The Minimum Film Thickness in Line Contacts During Reversal of Entrainment

1993 ◽  
Vol 115 (1) ◽  
pp. 191-199 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Rate Of Change ◽  
Radius Of Curvature ◽  
Operating Cycle ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Involute Gears ◽  
Shaft Seals ◽  
Steady State Predictions

In contacts, such as cams, non-involute gears and shaft seals, where the direction of entrainment reverses during the operating cycle, the minimum film thickness is typically found just after the reversal. This paper shows that this minimum film thickness is determined by the rate of change of the entraining velocity and by the fluid and surface properties. For line contacts, four regimes of lubrication are found—as for the steady-state situation—and expressions for the film thickness in each regime are developed. This enables an outline design chart for the minimum film thickness to be constructed. It is shown that this information, together with the steady-state predictions is sufficient to determine the variation of film thickness with time in most situations where load, radius of curvature, and entraining velocity vary.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—General Solution and the Development of a Design Chart

1994 ◽  
Vol 208 (1) ◽  
pp. 53-64 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Radius Of Curvature ◽  
Velocity Change ◽  
Surface Separation ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Interpolation Procedure

In most line contacts the load, effective radius of curvature and entraining velocity change with time. Generally this is ignored when calculating the film thickness and a quasi-steady solution is obtained. Under most conditions the errors introduced by this are either small or are not critical. However, when the entraining velocity reverses, as, for example, in some designs of cams, the quasi-steady approach predicts that the film thickness will be zero. In practice a residual film persists and can provide adequate surface separation. Previous papers by the author have shown that the minimum film thickness at entrainment reversal depends on the rate of change of the entraining velocity. Expressions for the film thickness in the four regimes of lubrication—rigid isoviscous, rigid piezoviscous, elastic isoviscous and elastic piezoviscous—were obtained and the variations of the film thickness in the transitions between adjacent regimes examined. The present paper examines the region where more than two regimes overlap. The values of film thickness obtained are then used to develop an interpolation procedure for the accurate calculation of the minimumfilm thickness under all operating conditions.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Piezoviscous Behaviour

1992 ◽  
Vol 206 (6) ◽  
pp. 417-424 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubrication Theory ◽  
Rate Of Change ◽  
Operating Conditions ◽  
Entrainment Velocity ◽  
Residual Film ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Important Exception

In many line contacts the operating conditions, such as load, entrainment velocity and contact radii, vary with time. Generally, the results from standard elastohydrodynamic lubrication theory, derived for constant conditions, can be used to obtain a quasi-steady prediction of film thickness that is sufficiently accurate for design purposes. An important exception to this is where the entrainment direction changes because, under those conditions, the quasi-steady approach predicts that there will be no clearance between the surfaces while in practice a residual film will persist. A previous paper showed that the minimum film thickness during entrainment reversal depends primarily on the rate of change of entrainment velocity. Limit expressions for the minimum clearance in the four regimes of lubrication were obtained. The present paper is part of a programme to develop a minimum film thickness chart for entrainment reversal and deals with the transition between the rigid-piezoviscous and the elastic-piezoviscous regimes.

The Minimum Film Thickness in Lubricated Line Contacts during a Reversal of Entrainment—Isoviscous Behaviour

1992 ◽  
Vol 206 (5) ◽  
pp. 337-345 ◽  
Author(s):  
C J Hooke
Keyword(s):  
Film Thickness ◽  
Transition Zone ◽  
Static Analysis ◽  
Rate Of Change ◽  
Entrainment Velocity ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Static Approach ◽  
The One

In most line contacts, the film thickness can be adequately determined using a quasi-static analysis. The one exception appears to occur when the direction of entrainment changes. Here, the quasi-static approach predicts that the film will fall to zero while, in practice, there will always be a finite clearance between the surfaces. It was shown in a previous paper that this minimum clearance depends upon the rate of change of entrainment velocity, and limit expressions for the film thicknesses in the four regimes of lubrication were developed. The present paper examines the transition between the rigid-isoviscous and the elastic-isoviscous regimes and determines how the minimum film thickness behaves in this transition zone.

scholarly journals Lubrication Analyses of Cam and Flat-Faced Follower

Lubricants ◽  
2019 ◽  
Vol 7 (4) ◽  
pp. 31 ◽  
Author(s):  
Hazim U. Jamali ◽  
Amjad Al-Hamood ◽  
Oday I. Abdullah ◽  
Adolfo Senatore ◽  
Josef Schlattmann
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Surface Deformation ◽  
Numerical Study ◽  
Point Contact ◽  
Radius Of Curvature ◽  
Operating Cycle ◽  
Essential Step ◽  
Parabolic Shape ◽  
Principal Factors

