Showing papers on "Fluid bearing published in 2011"

Analysis of the dynamics of a slider–crank mechanism with hydrodynamic lubrication in the connecting rod–slider joint clearance

Abstract: The conventional slider-connecting rod–crank mechanism is widely applied in mechanical systems. The use of hydrodynamic bearings in the mechanism joints is of particular interest in reducing friction, mainly in special conditions of lubrication such as the connecting rod–slider joint. This bearing belongs to a class of bearings with alternating rotational motion. This paper proposes a mathematical model for this particular problem, considering the dynamics of the slider-connecting rod–crank system interacting with the lubrication phenomenon in bearings with alternating motion. Two models were used to analyze the dynamics of the system. The first model (by Eksergian Equation of Motion) represents the system when the connecting rod end is in contact with the bearing surface, assuming, in this condition, the same behavior as that of rigid bearings (without clearance). The second model (by Lagrange Method) represents the system when the connecting rod end is in the hydrodynamic lubrication mode in the slider bore clearance. In this condition, the slider moves in relation to the connecting rod, presenting a problem of multi-degrees-of-freedom. The mathematic model of hydrodynamic lubrication was introduced to obtain more realistic results of the system's dynamic behavior.

Investigation of the High Speed Rolling Bearing Temperature Rise With Oil-Air Lubrication

Abstract: The oil-air lubrication system has been widely used for rolling ball bearing. However, as the rotation speed increases, the temperature rise will increase dramatically, resulting in shortening the service life of the ball bearing. The existing literature has offered valuable fundamental data about the oil-air lubrication of rolling bearing; however, there are still some problems that concerned the oil-air lubrication, which are not addressed. In this study, an experiment setup to investigate the oil-air lubrication for the high speed ball bearing has been developed, and performance tests of hybrid ceramic and steel ball bearings under the extensive operating conditions including oil-air supply pipe length, bearing preload, lube interval, oil type, oil viscosity, nozzle design, and rotation speed have been conducted. The test results show that the bearing has the lowest temperature rise with the pipe length of 1.5 m. For the steel ball bearing, the proper preload decreases with increasing of the rotating speed, and the temperature rise of the hybrid ceramic ball bearing is not sensitive to the axial preload. There exists a proper amount of lubricant for the bearing at each rotational speed; and a larger amount of lubricant is required for the bearing as the rotating speed increases. The tested bearings under different speeds have almost the same lowest temperature rise under the lubricant with the viscosity of 100 cSt; a higher or lower viscosity will increase the bearing temperature rises. The nozzle design is an important factor to affect the temperature rise of the ball bearing, and the suitable geometric parameter of the nozzle is closely related to the cage landing method of the bearing. The temperature rise of tested bearings increases with the increase in the rotation speed; and the hybrid ceramic ball bearing always has a lower temperature rise than that of the steel ball bearing at the same operating conditions.

Theoretical and Experimental Analysis of a Laser Textured Thrust Bearing

Abstract: In this article, a laser partially textured thrust bearing is theoretically and experimentally analyzed. An adiabatic model is developed in order to theoretically investigate the performances of the bearing. The bearing sample is partially textured both in radial and circumferential direction using the laser texturing process. The performance of the bearing (fluid film thickness and friction torque) is evaluated on a specially adapted test rig and the experimental results are compared with the theoretical model. A good agreement is found between the theoretical model and the experimental data. Also a comparison between a laser textured bearing and a bearing textured using the photolithographic method is presented.

Comparison between grooved and plane aerostatic thrust bearings: static performance

Abstract: The demand of air bearings is increasing for those applications that require precision linear movements or high-speed rotations. In particular in this paper air pads for air motion technology are studied. The paper analyses the effect of a circumferential groove machined on the pad surface on pressure distribution, air flow consumption and stiffness. Two geometries are investigated and compared: one with three supply orifices and the other with a circumferential groove as well. The static characteristics of the pads are experimentally determined with also the pressure distributions under the pads along the radial and circumferential directions. The experimental pressure distributions are compared with the simulated ones, obtained with a numerical program at the purpose developed. The numerical model considers a general formulation of the supply holes discharge coefficient that can be used also in presence of a circumferential groove.

