Showing papers on "Fluid bearing published in 2004"

A Systems Approach to the Solid Lubrication of Foil Air Bearings for Oil-Free Turbomachinery

Abstract: Foil air bearings are self-acting hydrodynamic bearings which rely upon solid lubricants to reduce friction and minimize wear during sliding which occurs at start-up and shut-down when surface speeds are too low to allow the formation of a hydrodynamic air film This solid lubrication is typically accomplished by coating the non-moving foil surface with a thin, soft polymeric film The following paper introduces a systems approach in which the solid lubrication is provided by a combination of self lubricating shaft coatings coupled with various wear resistant and lubricating foil coatings The use of multiple materials, each providing different functions is modeled after oil-lubricated hydrodynamic sleeve bearing technology which utilizes various coatings and surface treatments in conjunction with oil lubricants to achieve optimum performance In this study, room temperature load capacity tests are performed on journal foil air bearings operating at 14,000 rpm Different shaft and foil coating technologies such as plasma sprayed composites, ceramic, polymer and inorganic lubricant coatings are evaluated as foil bearing lubricants The results indicate that bearing performance is improved through the individual use of the lubricants and treatments tested Further, combining several solid lubricants together yielded synergistically better results than any material alone

Thermohydrodynamic Behavior of Misaligned Plain Journal Bearings: Theoretical and Experimental Approaches

Abstract: Hydrodynamic journal bearings are essential components for supporting and guiding the rotating shafts of high-speed machinery. Manufacturing defects in assembly or thermal distortions may introduce problems during running, such as misalignment. The destructive effects of this kind of running problem have justified the development of a numerical model to predict the bearing operating characteristics under steady-state conditions. The present work presents in detail the three-dimensional thermohydrodynamic approach adopted in this study in order to consider the thermal field variations. This model also includes lubricant film rupture and reformation phenomena by conserving the mass flow rate. In addition, an experimental validation is made by comparison with measurements carried out on our test device for various operating conditions and misalignment torques. The influence of misalignment direction is also investigated by considering numerical and experimental approaches used in the study of bearing behavio...

Journal Design Considerations for Turbomachine Shafts Supported on Foil Air Bearings

Abstract: Foil air bearings can offer substantial improvements over traditional rolling element bearings in many applications and are attractive as a replacement to enable the development of advanced oil-free turbomachinery. In the course of rigorous testing of foil journal bearings at NASA Glenn Research Center, shaft failure was repeatedly encountered at high ambient temperature and rotational speed, with moderate radial load. The cause of failure is determined to be excessive non-uniform shaft growth, which increases localized viscous heating in the gas film and eventually leads to a high-speed rub and destruction of the bearing and journal. Centrifugal loading of imbalance correction weights and axial temperature gradients within the journal due to the hydrodynamic nature of the foil bearings, determined by experiment and finite element analysis, are shown to be responsible for the non-uniform growth. Qualitative journal design guidance is given to aid in failure prevention.

Lubrication of Silicon Nitride and Silicon Carbide by Water: Running in, Wear and Operation of Sliding Bearings

Abstract: The purpose of this work was to establish the conditions for the operation and break-in of water-lubricated ceramic bearings. The experiments consisted of sliding 1/4″ silicon nitride or—carbide balls against pre-polished disks of the same material in water until tribochemical wear generates smooth conformal surfaces that allow hydrodynamic lubrication (μ<0.002) by very thin water films. This “running in” was performed at various sliding speeds (0.01-4m/s) and loads (0.5-20N). The minimum sliding speed for low friction were 0.04m/s for silicon nitride and 0.5m/s for silicon carbide, much lower than for conventional bearings. The load carrying pressures were 60-80MPa, which is higher than the usually pressures of thrust bearings. The hydrodynamic fluid film thickness was estimated with a standard integration of Reynolds' equations modified for circular geometry, it was to be 5-15nm for silicon nitride, 25nm for silicon carbide. Operation over long distances (80km) allowed us to measure the wear rate during hydrodynamic lubrication; this was found to be <2×10−11mm3/nm, a rate acceptable for industrial application. A novel method completed during this work allows the determination of the wear rate during run-in. It varies with sliding velocity for silicon nitride, from 1 to 6×10−5mm3/nm; it is constant at 4×10−6mm3/nm for silicon carbide.

