Coefficients Of Bearings Research Articles

Experimental measurement on friction performance of PDC bearings for oil drilling under different working conditions

Abstract As a kind of superhard material, the polycrystalline diamond compact (PDC) has been extensively used in engineering with its high strength and high wear resistance. Meanwhile, PDC has been increasingly used in bearing design to improve bearing capacity and service life. However, as a bearing material, its friction coefficient under different working conditions is not clear although it is a very important parameter. In this paper, the authors proposed a theoretical model of friction measurement and design a set of measurement rig to investigate the friction characteristics of the PDC bearing. The measurement equipment is developed based on the Coulomb friction model, with the three measurement environments taken into consideration: dry, water and drilling mud. A pair of thrust ball bearing was used in the measurement equipment to equilibrium axial load. But the friction coefficient of thrust ball bearing is proved far less than that of the PDC bearing in the experiment. The frictional coefficient of PDC bearings can be stabilized at about 0.12 under dry friction or water lubrication conditions and increase to 0.2 when tested under drilling fluid environment. Measuring the friction coefficient of PDC bearing -especially under drilling fluid environment can not only provide support for the design of the downhole tool where the bearing friction coefficient obviously affects the feasibility and agility of the tool but also help people to deepen the understanding of PDC materials.

Influence of Fluid Film Boundary Migration on Dynamic Coefficients of Journal Bearings and Behavior of Rotor System

Abstract The position of fluid film in journal bearing will change while the journal moving in bearing, which can be named fluid film boundary migration (FFBM). It is usually ignored in the calculation of linear dynamic coefficients. While, the errors brought by this neglection was not ever investigated in detail. In this paper, the influence of FFBM on bearing dynamic coefficients and rotor system dynamic behaviors are investigated. A new perturbation-based model is proposed to take the FFBM into account by modifying the boundary conditions of governing equations. It is then verified by the experimental results and analytical results from previous research. Furthermore, the effects of FFBM on stiffness and damping in two typical journal bearings are investigated. The result indicates that the FFBM has a significant influence on dynamic coefficients of full circular journal bearing but little impact on journal bearing with axial grooves. Moreover, it affects the stiffness and damping more significantly in the cases of large length-to-diameter ratios or small eccentricity ratios in full circle bearing. Finally, the dynamical behavior of a rotor-bearing system with considering the FFBM is also investigated. The result shows that the FFBM of oil film has remarkable influences on the instability threshold and imbalance responses of the rotor system, which should not be ignored. The conclusions obtained in this research are expected to be helpful for the design of full circular journal bearings or rotor-bearing systems.

Study on the performance of novel gas foil conical bearings

To reduce the mass and size of low-power turbine machinery, a new type of gas foil conical bearing was proposed, and its static and dynamic performance was systematically studied. Based on a nonlinear bump stiffness model considering rounding and friction, the structural stiffness distribution, load capacity, dynamic stiffness, and damping coefficients of gas foil conical bearing were calculated, and the influence of bearing parameters on its static and dynamic characteristics was studied. In addition, a pair of gas foil conical bearings was used to replace the traditional radial-thrust foil bearing support scheme on an air compressor to explore the practicability of the novel bearing. The results show that the new gas foil conical bearing has an excellent supporting performance and broad prospects for application. The bump radius, rounding radius, friction coefficients, and foil thickness will significantly influence the bump foil stiffness. The bearing parameters such as structural stiffness, nominal clearance, cone angle, and eccentricity have a large effect on its static and dynamic performance, and we can obtain the desired bearing characteristics by tailoring these parameters.

Computational evaluation of dynamic coefficients of thrust bearings; effect of artificial texturing on thermohydrodynamic performance

Fluid film thrust bearings are commonly used in industry, providing durable and reliable operation at high values of load carrying capacity, accompanied by low friction losses. A major advantage of hydrodynamic fluid film bearings, over other types of bearings, is their enhanced dynamic behaviour, especially under transient or impact loads. Currently, a systematic approach to identify the dynamic coefficients of thrust bearing geometrical configurations utilising high complexity CFD simulation data has not yet been established. It is therefore imperative to develop a method, capable of evaluating the dynamic characteristics of complex bearing designs and allow the evaluation of bearing response under transient loads. In the present work, a computational approach is proposed to estimate the stiffness and damping coefficients of fluid-film thrust bearings. A CFD-based ThermoHydroDynamic (THD) numerical model of the bearing is developed and utilised for performing an initial steady-state simulation at given rotational speed and thrust load, as well as subsequent transient simulations at increasing or decreasing thrust loads. The former simulation is used to calculate the stiffness coefficient of the bearing at the specified conditions, while the latter are appropriately post-processed to estimate the damping coefficient of the bearing at different values of rotor acceleration. The procedure is repeated at different operating conditions, yielding a map of the dynamic coefficients of the bearing. Finally, a single degree of freedom model is generated, which utilises the calculated values of dynamic coefficients to evaluate transient bearing performance under any given thrust load history. The proposed methodology is applied to compare the dynamic response characteristics of a conventional sector-pad tapered-land thrust bearing and a textured tapered-land thrust bearing of the same principal dimensions.

