Numerical investigation of pocketed slip slider bearing with non-Newtonian lubricant

Boundary slip as well as surface texturing is an effective method to improve the tribological performance of lubricated mechanical components. This article analyzes the combined effect of single texturing (pocketing) and wall slip on pressure that strongly related to the load-carrying capacity of slider bearing. The modified Reynolds equation for lubrication with non-Newtonian power-law fluid is proposed. The equation was solved numerically using a finite difference equation obtained by means of the micro-control volume approach. Further, numerical computations for slider bearing with several power-law indexes were compared with the presence of the pocket and slip. The numerical results showed that the characteristic of non-Newtonian is similar to Newtonian fluid with respect to hydrodynamic pressure distribution. The maximum load support is achieved when the pocket depth is equal to the film thickness.     

An analytical approach for analysis and optimisation of slider bearings with infinite width parallel textures

This paper introduces an analytical approach to study the textured surfaces in hydrodynamic lubrication regime. For this purpose, a method of integrating the Reynolds equation for slider bearings with surface discontinuities is presented. By introducing appropriate dimensionless parameters, analytical relations for various texture profiles in both indented and projected forms are delivered. These relations express the nature of mathematical dependence between textured bearing performance measures and geometrical/operational parameters. An optimisation procedure is employed to achieve the optimum texturing parameters promoting maximum load capacity, load capacity to lubricant flow rate ratio and minimum friction coefficient for asymmetric partially textured slider bearings.     

Thermal diagnostics of friction in self-lubricating radial slider bearings with swinging movement: Part 1. Algorithm for determination of power function of heat generation

It is proposed to find the moment of friction in a slider bearing undergoing oscillatory motion by the solution of the inverse boundary problem of frictional heat generation on the values of temperature measured in the vicinity of a friction zone. Basic boundary value problems and relationships for construction of the algorithm to determine the specific power of heat generation are obtained.     

A study of optimum load-bearing capacity for slider bearings lubricated with couple stress fluids in magnetic field

A theoretical study of slider bearings in general form is presented, considering the lubricant to be an isothermal, incompressible electrically conducting couple stress fluid in the presence of a uniform magnetic field. An expression for a modified Reynolds equation is derived in order to obtain pressure gradient in terms of inlet–outlet (IO) film height ratio (simply IO film ratio) of slider bearings. As a special case, a study of the IO film ratio of four particular types of slider bearings is analysed. For the study of optimum load capacity, three-dimensional geometry has been assumed in order to consider side flow. Values of maximum load capacity for various values of couple stress and magnetic parameters, and the corresponding IO film ratio of the four bearings are obtained numerically, and a comparative study of these values has been presented. A comparative study of optimum load-carrying capacity for finite and infinite slider bearings has also been made. It is observed that both the values of maximum load capacity and the corresponding IO film ratio depend on couple stress and magnetic parameters and the shape of bearings conjointly. The present results are also compared with the similar available data in Newtonian cases.     

Non-Newtonian effects on the dynamic characteristics of one-dimensional slider bearings: Rabinowitsch fluid model

The non-Newtonian effects of an isothermal incompressibe laminar-flow lubricant on the dynamic stiffness and damping characteristics of one-dimensional slider bearings are theoretically examined. On the basis of Rabinowitsch fluid (cubic equation) model, the modified Reynolds equation considering bearing-squeeze action is derived to take into account the transient motion of the slider, and the non-Newtonian properties of lubricants. Applying a small perturbation technique, both the steady-state performance and the dynamic characteristics are evaluated. According to the results, the steady film pressure, load-carrying capacity, and the dynamic stiffness and damping behaviors are significantly affected by the values of the dimensionless nonlinear factor accounting for non-Newtonian effects, the wedge parameter of a slider profile and the squeeze number of bearing-squeeze action.     

