Optimization of the Supporting Surface of a Slider Bearing according to the Load-Carrying Capacity Taking into Account the Lubricant Viscosity Depending on Pressure and Temperature

A technique and implementation of an exact self-similar solution for the problem of a thrust slider bearing that operates in a hydrodynamic mode with an incompressible lubricant is considered, taking into account the viscosity simultaneously depending on the pressure and temperature. Based on the equation of motion of a viscous incompressible liquid for the case of a “thin layer” and the continuity equation, the velocity and pressure fields are found and analytical expressions for the load-carrying capacity and friction force are obtained. It is shown that it is possible to increase the load-carrying capacity of bearings by applying a supporting profile of bearing bushings adapted to hydrodynamic conditions. The effect of the adapted profile of the supporting surface exerted on the main operating characteristics of a bearing is estimated.     

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 Hydrodynamic Lubrication of Slider Bearings

The effect of surface roughness on the performance of hydrodynamic slider bearings is studied. A generalized form of surface roughness characterized by a stochastic random variable with non-zero mean, variance and skewness is assumed to define the bearing surface topography. Various film shapes such as: plane slider, exponential, secant and hyperbolic are considered. The results are obtained for the general lubricant film shape in integral form which are numerically computed for the shapes under consideration. The results are presented both graphically as well as in tabular form. The performance of a rough bearing can be considered in terms of an identical smooth bearing with an equivalent film thickness. It is observed, for the lubricant film shapes under consideration, that the increasing positive values of α, σ and ε decrease the load carrying capacity, frictional force and temperature rise while it increases the coefficient of friction. Increasing positive values of α and ε shift the center of pressure towards the outlet edge. For negative values of α, the increasing value reverses the trend of the effect on performance characteristics which is in conformity with the physical aspects of the problem. A similar trend is observed in case of the effect of negative values of ε. Thus, a negatively skewed surface roughness modifies the performance of the slider bearings whereas the performance of a bearing suffers on account of positively skewed surface roughness. Moreover, it is noticed that in the case of exponential and hyperbolic slider bearings the effect of increasing values of σ is more pronounced whereas in case of plane slider and secant shaped slider this effect is marginal.     

Film height optimization of dynamically loaded hydrodynamic slider bearings

A method is presented to determine the optimal surface shape distribution for a hydrodynamic slider bearing. This is the surface shape distribution that is able to carry a prescribed load while maintaining a maximum separation between the surfaces. This method is first derived for a bearing with constant load and sliding speed. It is subsequently extended for a bearing with periodic load and sliding speed. Results for slider bearings with different shapes, loads and speeds are presented. It is shown that the numerical procedure developed in this paper is numerically more efficient than a reference optimization method.     

Lubrication of a slider bearing with oils containing additives and contaminants

The hydrodynamic lubrication of a slider bearing with oils containing additives and contaminants was studied by taking into consideration the fact that the volume concentration is governed by the equation of mass transfer. By solving numerically the generalized Reynolds and mass transfer equations under appropriate boundary conditions it is shown that both the load capacity and the frictional force of the slider bearing increase with increasing concentration of additives and contaminants.     

Optimal design of one-dimensional porous slider bearings using the Brinkman model

On the basis of the Brinkman model, a theoretical study of the optimal load-carrying capacity and friction coefficient for one-dimensional curved porous slider bearings with the gap width varying slowly is presented. The modified Reynolds equation is obtained by applying Brinkman equations to guide oil motion through the porous matrix. By using the technique of calculus of variations, the optimization is performed over a class of step profiles. According to the analysis, the step height ratio and riser location of the optimal geometry are found to depend upon the permeability parameter of the porous matrix. Compared with the inclined-plane bearing case, the stepped porous slider bearing provides an enhancement in the load-carrying capacity as well as a reduction in the friction parameter. An illustrative design example is also included for engineering and industrial applications.     

Refined simulation of friction power loss in crank shaft slider bearings considering wear in the mixed lubrication regime

