Load Carrying Capacity Of Bearing Research Articles

Load carrying capacity of a heterogeneous surface bearing

Abstract It has been shown before that liquids can slip at a solid boundary, which prompted the idea that parallel-surfaces bearings can be achieved just by alternating slip and non-slip regions in the direction of fluid flow. The amount of slip at the wall depends on the surface tension at the liquid–solid interface, which in turn depends on the chemical state of the surface and its roughness. In the present study a heterogeneous surface was obtained by coating half of a circular glass disc with a coating repellant to glycerol. A rotating glass disc was placed at a known/calibrated distance and the gap was filled with glycerol. With the mobile surface moving from the direction of slip to non-slip region it can be theoretically shown that a pressure build up can be achieved. The pressure gradient in the two regions is constant, similar to that in a Rayleigh step bearing, with the maximum pressure at the separation line. The heterogeneous disc was placed on a holder supported by a load cell thus the force generated by this pressure increase can be measured accurately. Tests were carried out at different sliding speeds and gaps and the load carried was measured and subsequently compared with theoretical calculations. This allowed the slip coefficient to be evaluated.

The effect of manufacturing tolerances on the load carrying capacity of large diameter bearings

This paper deals with simplified 3D finite element (FE) analysis on the effect of manufacturing tolerances on the load carrying capacity of large diameter bearings based on Hertz theory. The nonlinear connector elements are used to model the rolling elements. This model enables us to evaluate the contact load on the rolling elements with relatively reduced calculation time. FE study has been carried out by allocating tolerance on balls and raceways using Monte Carlo simulation technique. The variation in dimension on balls is taken as per IS 2898-1976. A coding has been developed and employed for Monte Carlo simulation. Using the results of Monte Carlo simulation, tolerance has been assigned to the elements of large diameter bearing. From the results of finite element analysis, it is identified that analysis of large diameter bearing with tolerance on ball and raceway will lead to safe design.

The Effect of Rotational Speed on Fluid Compressibility and Gap Pressure of a Partially Porous Aerostatic Thrust Bearing

This study investigated the effect of the spindle speed on pressure distribution in the air gap and the load carrying capacity of a porous aerostatic annular thrust bearing. Based on the finite volume method and the pressure-velocity coupling scheme of the SIMPLE algorithm with the standard k-ε turbulent model, a CFD software was used to solve the Navier-Stokes equations to calculate pressure and velocity of the air flow. The results revealed there were positive pressure zones and vacuum pressure zones in the air gap between the thrust disk and the bearing. Under the same spindle speed, the pressure difference between the positive peak and the negative peak in the case of incompressible air was greater than that in the case of compressible air. The averaged pressure on the surface of the thrust disk with compressible air flow was higher than that with incompressible air flow. So was the load carrying capacity of the bearing, which increased when the spindle rotated faster.

Optimization of molecularly thin lubricant to improve bearing capacity at the head-disk interface

A molecularly thin lubricant layer (of the order of 1---2 nm thick) has been shown to provide bearing forces at the interface between contacting solid surfaces under light loads and high shear rates. This phenomenon is important, for example, in the head-disk contact in magnetic storage hard disk drives to ensure that some of the contact is sustained by the lubricant layer and thus avoiding damage of the solid surfaces. The magnitude of the normal and tangential bearing forces that the lubricant layer can provide depends on temperature, viscosity of the lubricant, sliding velocity and radius of gyration of the lubricant molecules. This study shows that viscosity has the greatest effect on the load bearing capacity of the molecularly thin lubricant. Thus, by controlling the flash temperature and the ratio of molecularly thin lubricant-to-bulk viscosity, the bearing load carrying capacity of the layer can be controlled. This would allow for the contact to be sustained within the mobile lubricant layer, avoiding solid contact so as to protect the diamond-like carbon coating, and thus reduce wear and potential catastrophic failures.

Study of TiO2 Nanoparticles as Lubricant Additive in Two-Axial Groove Journal Bearing

Load carrying capacity of an oil lubricated two-axial groove journal bearing is simulated by taking into account the viscosity variations in lubricant due to the addition of TiO2 nanoparticles as lubricant additive. Shear viscosities of TiO2 nanoparticle dispersions in oil are measured for various nanoparticle additive concentrations. The viscosity model derived from the experimental viscosities is employed in a modified Reynolds equation to obtain the pressure profiles and load carrying capacity of two-axial groove journal bearing. Results reveal an increase in load carrying capacity of bearings operating on nanoparticle dispersions as compared to plain oil.

