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RESEARCH PAPERS

J. of Lubrication Tech. 1982;104(4):439-447. doi:10.1115/1.3253244.

In this paper the results of experimental investigations of the effects of radial taper on mechanical face seals are presented and compared to theory. The previously published theory considers the effects of thermal taper caused by a temperature gradient in the seal rings; mixed friction in the case where load support is shared between hydrostatic support and partial contact of the seal faces; surface roughness, which affects both load sharing and leakage; and wear, which alters the radial profile. Fifteen tests were run using a 100 mm diameter carbon versus tungsten carbide seal at 1800 rpm and 3.45 MPa in water. Test duration was up to 100 hr. Varying amounts of radial taper were used. Tests were run at balance ratios of 1.00 and 0.75. Initial and final surface profiles were recorded. Seal torque, leakage, and face temperatures were recorded as functions of time. Results show that theory predicts initial torque and leakage as functions of initial taper quite well, given knowledge of seal surface characteristics. Predicted equilibrium thermal taper as a function of torque for a balance ratio of 1.0 is good. For a seal having a balance ratio of 0.75, predicted equilibrium thermal rotation shows some agreement but more experimental data are needed. The results of 1.00 balance ratio tests suggest that after a long period of operation, any initial taper will be worn away and the seal would continue to operate as a parallel face seal. Results from long-term tests indicate that the wear coefficient is not a constant. While the experimental results support the basic concepts of the model, the results show where further work must be done to better understand the role of surface roughness and wear processes in mechanical face seals.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):449-453. doi:10.1115/1.3253248.

The behavior of seal-ring in the shaft seal which operates on oil film to seal high pressure gas is studied. The experiment on the 60 cm diameter seal-ring shows the slow whirl phenomenon, i.e., the local oil film thickness and that temperature varies with the period of about 100 seconds. The analytical model is formulated and predicts the oval deformation of seal-ring due to hot spots, and that the oval shape rotates slowly but periodically according to the shift of hot spots. Theoretical predictions are confirmed to agree well with the experiment. Also, the effects of some design parameters are described to prevent the relevant slow whirl.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):455-459. doi:10.1115/1.3253252.

This paper describes an experimental program concerned with the elasto-hydrodynamic behavior of sliding elastomeric seals for the Stirling engine. During this program, an experimental apparatus was designed, built, and used to measure the oil film thickness distribution. For this oil film thickness measurement, an optical interferometric procedure was developed. Tests were conducted on commercial elastomeric seals having a 76 mm o.d. Testing conditions included seal durometers of 70 and 90, a sliding velocity of 0.8 m/s, and no pressure gradient across the seal. An acrylic cylinder and a typical synthetic base automotive lubricant were used. The work produced a first-time comparison of analytical and experimental oil film profiles for an elastomeric seal in a reciprocating environment. This comparison shows an overall qualitative agreement.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):460-468. doi:10.1115/1.3253255.

The dynamic behavior of a noncontacting coned face seal is analyzed for the case of a rigidly mounted rotating seat and a flexibly mounted stationary ring taking into account various design parameters and operating conditions. The primary seal ring motion is expressed by a set of nonlinear equations for three degrees of freedom. These equations, which are solved numerically, allow identification of two dimensionless groups of parameters that affect the seal dynamic behavior. Stability maps for various seals are presented. These maps contain a stable-to-unstable transition region in which the ring wobbles at half the shaft frequency. The effect of various parameters on seal stability is discussed and an approximate expression for critical stability is offered. The theoretical model assumes frictionless flexible mounting of the seal ring such as in metal bellows. However, the results for critical stability can also be used as an upper limit for cases when friction in the secondary seal is present.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):469-476. doi:10.1115/1.3253258.

A general analysis and computational method is presented for calculating the unbalance and self-excited response of high-speed rotor-bearing systems. The analysis is applied to the calculation of the transient response of a rotor supported by two floating ring bearings. Included in the analysis are rotor gyroscopic moments as well as the flexibility of the shaft. Emphasis is placed on determining rotor whirl orbits as influenced by rotor unbalance, the phase angle of the unbalance masses, the clearances of the bearings, the viscosity of the lubricant, and the shock loads that the rotor may be subjected to. It is found that the rotor-bearing system normally operates in an unstable mode in the linear stability sense. However, the nonlinear forces developed by the fluid films of the floating ring bearing will bring the rotor-bearing system to whirl at a limit cycle well within the clearance circles. It is also shown that the rotor assembly will undergo a conical motion when the rotor and wheel configuration is asymmetrical.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):478-487. doi:10.1115/1.3253261.

