Showing papers on "Bearing (mechanical) published in 1999"

Fundamentals of Machine Elements

Abstract: Part I - Fundamentals Introduction What is Design? Design of Mechanical Systems Design as a Multidisciplinary Endeavor Design of Machine Elements Computers in Design Catalogs and Vendors Units Unit Checks Significant Figures Summary Load, Stress, and Strain Introduction Critical Section Load Classification and Sign Convention Support Reactions Static Equilibrium Free-Body Diagram Supported Beams Shear and Moment Diagrams Stress Stress Element Stress Tensor Plane Stress Mohr's Circle Three-Dimensional Stresses Octahedral Stresses Strain Strain Tensor Plane Strain Summary Introduction to Materials and Manufacturing Introduction Ductile and Brittle Materials Classification of Solid Materials Stress-Strain Diagrams Properties of Solid Materials Stress-Strain Relationships Two-Parameter Materials Charts Effects of Manufacturing Summary Stresses and Strains Introduction Properties of Beam Cross Sections Normal Stress and Strain Torsion Bending Stress and Strain Transverse Shear Stress and Strain Summary Deformation Introduction Moment-Curvature Relation Singularity Functions Method of Superposition Strain Energy Castigliano's Theorem Summary Failure Prediction for Static Loading Introduction Stress Concentration Fracture Mechanics Modes of Crack Growth Fracture Toughness Failure Prediction for Uniaxial Stress State Failure Prediction for Multiaxial Stress State Summary Fatigue and Impact Introduction Fatigue Cyclic Stresses Strain Life Theory of Fatigue Fatigue Strength Fatigue Regimes Stress Concentration Effects The Modified Endurance Limit Cumulative Damage Influence of Nonzero Mean Stress Influence of Multi-Axial Stress States Fracture Mechanics Approach to Fatigue Linear Impact Stresses and Deformations Summary Lubrication, Friction, and Wear Introduction Surface Parameters Conformal and Nonconformal Surfaces Hertzian Contact Bearing Materials Lubricant Rheology Regimes of Lubrication Friction Wear Summary Part II - Machine Elements Columns Introduction Equilibrium Regimes Concentrically Loaded Columns End Conditions Euler's Buckling Criterion Johnson's Buckling Criterion AISC Criteria Eccentrically Loaded Columns Summary Stresses and Deformations in Cylinders Introduction Tolerances and Fits Pressurization Effects Rotational Effects Press Fits Shrink Fits Summary Shafting and Associated Parts Introduction Design of Shafts for Static Loading Fatigue Design of Shafts Additional Shaft Design Considerations Critical Speed of Rotating Shafts Keys, Roll Pins, Splines and Set Screws Retaining Rings and Pins Flywheels Couplings Summary Hydrodynamic and Hydrostatic Bearings Introduction The Reynolds Equation Thrust Slider Bearings Journal Slider Bearings Squeeze Film Bearings Hydrostatic Bearings Summary Rolling-Element Bearings Introduction Historical Overview Bearing Types and Selection Geometry Kinematics Separators Static Load Distribution Elastohydrodynamic Lubrication Fatigue Life Variable Loading Summary General Gear Theory Spur Gears Introduction Types of Gears Gear Geometry Gear Ratio Contact Ratio and Gear Velocity Tooth Thickness and Backlash Gear Trains Gear Manufacture and Quality Gear Materials Loads Acting on a Gear Tooth Bending Stresses in Gear Teeth Contact Stresses in Gear Teeth Elastohydrodynamic Film Thickness Gear Design Synthesis Summary Helical, Bevel, and Worm Gears Introduction Helical Gears Bevel Gears Worm Gears Summary Fasteners, Connections, and Power Screws Introduction Thread Terminology, Classification, and Designation Power Screws Threaded Fasteners Riveted Fasteners Welded, Brazed, and Soldered Joints Adhesive Bonding Integrated Snap Fasteners Summary Springs Introduction Spring Materials Helical Compression Springs Helical Extension Springs Helical Torsion Springs Leaf Springs Gas Springs Belleville Springs Wave Springs Summary Brakes and Clutches Introduction Thermal Considerations Thrust Pad Clutches and Brakes Cone Clutches and Brakes Block or Short-Shoe Brakes Long-Shoe, Internal, Expanding Rim Brakes Long-Shoe, External, Contracting Rim Brakes Symmetrically Loaded Pivot-Shoe Brakes Band Brakes Slip Clutches Summary Flexible Machine Elements Introduction Flat Belts Synchronous Belts V-Belts Wire Ropes Rolling Chains Summary Appendices Index

