Appearance of craters on track surface of rolling element bearings by spark erosion

A theoretical investigation has been carried out to determine the time span for the appearance of craters by spark erosion on the track surfaces of rolling-element bearings operating under the influence of shaft voltages. An analytical model has been developed using the continuum theory of Griffith to determine energy per unit area required for the development of craters on the track surfaces. Also, an expression is deduced for the net energy transmitted per unit area on the track surfaces by the leakage of stored charge energy resulting in the appearance of craters under the effect of shaft voltage and bearing capacitance depending on operational and dimensional parameters of a bearing in a given span of operation. By the formulation of capacitive stored energy in a bearing using high resitivity lubricant, along with the developed model and expressions using the ratio of cycles to accumulate and discharge of the accumulated charge energy at the various levels of bearing to shaft voltage, the time span/cycles for the appearance of craters of specified dimensions by spark erosion has been determined. Matching time span/cycles has been ascertained by the investigation of a case history of the diagnosis of bearings that failed by crater formation. The analysis can also be used for determination of shaft voltage if the time span/cycles for the formation of known size craters and bearing capacitance are established.     

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.     

Cage Speed of Hydrodynamic Rolling Hybrid Bearings

Hydrodynamic bearings are subjected to wear during starts and stops due to the absence of sufficient film pressure to effect complete separation of the sliding surfaces. In an earlier publication, our group reported the development of a new hydrodynamic rolling hybrid bearing (HRHB) to overcome the wear problem in hydrodynamic bearings. In the configuration, the transition of operation modes between the rolling bearing supporting state and the hydrodynamic bearing supporting state was realized by the clearance of the rolling bearing. Here we report on the development of a method to identify the operation modes for HRHBs based on monitoring the cage speed of the rolling bearing. The variation of cage speed with the shaft speed is measured. The effects of external load and starting time on the cage speed are also investigated experimentally. The results show that variation in the cage speed reflects changes in the load on the rolling bearing, as well as the operation modes of the HRHBs. With increases in the shaft speed, the variation in the cage speed presents three stages: the increasing stage, the decreasing stage, and the stationary stage. In the first two stages, the HRHB works at the rolling bearing supporting state while in stationary stage, the HRHB works at the hydrodynamic bearing supporting state. In additions to its property of no wear sufferance during starts and stops, compared to hydrodynamic bearings there is little risk of catastrophic failure with HRHBs during any interruption to the lubricant supply and compared to rolling bearings there is no fatigue failure. Therefore this hybrid design is useful at very high speeds.     

Linear Stability Analysis of Hydrodynamic Journal Bearings with a Flexible Liner and Micropolar Lubrication

A linear stability analysis of hydrodynamic journal bearings is presented, including the effects of elastic distortion of the liner and micropolar lubrication. Hydrodynamic equations of the lubricant and equations of motion of the journal are solved simultaneously with the deformation equations for the bearing surface to predict the fluid film pressure distributions theoretically. The components of stiffness and damping coefficients, critical mass parameter, and whirl ratio, which reflect the dynamic characteristic of the journal bearing, are calculated for varying eccentricity ratio taking into account the flexibility of the liner and the micropolar properties of the lubricant. The results presented show that stability decreases with an increase in the value of the elasticity parameter of the bearing liner and micropolar fluids exhibit better stability in comparison to Newtonian fluids.     

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.     

考虑粗糙度的船舶水润滑高分子轴承弹流润滑性能研究

为了揭示表面粗糙度对船舶水润滑高分子材料轴承润滑性能的影响规律,开展水润滑轴承弹流混合润滑理论研究;建立考虑内衬材料粗糙度和弹性变形的水润滑轴承混合润滑模型,并对模型进行仿真验证;分析内衬粗糙峰对水膜厚度、水膜压力分布和承载能力的影响规律。研究结果表明：在转速增大的过程中,内衬粗糙度的增大会减缓水膜厚度的增幅比,使轴承需要更高的转速来进入流体动压润滑状态;减小轴承内衬粗糙度能有效降低轴承起飞转速,加快轴承由混合润滑转变为流体动压润滑的过程,减小轴承与轴颈的局部接触,降低轴承异常振动噪声发生的可能性。研究结果揭示了内衬粗糙度变化对轴承润滑特性的影响机制,为水润滑轴承的优化设计提供理论参考。     

Dynamic analysis of hydrodynamic bearing performance in ic engines by using Taguchi technique and Response Surface Methodology (RSM)

