Roller bearing lubrication with shear thinning lubricants

Lubricants are continually being subjected to increasing mechanical shearing forces. Consequently the interest in materials of variable viscosity has increased. The problem of a roller bearing lubricated by a Casson fluid, which is a shear thinning lubricant, has been investigated; the non-sliding steady state and the squeezed film situation have been studied. At high speeds the load capacity of the Casson fluid is equal to that for a Newtonian fluid of the same viscosity. At low speeds the difference is significant; the Casson fluid film has a load capacity even if the velocities of both cylinders in contact are zero.     

Influence of pad–pivot friction on tilting pad journal bearing

Some experimental studies reported that the performance of tilting pad journal bearing is related with the pad–pivot friction. Only a few researches, however, consider the friction as a factor even though many ones have theoretically analyzed the performance of bearing. Also, there is no mathematical model for the friction to explain the effect of friction on the performance of bearing. Therefore, this study proposes a mathematical model for the pad–pivot friction and analyzes the effect of friction on the tilting pad journal bearing.The results of this analysis show that the friction has a large influence on the attitude angle of the journal. It is found that the eccentricity direction of the journal does not coincide with the load direction when the friction is not zero. According to working conditions, the attitude angle can be up to 25° when friction coefficient is equal to 0.5. It is also found that the tilt angle of the pad is not determined as a fixed value in case of the bearing with non-zero friction, even though working conditions is given for the static analysis. This study represents four different tilt angles under same working conditions.     

Wear and friction of synthetic esters in a boundary lubricated journal bearing

This study concerns the case of a slow intermittent motion, conformal contact, high load bronze journal bearing against a hardened steel shaft lubricated in an oil bath at a temperature about of 13 °C. Three synthetic esters were used: one pure and two formulated ones. Worn surfaces were examined using SEM-EDS to determine the wear mechanism. The tested lubricants were examined using ICP-AES to identify the elements present.The results show the wear rate, friction and temperature in the subsurface of the journal bearing material. An initial bronze–steel contact develops into a copper–copper contact along the sliding distance. Wear element concentration in the oil and friction surfaces departs from the elementary concentration in the journal bearing bronze base material. The copper layer thickness depended on additives in the synthetic esters, load and wear rate.     

Measurement of circumferential viscosity profile in stationary journal bearing by shear ultrasonic reflection

Viscosity is the most important property of a lubricant that can affect bearing performance. It controls the film thickness that is established during an operation. In this study, the ultrasonic method was used to measure the static viscosity profile around a journal bearing by using shear reflection coefficients at several locations around the journal bearing. This enables the viscosity profile to be established. The technique introduced was found to be successful and acceptable results were obtained from certain regions of the journal bearing flow. This study serves as a preliminary work for developing viscosity measurement in a rotating journal bearing.     

A high shear rate, high pressure microviscometer

The development of a high shear rate, high pressure microviscometer is described. This viscometer was developed specifically to examine a highly loaded, dynamic contact generated in a small volume of fluid. The viscometer was used to examine the fluid film formed by the mechanism of elastohydrodynamic lubrication in the presence of an SAE 50 oil. A complete numerical analysis of the resulting elastohydrodynamic contact was performed.     

The contact pressure distribution in the friction region of miniature journal bearings

The contact pressure distribution in miniature journal bearings is theoretically studied taking into consideration the friction between the contacting surfaces of the journal and the bearing bush. The experimentally confirmed formulae for the contact pressure distribution, the angle of contact and the ratio of the maximum contact pressure to the bearing contact pressure are derived. The contact pressure distribution may be described with a parabolic function.     

Effect of high hydrostatic pressure on the external friction coefficient

Experiments are carried out to determine the molecular and mechanical components of the specific friction force under the effect of hydrostatic pressure of up to 140 MPa. The molecular component of the friction coefficient declines by up to two times under the effect of the hydrostatic pressure in various fluids. It is found that the combined influence of the temperature and hydrostatic pressure on the mechanical properties and the contact pressure leads to considerable variations in the deformation component of the static friction coefficient in plastic contact at temperatures of up to 200°C and under pressures of up to 140 MPa. The dependence of the hardness of structural materials on the hydrostatic pressure is analyzed to predict the effect of the latter on the deformation component of friction. It is shown that with increasing pressure within the above range the hardness grows in proportion to the square of the pressure and is inversely proportional to the initial hardness. The formula for calculating the dependence of the indentation depth of a spherical indenter in elastic contact on the hydrostatic pressure is derived.     

