The tribological characteristics of JS material under lubrication of oil

A material composed of a steel backing, a sintered porous bronze middle layer and a layer of reinforced PTFE, which is named JS material, was prepared. The friction, wear and limiting PV values of this material under dry friction as well as the lubrication of number 20 mechanical oil were studied using a MPV-1500 friction tester. The worn surface of JS material and the transfer film formed on the counterface of carbon steel were investigated using scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The results show that the friction, wear and limiting PV values of JS material can be greatly improved with the lubrication of oil. The results of SEM and EPMA analyses indicate that, under dry friction conditions, the solid lubricant PTFE and Pb easily transfer to the steel counterface and results in the reduction of friction and wear; while under the lubrication of oil, little transference of PTFE and Pb to the steel surface occurs and very small friction and wear are achieved. Analyses of frictional surfaces also suggest that the Pb filler gets enrichment on the rubbing surfaces, which is beneficial in increasing the adhesion of the transfer film with the steel surface.     

Comparative tribological evaluation of journal bearings

Performance of sliding bearings with reeled bimetallic bushes of three different bronzes was compared with the performance of solid bushes of aluminium alloy with a view to replacing aluminium bushes in gear pumps by reeled bimetallics. a set of tribological selection criteria was proposed and comparative investigations were carried out.     

Linear stability analysis of hydrodynamic journal bearings under micropolar lubrication

The dynamic characteristics of hydrodynamic journal bearings lubricated with micropolar fluids are presented. The modified Reynolds equation is obtained using the micropolar lubrication theory. Applying the first order perturbation of the film thickness and steady state film pressure, the dynamic characteristics in terms of the components of stiffness and damping coefficients, critical mass parameter and whirl ratio are obtained with respect to the micropolar property for varying eccentricity ratios and slenderness ratios. The results show that micropolar fluid exhibits better stability in comparison with Newtonian fluid.     

Micropolar fluid lubrication of one-dimensional journal bearings

A study of the characteristics of one-dimensional journal bearings shows that the load capacity increases and the coefficient of friction decreases as the parameter $\text{μ}{}_1$, which characterizes the microstructure of the base oil due to the presence of additives, increases. The time of approach increases as the parameter $\text{μ}{}_1$ increases.     

Investigation of the tribological properties of silicon containing zinc–aluminum based journal bearings

In this study, frictional behavior of thin-walled journal bearings produced from Zn–Al–Cu–Si alloys was investigated using a purpose-built journal bearing test rig. The alloys were produced by permanent mould casting. Mechanical properties such as ultimate tensile strength, elongation, hardness and microstructure of these alloys were determined. The friction properties of the bearings produced from these alloys were also investigated. In this investigation, the effects of surface roughness and bearing pressure on the frictional properties of the journal bearings were taken into account. The results showed that friction factor decreased with increasing bearing pressure especially in the mixed and full-film lubrication zones. It was found that high surface roughness led to high friction factor. The ZnAl27Cu2Si1 and ZnAl40Cu2Si1 bearings showed full Stribeck curve tendency while ZnAl27Cu2Si2 bearing did not exhibit the typical diagram having no full-film lubrication zone at the pressure of 0.7 and 1.1 MPa.     

Elasto-hydrodynamic lubrication analysis of partial arc journal bearings

Centrally loaded partial arc bearings having deformable bearing surfaces have been analysed. The coupled Reynolds equation satisfying the pressure field in the fluid and the three-dimensional elasticity equations governing the deformations in the bearing lining are solved simultaneously using the finite element method. The steady state solution for the coupled problem is obtained by using a doubly nested iteration scheme which determines the positive pressure field in the fluid film and the orientation of the load line. The influence of bearing deformation on the load capacity, attitude angle, friction coefficient parameter and oil flow are reported for 60° and 120° partial arc bearings. The analysis is extended for lubricants having pressure-dependent viscosity     

A study of friction in worn misaligned journal bearings under severe hydrodynamic lubrication

Friction occurs in all mechanical systems such as transmissions, valves, piston rings, bearings, machines, etc. It is well known that in journal bearings, friction occurs in all lubrication regimes. However, shaft misalignment in rotating systems is one of the most common causes of wear. In this work, the bearing is assumed to operate in the hydrodynamic region, at high eccentricities, wear depths, and angular misalignment. As a result, the minimum film thickness is 5–10 times the surface finish, i.e., near the lower limit of the hydrodynamic lubrication when taking into account that in the latest technology CNC machines the bearing surface finish could be less than 1–2 μm.An analytical model is developed in order to find the relationship among the friction force, the misalignment angles, and wear depth. The Reynolds equation is solved numerically; the friction force is calculated in the equilibrium position. The friction coefficient is presented versus the misalignment angles and wear depths for different Sommerfeld numbers, thus creating friction functions dependent on misalignment and wear of the bearing. The variation in power loss of the rotor bearing system is also investigated and presented as a function of wear depth and misalignment angles.     

