Wave Journal Bearing with Compressible Lubricant—Part II: A Comparison of the Wave Bearing with a Wave-Groove Bearing and a Lobe Bearing

To identify the potential advantages of the wave journal bearing, a three-wave journal bearing was compared to both a three-wave-groove bearing (a wave bearing with axial grooves that isolate each wave) and a three-lobe bearing. The lobe bearing's profile was selected to approximate the wave journal bearing's profile. The lubricant was assumed to be compressible (gas). The bearing number, A, was parameterized from 0.01 to 100, and the eccentricity ratio, ε, was varied from 0 to 0.4. Data at bearing numbers 0.1, 1, and 50, and eccentricity ratios of 0.1 and 0.4, were selected as representative of the bearing performance. The calculated load capacity and the critical mass are presented for the three bearings. The wave bearing shows a better load capacity than the other bearings at any applied load and running regime. However, at high bearing numbers the lubricant compressibility effect is predominant and all three analyzed bearings show similar load capacity. The critical masses of the wave-groove and lobe bearing are greater than the critical mass of the wave bearing if the applied load is small. For low and intermediate bearing numbers the wave-groove bearing is more stable than the other bearings especially at low wave's amplitude ratio. The lobe bearing is more stable than the other analyzed bearings at high bearing numbers or at large preload ratios. If the applied load increases, the wave bearing dynamic performance is competitive with both wave-groove and lobe bearings. In addition, at high bearing numbers, the wave bearing could run stably for any allocated rotor mass over a wide range of wave position angle. Three wave bearings are more sensitive to the direction of the applied load than the other bearings especially at low and intermediate bearing numbers. Therefore, a careful selection of the waves position angle has to be done to maximize the wave bearing performance.     

Numerical calculation and experimental verification of static and dynamic characteristics of aerostatic thrust bearings with small feedholes

In this work, aerostatic annular thrust bearings with feedholes of less than 0.05 mm in diameter are considered, and the static and dynamic characteristics of these bearings are investigated experimentally and numerically. In numerical calculations using the finite difference method (FDM), the discharge coefficients of a small feedhole were determined based on computational fluid dynamics (CFD) software and verified experimentally. In addition, the effect of the bearing surface roughness on the bearing characteristics was analyzed experimentally and numerically. It was confirmed that aerostatic thrust bearings with small feedholes could have larger stiffness and damping coefficient than bearings with compound restrictors.     

Numerical calculation and experimental verification of static and dynamic characteristics of aerostatic thrust bearings with small feedholes

In this work, aerostatic annular thrust bearings with feedholes of less than 0.05 mm in diameter are considered, and the static and dynamic characteristics of these bearings are investigated experimentally and numerically. In numerical calculations using the finite difference method (FDM), the discharge coefficients of a small feedhole were determined based on computational fluid dynamics (CFD) software and verified experimentally. In addition, the effect of the bearing surface roughness on the bearing characteristics was analyzed experimentally and numerically. It was confirmed that aerostatic thrust bearings with small feedholes could have larger stiffness and damping coefficient than bearings with compound restrictors.     

Computation model of composite cylindrical bearing working in steady-state regime for partial filling of gap with lubricant material

In [1–10], devoted to theoretical analysis of finite-length porous bearings working in non-steady-state regime, it is assumed that the gap is completely filled with lubricant material. In addition, bearing structures considered in this work possessing damping properties have low bearing capacity. Therefore it is necessary to make bearing structures so that the bearings have both damping properties and higher bearing capacity. Existing computational models of composite bearings [10] assume complete filling of the gap with lubricant material. Two cases of supplying lubricant material (axial and radial) are considered in turn. This work presents a solution to the problem of partial filling of lubricant material without allowance for its supply.     

