Interpretations of the Thickness of Lubricant Films in Rolling Contact. 2. Influence of Possible Rheological Factors

1971 ◽  
Vol 93 (4) ◽  
pp. 485-497 ◽  
Author(s):  
J. C. Bell ◽  
J. W. Kannel
Keyword(s):  
Time Delay ◽  
Film Thickness ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Rolling Contact ◽  
X Rays ◽  
Load Effect ◽  
Simple Theories ◽  
Lubricant Films ◽  
Inlet Zone

Several theories involving rarely analyzed but yet realistic rheological effects have been developed in an effort to find why lubricant film thicknesses in rolling contact, as measured by X rays for rigorous operating conditions, do not obey simple theories well, especially with respect to load effect. The analysis is based on actions in the inlet zone, using the approximate geometry implied for previous simple theories. Effects investigated include a generalized pressure variation of viscosity, a non-Newtonian rheology of Ree-Eyring form, and a time delay in pressure effect on viscosity. Simple formulas are found for the influence of all these factors on lubricant film thickness. The time delay theory is found to provide the best correlation with experimental measurements of film thickness, and it is suggested to offer an attractive field for further research embracing friction effects as well as film thickness.

Effects of slide-roll ratio and lubricant properties on elastohydrodynamic lubrication film thickness and traction

2001 ◽  
Vol 215 (3) ◽  
pp. 301-308 ◽  
Author(s):  
J Lord ◽  
R Larsson
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Mineral Oil ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Thickness Reduction ◽  
Lubrication Film ◽  
Synthetic Ester ◽  
Lubricant Films ◽  
Two Factors

With tribology research aimed at decreasing energy consumption, two factors are inherently in focus: lubricant film thickness and traction. These factors are effectively decoupled and depend on lubricant properties which are sometimes contradictory-favourable for one factor and disadvantageous for the other. The film thickness ought to be maximized to reduce the number of asperities in contact and thus wear, whilst the traction should be minimized in order to reduce energy losses. In this experimental investigation the tested lubricants were investigated to see whether they possess beneficial properties for forming thick lubricant films under severe operating conditions while maintaining low traction forces. This is done by experimentally studying the film thickness reduction due to thermal and rheological effects for a fully flooded electrohydrodynamic lubrication (EHL) contact. The base oils tested were a naphthenic mineral VG150, a synthetic poly-α-olefin VG68 and a synthetic ester VG46. It was found that the synthetic ester maintained a relatively thicker lubricant film during sliding than the poly-α-olefin and mineral oil. The film thickness reduction for the mineral oil was greater than for the poly-α-olefin.

Interpretations of the Thickness of Lubricant Films in Rolling Contact. 1. Examination of Measurements Obtained by X-Rays

1971 ◽  
Vol 93 (4) ◽  
pp. 478-484 ◽  
Author(s):  
J. W. Kannel ◽  
J. C. Bell
Keyword(s):  
Film Thickness ◽  
Rolling Contact ◽  
X Rays ◽  
Measuring Process ◽  
X Ray ◽  
Lubricant Films ◽  
Two Temperatures ◽  
Thickness Measurements ◽  
X Ray Absorption ◽  
Higher Sensitivity

The thickness of the film formed by each of five lubricants between a pair of disks in rolling contact has been measured by an X-ray technique for a range of loads (80,000 to 225,000 psi maximum Hertz stress), two temperatures (178 F and 250 F), and three speeds (4300 fpm to 9100 fpm). An empirical formula fitted to the X-ray data shows a much higher sensitivity of film thickness to load than is normally predicted. In order to judge whether the measurements themselves are at fault, the X-ray measuring process has been reexamined for accuracy, especially where load-dependent errors might arise. Some weaknesses are noted, such as in the amount of X-ray absorption, but these should not affect load sensitivity greatly. New experiments designed to find effects of imperfect collimation of X-rays indicate that reflection of X-rays may be significant, but these effects too do not seem to account for the anomalies of the film thickness measurements.