A self-acting gas thrust bearing for high-speed microrotors

Abstract: Micromachines rotating at high speeds require low drag bearings with adequate load capacity and stability. Such bearings must be compatible with the capabilities of microfabrication technology. A self-acting (hydrodynamic) gas thrust bearing was designed, fabricated and tested on a silicon microturbine. Conventional thrust bearing design techniques were adapted from macroscale literature. Microbearing design charts are presented that relate bearing performance to geometry. Such bearings exhibit a design tradeoff between load bearing capability and maximum operating speed (as limited by instabilities). The specific geometry described herein was intended to replace externally pressurized, hydrostatic thrust bearings in an existing device (a 4-mm-diameter silicon microturbine), thus the hydrodynamic bearing design was constrained to be compatible in geometry and fabrication process. The final design consisted of 2.2-/spl mu/m deep by 40-/spl mu/ wide spiral grooves around the 700-/spl mu/m diameter bearing. The bearings were fabricated in silicon with standard RIE and DRIE techniques. Test devices demonstrated lift-off and operation up to 450,000 rpm with a load capacity of 0.03 N. Measurements of load capacity and stiffness were consistent with the analysis.

Air bearing and motor cooling

Abstract: A motor includes a housing including separate motor and bearing cooling inlets. A motor is arranged within the housing and includes a stator and rotor assembly that is supported on air bearings. The motor cooling inlet is in fluid communication with the stator, and the bearing cooling inlet is in fluid communication with the air bearings. A vent is arranged in the housing and is common to the motor and bearing cooling inlets. The vent is in fluid communication with a low pressure side of a ram air duct. The bearing cooling duct is in fluid communication with a high pressure side of a ram air duct, such as through a reverse J-tube. A differential pressure between the high and low pressure sides moves cooling fluid from the bearing cooling inlet to the vent to cool the bearings.

Compensation of Cross-Coupling Stiffness and Increase of Direct Damping in Multirecess Journal Bearings Using Active Hybrid Lubrication: Part I—Theory

Abstract: Fluid film forces are generated in hydrostatic journal bearings by two types of lubrication mechanisms: the hydrostatic lubrication in the bearing recesses and hydrodynamic lubrication in the bearing lands, when operating in rotation. The combination of both lubrication mechanisms leads to hybrid journal bearings (HJB). When part of hydrostatic pressure is also dynamically modified by means of hydraulic control systems, one refers to the active lubrication. The main contribution of the present theoretical work is to show that it is possible to reduce cross-coupling stiffness and increase the direct damping coefficients by means of the active lubrication, what leads to rotor-bearing systems with larger threshold of stability.

Operation of a Mesoscopic Gas Turbine Simulator at Speeds in Excess of 700,000 rpm on Foil Bearings

Abstract: A small mesoscopic gas turbine engine (MGTE) simulator was tested at speeds over 700,000 rpm. The MGTE was operated with specially designed miniature compliant foil journal and thrust air bearings. The operation of the simulator rotor and foil bearing system is a precursor to development of turbine powered micro aerial vehicles and mesoscopic power generators. The foil bearings use a new fabrication technology in which each bearing is split. This feature permits the use of these bearings in highly advanced engines where single piece ceramic rotors may be required. The simulator weighed 56 grams (including the 9 gram rotor) and included two non-aerodynamic wheels to simulate the compressor and turbine wheels. Each compliant foil journal bearing had a diameter of 6 mm and was located equidistant from each end of the rotor. Experimental work included operation of the simulator at speeds above 700,000 rpm and at several different orientations including having the spin axis vertical. Results of the rotor bearing system dynamics are presented along with experimentally measured natural frequencies at many operating speeds. Good correlation between measurement and analysis is observed indicating the scalability of the analysis tools and hardware used. The rotor was very stable and well controlled throughout all testing conducted. Based on this successful testing it is expected that the goal of operating the rotor at speeds exceeding 1 million rpm will be achieved.Copyright © 2004 by ASME

A Theoretical Analysis Considering Cavitation Occurrence in Oil-Lubricated Spiral-Grooved Journal Bearings With Experimental Verification

Abstract: Performances of an oil-lubricated spiral-grooved journal bearing are investigated in this paper with special attention paid to cavitation occurrence. The equivalent flow model, which is a theoretical scheme for taking the cavitation occurrence into hydrodynamic lubrication theory, is applied to the analyses by a finite difference treatment of the Reynolds equation that deals with the geometry of a finite number of grooves. The calculated results are compared with experimental results under eccentric states, and verified in terms of cavitation map and pressure distribution. The cavitated area ratio, load capacity and bearing stiffness are also theoretically calculated. The difference between the theoretical results with and without consideration of the cavitation occurrence is considerable, and thus the influence of cavitation occurrence should not be ignored in theoretical studies on bearing characteristics.