Effects of magnetic fields on the dynamic characteristics of wide parallel step slider bearings with electrically conducting fluids

By the use of electrically conducting fluids as lubricants together with the application of externally magnetic fields, the dynamic lubrication problems of parallel step slider bearings lubricated with a nonconducting fluid are extended in this paper. A closed‐form solution has been derived for the magneto‐hydrodynamic characteristics of wide parallel step slider bearings. Comparing with the bearing lubricated with nonconducting fluids, the magneto‐hydrodynamic parallel step slider bearings signify an improvement in the load capacity, as well as the dynamic stiffness and damping coefficients. A numerical example and calculated values are also provided in tables for engineers in bearing selection and designing. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of surface roughness on the static characteristics of inclined plane slider bearing: Rabinowitsch fluid model

In this paper, a theoretical study of the effect of surface roughness on the static characteristics of inclined plane slider-bearing lubricated with Rabinowitsch fluid is analysed. Christensen’s stochastic theory for the lubrication of rough surfaces has been used for the derivation of generalised stochastic Reynolds-type equation. The two types of one-dimensional roughness patterns (Longitudinal and Transverse) are considered. Expressions for pressure, load carrying capacity, frictional force and coefficient of friction are obtained. It is found that the presence of transverse roughness pattern on the bearing surface increases pressure and load carrying capacity. Results are well agreement with smooth case.     

The effect of texture shape on the friction coefficient and stiffness of gas-lubricated parallel slider bearings

Surface texturing is used to increase hydrodynamic pressure and reduce friction and wear between gas-lubricated parallel sliding surfaces in a variety of applications. The shape, geometry, and density of the patterned microtexture features (“dimples”) play a key role in the tribological performance of textured slider bearings. In this paper we evaluate the friction coefficient and stiffness of gas-lubricated textured parallel slider bearings as a function of six different texture shapes. The texture geometry and density are optimized in terms of minimum friction coefficient and maximum bearing stiffness for each individual texture shape, and then compared relative to each other. The ellipsoidal shape is found to yield the minimum friction coefficient and the highest bearing stiffness, independent of the operating conditions.     

Investigation on MoS2 and graphite coatings and their effects on the tribological properties of the radial spherical plain bearings

With constant enlargement of the application areas of the spherical plain bearings, higher quality lubrication of the bearings is required. To solve the lubricating problems of spherical plain bearings under high temperature, high vacuum, high speed, heavy loads and strong oxidation conditions, it is urgent for us to develop more excellent self-lubricating technologies. In this paper, the bonded solid lubricant coatings, which use inorganic phosphate as the binder, the mixture of MoS2 and graphite with two different weight proportions as the solid lubricant, are prepared by spraying under three different spray gun pressures. The bonding strength tests on the coatings show that the best spraying pressure is 0.2 MPa and the better mixing proportion of MoS2 to Graphite is 3:1. Then for the radial spherical plain bearings with steel/steel friction pair, after the coatings are made on the inner ring outer surfaces, the friction coefficient, the wear loss and the friction temperature of the bearings under four oscillating frequencies are investigated by a self-made tribo-tester. The test results, SEM of the worn morphologies and EDS of worn areas show that tribological properties of the bearing are obviously improved by the bonded solid lubricant coatings. When sprayed under the spray gun pressure of 0.2 MPa, the bearings have better anti-friction and anti-wear properties than those sprayed under 0.1 MPa and 0.3 MPa. Further as proved from the XPS analysis, between the coating with 3:1 mixing ratio of MoS2 to Graphite and the coating with 1:1 ratio, the former has less oxidation occurred on the surface and therefore has better tribological characteristics than the latter. This paper provides a reference to developing a new product of the radial spherical plain bearings with high bonding strength, oxidation resistance and abrasion resistance.     

Numerical investigation of the combined effects of slip and texture on tribological performance of bearing

Slider bearings are used in many applications. An increase in the load support may allow for saving of energy. In this work, in order to enhance the load support and decrease the friction force, a combined textured surface bearing using boundary slip is discussed. A modified Reynolds equation with slip is adopted. With the main goal of evaluating the effects of slip and texture, a parametric analysis is performed. For the given operating conditions, texturing features as well as slip pattern are analysed in detail. The numerical analysis is undertaken under the condition of different gap ratio values and the slip-textured area. The results show that combined techniques of slip and texture have a significant effect on the improvement of the tribological performance of bearing, that is, a high load support but low friction force. The gap ratio of the bearing is shown to have a significant effect on the lubrication behaviour. It is found that even with a smallest gap ratio (parallel gap), a high load support can be produced. However, it is also shown that the gap ratio appears to contribute to the generated friction force and the volume flow rate more than the boundary slip. Further analysis indicates that the optimum slip-text zones for certain gap ratio are highlighted. These findings may provide references for designing hydrodynamic-textured slider bearing considering boundary slip.     

