Rolling-Element Bearing Internal Temperatures

The internal temperature distribution within tapered rolling-element bearings was investigated. A simple experimental procedure using thermocouples for the stationary outer race and a temperature-sensitive medium on the moving components was used to determine bearing operating component temperatures. Circulating oil was used to lubricate the bearings. Temperatures for two different loads and three taper conditions (simulating bearing misalignment) are given. Corresponding contact pressure distributions and the calculated EHL films are shown. The correlation between temperatures and changes in pressure distributions, as well as their calculated effects on the lubricant film, can be easily seen.     

TEHD Analysis for Tilting-Pad Journal Bearings Using Upwind Finite Element Method

A general approach for incorporating heat transfer and elastic deformation effects into a tilting-pad journal bearing simulation model is presented. A global analysis method is used, which includes variable viscosity and heat transfer effects in the fluid film, elastic deformation and heat conduction effects in the pads, and elastic deformation effect in the pivots. The two-dimensional variable viscosity. Reynolds equation produces pressure distributions in the axial and circumferential directions. The energy equation is two-dimensional, assuming that the temperature variation in the axial direction is negligible. The elasticity and heat conduction models are also two-dimensional, being in the midline cross-section of the bearing, including the circumferential and cross-film directions. An upwind technique is used in the finite element formulation of the energy equation to remove numerical instability due to the convective term. Simulation results are compared with the test and predicted values of previous researchers.     

A Numerical Model of a Rock Bit Bearing Seal

The mechanical seal with metal faces, used to seal the bearings in rock drill bits, plays a critical role in ensuring a long service life of the drill bit. A numerical model of such a seal has been developed for use as a design tool. The axisymmetric model encompasses a mixed lubrication elastohydrodynamic analysis, and predicts such quantities as leakage rate, film thickness distribution, fluid pressure and contact pressure distributions, interface temperature and face deformation. Model results show that the behavior of this seal, unlike that of conventional industrial seals, depends strongly on the ambient pressure, not just on the pressure drop across the seal.     

Influence of Mixed-Lubrication and Rough Elastic-Plastic Contact on the Performance of Small Fluid Film Bearings

A previously developed deterministic elastohydrodynamic (EHD) numerical model for small fluid film bearings functioning in the mixed lubrication regime is extended in this work by considering the rough contact. Several simplifying hypotheses are made: the shaft is considered rigid and smooth, turning at low speeds (isothermal regime), and the pad is assumed to have an elastic-perfectly-plastic behavior. The Reynolds equation is solved on a very fine mesh and the elasto-plastic pad deformation caused by the hydrodynamic pressure is taken into account. A deterministic active set-based method is used for determining the contact pressure, the contact extent, and the corresponding deformation. The results are presented for a partial journal bearing configuration, with a linear shaft velocity of 0.47 m/s under specific pressures varying up to 50 MPa. Two pad materials are considered, and the lubricant is either isoviscous or piezoviscous oil. The simulation results, presented as a function of the bearing specific pressure, include eccentricity, the film thickness, the friction torques, the contact extent, etc. Stribeck curves showing the evolution of the friction coefficient in the hydrodynamic and mixed lubrication regimes are also discussed.     

Thermoelastohydrodynamic Analysis of Fixed Geometry Thrust Bearings Including Runner Deformation

A thermoelastohydrodynamic theory for the analysis of sector thrust bearings is presented. The analysis includes the generalized Reynolds equation and a fully elliptic three-dimensional energy equation in the film. In addition, full three-dimensional heat transfer is allowed in the pad while axisymmetric conduction is allowed in the runner. Three-dimensional elastic deformation due to mechanical and thermal loading is allowed in the pad while axisymmetric mechanical elasticity is allowed in the runner. The performance of a parallel tapered-land thrust bearing including runner deformation effects is analyzed as a function of different models. It is seen that mechanical deformation of the pad affects the operating characteristics only slightly while thermal deformation of the pad can cause large increases in operating temperature. The runner deformation effects can include a reduction of the maximum film temperature at slight deformation or a large increase in film temperature at the inner radius of the pad at larger deformations.     

