Showing papers on "Fluid bearing published in 1996"

Effect of Roughness on the Behavior of Squeeze Film in a Spherical Bearing

Abstract: The behavior of a hydrodynamic squeeze film between a non-rotating spherical surface and a hemispherical bearing under a steady load is analyzed. It is assumed that the bearing surface as well as the surface of the approaching sphere have a longitudinal random roughness which is distributed throughout the surfaces. The stochastic film thickness characterizing the roughness is assumed to be symmetric and its mean value is equal to zero. The modified Reynolds equation is solved and the expressions for pressure, load-carrying capacity and the response lime are obtained. The results are presented graphically. It is observed that the performance of the bearing is adversely affected by the composite roughness of the surfaces.

Turbulent Flow, Flexure-Pivot Hybrid Bearings for Cryogenic Applications

Abstract: The thermal analysis of flexure-pivot tilting-pad hybrid (combination hydrostatic-hydrodynamic) bearings for cryogenic turbopumps is presented. The advantages of this type of bearing for high speed operation are discussed. Turbulent bulk-flow, variable properties, momentum and energy transport equations of motion govern the flow in the bearing pads. Zeroth-order equations for the flow field at a journal equilibrium position render the bearing flow rate, load capacity, drag torque, and temperature rise. First-order equations for perturbed flow fields due to small amplitude journal motions provide rotordynamic force coefficients. A method to determine the tilting-pad moment coefficients from the force displacement coefficients is outlined. Numerical predictions correlate well with experimental measurements for tilting-pad hydrodynamic bearings. The design of a liquid oxygen, flexure-pad hybrid bearing shows a reduced whirl frequency ratio and without loss in load capacity or reduction in direct stiffness and damping coefficients.

An Efficient Finite Element-Based Air Bearing Simulator for Pivoted Slider Bearings using Bi-Conjugate Gradient Algorithms

Abstract: A computationally efficient air bearing simulator-for pivoted slider bearings has been developed that is based on finite element theory and uses bi-conjugate gradient algorithms in conjunction with a sparse matrix storage scheme. The air bearing simulator involves the simultaneous solution of the Reynolds equation and the slider equilibrium equations. The highly nonlinear problem requires the repeated solution of a nonsymmetric system of equations, typically with a large number of unknowns depending on the complexity of the slider geometry. Iterative solvers, such, as the bi-conjugate gradient algorithms used for this study, require significantly less core memory as compared to direct solvers and reduce the solution time if combined with a suitable preconditions. Of the bi-conjugate gradient algorithm/preconditioner combinations implemented, the Bi-CGSTAB algorithm combined with an ILU preconditioner provided the best performance in terms of smooth convergence and computational efficiency. Presented as a ...

Performance of Plain Bearings with Circumferential Microgrooves

Abstract: Higher performance of recent automotive engines requires their bearings to operate under more severe conditions like higher speeds, higher loads and higher temperatures. To meet this requirement, plain bearings with circumferential microgrooves have been developed. Experimental evaluation as well as theoretical analysis has revealed that the ease of initial wear and deformation at the ridges leads to superior conformabilily, increased oil flow along the microgrooves achieves lower bearing temperature, and the oil retained in the microgrooves prevents seizure tinder starved lubricating conditions. Presented at the 50th Annual Meeting in Chicago, Illinois May 14–19, 1995

On the Dynamic Thermal State in a Hydrodynamic Bearing With a Whirling Journal Using CFD Techniques

Abstract: A thermohydrodynamic analysis, based on computational fluid dynamics (CFD) techniques, that accounts for conduction in the rotating and orbiting shaft of hydrodynamic bearing is presented. No restrictions apply to the circumferential or axial variation of journal/shaft temperature. Dynamic cavitation effects are also introduced, such that pressures in the cavitation region are predicted rather than set. The model predictions are validated against analytical and published experimental results. For the case of a centrally located synchronous forward circular whirl orbit, it is demonstrated that the journal does not behave as a circumferentially isothermal element and that significant steady temperature differentials across the journal may occur.