Plane vibration characteristics of multired externally pressurized oil journal bearings

Externally pressurised oil journal bearings are often subjected to dynamic loading and vibration. A theoretical analysis of the dynamic behaviour of orifice compensated bearings is presented and a design procedure outlined. The analysis assumes that the journal undergoes plane harmonic vibration about its mean steady state position in the absence of shaft rotation. The lubricant is assumed to be isovicous and incompressible. Stiffness and damping characteristics are presented.     

Ferrofluid lubrication of finite journal bearings using Jenkins model

The present study investigates hydrodynamic lubrication by ferrofluids of finite journal bearings using the Jenkins model. A magnetic field created by displaced finite wire is used. A numerical solution for the modified Reynolds equation using the finite difference method is obtained. Static characteristics of finite journal bearings are analyzed using 2 control parameters: magnetic force coefficient and Jenkins viscosity. The obtained results are compared to those from Neurenger‐Rosensweig model. It is shown that pressure, load capacity, attitude angle, and side leakage increase and friction factor decreases when increasing the value of each control parameter at low and medium eccentricity ratios. However, the Jenkins viscosity parameter decreases the load capacity and increases the friction factor at high eccentricity ratios.     

Performance of finite journal bearings in non-laminar lubrication regime

Fluid dynamic lubrication of journal bearings in a superlaminar regime, ie a transition or turbulent regime, is the subject-matter of this study.Results obtained by solving an appropriately modified Reynolds bidimensional equation have been put in the form of operating diagrams which allow the correct design of journal bearings in real conditions of flow     

Friction and wear characteristics of lead and its compounds filled polytetrafluoroethylene composites under oil lubricated conditions

The friction and wear properties of Pb, PbO, Pb₃O₄, or PbS filled polytetrafluoroethylene (PTFE) composites sliding against GCr15 bearing steel under both dry and liquid paraffin lubricated conditions were studied by using an MHK-500 ring-block wear tester. The worn surfaces and the transfer films of these PTFE composites formed on the surface of GCr15 bearing steel were then investigated by using a scanning electron microscope (SEM) and an optical microscope, respectively. Experimental results show that filling Pb, PbO, Pb₃O₄ or PbS to PTFE can greatly reduce the wear of the PTFE composites, but the wear reducing action of Pb₃O₄ is the most effective. Meanwhile, PbS increases the friction coefficient of the PTFE composite, but Pb and Pb₃O₄ reduce the friction coefficients of the PTFE composites. However, the friction and wear properties of lead or its compounds filled PTFE composites can be greatly improved by lubrication with liquid paraffin, and the friction coefficients of the PTFE composites can be decreased by one order of magnitude. Optical microscope investigation of transfer films shows that Pb, PbO, Pb₃O₄ and PbS enhance the adhesion of the transfer films to the surface of GCr15 bearing steel, so they greatly reduce the wear of the PTFE composites. However, the transfer of the PTFE composites onto the surface of GCr15 bearing steel can be greatly reduced by lubrication with liquid paraffin, but the transfer still takes place. SEM examination of worn surfaces shows that the interaction between liquid paraffin and the PTFE composites creates some cracks on the worn surfaces of the PTFE composites; the creation and development of the cracks reduces the load-carrying capacity of the PTFE composites, and this leads to deterioration of the friction and wear properties of the PTFE composites filled with lead or its compounds under higher loads in liquid paraffin lubrication.     

A parametric study on bubbly lubrication of high-speed journal bearings

The influence of aerated oil on high-speed journal bearings is examined by classical thermohydrodynamic lubrication theory coupled with analytical models for viscosity and density of the air–oil mixture in the fluid-film bearing. Convection to the walls, mixing with supply oil and recirculating oil, and some degree of journal misalignment are considered. The parameters considered for the study of bubbly lubrication are oil aeration level, air bubble size, shaft misalignment and shaft speed. The results show that air bubbles can more clearly bring on increasing load capacity under high-speed operation of a plain journal bearing than under previous normal speed operation. Moreover, the load capacity may be increased more by oil aeration under the conditions of shaft misalignment and increasing speed.     

