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Bearing test machines with dynamic loading or nonuniform motion are described in this paper and classified according to the type of loading employed. Over thirty such machines have been disclosed in the published literature, including both endurance machines and research machines for investigating oil-film performance. The authors have endeavored to find answers to six questions concerning each machine—(a) its loading mechanism, (b) test bearing details, (c) range of variables, (d) performance criteria, (e) characteristic limitations or advantages, and (f) extent of use.

This paper describes an engine-bearing test machine consisting of a motor-driven modification of a commercially available diesel engine. The machine combines the advantages of engine operation with those of a standardized test machine. It was developed primarily for endurance testing of engine-bearing materials and design. A rating system is described for evaluating the extent of various kinds of failure elements so that bearings may be compared without testing them to destruction. Test results and the use of an oil-film-thickness indicator also are described briefly.

This paper deals with the physics of lubrication. The principal purpose is to set up certain general relations which may be taken as a guide in the planning and interpretation of experiments to secure data for design. Readers interested only in results available for immediate use are referred to the discussion of the Ideal Bearing in Section V. That part of the paper is intended merely as an illustration of the way in which the foregoing general relations may be applied to particular cases, but the results are doubtless applicable as a first approximation to bearings of whatever type.

A new general program for experimental work and publications recently formulated by the Committee is outlined in this report, and is followed by a brief statement of results already accomplished. Particular attention has been given to the coordination of data obtained by various investigators on viscosity under high pressure, to the study of pressure distribution in the oil film as applied to both thrust bearings and journal bearings, and to the development of methods for measuring oiliness. From experiments on the flow of liquids through very fine glass and platinum capillaries, it appears that the ordinary laws of viscosity may safely be relied upon down to a film thickness at least as small as one-millionth of an inch. The report concludes with a brief review of recent European investigations.

This investigation completes a solution, undertaken by K. G. Karlson in his little-known Swedish paper of 1926, for the oil-film thickness between gear teeth. Karlson’s problem is characterized by the use of a parabolic curve for the viscosity-pressure relation. The numerical results here obtained are comparable with those previously published by Gatcombe, who used a more conventional viscosity-pressure formula. It is hoped that the present analysis will help to clarify the assumptions and calculations required in the hydrodynamic theory of gear-tooth lubrication. As an aid to its practical application, the relative film thicknesses found for geometrically similar pairs of gears are here shown by a chart constructed in terms of the appropriate dimensionless variables, and extending from zero to 10 microinches per in. of pitch diameter of the pinion. The limiting case of a lubricant whose viscosity is unaffected by pressure, for which an analytical solution had been given by Karlson, is represented by a straight line on this chart.

This brief paper is based upon a full report of certain experiments conducted for the ASME Research Committee on Lubrication. The experimental work comprised friction measurements under imperfect lubrication conditions up to loads of 10,000 psi or more. Eight lubricants were compared whose viscosity-pressure characteristics were known. A Kingsbury oil-testing machine was used, with bearing surfaces designed to eliminate hydrodynamic action so far as possible. A condition of mixed lubrication prevailed, in which rapid wear of brass on steel occurred simultaneously with hydrodynamic effects. All tests were run well to the left of the familiar minimum point on the coefficient-of-friction diagram. Three methods of plotting the data were tried: (a) The direct plot of friction per unit area against load per unit area, holding the speed and viscosity constant; (b) a conventional plot of the coefficient against Z1N/P, where Z1 is the viscosity at atmospheric pressure, N the speed, and P the load per unit of projected area; and (c) a modified diagram in which each of the foregoing curves is replaced by a family of curves with different values of the pressure-viscosity parameter. This parameter, the product of load per unit area by the pressure coefficient of viscosity, helps to explain earlier discrepancies and to set up a better correlation. The usual contrast between friction of fatty and mineral oils was confirmed, and it was concluded that boundary lubrication and wear are accompanied by hydrodynamic action on a microscopic scale.

Rolling friction was increased by flange contact and by sand or leather on surfaces. It was but slightly decreased by water. It could be increased by a thick oil film and decreased by a thinner one. Increasing the wheel hardness diminished rolling friction. Roughness raised static resistance with little effect on kinetic.