The Importance of the Heat Capacity of Lubricants With Nanoparticles in the Static Behavior of Journal Bearings

Nanoparticle additives increase the viscosity of lubricants, thus being an interesting solution for improving the load carrying capacity of hydrodynamic bearings. But, nanoparticles also change the thermal properties of the lubricant. Would these thermal properties be important to the static characteristics of lubricated bearings? The answer is yes, being the volumetric heat capacity an important parameter. In this work, the static behavior of journal bearings is studied when nanoparticles are added to the lubricant. A thermohydrodynamic analysis is performed with oil ISO VG68 (base fluid) and six different nanoparticles are considered as additives: Si, SiO2, Al, Al2O3, Cu, and CuO. The numerical results show that the bearing load capacity can be increased up to 10%, not only because of the higher viscosity, but also because of the higher volumetric heat capacity of the lubricant with nanoparticles. Higher volumetric heat capacity of the lubricant decreases temperature development in the bearing gap, thus resulting in higher viscosity distribution for the same operating conditions. In fact, the best results were obtained with ISO VG68 + copper oxide (CuO), whose volumetric heat capacity is the highest among the tested nanofluids. Such results were not equaled when only the viscosity of the lubricant had been changed.

CFD Investigation of Influences of Reverse Textures on Bearing Surface of a Journal Bearing

It has always been the subject of interest and research to find out most efficient method to minimize the frictional loss of any mating surface in any mechanism. But it has been identified that only improvement of lubricating material cannot help much. For this reason research on design modification was started and still going on to optimize the design of mating surfaces so that losses be minimum. In this paper a research has been done on the design of bearing surface of a journal bearing. Journal bearing is a very important part of many machines specially turbines used in Power generation and rolling mills used in steel making sectors. By modifying the design of the bearing surface, load carrying capacity of a journal bearing can be increased and thus its performance can be improved. It is proved by many researches that, by putting cylindrical dimples on bearing surface the performance of a journal bearing can be increased. To measure the performance of a journal bearing three parameters are usually used. Those are, (i) Load Carrying Capacity, (ii) Frictional resisting force and (iii) Ratio of Frictional resistance and Load carrying capacity, which is called Frictional coefficient. In this work a modification has been done on the work of Cupillard. Cupillard considered only the cylindrical dimples for the sake of manufacturing simplicity, but in this work a different configuration of dimple has been considered and its influence on bearing performance has been studied.

Studying The Effect of The Surface Roughness on the Maximum Eccentricity Ratio and The Load Carrying Capacity in The Journal Bearing

The focus of this investigation is to study the effect of the two dimensional isotropic surface roughness of both , journal and bearing on the maximum eccentricity ratio and the load carrying capacity of the finite length plain journal bearing , on the basis of full film lubrication regime to reduce the wear and heat produced by friction to extend the machine element life , in the steady state operation conditions. The appropriate equation to predict the suitable minimum film thickness which include the surface roughness is used . The Conventional Reynolds equation in two dimensional forms are solved numerically . The change of viscosity due to temperature and pressure , using adiabatic solution ,were taken into account. To investigate the effect of surface roughness on the maximum eccentricity ratio value and load capacity , it was assumed that there are two surfaces smooth and rough and are compared with each other . The results of this work show that the increase of the surface roughness case the maximum eccentricity ratio decreases at L / D ratios of 0.5 , 1 at range of roughness 0.3 – 1.2 Mm , which means that the limit of bearing to work with a steady state , full film lubrication . The load ratio at L / D = 0.5 is greater than at L / D = 1 for clearance ratio 0.001 , 0.002 . The surface roughness have no influence on the bearings that have 90 mm diameter or larger at clearance ratio 0.002 .

A New Structural Stiffness Model for Bump-Type Foil Bearings: Application to Generation II Gas Lubricated Foil Thrust Bearing

A new structural stiffness model for the compliant structure in foil gas bearings is introduced in the first part of this work. The model investigates the possibility that the flat segment between bumps, in bump foil strip, may deflect laterally and separate from the rigid bearing surface, and it also considers the interaction between bumps in the bump foil strip, the friction between the bump foil, and the surrounding structure. The validity of the analytical solution was verified through direct comparison with previous numerical and analytical models. In the second part of this work, the introduced bump foil model is used to investigate the static characteristics of generation II gas foil thrust bearing. The numerical simulations of the coupled fluid-structure interactions revealed that the foil thrust bearings share many features with their rigid bearing counterpart and the results showed clearly that the load carrying capacity of foil thrust bearings increases nonlinearly with the rotation speed and is expected to reach an asymptote as the rotation speed exceeds a certain value. The effects of ramp height and interface friction (i.e., friction at bump foil/rigid bearing interface and bump foil/top foil interface) on the static characteristics of generation II foil thrust bearings are investigated.

