Lubricating Grease Replenishment in an Elastohydrodynamic Point Contact

1993 ◽  
Vol 115 (3) ◽  
pp. 501-506 ◽  
Author(s):  
Henrik A˚stro¨m ◽  
Jan Ove O¨stensen ◽  
Erik Ho¨glund
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Video Recording ◽  
Point Contact ◽  
Video Camera ◽  
Lubricating Oil ◽  
Spin Motion ◽  
Lubricating Grease ◽  
Lubricating Film ◽  
Theoretical Predictions

A ball and disk apparatus was used to investigate the lubricant replenishment of an elastohydrodynamically lubricated point contact. This replenishment of the contact is crucial for building up a lubricating film. Whereas lubricating oil manages to achieve replenishment, lubricating grease appears not to achieve this, with lubricant starvation and a dramatic decrease in film thickness as a result. The distribution of grease around the contact was studied using normal and high-speed video. The movements of grease in the vicinity of the contact could be seen by adding molybdenum disulfide particles to the grease. A recording was then made, using highspeed video recording. The overall cavitation regions were studied using an ordinary video camera and grease without particles. On the basis of the results, possible lubricating grease replenishment mechanisms are discussed. The resulting film thickness was also compared with theoretical predictions using the Hamrock and Dowson starvation criterion, assuming negligible replenishment. The measured film thickness was larger than the predicted, which indicated that some replenishment occurs. In the case of an ordinary thrust ball bearing, replenishment was found to rely on the spin motion of the balls.

scholarly journals Optical Analysis of Ball Bearing Starvation

1971 ◽  
Vol 93 (3) ◽  
pp. 349-361 ◽  
Author(s):  
L. D. Wedeven ◽  
D. Evans ◽  
A. Cameron
Keyword(s):  
Film Thickness ◽  
Ball Bearing ◽  
Point Contact ◽  
Experimental Measurements ◽  
Line Contact ◽  
Optical Analysis ◽  
Grease Lubrication ◽  
Theoretical Predictions ◽  
Pressure Stress ◽  
Starvation Conditions

Elastohydrodynamic oil film measurements for rolling point contact under starvation conditions are obtained using optical interferometry. The experimental measurements present a reasonably clear picture of the starvation phenomenon and are shown to agree with theoretical predictions. Starvation inhibits the generation of pressure and, therefore, reduces film thickness. It also causes the overall pressure, stress, and elastic deformation to become more Hertzian. Additional experiments using interferometry illustrate: the cavitation pattern, lubricant entrapment, grease lubrication, ball spin, and edge effects in line contact.

Grease soap particles passing through an elastohydrodynamic contact under side slip conditions

2000 ◽  
Vol 214 (4) ◽  
pp. 317-325 ◽  
Author(s):  
P Eriksson ◽  
V Wikström ◽  
R Larsson
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Previous Investigation ◽  
Video Camera ◽  
Slip Conditions ◽  
High Speed Video ◽  
Elastohydrodynamic Contact ◽  
High Speed Video Camera ◽  
Pure Rolling ◽  
Minimum Film Thickness

In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used. Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.

Some Limitations in Applying Classical EHD Film Thickness Formulas to a High-Speed Bearing

1981 ◽  
Vol 103 (2) ◽  
pp. 295-301 ◽  
Author(s):  
J. J. Coy ◽  
E. V. Zaretsky
Keyword(s):  
Film Thickness ◽  
High Speed ◽  
Heating Effects ◽  
Theoretical Predictions ◽  
Traction Fluid ◽  
Shear Heating ◽  
Thickness Measurements ◽  
Inner Race ◽  
Maximum Stresses ◽  
Good Agreement

Elastohydrodynamic film thickness was measured for a 20-mm ball bearing using the capacitance technique. The bearing was thrust loaded to 90, 448, and 778 N (20, 100, and 175 lb). The corresponding maximum stresses on the inner race were 1.28, 2.09, and 2.45 GPa (185,000, 303,000, and 356,000 psi). Test speeds ranged from 400 to 14,000 rpm. Film thickness measurements were taken with four different lubricants: (a) synthetic paraffinic, (b) synthetic paraffinic with additives, (c) neopentylpolyol (tetra) ester meeting MIL-L-23699A specifications, and (d) synthetic cycloaliphatic hydrocarbon traction fluid. The test bearing was mist lubricated. Test temperatures were 300, 338, and 393 K. The measured results were compared to theoretical predictions using the formulae of Grubin, Archard and Cowking, Dowson and Higginson, and Hamrock and Dowson. There was good agreement with theory at low dimensionless speed, but the film was much smaller than theory predicts at higher speeds. This was due to kinematic starvation and inlet shear heating effects. Comparisons with Chiu’s theory on starvation and Cheng’s theory on inlet shear heating were made.

