Flow Visualization in a Pocketed Thrust Washer

The objectives of this study were to experimentally and numerically investigate oil flow in surface-pocketed thrust washers. In order to achieve the experimental aspects of this investigation, a thrust washer test rig was designed and developed to visualize the lubricant flow at the contact interface. A novel approach for creating the pockets was developed to allow optical inspection of the lubricant during thrust washer operation. The thrust washers were fabricated using a glass disk with a thin layer of steel shim stock adhered to the surface. The micrometer-thick shim stock was machined using an Nd:YAG laser to create the circular pocket geometries and then glued to the glass disk. A mirror and camera were placed below the semitransparent washer to observe the lubricant flow in the pocket. The results obtained from this configuration illustrate a cavitation bubble forming on the leading edge of the pocket followed by a sharp transition back to liquid. The size of the cavitation area was found to be a function of rotational speed, nominal bearing pressure (NBP), viscosity, and pocket geometry. The cavitation area ratio (gaseous region divided by the pocket area) increased for greater speeds and higher viscosities and decreased for larger pocket diameters, deeper pockets, and higher NBPs. The friction force for various thrust washer designs was also measured as a function of load, speed, and lubricant. The results showed that shallower, wider pockets provided the lowest friction. It was found that, generally, the conditions that minimize friction also result in a stable cavitation region. ANSYS Fluent computational fluid dynamics software was used to develop a three-dimensional model of the pocketed thrust washer utilizing the full Navier-Stokes equations to investigate the cavitation and pressure distribution occurring at the contact and corroborate the experimental results.     

Experimental Investigation of Thermal and Hydrodynamic Effects on Radially Grooved Thrust Washer Bearings

In this study, an experimental investigation on the effects of grooves on thrust washer bearings is investigated. Eight equally sized grooves are machined about 100 μ m deep into one side of a flat-faced steel washer. This thrust washer bearing is located between a helical gear and its carrier and is tested on a test rig capable of measuring frictional torque and the temperature of the bearing at different speeds. It is found that the grooved washers had lower bearing temperatures and failed at significantly higher loads than the control washer with no grooves. For a test procedure with varying operating conditions, the coefficient of friction is also significantly lower for the grooved washers. However, the grooved washers had about the same coefficient of friction as the control washers at each step when the speeds are very high. The results from various tests suggest that the increased amount of lubricant passing through the grooved surface of the washer removes heat from the washer bearing by convection. This decrease in stored heat conducted from friction deters thermoelastic instabilities and the reduction of hydrodynamic stiffness due to the decrease in viscosity. Enhanced hydrodynamic load-carrying capacity is also evident in the grooved washers test results.     

Hydrodynamic Performance of a Thrust Bearing with Micropatterned Pads

The primary objective of this study was to investigate the influence of surface texturing on hydrodynamic lubrication of tilting-pad thrust bearings in terms of bearing power loss, operating temperature, and oil-film thickness. For this purpose, the working faces of six thrust pads from a 228.6-mm-outer-diameter bearing were textured. The textured surface consisted of a system of crossing channels of less than 10 μm in depth. Tests were conducted with a VG68 mineral turbine oil supplied to the bearings at a constant temperature of 50°C and flow rate of 15 L/min. The following parameters were measured: frictional torque, pad and collar temperatures, oil-film thickness, and pressure profiles along two circumferential lines. No significant change in collar and pad temperature could be observed when the patterned bearing was used. However, the textured bearing showed a tendency to exhibit lower power loss especially when an optimum oil flow supply rate was used. At the same time, inlet and outlet film thicknesses for the patterned bearing showed larger values than those obtained during tests on the plain babbitt pads.     

大型可倾瓦推力轴承弹流润滑问题的域外法解

介绍域外在处理弹流润滑问题是的应用，和边界元不相比，域外不需要对边界单元作繁琐的奇异积分处理，因而编程简捷，计算精确。作为算例，用域外法联立求解雷诺方程和弹性变形方程，计算了大型可倾瓦推力轴承的油膜压力、弹性变表和相应的特性参数。     

大型推力轴承几何参数对润滑性能的影响

本文对排力轴承的瓦张角,瓦宽,瓦内径,载荷,转速,进油边温度对润滑性能的影响,进行了分析,提出了改进建议,对指导推力轴承设计具有重要的实际意义。     

On the Hydrodynamic Sealing in Lubricated Viscoseals

In this article, an investigation on viscoseal behavior is presented. In a laminar flow and a hydrodynamic regime, the finite element model is chosen, associated with lubrication hypotheses. The mathematical model corresponds to the classical Reynolds equation. However, this equation is modified, introducing a mass conservative algorithm assuming the film breakdown and re-formation. A different approach for sealing analysis is proposed based on the sealing length factor that characterizes the liquid-filled area in the seal.

First, an adequate geometry, enabling optimal operation, is set. The proposed parametrical study refers to the groove angle, width, and depth calibration. Second, the influence of the journal speed and the groove number on the sealing length is discussed.     

