Showing papers on "Fluid bearing published in 2008"

Magnetic Bearing Configurations: Theoretical and Experimental Studies

Abstract: A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping, and high axial instability. To enhance the radial load and radial stiffness, and reduce the axial thrust, we have made a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing. We developed an experimental setup to investigate the performance of bearing configurations under different operating conditions. The motion of a rotating shaft is mapped by two displacement sensors with a data acquisition system and personal computer. The first critical speed of each configuration is determined experimentally and verified through frequency analysis. We present a polar plot of displacement data.

Design, Fabrication, and Performance of Open Source Generation I and II Compliant Hydrodynamic Gas Foil Bearings

Abstract: Foil gas bearings are self-acting hydrodynamic bearings made from sheet metal foils comprised of at least two layers. The innermost “top foil” layer traps a gas pressure film that supports a load while a layer or layers underneath provide an elastic foundation. Foil bearings are used in many lightly loaded, high-speed turbomachines such as compressors used for aircraft pressurization and small microturbines. Foil gas bearings provide a means to eliminate the oil system leading to reduced weight and enhanced temperature capability. The general lack of familiarity of the foil bearing design and manufacturing process has hindered their widespread dissemination. This paper reviews the publicly available literature to demonstrate the design, fabrication, and performance testing of both first- and second-generation bump-style foil bearings. It is anticipated that this paper may serve as an effective starting point for new development activities employing foil bearing technology.

Optimization of Groove Geometry for Thrust Air Bearing to Maximize Bearing Stiffness

Abstract: Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified.

Basic Characteristics of an Active Thrust Magnetic Bearing With a Cylindrical Rotor Core

Abstract: Magnetic bearings, which can suspend rotor shafts by electromagnetic force without mechanical contacts and lubrication, have been developed and commercialized. In the various types of magnetic bearings, thrust magnetic bearings with thrust disks are generally used for active suspension control of thrust direction. However, the large thrust disks of the thrust magnetic bearings have caused various problems. Therefore, this paper proposes a novel structure of an active thrust magnetic bearing using a cylindrical rotor core without the large thrust disk, and it is shown with 3-D-FEA and experiment that the proposed thrust magnetic bearing with the cylindrical rotor core is effective in producing thrust force.

Free Surface Thin Layer Flow on Bearing Raceways

Abstract: In this paper, the effects of rotation on the distribution of a layer of oil on a bearing raceway are analyzed in relation to the geometry of the raceway. The research is motivated by the need to understand the behavior of grease lubricated bearings. Some specific aspects of grease lubrication can be understood by approximating the contact as a starved lubricated elastohydrodynamic lubrication contact. In such a contact, the shape and thickness of the inlet layer of oil, supplied to the contact on the running track, are of crucial importance to the film formation and contact performance. Small changes in the distribution of lubricant on the rolling track, as a result of reflow or redistribution, may have a large (local) effect on the film thickness inside the contact. Starting from the Navier–Stokes equations, the free surface thin layer flow equation for axisymmetric rotating surfaces is derived. For the case of bearing applications, it is shown that a simple quasilinear equation can be derived for the layer thickness, as a function of location and time, which can be solved analytically. Experiments have been carried out, measuring the changes of a layer of oil on rotating raceways in time in relation to the rotational speed and the raceway geometry. It is shown that the simplified model accurately predicts the thin layer flow, except in a region near the outflow boundary, where the effect of the boundary condition on the layer shape is crucial. This is further illustrated by results of numerical simulations.

On Nonlinear Rotor Dynamic Effects of Aerodynamic Bearings With Simple Flexible Rotors

Abstract: The last decades have experienced a growing enhancement of aeronautical oil free turbomachinery. The classical linear approach of rotor dynamics commonly uses stiffness and damping coefficients to model journal bearings. In the present study, a nonlinear time dependant calculation is used for the dynamic simulation of a rotor mounted with aerodynamic (gas) bearings. A comparison between the two approaches indicates that the dynamic behavior of such bearings can be nonlinear in operating ranges where the rotor eccentricity reaches high values. In that case, the linear approach may lead to incorrect results and the nonlinear approach should be performed for better rotor dynamic prediction. A numerical procedure which analyzes the dynamic behavior of simple flexible rotors taking into account the nonlinear (transient regime) characteristics of aerodynamic bearings is presented. A simple example highlights the needs of nonlinear simulations in order to predict dynamic performance in oil-free turbomachinery.