Novel “offset” designs offer greatly improved durability and reduced power loss in applications for which conventional journal bearings are only marginally satisfactory. They are particularly attractive for duty cycles which combine nonreversing loading with limited angular oscillation. Production applications presently include piston-pin / cross-head bearings for two-stroke Diesel engines. The present analysis combines impedance concepts with a generalized short bearing film model for partial arc bearings. A numerical example compares performance of offset and conventional designs for a specific application.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):491-496. doi:10.1115/1.3253267.

This paper deals with an analysis of the dynamic behavior of compensated hydrostatic circular step thrust bearings taking into account fluid inertia and recess volume fluid compressibility effects. The Reynolds equation for fluid film and the recess flow continuity equations are linearized using perturbation methods. Results in terms of dimensionless load capacity, oil flow rate, stiffness, and damping are presented for capillary and orifice compensated bearings. Results show a marked influence of fluid inertia and recess volume fluid compressibility on the performance of the bearing.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):497-502. doi:10.1115/1.3253268.

This paper presents both theoretically and experimentally determined characteristics of an oil squeeze film. In the experimental arrangement, an oil film was contained within two plane surfaces having only normal oscillatory relative motion. The effects of initial oil film thickness, peak to peak amplitude, and frequency of oscillation were measured. A finite difference treatment gave theoretical oil pressure fields and forces for any specified normal velocity. Comparisons were made between the pressure measured at one position and its theoretical counterpart over an oscillatory cycle. Subzero oil film pressures were measured. A steady state (in addition to the dynamic) oil film force was identified, whose magnitude and direction depend on the mean oil film thickness, oscillatory amplitude, and frequency. A region of unstable behavior was found. Theory agreed reasonably with practice, but over estimated some oil film pressures and gave time histories which exhibited phase differences with the measured counterpart. These differences were not explained by including the measured pad misalignment in the theoretical model. Further extensions to the theory are suggested.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):504-508. doi:10.1115/1.3253271.
Abstract
Topics: Lubrication , Pistons
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):510-515. doi:10.1115/1.3253274.

The momentum equations are written for viscous fluids exhibiting magnetic stresses. The velocity profiles are deduced; then from continuity, a pressure differential equation, equivalent to Reynolds equation is obtained. This equation is discussed with emphasis on the case when magnetic stresses derive from a potential, also when the pyromagnetic coefficient vanishes. The boundary conditions for lubrication problems are then formulated. In particular, short bearings with ferromagnetic lubricants are considered. A numerical example yields the pressure diagrams at low and moderate eccentricity ratios and for different speeds. In conclusion, it is shown that ferromagnetic lubricants may improve substantially the performance of bearings operating under low loads and/or at low speeds. However, a correct variation of the magnetic field, toward the center of the lubricated area, is required. Under such conditions, the extent of the active area of the film is increased and bearing stiffness and stability are improved.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):516-522. doi:10.1115/1.3253277.

It is shown that amplitude and phase spectra should not be used to assess the quality of estimates of oil-film coefficients unless the results are interpreted in conjunction with a sensitivity analysis of the bearing model. The implications of using only the amplitude spectrum are discussed. Sensitivity analysis is shown to give valuable insight into the problem of selecting test signals for estimating oil-film coefficients. Moreover the analysis gives an indication of the validity of the model structure.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):523-529. doi:10.1115/1.3253278.

The advantages of operating multistage axial compressors on 4 pad tilting pad bearings are discussed and compared to other fixed bore and tilting pad bearing designs. These advantages include operation free of subsynchronous vibration and, with between pivot loading, placement of peak response speeds well outside of the operating speed range. Examples of analytical design studies of 3 actual rotor systems are presented and discussed to illustrate the design recommendations. Test stand results are also included for 3 axial compressors to help substantiate the analytical results.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):533-537. doi:10.1115/1.3253282.

