Showing papers on "Bearing (mechanical) published in 2001"

Base isolation for near-fault motions

Abstract: Three analytical studies of base-isolated structures are carried out. First, six pairs of near-fault motions oriented in directions parallel and normal to the fault were considered, and the average of the response spectra of these earthquake records was obtained. This study shows that in addition to pulse-type displacements, these motions contain significant energy at high frequencies and that the real and pseudo-velocity spectra are quite different. The second analysis modelled the response of a model of an isolated structure with a flexible superstructure to study the effect of isolation damping on the performance of different isolation systems under near-fault motion. The results show that there exists a value of isolation system damping for which the superstructure acceleration for a given structural system attains a minimum value under near-fault motion. Therefore, although increasing the bearing damping beyond a certain value may decrease the bearing displacement, it may transmit higher accelerations into the superstructure. Finally, the behaviour of four isolation systems subjected to the normal component of each of the near-fault motions were studied, showing that EDF type isolation systems may be the optimum choice for the design of isolated structures in near-fault locations. Copyright © 2001 John Wiley & Sons, Ltd.

Wavelet Analysis and Envelope Detection For Rolling Element Bearing Fault Diagnosis—Their Effectiveness and Flexibilities

Abstract: The components which often fail in a rolling element bearing are the outer-race, the inner-race, the rollers, and the cage. Such failures generate a series of impact vibrations in short time intervals, which occur at Bearing Characteristic Frequencies (BCF). Since BCF contain very little energy, and are usually overwhelmed by noise and higher levels of macro-structural vibrations, they are difficult to find in their frequency spectra when using the common technique of Fast Fourier Transforms (FFT). Therefore, Envelope Detection (ED) is always used with FFT to identify faults occurring at the BCF. However, the computation of ED is complicated, and requires expensive equipment and experienced operators to process. This, coupled with the incapacity of FFT to detect nonstationary signals, makes wavelet analysis a popular alternative for machine fault diagnosis. Wavelet analysis provides multi-resolution in time-frequency distribution for easier detection of abnormal vibration signals. From the results of extensive experiments performed in a series of motor-pump driven systems, the methods of wavelet analysis and FFT with ED are proven to be efficient in detecting some types of bearing faults. Since wavelet analysis can detect both periodic and nonperiodic signals, it allows the machine operator to more easily detect the remaining types of bearing faults which are impossible by the method of FFT with ED. Hence, wavelet analysis is a better fault diagnostic tool for the practice in maintenance.

Applied Tribology: Bearing Design and Lubrication

Abstract: Series Preface. Preface. Part I: General Considerations. 1 Tribology - Friction, Wear, and Lubrication. 2 Lubricants and Lubrication. 3 Surface Texture and Interactions. 4 Bearing Materials. Part II: Fluid-Film Bearings. 5 Fundamentals of Viscous Flow. 6 Reynolds Equation and Applications. 7 Thrust Bearings. 8 Journal Bearings. 9 Squeeze-Film Bearings. 10 Hydrostatic Bearings. 11 Gas Bearings. 12 Dry and Starved Bearings. Part III: Rolling Element Bearings. 13 Selecting Bearing Type and Size. 14 Principles and Operating Limits. 15 Friction, Wear and Lubrication. Part IV: Seals and Monitoring. 16 Seal Fundamentals. 17 Condition Monitoring and Failure Analysis. Appendix A Unit Conversion Factors. Appendix B Viscosity Conversions. Index.

Posterior stabilized prosthetic knee replacement with bearing translation and dislocation prevention features

Abstract: A prosthetic replacement knee joint includes a tibial component, a femoral component, a bearing and a control arm. The tibial component has a superior bearing surface and a conical recess extending into the superior bearing surface. The bearing has an inferior surface slidably engaged with the superior surface of the tibial component and formed with a dovetailed groove therein. The bearing also has a concave superior surface. A notch extends into the posterior extreme of the bearing. The femoral component has a pair of convex arcuate condyles in articular bearing engagement with the superior surface of the bearing. The femoral component also includes a posterior notch having a minor medial-lateral width at the inferior surface of the femoral component and a major width at more superior locations on the femoral component. The control arm has a conical bearing rotatable positioned in the conical recess of the tibial component. The control arm further has a dovetail guide slidably engaged in the dovetail groove of the bearing. A post projects through the notch in the bearing and into the notch of the femoral component. The post has medial and lateral projections that engage portions of the notch in the femoral component that define the major width thereof.