Optimization of crankpin bearing lubrication under dynamic loading considering effect of micro asperity contact

Purpose To improve the lubrication and tribology performance (LTP) of the crankpin bearing, this paper aims to propose the optimization of the crankpin bearing parameters considering effect of the high-speed dynamic load and micro asperity contact. Design/methodology/approach A numerical simulation method combined by the slider-crank-mechanism dynamic and lubrication models is applied to solve the dynamic and lubrication equations of crankpin bearing. These equations are then computed via an algorithm program written in Matlab software. The contact force (Wac) in the asperity contact region, friction force (Ff) and friction coefficient (μ) of crankpin bearing are chosen as objective functions. The original parameters and experimental data of the engine are used for the simulation to enhance the reliability of the research results. The parameters are then optimized to obtain the minimum values of Wac, Ff and μ. Findings The research results show that the LTP is significantly improved with optimized parameters. Particularly, the maximum values of Wac and Ff are greatly decreased by 27 and 32%, respectively. Originality/value Reducing the width, radius and surface roughness and increasing the radial clearance of crankpin bearing can improve better the LTP. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-02-2020-0072/

An experimental study on the tribological performance of water-lubricated journal bearings with three different materials

Purpose The tribological behavior, i.e. friction coefficient and wear rate, and vibration characteristics of the water-lubricated bearing was investigated. The water-lubricated bearing is made of three different materials, i.e. polyether-ether-ketone (PEEK), polyimide (PI) and nitrile-butadiene rubber (NBR). Design/methodology/approach The tribological behavior was investigated experimentally on a specially designed test rig. Three vibration sensors were used to record the vibration of the bearing. Findings The results indicated that the variation of friction coefficient with rotation speed agrees well with the trend of Stribeck curve. The tested friction coefficient of rubber bearing is higher than that of the other two bearings whether it is in the state of mixed-lubrication or hydrodynamic lubrication, and which causing a larger wear rate in rubber bearing. The PEEK bearing exhibits the best tribological properties due to it has smaller friction coefficient and wear rate. However, it can be found that the rubber bearing gives the minimum vibration acceleration, which means that the rubber bearing has the most potential to improve the stability of water-lubricated bearing rotor system. Originality/value In this study, a group of experiment studies conducted on a specially designed test rig. The comprehensive performance, including friction coefficient, vibration acceleration and wear rate, of water-lubricated bearing with three different materials, i.e. PEEK, PI and NBR, was compared systematically. The experiment research may offer a reference for the selection of material in water-lubricated bearing in specific operating conditions. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2019-0447/

Comparative Study on Dynamic Characteristics of Double-Pad Inwardly and Outwardly Pumping Water-Lubricated Spiral-Groove Thrust Bearings

AbstractThe dynamic characteristics of the double-pad inwardly pumping water-lubricated spiral-groove thrust bearing (SGTB) is different from that of the outwardly pumping version, especially under a high-speed condition. However, no literature on this topic can be found up to now. In this study, a comparative study on the dynamic characteristics of the two types of SGTBs is conducted. First, a turbulent lubrication model considering centrifugal and cavitating effects for the double-pad SGTB is developed based on gas–liquid two-phase flow. The steady-state and perturbed Reynolds equations of liquid phase are derived using linear perturbation method. Subsequently, the boundary fitted coordinate system and control volume method are applied to solve the Reynolds equations. Then, the axial stiffness coefficients of high-speed water-lubricated bearings are verified by an experimental study. Finally, the influence of operating conditions and configuration parameters on the dynamic behaviors for the two types of SGTBs is investigated. The results show that the double-pad outwardly pumping bearing is superior to the inwardly pumping version in all the dynamic coefficients when the radius ratio exceeds 0.65. When the tilt angle exceeds 1.2 × 10−4 as well as when the eccentricity ratio exceeds 0.7, the dynamic damping, angular and cross-coupled stiffness coefficients of the outwardly pumping bearing may be larger than those of the inwardly pumping one.