Motor shaft voltages and bearing currents and their reduction in multi-level medium voltage PWM voltage source inverter drive applications

Abstract: This paper presents test results on problems and solutions of motor shaft voltages and bearing currents in medium-voltage pulsewidth modulated (PWM) drive systems. Tests show that multilevel medium-voltage PWM voltage-source inverter drives can cause motor bearing currents, similar to a low-voltage PWM drives, even with one motor bearing insulated. Common-mode voltages generated as a result of PWM switching are observed on motor windings and capacitively coupled to the motor shaft, leading to bearing currents. Potential solutions, including altering common-mode circuitry, changing the grounding scheme, providing common-mode filtering, and grounding the motor shaft, are investigated. Test results on their effectiveness are presented.

Analysis of an Aerodynamic Compliant Foil Thrust Bearing: Method for a Rapid Design

Abstract: A very simple design method for an aerodynamic compliant foil thrust bearing is presented in this paper. It is based on 3D modeling (called: complete direct calculation) of the elastoaerodynamic problem. In this approach, the structural analysis has been simplified. This enables the calculation to be carried out faster. However this model, based on the resolution of the Reynolds equation, only gives the performance of a thrust bearing for a given geometric profile. An efficient method for solving the inverse problem for predicting the desired bearing performance parameters is presented. The complete direct calculation is only used to improve the profile geometry thus found. Finally, the proposed method has been applied for the design of a 80 mm outer diameter 40 mm inner diameter thrust bearing operating between 20,000 and 50,000 rpm. It is shown that the thrust bearing designed by this approach has a high load capacity (300 kPa) at a speed of 50,000 rpm. It is also shown that the predicted performance of the bearing agrees well with the complete direct calculation.

Stability of Elastomeric Seismic Isolation Bearings

Abstract: Elastomeric seismic isolation bearings are subjected to large axial loads and lateral displacements during strong earthquakes. The existing Koh-Kelly model (1986, 1988, 1989) for elastomeric bearings accounts for axial load effects on horizontal stiffness. This linear model is based on small displacements and rotations and predicts stable postcritical behavior or increasing critical load with increasing horizontal displacement; however, unstable postcritical behavior is observed in the bearing test results presented in this study. The analytical model developed in this study, based on the Koh-Kelly model, includes large displacements, large rotations, and nonlinearity of rubber, and it predicts unstable postcritical behavior. The formulation of the analytical model, calibration, and verification using experimental results are presented. It is shown that the critical load reduces with increasing horizontal displacement and that the horizontal stiffness reduces with increasing horizontal displacement and axial load. It is also shown that the critical load capacity at a horizontal displacement equal to the width of the bearing is not equal to zero, as predicted by the approximate procedure used in design, but higher.

Minimizing electric bearing currents in ASD systems

Abstract: During recent years, an increase in bearing failures has been seen in ASD-fed electric motors, as well as in gearboxes, and other connected machinery, caused by electric current flow through such bearings. The theories presented in this paper focus on bearing currents in ASDs of the voltage source pulse width modulated (PWM) type, for use with AC induction motors, although the concepts are applicable to various types AC and DC drive systems.

Method for providing a jewel bearing for supporting a pump rotor shaft

Abstract: Methods for a blood pump bearing system within a pump housing to support long-term high-speed rotation of a rotor with an impeller blade having a plurality of individual magnets disposed thereon to provide a small radial air gap between the magnets and a stator of less than 0.025 inches. The bearing system may be mounted within a flow straightener, diffuser, or other pump element to support the shaft of a pump rotor. The bearing system includes a zirconia shaft having a radiused end. The radiused end has a first radius selected to be about three times greater than the radius of the zirconia shaft. The radiused end of the zirconia shaft engages a flat sapphire endstone. Due to the relative hardness of these materials a flat is quickly produced during break-in on the zirconia radiused end of precisely the size necessary to support thrust loads whereupon wear substantially ceases. Due to the selection of the first radius, the change in shaft end-play during pump break-in is limited to a total desired end-play of less than about 0.010 inches. Radial loads are supported by an olive hole ring jewel that makes near line contact around the circumference of the shaft to support high speed rotation with little friction. The width of olive hole ring jewel is small to allow heat to conduct through to thereby prevent heat build-up in the bearing. A void defined by the bearing elements may fill with blood that then coagulates within the void. The coagulated blood is then conformed to the shape of the bearing surfaces.