Modular led assembly

Abstract: Two substantially identical LED modules each have a nonconductive base having a straight edge and a pair of faces, at least one LED on the base, and two conductive traces on the base connected to the LED and forming on one of the faces inner and outer contacts spaced along a line perpendicular from the edge with the outer contact between the inner contact and the edge. The modules are juxtaposed at the edges with the lines aligned with each other and the one faces generally coplanar. A clip has a nonconductive body bearing on the one faces of both of the bases at the edges and two respective conductors on the clip body having portions spaced apart along the aligned lines and bearing on the contacts of both bases. The clip body and conductors are pressed against the bases to engage the conductors with the respective contacts and secure the bases together.

Method of applying a wear-resistant layer to a surface of a downhole component

Abstract: A method is disclosed comprising the steps of locating, on a surface of a downhole component, a plurality of thermally stable polycrystalline diamond (TSP) bearing elements, and then applying to the surface a settable facing material which bonds to the surface between the bearing elements and embraces the elements to hold them in place. A method in which bearing elements each comprising a body of TSP at least partly surrounded by a layer of less hard material are secured to the surface by welding or brazing part of the surface of each bearing element which comprises said less hard material to said component is also described.

A new bearing fault detection and diagnosis scheme based on hidden Markov modeling of vibration signals

Abstract: This paper introduces a new bearing fault detection and diagnosis scheme based on hidden Markov modeling (HMM) of vibration signals. First features are extracted from amplitude demodulated vibration signals obtained from both normal and faulty bearings. The features are based on the reflection coefficients of the polynomial transfer function of the autoregressive model of the vibration signal. These features are then used to train HMMs to represent various bearing conditions. The technique allows for online detection of faults by monitoring the probabilities of the pre-trained HMM for the normal case. It also allows for the diagnosis of the fault by the HMM that gives the highest probability. The new scheme was tested with experimental data collected from drive end ball bearing of an induction motor (Reliance Electric 2HP IQPreAlert) driven mechanical system.

Thermal Features of Compliant Foil Bearings—Theory and Experiments

Abstract: The paper presents an analytical and experimental investigation aimed at eliciting the thermal characteristics of air lubricated compliant foil bearings. A Couette Approximation to the energy equation is used in conjunction with the compressible Reynolds equation to obtain a theoretical temperature distribution in the air used as a lubricant. The effect of temperature on the thermal properties of the working fluid is included. In parallel, an experimental program was run on a 100 mm diameter foil bearing operating at speeds up to 30,000 rpm employing cooling air across the bearing. The temperature rise of the cooling air provided an indication of the amount of heat energy conducted across the top foil of the bearing from the hydrodynamic film. The temperatures resulted from some tests are compared with the temperatures predicted by the analysis, and maximum over-prediction of about 19 percent was obtained. This simplified approach provides us with reasonably predicted temperatures. By comparing the theoretical heat dissipation obtained from the analytical predicted temperatures with the amount of heat carried away by the cooling air it was possible to arrive at the relative quantities of heat transferred from the bearing by convection via side leakage and by conduction via the top foil. From these comparisons it was deduced that about an average of 80 percent of the heat energy is carried away by conduction. The transient temperatures of the foil bearing in conducted tests for various speeds and loads are also presented.

Motor bearing damage detection via wavelet analysis of the starting current transient

Abstract: Preventive maintenance of induction motors plays an important role in avoiding expensive shut-downs due to motor failures. Motor Current Signature Analysis, MCSA, provides a non-intrusive way to assess the health of a machine. In this paper, the starting current transient of an induction motor is analyzed via discrete wavelet transform to detect bearing faults. The frequency subbands for bearing pre-fault and post-fault conditions are compared to identify the effects of bearing/machine resonant frequencies as the motor starts.