High-Speed Rotor With Air Bearings Mounted on Flexible Supports : Test Bench and Experimental Results

Abstract: A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1 kg mass and 37 mm diameter is rotated up to 75,000 rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown.

Optimization of Groove Geometry for a Thrust Air Bearing According to Various Objective Functions

Abstract: Grooved thrust air bearings are widely used to support high-speed, low-loaded shafts in many rotating systems because of their low friction, noiseless operation, and simple structure. Several types of groove geometries, such as straight line, spiral, and herringbone, are commonly used in actual applications. Among them the spiral groove is mainly used. However, as far as the authors know, there is no theoretical evidence that the spiral groove is an optimized groove geometry in all possible groove geometries. This paper describes the optimum design for the groove geometry of thrust air bearings according to various objective functions, such as air film thickness, bearing torque, dynamic stiffness of air film, and combinations of same. In an optimum design, groove geometries are expressed by the third degrees of spline function, and sequential quadratic programming is used as the optimization method. We found that groove geometry optimizing air film thickness or friction torque takes the form of a spiral groove. The geometry optimizing the dynamic stiffness is the modified spiral groove. Some numerical results are compared with the measured data, and good agreements can be seen between them.Copyright © 2008 by ASME

Performance of hydrodynamic lubrication journal bearing with a slippage surface

Abstract: Purpose – The aim of this paper is to propose a design idea for an infinite journal bearing with the optimized slip zone on the bearing sleeve surface.Design/methodology/approach – The approach is to use finite element analysis and the quadratic programming algorithm to study the performance of the journal bearing with a slip zone on the sleeve surface. The fluid film pressure and slip velocity can be obtained in one solution step.Findings – A journal bearing with a slip zone on the sleeve surface produces many different advantages over the traditional journal bearing. Even in a parallel sliding gap there is still a considerable large load support, but a very low friction drag. The effect of the enhancement of such a slip wedge on the journal bearing performance is much greater at a small eccentricity ratio than at a large eccentricity ratio. Numerical analyses indicate that the location and size of the slip zone greatly affect the journal performance. When the eccentricity ratio ϵ=0.8, the maximum load s...

High-speed electrospindle running on air bearings: design and experimental verification

Abstract: In high-speed machining there are a number of applications in which the spindle is supported by air bearings. This type of bearings has very low friction and wear, resulting in virtually unlimited life. If the system is designed correctly the radial stiffness on the tool is comparable to that of ceramic ball bearings.

Simulating the Air Bearing Pressure and Flying Height in a Humid Environment

Abstract: For a hard disk drive operating in a humid environment, the water vapor in the slider's air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the slider's flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using two air bearing designs, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives.

Fluid dynamic bearing pattern and fluid dynamic bearing

Abstract: The invention relates to a fluid dynamic bearing pattern that is disposed on at least one bearing surface of the two bearing parts of a fluid dynamic bearing that are moveable with respect to each other along a direction of movement. The bearing pattern comprises two related grooved sections, each section extending at an acute angle with respect to the direction of movement and exerting a defined pumping effect on the bearing fluid found in the bearing when the bearing parts move with respect to each other. According to the invention, the first section is disposed at an angle α and the second section at an angle β with respect to the direction of movement, the two angles varying in size.

Development of a Miniature Air-bearing Stage with a Moving-magnet Linear Motor

Abstract: We propose a new miniature air-bearing stage with a moving-magnet slotless linear motor. This stage was developed to achieve the precise positioning required for submicron-level machining and miniaturization by introducing air bearings and a linear motor sufficient for mesoscale precision machine tools. The linear motor contained two permanent magnets and was designed to generate a preload force for the vertical air bearings and a thrust force for the stage movement. The characteristics of the air bearings, which used porous pads, were analyzed with numerical methods, and a magnetic circuit model was derived for the linear motor to calculate the required preload and thrust forces. A prototype of a single-axis miniature stage with dimensions of 120 (W) × 120 (l) × 50 (H) ㎜ was designed and fabricated, and its performance was examined, including its vertical stiffness, load capacity, thrust force, and positioning resolution.