Determination of Dynamic Coefficients of Air-Ring Bearings

An externally-pressurized journal air bearing (AB) with an air-ring (AR), or air-ring bearing (ARB), for a balanced, rigid and light-weight rotor is studied. An elastic structure in the form of an AR is provided between the bearing-bushing and the casing. The ARB is analyzed to determine the dynamic coefficients (DC) at various angular velocities and angular frequencies of vibration of the journal in its range of operation. These DC can then be used to predict the dynamic stability of the rotor ARB system against self-excited (SE) vibration. A numerical simulation procedure is followed to determine the DC. The ARB is modeled as a two-degrees of freedom system. During the simulation, the journal follows a prescribed harmonic motion. Self-exciting forces due to flow dynamics inside an ARB induce this motion. Three-dimensional (3-D) flow equations are solved on a moving/deformable grid using ANSYS®, to compute the pressure (p) distribution in the ARB. Unlike in previous studies, in this study the bushing displacement is determined by the instantaneous p-distribution in the ARB. DC of both AB and AR are determined simultaneously by considering the interaction between the AR and the AB regions through the feed-holes in the bushing. Time-dependent displacement, velocity, and load-carrying capacity obtained by numerical simulation are used to evaluate the DC. Incorporation of an AR around an AB can prevent SE vibration due to positive values of direct damping coefficients of AR. A 3-D flow analysis can reveal the realistic nature of flow in an ARB.

Оценка влияния упругих свойств подшипников скольжения дейдвудного устройства судна на значение коэффициента жесткости

The article considers the ship shaft line as a complex dynamic system influencing the operation of the ship. There has been given a diagram of the shaft line with one stern bearing and one remote bearing of the propeller shaft. The shaft line service life depends on the material of the slide bearing of the stern gear (lignum vitae, babbitt, textolite, caprolon, bronze, polyurethanes, rubber). The analysis of the research of static and dynamic calculations of ship shafting has been carried out. The design scheme of the ship shafting on elastic point supports is presented. It has been referred to consider feasibility of the elastic and mechanical properties of stern bearings at the stage of designing a ship shaft line. The method of calculating the transverse vibrations of the shaft line is studied, the purpose of which is to determine the natural frequency. The formula for calculating the lowest natural frequency of bending vibrations is given. The results of experimental studies at the KMV-200 stand based on uneven distribution of loads along the stern bearings are considered. It has been suggested that the greater the wear, the lower the stiffness coefficient. At a certain degree of wear of stern bearings, a resonance phenomenon occurs at the lowest operating frequencies. The value of the stiffness coefficient is studied depending on the modulus of elasticity of the stern bearing material. Static analysis of the ship shaft line was made taking into account the stiffness coefficient of the stern bearing. The universal equation of the curved axis of the beam is used according to the initial parameters method. As it has been found, the greater the deflection at the propeller attachment point, the lower the natural frequency of the transverse vibrations of the shaft line. In calculations it is necessary to take into account the separation of the shaft line from the stern bearing, since it helps to reduce the natural frequency and the appearing resonance during transverse vibrations.

Friction coefficient and performance evaluation of plain journal bearing using SAE 5W-30 engine oil

Friction is a crucial parameter in tribological applications such as power transmission, crankshafts, gears, cams, bearings, and other rotating machine parts or components. Due to the relative motion of the shaft and bearing, friction needs to be analyzed according to all lubrication states of the journal bearing. The friction coefficient was significantly reduced using piezo-viscous SAE 5W-30 engine oil in this study. An adequate lubricant pressure is obtained using this approach to produce a suitable oil film thickness. Minimal variation in lubricant temperature was obtained which prescribes the sustainability of the lubricant. The bearing performance was observed through computational fluid dynamics analysis under different viscosities. The SAE 5W-30 lubricant-containing 0.052693 Pa s viscosity minimized bearing deformation and stress formation at 500, 750, and 1000 r/min. A new bearing material as gun-metal having good bearing properties and good resistance to corrosion has been proposed in this study.

Effects of Manufacturing Tolerances on Dynamic Properties of Journal Bearings

Dynamic properties of journal bearings were analysed when manufacturing tolerances existed. A methodology was proposed to predict journal bearing properties and to seek a relationship between the manufacturing tolerances and the dynamic coefficients. All the dynamic coefficients of journal bearings were investigated against Sommerfeld number and four types of standard tolerance grades in laminar flow regimes respectively. The results showed that manufacturing tolerances had a significant influence on the dynamic coefficients, especially the cross terms of both stiffness and damping coefficients. The more the magnitude of manufacturing tolerance grade is, the more variations of dynamic coefficients are. It is recommended to take the effect of tolerances on the dynamic performance of journal bearings on its design stage.