Surface roughness effects on thermo‐hydrodynamic lubrication of journal bearings lubricated with bubbly oil

In this paper, the combined effect of surface roughness and bubbles content on the hydrodynamic performance of journal bearings is studied. In the analysis, it is assumed that the bearing and shaft surfaces are covered with homogeneous isotropic roughness, the air bubbles are evenly distributed through the lubricant and the bubble size is very small. The modified Reynolds equation governing the pressure generation in the bearing gap for compressible fluid is solved simultaneously with the energy equation. Temperature and pressure distributions, coefficient of friction, bearing load capacity and attitude angle as affected by surface roughness, bubble content and some bearing parameters are presented. Results showed that the bearing load carrying capacity is higher at higher values of average roughness and higher bubble content as a direct consequence of the higher pressure values attained, and the average roughness and the bubbles content had no significant effect on the attitude angle. Copyright © 2006 John Wiley & Sons, Ltd.     

Improvement of tribological characteristics under water lubrication of DLC-coatings by surface polishing

To achieve a hydraulic power system, it is important to control tribology because water has a lack of lubricity. Therefore, coated surface is necessary under water lubrication. Diamond-like-carbon (DLC)-coating is known as a useful material because of its high hardness and low friction, therefore it can be used as a coating durable for the water lubrication. Deposition methods of DLC-coating are developed in various ways. Particles called “droplets” are observed on the surface of DLC-coating depends on deposition methods and it can affect friction and wear properties. In this study, DLC-coating was prepared using a multi-cathode unbalanced magnetron sputtering (UBMS) system. The surface was polished with diamond slurry solution and aero lap to remove droplets. DLC-coatings were evaluated by tribo-tests before and after polishing. It is considered that some surface modification occurred. Moreover, the results of tribo-tests show that friction coefficients became lower and more stable than before polishing. Although partial delamination was observed after tribo-tests without polishing, no appreciable wear was observed after polishing.     

The thermohydrodynamic solution of oil journal bearings

An estimate of temperature and pressure of full hydrodynamic journal bearings has been obtained by simultaneous numerical solution of the energy and the Reynolds' equations. Both viscosity and density of the lubricant vary with temperature. The computed results of pressure distribution have been compared with the classical solution (which assumes uniform lubricant properties). The temperature distribution has also been verified with published experimental data. The viscosity and density changes contribute to a small decrease in the load capacity calculated using constant properties.     

Design of multirecess hydrostatic oil journal bearings

This paper presents computer generated design data in terms of load capacity and oil flow for multirecess hydrostatic journal bearings. The Reynolds equation for a finite bearing was solved on a high speed digital computer satisfying appropriate boundary conditions and using the finite difference method. Results for various L/D ratios, recess to bearing area ratios, number of recesses etc are presented for capillary and orifice compensated bearings.     

Numerical study of the thermo-hydrodynamic lubrication phenomena in porous journal bearings

In this work, a numerical simulation is presented for the thermo-hydrodynamic self-lubrication aspect analysis of porous circular journal bearing of finite length with sealed ends. It consists in analyzing the thermal effects on the behavior of circular porous journal bearings. The Reynolds equation of thin viscous films is used taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The presented results are in good agreement with those cited in the literature. The effects of dimensionless permeability parameter and eccentricity ratio on performance parameters are presented and discussed. The results showed that the temperature influence on the journal bearings performance is important in some operating cases, and that a progressive reduction in the pressure distribution, in the load capacity and attitude angle is a consequence of the increasing permeability.     

Relationship between the tribological properties of experimental aluminum alloys and their chemical composition

New complex alloying has been designed for aluminum antifriction alloys. Their tribological behavior has been determined, including the running-in ability, scoring resistance, and wear resistance. The interconnection of the tribological properties of experimental alloys with a doping level by different elements has been analyzed. Recommendations on the optimum content of alloying elements for the antifrictionality of the aluminum based alloys have been given.     

Comparative investigation on the tribological behaviors of CF/PEEK composites under sea water lubrication

Carbon fiber (CF) reinforced polyetheretherketone (PEEK) composites were prepared and their tribological behaviors under sea water lubrication were comparatively investigated. The results showed that the incorporation of CF can greatly improve the wear resistance of PEEK under sea water lubrication, especially when the volume fraction of CF was about 10%, because exposed CF can effectively share the main load between the contact surfaces and consequently protect the matrix from severe wear. In addition, CF/PEEK had better friction and wear properties under sea water lubrication than under dry friction and pure water lubrication due to better lubricating effect of sea water.     

Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean‐based oil

Vegetable‐based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable‐based oils have been combined with synthetic esters to produce modified vegetable‐based oils. This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non‐Newtonian soybean‐based oil. The soybean‐based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time‐dependent modified Reynolds equation including non‐Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero‐ and first‐order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non‐Newtonian soybean‐based oil strongly affected the performance characteristics of the journal bearings.