0


REVIEW ARTICLES

J. of Lubrication Tech. 1970;92(2):185-215. doi:10.1115/1.3451363.

The volume of lubrication literature continued to expand, reflecting the increased experimental and theoretical attention being focused upon this discipline. Eight categories of lubrication technology are summarized by authorities in each particular field. 481 reference publications are included in the review.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS

J. of Lubrication Tech. 1970;92(2):216-219. doi:10.1115/1.3451364.

It is argued theoretically that in normal bearing and squeeze film geometries, when using a nonlinear Maxwell constitutive relation, that elongation and normal stress effects are of minor importance.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):220-226. doi:10.1115/1.3451365.

For 14 chromium steels of different composition and structure, cavitation-erosion damage has been studied and interpreted in terms of structure and strength properties. The use of chambered cylindrical specimens ensured a uniform attack from the very beginning of the erosion process and, thus, highly reproducible wear values. As could be expected on the basis of existing evidence, the duration of the incubation period is a function of the initial condition of the surface, as determined by the finishing process. The reciprocal rate of volume loss, occurring during the first steady-state period (which is characterized by a uniform attack of the surface, without formation of deep craters) (Rc ), turned out to be a linear function of the “true” tensile strength, measured at maximum load. It does not depend on grain size, structure and elongation properties of the material. On the other hand, the tendency toward the formation of craters in the surface and the ratio Rc /R∼ , in which R∼ is the reciprocal rate of volume loss, during the second, and final, steady-state period, are shown to be exclusively determined by structural parameters.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):228-240. doi:10.1115/1.3451368.

Numerical solutions for an isothermal case are presented for the direct extrusion process of a cylindrical body with viscous plastohydrodynamic lubrication at high operating temperature and pressure. The extrusion pressure at die predicted by the present theory, and measured correspondingly by experiment are seen to agree well. As such, this agreement supports the validity of the assumptions in the present theory. For this typical experimental case, the additional data, which are not measured by experiment, are calculated by the present theory. Furthermore, a more fundamental understanding is provided for design data with regard to the interaction of the physical parameters such as extrusion ram speed, percent reduction in area, half of the included die angle, preheat billet temperature, exit pressure of lubricant film, lubricant properties, and extruded materials. These design data are offered in a form whereby they may be applied broadly to a variety of practical direct extrusion processes.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):243-244. doi:10.1115/1.3451372.

The belief that the roughness theory of friction cannot explain frictional heat is shown by a thermodynamic reasoning to be incorrect. The adhesion theory of friction contradicts the modern science of adhesive joints and, hence, is erroneous.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):252-257. doi:10.1115/1.3451379.

A new thermally stable organic resin is described. Results are presented for the development of polybenzimidazole (PBI) resin-bonded solid-film lubricants. These solid-film lubricants are composed of molybdenum disulfide, antimony trioxide, and the PBI resins. Steps followed for mixing, applying, and curing these films are presented. The test equipment and procedures used to test the film formulations are described. Wear-life comparisons to conventional commercially available resin-bonded films qualified under MIL-L-8937 are presented.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):258-263. doi:10.1115/1.3451380.

This paper presents a simple model for the stress concentration around a furrow shaped surface defect in rolling contact. An idealized two-dimensional defect profile, consisting of two curved shoulders smoothly connected to the remaining surface of an elastic half space under compression, is considered. The “undisturbed” stress state in the contacting cross section plane is assumed to be hydrostatic compression, corresponding to the “localized” stress state near the surface in the contact zone of two cylinders in contact. Numerical results are obtained for the contact pressure distribution and subsurface stress (octahedral shear stress). In this solution, which corresponds to the particular undisturbed stress state, the maximum value of the octahedral yield stress occurs underneath the curved “shoulders” of the defect.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):264-272. doi:10.1115/1.3451381.