Experimental discrimination of plowing friction and shear friction

The friction of a diamond spherical indenter sliding on CrN coated nitrided steel was investigated. A friction model was proposed that takes into account plowing and shear friction. With the model the separate contributions of substrate properties and surface condition to the friction were successfully extracted: the shear friction coefficient μ _sh was found to depend exclusively on the surface condition, i.e., not on load on the indenter, hardness of the substrate, and thickness of the coating. On the other hand, the plowing component of friction was independent on surface condition.     

基于CFD方法的滑动轴承实际油膜特性

应用CFD工具FLUENT软件中的多相流模型,建立了滑动轴承中实际油膜的模型,计算了实际油膜的压力分布,探讨了油膜在轴承收敛和开阔楔形区域中的形式.比较了CFD方法下,实际油膜载荷、全周油膜载荷和半周油膜载荷的差别,并对差别加以分析.结果表明:该模型能更准确地计算出滑动轴承油膜的承载力.     

The friction characteristics of the journal bearing in a reciprocating compressor for refrigeration and air conditioning systems

The performance of a reciprocating compressor in refrigeration and air-conditioning systems is influenced by the lubrication characteristics of the critical sliding components. Thus, the lubrication characteristics between the crankshaft and journal bearing have to be researched in order to improve the design and performance of a reciprocating compressor. Therefore, in this study, to enhance the EER (energy efficiency ratio) to reduce power consumption, and to improve the reliability of a reciprocating compressor for refrigeration and air conditioning systems, theoretical analysis of the friction characteristics between the crankshaft and journal bearing in a reciprocating compressor is studied. The results demonstrate that frictional characteristics are significantly influenced by the clearance between the crankshaft and journal bearing and the viscosity of the lubricating oil.     

Static friction at high contact temperatures and low contact pressure

The problem of measuring static friction at high temperatures and low contact pressures is theoretically analyzed, as well as the instruments for the accurate determination of the coefficient of static friction at high temperatures for contact pairs made of steel and bronze. The results of experimental investigation show that at low contact pressure and temperature above 120°C coefficient of static friction dramatically increases. This increase in the coefficient of friction can be of great practical value with regard to the load capacity of contacts where external forces are balanced with friction forces.     

Dry friction of steel under high pressure in quasi-static conditions

Measurements were carried out for static and kinetic friction coefficients for steel as a function of the normal pressure for two surface roughness conditions of the matrix: ground and sand blasted. The samples were interstitial free steels, the tests were done at room temperature, in quasi-static and dry contact conditions. Very high pressures were applied in the range of 230–1100 MPa in order to simulate the conditions of testing in severe plastic deformation processes of metals. A new device was designed for this purpose. The results showed a decrease of the friction coefficients with the applied normal stress with stronger dependence for sand blasted surfaces.     

The effects of journal lobing on the performance of a hydrodynamic plain journal bearing

Accurately ground journals nominally of 44.25 mm diameter and 63.5 mm wide were produced. One was cylindrical and the others had three, four, five, six, nine or twelve equispaced lobes, 0.025 mm high, on their peripheries. Each journal was fitted into a cylindrical lead-bronze bearing liner with a radial working clearance of 0.05 mm and operated at speeds of up to 1000 rev min^?1 and at bearing loads of up to 10 kN whilst the oil pressure was maintained at or just above atmospheric pressure.The test results indicated that when a comparison is made between the lobed journals and the cylindrical journal (1) there are no significant differences in the load-carrying capacity of the bearing and (2) in the higher portion of the loading range the boundary lubrication conditions are improved when using three- or four-lobed journals whilst the presence of lobes on the other journals produces only a slightly adverse effect,It was concluded that the effect of lobing, which often occurs accidentally during the manufacture of plain cylindrical journals, is not detrimental to the performance of the bearing when operated within the range of speeds and loads used.     

Wall slip and hydrodynamics of two-dimensional journal bearing

In the present paper, based on the limiting shear stress model, a multi-linearity finite element algorithm and quadratic programming technique are used to study the influence of wall slip on the hydrodynamic lubrication performance of a two-dimensional journal bearing (finite length journal bearing). It is found that if the lubricated surfaces are designed as homogeneous slip surfaces, the hydrodynamic force will be decreased. If the shaft surface (rotation) is a slippery surface with very low limiting shear stress, almost no fluid load support can be generated. If the sleeve surface is designed as the homogeneous slip surface, a low fluid load support together with a small friction drag can be obtained. However, if the sleeve surface is designed as an optimized slip surface with a slip zone in the inlet region, a high load support and low friction coefficient can be obtained. Optimization of the shape and the size of the slip zone can give the journal bearing many advanced properties.     