Much work has already been carried out on hydrodynamic bearings under static loads, but very little literature is available on the investigation under dynamic loads and its effect on inertia forces of engine parts like pistons, connecting rods, crank shafts and flywheels. An attempt is made in this paper to analyze the effect of load, journal speed, bearing width and mass flow rate with respect to variations in oil film thickness on power loss by fluctuations in pressure gradient, stiffness and damping effect during dynamic loading conditions. The oil film thickness is measured under various conditions of fluctuating/steady load, journal speed, bearing width and mass flow rate. The oil film thickness is measured by an eddy current gap sensor to deduce the shaft trajectories by using the experimental setup. The same concept is analyzed and compared with Taguchi techniques and response surface methodology (RSM). The vital role of this technique is considered for designing the experiment (robust design) and analyzing the dynamic sinusoidal loading effect. Also we analyze whether the solution for minimizing effect of the change in load causes a change in pressure gradient, which will create a delay in time response in the pressure gradient, which creates physical contact between the journal and bearing, causing power loss.     

Surface roughness effect on finite journal bearings with flexible porous liners

The effects of surface roughness on the static characteristics of finite porous journal bearings under hydrodynamic lubrication conditions are investigated in this paper. The well‐established Christensen stochastic theory of hydrodynamic lubrication of rough surfaces is used to incorporate the effects of surface roughness into the Reynolds equation. The analysis takes into account the flexibility of the porous liner by using a thin liner model. The effects of velocity slip at the surface of the porous medium are considered in the analysis by using the Beavers‐Joseph criterion. The mathematical model is then solved numerically by finite‐difference methods for mean hydrodynamic pressure, which in turn gives the hydrodynamic load. The effects of the surface roughness parameter, surface pattern, eccentricity ratio, length‐to‐diameter ratio, permeability parameter, and flexibility parameter on the hydrodynamic load‐carrying capacity, attitude angle, and friction factor are discussed.     

Wear mechanisms of statically loaded hydrodynamic bearings by contaminant abrasive particles

Wear mechanisms in hydrodynamic bearings by contaminant abrasive particles in the oil were investigated. This type of wear is one of the main factors responsible for failure of hydrodynamic bearings especially when operating in dusty environments. A test bearing system was developed to study this type of wear under carefully controlled conditions. Experiments were conducted with two shaft materials and three liner materials, giving a total of six material combinations. The circumferential liner wear distribution and the relative magnitude of shaft and liner wear were found to depend mainly on the shaft-to-liner hardness ratio. A smaller hardness ratio resulted in relatively more liner wear and less shaft wear. A model is proposed to account for this behaviour whereby the action of the abrasive particle is considered to consist of both cutting and rolling motions.     

Stability analysis of rough journal bearings under TEHL with non-Newtonian lubricants

The combined effects of surface roughness and lubricants rheology on stability of a rigid rotor supported on finite journal bearing under thermal elastohydrodynamic lubrication have been investigated using the transient method. The newly derived time dependent modified Reynolds and the adiabatic energy equations were formulated using a non-Newtonian Carreau viscosity model. The simultaneous systems of modified Reynolds equation, elasticity equation, energy equation, and the rotor motion equation with initial conditions were solved numerically using multigrid multi-level method with full approximation technique. From the characteristic equation, the instability threshold is then obtained with various surface roughness parameters and the elastic modulus of the bearing liner materials. The results show that stability of the bearing system deteriorates with decreasing both the power law exponent and the elastic modulus of bearing liner material. The rough surface journal bearing with transverse pattern under TEHL regime exhibits better stability when compared with the rough surface journal bearing with longitudinal pattern.     

Investigations on a permanent magnetic–hydrodynamic hybrid journal bearing

In the present work, a permanent magnetic–hydrodynamic hybrid journal bearing is developed. The force of the journal bearing comes from the hydrodynamic film and the permanent magnetic field. When a hydrodynamic film does not form, such as during starting and stopping a machine, the journal bearing relies on the magnetic force to support the rotor system. This paper studies a model of the permanent magnetic force and develops an experimental rig of the journal bearing. Experiments show that the hydrodynamic film force uncouples with the magnetic force in the journal bearing. Predictions from the model are compared with experimental data.     