Measurements of Temperature Distributions around Longitudinally Grooved Rough Surfaces in Sliding Elastohydrodynamic Point Contacts

This paper describes the temperature measurements in the EHL conjunction area comprising a longitudinally grooved steel ball and a sapphire disk under high slip conditions. The authors measured the temperatures of the oil film as well as both the disk and ball surfaces; furthermore, they estimated the temperature profile across the oil film by means of experimental values. The experimental results show that the temperature of the grooved ball surface increased considerably compared with that of a non-grooved ball. The temperatures of the faster surface for the grooved ball became sensitive to the slip ratio, whereas that for the non-grooved surface was almost constant. The temperature distribution had a higher value at the land zones and a lower one at the grooved zones. The temperature rise in the grooved zones varied qualitatively depending on the thermal conditions of both the sliding surfaces.     

An Evaluation of Starting-Load Capacity and Static Friction in Babbitt-Lined,Hydrodynamic Journal Bearings

A recent application called for starting 127-mm (5-in) diameter, babbitt-lined hydrodynamic journal bearings under unit loads of about 10.34 MPa (1500 psi). In this application, the load was imposed only a few seconds before rotation could be started and hydrostatic jacking was not permitted. This paper presents the results of a test effort in which one full-size bearing was subjected to several hundred starts under unit loads ranging from 3.4 to 15.5 MPa (500 to 2250 psi). The dwell time between load application and start of rotation was varied in the test from less than one second to more than one hour. The paper also provides a review of the relevant literature, as well as calculations of the contact zone temperature during starts under boundary lubrication conditions.     

A Mixed Thermoelastohydrodynamic Lubrication Analysis of Mechanical Face Seals by a Multiscale Approach

This article presents an improvement to a previous multiscale approach used to model the mixed lubrication regime in a mechanical face seal. The physical mechanisms considered by the improved model are the surface roughness effects on the fluid film lubrication, the thermal deformations, and the heat transfer in the seal rings due to viscous and dry friction. The developed numerical model determines the pressure distribution by taking into account the effect of cavitation and contact asperity between the surfaces. Heat dissipation, heat transfer, and deformations are computed from the heat dissipated at the seal interface by a finite element technique. The multiscale model significantly reduces computation time while maintaining the accuracy of the results. The results obtained through a parametric study show that there are different operating zones where the lubricating film thickness is controlled by the roughness height or by the thermal effect.     

Surface Characterization and Experimental Design for Testing of a Radial Lip Seal

In radial lip seals, it is generally accepted that sealing occurs through microasperities that form on the surface of the elastomer. It is most often thought that these asperities form during the first few hours of operation due to the stresses and wear in the seal. Thus, the formation of these asperities is highly dependent upon the specific operating conditions of the seal. This article studies the size, shape, and quantity of the asperities that are present on a specific seal design, when run at a certain set of operating conditions. From this analysis it has been determined that the hydrodynamic pumping aids that are present on the seal significantly affect the formation of microasperities. Radial lip seal samples affected by pumping aids had more distinct microasperities, but these asperities are clustered on the edges of the sealing zone, which is not the case for samples unaffected by pumping aids.     

An Experimental Comparison of Two Steadily Loaded Plain Journal Bearings

A potentially powerful effect on the characteristics of plain journal bearings is local thermal deformation of the bearing surface. Although there are a few analyses that consider the effect, it is ignored by most journal bearing codes used by industry. There is also almost no experimental data in the literature that focuses on this effect. To generate such data, two identical, 101 mm dia., 57 mm long bearings—one fabricated from steel and one from bronze—have been tested in a precision journal bearing test rig. Comparisons between shaft displacement data for steady loading of the two bearings show that the deformations are important to consider.     

