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RESEARCH PAPERS

J. of Lubrication Tech. 1973;95(4):401-416. doi:10.1115/1.3451843.

An interdisciplinary systems analysis is presented for high-speed gas turbine engine mainshaft roller bearings which will enable the designer to meet the demands for ever higher rotative speeds and operating temperatures. The latest elastohydrodynamic experimental traction data are included. Analytical results cite a need for better definition of the rolling friction portion of the total traction. A fluid mechanics model for the detailed analysis of fluid drags is developed based upon a turbulent vortex-dominated flow and includes the effect of lubricant flow through the bearing. A complete thermal analysis including dynamic and thermal effects upon bearing dimensions and resulting clearances is also included. Heat transfer coefficients are given in detail. Shaft power loss and cage slip predictions as a function of load, speed, and lubricant supply correlate well with available experimental data.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):417-423. doi:10.1115/1.3451844.

In EHL, the oil film thickness of rollers is controlled by the rate at which the oil is drawn into the conjunction of the disks by the moving surfaces of the rollers. The theory often assumes isothermal conditions in the inlet although it can be shown that the maximum shear rate often exceeds 106 sec−1 , even in pure rolling. A theoretical analysis is presented for the oil temperature rise in the inlet of rollers, and the result is applied to predict the consequent film thickness. It is found that thermal effects on film thickness are only negligible at low rolling speeds. A comparison with experiment supports the conclusion that the thinning of the film thickness below that predicted by isothermal theory is substantially explained by inlet shear heating of the lubricant.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):427-432. doi:10.1115/1.3451848.

Mechanical behavior of surface-coated bearing materials is analyzed and the possibilities of high tensile and shear stresses, which may lead to ultimate cracking of the coating, is investigated. An analysis for the stress distribution in layered elastic solids subjected to an arbitrary boundary loading is presented in terms of Fourier transforms of the Airy stress function. Stresses at the layer substrate interface as obtained by normal elliptical pressures at the layer surface are compared with those obtained by true pressure profiles. It is shown that for most cases the analysis for stress distributions in the materials of the layered solid may be performed by assuming an elliptical pressure at the boundary. However, the parameters for the ellipse should be obtained from the general solution to the contact problem. It is shown that extremely high tensile stress may be developed in the layer when the layer is relatively rigid compared to the substrate. Also, the shear stresses on the layer surface can induce high tensile stresses in the layer. These stresses will generally be responsible for brittle fracture or rupture of surface coatings used in many bearing applications.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):434-445. doi:10.1115/1.3451852.

Stability tests were conducted with 3.8 centimeter-(1.5 in.-) diameter, 3.8 centimeter-(1.5 in.-) long, fixed geometry hydrodynamic journal bearings in water at 300 K (80 deg F) with zero load. Five fixed geometry bearings were rated in order of diminishing stability as follows: (1) three-tilted-lobe bearing (offset factor of 1.0), (2) herring-bone-groove bearing, (3) one-segment, three-pad, shrouded Rayleigh-step bearing, (4) three-tilted-lobe journal with axial grooves (offset factor of 1.0) mated with a plain bearing, and (5) three-centrally-lobed bearing with axial grooves (offset factor of 0.5). Maximum stability in lobed bearings and journals is achieved when the lobes are tilted so that the points of minimum film thickness occur near the trailing edges. The herringbone-groove journals had a maximum stability (maximum fractional frequency whirl onset speed) when the groove to ridge clearance ratio was closest to 2.1, as predicted by incompressible flow theory. The one-segment, three-pad shrouded Rayleigh-step bearing configuration was the most stable of the four step-bearing configurations tested. The tilted-lobe journals mated with plain bearings were unique in that, in some tests, the bearings could be run to a shaft speed twice the shaft speed at which initial fractional frequency whirl occurred before any sign of bearing distress was observed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):447-456. doi:10.1115/1.3451856.

A theoretical analysis including linear perturbation is presented, investigating the stability against fractional frequency whirl (“oil whip”) for a symmetrical rotor supported in plain journal bearings or in floating-ring journal bearings operating with an incompressible lubricant under laminar fluid film flow conditions. In order to improve the conventional theoretical model of the bearing behavior, emphasis is put on the effect on stability of the considerable viscosity gradient which can arise in the bearing film due to film friction. The results are presented in the form of design data diagrams for the two bearing types. In the area of practical interest, the average effect on stability arising from the consideration of the viscosity gradient can be characterized as moderate. Concerning the floating-ring bearing superior stability characteristics are obtained primarily from correct choice of clearance ratio.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):457-468. doi:10.1115/1.3451857.

A linear stability analysis is carried out for a porous thrust bearing considering only the axially symmetric mode of oscillation. It is found that the stability characteristics of the bearing are determined by three competing mechanisms, namely, the compressibility of the lubricant, the mass of the bearing, and the viscous resistance to the thin film flow. To avoid pneumatic hammer, the bearing should be designed to be light weight and to operate at the smallest possible film thickness and supply pressure.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):469-476. doi:10.1115/1.3451858.

This paper investigates the adequacy of the theoretical model in predicting the unbalance response of a rotor supported in hydrostatic gas-lubricated journal bearings. The magnitude of experimental whirl amplitudes induced by applying various unbalances to a rotor supported in hydrostatic journal bearings were measured and compared to the theoretical predictions. Variables investigated were rotor unbalance, rotor speed, and bearing supply pressure. Reasonable agreement between the experimental and theoretical results was obtained.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):478-483. doi:10.1115/1.3451861.