Impact Loads due to Wheel Flats and Shells

Abstract: A Finite Element (FE) model of vehicle-track system is employed to duplicate the experiments carried out by British Rail and CP Rail System. The theoretical results of the wheel/rail contact forces, rail-pad forces and strains in the rail showed very good correlation to the experimental data. Extensive results are compared with experimental data in the time domain for through validation of the developed model. The characteristics of the impact loads due to wheel flats and shells are investigated based on the validated FE model. The study shows that the shape and size of flat or shell, axle load, vehicle speed and rail-pad stiffness mainly affect the impact loads. Adding elastomeric shear pads on the wheelset bearing does not reduce the wheel/rail dynamic contact force but it may reduce the dynamic force on the bearing. Reducing rail-pad stiffness to a certain level on a concrete-tie track may significantly reduce the dynamic load and the force transmitted to the concrete tie.

The Effect of Waviness on Vibrations Associated Witli Ball Bearings

Abstract: In this paper, the radial and axial vibrations of a rigid shaft supported by a pair of angular contact ball bearings is studied. The effect of bearing running surface waviness on the vibration of the shaft is investigated. A computer program was developed to simulate inner race, outer race, and rolling surface waviness with the results presented in time and frequency domains. Results obtained from the similation programme are quantatively in good aggrement with various authors' experimental researches.

Femoral component for knee endoprosthesis

Abstract: A femoral component of a knee prosthesis includes a bearing surface defined by a smooth, continuous surface which in one embodiment is entirely formed by a series of three segments of surfaces of revolution, the respective shapes of which are generated by rotating a common generating curve around three separate generating axes at respective pairs of major generating radii and through respective angles of rotation. The central segment of the surfaces of revolution constantly maintains the substantially same contact configuration with the superior bearing surface of a bearing insert over a range extending from full extension (0° of flexion) to at least 45° of flexion and up to 105° of flexion. The maintenance of the substantially same contact configuration ensures area, point or line contact between the articulating surfaces which reduces contact stress and wear in flexion. In a second embodiment, the bearing surface is defined by four segments of surfaces of revolution shaped for implantation in a knee where one or both cruciate ligaments are retained.

BEAST—a rolling bearing simulation tool:

Abstract: Rolling bearings are high-precision, low-cost machine elements used in all kinds of rotating machinery. Dynamic simulations of rolling bearings bring increased understanding of their dynami...

Calculation of dynamic coefficients in a hydrodynamic bearing considering five degrees of freedom for a general rotor-bearing system

Abstract: A complete method is presented to calculate the stiffness and the damping coefficients in a hydrodynamic bearing considering five degrees of freedom for a general rotor-bearing system. Perturbation equations are obtained from Reynolds equation by assuming the small amplitude motion of a bearing center, and are solved by the finite element method. Their characteristics due to eccentricity and misalignment are investigated for herringbone groove journal and thrust bearings in the spindle motor of a hard disk drive. This research shows that the dynamic coefficients increase with increasing the misalignment as well as the eccentricity due to the wedge effect. It also shows that the moment coefficients, which have been neglected in most of the previous analyses, are of significant magnitude in a journal bearing and have even bigger values for the thrust bearing when they are compared with the ball bearing in the same type of a spindle motor.