Life ratings for ball and roller bearings

Abstract: Since the beginning of the twentieth century, bearing manufacturers and users have sought to predict the fatigue endurance of ball and roller bearings. The first generally accepted method t...

Rolling bearing device and ring with sensor for the rolling bearing device

Abstract: A rolling bearing with sensor includes an inner ring, an outer ring, a plurality of rolling elements disposed between the inner and outer rings, and a sensor having a detecting part detecting a state of the rolling bearing and a circuit part connected to the detecting part. The detecting part and the circuit part are attached to the rolling bearing.

Prediction of thermo-elastic behavior in a spindle–bearing system considering bearing surroundings

Abstract: This paper presents a simulation method based on system dynamics to establish a comprehensive prediction model for the thermal and mechanical behavior of a spindle–bearing system in consideration of bearing surroundings such as assembly tolerance, geometric dimension, cooling conditions, operating conditions and thermal deformation. By introducing a lumped element into the system, not only mechanical properties but also thermal behaviors can be readily examined and predicted. The most important behavior in the spindle–bearing system is the bearing pressure, which determines the spindle characteristics and friction moment. In this study three different simplified assemblies are investigated. One is the bearing inner race–shaft subassembly that includes a negative assembly clearance, and another is the outer race–housing assembly that includes a positive assembly clearance. The third is the entire system that is composed of a rolling element bearing, an inner race–shaft subassembly and an outer race subassembly. The two subassemblies are coupled by rolling elements in which the frictional moment and heat generation vary with the assembly clearance and thermal deformation of the bearing surroundings. The new method can be applied to spindle cooling as well as the optimal thermal and mechanical design of the spindle–bearing system for various surrounding conditions. Furthermore, on the basis of the proposed model, the effect of steel and ceramic bearing materials on the thermo-elastic behavior of the spindle system was investigated.

Patellar bearing implant

Abstract: A patellar bearing (21) having extended, rounded contours (24) on the superior and inferior edges of its articulating surface.

Condition based monitoring by vibrational analysis

Abstract: An apparatus and method monitors the condition of a bearing/shaft assembly by forming diagnostics based on spectral analysis of assembly's vibration. Baseline parameters are determined by a microprocessor analysis of the vibration spectra, comparing actual peaks to the peaks predicted by a model. The microprocessor estimates rotation rate and preferably number of rolling elements by attempting to fit the model to the actual vibrational spectrum, by varying the assumptions. Baseline profiles are formed from one or more selected tones and preferably also harmonics thereof, to characterize the bearing/shaft assembly. The baseline profiles and parameters are compared against later acquired vibrational characteristics, and the comparison is used to diagnose bearing and/or shaft conditions.

An Engineering Approach to Hertzian Contact Elasticity—Part I

Abstract: Results given in this paper are threefold. In the case of Hertzian line contact, a new load/deformation relationship is derived analytically and use is made of the thickness of the outer race section. A minor effect of the section thickness is shown. The exponent on the deformation is 1.074 (instead of 1.1 usually accepted). Results calculated with the new relationship are successfully compared to results calculated with other published relationships and also are compared successfully to some available experimental results. For the case of point contact, useful relationships, obtained by curve-fitting, are given to calculate easily the load versus deformation, maximum Hertzian pressure and ellipse contact dimension as a function of a dimensionless load parameter and ratio k of equivalent radii (instead of sum of curvatures and elliptical integrals before). A large range of k is covered, from 0.05 (found at roller rib contact) to 13,000 to cover all bearing cases, from ball bearings to spherical and tapered roller bearings. Finally, an important analytical relationship, based on curve-fitting, also is suggested to describe a smooth transition from point contact to line contact as the load increases. It is recommended to define bearing setting and bearing preload with the suggested relationship.

Sensor and rolling bearing apparatus with sensor

Abstract: A rolling bearing apparatus with sensor includes a sensor unit retaining a plurality of types of sensors for detecting the status of a rolling bearing, in a single holder. The plurality of types of sensors are at least two types of sensors of a rotation speed sensor, a temperature sensor, and an acceleration sensor.