Grooved hydrodynamic bearing arrangement including a porous lubricant reservoir

Abstract: The hydrodynamic bearing arrangement comprises a journal sleeve defining a journal bore and a journal thrust surface. A shaft is mounted in the journal bore by means of a hydrodynamic journal bearing which permits rotation of the shaft and the journal sleeve relative to one another. A thrust plate extends transversely from the shaft and defines two hydrodynamic thrust bearings in combination with the journal thrust surface and a counterplate which is mounted adjacent to the thrust plate. A porous lubricant reservoir is mounted adjacent to the thrust plate. The porous lubricant reservoir serves to remove wear particles from the lubricant in the bearing arrangement, and provides a supply of lubricant to the hydrodynamic journal and thrust bearings should they become depleted of lubricant.

Hydrodynamic bearing unit

Abstract: A self-contained hydrodynamic bearing unit with improved sealing and performance is disclosed. Centrifugal capillary seals are angularly defined between an outwardly tapered outer surface of a top screw and an inwardly tapered inner surface of an annular clamp ring at the top of the bearing unit as well as between an outwardly tapered outer surface of a seal plate and an inwardly tapered inner surface of an annular clamp ring at the bottom of the bearing unit. During operation, bearing lubricant is pumped away from the seal opening and toward the bearings by centrifugal force at the seals, providing dynamic sealing. When the bearing unit is not rotating, capillary forces retain the lubricant within the seal, preventing the lubricant from leaking. The tapered configuration of the seals also shortens the vertical seal length for a given effective seal length, thereby maximizing the journal bearing length/span and improving dynamic performance of the bearing unit.

Method and apparatus for applying lubricant to a hydrodynamic bearing

Abstract: A method, and associated apparatus, of applying fluid lubricant to a hydrodynamic bearing. Clearance spaces of the bearing which are to be filled with the fluid lubricant are evacuated. The fluid lubricant is then applied to the clearance spaces. Once the fluid lubricant has been applied to the clearance spaces, or concurrent therewith, the clearance spaces are returned to ambient pressure levels. Any pockets of air, or other gas, trapped within the bearing are collapsed as the clearance spaces are returned to the ambient pressure levels. The method is amenable to a high volume, assembly line-like process wherein large numbers of bearings may be filled with the fluid lubricant in a short period of time.

Dynamic Characteristics of Hard Disk Drive Spindle Motors—Comparison Between Ball Bearings and Hydrodynamic Bearings

Abstract: Recently, many computer hard disk drive companies and spindle motor manufacturers have been looking for a substitute for ball bearings to continue making dramatic progress in increasing the capacity of data storage systems. In this paper, the frequency-forced responses of hard disk drive spindle motors supported by both ball bearings and liquid-lubricated spiral groove bearings (SGBs) were studied experimentally. It is found that both shaft rigidity and disk flexibility have great effects on the natural frequency of the spindle motor conical (rocking) mode. The high damping capacity of the SGB is able to suppress the vibration amplitudes of both motor rocking mode and the flexible disk modes. But at a very low frequency range, the SGB motors displayed a large amplitude in the axial direction vibration test. With an adequate bearing design, the SGB motors have proven their superior dynamic characteristics.

Memory disk driving apparatus

Abstract: A memory disk driving apparatus has a dynamic pressure fluid bearing type spindle motor 1, wherein herringbone grooves 12a are formed on the shaft 12. In the dynamic pressure fluid bearing relatively rotatable with the intermediary of the lubricant injected into a gap between the shaft 12 and the sleeve 13; the shaft diameter D is selected 4 mm or less, and the ratio of the radial gap R between the shaft and the sleeve to the diameter D of the shaft (R/D) is between 0.0005 and 0.002.

Dynamic-pressure fluid bearing

Abstract: A dynamic-pressure fluid bearing comprises bearing parts formed by a pair of dynamic-pressure surfaces. One of the dynamic-pressure surfaces of the bearing parts is a polyamideimide coating thicker than 3 μm and the other surface is metal. The bearing is particularly applicable to driving motors for polygon mirrors.