Turbo test rig with hydroinertia air bearings for a palmtop gas turbine

Abstract: This paper describes a turbo test rig to test the compressor of a palmtop gas turbine generator at low temperature (<100 °C). Impellers are 10 mm in diameter and have three-dimensional blades machined using a five-axis NC milling machine. Hydroinertia bearings are employed in both radial and axial directions. The performance of the compressor was measured at 50% (435 000 rpm) and 60% (530 000 rpm) of the rated rotational speed (870 000 rpm) by driving a turbine using compressed air at room temperature. The measured pressure ratio is lower than the predicted value. This could be mainly because impeller tip clearance was larger than the designed value. The measured adiabatic efficiency is unrealistically high due to heat dissipation from compressed air. During acceleration toward the rated rotational speed, a shaft crashed to the bearing at 566 000 rpm due to whirl. At that time, the whirl ratio was 8.

Fluid bearings and vacuum chucks and methods for producing same

Abstract: Fluid bearings, vacuum chucks and methods for producing these devices. One example of a method for forming a fluid bearing includes forming a plate having a face surface and a bonding surface, coupling a first side of a body to the bonding surface, placing the face surface of the plate against a predetermined surface, and generating a pressure difference to conform the face surface to the predetermined surface. One example of a fluid bearing of the invention includes a plate support and a flexible bearing plate having a bonding surface which is attached to the plate support with an adhesive which is flexible before hardening. The flexible bearing plate conforms to a predetermined surface during a portion of the time that the adhesive hardens. Examples of vacuum chucks, and methods for forming vacuum chucks, and other aspects of the invention are described.

Concept for a new hydrodynamic blood bearing for miniature blood pumps.

Abstract: The most crucial element of a long-term implantable rotary blood pump is the rotor bearing. Because of heat generation and power loss resulting from friction, seals within the devices have to be avoided. Actively controlled magnetic bearings, although maintenance-free, increase the degree of complexity. Hydrodynamic bearings for magnetically coupled rotors may offer an alternative solution to this problem. Additionally, for miniature pumps, the load capacity of hydrodynamic bearings scales slower than that of, for example, magnetic bearings because of the cube-square-law. A special kind of hydrodynamic bearing is a spiral groove bearing (SGB), which features an excellent load capacity. Mock-loop tests showed that SGBs do not influence the hydraulic performance of the tested pumps. Although, as of now, the power consumption of the SBG is higher than for a mechanical pivot bearing, it is absolutely contact-free and has an unlimited lifetime. The liftoff of the rotor occurs already at 10% of design speed. Further tests and flow visualization studies on scaled-up models must demonstrate its overall blood compatibility.

Comparison of the Dynamic Behavior and Lubrication Characteristics of a Reciprocating Compressor Crankshaft in Both Finite and Short Bearing Models

Abstract: The compression force of refrigerant gas, the viscous and inertial force of the piston, and the centrifugal force of balancer weight induce rotating whirl of the crankshaft in a small reciprocating compressor. It is necessary to develop an analytical model for the accurate prediction of dynamic behavior of the compressor mechanism having coupled characteristics between the piston and crankshaft. The reciprocating compression mechanism is dynamically modeled by considering the viscous frictional force of a piston and the variation in the contact length of the piston-cylinder system, and then numerical analysis is performed for the coupled dynamic behavior of the piston and crankshaft. For the accurate predictions of the dynamic behavior and characteristics of lubrication of the crankshaft-journal bearing system, a finite bearing model is adopted. In addition, the dynamic trajectory and characteristics of lubrication of the crankshaft such as power consumption and oil leakage are compared between the finite...

Hydrodynamic bearing runner for use in tilting pad thrust bearing assemblies for electric submersible pumps

Abstract: An electrical submersible pump runner having a core layer and a wear layer affixed to the core layer. One embodiment of the invention provides an electrical submersible pump that includes a motor section and a centrifugal pump section. A seal section and rotary gas separator may also be included. The pump is powered by an electric cable that connects the pump, located in a bore hole, to a power source on the surface. A thrust runner coated with a wear layer (e.g., polymer) is provided in the motor and/or seal section to reduce bearing temperature, provide longer bearing life, reduce costs, and facilitate overhaul. The runner may also function as a rotating up-thrust bearing when the runner is coated with a wear layer on one side that is formed with a bearing geometry. In this case, the up-thrust bearing may be eliminated.

