurized thrust spherical bearings. The solutions are presented for the fitted type of bearings, un-recessed and recessed hemispherical and partial hemispherical seats, with capillary tube and orifice restrictors. On the basis of the stochastic theory, Reynolds equation is developed. The bearing surfaces are assumed to have randomly distributed roughness. Expressions for the pressure distribution, load carrying capacity, volume flow rate, frictional torque, friction factor, power factor, power losses and stiffness factor are obtained. The paper shows the combined effects of the centripetal inertia and the surface roughness on the bearing performance. An optimum design based on the minimum power losses, minimum flow rate and optimal restrictor dimensions is theoretically examined.