Failure analysis for overall stability against sliding and overturning of a girder bridge

In recent years, several similar girder bridge failures due to the overall instability have occurred one after another in China, and the crucial factor of the failures was reported to be the overturning. However, girder bridge sliding, an unusual failure mode for the overall instability, has been rarely mentioned. The Chunhui E-ramp bridge, which failed and collapsed under the joint action of four trucks with a total weight of 389.3 ton, was a typical case. Thus firstly, this paper aims to evaluate the response of girder to the passing eccentric heavy vehicles over the bridge. Secondly, this paper intends to analyze the process of overall instability against sliding and overturning. In order to achieve these two aims, we employed a nonlinear finite element model and the step-by-step method to obtain the dynamic response of girder bridge; and established a transverse anti-slip equilibrium equation. Analysis of the result showed that the failure began with the uplift and ended up with the sliding, rather than a rigid body overturning. Additionally, the specification limitations and the friction coefficient of bearings were both discussed based on the results of numerical analysis.

Dynamic analysis of 5-DOFs aerostatic spindles considering tilting motion with varying stiffness and damping of thrust bearings

Aerostatic bearings are of great importance for improving machining accuracy of a workpiece surface. The dynamics of air bearings and aerostatic spindle system in ultra-precision machine, which mainly causes mid-spatial waviness errors, has a great effect on surface topography. The dynamic coefficients of the thrust bearings were determined by adopting the perturbation method and finite difference method with MATLAB® software. In addition, the influences of the spindle speed and tilt angle conducted upon the dynamics of the thrust bearings were investigated in detail. The dynamic response of the spindle system, which is closely related to the performance of the thrust bearing and does not work only by the effect of the journal bearing, supported by pressured air film was obtained. The simulation analysis of spindle responses under cutting force and experiment results is well matched, and the analysis method proposed in this paper can be also applicable to other air bearing spindle systems.

Dynamic coefficients and stability analysis of a water-lubricated hydrostatic bearing by solving the uncoupled Reynolds equation

This paper concerns the dynamic characteristics of incompressible laminar flow hydrostatic bearings. An improved method based on the mathematical perturbation technique for calculating the stiffness and damping coefficients of hydrostatic bearings is presented; it raises the calculation efficiency by uncoupling the recess flow continuity equations from the solving of the Reynolds equation. The dynamic coefficients of a water-lubricated four-recess hydrostatic bearing are calculated with both the improved method and the conventional method. The comparisons between these two methods validate the effectiveness and correctness of the improved method. Furthermore, the dynamic response and stability characteristics of a rotor supported by the hydrostatic bearing are calculated and compared with experimental results. First, the dynamic responses calculated with the linear and nonlinear bearing dynamic coefficients models show that the linear model is inaccurate if the rotor whirls in a large eccentricity ratio range, owing to the nonlinearity of stiffness and damping. Second, according to the numerical and experimental results, the nonlinearity of bearing stiffness and damping coefficients could induce double rotational frequency component in the unbalance response frequency spectrum. Finally, the numerical results indicate that the stability threshold speed of the bearing increases with eccentricity ratio. The improved method proposed can be used to evaluate the dynamic performance of hydrostatic bearings efficiently, and the bearing characteristics presented could contribute to a better understanding of the performance of water-lubricated hydrostatic bearings.

A method to obtain the linear dynamic coefficients for journal bearing in vertical rotors

PurposeThe infinitesimal perturbation (IP) method is commonly used in calculating stiffness and damping of journal bearing in horizon rotor systems. The boundary condition (BC) for the perturbed pressure is assumed being zero at leading edge of film, although it is usually not zero because of nonzero pressure gradient. This assumption is sufficiently accurate for most purpose in horizon rotors. However, for journal bearing in vertical rotor-bearing systems, the BC with the assumption in IP method will bring in significant errors in calculating linear dynamic coefficients. This paper aims to propose a method to obtain the dynamic coefficients of journal bearing in vertical rotors.Design/methodology/approachThe stiffness and damping are approached based on IP method and the modified BC of perturbed pressure. As it is difficult to predict perturbed pressure at leading edge at a fixed coordinate system using IP method, a dynamic coordinate system is introduced in this method, of which the origin on circumferential direction is defined as the leading edge of film.FindingsThe effectiveness and accuracy of proposed IP method in dynamic coordinate (IPMDC) system are verified by comparing the obtained results with analytical solutions. The comparison shows that the results from IPMDC present a good agreement with the analytic solutions.Originality/valueThe proposed method can be applied in obtaining linear dynamic coefficients of journal bearing in vertical rotors with high precisions. Instead of the usual nonlinear analysis of vertical rotors, this method provides a feasibility of predicting the instability threshold of vertical rotor-bearing systems via linear models.