Load Capacity and Durability of H-DLC Coated Hydrodynamic Thrust Bearings

Abstract: Hydrogenated diamondlike carbon (H-DLC) coatings provide excellent wear resistance and low friction for bearing applications. However, the use of such coatings with aqueous lubricants could pose some difficulties due to the hydrophobic nature of the surface. A thrust bearing tribometer was used to compare performance of hydrophilic and hydrophobic surfaces in hydrodynamic lubrication with a mixture of water and glycerol as the lubricant. Hydrophobic surfaces on both runner and bearing were achieved with the deposition of H-DLC films on titanium alloy surfaces. Hydrophilic surfaces were created through modification of H-DLC surface with covalently bonded heparin. Several possible combinations of hydrophobic and hydrophilic surface conditions were used on the bearing and runner surfaces to provide full-wetting, partial-wetting, and half-wetting conditions. The experimental results confirmed that load support is still possible, when the bearing is half-wetted or partially wetted. However, the full-wetted bearing combination (i.e., Reynolds no-slip boundary condition) provided the highest load support. Introduction of slip at the surface resulted in a lower measured torque. Heparin treatment resulted in a lower than expected static friction and friction in full lubrication regime. The durability of coated surfaces was evaluated in a series of start–stop tests and in impact tests. The results confirmed that the coatings are stable and survive the test regiment that exceeded 50 test cycles; whereas the uncoated titanium alloy bearing surfaces were damaged after ten test cycles.

Fluid dynamic bearing apparatus, spindle motor, and disk drive apparatus

Abstract: In a fluid dynamic bearing apparatus, an oil buffer is defined between a thrust gap and a pumping gap. The oil buffer has an axial dimension greater than that of the thrust gap, and/or has a radial dimension greater than that of the pumping gap. An air bubble generated in the thrust gap due to cavitation, for example, when a fluid dynamic bearing apparatus experiences a vibration can be dissolved in lubricating oil provided within the oil buffer. This prevents leakage of the lubricating oil due to the air bubble residing in the fluid dynamic bearing apparatus.

On the modelling of hybrid aerostatic-gas journal bearings:

Abstract: Gas journal bearings have been increasingly adopted in modern turbo-machinery applications as they meet the demands of operation at high rotational speeds, in clean environment, and with great efficiency. Due to the fact that gaseous lubricants, typically air, have much lower viscosity than more conventional oils, carrying capacity and dynamic characteristics of passive systems are generally poorer. In order to enhance these characteristics, one solution is used to combine the aerodynamic effect with the addition of external pressurization. This study presents a detailed mathematical model for hybrid lubrication of a compressible fluid-film journal bearing. Additional forces are generated by injecting pressurized air into the bearing gap through orifices located on the bearing walls. A modified form of the compressible Reynolds equation for active lubrication is derived. By solving this equation, stiffness and damping coefficients can be determined. A multibody dynamics model of a global system comprised ...

A compact ultra-precision air bearing stage with 3-DOF planar motions using electromagnetic motors

Abstract: We designed a novel surface motor stage supported by air bearings and driven by linear electromagnetic motors. This compact and simple planar stage is proposed for compact-sized precision machine systems, such as micro-machine tools or measurement systems requiring minimum X-Y stage height. Four single-phase linear motors with coils and iron cores are located under the base plate, and air bearings and cores with permanent magnets are attached under the moving table. The hard, non-magnetic alumina-ceramic base plate surface acts as a planar guide for the air bearings. The attractive magnetic force between the magnets and motor cores preload the air bearing to increase vertical stiffness. By simultaneously combining actuations of the motors, linear X and Y motion can be controlled, and angular motions can also be generated. A grid encoder is used to control planar motion, and the system is run by a programmable numerical controller. The thrust and attractive force were calculated using a magnetic circuit model. The designed prototype is 220 (L) × 220 (W) × 66 (H) mm3 in size with a 20 mm × 20 mm range of motion. After fabrication, basic aspects of the prototype, such as vertical stiffness and thrust force, were evaluated. Twenty nanometers of positioning resolution was obtained for the X and Y axes, and the three motions could be controlled independently.

