Lubricant film thickness variations in frictionless bearings

The possibilities are considered of diagnostics and monitoring of the technical state of frictionless bearings on the basis of the analysis of on-line recorded and processed oscillations of the lubricant film thickness. A possibility is shown of a significant increase in the monitoring efficiency when using the technique of automated processing of the diagnostic data received by using modern microprocessor means. Implementation of the proposed methodical approach will significantly shorten the duration of the frictionless bearing tests and will make it possible to govern the operating mode of the bearings in order to prolong their operation life.     

Measurement of oil film thickness in big-end bearings and its relevance to engine oil viscosity classifications

Minimum oil film thickness MOFT measurements have been carried out in big-end bearings of V6 and in-line four-cylinder gasoline engines during engine operation. MOFT decreases with increasing crankshaft speed above 2000 r/min. The most severe practical steady-state operation is high-speed cruising. Maximum shear rates are in the region of 10⁷s⁻¹ at 4000 r/min. the dynamic viscosities at a shear rate of 10⁶s⁻¹ correlate significantly better with monograde MOFT data than with multigrade data; the correlation parameters for mono- and multigrade data are also significantly different. Although the dynamic viscosity measurement correlates with multigrade data better than the low-shear rate kinematic viscosity, the differences are not always significant at the 95% confidence level. Some other rheological parameter or combination of parameters may be better than either kinematic or dynamic viscosities.     

Identification of oil film coefficients of large journal bearings on a full scale journal bearing test rig

An attempt of adding a facility of investigating dynamic characteristics of oil film to a large full scale journal bearing test rig which was designed with only the function of static measurement is implemented. The considerations of impulse excitation, vibration measurement, data log and process, and dynamic characteristics identification are presented. The measured results are compared with theoretical data and the errors discussed.     

The cooling effects of supply oil on journal bearings for varying inlet conditions

The cooling effects of the lubricating oil supplied to a full journal bearing through two axial feed grooves each at right angles to the load line are studied. The thermohydrodynamic analysis assumes no heat is removed through either the journal or bush. The results show that the oil temperature distribution along the axial direction of the bearing is usually not uniform. Only if the axial length of the feed grooves approaches the bearing length will the temperature in the high pressure zone be uniformly distributed over its axial length. Both the oil supply pressure and the geometry of the feed grooves control the oil supply rate, which determines the cooling effect of the supply oil. Finally, a formula is suggested for the rate of supply flow     

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.     

Performance characteristics of oil‐in‐water mixtures in a journal bearing using different bearing materials

Oil‐in‐water (o/w) mixtures have an interesting property that has attracted the attention of tribologists, namely, that they can form thicker hydrodynamic films than those inferred from their rheological properties. The oil phase is believed to separate out on the metal surface in concentrated contacts lubricated with o/w mixtures. In this paper the performance characteristics of water‐based oils have been systematically explored for their film‐generating capabilities. The lubrication properties of o/w lubricants are studied and compared in a journal bearing rig assembly with different bearing materials. The rig is run under increasing loads and speeds in conditions pertinent to hydrodynamic lubrication. The rig has been able to operate with o/w mixtures at a concentration as low as 10 vol.%. However, the results have shown that the bearings exhibited signs of high eccentricities with o/w mixtures compared to Engineering Sciences Data Unit (ESDU) predictions. This behaviour has been attributed to shear rate effects on water‐based lubricants.     

Thermal effects in cylindrical journal bearings of high‐speed gearboxes

The high rotational speeds and loads of gears operating in acceleration gearboxes causes problems related to the correct choice and design of journal or rolling bearings. In the case of journal bearings, these problems are connected with thermoelastohydrodynamic lubrication theory and the dynamics of the bearing system. However, of major importance is the problem of thermal effects in journal bearings. This has been considered for bearings used in a double‐helical gearbox with the pinion and output shaft operating in cylindrical journal bearings. The oil film pressure, temperature, viscosity distributions, and maximum and mean oil film temperatures have been determined. In calculations, laminar adiabatic and turbulent adiabatic models of oil films have been applied. The results of the calculations can be used in the design of cylindrical or other types of journal bearing in rotating machinery, including acceleration or reduction gearboxes.     

Simultaneous monitoring of oil film thickness and temperature in fluid film bearings

This paper reports on the application of an eddy current sensor with an active compensation for changes in sensor temperature to simultaneous monitoring oil film thickness and temperature in a tilting pad thrust bearing. Sensor design, calibration procedure, sensitivity and accuracy are described. Test equipment along with sensor mounting is also presented. Tests were run at different rotational speeds and bearing loads as well as different supplied oil flow rates to evaluate sensor performance in various operating conditions. During the tests film thickness and temperature were simultaneously measured. Temperatures were compared with data from thermocouples installed in the pads and thermistors mounted in the collar. Tests have shown that the sensor can successfully be used to reliably monitor the conditions within the bearing.     