Oil Film Thickness and Pressure Distribution in Elastohydrodynamic Point Contacts

1982 ◽  
Vol 24 (4) ◽  
pp. 173-182 ◽  
Author(s):  
A. Mostofi ◽  
R. Gohar
Keyword(s):  
Contact Problem ◽  
Film Thickness ◽  
Numerical Solutions ◽  
Point Contact ◽  
Point Contacts ◽  
Rolling Velocity ◽  
Oil Film ◽  
Static Contact ◽  
Theoretical Predictions ◽  
Interferometry Method

In this paper, a general numerical solution to the elastohydrodynamic point contact problem is presented for moderate loads and material parameters. Isobars, contours and regression formulae describe how pressure and oil film thickness vary with geometry, material properties, load, and squeeze velocity, when the rolling velocity vector is at various angles to the static contact ellipse long axis. In addition, the EHL behaviour under spin is examined. The theoretical predictions of film thickness compare favourably with other numerical solutions to the point contact problem, as well as with experimental results which use the optical interferometry method to find film thickness and

Prediction of transient lubricating film thickness in knee prostheses with compliant layers

1998 ◽  
Vol 212 (3) ◽  
pp. 157-164 ◽  
Author(s):  
Z M Jin ◽  
D Dowson ◽  
J Fisher ◽  
N Ohtsuki ◽  
T Murakami ◽  
...  
Keyword(s):  
Knee Joint ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Contact Radius ◽  
Knee Prostheses ◽  
Stroke Length ◽  
Additional Advantage ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricating Film Thickness

The transient lubricating film thickness in knee prostheses using compliant layers has been predicted under simulated walking conditions based upon the elastohydrodynamic lubrication theory. Qualitative agreement has been found between the present theoretical predictions and the experimental measurements using an electric resistance technique reported earlier. It has been shown that the contact geometry plays an important role in the generation of fluid film lubrication in knee prostheses using compliant layers. The maximum lubricating film thickness is predicted for the maximized contact area of a transverse conjunction where the semi-minor contact radius lies in the direction of entraining. The additional advantage of the transverse contact conjunction is that the possibility of lubricant starvation due to small stroke length can be minimized. All these factors, together with the kinematic requirements in the natural knee joint, should be taken into consideration when designing artificial knee joint replacements.

The Effect of Kinematic Conditions on Film Thickness in Compliant Lubricated Contact

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
David Nečas ◽  
Tomáš Jaroš ◽  
Kryštof Dočkal ◽  
Petr Šperka ◽  
Martin Vrbka ◽  
...  
Keyword(s):  
Film Thickness ◽  
Optical Glass ◽  
Film Formation ◽  
Fluorescent Microscopy ◽  
Elastohydrodynamic Lubrication ◽  
Constant Load ◽  
Fluid Viscosity ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricated Contact

The present paper deals with an investigation of film formation in compliant lubricated contact. Despite these contacts can be found in many applications of daily life including both biological and technical fields, so far little is known about the lubrication mechanisms inside the contacts. The main attention is paid to the effect of kinematic conditions on central film thickness. For this purpose, fluorescent microscopy method was employed. Experiments were realized in ball-on-disk configuration, while the ball was made from rubber and the disk was from optical glass. The contact was lubricated by glycerol and polyglycol to examine the effect of fluid viscosity. The measurements were conducted under pure rolling and rolling/sliding conditions. The entrainment speed varied from 10 to 400 mm/s and constant load of 0.2 N was applied. Experimental results were compared with two theoretical predictions derived for isoviscous-elastohydrodynamic lubrication (I-EHL) regime. It was found that the thickness of lubricating film gradually increases with increasing entrainment speed, which corresponds to theoretical assumptions. Against expectations, evident influence of slide-to-roll ratio (SRR) on film formation was observed. In the last part of the paper, some limitations of this study are discussed and several recommendations for further methodology improvement are suggested.

Measurement of Lubricating Film Thickness in Low Elastic Modulus Lined Bearings, with Particular Reference to Models of Cushion Form Bearings for Total Joint Replacements: Part 2: Squeeze-Film Motion

1994 ◽  
Vol 208 (3) ◽  
pp. 213-217 ◽  
Author(s):  
Z M Jin ◽  
G McClure ◽  
D Dowson ◽  
J Fisher ◽  
B Jobbins
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Thick Layer ◽  
Squeeze Film ◽  
Synovial Joint ◽  
Joint Replacements ◽  
Total Joint Replacements ◽  
Lubricating Film ◽  
Low Elastic Modulus ◽  
Theoretical Predictions

An optical interferometry technique has been successfully used to study the lubricant film thickness in a compliant layered bearing model for total joint replacements under squeeze-film motion. Experiments have been carried out for both thin and thick layers of compliant bearing material. It has been demonstrated that the film thickness patterns depend significantly upon the layer thickness if other parameters are kept constant. For the thin layer, the film thickness in the contact region was found to be essentially uniform and quite good agreement was found with the theoretical predictions based upon a simplified analysis due to Dowson et al. (13) and Higginson (14). However, for the thick layer, a central dimple or pocket was formed and a relatively large difference was found between the experimentally determined central film thickness and the simple parallel circular disc theoretical predictions. The practical implications of the present results are discussed in relation to the lubrication mechanism in the natural synovial joint and its replacement.