Elastohydrodynamic analysis and Pareto optimization of intact, worn and misaligned journal bearings

Abstract: In this paper, we propose an engineering approach for the elastohydrodynamic (EHD) analysis and optimization of the steady operation of intact, worn or/and misaligned journal bearings. We develop an iterative algorithm, based on finite element formulations for both the hydrodynamic lubrication and the elastic deformation of the bearing pad, which converges to the solution of the coupled problem. In addition, we formulate a multi-objective optimization problem, and seek combinations of the design variables, namely, length-to-diameter ratio, Sommerfeld number and bearing deformation coefficient, which minimize simultaneously the normalized friction coefficient and the normalized maximum pressure, under intact and representative fault conditions. Optimal solutions are identified based on the Pareto dominance, and are physically interpreted. The present development provides a tool for optimally reducing the parameter space of independent variables in EHD journal bearing design.

Measurement of Normal Force in Magnetorheological and Ferrofluid Lubricated Bearings

Abstract: Preliminary analysis of magnetorheological fluid usability in fluid lubricated bearings has been described in the present study. Results of the study aimed at rheological properties of chosen fluids, which possess magnetic properties (both ferrofluids and magnetorheological fluids) with respect to their application in slide bearings have been presented Preliminary analysis of potential advantages related with the magnetic fluid bearing construction was carried out. Results of measurements of normal force developed within magnetorheological fluid and ferrofluid in result of magnetic field action at various shear rate values have been presented.

A computational investigation of the disk-housing impacts of accelerating rotors supported by hydrodynamic bearings

Abstract: As the radial clearance between disks and the casing of rotating machines is usually very narrow, excessive lateral vibration of accelerating rotors passing critical speeds can produce impacts between the disks and the housing. The computer modeling method is an important tool for investigating such events. In the developed procedure, the shaft is flexible and the disks are absolutely rigid. The hydrodynamic bearings and the impacts are implemented in the mathematical model by means of nonlinear force couplings. Most of the publications and computer codes from the field of rotor dynamics are referred only in the case when the rotor turns at a constant angular speed and in simple cases of disk-housing impacts. Moreover, if the disks turning at variable speed are investigated, the resulting form of the equations of motion derived by different authors slightly differs and the differences depend on the method used for their derivation. Therefore, particular emphasis in this article is given to the derivation of the motion equations of a continuous rotor turning with variable revolutions to explain the mentioned differences, to develop a computer algorithm enabling the investigation of cases when impacts between an arbitrary number of disks and the stationary part take place, and to analyze the mutual interaction between the impacts and the fluid film bearings. The Hertz theory is applied to determine the contact forces. Calculation of the hydrodynamic forces acting on the bearings is based on solving the Reynolds equation and taking cavitation into account. Lagrange equations of the second kind and the principle of virtual work are used to derive equations of motion. The Runge―Kutta method with an adaptive time step is applied for their solution. The applicability of the developed procedure was tested by computer simulations. The results show that it can be used for the modeling of complex rotor systems and that the short computational time enables carrying out calculations for a number of design and operation parameters.

Air Injection as a Thermal Management Technique for Radial Foil Air Bearings

Abstract: A thermal management technique for radial foil air bearings was experimentally evaluated. The technique is based on injecting air directly into the internal circulating fluid-film to reduce bulk temperatures and axial thermal gradients. The tests were performed on a single top foil, Generation III, radial foil bearing instrumented with three thermocouples to monitor internal temperatures. A through hole in the bearing shell coincident with the gap between the top foil's fixed and free ends provided entry for the injection air. The tests were conducted at room temperature with the bearing operating at speeds from 20 to 40 krpm while supporting 222 N. Two different mass flow rates of injection air were evaluated for this method, 0.017 and 0.051 kg/min. Test results suggest that the air injection approach is a viable thermal management technique capable of controlling bulk temperatures and axial thermal gradients in radial foil air bearings.