Static characteristics of a fluid film bearing with TiO2 based nanolubricant using the modified Krieger–Dougherty viscosity model and couple stress model

Static characteristics of a journal bearing operating on TiO2 based nanolubricant is obtained by a variable viscosity approach. The predicted shear viscosities of TiO2 based nanolubricant at different volume fractions and aggregate particle sizes are obtained using modified Krieger–Dougherty model and are found to be in good agreement with experimental shear viscosities. The modified Reynolds equation considers the Krieger–Dougherty viscosities and couple stress effects of TiO2 nanoparticle additives at different volume fractions and particle sizes. Results reveal a significant improvement in load carrying capacity of journal bearing operating on TiO2 based nanolubricant as compared to plain oil without TiO2 nanoparticles.

Load Carrying Capacity of Adiabatically Lubricated Thrust Bearings with Various Film Profiles

The effect of various film profiles on the load carrying capacity of adiabatically lubricated fixed pad thrust bearing is analyzed in this work. One dimensional film thickness profiles such as taper, polynomial, catenoidal, exponential and truncated cycloidal are employed here to predict the load carrying capacity of the fixed pad thrust bearings. Results are computed for various levels of speeds (5m/s, 15m/s, 25m/s) at two levels of viscosity (0.5Pas, 0.05Pas). The shape of the film profile do influence the load carrying capacity of the thrust bearings and the polynomial film thickness profile has the maximum influence when compared to other film profiles.

A Variable Viscosity Approach for the Evaluation of Load Carrying Capacity of Oil Lubricated Journal Bearing with TiO2 Nanoparticles as Lubricant Additives

Influence of TiO2 nanoparticle lubricant additive on the load carrying capacity of a journal bearing is studied. Increase in lubricant viscosity due to presence of TiO2 nanoparticles is modelled using a modified Krieger-Dougherty viscosity model. Validity of modified Krieger-Dougherty model in simulating the viscosities of TiO2 nanoparticle dispersions in engine oil is experimentally verified. The pressure distribution and load carrying capacity are theoretically evaluated using a modified Reynolds equation for various TiO2 nanoparticle concentrations and aggregate sizes. Results reveal an increase in load carrying capacity of journal bearing using TiO2 nanoparticle lubricant additive as compared to plain oils without nanoparticle additive.

Effects of manufacturing errors on tribological characteristics of 3-D textured micro- thrust bearings

The performance sensitivity of textured micro- thrust bearings to manufacturing errors is investigated by means of Navier–Stokes Computational Fluid Dynamics simulations, for incompressible isothermal flow. Bearings of optimized geometry are modelled as three-dimensional micro-channels, consisting of a smooth moving wall, and a stationary wall exhibiting periodic rectangular dimples. Discrepancies in the size and shape of the texture geometry, as well as macroscopic errors in the stationary surface (concavity/convexity and waviness) are considered and parametrically modelled. The effects of manufacturing errors on the bearing load carrying capacity and friction coefficient are analyzed, for representative width-to-length bearing ratios. In a number of cases, manufacturing errors result in improved performance of textured micro- thrust bearings.

EXPERIMENTAL STUDIES OF PRESSURE DISTRIBUTION IN TILTING PAD THRUST BEARING WITH SINGLE CONTINUOUS SURFACE PROFILED SECTOR SHAPED PADS

The effect of the film shape on the load carrying capacity of a hydrodynamically lubricated bearing has not been considered an important factor in the past. Flat faced tapered bearing and the Raileigh's step bearing of constant film thickness have been the primary forms of film shapes for slider bearing studies and design data developments. There are indications in the literature that surface profiling/texturing can have significant and positive influence on the load carrying capacity of hydrodynamic pad thrust bearings. Therefore, the objective of this paper is to compare the experimental results of pressure temperature distributions in slider bearing with flat surface and with different single continuous surface profiled (Cycloidal,Catenoidal,Quadratic) sector shaped pads. Pressure results presented in this paper can provide a platform for validation of theoretical models. An experimental study has been performed to investigate the influence of single continuous surface profiled sector shaped pads in tilting pad thrust bearing. It has been found that with cycloidal shaped surface profiled sector shaped pads the pressure generated within fluid film is enhanced which in turn causes enhancement in load bearing capacity of hydrodynamic bearing.