A study on accuracy of porous journal air bearing

In order to predict error motion of continuous porous journal air bearing, an accuracy model is established to reveal the relationship among error motion, roundness error and structure parameter under quasi-static conditions. Based on the model, averaging coefficient is defined to quantitatively characterize the error averaging ability. The study finds that whether the bush and shaft roundness errors match is the cause of error motion. The trilobal roundness error of shaft has a major impact on accuracy for a porous journal air bearing with an elliptical bush, while the elliptical roundness error of shaft has a major impact on accuracy for that with a trilobal bush. On the two-dimensional plane of bush wave numbers n₂ = 2~7 and shaft wave numbers n₁ = 2~15, the averaging coefficients are symmetrical along the line n₁ = n₂. The shaft wave numbers which equal integer multiples of prime numbers of bush wave number have no impact on accuracy, while the remaining shaft wave numbers have impact. Among them, those at points n₁ = n₂*i ± 1 are with obvious averaging coefficients and have a major impact on accuracy where i is a positive integer. The main peaks of averaging coefficients appear at the points n₁ = n₂ ± 1, which have the most important impact on accuracy. The theory has many potential applications such as prediction of error motion, structural optimization and selection of parts grinding method, which is of significant importance for design and testing of porous journal air bearings used widely in ultra-precision machine tools.     

Effect of non-Newtonian behaviour of lubricant and bearing flexibility on the performance of slot-entry journal bearing

This work describes the theoretical study concerning the effect of non-linear behaviour of the lubricant on the performance of a slot-entry journal bearing. The analysis considers the generalized Reynolds equation governing the flow of lubricant having variable viscosity in the clearance space and the three dimensional elasticity equations governing the displacement field in the bearing shell, and equation of flow of lubricant through slot restrictor. The non-Newtonian lubricant is assumed to follow the cubic shear stress law ( ). Bearing performance characteristics have been presented for a typically selected values of non-linearity factor ( ) and deformation coefficient ( ). It has been observed that the combined effect of non-linearity factor ( ) and bearing flexibility ( ) affects the performance characteristics of slot-entry journal bearing quite significantly.     

Identification of the dynamic performance of a gas foil journal bearing operating at high temperatures

This paper presents an experimental investigation of the dynamic force performance of gas foil bearings (GFBs) at high temperatures. A dynamic performance test rig with a GFB mounted on a rotating hollow shaft, heated by a cartridge heater inside the hollow shaft, and excited by two orthogonally positioned electromagnetic shakers determines the frequency dependent stiffness and damping coefficients of the test GFB for increasing shaft temperatures. The test heater temperatures are 21°C (room temperature without heating), 100°C, 200°C, 300°C, and 400°C, and the excitation frequencies are 120 Hz, 140 Hz, 160 Hz, and 180 Hz. The test rotating speed and static load are 12 krpm and 30 N, respectively. The vibration amplitude of the test GFB is adjusted to approximately 30 μm by controlling the power amplifier connected to the electromagnetic shakers throughout the series of experiments. The test results show that both the direct stiffness and damping coefficients of the test GFB increase with increasing excitation frequencies. As the shaft temperature increases, the direct stiffness coefficients decrease by ～ 8%, and the direct damping coefficients decrease by approximately 30%. A model prediction benchmarked against the test data reveals that the cross-coupled stiffness coefficients are smaller than the direct stiffness coefficients for the test GFB.     

Dynamic characteristics of a hydrostatic journal bearing

The results of experimental investigations into the performance of a six-pocket hydrostatic journal bearing subjected to a range of dynamic loads are presented. The bearing performance was studied in terms of the load-carrying capacity and oil-film stiffness. The experimental results show that the test bearing has a better load-carrying capacity under dynamic load than under static load and that the load-carrying capacity and stiffness of the bearing are only limited by its mechanical strength.     

Thermo-hydrodynamic performance of grooved oil journal bearing

Steady state thermo-hydrodynamic analysis and its comparison at five different feeding locations of an axial grooved oil journal bearing is obtained theoretically. Reynolds equation is solved simultaneously along with the energy equation and heat conduction equation in bush and shaft. From parametric study it is found that 12° feeding groove position is better in comparison to other feeding locations. Feeding from the bottom is very less preferable since the load capacity is lesser and temperature development is more. It is very difficult to obtain the solution due to numeric instability when the bearing operates at higher eccentricity ratio.