Three dimensional surface signatures were calculated from radial profile measurements of two lapped specimens, two ground specimens and a milled specimen. These signatures are polar autocorrelation function (ACF) maps and Ra maps. The ACF maps were obtained by plotting contours of equal autocorrelation values. The ACF maps reveal more structure than the Ra maps and their shapes appear to be characteristic of the corresponding manufacturing methods. Therefore, radial profile measurement together with the use of ACF maps is a useful technique for relating surface topographies to manufacturing processes.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):538-544. doi:10.1115/1.3253283.

This paper deals with the influence of the metallurgical parameters of dies and sheet on the friction shear-stress which could be measured by P.S.C.T. The metallurgical parameters of the dies have a marked effect on the kinetics of formation of transfer layers. The metallurgical parameters of the sheet have an effect both on the kinetics of formation, and the chemical nature of the transfer layers. Many parameters must be controlled to have good reliability in PSCT. Then the results can be correlated with boundary lubrication in cold rolling.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):545-551. doi:10.1115/1.3253284.

The Plane Strain Compression Test is used to measure the mean friction shear stress at the sheet-die interfaces. It is found that the shear-stress level is strongly influenced by transfer film formation on the dies. The thickness of these films, and their elementary chemical composition, have been determined by Auger Electron Spectroscopy and rugosimetry. The effect of contact mechanics and lubricant parameters on transfer film formation is discussed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):552-557. doi:10.1115/1.3253285.

The lubricating behavior of polytetrafluoroethylene, polyvinyl chloride, polychlorotrifluoroethylene, low density polyethylene, and high density polyethylene powders in the extrusion of 1100-0 aluminum has been investigated in terms of the extrusion force requirement and the quality of extrudate surface finish. Extrusion experiments which provided a measure of the extrusion force and friction force with varying ram travel were performed under both ambient and high temperature conditions. From these data the variation of coefficient of friction with ram travel and normal pressure has been calculated using the analysis based on von Mises’ yield criterion and spherical velocity fields. The effect of polymer powder particle size on the extrusion force was investigated. The extrudate surfaces were examined by scanning electron miscroscopy in order to study the film formation capability of polymers and to get an insight into the mechanism of polymer lubrication.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):559-567. doi:10.1115/1.3253288.

The friction coefficients and wear rates of two dry-bearing materials have been measured during oscillatory motion at different amplitudes. The materials were composites incorporating fabrics of interwoven PTFE and glass fibers and differed in the pitch of the glass fiber at the surface. The worn surfaces were examined by SEM, EPMA, and XPS. The results show that when the amplitude of oscillation becomes less than the glass fiber pitch, third-body debris films on the counterface become increasingly nonuniform and surface roughness increases. The resulting trend toward increased bearing liner wear, however, is small provided that the amplitude of oscillation remains constant. The relevance of the results to the operation of airframe dry bearings operating under active control is discussed.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):568-574. doi:10.1115/1.3253289.

Theoretical analyses for the lubrication of rigid wedge-shaped asperities by a viscoplastic liquid are developed. Two cases are considered in which wedge action and squeeze action are dominant. The results of the analyses are compared with previous experimental investigations of the factors influencing susceptibility to lubrication failure.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):575-581. doi:10.1115/1.3253290.

An effort is made to functionally connect the morphology of a surface damaged by friction with the sequence of events leading to the damage. The connection between a destructive situation and the resulting morphology is established. The reverse connection, i.e., the use of the morphology as a diagnostic tool, is not complete, mainly because some of the characteristics suggestive of the mechanisms are erased. Still, for cases of one friction pass, e.g., on a spiral track friction machine, the reverse connection is also established.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1982;104(4):582-588. doi:10.1115/1.3253293.

This paper describes an experimental and analytical investigation of the temperatures and deformations which occur during a single traverse of a steel blade tip over a flat, smooth, fully-dense copper surface. Experimental work was carried out on a pendulum-type test device, with forces, rub energy, surface temperature, and residual deformation being determined for each single-pass rub test. An analytical model was developed for studying the thermal and mechanical factors influencing surface temperature in these single-pass rubs. The analytical surface temperature predictions were verified by the experimental results.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

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