Modified Reynolds equation for coupled stress fluids – a porous media model

Abstract: In this paper, the rheological effects of coupled stress fluids on thin film lubrication modeling are developed. Thin porous layers attached to the impermeable substrate are utilized to model the microstructure of bearing surfaces. In the fluid film region, the constitutive equations for coupled stress fluids proposed by Stokes [1] as well as the continuity and momentum equations are applied to model the flow. In the porous region, the Brinkman-extended Darcy equations are applied to model the flow. Under the usual assumption of hydrodynamic lubrication applicable to thin films, the effects of viscous shear and the stress jump boundary condition at the porous media/fluid film interface are included in deriving the modified Reynolds equation. The effects of material properties such as coupled stress parameter Open image in new window viscosity ratio (αi2), thickness of porous layer (Δi), permeability (Ki), and stress jump parameter (βi), on the velocity distributions and load capacities of one-dimensional converging wedge problems are discussed.

Effects of misalignment on the performance of finite journal bearings lubricated with couple stress fluids

Abstract: A mathematical model for the hydrodynamic lubrication of misaligned journal bearings with couple stress lubricants is presented. A modified form for Reynolds equation in which the effects of couple stresses arising from the lubricant blended with various additives is used. The journal misalignment is allowed to vary in magnitudes as well as in direction with respect to the bearing boundaries. The flexibility of the bearing liner was incorporated into the analysis by using the thin liner model. A numerical solution for the mathematical model using a finite difference scheme is introduced. The predicted performance characteristics are compared with available theoretical and experimental results. The effects of the degree and angle of misalignment, the length-to-diameter ratio, and the couple stress parameter on static performance such as pressure distribution, load-carrying capacity, friction coefficient, and side leakage flow and misalignment moment are presented and discussed.

Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity

Abstract: As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.Copyright © 2004 by ASME

Hydrodynamic bearing, manufacturing method of hydrodynamic bearing, spindle motor provided with hydrodynamic bearing and disk drive device provided with this spindle motor

Abstract: A suitable the inner point is set on a vapor-liquid face of lubricating fluid formed in a composite capillary seal section that utilizes capillary force and rotational centrifugal force acted on the lubricating fluid. An inner peripheral surface of a ring-shaped portion is formed such that the minimum value R1 in radial-direction distances of the inner peripheral face of the ring-shaped portion becomes greater than a radial-direction distance R2 of the inner point (R1>R2). This can observe the inner point of the lubricating fluid from the immediately-above position, whereby the filling amount of the lubricating fluid can easily and surely be measured, thereby being capable of adjusting the filling amount of the lubricating fluid to a preset amount.

Stability Margin of Hybrid Journal Bearing: Influence of Thermal and Elastic Effects

Abstract: This paper deals with the stability margin of a constant flow valve compensated hole-entry hybrid journal bearing system considering bearing flexibility and variation of viscosity due to temperature rise of the lubricant. The journal temperature is computed on the basis of average fluid-film temperature and axisymmetric isothermal element is assumed. The coupled solution of Reynolds, energy, conduction, and elasticity equations is obtained using finite element method. The performance of a symmetric and asymmetric hole-entry hybrid journal bearing configurations is studied. The results presented in the study indicate that the bearing flexibility and temperature rise of the lubricant fluid-film affects the performance of the hole-entry hybrid journal bearing system quite significantly and proper selection of restrictor design parameter is quite useful in maintaining the fluid film thickness and threshold speed of the journal.

Hydrodynamic bearing system

Abstract: The invention relates to a hydrodynamic bearing system particularly for use as a rotary bearing in a spindle motor for a hard disk drive, comprising a shaft, a thrust plate firmly connected to the shaft by means of a pressfit connection and a bearing sleeve closed at least at one end by a cover plate, the bearing sleeve enclosing the shaft and the thrust plate with a slight radial or axial spacing forming a concentric bearing gap filled with a lubricant. In the hydrodynamic bearing system according to the invention, it is provided that the outer circumference of the shaft, in the area of connection with the thrust plate, has a surface interrupted by regular depressions, preferably formed by knurling, in order to decrease the contact surface proportion of the fit surface. As an alternative, the inner circumference of the thrust plate can also be knurled in the area of connection with the shaft.