A new approach to measure the friction coefficient of micro journal bearings

A new approach and relevant test rig to measure the friction of micro journal bearings are introduced in this paper. The micro bearings under the load of milliNewton scale can be tested to indicate their tribological behavior. The test rig has the following features. (1) The separated bearing halves are attached to the journal with a soft string wrapped around them. The string is strained in a vertical line with the upper end located at a beam and the lower end hanged with a standard weight, which supplies pressure between the bearing and the journal, without bending the spindling journal. (2) The frictional force of the rotating journal on the bearing halves will result in a difference between the forces at the two string ends. (3) This force difference can be sensitively detected by strain gauges on the beam. Therefore, the micro friction between the bearing and the spinning journal can be detected and indicated.     

静压支承球铰副支承反力的求解

提出了一种基于静压支承原理的球铰副的设计方法,并对该摩擦副油膜支承反力进行了求解,为高速高压轴向柱塞泵的设计提供了一定的理论依据。     

Design effects on the fretting wear behaviour of ball bearings

A change in design of a ball bearing is described based on the results of numerical and experimental analysis to reduce fretting wear. Increasing the radii of curvature of the inner and outer races by a small amount reduces the product of the relative slip δ and the tangential traction τ at the contact region, both of which are caused by Heathcote slip. This results in the consequent reduction in fretting wear because there is a good correlation between the amount of fretting wear and τδ. This prediction is confirmed experimentally by increasing the groove radius of the inner race from 4.02 to 4.21 mm for a ball of radius 3.97 mm.     

小孔节流深浅腔动静压轴承承载特性解析研究

小孔节流深浅腔动静压轴承是一种采用小孔节流器实现节流作用及浅腔实现二次节流作用的动静压混合轴承。针对现有理论不能解析研究油腔结构参数及工作参数对承载特性影响规律的不足,以及计算流体力学数值仿真软件计算时周期长,而不便于工程设计人员应用的缺点,基于油腔压强分段线性化的思想,建立分析小孔节流深浅腔动静压轴承的油腔压强、承载能力、静刚度、进油流量及温升等承载特性的解析方法。进而以该方法研究动静压轴承的供油压强、主轴转速、进油孔径、浅腔深度、初始油膜厚度等参数对轴承承载特性的影响规律。研究发现,在其他结构参数及工作参数一定的条件下,浅腔深度为初始油膜厚度的2～3倍时,轴承刚度接近最大、温升接近最低。通过油腔压强的解析值与试验值的比较,证实了该方法的有效性和研究结果的正确性。     

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.     

一种新型齿形滑块机械式自动抓具的设计

为完成核电工程中固体废料更换和转运,设计了一种新型的机械式自动抓具。主要阐述了抓具采用齿形滑块机构和连杆机构设计,在无外动力的条件下可自动抓取和释放固体废物,实现了抓力自锁,可靠性高、抓爪形式可变、适用性广等特点,特别对放射性、有毒、缺氧等恶劣工作环境具有很好的应用价值。     

Influences of the geometrical parameters of aerostatic thrust bearing with pocketed orifice -type restrictor on its performance

This paper describes the study on the performance of aerostatic thrust bearing with pocketed orifice -type restrictor. Firstly, the performance of the bearings with different geometrical parameters was simulated and some experiments were made to verify the simulations. Then, the rational dimension of this kind of bearing is obtained by analyzing the influences of the bearing's geometrical parameters on its load carrying capacity (LCC), stiffness, mass flow rate (MFR) and the maximum gas velocity (MGV). Therefore, the design and optimization of the bearing is simplified, and further analysis shows that ignoring the influences of orifice length on the bearing's performance will result in large errors, when orifice diameter is small enough.