A study on the wear behavior of tin-based journal bearing under different working conditions

PurposeThe purpose of this paper is to study the friction and wear properties of journal bearings under different working conditions.Design/methodology/approachFriction coefficient and wear losses of journal bearing under different working conditions have been determined by a bearing test rig. The worn surfaces of bearing were examined by scanning electron microscopy and laser three-dimensional micro-imaging profile measurements, and the tribological behavior and wear mechanisms were investigated.FindingsThe wear loss and friction coefficient of bearing under starting-stopping working condition is far greater than that of steady-state working conditions. In addition, the maximum wear loss under start-up and stop conditions is about 120 times of that under stable operating conditions. Under stable working conditions, the main wear forms of bearings are abrasive wear, under starting-stopping working conditions the main wear mechanisms of bearings are adhesion wear, abrasive wear and fatigue wear.Originality/valueThese research results have certain practical value for understanding the tribology behavior of journal bearings under different working conditions.

Study on Lubrication and Friction Performance of Grease Lubricated Sliding Bearings

In order to study the friction performance of grease lubricated sliding bearings of construction machinery under long-term radial heavy load, a bearing testing machine was developed to measure the changes of friction force, friction coefficient and temperature rise of such bearings. The testing machine can not only simulate the operation process of bearings under low speed and heavy load conditions, but also evaluate the operation state of grease during grease lubrication. Through durability tests on bearings designed and produced by three different manufacturers, the friction coefficient between bearings and pin shafts can be accurately obtained, the current lubrication and wear conditions of bearings can be detected, the advantages and disadvantages of bearing performance can be judged, and at the same time, reference can be provided for designers to estimate bearing life and optimize design.

Rotor dynamic experimental investigation of an ultra-high-speed permanent magnet synchronous motor supported on a three-pad bidirectional gas foil bearing

With a 10-kW, 120,000-r/min, ultra-high-speed permanent magnet synchronous motor taken as a prototype, experimental research is conducted on the rotor dynamic behaviours of a three-pad bidirectional gas foil bearing high-speed motor rotor system. Load-carrying properties of the three-pad bidirectional gas foil bearing are analysed, and natural frequencies of conical and parallel whirling modes of the elastically supported rotor are calculated based on an appropriate simplification to the stiffness and damping coefficients of the gas foil bearings. The prototype passes through a 90,000-r/min coast-down experiment. Experiments show that there are violent subsynchronous whirling motions that are evoked by the gas foil bearing–rotor system itself. The cause of shaft orbit drift is analysed, and the corresponding solution is put forward. The theoretical analysis and experimental results can offer a useful reference to the bearing–rotor system design of ultra-high-speed permanent magnet motors and its subsequent dynamic analysis.

Influence of microscale effect on the radial rotation error of aerostatic spindle

This paper presents the influence of the microscale effect on the radial rotation error of aerostatic spindle, which is determined by the corresponding stiffness, damping, and unbalance mass. A microscale gas film flow model is used to simulate the static performance of the aerostatic bearing by introducing the microscale effect factor Q in this paper. Firstly, the radial stiffness and damping coefficients of aerostatic bearing were calculated considering microscale effect factor Q, therefore, the position of the rotating shaft in radial plane was deduced, and the corresponding rotation error was obtained. Finally, the simulation results of the stiffness and radial rotation error were verified by the experiment on the shaft test table, and the motion orbit was measured by a displace sensor with a high precision standard ball. The experimental results indicated that the simulated result considering the microscale effect factor Q was more consistent with the actual experimental value, which provided a reference for the design and optimization of the aerostatic spindle.

Analysis and experimental verification of dynamic characteristics of air spindle considering varying stiffness and damping of radial bearings

The dynamics of a radial bearing and aerostatic spindle system in an ultraprecision fly-cutting machine cause mid-spatial waviness errors, which have a significant effect on surface topographies. Air bearings, which are externally pressurized, comprise two journal bearings and two thrust bearings with orifice restrictors. The dynamic coefficients of the radial bearings are obtained by adopting the perturbation and finite difference methods with the MATLAB® software. In addition, the influences of the spindle speed and tilt angle on the dynamics of the radial bearings are investigated in detail. The simulation results show that the rotating speed has a little impact on stiffness but having a great impact on damping, and the theoretical values of static stiffness are almost the same as the experimental values. The dynamic responses of the spindle system supported by pressurized air film are obtained, and the simulation analysis of spindle responses under cutting forces is also well matched to the experiment results.