The usual laboratory tests of lubricants do not indicate to what degree a given oil may possess the important property of “oiliness,” a property, apparently independent of viscosity, upon which the ability of an oil to maintain lubrication between two surfaces under high pressure seems partly to depend and by which some sort of extremely tenacious and adherent thin layer of oil is held on one of or both the rubbing surfaces so that metal-to-metal contact is in part prevented. Oiliness is of special importance in metal-cutting operations and in some machine parts, such as gear teeth or cams under heavy loads, in which the pressures between the surfaces are far in excess of those permitted in plain bearings.
With a view to investigating the behavior of various lubricants, cutting compounds and bearing materials under high bearing-pressures, a special machine has been designed, of which a description is given and data are presented. These, however, are said to be rather illustrative of the results obtainable than indicative of the exact characteristics of the materials used. Tests were made to determine the points at which noticeable abrasion takes place; the adaptability of different cutting-oils to different metals; the approximate magnitude of the pressures involved; the effects of the speed of the rubbing surface, of temperature and of varying the amount of lubricant on the coefficient of friction; and the comparative friction-reducing properties of vegetable, animal and mineral oils.
Among the conclusions reached are that (a) with smooth and accurate grooves and balls, consistent and reproducible results can be obtained; (b) decided differences in the friction-reducing properties of different oils occur below the point of noticeable abrasion; (c) above this point the friction varies widely as the rubbing surfaces wear and no consistent values of the coefficient of friction have been obtained; and (d) the character of the abrasion seems to be related to the nature of the lubricant.


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