基于流固耦合的滑动轴承非线性油膜动特性研究

针对采用传统静态滑动轴承动力特性系数分析转子从启动到稳定在平衡位置这段时间内瞬态响应的误差较大的问题,提出了采用有限变分法和Newmark-β法相结合的非线性油膜动特性动态分析方法。该方法首先采用有限变分法计算非线性油膜动力特性系数, 解决了采用有限差分法时多次迭代的时效问题,大大提高了计算效率;然后根据计算得到的非线性油膜动力特性系数,通过Newmark-β法分析转子系统的瞬态响应,用学科间迭代方法实现了非线性油膜动力特性系数与转子瞬态响应之间的流固耦合;最后以Jeffcott转子系统为例,对比研究了传统静态分析方法与动态分析方法。结果证明,采用动态分析方法得到的转子系统瞬态响应幅值更小,精度更高。     

A study on compliant layers and its influence on dynamic response of a hydrodynamic journal bearing

For some hydrodynamic bearing applications polymer-lined bearings are chosen over traditional metal alloy bearings due to their better wear and friction properties when operating at very thin films, e.g. in the mixed lubrication region. The introduction of a compliant layer also affects the dynamic behavior of the bearing. The influence of the liner stiffness on the dynamic response of a highly dynamically loaded journal bearing is evaluated by varying the stiffness and comparing the response. The configurations with different liner stiffnesses are evaluated on the parameters that are traditionally used to evaluate hydrodynamic bearing designs: dynamic response, maximum pressure, minimum film thickness, wear, power loss and temperature response. The primary findings are that the maximum pressures are reduced significantly and this comes at the expense of slightly higher eccentricity ratios during operation.     

瞬变载荷作用下滑动轴承轴心轨迹计算仿真

为了研究动压滑动轴承在瞬变载荷作用下的润滑状况,在考虑轴颈惯性力和非线性油膜力的基础上,建立了滑动轴承轴心轨迹的运动方程,提出了采用欧拉法求解有限长滑动轴承瞬时轴心轨迹的数值方法。分别计算了在阶跃、矩形脉冲和正弦脉冲瞬变载荷作用下轴心轨迹、最大油膜压力及最小油膜厚度的变化规律。分析结果表明,在瞬变载荷作用时,轴心轨迹、最大油膜压力及最小油膜厚度都有较大的变化并呈现出一定的振荡过程。由于脉冲载荷的作用时间有限,随着其消失,轴心乃收敛于原平衡位置,而阶跃载荷则使轴心收敛于新的平衡位置。     

Thermohydrodynamic analysis of a worn plain journal bearing

Hydrodynamic journal bearings are widely used in industry because of their simplicity, efficiency and low cost. They support rotating shafts over a number of years and are often subjected to many stops and starts. During these transient periods, friction is high and the bushes become progressively worn, thus inducing certain disabilities. This paper seeks to present the thermohydrodynamic performance of a worn plain journal bearing. The study deals with a 100 mm diameter bearing, submitted to a static load varying from 5000 to 30,000 N with a rotational speed varying from 1000 to 10,000 rpm. The defects caused by wear are centered on the load line and range from 10% to 50% of the bearing radial clearance. Our main focus was on hydrodynamic pressure, temperature distributions at the film/bush interface, oil flow rate, power losses and film thickness. Defects caused by wear of up to 20% have little influence on bearing performance whereas above this value (30 to 50%) they can display an interesting advantage: a significant fall in temperatures, due to the tendency of the bearing to go into the footprint created by the wear. Thus, the worn bearing presents not only some disadvantages but also advantages, such as lower temperature, since in certain cases of significant defects due to wear the geometry approaches that of a lobe bearing.     

Rigidity and damping characteristics of hydrodynamic sliding bearing with deformable working surfaces

The model of a hydrodynamic sliding bearing has been developed that takes into consideration the effect of the deformation of sliding surfaces on the bearing characteristics. The deformations of the sliding surfaces are determined when solving the problem of elastohydrodynamic contact of the journal and bearing with account for the pressure in the lubricating film. Variation in the clearance size at the deformation of the bearing and shaft surfaces is found by iterations when solving jointly the problems of lubricant flow and working surface deformation. Elastic deformations of the working surfaces are calculated using a two-dimensional boundary element model and a three-dimensional finite element model of the shaft and bearing. The method of finite elements is applied to calculate the parameters of lubricant flow in the bearing based on the solution of Reynolds equation in the disturbed form. The rigidity and damping characteristics of the sliding bearing with the deformable surfaces are compared to those of the bearing with the rigid surfaces; the results of the two-dimensional model of bearing deformation are compared to those of the three-dimensional one.     

