Investigation of the discharge-voltage method of measuring the thickness of oil films formed in a disc machine under conditions of elastohydrodynamic lubrication

Wear ◽  
1967 ◽  
Vol 10 (5) ◽  
pp. 412
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Discharge Voltage ◽  
Oil Films

Investigation of the Discharge-Voltage Method of Measuring the Thickness of Oil Films Formed in a Disc Machine under Conditions of Elastohydrodynamic Lubrication

1966 ◽  
Vol 181 (1) ◽  
pp. 633-652 ◽  
Author(s):  
A. Dyson
Keyword(s):  
Film Thickness ◽  
Metal Surfaces ◽  
Thick Films ◽  
Elastohydrodynamic Lubrication ◽  
Discharge Voltage ◽  
Suitable Alternative ◽  
Electrical Capacity ◽  
Non Linear ◽  
Oil Films ◽  
Lubrication Conditions

It is reported in the literature that the ‘discharge-voltage’ method offers a simple means of measuring the thickness of oil films between moving metal surfaces. To confirm this report it is necessary to compare discharge-voltage measurements with film thickness measured by an alternative method. So far as the author is aware no such comparison of measured film thicknesses in elastohydrodynamic lubrication conditions has been published. Under these conditions, a suitable alternative way of estimating the thicknesses of oil films between moving metal surfaces is to measure the electrical capacity between them. This method has been applied to a disc machine and a short programme of work undertaken to compare film thickness estimated in this way with the results of discharge-voltage determinations. It was found that there was some relation between discharge voltage and film thickness but that, in general, this relation was non-linear and depended on the slide/roll ratio and on the temperature. It is therefore concluded that the discharge voltage does not measure the thickness of oil films in the simple way suggested; there were some indications that it may be possible to use it to measure relatively thick films, of the order of 40 μin (1 μm) or thicker, at high slide/roll ratios.

Observation of Wall Slip in Elastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 447-452 ◽  
Author(s):  
M. Kaneta ◽  
H. Nishikawa ◽  
K. Kameishi
Keyword(s):  
Experimental Technique ◽  
Elastohydrodynamic Lubrication ◽  
Wall Slip ◽  
Optical Interferometry ◽  
Stepping Motor ◽  
Ehd Lubrication ◽  
Pure Rolling ◽  
Direct Indication ◽  
Contact Surfaces ◽  
Oil Films

A new experimental technique using optical interferometry has been developed to obtain a direct indication of non-Newtonian response of an oil film under conditions of elastohydrodynamic (EHD) lubrication. A glass disk or a steel ball has been driven by a stepping motor so that crescent-shaped thick oil films with undulation in thickness along the direction of motion have been generated. The experiments have been carried out under pure rolling and pure sliding conditions. It has been found that the oil in an EHD contact behaves like a solid and slips at or near the contact surfaces.

Non-Newtonian behaviour in elastohydrodynamic lubrication

1974 ◽  
Vol 337 (1608) ◽  
pp. 101-121 ◽  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Film Thickness ◽  
Pressure Distribution ◽  
Critical Stress ◽  
Elastohydrodynamic Lubrication ◽  
Critical Factor ◽  
Molecular Size ◽  
High Speeds ◽  
Oil Films

The relation between shear stress and shear rate has been determined for elastohydrodynamic oil films. At low values the rate of shear is directly proportional to the shear stress, but at higher values the shear rate increases more rapidly than the stress. It is shown that the critical factor is the magnitude of the shear stress, not the shear rate, and that this critical magnitude depends upon the pressure and the molecular size. Above the critical stress, in the non-Newtonian region, the shape of the curve relating the stress to the rate of shear depends upon the distribution of the sizes of the molecules in the oil. It is shown that in elastohydrodynamic conditions the limits of Newtonian behaviour are frequently exceeded and that this is liable to influence the pressure distribution, the magnitude of the traction, the generation of heat, and, at high speeds, the value of the film thickness.

Film Thicknesses in Elastohydrodynamic Lubrication of Rollers by Greases

1969 ◽  
Vol 184 (6) ◽  
pp. 1-11 ◽  
Author(s):  
A. Dyson ◽  
A. R. Wilson
Keyword(s):  
Viscoelastic Properties ◽  
Elastohydrodynamic Lubrication ◽  
Mineral Oils ◽  
Base Oils ◽  
Electrical Capacity ◽  
Oil Films ◽  
Continuous Running

The object of this work was to measure the thickness of the films formed by greases under conditions of elastohydrodynamic lubrication. The thicknesses of the films were estimated from measurements of the electrical capacity between two discs. In general, the mineral oils from which the greases were made formed films whose thickness did not vary with time. The films formed by the greases were initially thicker than those formed by the corresponding base oils but, after continuous running, became thinner than the oil films. Evidence is offered that the differences observed between oils and greases are related to the viscoelastic properties of the lubricants.

Traction Measurements in Mixed Elastohydrodynamic Lubrication with a Controlled Circumferential Roughness

1991 ◽  
Vol 205 (4) ◽  
pp. 265-273 ◽  
Author(s):  
M P F Sutcliffe
Keyword(s):  
Film Thickness ◽  
Transition Region ◽  
Reasonable Agreement ◽  
Hydrodynamic Lubrication ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Theory ◽  
Good Picture ◽  
Sliding Speed ◽  
Simple Variation ◽  
Oil Films

The transition between smooth elastohydrodynamics (EHL) and micro-EHL is investigated. Traction measurements in a disc machine with a controlled circumferential roughness are used to infer film thicknesses under the asperity tops. These are then compared with hydrodynamic theory. At the two extremes where there is little pressure rippling between the asperity tops and the adjoining valleys or where there is little pressure in the valleys the theoretical and experimentally inferred films are in reasonable agreement. In the transition region the experimentally deduced films are not reliable. Traction behaviour is estimated in the transition region by making some simple assumptions. The film thickness under the asperities is taken as that given by theory for no pressure in the valleys, and the valley pressure in the transition region is estimated by assuming a simple variation with speed. Theoretical traction curves are calculated by apportioning the load between the valleys and the asperity tops and agree well with measured curves, suggesting that this is a good picture of the contact. The traction behaviour was found to depend on sliding speed in a way typical of hydrodynamic lubrication even for estimated oil films as small as 8 nm.

Reynolds equation and elastohydrodynamic lubrication in metal seals

1976 ◽  
Vol 349 (1658) ◽  
pp. 383-396 ◽  
Keyword(s):  
Numerical Solution ◽  
Reynolds Equation ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Hydraulic Jack ◽  
Oil Film ◽  
Metal Seal ◽  
Oil Films ◽  
Theoretical Results ◽  
Film Profile

Oil film profile and pressure distribution between a metal seal and a reciprocating hydraulic jack rod have been measured. A rapidly diverging oil film, which would normally be expected to cause rupture of the fluid and severe cavitation, was observed near the centre of the contact, but the corresponding pressure in this region was found to be high; the two measurements therefore appeared to be incompatible. A re-examination of the inverse Reynolds equation, however, shows that in certain circumstances rapidly diverging oil films are consistent with high values of hydrodynamic pressure; these circumstances are defined. Experimental results are presented which demonstrate that a metal seal may satisfy these conditions. A numerical solution of the elastohydrodynamic equations is described briefly, and the theoretical results are compared with those from the experiments. Reasons why these unusual conditions should exist in the seal are discussed. It is concluded that working in this elastohydrodynamic régime is undesirable.

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