Effect of Lubricant Supply Starvation on the Thermohydrodynamic Performance of a Journal Bearing

Abstract: With judicious selection of supply groove location for journal bearings, the lubricant supply rate and power loss can be considerably reduced without sacrificing the load-carrying capacity. In addition, the lubricant supply rate can further be reduced, either accidentally or deliberately, and the applied load may still be maintained. In this parametric study, the effects of reduced lubricant supply rate compared to the flooded inlet is studied for an axial-grooved journal bearing. Cavitation effects in the fluid film are taken into account and a full THD model, including heat conduction to the metal surfaces, is included in the analysis. Performance parameters at various load values due to reduced supply rate and typical temperature distributions are presented. It is found that, it may be possible to operate the bearing with as much as 70 percent reduction in lubricant supply rate. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kissimmee, Fl...

Analysis of a gas lubricated hydrodynamic thrust bearing

Abstract: Experimental results from a gas thrust bearing test facility are reported in this paper. This fundamental investigation of the thermo-fluid dynamics of a gas lubricated bearing forms part of a wider programme aimed at their introduction into the aeroengine environment. The experiments provide the most detailed measurements to date of a hydrodynamic lubrication film which uses gas as a working fluid. The bearing tested was lubricated with air. The thrust pads had an outer radius of 0.125 m and during operation the clearance between the bearing surfaces was typically 10 μm. The design speed of the bearing was 10,000 rpm. Mean pad pressure and temperature distributions are presented for a range of bearing loads up to 3/4 kN, which were measured under steady operating conditions. Transient pressure and surface clearance measurements from fast response probes are also reported. These measurements show a complex relative motion of the bearing surfaces, the exact nature of which could only be determined from a more detailed set of surface clearance measurements than those in the present work. However, the transient pressure measurements show that these surface clearance fluctuations do not exert a strong influence on the lubrication film pressures, which can be considered to be essentially steady. The test data are compared with predictions obtained by solving Reynolds equation numerically, using a finite-volume based procedure. Thermal distortion of the bearing surface is not included in the model and this limits the agreement between measurements and calculations. The results suggest that this must be accounted for in the design of practical bearing systems, even though the lubrication film can be treated as isothermal. The measurements also show evidence of the inlet effects which raise the static pressure of the flow entering the bearing to above the ambient level.

Hydrodynamic lubrication of squeeze-film porous bearings

Abstract: Closed-form analytical solutions for three different types of squeeze-film porous bearing are introduced in this paper. The effects of the permeability parameter on the pressure profile, load-carrying capacity, and time required to squeeze the fluid out of the lubricated conjunction are presented. The results show that as the permeability parameter increases, both the pressure profiles and the load-carrying capacity of the bearing decrease in the case of pure squeeze motion. Furthermore, the results show that for dimensionless permeability parameters less than 0.001, the effect of the porous layer on the hydrodynamic lubrication of squeeze-film porous bearings can be neglected.

Crash tolerant air bearing spindle

Abstract: A rugged spindle for a disk certifier that test the disks of a hard disk drive. The spindle contains a first bearing and a second bearing that are coupled together by a shaft. The first bearing is coupled to a chuck that captures a disk. The second bearing is coupled to the spindle shaft of an electric motor which rotates the disk. The bearings each contain an outer graphite sheath that is separated from a hardened housing by an air bearing. The connecting shaft is bonded to the first and second bearings by an adhesive that is injected through longitudinal passages of the shaft. The bonding adhesive flows along the interface of the connecting shaft and bearings until the adhesive fills an indicator slot of the shaft. Air bearings are created during the bonding process of the second bearing to insure an accurate relationship between the two bearings and the housing.