Experimental Analysis of the Wear,Life and Behavior of PTFE Coated Thrust Washer Bearings Under Non-Axisymmetric Loading

In this work the behavior and life of a PTFE coating on a flat thrust washer bearing is investigated. The thrust washer bearing is located between a helical gear and its carrier, and is subjected to non-axisymmetric loading and wear. The volume of worn material is approximated by measuring the difference in height between the worn and unworn surfaces. It was also found that the surface roughness of tested washers increases with the severity of wear, in most cases. After a finite number of cycles the effective coefficient of friction between the surfaces increases, suggesting that the coating is wearing off and losing effectiveness. The rate at which the coating wears off also varies with load and speed, hence, there is a region of operation that minimizes the wear and friction.     

蜗杆传动的弹性流体动力润滑

从弹性流体动力润滑理论和蜗杆传动的特点出发，分析了有关文献对蜗杆传动弹性流体动力润滑条件分析中的不足，指出了滚动速度是建立润滑油膜和油压的重要条件，论证了滑动速度对润滑油膜和油压的形成也有较大影响。采用Dowson公式计算油膜厚度时，为了考虑滑动速度的影响可引入滑动速度系数Ks予以修正。     

Measurements of Compressibility Effects in Stepped Thrust Gas Film Bearings

Hydrodynamic gas film bearings are used for supporting high-speed, lightly loaded rotating machinery. Stepped-type gas film bearings are often used for such machinery because of theïr simple structure, high stability and load carrying capacity. This paper describes the measurements of compressibility effects on the static and dynamic characteristics of stepped thrust gas film bearings. In the experiments, the minimum film thickness, friction torque on the bearing surface and stiffness and damping coefficients of gas films are measured for a range of rotational speed from 10,000 rpm to 20,000 rpm under a constant stator mass and a fixed step height. The measured data are compared with the theoretical results and the gas film compressibility effects on the static and dynamic characteristics of the bearings are discussed. The experimental results agree well with the predicted results based on the compressible lubrication theory.     

Hydrodynamic Lubrication of Surfaces with Asymmetric Microdimple

Surface texturing has been recognized as a feasible method of surface engineering to improve the lubrication properties of mechanical components. This work focuses on the hydrodynamic lubrication properties of the textured surface with asymmetric microdimples. The validity of the Reynolds equation in asymmetric microdimples is discussed based on theoretical analysis and numerical simulation. The effects of modified Reynolds number, motion directions, and parameters of the microdimple profile are investigated. The following results were obtained: Firstly, the Reynolds equation is invalid under almost all of the general conditions used in experiments and industries. Secondly, the ultimate load-carrying capacity can be taken as a new characteristic parameter to assess the lubrication property of a textured surface. Thirdly, the motion directions have a great effect on the lubrication properties. The positive motion can generate more stable load capacity under all of the modified Reynolds numbers employed, even though the load-carrying capacity is smaller than the negative motion’under larger modified Reynolds numbers. Additionally, the asymmetric microdimple can obtain larger load-carrying capacity than a symmetric rectangular microdimple and will become a potential microdimple candidate.     

The Effectiveness of Boundary and Hydrodynamic Lubrication when Cold Rolling Aluminum Metal

How hydrodynamic and boundary lubrication affect a lubricant's film strength when cold rolling aluminum was studied using a laboratory mill. The film strength of the lubricant was determined by increasing the amount of reduction until a rapid rise in load and temperature produced a herringbone pattern on the surface of the metal. The hydrodynamic lubrication was changed by increasing the viscosity of the base oil or by increasing the rolling speed. The boundary lubrication was changed by increasing the concentration of the additives or by changing the type of additives. The results of the test showed that either increasing the amount of the hydrodynamic lubrication or increasing the amount of the boundary lubrication were effective ways to increase the film strength of the lubricant; however, the effectiveness of each decreased as the calculated film thickness of the lubricant increased. It is proposed that this can be explained by the decrease in contact area between the work roll asperities and the surface of the sheet as the thickness of the lubricant film increases.     

Incompressible and Analytical Study on Load-Carrying Capacity of a Complex Thrust Gas Bearing

ABSTRACT

A type of aerodynamic/aerostatic complex thrust gas bearing was presented in the investigation of the coupling between aerodynamics and aerostatics with the objective of further improving the performance of the thrust gas bearing. Its analytical model was also set up completely under incompressible conditions. Based on this model, the load-carrying capacity function apparently included pressure and structure coupling items. However, this structure cannot be used when the pressure ratio of the complex gas bearing is less than 1.

     

Thermoelastohydrodynamic Analysis of Fixed Geometry Thrust Bearings Including Runner Deformation

A thermoelastohydrodynamic theory for the analysis of sector thrust bearings is presented. The analysis includes the generalized Reynolds equation and a fully elliptic three-dimensional energy equation in the film. In addition, full three-dimensional heat transfer is allowed in the pad while axisymmetric conduction is allowed in the runner. Three-dimensional elastic deformation due to mechanical and thermal loading is allowed in the pad while axisymmetric mechanical elasticity is allowed in the runner. The performance of a parallel tapered-land thrust bearing including runner deformation effects is analyzed as a function of different models. It is seen that mechanical deformation of the pad affects the operating characteristics only slightly while thermal deformation of the pad can cause large increases in operating temperature. The runner deformation effects can include a reduction of the maximum film temperature at slight deformation or a large increase in film temperature at the inner radius of the pad at larger deformations.     