Posterior stabilized knee replacement with bearing translation for knees with retained collateral ligaments

Abstract: A knee joint prosthesis includes femoral and tibial components, a bearing and a control arm. The bearing includes an inferior surface in sliding bearing engagement with the tibial component and a superior surface in articular bearing engagement with the femoral component. A notch extends into the posterior end of the bearing and a groove extends anteriorly from the notch in the inferior surface of the bearing. The posterior portions of the femoral component define a cam box having medial and lateral walls and a cam extending therebetween. The control arm is slidably engaged in the groove of the bearing and pivotally engage on the tibial component. The control arm further includes a post that extends into the cam box. The post includes a cam surface that engages the femoral cam to generate roll back of the femoral component on the bearing during flexion. Roll back substantially avoids climb of the femoral component on the bearing during flexion and hence reduces shearing forces on the post.

Wheel bearing assembly

Abstract: A wheel bearing assembly is provided which can suppress brake judder. A film is disposed between the brake rotor-mounting surface of the wheel mounting flange and an abutment surface of a brake rotor to fill a gap therebetween to suppress the deformation of the brake rotor. Also, by concentrating the contact force between the wheel-mounting flange and the brake rotor when a disc wheel of the wheel is tightened to the hub bolts to a portion near the hub bolts, the contact between the wheel-mounting flange and the brake rotor on the surfaces between the hub bolts is suppressed so that undulation of the flat surfaces between the hub bolts will not cause deformation of the brake rotor.

Method for molding a cross-linked preform

Abstract: A method for forming a plastic prosthesis bearing, net-shape bearing or near net-shape bearing is provided. The method includes providing a cross-linked plastic resin preform in a volume sufficient to accommodate the bearing and molding the cross-linked preform. The molding is accomplished by applying heat and pressure to form the preform into a desired solid plastic shape. The heating and pressure is sufficient to melt the plastic resin so that the plastic resin flows under pressure and quench remaining free-radicals.

Methods for predicting polishing parameters of polishing pads, and methods and machines for planarizing microelectronic substrate assemblies in mechanical or chemical-mechanical planarization

Abstract: Methods for predicting polishing characteristics of polishing pads in mechanical or chemical-mechanical planarization of microelectronic substrate assemblies, and methods and machines for planarizing microelectronic substrate assemblies. One embodiment of a method in accordance with the invention includes ascertaining a surface parameter of a bearing surface of at least one raised feature projecting from a base portion of a raised feature polishing pad. The raised feature, for example, can be a pyramidal structure having a first cross-sectional area at the base portion of the pad and a second cross-sectional area at the bearing surface. The first cross-sectional area is generally greater than the second cross-sectional area. To ascertain the surface parameter of the bearing surface, one particular embodiment of the invention involves determining an indication of the surface area of the bearing surface. The surface area of the bearing surface can be estimated by illuminating the bearing surface with a light source and detecting an intensity of the light reflected from the bearing surface. The intensity of the reflected light is proportional to the surface area of the bearing surface, and thus the surface area of the bearing surface can be estimated by correlating the detected intensity of the reflected light with a predetermined relationship between the surface area and the light intensity. The actual surface area of selected bearing surfaces can also be measured by viewing the bearing surfaces through a confocal microscope or another type of optical device.

Grease Degradation in Rolling Element Bearings

Abstract: Grease is degraded during use in rolling element bearings and as a result the lubrication performance can deteriorate. Under severe conditions this can result in lubrication failure and, thus, the grease life will effectively limit the bearing life. At present there is a lack of detailed information regarding the changes that occur in the grease and the way in which this degradation affects lubrication performance and failure. This paper reports an initial study into grease degradation in bearings. The aim of the work was to characterize the changes that occur to the chemical and physical properties during use. A series of bearing tests using the modified DIN 51 806 test designated R2F(M) have been carried out using two greases: additized and non-additized. The tests have been run for different temperature and speed conditions for up to 300 hours. The aim was to examine the grease during normal running rather than after failure. At the end of the tests the bearings were dismantled and grease taken from di...