On the Vibration of Coupled Traveling String and Air Bearing Systems

Abstract: Air bearings are used to position and guide such axially-moving materials as high speed magnetic tapes, paper sheets, and webs. In each case, vibration of the moving medium couples with the air bearing's dynamics, and techniques are developed here to reduce the computational effort that is required to predict the natural frequencies, damping ratios, and vibration modes of the prototypical traveling string and self-pressurized air bearing model. Automatic nodal point allocation reduces the number of nonlinear equations that arise in finding the equilibrium string displacement and air pressure, and in subsequent vibration analysis, the response is obtained in closed form by using the Green's function for the traveling string. Global discretization of the air pressure alone then yields a matrix eigenvalue problem which is simpler than that obtained through previous methods which required discretization of both displacement and pressure. Overall, essentially a five-fold increase in computational speed is achieved, thus facilitating design and parameter studies. Changes in the natural frequencies, damping ratios, and coupled displacement-pressure mode shapes with respect to several design variables are discussed and compared with experiments.

Air lubricated hydrodynamic ceramic bearings

Abstract: An air lubricated hydrodynamic bearing assemblage has a ceramic body and a ceramic shaft each made of tetragonal zirconium ceramic material. The bearing has flange portions on opposite ends a a generally cylindrical body. At least one of the flange portions has air channels formed therein in fluid communications with air inlet ports formed in the bearing body.

A Model of Slider/Disk Interface Wear for Proximity Recording

Abstract: Slider/disk interface wear is inevitable for ultra-low flying hard disk drives and is the central issue for proximity recording. While disk wear has been addressed in the literature, slider wear has been largely considered to be trivial and is ignored. However, with the improvement of disk overcoat and introduction of diamond-like-carbon overcoat on slider air bearing surface, the surface hardnesses of the slider and disk are approaching each other and, therefore, the slider surface wear becomes significant or, in some conditions, even dominant. In this study, a theoretical model is developed for semi-steady-state slider/disk interface evolution of proximity recording which takes account of both the disk and slider wear. It includes the effects of the air bearing characteristics, pitch stiffness, material properties, and surface topography of both the slider and disk. Numerical results are illustrated for typical proximity recording interface, where the evolutions of the slider, disk, contact force, and pitch angle are evaluated for various air bearing stiffnesses, material properties, and surface topographies. This model is intended to provide some fundamental understanding of the slider/disk interface evolution during proximity recording process.

Boundary element method for transient viscoelastic flow : The MPTT model

Abstract: This paper deals with the modelling of viscoelastic flows in transient regimes using the Modified Phan Tien and Tanner (MPTT) model. This model is the most recent one which can predict stress overshoot in unsteady shear flow and is based on the description of the liquid microstructure rather than empirical and mathematical developments. Here, the analysis of the squeeze film between parallel plates is presented. It is an alternative in quantifying and understanding the two main factors which may enhance the carrying capacity (inertia effect and viscoelastic behavior) situation which can occur, for instance, in the case of overloading in journal bearings. A boundary element method is used here to model such complex flow. The main factors have been extracted and the restrictions due to a rough estimate of the lubricant's flow are shown. Presented as a Society of Tribologlsts and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Lahaina, Hawaii, October 16–20, 1994

Fluid dynamic bearing with low stiffness change over temperature

Abstract: A fluid dynamic bearing is described having an inner element made of a first material with a first coefficient of thermal expansion, an outer element made of a second material with a second coefficient, and a layer of viscous fluid in contact with and separating the inner element from the outer element such that said outer element is capable of rotation around said inner element. By choosing particular materials, the difference between the first and second coefficients of thermal expansion can be controlled, and the thickness of the layer of viscous fluid can be made to vary with temperature. This allows for some degree of control over the temperature dependence of the stiffness and drag of the fluid dynamic bearing. In particular, the coefficients of thermal expansion can be chosen so as to cancel out any temperature dependence of stiffness and/or drag due to a temperature dependence of the viscosity of the viscous fluid.

Lubrication of Long Porous Slider Bearings : Use of the Brinkman-Extended Darcy Model

Abstract: We apply the Brinkman-extended Darcy model to analyze the hydrodynamic lubrication of long porous slider bearings. The solutions are obtained and compared with those based on the Darcy model. The results show that the effects of viscous shear given by the Brinkman-extended Darcy model lead to a higher load capacity and a lower friction parameter. It is found that a thicker porous bearing gives a greater effect of viscous shear on load capacity and friction parameter.