A study was made of surface roughness effects on dry friction between two metals, assuming that the asperities are cones of the slopes which depend on the surface roughness. The theoretical explanations were offered for coefficients of friction of the hard cones and spheres ploughing along the soft metal surface. A comparison of calculated values based on these with experimental data shows good agreement. Moreover, theoretical discussion was carried out of surface roughness effects on dry friction between two metal surfaces on the basis of the analyses of the frictional mechanism for a hard slider on the metal surface. The theoretical estimation of the coefficient of friction between two metal surfaces can be carried out by using the relations between the surface roughness and the slopes of the asperities, and the coefficient of friction due to the adhesion at the interface. The experiments also showed that when two metal surfaces are first loaded normally and then subjected to gradually increasing tangential forces, real area of contact between them increases and the maximum tangential microslip of them increases with the increase of the surface roughness.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):274-279. doi:10.1115/1.3451385.

A review of the literature establishes that the wear of bonded solid lubricant films for conditions of low average contact stress (say 10,000 psi and below), obeys an equation of the form V = KPL, where V is the wear volume, P is the normal load, L is the total sliding distance, and K is a constant. The limits on allowable bonded film thickness are examined, in the light of this equation, and it is shown that for low contact stress situations optimum film thickness is on the order of 10−3 in., rather than the popularly believed value of 10−4 in. This latter figure is the unfortunate consequence of applying data obtained at very high contact stress to contact conditions which are fundamentally different. Practical aspects of using this equation are explored by the development of specialized expressions which allow a design engineer or engineering analyst to estimate film wear life in terms of hours of operation or number of operating cycles. To aid in this purpose, wear coefficients for common solid lubricant-binder combinations are tabulated. A series of examples show how these expressions can be applied to typical situations. Equations are derived for the contact stress, area of contact, and average contact stress, for solid lubricant film covered surfaces under cylindrical or spherical contact. The use of these equations should replace the use of the Hertz contact equations in analyzing solid lubricated contact conditions.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):281-288. doi:10.1115/1.3451388.

Roller bearing endurance tests have been run on groups of bearings with L10 and L50 lives established by Weibull analysis. Bearing roller path surface finish, shaft speed, lubricant viscosity and lubricant temperature were varied. Relevant tapered roller and cylindrical roller bearing life data was selected from prior tests for comparison. Weibull plots show the effect of the variables on life and a graph comparing the ratio of L10 test life to the calculated life and the ratio of elastohydrodynamic lubricant film thickness to composite rolling contact surface finish is given. An empirical equation to predict the effect of varying lubricant and surface finish conditions on fatigue life is given.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):292-301. doi:10.1115/1.3451394.

In this approach the fundamental hydrodynamic and elasticity equations that govern the problem are reduced to one single integral equation. Although the resulting integral equation in the present problem is at first sight similar in form to the one governing the steady rolling problem, on closer consideration it appears that the former constitutes a different type of equation, which is mainly characterized by the existence of a bifurcation point not occurring in the equation for steady rolling. By proper treatment of this complication, solutions also in the range of conditions where deformation may be expected to be large are obtained.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):303-307. doi:10.1115/1.3451396.
Abstract
Topics: Torque , Bearings
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):310-313. doi:10.1115/1.3451400.

An elastohydrodynamic solution for a high-pressure, low-clearance metal seal is presented. The fluid flow is assumed to satisfy Reynolds equation of hydrodynamic lubrication, and the deformation of the shaft and the seal is governed by the linear theory of elasticity. The viscosity of the fluid is assumed to have an exponential dependence on the pressure, while the density of the fluid is a linear function of the pressure. Closed-form solutions are obtained for two asymptotic limiting cases: (i) when the length of the seal is much greater than the radius of the shaft, and (ii) when it is much less. For intermediate ratios of the seal length to shaft radius, solutions are obtained numerically and examples are given to show the effect of seal length on the rate of mass flow.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):314-317. doi:10.1115/1.3451401.

An extended variational formulation is derived which can be applied to problems in isothermal compressible flow where the medium obeys the perfect gas law. The Reynold’s approximations for fluid film lubrication have been applied to this variational formulation to obtain an expression that is applicable to the field of gas-dynamic lubrication. This variational formulation for gas-dynamic lubrication has as its Euler-Lagrange equation, the Reynolds’ equation of lubrication for a perfect gas. The extended variational formulation is shown to differ from the classical Lagrangian expression with respect to its form and to its applicability to nonlinear problems.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):318-324. doi:10.1115/1.3451402.

