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RESEARCH PAPERS

J. of Lubrication Tech. 1970;92(4):535-542. doi:10.1115/1.3451467.

Frictional behavior in metalworking processes between the tool and the workpiece for unlubricated condition is discussed. The primary aim of the work was to develop means to predict frictional behavior in terms of which metal flow can be better understood. Experimental and theoretical work has been carried out to determine the important variables of metal working friction. It was found that friction is dependent upon the strength of the workpiece, the pressure, the surface adhesion, and the surface roughness. The pressure-dependence of shear strength based on experimental data is also discussed. Finally, although techniques are available to predict friction, they are dependent upon the ability to predict interface surface temperature.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):543-549. doi:10.1115/1.3451468.

The design, development, and application of a pin-on-disk tribometer for the measurement of friction and friction-induced vibration is described. Careful isolation techniques eliminated many of the errors in measurement which are associated with vibration arising from the apparatus or the surroundings. The use of acceleration, velocity, and displacement transducers in association with a one-cycle sequence triggering circuit and other electronic devices permitted the accurate measurement of kinetic friction forces in the presence of friction-induced vibration.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):550-556. doi:10.1115/1.3451469.

A theoretical and experimental investigation of quasi-harmonic friction-induced vibration is reported. The vibration is of near-sinusoidal form and is solely governed by dynamic friction forces. However, the friction-velocity curve must be of a particular shape for the vibration to occur. The amplitude of the quasi-harmonic vibration is shown to increase with sliding velocity until oscillation ceases at some upper velocity boundary. The introduction of suitable damping will quench the vibration entirely. The vibration can exist at high sliding velocities and as a consequence may influence the operation of automatic transmissions, brakes, and clutches.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):557-564. doi:10.1115/1.3451471.

A new approach to the material cleanliness problem in rolling contact fatigue involving the use of hardened electrolytically deposited iron (or iron-nickel alloy) is discussed. It was demonstrated that the fatigue strength of surfaces prepared by case hardening electrodeposited iron or iron–4 percent nickel can be equivalent to the best of commercial rolling element bearing materials. Three base materials to which the plated material was applied were investigated. These covered a broad range of quality. The associated deposit thickness problem was investigated. Excellent fatigue properties were obtained if the deposit thickness was great enough to avoid fatigue development in the base material. With deposit thicknesses less than this amount, some improvement in fatigue life was obtained over that of the unplated base material.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):567-571. doi:10.1115/1.3451477.

Previous work [4] has suggested a shear stress normal strain “potential” as a means of relating stress condition to fatigue of high-strength low-allow steels. Experimental data here permits the rationalization of the theory required in the prior analysis to be supported directly. An attempt is made to relate highly directed plastic deformations that have been observed in SKF 6309 ball bearing inner rings to directed shear-stress normal-strain configurations of the complex triaxial rolling contact stress cycle in the principal plane of rolling.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):572-577. doi:10.1115/1.3451478.

As a followup to an earlier paper in which a new type of design chart for full journal bearings was given a complete set of design charts for pivoted-pad thrust bearings (Michell bearings) shall now be presented. The dimensionless groups of parameters representing minimum film thickness and bearing traction for one single pad, respectively, have been plotted in a new design chart. Some illustrative examples demonstrating how to use the chart for optimization of pivoted-pad thrust bearings have been included. Some attention has also been paid to the stiffness of the film of lubricant. A design chart for film stiffness has been added to this purpose.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):578-587. doi:10.1115/1.3451479.

By means of numerical techniques, the behavior of a journal bearing of finite length running under steady load, including thermal effects, is investigated with reference to the two simpler models: the “isothermal” and the “adiabatic” cases. Different bearing operating parameters are obtained, which in the latter case are evaluated from the pressure and temperature distributions obtained from the simultaneous solution of the Reynolds and Energy equations. A simplified method, which uncouples the Reynolds and the Energy equations in the oil by neglecting all the pressure terms in the energy equation, is discussed and compared with the more exact numerical method of solving the two equations simultaneously. The case of heat being conducted through metal surfaces is described, with the assumption of zero net heat flow to the journal. In order to shorten the calculations, the uncoupling technique investigated in the adiabatic case is again used and the results obtained are compared with experimental findings.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):588-592. doi:10.1115/1.3451480.