Study of Direct Measuring of Lubricant Condition in Rolling Element Bearings With Microcomputer Technique

1990 ◽  
Vol 112 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Dongchu Zhao
Keyword(s):  
Film Thickness ◽  
Strain Gage ◽  
Lubricant Film ◽  
Rolling Element Bearings ◽  
Main Program ◽  
Test Apparatus ◽  
Lubricant Film Thickness ◽  
Rolling Element ◽  
Lubricant Films ◽  
Flow Charts

A method for measuring the lubricant condition with strain gage in rolling element bearings and the instrument used are introduced. In order to illustrate the method and the instrument, the theory of measuring lubricant films in rolling element bearings using strain technique, test apparatus, microcomputer hardware as well as software, flow charts for the main program and subprograms, are first described in detail. In addition, the lubricant film thickness is measured for several different lubricants and results are compared with theoretical ones. It is demonstrated that using the method and the instrument introduced in this paper, one can measure the lubricant condition inside bearings very accurately.

Optimized Mapping of Pressure in Lubricated Point Contacts Based on Measured Film Thickness

2007 ◽  
Author(s):  
Radek Polisˇcˇuk ◽  
Michal Vaverka ◽  
Martin Vrbka ◽  
Ivan Krˇupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Point Contact ◽  
Contact Fatigue ◽  
Lubricant Film ◽  
Rolling Contact ◽  
Experimental Film ◽  
Lubricated Contacts ◽  
Practical Performance ◽  
Traction Drives

The surface topography plays significant role in lifetime of highly loaded machine parts with lubricated contacts. Many elements like gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions, where the lubricant film behavior closely implies the main practical performance parameters such as friction wear, contact fatigue and scuffing. For prediction of wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are often required. The usual theoretical approach based on numerical solution of physical-mathematical models built around the Reynolds equation can be extremely time consuming, especially when lubricant films are very thin, and contact load and required resolution very high. This study presents a further refined approach to our previously published experimental method, based on on inverse elasticity theory and fast convolution transformation between the lubricant film thickness map and the pressure distribution within the point contact. The experimental film thickness maps of EHD lubricated contacts with smooth and dented surfaces were processed using colorimetric interferometry and validated using numerical solution, in order to calibrate numerical parameters and to find limits of the new approach.

A Mixed-Lubrication Study of Journal Bearing Conformal Contacts

1997 ◽  
Vol 119 (3) ◽  
pp. 456-461 ◽  
Author(s):  
Qian (Jane) Wang ◽  
Fanghui Shi ◽  
Si C. Lee
Keyword(s):  
Film Thickness ◽  
Contact Pressure ◽  
Contact Area ◽  
Numerical Solutions ◽  
Mixed Lubrication ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Lubricant Film Thickness ◽  
Asperity Contacts

Numerical analyses of finite journal bearings operating with large eccentricity ratios were conducted to better understand the mixed lubrication phenomena in conformal contacts. The average Reynolds equation derived by Patir and Cheng was utilized in the lubrication analysis. The influence function, calculated numerically using the finite element method, was employed to compute the bearing deformation. The effects of bearing surface roughness were incorporated in the present analysis for the calculations of the asperity contact pressure and the asperity contact area. The numerical solutions of the hydrodynamic and asperity contact pressures, lubricant film thickness, and asperity contact area were evaluated based on a simulated bearing-journal geometry. The calculations revealed that the asperity contact pressure may vary significantly along both the width and the circumferential directions. It was also shown that the asperity contacts and the lubricant film thickness were strongly dependent on the bearing width, asperity orientation, and operating conditions.

Pressure Distribution Within EHD Point Contacts Based on Measured Film Thickness

Tribology ◽  
2006 ◽  
Author(s):  
Radek Poliscuk ◽  
Michal Vaverka ◽  
Martin Vrbka ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Pressure Distribution ◽  
Elastic Deformation ◽  
Contact Fatigue ◽  
Lubricant Film ◽  
Rolling Contact ◽  
Lubricant Film Thickness ◽  
Machine Elements ◽  
Lubricated Contact