Dynamic Prognostic Prediction of Defect Propagation on Rolling Element Bearings

Abstract: Rolling element bearing failure is a major factor in the failure of rotating machinery. Current methods of bearing condition monitoring focus on determining any existing fault presence on a bearing as early as possible. Although a defect can be detected when it is well below the industry standard of a fatal size of 6.25 mm2 (0.01 in2), the remaining life of a bearing (the time it takes to reach the final failure size) from the point where a defect can be detected can vary substantially. As a fatal defect is detected, it is common to shut down machinery as soon as possible to avoid catastrophic consequences. Performing such an action, which usually occurs at inconvenient times, typically results in substantial time and economics losses. It is, therefore, important that the bearing's remaining life be more precisely forecasted, in a prognostic rather than diagnostic manner, so that maintenance can be optimally scheduled. Unfortunately, current bearing remaining life prediction methods have not been well dev...

Surface Roughness Effects in Infinitely Long Porous Journal Bearings

Abstract: Christensen's stochastic theory of hydrodynamic lubrication of rough surfaces is used to study the effect of surface roughness in an infinitely long porous journal bearing operating under steady conditions. It is shown that the surface roughness considerably influences the bearing performance; the direction of the influence depends on the roughness type.

A blower assembly for a pulsed laser system incorporating ceramic bearings

Abstract: A blower assembly (70) for circulating gases in a laser chamber (10). The blower assembly (70) includes a driving assembly (132) operatively engaged to a drive side shaft (72) for rotating a fan assembly (102). A first bearing assembly (90A) supports the drive side shaft (72). The blower assembly (70) may further include an idle side shaft (73) for supporting the fan assembly (102) and a second bearing assembly (90B) circumscribing the idle side shaft (73). The driving assembly (132) includes a motor (130) disposed over a rotor (110). The fan assembly (102) includes a pair of hubs (104A, 104B) supporting a plurality of blades (110). The first and second bearing assemblies (90A, 90B) comprise a ceramic compound, such as silicon nitride (Si3N4), and are lubricated with a synthetic oil, such as perfluoropolyalkylether (PFPE).

Superconducting magnetic bearings for energy storage flywheels

Abstract: We are investigating the use of flywheels for energy storage. Flywheel devices need to be of high efficiency and an important source of losses is the bearings. In addition, the requirement is for the devices to have long lifetimes with minimal or no maintenance. Conventional rolling element bearings can and have been used, but a noncontact bearing, such as a superconducting magnetic bearing, is expected to have a longer lifetime and lower losses. We have constructed a flywheel system. Designed to run in vacuum this incorporates a 40 kg flywheel supported on superconducting magnetic bearings. The production device will be a 5 kW device storing 5 kWh of retrievable energy at 50000 rpm. The Cambridge University system is being developed in parallel with a similar device supported on a conventional bearing. This will allow direct performance comparisons. Although superconducting bearings are increasingly well understood, of major importance are the cryogenics and special attention is being paid to methods of packaging and insulating the superconductors to cut down radiation losses. The work reported here is part of a three-year program of work supported by the EPSRC.

Apparatus and method for forming an image using a developing device capable of obtaining a high quality image

Abstract: An image forming apparatus includes a latent image bearing member to bear an electrostatic latent image, and a developer bearing member to bear a developer, in which the electrostatic latent image is formed on the latent image bearing member by first uniformly charging the latent image bearing member and then by performing an optical writing operation. The electrostatic latent image is visualized by supplying the developer borne on the developer bearing member to the latent image bearing member. A lubricant for reducing a friction coefficient of a surface of the latent image bearing member is supplied to the latent image bearing member and the lubricant has a charging polarity opposite to that of the developer. The friction coefficient of the latent image bearing member is maintained such that adhering of the developer to a background part of the latent image is prevented as a result of supplying the lubricant to the latent image bearing member. The lubricant, which includes a silicone resin, is supplied to the latent image bearing member such that the friction coefficient of the surface of the latent image bearing member is from about 0.1 to about 0.4. The friction coefficient of the surface of the latent image bearing member is set such that a cleaning device to remove a residual developer on the surface of the latent image bearing member is prevented from being dragged by the latent image bearing member by decreasing a contact resistance between the cleaning device and the surface of the latent image bearing member.