A second order regular perturbation solution for squeeze film flow of a Newtonian fluid between circular parallel surfaces is presented. All the inertial terms are included in the momentum equation. Experimental measurements of pressure in a squeeze film at high squeeze rates are shown to be in good agreement with the solution. The solution is particularly useful in assessing the extent to which fluid inertial effects would cause the classical lubrication theory to be in error for any particular squeeze film. The inertial effects are shown to be functions of two readily determined dimensionless parameters, the squeeze Reynold’s number Res and the squeeze acceleration number A.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):593-596. doi:10.1115/1.3451481.

An analysis is made of the squeeze-film behavior between two annular disks when one disk has a porous facing. The problem is solved analytically. Results are presented for pressure distribution, load-carrying capacity, and film thickness as functions of time.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):597-606. doi:10.1115/1.3451482.

The mechanical simplicity and damping qualities of fluid-film bearings makes them attractive possibilities for spool-shaft bearings of gas turbines. The simultaneous high-speed rotation of journal and bearing, however, causes whirl stability to be a major problem. Computerized analysis was utilized to screen a spectrum of practical candidate configurations. Stability threshold plots were expeditiously generated using accurately determined cross-coupled spring and damping coefficients to represent the bearings. Performance of each bearing type was determined as a function of configuration, ambient pressure, and machined clearance. The selected three-lobe design was further tested with a “time-transient” analysis that accurately traced a complete time history of the motions of the system in its various degrees of freedom.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):607-616. doi:10.1115/1.3451483.

A rather complete heat transfer analysis is carried out for a specific air hydrostatic bearing. The effects of viscosity variation and thermal deformations are included. The result is a prediction of film temperature of the bearing at high speed. Torque and temperature measurements are made on the subject bearing and show fair correlation with the theory.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):617-629. doi:10.1115/1.3451484.

The dynamic and static behavior of a gas lubricated bearing, consisting of stretched foil sectors, is analyzed. General equations describing the fluid film and valid for shaft excursions of the order of the clearance, are derived on the basis of planar motion and negligible fluid inertia. The analysis is then specialized to the case of a bearing consisting of three equally spaced foil sectors. For the static equilibrium condition, tensions and gaps are calculated and graphs are presented. For the dynamic case, the basic equations are linearized, and equations for the in and out-of-phase steady-state response to sinusoidal excitation are derived. This serves as an illustration of foil-bearing dynamic behavior as well as for stability investigation. For the case of zero radial load, the effects of speed, rotor radius, foil thickness, wrap angle, and initial tension on the coefficients of damping and stiffness are graphically presented. Within the range of parameters investigated, the following distinct characteristics of the foil bearing have been found: (a) The bearing is stable. (b) The stiffness coefficient is not sensitive to half frequency excitation nor to excitation of any other frequency. (c) The damping coefficient assumes nearly zero values whenever the ratio of frequency of excitation to frequency of rotation is an integral multiple of π /Θ , where Θ is the wrap angle. (d) In contrast with other fluid-film bearings, the increase in mass has no unstabilizing effect.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):630-647. doi:10.1115/1.3451485.

A 16-in-long rotor, weighing approximately 21 lb, was supported by air-lubricated foil bearings. In physical size and in mass distribution, the rotor was closely matched with that of an experimental Brayton cycle turboalternator unit. The rotor was stable in both the vertical and horizontal attitudes at speeds up to 50,000 rpm. A detailed description of the experimental apparatus and of the foil bearing design are given. The paper contains data of response of the rotor to rotating imbalance, symmetric and asymmetric, and to excitation by means of a vibrator (shake table). It is concluded that the gas-lubricated foil-bearing suspension is free from fractional-frequency whirl and suffers no loss of load capacity when excited at frequency equal half the rotational speed. On contrast with rigid gas bearings, the foil bearing imposes no stringent requirements with respect to dimensional tolerances, cleanliness, or limitations of journal motion within the narrow confines of bearing clearance.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):650-659. doi:10.1115/1.3451488.

A high-speed rotor, supported by gas-lubricated foil bearings, is free from self-excited whirl and displays no loss of load capacity when vibrated at frequency equal half the rotational speed [1]. It is demonstrated here that in addition to tolerance of geometrical imperfections, misalignment, and foreign particles [3, 4], the foil bearing performs well at elevated temperatures and accommodates appreciable temperature gradients. The foil bearing is endowed with superior wipe-wear characteristics, and the flexibility of the foil accounts not only for the stability of the foil bearing but also for its forgiveness with respect to distortion, contamination, and contact.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(4):661-662. doi:10.1115/1.3451492.
Abstract
Topics: Equations
Commentary by Dr. Valentin Fuster

DISCUSSIONS

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