Surface topography significantly influences the behavior of lubricated contacts between highly loaded machine elements. Most oil- or grease- lubricated machine elements such as gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions and the lubricant film thickness is directly related to the main practical performance parameters such as function, wear, contact fatigue and scuffing. For determination wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are required. The theoretical studies usually involve the numerical solution of pressure and film thickness in the contact, using some physical mathematical model built around the Reynolds equation to describe the flow and the theory of elastic deformation of semi-infinite bodies. Such calculations can be extremely time consuming, especially when lubricant films are very thin and/or contact load very high. This study is aimed at obtaining pressure distribution within lubricated contact from measured film thickness. Lubricant film thickness distribution within the whole concentrated contact is evaluated from chromatic interferograms by thin film colorimetric interferometry. Consequently, an elastic deformation is separated from the film thickness, geometry and mutual approach of the surfaces. Calculation of the pressure distribution is based on inverse elasticity theory. EHD lubricated contact with smooth surfaces of solids was first investigated. Calculated pressure, distributions were compared with data obtained from full numerical solution to check the accuracy. The approach was also applied to surfaces with dents and their influence on distribution of pressure in lubricant film.

Lubrication of 2D Soft Elasto Hydrodynamic Contacts: Extension of the Amplitude Reduction Theory

2011 ◽  
Author(s):  
F. Mora ◽  
P. Sainsot ◽  
A. A. Lubrecht ◽  
Y. le Chenadec
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Lubricant Film ◽  
Operating Conditions ◽  
Quantitative Prediction ◽  
Reduction Theory ◽  
Lubricant Film Thickness

This paper is an extension of the Amplitude Reduction Theory to soft ElastoHydrodynamic contacts. The ART permits a quantitative prediction of the influence of surface roughness on the lubricant film thickness modification as a function of the operating conditions.

Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording

2011 ◽  
Author(s):  
Norio Tagawa ◽  
Takao Miki ◽  
Hiroshi Tani
Keyword(s):  
Film Thickness ◽  
Laser Heating ◽  
Temperature Programmed Desorption ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Lubricant Depletion ◽  
Liquid Lubricant ◽  
Lubricant Films ◽  
Temperature Programmed ◽  
Thermally Assisted Magnetic Recording

In this study, the lubricant depletion caused by laser heating was investigated for lubricant films with thicknesses greater than and less than one monolayer. The conventional lubricants Zdol2000 and Ztetrao12000 were used. It was found that the critical temperature at which lubricants start to deplete by laser heating strongly depends on the lubricant film thickness. To analyze the lubricant depletion mechanism, we carried out temperature programmed desorption (TPD) spectroscopy on the tested lubricant films. It was found that the lubricant depletion characteristics induced by laser heating could be explained using the experimental TPD spectroscopy results for the tested lubricant films. It was also found that the depletion mechanism involved the desorption or decomposition of the lubricant molecules that interacted with the diamond-like carbon thin films when the lubricant film thickness was less than one monolayer.

The Effect of Thin Lubricant Films on Acoustic Emission Characteristics

2005 ◽  
Author(s):  
Hiroo Taura ◽  
Toshihiko Takaki ◽  
Masahiro Kawaguchi ◽  
Satoru Kaneko ◽  
Takahisa Kato
Keyword(s):  
Acoustic Emission ◽  
Friction Coefficient ◽  
Film Thickness ◽  
Sliding Friction ◽  
Protective Layer ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Lubricant Films ◽  
Circumferential Distribution ◽  
Ae Signals

This paper shows the effect of ultrathin lubricant films between sliding bodies on Acoustic Emission (AE) signals induced by the sliding friction. Experiments were conducted with a ball-on-disk friction tester to measure the friction coefficient, the raw AE signals and the root-mean-squarevalues of the AE signals (the AErms signals). The ball was a glass ball of 5mm diameter. The disk was a magnetic disk used for 2.5 inch HDD with a DLC protective layer on its surface, and was coated with PFPE Z-dol 4000 about 1.5nm thick. The AErms signals kept a low level for some time after the start of the test, and then increased. Its time variation was similar to that of friction coefficient. After the friction test, the circumferential distribution of the lubricant film thickness was measured with an ellipsometer. The distribution demonstrated the reduction of the lubricant film thickness at the circumferential position where the magnitude of AE signals became large. These facts showed that the AE signals correlated well with the lubricant film thickness.

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