Study of the Tribological Behavior of a Thrust Washer Bearing

This study addresses the mechanisms that distress a flat-faced thrust washer bearing system. This washer bearing system separates a helical gear and its carrier within a gearset. It was found that the bearing can experience distress by the combination of rotational speed, axial load, and the sequence and rate of their application. Distress is defined as a sudden rise in the real-time frictional torque and temperature.

The various tests suggest the presence of hydrodynamic effects at certain rotational speeds and axial load combinations marked by decreases in the calculated effective coefficient of friction with decreases in velocity. In the tested cases, a distinct increase in the coefficient of friction occurs at the instant of distress.     

Incompressible and Analytical Study on an Out-Pump Type Complex Thrust Gas Bearing

ABSTRACT

The structure of an out-pump type thrust gas bearing was described, and an analytical model was developed under completely incompressible condition. The objectives were to investigate the coupling between aerodynamics and aerostatics in a complex thrust gas bearing and to improve the performance of the bearing. The model showed that the load-carrying capacity had five parts to it and that apparently there were pressure coupling and structure coupling between aerodynamics and aerostatics. The surface feature function was identically positive: it increased the load-carrying capacity greatly. There was also no limit regarding the pressure ratio—when the pressure ratio was 0, the load-carrying capacity increased to about 25%.

     

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.     

Dynamic Characteristics and Stability Analysis of a Wavy Thrust Bearing

A numerical procedure to analyze wavy thrust bearings is described. The numerical model is developed by assuming that two circular plates rotate relative to each other. The upper plate is assumed to be flat and rotating, whereas the lower plate is assumed to be stationary and wavy in surface geometry. A Reynolds-equation-based procedure is used to simulate the dynamics engendered by various wavy geometries and loading conditions. The equilibrium position of the journal results from the equilibrium between the forces generated by the fluid-film pressures and the externally applied loads. A numerical small perturbation technique is applied to calculate the linear stiffness and damping characteristics of the bearing at the equilibrium position. Using a three-degrees-of-freedom system with one axial and two rotational displacements, nine linear stiffness coefficients (three principal and six cross-coupled coefficients) and nine linear damping coefficients are calculated. These linear coefficients are then used to calculate the eigenvalues of the system by solving the homogeneous equations of motion. The stability of the bearing system is then expressed using the lowest logarithmic decrement obtained from these eigenvalues. Using this procedure, a parametric study is carried out to examine the effects of external load, location of the applied load, bearing number, and bearing wave amplitude on journal equilibrium position, bearing linear stiffness, damping characteristics, and bearing stability.     

Hydrodynamic Lubrication of Microdimple Textured Surface Using Three-Dimensional CFD

Surface texturing has been recognized to be very efficient in modifying the tribological performances of sliding surfaces. In the present article, a three-dimensional hydrodynamic lubrication model of the incompressible Newtonian fluid is proposed on the textured surface with a single spherical cap microdimple based on the full Navier-Stokes equation. The three-dimensional pressure field and velocity field of lubrication film are obtained by employing the finite volume method (FVM). The effects of geometric parameters and Reynolds number on pressure field, load-carrying capacity, friction force, and friction coefficient are investigated. Numerical simulation led the authors to conclude that the load-carrying capacity of the lubrication film is monotonously enhanced with increasing microdimple width and Reynolds number, and a reverse tendency is obtained for friction force and friction coefficient. The dimensionless optimum microdimple depth increases with the increase of the width and decreases with the increase of the Reynolds in the range of 0.80–2.00, which is responsible for the largest load-carrying capacity and the smallest friction coefficient. It has also been found that the optimum depth becomes a critical value to produce a vortex in the bottom of the dimple. Further analysis indicates that the optimum dimple depth becomes a transition of lubrication mode from hydrodynamic to mixed lubrication for a textured surface with a fixed microdimple.     

水润滑扇形瓦推力轴承润滑性能的边界元分析

用边界元法分析水润滑扇形瓦推力轴承的润滑性能,将雷诺方程转化为类似泊松方程的形式,采用边界元法求解该方程,研制了一套C++计算程序,得到多组轴瓦参数下的水膜厚度、压力分布和相关润滑性能,可以显著降低代数方程组的阶数,从而减少计算所需时间,并可提高计算精度。研究表明瓦块张角和瓦块倾角对最小水膜厚度、最大水膜压力、摩擦功耗、压力中心位置和进水口流量有不同程度的影响,该研究将有助于合理的设计水润滑扇形瓦推力轴承的轴瓦参数。     

锥面螺旋槽推力轴承的有限元解

本文对用牛顿不可压流体润滑的锥面螺旋槽推力轴承进行了理论分析,螺旋角,槽深,槽台对数等不等时,轴承的承载量亦不同。本文用有限元法计算了轴承的膜压分布及承载量。