Operating Limits for Acoustic Measurement of Rolling Bearing Oil Film Thickness

An ultrasonic pulse striking a thin layer of liquid trapped between solid bodies will be partially reflected. The proportion reflected is a function of the layer stiffness, which in turn depends on the film thickness and its bulk modulus. In this work, measurements of reflection have been used to determine the thickness of oil films in elastohydrodynamic lubricated (EHL) contacts. A very thin liquid layer behaves like a spring when struck by an ultrasonic pulse. A simple quasi-static spring model can be used to determine the proportion of the ultrasonic waves reflected.

Experiments have been performed on a model EHL contact between a ball and a flat surface. A transducer is mounted above the contact such that the ultrasonic wave is focused onto the oil film. The reflected signals are captured and passed to a PC for processing. Fourier analysis gives the reflection spectrum that is then used to determine the stiffness of the liquid layer and hence its thickness. In further testing, an ultrasonic transducer has been mounted in the housing of a deep-groove ball bearing to measure the film generated at the outer raceway as each ball passes. Results from both the ball-flat and ball bearing measurements agree well with steady-state theoretical EHL predictions. The limits of the measuring technique, in terms of the measurable rolling bearing size and operating parameters, have been investigated.     

Pressure and Temperature Field Measurements of a Lightly Loaded Circumferential Groove Journal Bearing

The current study presents the experimental determination of the lubricant film pressure and temperature distributions on one land of a symmetrical two-land circumferential groove journal bearing (CGJB) operating under low-load steady-state conditions. Film pressure and temperature measurements are done both in axial and circumferential directions. Five axial planes, with three equally spaced pressure tappings per plane, construct the base pressure measurements grid. The pressure tappings circumferential location is shifted 20° from one plane to the neighboring plane. Similarly, the base temperature measurements grid consists of four axial planes, with three equally spaced thermocouples per plane. Hence, by rotating the bearing sequentially, with an angular step of 10°, it is possible to create fine measurement grids. This method of measurement is valid, because the circumferential groove journal bearing's operation is independent on the angle of loading. Two supply pressures were considered for the tests. The higher supply pressure leads to a smoother bearing operation. In the diverging zone, subatmospheric regions were measured. Superposing pressure and temperature fields reveals that the maximum temperatures are encountered in the sharp pressure drop region.     

Experimental Study of Central and Minimum Elastohydrodynamic Film Thickness by Colorimetric Interferometry Technique

Recently developed colorimetric interferometry technique was used for the study of both minimum and central film thicknesses for a wide range of operating parameters. Over 300 film thickness maps were obtained for the combination of four values of the materials parameter G, five values of the load parameter W and many values of the speed parameter U. The use of a spacer layer extended the range of film thickness measurement down to 5 nm. An excellent agreement was found between experimental values and data obtained from numerical solution presented by Venner and ten Napel, especially for thin lubrication films. An increase in a speed exponent with increasing material parameter G was observed for both central and minimum film thicknesses. The minimum film thickness and, thereby, the ratio between central and minimum film thickness was confirmed to be of a stronger dependence on material and load dimensionless parameters than Hamrock and Dowson equations predict.     

Film Formation in EHL Point Contacts under Zero Entraining Velocity Conditions

The contacts of adjacent balls in a retainerless bearing are subjected to the zero entrainment velocity (ZEV). The existence of an effective elastohydrodynamic lubrication (EHL) film between contacts running under ZEV conditions has long been proven experimentally. However, the classical EHL theory predicts a zero film thickness under ZEV conditions. Mechanisms, such as the thermal viscosity wedge effect and immobile film theory, have been proposed to tentatively explain the phenomenon. However, detailed numerical results are needed to provide theoretical evidence for such film formations. This paper aims to simulate, based on the viscosity wedge mechanism, the film formation of EHL point contacts under ZEV conditions. Complete numerical solutions have been successfully obtained. The results show that the thermal viscosity wedge induces a concave film profile, instead of a parallel film (Hertzian) as postulated by some previous researchers. By the simulation solver developed, the variation of film thickness with loads, oil supply conditions and ellipticity parameters have been investigated. Some unique lubrication behaviors under ZEV conditions are demonstrated. Furthermore, preliminary quantitative comparisons with the latest optical EHL experiments are finished. Both results are in good correlation.     

