Showing papers on "Bearing (mechanical) published in 2004"

Improving Tribological Performance of Mechanical Components by Laser Surface Texturing

Abstract: Significant improvement in load capacity, wear resistance, friction coefficient etc. of tribological mechanical components can be obtained by forming regular micro-surface structure in the form of micro-dimples on their surfaces. A feasibility study was performed both theoretically and experimentally using the Laser Surface Texturing (LST) technique to produce the micro-dimples. Each micro-dimple can serve either as a micro-hydrodynamic bearing in cases of full or mixed lubrication or as a micro-reservoir for lubricant in cases of starved lubrication conditions. Theoretical models were developed, and laboratory tests were performed, to investigate the potential of LST in tribological components like mechanical seals, piston rings and thrust bearings. In the entire laboratory tests, friction was substantially reduced with LST compared to the non-textured components.

Residual life predictions from vibration-based degradation signals: a neural network approach

Abstract: Maintenance of mechanical and rotational equipment often includes bearing inspection and/or replacement. Thus, it is important to identify current as well as future conditions of bearings to avoid unexpected failure. Most published research in this area is focused on diagnosing bearing faults. In contrast, this paper develops neural-network-based models for predicting bearing failures. An experimental setup is developed to perform accelerated bearing tests where vibration information is collected from a number of bearings that are run until failure. This information is then used to train neural network models on predicting bearing operating times. Vibration data from a set of validation bearings are then applied to these network models. Resulting predictions are then used to estimate the bearing failure time. These predictions are then compared with the actual lives of the validation bearings and errors are computed to evaluate the effectiveness of each model. For the best model, we find that 64% of predictions are within 10% of actual bearing life, while 92% of predictions are within 20% of the actual life.

Experimental Investigation of Laser Surface Textured Parallel Thrust Bearings

Abstract: Performance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Test results are compared with a theoretical model and good correlation is found over the relevant operating conditions. A comparison of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing is presented showing the benefits of LST in terms of increased clearance and reduced friction.

Bearing damage detection via wavelet packet decomposition of the stator current

Abstract: Bearing faults are one of the major causes of motor failures. The bearing defects induce vibration, resulting in the modulation of the stator current. In this paper, the stator current is analyzed via wavelet packet decomposition to detect bearing defects. The proposed method enables the analysis of frequency bands that can accommodate the rotational speed dependence of the bearing defect frequencies. The wavelet packet decomposition also provides a better treatment of nonstationary stator current than currently used Fourier techniques.

Fault classification and fault signature production for rolling element bearings in electric machines

Abstract: Most condition monitoring techniques for rolling element bearings are designed to detect the four characteristic fault frequencies This has lead to the common practice of categorizing bearing faults according to fault location (ie, inner race, outer race, ball, or cage fault) While the ability to detect the four characteristic fault frequencies is necessary, this approach neglects another important class of faults that arise in many industrial settings This research introduces the notion of categorizing bearing faults as either single-point defects or generalized roughness These classes separate bearing faults according to the fault signatures that are produced rather than by the physical location of the fault Specifically, single-point defects produce the four predictable characteristic fault frequencies while faults categorized as generalized roughness produce unpredictable broadband changes in the machine vibration and stator current Experimental results are provided from bearings failed in situ via a shaft current These results illustrate the unpredictable and broadband nature of the effects produced by generalized roughness bearing faults This issue is significant because a successful bearing condition monitoring scheme must be able to reliably detect both classes of faults

Edge loading in third generation alumina ceramic-on-ceramic bearings: Stripe wear

Abstract: Alumina ceramic-on-ceramic bearings perform exceptionally well under standard hip simulator conditions, but in vivo some retrieved bearings have shown an unusual stripe pattern of wear. We studied 16 bearings retrieved from a series of 1,588 cementless hip arthroplasties with third generation alumina ceramic-on-ceramic bearings to characterize the mechanism of stripe wear formation. None of these bearings were retrieved for bearing failure. The average wear volume was 0.4 mm(3) per year in the heads and 0.3 mm(3) per year in the liners. Mapping of wear stripes on the heads and liners showed that the majority do not occur with normal walking; instead they probably occur with edge loading when the hip is flexed, such as with rising from a chair or with climbing a high step.

Carbon Nanotube Based Bearing for Rotational Motions

Abstract: We describe the fabrication of a nanoelectromechanical system consisting of a plate rotating around a multiwalled nanotube bearing. The nanotube has been engineered so that the sliding happens between different shells. The motion is possible thanks to the low static intershell friction, which we have estimated to be ∼0.85 MPa.

