Oil whip-induced wear in journal bearings

This paper investigates the effect of oil whirl and oil whip in fluid film radial bearings due to possible metallic contact. The degree of metallic contact and thereby wear and tear between rotating shafts and bearing bushes is assessed by measuring electric currents through the oil film. The current as well as the voltage varied in accordance with the contact ratio between the shaft and bush in the fluid film radial bearing. The gauge signal thus indicates the degree of metallic contact based on the thickness of the oil film in the load zone. Some experimental results are provided to illustrate that at low normalised loads involving oil whirl and oil whip, no electric current is detected, while high levels of electric current are registered at high load levels when no oil whirl or oil whip occurred. It is therefore concluded that at low loads, oil whirl and oil whip have little influence on wear and tear in a journal bearing.     

Measurement of wear in radial journal bearings

In this article, the measurement of wear in radial journal bearings is discussed, where a distinction is made between stationary and non-stationary contact conditions. Starting with Holm/Archard's wear law, equations are derived for the calculation of the specific wear rate k of the bearing material as a function of the wear depth d, measured after an experiment or a period of use in practice. It is also possible to calculate a value for the maximum allowable apparent pressure p_a at given values of k, required lifetime and maximum allowable wear depth d, or a value of d at a given value of p_a. In order to facilitate the use of the equations mentioned above, non-dimensional diagrams are presented. Two examples are given to explain the use of these diagrams.     

Mathematical modeling of wear of journal bearings in outer space

The paper deals with a model of the wear process of journal bearings in outer space when they are exposed to significant temperature oscillations. Derived equations and experimental data are used to calculate the kinetics of wear of the bearings.     

The thermohydrodynamic solution of oil journal bearings

An estimate of temperature and pressure of full hydrodynamic journal bearings has been obtained by simultaneous numerical solution of the energy and the Reynolds' equations. Both viscosity and density of the lubricant vary with temperature. The computed results of pressure distribution have been compared with the classical solution (which assumes uniform lubricant properties). The temperature distribution has also been verified with published experimental data. The viscosity and density changes contribute to a small decrease in the load capacity calculated using constant properties.     

Tensile stress in journal bearings

The precise pressure distribution in the range of negative pressure of journal bearings was measured dynamically by a semiconductor pressure transducer fitted in the journal. Characteristics of the pressure distribution in the range of negative pressure were investigated and tensile stress was detected. A special apparatus was constructed to investigate the characteristics of tensile stress generation in lubricating oils. Currently available mineral oils of low viscosity, within a short standing time, were in a condition under which tensile stress could be generated.     

The role of lubricant feeding conditions on the performance improvement and friction reduction of journal bearings

Most conventional hydrodynamic journal bearing performance tools cannot suitably assess the effect of lubricant feeding conditions on bearing performance, even though these conditions are known to affect important performance parameters such as eccentricity and power loss.A thermohydrodynamic analysis suitable to deal with realistic feeding conditions has been proposed. Special attention was given to the treatment of phenomena taking place within grooves and their vicinity, as well as to the ruptured film region.The effect of lubricant feeding pressure and temperature, groove length ratio, width ratio and number (single/twin) on bearing performance has been analyzed for a broad range of conditions. It was found that a careful tuning of the feeding conditions may indeed improve bearing performance.     

Misaligned journal effects in liquid hydrostatic non-recessed journal bearings

The performance characteristics of a capillary-compensated hole-entry hybrid misaligned journal bearing have been studied theoretically. The journal of the bearing is allowed to tilt on an axial plane containing the load vector and on a plane perpendicular to an axial plane containing the load vector. The journal misalignment has been accounted for by defining a pair of misalignment parameters σ and δ. The finite element method has been used to solve Reynold's equation governing the lubricant flow field in the clearance space of the journal bearing. Static and dynamic performance characteristics are presented for the different representative values of the journal misalignment parameters for both hydrostatic and hybrid modes of operation of the bearing. The bearing performance characteristics are also compared for the two hole-entry bearing configurations so as to facilitate the selection of a suitable bearing configuration by the designer. The study suggests that the journal misalignment significantly affects the performance of the hole-entry journal bearing, and for a more accurate prediction of the bearing performance it must be considered in the analysis.     

Non-newtonian squeeze films in journal bearings

Non-newtonian behaviour, which occurs in various lubrication problems, was studied using a power law model. The geometry considered was that of a journal bearing. Bearing characteristics i.e. the load capacity and the response time, were obtained for full-journal and half-journal bearings and were compared with each other. As the flow behaviour index n increases the load capacity ratio and the response time ratio decrease.     