Friction reduction is a fundamental factor in decreasing fuel consumption of internal combustion engines. During the design stage of the engine the simulation of friction in the crank mechanism plays a vital role to develop optimum solutions. Due to the interaction of oil and elastic structures with rough surfaces in slider bearings, complex simulation models have to be used for representing the relevant physical behavior. The following article is focused on crank shaft slider bearings of large engines.The article describes a procedure evaluated by measurements showing how to model wear profiles of slider bearings to reach a high quality friction forecast. A fundamental influencing factor of bearing friction is given by the mixed lubrication regime and it is considered in the simulation model as part of asperity contact friction and hydrodynamic friction. Further effects result from the compliance in radial and width directions of the bearing structure and the wear of the bearing surface. Furthermore, the specific operating conditions of the slider bearing such as load, temperature, shaft speed and oil characteristics are essential and have to be taken into account.The objective of this investigation is to propose the wear profile of the bearing surface for the simulation model to be treated iteratively, where simulation results for the amount of mixed lubrication are successively assessed. For this purpose an iterative procedure is introduced and validated by measurements on a slider bearing test rig.The applied simulation method is based on elastic multi-body systems; the lubrication film contact is calculated based on Reynolds differential equation via the pressure balance calculated iteratively in the time domain. The model accounting for the mixed lubrication regime is based on the theory of Greenwood and Tripp.     

Effect of rotation in lubrication problems: A new fundamental solution

An extended theory of hydrodynamic lubrication is derived from the Reynolds equation; the theory takes into account the effects of uniform rotation about an axis that lies across the fluid film. The pressure and load capacity of bearing systems are obtained when the film thickness is a linear or an exponential function of the coordinate along the bearing length. While the load capacity increases with increasing coefficient of fluid viscosity for a plane inclined slider or an exponentially inclined slider using the classical theory, it is independent of the fluid viscosity using the extended theory when rotation is small.     

Experimental Study on Lubrication Film Thickness Under Different Interface Wettabilities

This paper describes some experimental studies about the effect of interface wettability on hydrodynamic lubrication film thickness by a custom-made slider bearing tester. The lubricated contact pair consists of a fixed-incline slider and a transparent disc, and a thin lubrication film can be generated when the disc rotates. The film thickness was measured by interferometry. The wettability of different slider surfaces was evaluated by the contact angle of the lubricant on them. The relationship of film thickness versus disc speed was measured under different liquid–solid interfaces, and the results showed that slider surfaces with strong wettability to the lubricant could generate higher film thickness. Furthermore, case experiments were carried out to validate the hydrodynamic effect by tailored-slippage. By numerical simulations, the experimental findings were tentatively explained with the phenomenon of wall slippage.     

Coupled couple stress and surface roughness effects on elasto‐hydrodynamic contact

This paper deals with the combined effects of couple stress and surface roughness to inspect the elasto‐hydrodynamic performance of slider bearing systems. On the basis of the couple stress Stokes theory and homogenisation method, the homogenised generalised Reynolds equation including the slider bearing stationary surface deformation is derived. The total deformation include the deformation of smooth surface, taken into account by the elastic thin layer model, and the deformation of roughness corresponding to a sinusoidal normal displacement on an elastic half space of identical wavelength. The governing equations are discretised by the finite difference method, and the obtained algebraic equations are solved using the iterative overrelaxation Gauss–Seidel technique. The load‐carrying capacity and friction coefficient are presented for transverse, longitudinal and anisotropic roughness patterns for different values of the couple stress parameter in both rigid and deformable cases. The simulation results indicate that the interaction between couple stress, surface roughness and elastic deformation effects is significant. Copyright © 2013 John Wiley & Sons, Ltd.     

Analysis of the dynamics of a slider-crank mechanism with hydrodynamic lubrication in the connecting rod-slider joint clearance

The conventional slider-connecting rod-crank mechanism is widely applied in mechanical systems. The use of hydrodynamic bearings in the mechanism joints is of particular interest in reducing friction, mainly in special conditions of lubrication such as the connecting rod-slider joint. This bearing belongs to a class of bearings with alternating rotational motion. This paper proposes a mathematical model for this particular problem, considering the dynamics of the slider-connecting rod-crank system interacting with the lubrication phenomenon in bearings with alternating motion. Two models were used to analyze the dynamics of the system. The first model (by Eksergian Equation of Motion) represents the system when the connecting rod end is in contact with the bearing surface, assuming, in this condition, the same behavior as that of rigid bearings (without clearance). The second model (by Lagrange Method) represents the system when the connecting rod end is in the hydrodynamic lubrication mode in the slider bore clearance. In this condition, the slider moves in relation to the connecting rod, presenting a problem of multi-degrees-of-freedom. The mathematic model of hydrodynamic lubrication was introduced to obtain more realistic results of the system's dynamic behavior.     

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.     

Magnetic-fluid-based porous inclined slider bearing

A porous inclined slider bearing, lubricated with a magnetic fluid, in the presence of an externally applied magnetic field which is oblique to the lower surface of the bearing is discussed. The load capacity of the magnetic-fluid-based porous inclined slider bearing is found to be greater than that of a viscous porous inclined slider bearing. It is shown that the magnetic-fluid-based porous inclined slider bearing has a performance superior to that of the viscous porous inclined slider bearing.     