Elastohydrodynamic study of vegetable oil–polyalphaolefin blends

Two polyalphaolefins, of higher and lower viscosity than vegetable oils, were used to make binary blends of varying compositions with soy bean and canola oils. The pure oils and the blends were used in viscosity and film thickness investigations. The effects of composition and temperature on viscosity were found to agree well with the theoretical predictions of a simple mixing law. The film thicknesses of the various blends under elastohydrodynamic conditions were measured at 20 N load, and varying entrainment speeds and temperatures. From the data, pressure–viscosity coefficients, α, as a function composition and temperature were obtained. The resulting α values were compared with theoretical predictions. Experimental values of α as a function of composition showed a slight negative or no deviation from the values predicted by an ideal mixing model. On the other hand, experimental values of α displayed a mild decrease with increasing temperature, while the model predicted a sharp decrease with increasing temperature. Published in 2008 by John Wiley & Sons, Ltd.     

精密多油楔动压轴系的楔形间隙参数与油膜运动稳定特性

针对精密仪器轴系的研制和精度分析,研究了立式三油楔动压轴系的结构、轴承轮廓结构,建立数学模型、分析模型,对轴系动压油膜的动力特性做了分析.对于主轴在动压油膜反力与外载荷作用下处于某一平衡位置(e,θb)运转时,能否经得起任意微扰动的干扰而失稳,建立了油膜运动稳定性的判据.应用数值模拟和计算机编程,深入研究了关键设计参数楔形间隙bm、cm相应的油膜运动稳定特性,揭示了楔形间隙值与轴系失稳的对应关系,给出了油膜稳定性因数Log(Sp)与偏心率ε(ε=e/c)之间的变化曲线图,并指出了楔形间隙参数最佳的取值范围.研究结果指出:楔形间隙是轴系设计和制造的重要敏感参数;最大楔形间隙bm和最小间隙cm值之间应保持一定的比例,否则油膜运动发散,轴系平衡失稳,导致主轴转动中产生较大的晃动.对于低速立式三油楔动压轴系,则bm-cm≥0.8 μm.比较研究结果与成功轴系实例,表明实例中bm、cm取得符合轴系的油膜稳定条件.证明研究结果对该类轴系的设计具有实用性.     

Effect of mechanical shear on the thin‐film properties of base oil‐polymer mixtures

The thickness and frictional characteristics of thin lubricant films are known to affect the fuel economy properties of oils. The base oil and polymer compositions of the lubricant are generally considered to be critical chemical factors that can influence these thin‐film lubricant properties in new oils. However, it is important to produce lubricants with good fuel economy properties that are maintained after the lubricant is degraded. Lubricants in use can undergo oxidation and mechanical shear degradation. The effect of oxidation degradation on thin‐film physical properties has previously been studied. This paper investigates the effect of mechanical shearing on thin‐film properties. Dispersant olefin copolymers are found to reduce thin‐film friction in simple mixtures and in fully formulated oils. In simple mixtures, shearing the dispersant olefin copolymers does not affect the friction‐reducing ability of these polymers. In fully formulated oils, even though shearing diminishes to a degree the friction‐reducing ability of dispersant olefin copolymers, these copolymers can still provide significant friction reduction.     

A study of electrical pitting of journal bearings with water‐contaminated lubricant

The investigations reported in this paper concern the effect of the use of a degraded lubricant on bearing life. A diagnosis of the premature failure of the hydrodynamic journal bearings of a synchronous condenser has been carried out. The surface of the failed bearings has been examined and the cause of the failure investigated. A theoretical analysis has also been undertaken to calculate the number of cycles that take place before failure occurs. The number of cycles thus established matched that of the cycles/duration of operation before the premature failure of the bearings. The process leading to the premature failure and the role of the degraded lubricant have been identified. Remedial measures have been successfully implemented to reuse the existing bearings. Measures have been suggested to avoid repeated failures. The theoretical analysis has the potential to ascertain the shaft voltage once the severity of the physical damage on the liner surface of the bearing and the duration of its operation have been established.     

Effects of sunflower oil added to base oil on the friction coefficient of statically loaded journal bearings

In this study, sunflower oil at different concentrations of between 1 and 50% was added to base oil to obtain lubricating oil candidates. The lubricating oil candidates were characterised by ASTM methods, and their effects on the friction coefficient at 25 and 100°C at different speeds and loads in a statically loaded journal bearing were determined. The technological characteristics of the sunflower oil were determined according to standard methods. The study shows clear evidence that the modification of friction by sunflower oil is at least equivalent to that by mineral oil, and the lubricationg oil candidates containing sunflower oil show a reduction in the coefficient of friction.     