Mathematical Background of U-joint Repair

AbstractThe universal joint – U-joint is type of mechanical coupling which consists of two shaft yokes connected with cross. The cross arms rides inside four needle bearings pressed into the yokes bores. With good lubrication and sealing, the life of U-joint is determined by material fatigue after more than million reversals. However, U-joint often does not achieve its predicted (calculated) fatigue life. When the lubrication is inappropriate and/or the sealing is not efficient enough, the U-joint service life is limited by the corrosion and wear. As U-joint loses its operational ability due to intensive wear it has to be replaced by a new one or to be repaired. The U-joint repair implies additional machining of worn out needle bearing parts. Therefore, dimensions are changed and entire needle bearing internal geometry is changed, as well. The internal geometry affects dynamics and load carrying capacity of the needle bearing, and appropriate geometrical and mathematical relations, primarily based on limited radial and circular internal clearance, must not be disturbed by repair process. Hence, it is necessary to establish a mathematical model of the needle bearing internal geometry and the corresponding algorithm for determining appropriate dimensions and it was carried out in this paper. This is the basis for further mathematical modelling of U-joint needle bearing dimensions, mechanical behaviour and load distribution, in order to optimize the geometry and increasing load carrying capacity.

Influence of Surface Texture on Lubrication Performance of Hydrodynamic Journal Bearing

A finite-difference numerical model is used to study the influence of surface texture on lubrication performance of hydrodynamic journal bearing. Reynolds equation is adopted to calculate the bearing load carrying capacity, friction force and friction coefficient under different width-diameter ratio, different eccentricity ratio and different texture location. Results show that partial texture along the circumferential direction on the bearing with small width-diameter ratio will increase bearing performance appreciably. Partial texture along the axial direction will decrease friction coefficient effectively, especially at the film inlet zone or the position of film pressure trending to zero.

Geometry Optimization of Textured Three-Dimensional Micro- Thrust Bearings

This paper presents an optimization study of the geometry of three-dimensional micro-thrust bearings in a wide range of convergence ratios. The optimization goal is the maximization of the bearing load carrying capacity. The bearings are modeled as micro-channels, consisting of a smooth moving wall (rotor), and a stationary wall (stator) with partial periodic rectangular texturing. The flow field is calculated from the numerical solution of the Navier-Stokes equations for incompressible isothermal flow; processing of the results yields the bearing load capacity and friction coefficient. The geometry of the textured channel is defined parametrically for several width-to-length ratios. Optimal texturing geometries are obtained by utilizing an optimization tool based on genetic algorithms, which is coupled to the CFD code. Here, the design variables define the bearing geometry and convergence ratio. To minimize the computational cost, a multi-objective approach is proposed, consisting in the simultaneous maximization of the load carrying capacity and minimization of the bearing convergence ratio. The optimal solutions, identified based on the concept of Pareto dominance, are equivalent to those of single-objective optimization problems for different convergence ratio values. The present results demonstrate that the characteristics of the optimal texturing patterns depend strongly on both the convergence ratio and the width-to-length ratio. Further, the optimal load carrying capacity increases at increasing convergence ratio, up to an optimal value, identified by the optimization procedure. Finally, proper surface texturing provides substantial load carrying capacity even for parallel or slightly diverging bearings. Based on the present results, we propose simple formulas for the design of textured micro-thrust bearings.

Combined influence of streaming potential and substrate compliance on load capacity of a planar slider bearing

In the present study, we investigate the combined interplay of streaming potential and substrate compliance with sliding dynamics on the load carrying capacity of a planar slider bearing. We relax previously utilized simplifying assumptions to model the electrokinetic effects and demonstrate that the streaming potential may augment the load carrying capacity of the bearing to a considerable extent. Interestingly, we also reveal that the electrokinetically augmented load carrying capacity exhibits strong dependencies on a combination of the compliance and the sliding dynamics, which have, hitherto, not been extensively explored. This rich interplay reveals certain parametric regimes of interest, which are significant from the viewpoint of practical design considerations.

Performance Study of Aerostatic Bearings with Arrayed Microhole Restrictors

Micro-vibration of aerostatic bearings has been the bottleneck in the improvement of the moving and positioning accuracy of ultra-precision fabrication and metrology equipments. In this study, a new type of aerostatic bearing restrictor has been proposed. The prototype of arrayed microhole restrictor, instead of the conventional single hole restrictor was developed with the aim of reducing the harmful micro-vibration of aerostatic bearings. Computational fluid dynamics (CFD) was employed to numerically calculate the air flow field. It is found that the employment of arrayed microhole restrictors can reduce the amount of micro-vibration while maintain the load carrying capacity and stiffness of the aerostatic bearing. Experimental measurement of the micro-vibration confirms the effectiveness of this new type of restrictor.

English

An Analysis is performed on load carrying capacity, friction variable and flow coefficient of micro elliptical textured journal bearing. In which texture density and texture depth are varied for better performance of journal bearing. Here elliptical dimples are used. For different texture depths, different performance characteristics are tested.When texture density and texture portion are concerned, there is increase in load carrying capacity has been observed with increase of texture density or texture portion and further Increase in flow and decrease in friction variable has been observed.