Gas discharge laser with magnetic bearings and magnetic reluctance centering for fan drive assembly

Abstract: The present invention provides an electric discharge gas laser having a laser cavity in which is contained a laser gas and a fan for circulating the laser gas. The fan is supported by an active radial magnetic bearing system and driven by a brushless DC motor in which the rotor of the motor and the rotors of at least two radial bearings are sealed within the gas environment of the laser cavity and the motor stator and the coils of the bearing magnets are located outside the gas environment. No thrust bearing is provided. Axial positioning of the shaft is provided by reluctance centering produced by the at least two radial magnetic bearings and the brushless DC motor. In a preferred embodiment the motor stator is larger in the axial direction than the rotor to increase the magnetic centering effect.

Axial force null position magnetic bearing and rotary blood pumps which use them

Abstract: A generally cylindrical rotor very closely confined between two rigid thrust bearing surfaces is radially suspended by an array of attracting or repelling magnets or by a combination of permanent magnets and ring shaped members composed of ferromagnetic material. The geometry permits very small spacing between magnetic components to achieve high radial stiffness. High magnetic axial forces exerted between the rotor and stationary component on one end of the rotor are counter-balanced by equal and opposite forces at the other end of the rotor. Precise positioning of the rotor in the location where the opposing axial magnetic forces counterballance each other yields a net magnetic axial force on the rotor of near zero, hence the reference to this as the null position. Wear resistant mechanical thrust bearings confine the rotor axially to maintain this position during rotatioin. Precisely balance the magnetic axial forces in the proper geometry with relation to the mechanical thrust bearings. Blood pumps utilizing this type of bearing are disclosed, including both axial flow pump and centrifugal flow pump configurations with high flow washing of the junction of the rotating and stationary parts to prevent thrombus accumulation.

On the Numerical Modeling of High-Speed Hydrodynamic Gas Bearings

Abstract: A numerical study of high-speed hydrodynamic gas bearing performance is presented using both finite element and finite difference methods. Efficient numerical procedures are developed to analyze diffusive-convective thin film gas flows in some simple geometries. A novel direct finite element formulation employing a new class of shape functions is specially devised to solve the Reynolds equation for compressible fluids, The formulation is as computationally efficient as the classical upwind finite element schemes without introducing artificial diffusion into the solution. Bearing load-capacity, static stiffness coefficients and frequency-dependent force coefficients are calculated for gas-lubricated plane and Rayleigh step slider bearings.

Motor rotor bearing assembly for a blood pump

Abstract: A motor rotor assembly for use in a blood pump can include a motor rotor disposed within a blood flow conduit, an inflow bearing having an inflow ball-and-cup bearing interface disposed within the blood flow conduit proximal to an inflow port of the blood flow conduit, and an outflow bearing having an outflow ball-and-cup bearing interface disposed within the blood flow conduit proximal to an outflow port of the blood flow conduit. The motor can be rotatably mounted between the inflow bearing and the outflow bearing and an outer diameter of the outflow ball-and-cup bearing interface can be larger than an outer diameter of the inflow ball-and-cup bearing interface. A motor rotor assembly for use in a blood pump incorporating aspects of the invention may improve performance, reliability and longevity of the pump. A blood pump incorporating a motor rotor can further include a motor stator. These rotors and pumps can be used in both implantable and extracorporeal blood pumps.

A 0.5 kWh flywheel energy storage system using a high-T/sub c/ superconducting magnetic bearing

Abstract: A flywheel rotor having a main shaft, two flywheel disks and one permanent magnet for a SMB (superconducting magnetic bearing) was designed and manufactured. The flywheel was made of CFRP material which is light weight and has high tensile strength. The permanent magnet was hooped by CPRP in order to prevent centrifugal bursting. The rotor was levitated by a SMB in the axial direction. The radial vibration of the rotor was damped by active magnetic bearings. The superconducting magnetic bearing was made of YBa/sub 2/Cu/sub 3/O/sub 7-X/ which had a strong pinning force. The whole rotor system was stably accelerated up to 30000 rpm by an induction motor in a vacuum chamber, and then its energy storage value reached 479 Wh. In this paper, the rotor design, bearing and rotational properties of the rotor are discussed.