Experimental and Analytical Investigation of a Dynamic Gas Squeeze Film Bearing Including Asperity Contact Effects

Abstract: This work presents a theoretical and experimental investigation of a flat circular gas squeeze film bearing. The thickness and the pressure profile of the gas squeeze film are obtained by simultaneously solving the Reynolds equation and the equation of motion for the squeeze film bearing. This work also accounts for the force due to asperity contact in the equation of motion. When the surfaces are in contact, the model predicts the contact force as a function of film thickness. Computational simulations were performed to study the development of the squeeze film from its initial state to a pseudo-steady state and also to evaluate its load- carrying capacity. For certain cases, the simulation results correlate well with the preestablished analytical results. However, corrections must be made to the preestablished analytical equations when they are used out of their effective range. In the experimental study, the squeeze film was developed by an applied relative normal motion between two parallel plates, of...

The influence of Oldroyd-B and PTT lubricants on moving journal bearing systems

Abstract: The influence of viscoelasticity on the performance of statically and dynamically loaded journal bearings is considered. The lubricant in the system is modelled using either the Oldroyd-B or linear PTT models. Significant viscoelastic effects are presented for both moderate and narrow gap journal bearing configurations. The dynamical behaviour of the journal bearing system is shown to be dependent on the fluid model, the relaxation time and also the gap size.

Dynamic analysis of hydrodynamic bearing performance in ic engines by using Taguchi technique and Response Surface Methodology (RSM)

Abstract: Much work has already been carried out on hydrodynamic bearings under static loads, but very little literature is available on the investigation under dynamic loads and its effect on inertia forces of engine parts like pistons, connecting rods, crank shafts and flywheels. An attempt is made in this paper to analyze the effect of load, journal speed, bearing width and mass flow rate with respect to variations in oil film thickness on power loss by fluctuations in pressure gradient, stiffness and damping effect during dynamic loading conditions. The oil film thickness is measured under various conditions of fluctuating/steady load, journal speed, bearing width and mass flow rate. The oil film thickness is measured by an eddy current gap sensor to deduce the shaft trajectories by using the experimental setup. The same concept is analyzed and compared with Taguchi techniques and response surface methodology (RSM). The vital role of this technique is considered for designing the experiment (robust design) and analyzing the dynamic sinusoidal loading effect. Also we analyze whether the solution for minimizing effect of the change in load causes a change in pressure gradient, which will create a delay in time response in the pressure gradient, which creates physical contact between the journal and bearing, causing power loss.

Research on elastohydrodynamic lubrication of a crankshaft bearing with a rough surface considering crankshaft deformation

Abstract: Journal misalignment in bearings caused by crankshaft deformation under load exists generally in internal combustion engines. When serious journal misalignment takes place, the minimum oil-film thickness of bearings is greatly reduced and the maximum oil-film pressure of the bearings increases markedly. Therefore, it is necessary to consider the surface roughness and deformation of bearing surface when analysing the hydrodynamic lubrication characteristics of a misaligned bearing. In this paper, the elastohydrodynamic lubrication properties of crankshaft bearings considering crankshaft deformation under load and the surface roughness for a four-cylinder internal combustion engine were studied. The lubrications of the crankshaft bearings were analysed by the dynamic method. The deformation of the bush surface under the oil-film pressure was calculated by the deformation matrix method. The results show that, when crankshaft deformation is considered, the surface roughness has a marked effect on the ...

Electrical submersible pump with equally loaded thrust bearings and method of pumping subterranean fluid

Abstract: A rotary pump having thrust bearings includes a system for equalizing the loading on the thrust bearings. The thrust bearings are each supported on pistons that are in fluid communication with a hydraulic circuit. The hydraulic circuit has substantially the same pressure throughout, thereby floating each piston at the same pressure to provide an equal support force to each thrust bearing via each piston.

Hydrodynamic lubrication of scroll compressor thrust bearing with grooves and circular pockets.