A General Method for the Modeling of Spindle-Bearing Systems

Abstract: In this paper we outline a general method that can be used to model spindle assembly, which consists of spindle shaft, angular contact ball bearings and housing. The spindle shaft and housing are modeled as Timoshenko's beam by including the centrifugal force and gyroscopic effects. The bearing is modeled as a standard nonlinear finite element based on Jones' bearing model that includes the centrifugal force and gyroscopic effects from the rolling elements of bearings. By applying cutting forces to the spindle for a given preload, the stiffness of the bearings, contact forces on bearing balls, natural frequencies, time history response, and frequency response functions of the spindle assembly can be evaluated. In the paper we provide details of the mathematical model supported by experimental results obtained from an instrumented test spindle.

An amplitude Modulation detector for fault diagnosis in rolling element bearings

Abstract: The purpose of this research is to identify single-point defects in rolling element bearings. These defects produce characteristic fault frequencies that appear in the machine vibration and tend to modulate the machine's frequencies of mechanical resonance. An amplitude modulation (AM) detector is developed to identify these interactions and detect the bearing fault while it is still in an incipient stage of development (i.e., to detect the instances of AM when the magnitude of the characteristic fault frequency itself is not significant). Use of this detector only requires machine vibration from one sensor and knowledge of the bearing characteristic fault frequencies. Computer simulations as well as machine vibration data from bearings containing outer race faults are used to confirm the proficiency of this proposed technique.

Calculation of circulating bearing currents in machines of inverter-based drive systems

Abstract: The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%

Two- and three-dimensional bearing capacity of foundations in clay

Abstract: Bearing capacity calculations are an important part of the design of foundations. Most of the terms in the bearing capacity equation, as it is used today in practice, are empirical. Shape factors for square and rectangular footings could not be derived in the past because three-dimensional bearing capacity computations could not be performed with any degree of accuracy. Likewise, depth factors could not be determined because rigorous analyses of foundations embedded in the ground were not available. In this paper, the bearing capacities of strip, square, circular and rectangular foundations in clay are determined rigorously based on finite element limit analysis. The results of the analyses are used to propose rigorous, definitive values of the shape and depth factors for foundations in clays. These results are helpful in reducing the uncertainties related to the method of analysis in bearing capacity calculations, paving the way for more cost-effective foundation design.

Characterization and Modeling of Friction Pendulum Bearings Subjected to Multiple Components of Excitation

Abstract: Experimental and numerical studies are used to examine the behavior of friction pendulum FP bearings to multiple com- ponents of excitation. In the experimental studies, a scaled rigid-frame model representing a rigid bridge superstructure on four FP bearings is subjected to displacement-controlled orbits and earthquake simulations. Using the test data from bidirectional displacement orbits, the constant friction coefficient is calibrated for a rate-independent plasticity model for FP bearings. The earthquake test data are compared with numerical simulations to evaluate the efficacy of the calibrated models. The studies show that the coupling between the two orthogonal components is important for representing the behavior of FP bearings. Modeling of the vertical load on the bearings, and the consideration of this force variation on the bearing response is necessary for an accurate determination of the forces transmitted by the bearings into the substructure. Tridirectional testing of the rigid-block frame shows that the vertical ground motion component has a small effect on the response of a bridge isolated with FP bearings.

Models for bearing damage detection in induction motors using stator current monitoring

Abstract: This paper describes new models for the influence of rolling-element bearing faults on induction motor stator current. Bearing problems are one major cause for drive failures. Their detection is possible by vibration monitoring of characteristic bearing frequencies. As it is possible to detect other machine faults by monitoring the stator current, a great interest exists in applying the same method for bearing fault detection. After a presentation of the existing fault model, a new detailed approach is proposed. It is based on two effects of a bearing fault: the introduction of a particular radial rotor movement and load torque variations caused by the bearing fault. The theoretical study results in new expressions for the stator current frequency content. Experimental tests with artificial and realistic bearing damage were conducted by measuring vibration, torque and stator current. The obtained results by spectral analysis of the measured quantities validate the proposed theoretical approach.

Fluid bearing device

Abstract: The preset invention aims to improve the assembly accuracy and rotation accuracy of a fluid bearing device, and to further reduce the cost thereof. A bearing sleeve is fixed on the inner periphery of a housing. An axial member is supported in a non-contact manner in a radial direction by an oil film formed in a radial bearing gap. The housing made of resin is injection molded with the use of a substrate as an insert part. On the substrate, a control circuit for controlling a polygon scanner motor is mounted.

Analysis of bearing configuration effects on high speed spindles using an integrated dynamic thermo-mechanical spindle model

Abstract: This work presents the effects of bearing configuration on the thermo-dynamic behavior of high speed spindles using the comprehensive dynamic thermo-mechanical model. The dynamic thermo-mechanical model consists of a comprehensive bearing dynamic model, a shaft dynamic model and a thermal model. The thermal model is coupled with the spindle dynamic model through bearing heat generation and thermal expansion of the whole system based on the bearing configuration. Thus the entire model becomes a comprehensive dynamic thermo-mechanical model. The new thermo-mechanical model also considers a pertinent mapping between bearing stiffness and shaft stiffness matrices based on bearing configurations, so that more general cases of bearing configurations can be modeled. Based on this model, the effects of bearing orientation on the spindle dynamics are systematically described and experimentally validated. It is shown that bearing orientation has a significant effect on spindle stiffness. Finally, the effects of various bearing configurations on spindle thermal and dynamic behavior are illustrated through numerical analysis with three different spindles.