Dynamically Loaded Finite Length Journal Bearings: Analytical Method of Solution

Abstract: A closed-form pressure distribution, using a combination of short- and long-bearing approximations, is proposed for dynamically loaded journal bearings. The angles for start and finish of positive pressure curve are determined employing simple analytical equations. The mobility method, based on the suggested pressure distribution is easy to use, predicts results of acceptable accuracy and the execution time is comparable to that required for the short bearing approximation. This paper also provides a conceptually simple analytical method for evaluating angular location of the instantaneous maximum pressure using proposed closed form pressure distribution. Simple algebraic equations are derived to obtain the instantaneous maximum pressure in dynamically loaded bearings directly, without involving any iteration. To illustrate the validity of present study, a connecting rod big end bearing and two crankshaft main bearings are analyzed. The mobility components, minimum film thickness and maximum pressure are plotted over a load cycle and compared with established analytical and curve fit methods. The results are also compared with those obtained using finite element method.

Bearing-sensor integration for a lubrication analysis system

Abstract: A bearing-sensor integration in which one or more multi-sensor lubrication sensing devices are positioned relative to the bearing to sense in situ certain parameters of the lubricating fluid. The lubrication sensing devices may be positioned on an interior surface of a bearing raceway (i.e, the outer raceway and/or the inner raceway), the bearing's cage, sealing cover, circulating system, a compliant structure positioned within the bearing chamber, a flowgate, and/or a reservoir. The lubrication sensing device(s) may include sensors for measuring certain parameters of the lubricating fluid, such as pH, chemical characteristics, electrical conductivity, temperature and/or viscosity. A processor receives lubrication-related data from the lubrication sensing device(s), processes the lubrication-related data, and provides information relating to lubrication health and/or health of the machine employing the lubricant.

Spindle motor having air dynamic pressure bearing and rotating device having the spindle motor as driving source

Abstract: A spindle motor has a rotor, a stator and an air dynamic pressure bearing for supporting the rotor for rotation about a rotational axis relative to the stator. The air dynamic pressure bearing comprises a first dynamic pressure bearing portion and a second dynamic pressure bearing portion. The first dynamic pressure bearing portion comprises a convex side bearing member having a conical convex portion, a concave side bearing member having a conical concave portion receiving the conical convex portion, and dynamic pressure generating grooves formed on one of a surface of the conical convex portion and a surface of the conical concave portion. The second dynamic pressure bearing portion comprises a shaft having a first end fixed to the concave side bearing member and extending along the rotational axis, a bore formed in the convex side bearing member for receiving a second end of the shaft to permit rotation of the convex side bearing member relative to the concave side bearing member about the shaft, and dynamic pressure grooves formed on one of an outer circumferential surface of the shaft and an inner circumferential surface of the bore.

Friction clutch bearing an electric machine rotor, in particular for a motor vehicle

Abstract: The invention concerns a friction clutch comprising a flywheel (3) with a front end designed to be fixed to a motor vehicle crankshaft (11) and a rear end in the form of a reaction plate (4) with a central recess (39) externally defined by a friction surface and a friction disc coupled with a central hub designed to be interlocked in rotation with the input shaft of a movement gear box comprising a clutch housing, the flywheel (13) bearing between its front and rear ends the rotor (6) of a rotating electric machine (2) comprising a fixed stator borne internally by a strut designed to be interlocked with at least one of the vehicle engine-clutch housing (14) block (62). The invention is applicable to a motor vehicle.

Linear actuator with anti-reverse-rotation mechanism

Abstract: A linear actuator includes two axially opposed bearings with built-in one-way clutch assembled in a housing member with respective outer races secured to the housing member such that respective directions in which inner races of the bearings are locked against rotation are opposed to each other, a ball bearing shaft relatively and rotatably supported on the inner races of the bearings with bearing bushings disposed between the ball screw shaft and the respective bearings, and two load transmitting collars fixed on the ball screw shaft. When the ball screw shaft is subjected to a thrust load applied from a ball nut in a direction to retract the ball screw shaft, one of the inner race is locked against rotation to thereby exert a braking torque to the corresponding load transmitting collar via an associated friction collar. Alternatively, when the ball screw shaft is subjected to a thrust load tending to extend the ball screw shaft, the other inner race is locked against rotation to thereby exert a braking torque to the corresponding load transmitting collar via an associated friction collar. Thus, rotation of the ball screw shaft under the effect of the thrust load in either direction can be avoided.