Influence of oil type on the performance characteristics of a two‐axial groove journal bearing

The use of environmentally adapted lubricants (EALs) is a subject of growing interest to industry as legislation increasingly demands the replacement of mineral oil lubricants. Vegetable‐based fluids are widely seen as providing lubricants from a renewable source, as well as meeting demands for improved biodegradability. However, at present, utilization of such fluids is limited due to their rapid oxidation. EALs produced from other base stocks (i.e. synthetic esters) have been shown to provide performance benefits in hydrodynamic thrust bearings. In the present study, a hydrodynamic journal bearing test rig has been employed to compare the performance of three EALs (a VG32 saturated ester, rapeseed base fluid and a propylene glycol dioleate) relative to three mineral turbine oils (ISOVG32, ISOVG46 and ISOVG68) in the hydrodynamic regime. Results are given in terms of temperature, power loss and minimum film thickness. The impact of oil viscosity index is also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Load performance analysis of three‐pad fixing pad aerodynamic journal bearings with parabolic grooves

Three‐pad fixing pad aerodynamic journal bearings (TPFPAJBs) have been widely used in precision instruments due to their low friction, high stability and non‐pollution. In order to improve the load performance of TPFPAJBs, parabolic grooves are opened in the bearing pad surfaces. By opening parabolic grooves in various bearing pad surfaces, the effects of the orientation angle, distance, width and depth of the grooves on the load performance of micro‐grooved TPFPAJBs can be investigated. The numerical results show that the location of the micro‐grooved bearing pads can greatly affect the load performance of micro‐grooved TPFPAJBs. When the given bearing pad surface is grooved, the effects of the bearing number and width‐to‐diameter ratio on the load performance of micro‐grooved TPFPAJBs can be studied. The bearing number and width‐to‐diameter ratio are observed to have significant influences on the load performance of micro‐grooved TPFPAJBs. Copyright © 2015 John Wiley & Sons, Ltd.     

Maximum oil film pressure and temperature of two‐iobe journal bearings with different bush profiles

This paper presents data on the maximum oil film pressure and temperature of two‐lobe journal bearings with different bore profiles. A bearing with a cylindrical non‐continuous bore profile, and another with a pericycloid continuous profile have been evaluated. For an assumed relative length of the bearings, and parallel orientation of the journal and bearing axes, the minimum values of oil film thickness, maximum pressure values, and temperatures of the oil film have been determined. The calculations were carried out on the assumption of an adiabatic oil film and a static equilibrium position of the journal.     

Analysis of hybrid journal bearing for non‐Newtonian lubricants

The performance characteristics of capillary compensated hole‐entry hybrid journal bearing systems have been studied theoretically. The analysis considers the generalized Reynolds equation governing the flow field of lubricant, having variable viscosity, taking the equation of lubricant flow through a capillary restrictor as constraint. The non‐Newtonian lubricant is assumed to follow the cubic shear stress law. The results obtained from the study suggest that bearing static performance characteristics can be optimized for the particular bearing operating conditions by proper selection of parameters such as bearing land width ratios (ā_b), the restrictor design parameter (C̄_s2), and the non‐linearity factor (K̄). Copyright © 2006 John Wiley & Sons, Ltd.     

A critical evaluation of film thickness‐derived pressure–viscosity coefficients

A single parameter, the pressure–viscosity coefficient, α, quantifies the pressure dependence of the viscosity of the liquid in elastohydrodynamic lubrication (EHL). Most published values of α have not been obtained from measurements of viscosity as a function of pressure. Rather, these effective pressure–viscosity coefficients have been derived from the measurement of the EHL film thickness, a more difficult procedure. In this article, five well‐characterized liquids that should be Newtonian in the EHL inlet are identified for which film‐derived coefficients have been reported. These coefficients are compared with coefficients derived from published viscosity correlations and new viscosity measurements. The film‐derived coefficients are found to not be an accurate representation of the piezoviscous response. The procedure of deriving a pressure–viscosity coefficient from a film thickness measurement does not offer an alternative to the simpler and easier viscometer measurement. Copyright © 2014 John Wiley & Sons, Ltd.     

Pressure distribution in small hydrodynamic journal bearings considering cavitation: a numerical approach based on the open‐source CFD code OpenFOAM®

Hydrodynamic journal bearings are traditionally designed using the half‐Sommerfeld theory. This consists in a semi‐analytical solution of the continuity and momentum conservation equations substituting negative pressures with the ambient pressure. This hypothesis provides acceptable results, but a better understanding of the phenomena considering the effective pressure distribution including 3D and cavitation effects can be achieved only by using numerical methods. For this reason, some different solvers and cavitation models were applied to different geometries for which literature provides experimental data. Once the numerical model was validated, a parametric analysis was performed in order to better understand the influence of the rotational speed and the relative eccentricity on the attitude angle, the reaction forces, the pressure distribution and the power losses of a small journal bearing. Copyright © 2016 John Wiley & Sons, Ltd.