Abstract: This theoretical work concentrates on improvement in the lubrication performance of the scroll compressor thrust bearing undergoing an orbital motion In order to achieve the objective, the thrust surface is patterned with various surface features such as grooves (triangular, circular and trapezoidal) and circular pockets The analytical model was developed to predict the hydrodynamic pressure distribution and film thickness at the thrust interface of an orbiting scroll An isothermal, time-dependent polar coordinate Reynolds equation containing both radial and tangential velocity components was solved using a control volume finite difference approach The results indicate that under an orbiting situation circular pockets are capable of carrying a significant amount of load as compared to that of uniformly distributed radial grooves Based on the performance results obtained for various operating conditions, work was focused on designing an optimum surface pocket configuration that would provide maximum load support and minimum friction

Development of a Miniature Vertical Milling Machine for Automation Used in a Microfactory

Abstract: In this paper, a compact-sized milling machine is proposed for using in the miniaturized manufacturing system, the Microfactory. The miniature milling machine was designed to achieve high positioning accuracy within the working volume 35x35x33 mm3, by utilizing air bearings for linear movement guides and spindle. The configuration of the 3-axis milling machine was determined to be vertical machine considering automation for the factory line usage, and the vertical air bearing stage was designed to carry the high speed air bearing spindle in the middle of the guide for maximum stiffness. We describe the design aspects of this machine and some experimental results.

A Dynamic Analysis of Hydrodynamic Wave Journal Bearings

Abstract: The purpose of this paper is to study the dynamic behavior of a three-wave journal bearing using a transient approach. The transient analysis permits the determination of the rotor behavior after the fractional frequency whirl appears. The journal trajectory is determined by solving a set of nonlinear equations of motion using the Runge-Katta method. The fluid film forces are computed by integrating the transient Reynolds equation at each time step location of the shaft with respect to the bearing. Because of the large values of the rotational speeds, turbulent effects were included in the computations. The influence of the temperature on the viscosity was also considered. Numerical results were compared to experimenta1 results obtained at the NASA Glenn Research Center. Comparisons of the theoretical results with experimental data were found to be in good agreement. The numerical and experimental results showed that the fluid film of a three-wave journal bearing having a diameter of 30 mm, a length of 27 mm, and a wave amplitude ratio greater than 0.15 is stable even at rotational speeds of 60,000 RPM. For lower wave amplitude ratios, the threshold speed at which the fluid film becomes unstable depends on the wave amplitude and on the supply pocket pressure. Even if the fluid film is unstable, the wave bearing maintains the whirl orbit inside the bearing clearance.

Studies on tribology

Abstract: In high speed rotating machines such as turbines and generators, vibrations of a rotating shaft often hinder the smooth operation of the machine or even cause failure. Oil whip is one of such vibrations due to oil film action of journal bearing. Its mechanism and preventive method is explained and proposed in this paper. Further theoretical and experimental analyses are made for considering heat generation and temperature rise in hydrodynamic lubrication. The usefulness of the lubrication theory based on the k–e model is also shown for bearings with high eccentricity ratios. In the latter half of this paper, water lubrication, nitrogen gas lubrication and tribo-coated indium lubrication are shown as new promising methods, and their mechanisms are discussed and the importance of tribo-layer is explained. Some mechanisms of wear are introduced for better understanding of tribo-layer. In the last part of this paper, the mechanisms of generating static friction are shown for the cases of plastic contact and elastic contact, which is the base for understanding the mechanism of initiation of macroscopic sliding.(Communicated by Hidesato ITO , M.J.A.)

Saw arrangement for cutting purposes comprises a sawing device, a bearing formed as a fluid bearing and units for driving the sawing device to move the sawing device relative to the bearing

Abstract: Saw arrangement (1) comprises a sawing device (2), a bearing (3) formed as a fluid bearing and units for driving the sawing device to move the sawing device relative to the bearing. Preferred Features: The bearing is formed as a hydrostatic sliding bearing. The bearing has a U-shaped bearing body, a base element and parallel side elements. The relative distance of the bearing can be adjusted.

Hydrodynamic bearing device, spindle motor, and information recording and reproducing apparatus

Abstract: The hydrodynamic bearing device comprises a sleeve 1 , a shaft 2 , a thrust bearing portion, and a lubricating fluid 5 . The sleeve 1 has a bearing hole 1 C. The shaft 2 is inserted into the bearing hole 1 C in a state of being able to rotate relative to the sleeve 1 . The thrust bearing portion has a hydrodynamic groove for generating pressure in the axial direction. The lubricating fluid 5 is held in a gap formed by the thrust bearing portion. The hydrodynamic bearing device is further constituted so that the value of a wear amount function F 6 falls into a specific range. With the hydrodynamic bearing device, the required bearing performance can be satisfied, and the thrust bearing portion has a longer intermittent service life.