Effect of Proteins on Film Formation in Bovine Serum Lubricated Contacts Under Rolling/Sliding Conditions

2012 ◽  
Author(s):  
Martin Vrbka ◽  
Tomas Navrat ◽  
Ivan Krupka ◽  
Martin Hartl ◽  
Jiri Gallo
Keyword(s):  
Film Thickness ◽  
Bovine Serum ◽  
High Speed ◽  
Film Formation ◽  
Research Work ◽  
Digital Camera ◽  
Protein Film ◽  
Lubricating Film ◽  
Ceramic Femoral Head ◽  
Optical Test

The aim of this study is to perform detail experimental mapping of the lubricating film thickness of bovine serum (BS) within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation under rolling/sliding conditions. The film thickness was studied experimentally using an optical test rig as a function of time under variety of constant mean speeds. Chromatic interferograms were recorded with a high-speed digital camera and evaluated with thin film colorimetric interferometry. Under pure rolling conditions it was observed that the central film thicknesses increased with time for all measurements. When the disc was slower than head then the measured central film thicknesses achieved values only about some few nanometres, whereas when the tests were realized with faster disc then measured central film thicknesses achieved significantly higher values. Distribution of the film thickness within the contact zone is not homogeneous and two different film thickness regions can be found; thicker protein film and thinner base film that both show specific behaviour over time. This study showed that protein formation plays an important role in the lubrication processes of artificial joints of the human. Due to challenging of this study the more complex research work is carried out at the present time.

Direct Observations of Emulsion Flow in EHL Contacts

2005 ◽  
Author(s):  
Haixia Yang ◽  
Steven R. Schmid ◽  
Ronald A. Reich ◽  
Thomas J. Kasum
Keyword(s):  
High Speed ◽  
Direct Method ◽  
Flow Behavior ◽  
Point Contact ◽  
Video Camera ◽  
Digital Video Camera ◽  
Droplet Behavior ◽  
Droplet Sizes ◽  
Emulsion Flow ◽  
Side Flow

Oil-in-water emulsions are widely used as lubricants in metal forming, machining and some machinery elements where non-flammable lubricants are required. Their lubricating mechanisms have been extensively investigated based on the measurements of film thickness and/or traction in the past few decades and a number of physical explanations for their performance have been forwarded. However, direct observation of the emulsion flow, as a direct method of evaluating suggested theoretical explanations, has been greatly restricted by the available instruments. In this paper, a newly devised digital video camera and microscope were used to directly observe the emulsion flow in EHL contacts at industrially relevant speeds for both line and point contacts. Previous low-speed results for line contact were confirmed and extended into high-speed cases. That is, some droplets were rejected from the inlet, others penetrated to the contact zone, and others remained fixed in position a certain distance from the edge of contact. For point contact, side flow behavior was also observed, and the number of droplets that remained stationary were limited to a single streamline. To clarify the oil droplet behavior and investigate the effect of particle size on entrainment, three tight emulsions with different mean droplet sizes were examined on an EHD rig at speeds from 12 mm/s up to 1.5 m/s.

Measurement of Lubricating Film Thickness in Low Elastic Modulus Lined Bearings, with Particular Reference to Models of Cushion Form Bearings for Total Joint Replacements: Part 1: Steady State Entraining Motion

1994 ◽  
Vol 208 (3) ◽  
pp. 207-212 ◽  
Author(s):  
Z M Jin ◽  
D Dowson ◽  
J Fisher ◽  
D Rimmer ◽  
R Wilkinson ◽  
...  
Keyword(s):  
Film Thickness ◽  
Glass Plate ◽  
Elastohydrodynamic Lubrication ◽  
Normal Incidence ◽  
Joint Replacements ◽  
Total Joint Replacements ◽  
Silicone Fluid ◽  
Lubricating Film ◽  
Theoretical Predictions ◽  
Lubricating Film Thickness

The lubricating film thickness in a model of compliant layered bearings for total joint replacements has been measured by means of optical interferometry under entraining motion. The essential features of the present interferometry technique were off-normal incidence light, a combination of polyurethane elastomer and a crown glass plate as bearing surfaces and the use of silicone fluid or water as lubricants. The film thickness in the lubricated contact was measured for both water and silicone fluid under a range of entraining velocities. Reasonable agreement was found between the experimental measurements of the lubricating film thickness and the theoretical predictions based upon elastohydrodynamic lubrication analysis.

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