Search results

As the companion paper of Part I, this paper aims to get more insight into the essence of lambda and to reveal its nature and role in the transition of lubrication states. Mixed lubrication (ML) model with micro-asperities contacts has been discussed in details in Part I.

Mimetic algorithm is used to get numerical solutions. Relationships between film thickness ratios and lubrication states transition with different external loads, rotating speeds, radial clearances, elastic modulus, surface hardness and roughness parameters are obtained.

The characteristic parameters of transitions from boundary lubrication (BL) to ML and ML to hydrodynamic lubrication (HL) are studied to determine how these parameters change with above factors. Finally, the essence and major influencing factors of lambda are summarized for such bearings.

In Part II, the authors believe that the paper presents for the first time: further insight into the essence of the lambda ratio, and its role in the lubrication states transition are given; the determinations of the characteristic parameters of transition from BL to ML and ML to HL are investigated for the first time; the characteristic parameters of transitions from BL to ML and ML to HL are also studied to determine how parameters (external load, rotating speed, radial clearance, elastic modulus, surface hardness and roughness parameter) change with above factors; a summary of the essence and major influencing factors of lambda for such bearings is given.

The aim of this paper is to study the effect of deterministic roughness and small elastic deformation of surface on flow rates, load capacity and coefficient of friction in Rayleigh step bearing under thin film lubrication.

Reynolds equation, pressure-density relationship, pressure-viscosity relationship and film thickness equation are discretized using finite difference method. Progressive mesh densification (PMD) method is applied to solve the related equations iteratively.

The nature and shape of roughness play a significant role in pressure generation. It has been observed that square roughness dominates the pressure generation for all values of minimum film thickness. Deformation more than 100 nm in bounding surfaces influences the film formation and pressure distribution greatly. Divergent shapes of film thickness in step zone causes a delay of pressure growth and reduces the load capacity with decreasing film thickness. The optimum value of film thickness ratio and step ratios have been found out for the maximum load capacity and minimum coefficient of friction, which are notably influenced by elastic deformation of the surface.

It is expected that these findings will help in analysing the performance parameters of a Rayleigh step bearing under thin film lubrication more accurately. It will also help the designers, researchers and manufacturers of bearings.

Most of the previous studies have been limited to sinusoidal roughness and thick film lubrication in Rayleigh step bearing. Effect of small surface deformation due to generated pressure in thin film lubrication is significant, as it influences the performance parameters of the bearing. Different wave forms such as triangular, sawtooth, sinusoidal and square formed during finishing operations behaves differently in pressure generation. The analysis of combined effect of roughness and small surface deformation has been performed under thin film lubrication for Rayleigh step bearing using PMD as improved methods for direct iterative approach.

This paper aims to provide efficient methods to calculate the friction coefficients and film thickness ratios in mixed lubrication (ML) regime for water lubricated bearings. Mathematical models consider influence of micro-asperities contacts which is based on the Gauss random distribution.

Effects of external loads, rotating speeds and radial clearances are obtained. Algorithm shown here is applied to a class of common industrial problems. Calculated Stribeck values are given and evaluated. The calculated and experimental results agree well which proves the correctness of the model.

In Part I, the authors believe that the paper presents the following for the first time: universal methods are developed for the calculation of friction coefficients and film thickness ratios (lambda) in ML regime; effects of different external loads, rotating speeds and radial clearances on friction coefficients and film thickness ratios are presented in detail; comparisons are made between the results predicted by the model and experimental results, and they agree rather well which proves the correctness of the model.

Present work successfully develops universal methods for predicting the friction coefficients and film thickness ratios.

The purpose of this paper is to propose a wheel/rail mixed lubrication model to study the water lubrication behavior of wheel/rail contact interface.

The numerical simulation method is applied in this paper. A deterministic mixed lubrication model considering surface roughness and transient state is established. The quasi-system numerical and finite difference method are used for numerical solution. The model is verified by comparing with the experimental data in the literature under the same conditions.

Under wet conditions, the change of train speed will change the lubrication state of the wheel/rail contact interface. With an increasing speed, the average film thickness and the film thickness ratio increase, while the adhesion coefficient, the contact load ratio and the contact area ratio decrease. When the creep ratio increases from 0% to 0.5%, the wheel/rail adhesion coefficient and subsurface stress increase sharply. With the increase of axle load, the average film thickness decreases and the adhesion coefficient increases.

This paper aims to improve the mixed lubrication theory by analyzing the characteristics of wheel/rail friction and lubrication, so as to provide some guidance and theory for train driving behavior.

Using the deterministic model, the lubrication state of the wheel/rail contact interface affected by various external factors and the adhesion behavior of wheel/rail progressive process from boundary lubrication to mixed lubrication are studied.

The well-operating condition of journal bearing is the assurance to keep superior performance of water-lubricated twin-screw compressor. To design the journal bearing more reasonably for this type of compressor, this paper aims to study the effects of rotating speed and design parameters on bearing characteristics, considering surface roughness and bending deformation of the shaft at the same time.

The average Reynolds equation considering the effect of surface roughness is adopted and solved by finite difference method and successive over-relaxation method to calculate pressure distribution with real bearing shapes and boundary conditions. The bending deformation of the shaft is calculated using simply supported beam model of variable cross-section.

The dynamic lubrication characteristics of four water-lubricated journal bearings in twin-screw air compressor are calculated and analyzed. In addition, the static characteristics of journal bearing including friction coefficient, film thickness ratio distribution and water film pressure distribution are calculated numerically with different rotating speed and design parameters. Moreover, some design principles of water-lubricated bearing for twin-screw compressor are put forward.