Experimental Investigation of Friction and Electrical Characteristics of the Porous Bearings with Axial Grooves for Laser Scanner

The electrical and frictional properties of axially grooved oil-impregnated sintered-metal bearing (porous metal bearing) with varying loads and speeds were measured. The results were compared with the performance of bearings without grooves and conventionally used ball bearings. The test results showed that the frictional values of the porous bearings were lower than those of ungrooved bearings and ball bearings, and that the porous bearings operated in a full-hydrodynamic lubrication regime. The values of rating current, starting time and jitter revealed that the grooved-bearing had better electrical characteristics than the ungrooved bearing as well as the ball bearing. From the endurance tests on start-stop and continuous operating, it was confirmed that this bearing could be mass-produced for use in a laser scanner unit.     

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than that of an all-steel rolling element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58% for deep-groove bearings, 41% for angular contact bearings, and 28% for cylindrical roller bearings.     

A variational solution of two lobe bearings

Non-circular bearings are finding extensive use in high speed machinery as they enhance shaft stability, reduce power losses and increase oil flow (as compared to circular bearings), thus reducing bearing temperatures. Elliptical bearings are among the commonly used non-circular bearings. In this paper, a solution using a variational approach has been presented to analyse elliptical bearings. The results of an elliptical bearing actually in use in a 110 mW turbo-set have been compiled.     

Investigations of Bearing Failures Associated with White Etching Areas (WEAs) in Wind Turbine Gearboxes

A critical problem for wind turbine gearboxes is failure of rolling element bearings where axial cracks form on the inner rings. Metallurgical analyses show that the failure mode is associated with microstructural alterations manifested by white etching areas (WEAs) and white etching cracks (WECs). This article presents field experience from operating wind turbines that compares performance of through-hardened and carburized materials. It shows that through-hardened bearings develop WEA/WECs and fail with axial cracks, whereas carburized bearings do not. In another comparison of two rotor bearings with different carburized metallurgies, one bearing developed WEA/WECs and failed by macropitting, whereas the other bearing did not develop WEAs or WECs and did not fail. The field experience shows that a carburized bearing that has a core with low carbon content, high nickel content, greater compressive residual stresses, and a higher amount of retained austenite provides higher fracture resistance and makes carburized bearings more durable than through-hardened bearings in the wind turbine environment.     

Comparison of tribological characteristics between aluminum alloys and polytetrafluoroethylene composites journal bearings under mineral oil lubrication

This study examined the tribological behavior of journal bearings made from polytetrafluoroethylene (PTFE) composites and aluminum (Al) alloys. The PTFE composite journal bearings consisted of a steel backing with a thickness of 1.6 mm, a middle layer of sintered porous bronze with a thickness of 0.24～0.27 mm, and a surface layer of PTFE filled with fluorinated ethylene propylene (FEP) powder and carbon fibers with a thickness 0.06～0.14 mm. The other was an aluminum alloy journal bearing consisted of a steel backing with a thickness of 1.5 mm and a surface layer of an Al-6Sn-6Si alloy with a thickness 0.35～0.75 mm. A series of lubrication tests were performed using a journal bearing tester under various normal loads. The tribological properties for each journal bearing were evaluated by measuring the lubricant oil temperature and friction coefficient as a function of the applied normal load. In addition, the chemical compositions and microstructures of the journal bearing materials used in this study was analyzed by inductively coupled plasma (ICP), optical microscopy (OM), and scanning electron microscopy (SEM), respectively. The experimental results showed that the Al alloy journal bearings reduce the friction coefficient by 28 % compared to the PTFE composites bearings. In addition, the Al alloy journal bearing worked properly at the maximum load of ～ 8,000 N without adhesion. However, the PTFE composite journal bearings exhibited strong adhesion at the loads ranging from 6300 to 8000 N. This suggests that the Al alloy is a more promising material in journal bearings than PTFE composites.     

An experimental investigation of thermal effects in circular and elliptical plain journal bearings

Hydrodynamic journal bearings can experience a significant variation in film (bush) temperature. Reliable data of operating temperatures in these bearings are very useful and important for practical bearing designers and mathematical modellers. A two-axial-groove circular bearing and an elliptical (lemon-bore) bearing, both 110 mm in diameter, have been tested at specific loads up to 4 MPa and rotational frequencies up to 120 Hz. Power loss and flow rate were measured directly and detailed temperature information was collected by an automated data acquisition system. In this paper, the experimental apparatus is described and some of the experimental data are presented. The results show that the thermal effects are significant in both bearings.     