The relative importance, with respect to load-carrying capacity, of each geometrical parameter in a self-lubricated thrust bearing, with an enclosed pocket, is examined at Λ = 0.55. The bearing geometries, including the pocket configurations, for three types of film profiles are optimized. The film profiles in the pocket considered are flat-step, tapered, and taper-step, Fig. 1. Of these three profiles of film, the taper-step film, in an enclosed-pocket bearing, offers the best load-carrying capacity. The variations of load versus each geometrical parameter are shown graphically to facilitate design procedure. These results are obtained from the solution of Reynold’s equation for a compressible fluid film as approximated by the finite-difference method [5]. The load-carrying capacity of an enclosed-pocket bearing with taper-step profile can be significantly higher than that of a bearing with the spiral-grooved pattern under the conditions investigated.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):325-334. doi:10.1115/1.3451403.

A small eccentricity analysis was performed for a bearing having two feeding planes, each of which is assumed to be a line source. Numerical results were obtained for a range of bearing number, pressure ratio, feeding parameter, and orifice recess volume by means of a digital computer. Steady-state load and attitude angle were obtained, as well as stability data. Stability decreased markedly with increasing recess volume; moreover, for large recess volume and low bearing number, an increase in pressure ratio decreased stability. There was no correlation between stability and steady-state attitude angle for any of the cases studied. Fair agreement was obtained with available experimental data.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):336-345. doi:10.1115/1.3451406.

Experimental load, stiffness and attitude angle data for a pair of 2 1/2-in-dia, 3 3/4-in-long externally pressurized air journal bearings are compared with two small eccentricity perturbation theories. Results show that load capacity is generally less than predicted by either theory, however, agreement with the small eccentricity pressure perturbation theory is better than with the linearized PH theory. Self-acting effects from journal rotation are greatest at the higher eccentricity ratios and lower supply pressures. Attitude angles vary with shaft speed as predicted by theory but are generally larger in magnitude. Measured air mass flow through the bearings agreed well with calculated values. Results were obtained for speeds up to 25,000 rpm and radial loads varied up to 20.2 psi.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):346-357. doi:10.1115/1.3451407.

An analysis for helical bearings operated in turbulent regime, with negligible inertia in an incompressible fluid film, was performed [10, 11]. The analysis is based on the linearised lubrication theory developed by Ng and Pan [4]. The outlines for this analysis and, in particular, the bearing performance data for various helical groovings are given in this paper. The data presented include the bearing performance at the steady state, the stiffness and damping coefficients, and the critical mass of journal in both laminar and turbulent regimes. To facilitate designs, these data are computed for optimal geometries of helical grooved bearings to provide maximum radial stiffness at various Reynolds numbers. In addition, the effect of external pressurized supply of lubricant are shown in the performance curves.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):359-362. doi:10.1115/1.3451411.

Some factors useful in overcoming excessive air gaps in foil bearings are investigated. Since the gaps of interest are small, the foil bearing equations are modified to include the effects of the molecular mean free path. It is shown that by small corners in the solid wall, one can reduce the air film thickness considerably. A change in curvature with continuous slope has also a marked effect on the film thickness. Theoretical prediction curves allowing the calculation of the air gap as a function of corner angle, change in radius of curvature, and the molecular mean free path are presented.

Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):363-369. doi:10.1115/1.3451412.

The dynamic response of a double squeeze-film thrust plate was analyzed theoretically. Asymptotic approximations were used in calculating the squeeze-film forces. The dynamic response was found to be essentially synchronous; sub-harmonic responses are negligibly small in magnitude. When the squeeze frequency is higher than a critical frequency, the synchronous response is 180 deg out-of-phase with the squeeze motion. This enhances the squeeze action, and thus increases the load capacity and stiffness. The converse is true when the squeeze frequency is lower than the critical frequency.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):307-308. doi:10.1115/1.3451397.
FREE TO VIEW
Abstract
Topics: Torque , Bearings
Commentary by Dr. Valentin Fuster
J. of Lubrication Tech. 1970;92(2):308. doi:10.1115/1.3451398.
FREE TO VIEW
Abstract
Topics: Torque , Bearings
J. of Lubrication Tech. 1970;92(2):308-309. doi:10.1115/1.3451399.
FREE TO VIEW
Abstract
Topics: Bearings
Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In