The lubrication characteristics of the water-lubricated journal bearing in twin-screw air compressor are calculated considering surface roughness and bending deformation of the shaft at the same time. The paper’s results may provide design guidelines for journal bearing in this kind of twin-screw compressor.

The purpose of this study is to investigate lubricant film-forming capability of oil-impregnated sintered material in highly loaded non-conformal contacts. This self-lubrication mechanism is well described in lightly loaded conformal contacts such as journal bearings; however, only a little has been published about the application to highly loaded contacts under elastohydrodynamic lubrication regime (EHL).

Thin film colorimetric interferometry is used to describe the effect of different operating conditions on lubricant film formation in line contacts.

Under fully flooded conditions, the effect of porous structure can be mainly traced back to the different elastic properties. When the contact is lubricated only by oil bleeding from the oil-impregnated sintered material, starvation is likely to occur. It is indicated that lubricant film thickness is mainly governed by oil bleeding capacity. The relationship between oil starvation parameters corresponds well with classic starved EHL theory.

To show practical, relevant limitations of the considered self-lubrication system, time tests were conducted. The findings indicate that EHL contact with oil-impregnated sintered material may provide about 40 per cent of fully flooded film thickness.

For the first time, the paper presents results on the EHL film-forming capability of oil-impregnated sintered material by measuring the lubricant film thickness directly. The present paper identifies the phenomena involved, which is necessary for the understanding of the behavior of this complex tribological system.

The purpose of this paper is to investigate the effect of different wedge shapes on the performance of air foil thrust bearing (AFTB).

During the study, a bump foil stiffness model considering slip deformation and a two-dimensional sheet top foil model is established, and the Reynolds equation and film thickness equation is solved using the finite difference method and finite element method. The static performance such as load carrying capacity, friction torque and power loss of AFTB under different taper parameters is obtained. The influence of different pitch ratio, film thickness ratio and wedge shapes on the bearing characteristics is studied.

There is an optimal height and a pitch ratio for the taper of AFTB with certain tile number. Compared to the plane and concave wedge shape, the upper convex shape can enhance the convergence effect of the wedge region, increase the effective film pressure distribution area of the bearing and reduce the local concentrated load of the top foil, which is more conductive to the increase of load capacity.

The wedge shape parameters bring a fundamental difference in the static performance of AFTB. The results are expected to be helpful to bearing designers, researchers and academicians concerned.

This paper aims to solve the lubrication failures in the turning arm bearing of RV reducer, give some help in perfecting the bearing structure design and provide theoretical basis for the reducer’s performance improvement.

The paper establishes a mixed lubrication analysis model to study performance parameters. According to the discretization of parameters and iteration of equations, numerical simulation and theoretical analysis are achieved in computational process.

Considering influences of contact load, real rough surface and realistic geometry of RV reducer turning arm roller bearing, the mixed lubrication analysis model is established to study the ratio of oil film thickness, pressure distribution and maximum von Mises stress in different speeds, temperatures and fillets. The results of mixed lubrication show that reasonable round corner modification, increase in temperature and speed, decrease of surface roughness and lubricant types can improve the lubrication performance.

The mixed lubrication analysis model is established to study the influences of contact load, real rough surface and realistic geometry of RV reducer turning arm roller bearing. Different speed, temperature, lubricant and fillet modification are also considered in the research to analyze oil film thickness, pressure distribution and maximum von Mises stress. These studies can optimize structural design of bearing and direct engineer operations.

This paper aims to study the startup performance of thrust bearing. The effects of acceleration scenarios, roughness, the area ratio of texture and texture depth on the transient startup performance of the thrust bearing were analyzed.

The lubrication model is solved by the Reynolds equation with the mass-conservation boundary condition. The Greenwood and Tripp contact model is used to predict asperity contact load. The finite volume method is used to discretize the governing equations.

By studying the bearing performance with different acceleration functions, it was found that the higher the acceleration at the beginning of the startup, the faster the thrust bearing operates under the hydrodynamic lubrication regime in the start stage. It appears that the friction and contact time of asperity increase with the increasing roughness. The optimal area ratio of texture is within 30%–50%. The depth of texture ranging from 1 to 2 is the best.

This paper proposes a transient mixed lubrication analysis model of the thrust bearing. This model can be used to analyze the variations of tribological performance and lubrication regime of the thrust bearing under different acceleration scenarios.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-09-2022-0268/

The purpose of this paper is to study a multiphase-flow instrumentation for film thickness measurement, especially impedance-based, not only for gas–liquid flow but also for mixtures of immiscible and more viscous substances such as oil and water. Conductance and capacitive planar sensors were compared to select the most suitable option for oil – water dispersed flow.

A study of techniques for measurement of film thickness in oil – water pipe flow is presented. In the first part, some measurement techniques used for the investigation of multiphase flows are described, with their advantages and disadvantages. Next, examinations of conductive and capacitive techniques with planar sensors are presented.

Film thickness measurement techniques for oil–water flow are scanty in the literature. Some techniques have been used in studies of annular flow (gas–liquid and liquid–liquid flows), but applications in other flow patterns were not encountered. The methods based on conductive or capacitive measurements and planar sensor are promising solutions for measuring time-averaged film thicknesses in oil–water flows. A capacitive system may be more appropriate for oil–water flows.

This paper provides a review of film thickness measurements in pipes. There are many reviews on gas – liquid flow measurement but not many about liquid – liquid flow.