A study of slot-entry hydrostatic/hybrid journal bearing using the finite element method

A theoretical study concerning the static and dynamic performance of hydrostatic/hybrid journal bearing compensated by slot restrictor has been presented using the finite element method (FEM). Results have been presented for a double row symmetric as well as asymmetric configurations for different values of slot width ratios (SWR) and external load ( ). In order to have a better understanding of their performance vis-à-vis other non-recessed bearing configurations, the performance characteristics of slot-entry journal bearings have been compared with that of similar hole-entry compensated journal bearings using capillary, orifice and constant flow valve restrictors for the same bearing geometric and operating parameters. The comparative study indicates that asymmetric slot-entry journal bearings provide an improved stability threshold speed margin compared with asymmetric hole entry journal bearings compensated by capillary, orifice and constant flow valve restrictors.     

A Simulation Study on the Behavior of Magnetorheological Fluid on Herringbone-Grooved Hybrid Slot-Entry Bearing

Abstract

In recent years, extensive use of smart lubricants has been made in order to control the tribological performance of fluid film bearings. The grooved surfaces of the journal bearing greatly influence the performance of bearings. In the present work, various geometric shapes of herringbone grooves (rectangular, triangular, and parabolic) with groove angles (30° and 60°) have been considered to numerically simulate the performance of slot-entry bearings. The work reported in this article deals with the numerical simulation of magnetorheological (MR) fluid–lubricated slot-entry herringbone-grooved hybrid journal bearings. Dave equation, a constitutive relation of the Bingham model, was employed to simulate the flow behavior of MR fluid. Using the finite element method (FEM), the governing Reynolds equation for a hybrid slot-entry bearing model was solved. The result shows that the use of a herringbone-grooved surface and application of MR fluid in a slot-entry bearing offers better stability and higher fluid film stiffness and minimizes frictional torque.     

Lubrication Performance of Connecting-Rod and Main Bearing in Di erent Engine Operating Conditions

Only the lubrication performance at rated engine operating condition was generally analyzed in current design and research of engine connecting-rod and main bearing. However, the actual engine(especially vehicle engine) does not always operate in rated operating condition and its operating condition changes constantly. In this paper, a fourstroke four-cylinder engine is taken as the studying object, the load and lubrication of connecting-rod and main bearing in di erent operating conditions are analyzed. The load of connecting-rod bearing is calculated by the dynamic calculation method, the loads of all main bearings are calculated by the whole crankshaft beam-element finite element method, and the lubrication performance of connecting-rod and main bearings are analyzed by the dynamic method. The results show that there are major di erences in the changes and numerical value at corresponding moment of the loads and lubrication performance of connecting-rod and main bearings in an engine operating cycle in di erent engine operating conditions; the most unfavorable case of the lubrication performance of connectingrod and main bearings may not take place in the rated engine operating condition. There are also major di erences between the lubrication performance of connecting-rod bearing and that of main bearing and between the lubrication performances of main bearings one another. Therefore, it will not be reasonable that the lubrication performance of a certain connecting-rod bearing or main bearing is analyzed in the design of the engine bearing. It is necessary to analyze simultaneously the lubrication performances of all bearings in di erent engine operating conditions.     

向心透平发电膨胀机静压气体轴承设计与承载特性分析

为提升有机朗肯循环（organic Rankine cycle,ORC）系统向心透平发电膨胀机静压气体轴承的承载力与刚度,采用表压比法设计了以R245fa为润滑工质的静压气体轴承,分析转子偏心率、供气孔尺寸、进气压力对静压气体轴承承载力与刚度的影响。实验结果表明：在相同供气压力下,轴承承载力与刚度随着转速的增大而增大;在相同转速下,0.7 MPa供气压力相对于其他气体供气压力轴承的承载力与刚度略高;静压气体轴承的偏心率越大承载力越大;相同供气孔直径下,静压气体轴承的承载力与刚度随着转速的升高而升高;随供气孔直径增大,静压气体轴承的承载力和刚度也随之增大。     