Properties of MoS2 refined by chemically processing molybdenite from a copper-bearing ore are compared to those of MoS2 from the primary commercial material in the United States. The properties include crystal structure, chemical composition, oxidation resistance, and lubricating ability in bonded solid lubricant films. Both materials have the same crystal structure and similar chemical compositions. However, the chemically processed MoS2 does not have the carbon impurities present in the other MoS2 . This new material performed just as well as the commercially available MoS2 in three types of bonded solid lubricant films in wear-life tests.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):484-489. doi:10.1115/1.3451862.

Earlier work by others concerning the effects of striated roughness and grooving upon the load-carrying capacity of lubricating films is summarized, substantiated, and generalized. A multiple-scale double-variable technique is used on such lubrication problems for the first time. The present analysis applies to one-face roughness having striation wavelengths sufficiently long for the applicability of Reynolds equation. Transient effects are included. The final differential equation for support pressure is simple in form. In addition to predicting the effects of striated “Reynolds roughness”, this equation can be directly used in grooved-bearing design.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):490-498. doi:10.1115/1.3451863.

The gyro system under consideration consists of a hollow porous sphere supported in a hydrostatic gas-lubricated spherical bearing. High pressure gas leaking into the sphere through the pores from the bearing film pressurizes the inside of the sphere and is exhausted from a series of Hero jets located around the equator to counter the viscous drag from the bearing and maintain a constant speed. Analysis has been presented for predicting equilibrium speed, flow rates, and stiffness for axisymmetric condition as a function of various dimensionless system parameters representing porosity, drive nozzles, inlet feeding holes, supply pressure, etc. Effects of the various system parameters on the performance of the gyro are illustrated. A preliminary feasibility study has been made for a wide angle and a narrow angle bearing. It is found that the small angle bearing is less subject to lock-up without significant loss of stiffness, but suffers from a lower speed and a less efficient gas utilization. A particular design will represent a compromise between stiffness and speed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):499-510. doi:10.1115/1.3451864.

An analytical investigation of both a simplified and a comprehensive mathematical model of a spiral groove face seal, using the “narrow seal” approximation. The sealing fluid is assumed to be incompressible and Newtonian. The inertial effects associated with seal curvature are incorporated in the comprehensive model. The results of the analysis are programmed for computer computation in order to facilitate their application in parametric design studies. Performance characteristics are calculated for some particular seal designs.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):511-517. doi:10.1115/1.3451865.

An analysis is given for the hydrodynamic lubrication of short porous metal bearings that are press-fitted into a solid housing. An exact solution is given for the pressure of the lubricant in the bearing material using modified Bessel functions and the modified Reynolds equation for the problem is solved by the Galerkin method. Numerical results obtained on a digital computer indicate a progressive reduction in the load capacity and increment in the friction parameter and attitude angle as the permeability parameter is increased. These results are presented in graphical and tabular forms. A side result of this analysis is the emergence of a new permeability parameter and its convenience in bearing selection is discussed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):518-523. doi:10.1115/1.3451866.

The experimental work of Beavers, et al., established that velocity slip takes place over a permeable boundary. The presence of slip flow is taken into account while deriving the appropriate modified Reynolds equation that governs the flow of lubricant in a finite porous bearing. The performance of a thin-walled bearing is then analyzed making use of the narrow bearing approximation. It is found that slip flow adversely affects the load capacity and reduces the friction force on the journal; the attitude angle, however, is not significantly affected. Also the analysis indicates that the effects of velocity slip are prominent when the bearing operates at a lower eccentricity ratio and/or the bearing-matrix has a low permeability.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):524-532. doi:10.1115/1.3451867.

Inertia and temperature effects in entrance flow between parallel flat plates are investigated with the use of boundary-layer theory. In addition, an approximate theory is developed which is implemented by a “gas table” similar to that employed for conventional Fanno-line computations.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):546-552. doi:10.1115/1.3451875.

Oil feed rate is an important parameter governing the operating characteristics of a journal bearing. In the present paper investigation is carried out to explore the effect of oil groove location and supply pressure on the oil feed rate to the bearing. These results are further used to get variation in Sommerfeld number and attitude angle for different oil groove locations and supply pressures. The results indicate that oil groove location has a great influence on oil feed rate to the bearing. It is also observed that oil supply arrangement does not have a significant influence on Sommerfeld number and attitude angle.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

TECHNICAL BRIEFS

J. of Lubrication Tech. 1973;95(4):535-536. doi:10.1115/1.3451870.
Abstract
Topics: Temperature
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):536-538. doi:10.1115/1.3451871.
Abstract
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):539-541. doi:10.1115/1.3451872.
Abstract
Topics: Flow (Dynamics) , Heat
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1973;95(4):543-545. doi:10.1115/1.3451874.
Abstract
Commentary by Dr. Valentin Fuster

BOOK REVIEWS

J. of Lubrication Tech. 1973;95(4):553. doi:10.1115/1.3451876.
FREE TO VIEW
Abstract
Topics: Corrosion
Commentary by Dr. Valentin Fuster

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