Bearing Currents in Inverter-fed AC-motors

Abstract: v

Integrated Dynamic Thermo-Mechanical Modeling of High Speed Spindles, Part 1: Model Development

Abstract: This paper presents a comprehensive integrated thermo-dynamic model for various high speed spindles. The entire model consists of fully coupled three sub-models: bearing, spindle dynamic and thermal models. Using a finite element approach, a new thermal model has been generated, which can describe complex structures of high-speed motorized spindles, and can predict more accurate temperature distributions. The spindle dynamic model is constructed using finite elements based on Timoshenko beam theory and has been improved by considering shear deformation, material and bearing damping, and the spindle/tool-holder interface. Using the new thermo-dynamic model, more general and detailed bearing configurations can be modeled through a systematic coupling procedure. The thermal expansions of the shaft, housing and bearings are calculated based on predicted temperature distributions and are used to update the bearing preloads depending on the operating conditions, which are again used to update the thermal model. Therefore, the model is fully integrated and can provide solutions in terms of all the design parameters and operating conditions.

Identification of Dynamic Bearing Parameters: A Review

Abstract: In this paper, we present a review of the experimental identification of dynamic parameters of bearings in a rotating machine. Major emphasis is given to vibration-based identification methods and the review encompasses descriptions of experimental measurement techniques, mathematical modeling, parameter extraction algorithms and uncertainty in the estimates applied to a variety of bearings. The parameter extraction algorithms include the descriptions of governing equations of the rotor-bearing system and identification methods in both time and frequency domains. The identification techniques have been classified based on methods used to excite the system. The review includes a variety of bearings and similar components, which play an active link between the rotating and stationary parts of a machine. Based on the state of the art in bearing identification, conclusions are made and future directions are suggested.

Wear resistance of Zr-based bulk metallic glass applied in bearing rollers

Abstract: Bearing rollers, 7.5 mm in diameter and 7.5 mm in length, were prepared from Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass (BMG). The working life of the bearing rollers was evaluated through a real rotation test with a large-load and at a high-speed, and compared with that of commercial GCr15 steel rollers. The results show that the bearing rollers of Zr-based bulk metallic glass have a better wear resistance than the commercial GCr15 ones. And the wear behaviors are different for these two kinds of bearing rollers.

Detecting motor bearing faults

Abstract: Three-phase induction motors are the workhorses of industry because of their widespread use. They are used extensively for heating, cooling, refrigeration, pumping, conveyors, and similar applications. They offer users simple, rugged construction, easy maintenance, and cost-effective pricing. These factors have promoted standardization and development of a manufacturing infrastructure that has led to a vast installed base of motors; more than 90% of all motors used in industry worldwide are ac induction motors. Causes of motor failures are bearing faults, insulation faults, and rotor faults. Early detection of bearing faults allows replacement of the bearings, rather than replacement of the motor. The same type of bearing defects that plague such larger machines as 100 hp are mirrored in lower hp machines which has the same type of bearings. Even though the replacement of defective bearings is the cheapest fix among the three causes of failure, it is the most difficult one to detect. Motors that are in continuous use cannot be stopped for analysis. We have developed a circuit monitor for these motors. Incipient bearing failures are detectable by the presence of characteristic machine vibration frequencies associated with the various modes of bearing failure. We will show that circuit monitors that we developed can detect these frequencies using wavelet packet decomposition and a radial basis neural network. This device monitors an induction motor's current and defines a bearing failure.

Orthopaedic bearing and method for making the same

Abstract: An orthopaedic bearing includes a metallic component having a polymer composite secured thereto. A method of making an orthopaedic bearing is also disclosed.

Bearing current remediation options

Abstract: The vast majority of bearing failures in electric motors and electric motor-driven equipment are due to mechanical and thermal causes. Bearing current in induction motor can result in premature bearing failure. Proper remediation methods depend upon a thorough understanding of the potential current paths in a given installation. Diagrams of current flow paths were presented here to illustrate potential issues. Proper grounding is a key to shunting currents away from paths that flow through motor or driven equipment bearings.

Electrical generator with ferrofluid bearings

Abstract: An electrical generator includes a magnet constrained to move relative to a conductor by a support structure, with a ferrofluid bearing providing an ultra low friction interface between the magnet and support structure. The assembly has a critical angle of displacement from a horizontal static position of less than 1 degree, and preferably less than 10 minutes. An electrical signal is generated in the conductor by the moving magnetic field.