Lubrication Analysis of a Connecting-Rod Bearing in a High-Speed Engine. Part I: Rod and Bearing Deformation

Analysis was performed on a connecting rod assembly operating at 6,500 rpm. The analysis was based on the finite element method, which includes effects of interference fitted bearings and pre-loaded bolts. The rod inertia force associated with the gas pressure was found to have a significant effect on the variation of the rod bearing shape. The shape variation of a connecting rod assembly is commonly ignored in rod bearing analyses. Investigation of bearing deformation was conducted in order to evaluate the lubrication characteristics.     

纯滚动集中接触润滑入口区热效应的数值分析

在对入口区膜厚形状和压力分布的简化处理前提下，采用数值分析方法全面地分析了纯滚动集中接触润滑入口区的热效应，得到了的结论与其它学者的试验及分析结果较为一致。     

A Method for Identification of Bearing Force Coefficients and Its Application to a Squeeze Film Damper with a Bubbly Lubricant

A general formulation of the instrumental variable filter (IVF) method for parameter identification of a n-DOF (Degrees Of Freedom) mechanical linear system is presented. The IVF is a frequency domain method and an iterative variation of the least-squares approximation to the system flexibilities. Weight functions constructed with the estimated flexibilities are introduced to reduce the effect of noise in the measurements, thus improving the estimation of dynamic force coefficients. The IVF method is applied in conjunction to impact force excitations to estimate the mass, stiffness, and damping coefficients of a test rotor supported on a squeeze film damper (SFD) operating with a bubbly lubricant. The amount of air in the lubricant is varied from nil to 100 percent to simulate increasing degrees of severity of air entrainment into the damper film lands. The experimental results and parameter estimation technique show that the SFD damping force coefficients increase as the air volume fraction in the mixture increases to about 50 percent in volume content. The damping coefficients decrease rapidly for mixtures with larger air concentrations. The unexpected increase in direct damping coefficients indicates the complexity of the SFD bubbly flow field and warrants further experimental verification.     

Convection of Heat in Short-Bearings and Face Seals

For a short bearing or face seal, the temperature is determined by a steady Couette flow component and a zero-average perturbation, or waviness. In terms of these component flows, convection along the film and conduction into the surfaces is derived, and conditions are determined under which convection significantly influences the circumferential distribution of heat flux into the solid surfaces. For a stationary sinusoidal wave on a bearing surface, the phase relationship between this displacement perturbation and the wall heat input is found. The result is primarily of interest in systems where frictional heating may excite the thermoelastic growth of surface waviness, and where weak perturbations on heating may excite thermoelastic instability.     

Starvation and Reflow in a Grease-Lubricated Elastohydrodynamic Contact

The lubrication mechanisms of a grease in a rolling-element bearing has been studied through the measurement of film thickness in a rolling point contact. To simulate bearing conditions the contact runs under fully starved conditions; there is no attempt to maintain bulk flow of the grease into the inlet using an external supply. In consequence the film thickness drops off rapidly as the contact progressively starves. After a few minutes rolling (at constant speed) an equilibrium film thickness is attained which has two components: a residual film (h_R) comprised of degraded grease thickener and a hydrodynamic component (h_EHD) due to the liquid phase from the grease. The hydrodynamic contribution represents a balance between lubricant lost from the contact and replenishment from the grease close to the track. The ability of the grease to replenish the rolling track has been inferred from measurements of lubricant reflow around the static contact. These results are discussed in light of current starvation and grease lubrication models.