Modeling of a Grooved Parallel Bearing with a Mass-Conserving Cavitation Algorithm

Abstract: Several load-supporting mechanisms have been studied to deal with the cavitation problem in parallel bearings. The formation of cavities and their disposition affect the pressure generated in a continuous thin film and hence the load capacity of bearings. In solving the Reynolds equation, proper cavitation boundary conditions must be applied. In this article, the mass-conserving Vijayaraghavan-Keith cavitation algorithm is utilized to analyze the hydrodynamic lubrication performance of parallel bearings with one or more grooves. Using the finite difference method, a one-dimensional Reynolds equation is discretized. Gauss-Seidel iteration is used to solve the obtained set of linear algebraic equations. For a given lubricant, sliding speed, and minimum film thickness, several comparative studies are made between the Vijayaraghavan-Keith cavitation algorithm and a published analytic solution. Several factors affecting the hydrodynamic lubrication performance are considered, such as cavitation pressure, inlet...

Thermal Structural Effects in a Gas-Lubricated Foil Journal Bearing

Abstract: A theoretical model for gas-lubricated foil journal bearings that incorporates thermal structural effects is presented. Bending and membrane effects in the top foil resulting from temperature are included along with thermal expansion of the journal, subfoil, and bearing housing. The model includes thermal transport through the journal, foils, and bearing housing. Pressure in the gas film is predicted using the Reynolds equation, and a thermal bulk flow model is used to predict temperature. The results demonstrate that models will overpredict film thickness along the side edge of a bearing if thermal strain in the top foil is not included. In addition, the results show the need for a three-dimensional thermal flow model at the trailing edge of a bearing when backflow occurs.

Lubrication and roughness

Abstract: This chapter introduces the basics of hydrodynamic lubrication theory and highlights its application to some machine parts with un-roughened (slider and cylindrical journal bearings) and roughened surfaces (parallel parts in relative motion). It first presents a theoretical analysis and results for two-dimensional sinusoidal and triangular wave roughened surfaces.

Numerical Analysis of Hydrodynamic Lubrication on Water-Lubricated Rubber Bearings

Abstract: Water lubricated rubber bearings are one of the most appropriate bearings for underwater use. The most popular design used widely today is the straight fluted rubber bearing. The special configuration leads to partial hydrodynamic lubrication and low load capacity. A new bearing bush structure which is favorable for constructing continuous hydrodynamic lubrication was designed and produced for experiment in the paper. The eccentricity ratio of the new structure rubber bearing was measured under different loads in experiment. Used the measured eccentricity ratios, the load capacity was calculated by numerical simulation and compared with the given test values. The calculated values were in good agreement with the given test results. The results show that complete hydrodynamic lubrication can be formed in the new designed rubber bearing. The experimental results also indicate that there is an appropriate bearing clearance which the load capacity is up to the maximum.

The role of lubricant feed temperature on the performance of twin groove journal bearings: an experimental study

Abstract: An experimental assessment of the influence of lubricant feed temperature (Tf) on the behaviour of twin groove hydrodynamic journal bearings has been undertaken. Several loads, shaft speeds and bearing geometries were tested under constant lubricant feed pressure (pf), while Tf took four different values between 29°C and 58°C. It was found that the increase of Tf has an effect in bearing performance which is analogous in many ways to the effect of the increase in eccentricity: increase in lubricant flow rate (especially in the low eccentricity range), in outlet temperature (Tout) and in maximum bush temperature (Tmax). Nevertheless, the latter increase was lower than the corresponding increase in Tf. Also, in the high eccentricity range the increase in flow rate due to the increase of Tf could be deceiving in the sense that the additional flow was supplied mainly to the inactive region of the bearing (the unloaded land of the bearing).

Fluid dynamic bearing device and assembly method for same

Abstract: Providing a fluid dynamic bearing device, wherein the outer member comprises a member formed by a pressing process on a plate member, the radial bearing surface and at least the one of the thrust bearing surfaces of the outer member being formed by the pressing process, and wherein at least a part of the inner member, which forms the radial bearing surface and the thrust bearing surfaces of the inner member, is made of a sintered metal.