Wave Journal Bearing with Compressible Lubricant—Part I: The Wave Bearing Concept and a Comparison to the Plain Circular Bearing

To improve hydrodynamic journal bearing steady-stale and dynamic performance, a new bearing concept, the wave journal bearing, was developed at the author's lab. This concept features a waved inner bearing diameter. Compared to other alternative bearing geometries used to improve bearing performance such as spiral or herringbone grooves, steps, etc., the wave bearing's design is relatively simple and allows the shaft to rotate in either direction. A three-wave bearing operating with a compressible lubricant; i.e., gas, is analyzed using a numerical code. Its performance is compared to a plain (truly) circular bearing over a broad range of bearing working parameters, e.g., bearing numbers from 0.01 to 100. The geometry of the wave bearing gives the bearing its high load; i.e., stiffness, and stability characteristics. The wave bearing's performance is dependent upon the amplitude of the wave and the position of the waves relative to the applied load. To maximize wave bearing performance, the waves' position relative to the applied load should be carefully selected. The wave journal bearing offers better stability than the plain circular bearing' under all operating conditions and all wave-load orientations. Specifically, an unloaded journal bearing can be made to run stably in any operating regime by incorporating the wave geometry.     

卧式水电机组用径向滑动轴承热弹流特性分析

研究轴颈挠度和瓦块表面热弹变形对卧式水电机组径向滑动轴承静态润滑性能的影响。推导考虑轴颈挠度和轴瓦热弹变形后的油膜厚度表达式;用中心差分法结合ANSYS软件联立求解雷诺方程、能量方程、固体热传导方程、密度方程、黏度方程和轴瓦热弹变形等,得到径向滑动轴承的热弹流润滑(TEHD)特性,并与不计入轴颈挠度及轴瓦热弹变形的油膜动压润滑特性进行比较。结果表明:在考虑轴颈挠度和轴瓦瓦面热弹变形的影响后,油膜压力、温度、厚度沿着轴承宽度中心线的对称特性消失;油膜压力峰值增大,峰值点位置由轴向中心区偏移至出口区;油膜温度峰值增大,最高温度发生在出口区;润滑区内的最小油膜厚度大幅度减小,油膜最小厚度处于出口侧边界附近;轴承润滑流量减小,损耗略有增大;轴承稳态运行时,轴颈偏位角基本一致。     

考虑不同加速工况的滑动轴承的启停性能分析*

滑动轴承的摩擦磨损主要发生在启停阶段。为了研究启停工况下的滑动轴承的摩擦学性能,建立一种面向径向滑动轴承的混合润滑数值分析模型。采用质量守恒边界条件的雷诺方程求解流体压力,采用Greenwood和Tripp接触模型预测固体表面接触,而通过Johnson载荷分配概念将润滑模型和接触模型联系起来,从而实现对滑动轴承在启停工况下从混合润滑过渡到动压润滑的摩擦学行为分析。利用该模型,研究轴承系统在启停阶段从边界润滑、混合润滑到动压润滑演化过程中的摩擦学性能;以径向滑动轴承系统为例,结合不同的轴承转速变化函数,分析轴承加速对轴承启停性能的影响;同时研究工作工况、润滑油温度、轴承的结构参数对轴承启停性能的影响。结果表明：轴承启动加速度在合理范围内越大越好,能使轴承更快进入动压润滑;较高的转速、较低的润滑油温度和较大的径向轴承间隙能使轴承拥有更好的启停性能。     

轴变形产生的轴颈倾斜对滑动轴承润滑影响的试验研究

针对各种机械装置使用最普遍、最基本的轴-滑动轴承摩擦副系统,设计研制了专用试验装置,对轴受载荷作用产生弯曲变形,导致轴颈在轴承孔中倾斜时滑动轴承的润滑性能进行了试验研究。结果表明,在轴-滑动轴承摩擦副系统中,轴受载荷作用产生变形将导致轴颈在轴承孔中倾斜;轴变形导致轴颈倾斜时,滑动轴承的油膜压力、油膜厚度和温度的分布状况及数值发生了明显变化。轴受载越大,其变形产生的轴颈倾斜越严重,对滑动轴承润滑性能的影响越明显;轴承半径间隙与轴承宽度比值越小,轴变形产生的轴颈倾斜对轴承油膜压力、油膜厚度和温度的数值及分布的影响越大。因此,滑动轴承设计中应该考虑轴受载荷作用产生的变形导致轴颈倾斜的影响,对于重要的机械设备,尤其应当考虑这种影响。