The lubrication of rollers

Abstract

When lubricated rollers are run together they are separated by a hydrodynamically formed oil film. The thickness of this film has been measured by a capacitance method up to loads of 1000 Lb. per inch of face (1.76 x 10 3 dyn cm - 1 ) for conditions of pure rolling and for conditions of rolling with sliding such as exist at the contacts of gear teeth. It has been found, at low loads, that the film thickness varies inversely with load and proportionately with speed, as simple hydrodynamic theory suggests, but that the actual thickness is approximately one-half of the theoretical thickness. At higher loads, of greater practical importance, the film thickness is shown to be of the order 1u (-4x10 -5 in) which is greater than that predicted by simple theory. Experimental evidence is presented that this failure of the simple theory is due to the increased viscosity of the oil under pressure and to the deformation of the surfaces by the load. The film thickness, at practical loads, has been found to vary little with load, less than proportionately with speed but to vary greatly with the temperatures of the surfaces. Estimates of the temperature reached by the oil in its passage through the conjunction of the surfaces have been made from measurements of the electrical resistivity of the oil. This temperature, which depends upon load and the peripheral speeds and which may exceed 250° C, appears to have little influence upon the film thickness. From this it is argued that the film thickness is largely determined by the conditions, on the entry side of the conjunction, ahead of the region in which the viscous losses and heating of the oil become intense.

Electrical Methods for the Evaluation of Lubrication in Elastohydrodynamic Contacts

“…Experiments carried out by Siripongse et al [9,10], voltage discharge, and Crook [11], electrical resistance have shown that a continuous lubricant film can form even in the conditions of extremely large pressures generated in nominally line and point contacts. Siripongse and co-workers focused their study on the relation between the voltage/current characteristics and film thickness in line contacts [9] and point contacts [10].…”

“…In a series of papers intended to elucidate the mechanisms of lubrication of concentrated contacts Crook [11] evaluated the lubricant film thickness formed between lubricated discs, with parallel axes, by a capacitance method.…”

History, Origins and Prediction of Elastohydrodynamic Friction

“…The initial focus of experimental work was on film thickness [10][11][12] but by the end of the 1950s, disc machines started to be used to measure friction in controlled, mixed rolling-sliding conditions. It was soon realised that when the effect of the contact pressure on viscosity was taken into account, the friction in EHD contacts was much lower than that predicted based on Newtonian behaviour.…”

An Analytical Approach for Prediction of Elastohydrodynamic Friction with Inlet Shear Heating and Starvation

“…Consequently, an inaccurate estimation of load carrying capacity and contact friction can occur [7]. This inaccuracy arises as the result of three interacting phenomena in the inlet region: lubricant inlet shear heating [8,9], inlet lubricant shear thinning [10] and starvation [11,12], which often occurs as the result of inlet swirl and back flows [13,14]. The inlet shear heating is caused by viscous shear of the lubricant in the inlet zone, which leads to a subsequent decrease in the lubricant dynamic viscosity.…”