Hydrodynamic bearing, spindle motor and hard disk drive

Abstract: The invention relates to a hydrodynamic bearing, particularly for a spindle motor, comprising a shaft, a thrust plate connected to the shaft and a bearing sleeve closed at one end by a cover plate, the bearing sleeve enclosing the shaft and the thrust plate with a slight radial spacing forming a concentric bearing gap filled with a lubricant. As is already known, the surfaces of the bearing sleeve and the shaft facing each other form at least one radial bearing region and the surfaces of the bearing sleeve, the cover plate and the thrust plate facing each other form at least one axial bearing region. In the hydrodynamic bearing according to the invention, at least one connecting channel is provided which connects a section between the bearing sleeve and the shaft abutting the radial bearing region and a section of the bearing gap abutting the axial bearing region to each other.

Measuring the performance of a novel fluid film bearing supporting a rotor on a stationary shaft, by non-contacting means

Abstract: A description is given of a multi-body dynamics rig for testing a novel rotor fluid film bearing system. The design included a composite rotor supported on a stationary central shaft, with loading applied by non-contacting electromagnets. The shaft included hydrostatic bearing pockets and continuously adjust- able hydrodynamic bearing segments. A technique is described for deriving displacement coefficients for both types of bearing. Observations are given on the use of the rig and test techniques, along with some results, and on implications of the results regarding the bearing system.

Analysis of a Hydrodynamic Bearing of a HDD Spindle Motor at Elevated Temperature

Abstract: This paper presents a method to investigate the characteristics of hydrodynamic bearings of a HDD spindle motor considering the variation of the clearance as well as the lubricant viscosity due to elevated temperature. Iterative finite element analysis of heat conduction and thermal deformation is performed to determine the viscosity and clearance of hydrodynamic bearings at elevated temperature until the temperature in the bearing area converges. The proposed method is verified by comparing the calculated temperature with the measured one at elevated surrounding temperature as well as in room temperature. This research shows that elevated temperature changes the clearance as well as the lubricant viscosity of the hydrodynamic bearings of a HDD spindle motor. Once the viscosity and clearance of hydrodynamic bearings of a HDD spindle motor are determined, finite element analysis of the Reynolds equation is performed to investigate the static and dynamic characteristics of hydrodynamic bearings of a HDD spindle motor at elevated temperature. It also shows that the variation of clearance due to elevated temperature is another important design consideration which affects the static and dynamic characteristics of the hydrodynamic bearings of a HDD spindle motor

Wave bearings in high performance applications

Abstract: The present disclosure concerns the application of the “Wave Bearing Concept” to journal and thrust fluid film bearings to increase performance and reliability. The wave surface is present on whichever member is stationary or non-rotating. Some applications are: pressurized gas journal wave bearings for increased load capacity and dynamic stability; journal wave bearings with liquid lubricants for extreme load capacity and excellent thermal and dynamic stability under any load; thrust wave bearings for axial positioning and axial loads; journal bearings with an elastic wave sleeve that can be activated via actuators (“active/passive control fluid film bearing”) or may change by itself (“smart bearings”) to adapt the bearing performance to the applied bearing load and speed. Journal and thrust bearings incorporating the present invention are appropriate for either mono-directional or bi-directional rotation.

Fluid bearing device

Abstract: PROBLEM TO BE SOLVED: To provide a fluid bearing device which is capable of reliably eliminating dust generation attributable to a structure for preventing detachment or side deviation of a shaft, or any wear and seizure caused during the low-speed rotation, and excellent in simplicity and maintainability SOLUTION: The fluid bearing device in which a shaft 15 of a rotating body 1 is supported by a bearing surface 28 in a non-contact manner with fluid S fed between the bearing surface 28 and the shaft 15 from a fluid feed means 3 has an injection unit 29 for preventing side deviation which is provided facing a side surface 11 across the axis of the rotating body 1 and connected to the fluid feed means 3 so that the fluid S fed from the fluid feed means 3 is injected from the injection unit 29 to keep the distance between a bearing body 2 and the rotating body 1 COPYRIGHT: (C)2004,JPO&NCIPI

Investigation of grooved hybrid air bearing performance

Abstract: Herringbone grooves machined into aerodynamic bearings are well known to produce improvements in bearing stiffness and stability at high operating speeds In this investigation the effect of herringbone grooves on the performance of an externally pressurized bearing is examined A mathematical model based on previous research has been developed and used to optimize the design of an air bearing suitable for use in ultrahigh-speed machining spindles Experimental results show the spindle to run satisfactory at speeds in excess of 30 × 106 DN (bearing diameter in mm x shaft speed in r/min), being limited only by the maximum speed of its drive rotor