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.     

Numerical simulation and experimental research on passive hydrodynamic bearing in a blood pump

The current research of hydrodynamic bearing in blood pump mainly focuses on the bearing structure design.Compared with the typical plane slider bearing and Rayleigh step bearing,spiral groove bearing has excellent performance in load-carrying capacity.However,the load-carrying capacity would decrease significantly with increasing flow rate in conventional designs.In this paper,the special treatment is made to the upper spiral groove bearing to make sure that both the circulatory flowing and load-carrying capacity are high.Three-dimensional computational fluid dynamics(CFD) models in the space between rotor and shaft are developed by using FLUENT software.Effects of groove number,film height and groove depth on load-carrying capacity of the spiral groove bearings are investigated by orthogonal experiment design.The experimental results show that film height is the most remarkable factor to the load-carrying capacity.The variation tendency of load-carrying capacity reveals that the best combination of geometry is the one with groove number of 8,film height 0.03 mm and groove depth 0.08 mm.The velocity and pressure distributions in spiral groove bearings are also analyzed,and the analysis result shows that the distributions are in conformity with the design of the blood pump based on the principle of hydrodynamic bearing.The displacement of the rotor with the best combination parameters is tested by using laser displacement sensors,the testing result shows that the suspending performance is satisfactory both in axial and radial directions.This research proposes a bearing design method which has sufficient load-carrying capacity to support rotor as an effective passive hydrodynamic bearing.     

Static and dynamic characteristics of finite exponential film shaped slider bearings lubricated with micropolar fluid

Abstract

In this paper, the general dynamic Reynolds equation of sliding–squeezing surfaces of exponential shaped slider bearings with micropolar fluid is solved numerically for the assessment of dynamic characteristics. The two Reynolds type equations governing the steady performance and the perturbed characteristics are obtained using the perturbation technique and are solved numerically using the finite difference method. The results are compared with that of the inclined plane slider bearing. It is found that the exponential shaped slider bearing lubricated with micropolar fluids results in higher steady state film pressure, load carrying capacity and better dynamic stiffness and damping characteristics.     

Non-Newtonian dynamics characteristics of parabolic-film slider bearings: Micropolar fluid model

The non-Newtonian influences of micropolar fluids on the dynamic stiffness and damping characteristics of parabolic-film slider bearings are investigated in the present paper. A closed-form solution for the bearing performances has been derived by applying the linear theory to the equation of the hydrodynamic film force. Comparing with the case of Newtonian lubricants, the non-Newtonian effects of micropolar fluids provide higher load capacities and higher dynamic coefficients. The improved performances are emphasized especially for the bearing with smaller film heights and larger fluid-gap interacting parameters and coupling parameters.     

Effect of environment humidity and temperature on stationary and transient flying responses of air bearing slider

It is well known that the environment humidity and temperature have a significant influence on the flying height of an air bearing slider. However, not many research papers address this topic, especially when the transient flying response is considered. This paper studies the influences of the environment humidity and temperature on both the stationary and transient flying responses of slider by simulation. A slider design for the thermal protrusion application is addressed. The reason for causing the drop of the air bearing pressure is discussed, and the methods for decreasing the drop are proposed. It is observed that the environment humidity and temperature may determine whether the slider is in full flying state or in partial flying/partial dragging state, when the slider is released from a certain height. The reason may be due to the high humidity and temperature which weakens the air bearing. As a result, the air bearing becomes not strong enough to support well the full flying of slider when the influence of the intermolecular force is significant. Slider vibrations for the full flying case and the partial flying/partial dragging case are analyzed in frequency domain, and the slider vibration frequencies are discussed. It shows that the environment temperature and humidity have significant effects on both the stationary and transient flying responses of the slider.     

A numerical method for the calculation of lubricant pressures in bearings with mixed lubrication

A model for mixed lubrication, assuming that the total normal load applied to the plane of the lubricated surfaces is carried partly by the hydrodynamic action of the lubrication film and partly by asperity contacts and that the total friction force between the lubricated surfaces is partly due to viscous friction and partly to asperity contacts, was used to develop a numerical solution for pressure distribution in a bearing experiencing mixed lubrication. The geometry treated and the pressure distribution obtained were for a simple slider bearing, but the method could easily be extended to other shapes. The model is based on measured roughness of a real surface. Real load carrying capacity and drag can therefore be determined since they are related directly to bearing pressure distribution