Numerical investigation of static and dynamic characteristics of aerostatic thrust bearings with small feed holes

Recently, laser beam machining and micro drills have made it easier to manufacture small feed holes of less than 0.1 mm diameter. Accordingly, aerostatic bearings with these small feed holes have become commercially available for improving bearing performance. In this work, an aerostatic annular thrust bearing with small feed holes of less than 0.05 mm diameter was treated and the static and the dynamic characteristics of this type of bearing were investigated numerically. In numerical calculations, computational fluid dynamics (CFD) was used to determine discharge coefficients for a small feed hole and the finite difference method (FDM) was used to obtain the bearing characteristics. In addition, the characteristics of this type of bearing were compared with those of aerostatic thrust bearings with typical compound restrictors to show clearly the features of this type of bearing.     

Hydrodynamic slip bearings for high-precision low-noise machines

A three-key (three-insert) bearing with self-steadying inserts is proposed. This bearing differs from single-key bearings in that the shaft position is stable with small external radial loads on the bearing, at high shaft speeds, and with displacement of small amplitude. The bearing is dimensionally consistent with the intermediate series of ball bearings.     

多列组合角接触球轴承刚度和位移量

以滚动轴承动力学分析和滚道控制理论为基础,提出了应用Powell优化算法和Newton-Raphson算法相结合的方式计算非线性方程组,给出了预紧力和转速的多列组合角接触球轴承组合刚度相应程序。对7016A5轴承DBD组合的研究结果表明:预紧力和转速与单个轴承和轴承的组合刚度及位移量呈现非线性关系。轴承的组合轴向刚度小于单个轴承的轴向刚度,其径向刚度大于单个轴承的径向刚度。为实现预定的轴承动态性能,单双侧轴承内圈的间隙量须大于两侧轴承位移量之和。     

Fundamental dynamic performance of fluid-pivot and squeeze-film damper bearings

Due to the increase in rotational speeds and performance of modern turbomachinery the rotordynamic stability of such machinery has reduced. In order to improve rotordynamic stability, fluid-pivot and squeeze-film damper bearings have been developed. By using a simple analytical model to predict the unbalance response of a single mass rotor and by modelling the above bearings as a two-mass-spring and damper system the fundamental performance of these types of bearings has been determined. The results are that these bearings can significantly improve rotordynamic performance over a certain frequency range. This is mainly due to the ability of these bearings to reduce the effective bearing stiffness and hence improve the damping efficiency of the bearings. These auxiliary damped bearings increase the bearing damping efficiency rather than increase the bearing damping.     

无心磨床常用主轴轴承分析

对无心磨床的两种砂轮主轴轴承——动压滑动轴承和精密双列短圆柱滚子轴承的性能进行了分析，通过对砂轮主轴的回转精度、轴承刚度、热温升和热平衡时间的对比，得出了滚动轴承宜作为无心磨床的砂轮主轴轴承的结论。     

Fluid Flow Analysis for Friction Torque around Rolling Element in Ball Bearings

Ball bearings (e.g., deep-groove, angular-contact, and roller bearings) support loads in a rotor system and provide lubrication between the shaft and housing. The deep-groove ball bearings used in a turbopump do not differ significantly from angular-contact ball bearings or the bearings found in other applications. Deep-groove ball bearings consist of rolling elements, an inner raceway, an outer raceway, and a retainer to guide the rolling elements. In ball bearings, the resistive (churning or drag) forces and torques acting on the rolling elements and raceways are affected by the fluid flow rate and direction, as well as the rotational speed. These churning and drag forces and torques affect the internal dissipation or power losses into the bearing, which become very significant for high-speed applications. This study numerically investigated the characteristics of the flow conditions for deep-groove ball bearings, with a particular focus on the friction distribution on the rolling elements. A simple analytical model of the fluid flow inside a ball bearing was developed using a computational analysis, and the flow characteristics at high rotational speeds are presented.