Experimental study of journal bearings with undulating journal surface

A journal bearing test rig was designed and constructed to test the behaviour of journals with wavy surfaces, the circumferential undulations being varied both in amplitude and in number. Results show that wavy journal surfaces may well enhance the load carrying capacity of a bearing. Moreover, surface undulations are shown to move the journal centre locus closer to the load line, ie cause a lower attitude angle. These effects are found to be more pronounced with larger wave amplitudes, and with higher numbers of waves around the journal circumference. In general, friction is found to be reduced with increase in surface wave amplitude.Good agreement is shown to exist between test results and a computer aided analysis conducted by the authors to predict wavy journals performance¹. It has been established that a wavy journal surface may, under certain conditions, display higher load capacity, lower friction and permit safer running of journal than bearings with perfectly smooth surfaces.     

Abrasive wear of rolling bearings

Various mechanisms of microslip are discussed; abrasive wear is considered the most important. An equation to predict the wear rate of rolling bearings is presented, based on previous work, and illustrated by an example     

The contact pressure distribution in the friction region of miniature journal bearings

The contact pressure distribution in miniature journal bearings is theoretically studied taking into consideration the friction between the contacting surfaces of the journal and the bearing bush. The experimentally confirmed formulae for the contact pressure distribution, the angle of contact and the ratio of the maximum contact pressure to the bearing contact pressure are derived. The contact pressure distribution may be described with a parabolic function.     

Comparative tribological evaluation of journal bearings

Performance of sliding bearings with reeled bimetallic bushes of three different bronzes was compared with the performance of solid bushes of aluminium alloy with a view to replacing aluminium bushes in gear pumps by reeled bimetallics. a set of tribological selection criteria was proposed and comparative investigations were carried out.     

Lubrication of finite porous journal bearings

An analytical solution is attempted for a finite porous bearing, press-fitted into the housing and working with a full film of lubricant. The pressure distribution is determined by a simultaneous solution of Reynolds equation for the film and the Laplace equation for the bearing material while maintaining the continuity of pressure at the film-bearing interface.The pressure in the bearing material and film are taken in series form so that all the boundary conditions are satisfied. Using a suitably truncated series, the modified Reynolds equation is then solved by the Galerkin method. It is shown that two dimensionless parameters—(1) the permeability parameter and (2) the thickness to breadth ratio ($\text{H}\text{b}$)—adequately describe the operation of these bearings. Numerical calculations for all the bearing characteristics were carried out by digital computer. The results are tabulated so that designers can interpolate values required.The results indicate the progressive reduction in Sommerfeld number with permeability parameter; the dimensionless coefficient of friction and the attitude angle progressively increase with permeability parameter.     

Experimental investigation of hybrid journal bearings

Experimental pressure distribution measurements in hybrid journal bearings are presented and the influence of inertia forces in the recess outlets and pressure generation in the pockets for high rotating speeds are shown. These results are in good agreement with the theoretical results given by an established model.     

Acoustical properties of hydrodynamic journal bearings

Results of theoretical investigations on acoustical properties of hydrodynamic journal bearings are presented. Nonlinear analysis including rotor imbalance is performed for a rotor-bearing system in order to obtain acoustical properties of the bearing. Furthermore, a cavitation algorithm, implementing the Jakobsson–Floberg–Olsson boundary condition, is adopted to predict cavitation regions in a fluid film. Acoustical properties are investigated through frequency analysis of pressure fluctuation calculated from the nonlinear analysis. Results show that the acoustical frequency spectra of the fluid film are pure tone spectra, containing the frequency of the shaft rotation and its super-harmonics. The analysis also shows that super-harmonics are predominant at the neighborhood of the fluid film reformation and rupture regions.     

Thermal considerations in the solution of finite journal bearings

The full journal bearing of finite length is solved for the thermohydrodynamic case in which the energy transmitted by conduction is included. The three-dimensional temperature distribution and the pressure distribution are numerically obtained. The operating parameters of the bearing are calculated and are compared with those obtained from the classical adiabatic solution. The effect of the consideration of temperature variation across the film thickness on bearing performance is investigated.     

Thermodydrodynamic analysis of multi-arc journal bearings

A technique for analysing liquid-lubricated multi-arc journal bearings is described which includes a thermohydrodynamic analysis of the oil film and heat conduction in the bearing housing. Results from a computer program based on the method are compared with experimental data for a two-arc bearing. Good agreement between theoretical and experimental temperatures is achieved     

Rapid performance evaluation of journal bearings

This paper describes a rapid method for evaluating the significant design parameters such as load capacity, maximum pressure, flow, power loss, and maximum temperature in the oil film. The proposed analytical pressure expression is a modification of that given by Reason and Narang. An analytical expression for maximum pressure is presented. The accuracy of the proposed modification is validated up to an eccentricity ratio of 0.99. The effective temperature rise, which depends on the fraction of heat generation carried away by lubricant, is chosen to be a function of the eccentricity ratio. An expression for maximum temperature, based on existing experimental findings, is given. A journal bearing design table is provided to help the designer without the involvement of numerical and mathematical complexities.     

Feed pressure flow in plain journal bearings

The purpose of this short technical note is to update the literature on feed pressure flow in plain bearings and to give a summary of suitable equations for predicting such flows. The work is part of a detailed study of feed pressure flow¹.