The principal factors that affect the characteristics of contact problem between cam and follower vary enormously during the operating cycle of this mechanism. This includes radius of curvature, surface velocities and applied load. It has been found over the last decades that the mechanism operates under an extremely thin film of lubricant. Any practical improvement in the level of film thickness that separates the contacted surfaces represents an essential step towards a satisfactory design of the system. In this paper a detailed numerical study is presented for the cam and follower (flat-faced) lubrication including the effect of introducing an axial modification (parabolic shape) of the cam depth on the levels of film thickness and pressure distribution. This is achieved based on a point contact model for a cam and flat-faced follower system. The results reveal that the cam form of modification has considerable consequences on the level of predicted film thickness and pressure distribution as well as surface deformation.

The Elasto-Hydrodynamic Lubrication of Soft, Highly Deformed Contacts Under Conditions of Nonuniform Motion

1986 ◽  
Vol 108 (4) ◽  
pp. 545-550 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Steady State ◽  
Film Thickness ◽  
Dynamic Analysis ◽  
Hydrodynamic Lubrication ◽  
Steady State Analysis ◽  
Entrainment Velocity ◽  
Sinusoidal Motion ◽  
Minimum Film Thickness ◽  
Rapid Reversal ◽  
Nonuniform Motion

A method is described for the calculation of the film thicknesses in soft, highly deformed contacts for situations where the entrainment velocity is not constant. Two particular results are presented. It is shown that, where there is a rapid reversal of motion, the steady state analysis remains acceptable. However, for a contact reciprocating with a sinusoidal motion, it does not, and here the minimum film thickness occurs at the end of the stroke. The minimum film thickness lies at the end of the contact furthermost from the area swept during the stroke and can only be determined by a dynamic analysis.

Multigrid, An Alternative Method for Calculating Film Thickness and Pressure Profiles in Elastohydrodynamically Lubricated Line Contacts

1986 ◽  
Vol 108 (4) ◽  
pp. 551-556 ◽  
Author(s):  
A. A. Lubrecht ◽  
W. E. ten Napel ◽  
R. Bosma
Keyword(s):  
Film Thickness ◽  
Multigrid Method ◽  
Computing Time ◽  
Alternative Method ◽  
Pressure Profiles ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Order Of Magnitude

Film thickness and pressure profiles have been calculated for line contacts at moderate and high loads, using a Multigrid method. Influence of the compressibility of the lubricant on the minimum film thickness and on the pressure spike has been examined. The required computing time is an order of magnitude less than when using the previous methods.

Thermal Elastohydrodynamic Lubrication of Axially Crowned Rollers

2021 ◽  
pp. 1-21
Author(s):  
Wassim Habchi
Keyword(s):  
Film Thickness ◽  
Design Parameter ◽  
Numerical Study ◽  
Elastohydrodynamic Lubrication ◽  
Negative Influence ◽  
Reference Case ◽  
Critical Design ◽  
Lubrication Performance ◽  
Minimum Film Thickness ◽  
Line Contacts

Abstract This work presents a comprehensive numerical study of thermal elastohydrodynamic lubrication performance in axially crowned rollers, based on a full-system finite element approach. Axial crowning has always been introduced to finite line contacts, as a mean for improving film thickness. Its influence on friction has often been overlooked though. The current work reveals that axial crowning has a negative influence on friction, increasing it significantly with respect to the reference case of straight rollers. It is shown that, with increased crowning height (or reduced crowning radius), minimum film thickness is increased, but so is friction. Therefore, film thickness enhancement comes at the expense of a deterioration in friction. Besides, achieving sufficient enhancements in minimum film thickness would require using relatively low crowning radii, which would lead to a substantial increase in friction. The frictional increase is traced back to an overall increase in contact pressures and effective contact area within the lubricating conjunction. It is also shown that, when film thickness is the most critical design parameter, the best compromise between enhanced film thickness and deteriorated friction would be to combine axial crowning with roller-end profiling. However, when friction is the most critical design parameter, a simple roller-end profiling would offer the best compromise.

An Efficient Algorithm for Thermal Elastohydrodynamic Lubrication Under Rolling/Sliding Line Contacts

1994 ◽  
Vol 116 (4) ◽  
pp. 762-769 ◽  
Author(s):  
Chao-Ho Hsu ◽  
Rong-Tsong Lee
Keyword(s):  
Film Thickness ◽  
Thermal Loading ◽  
Reduction Factor ◽  
Difference Approximation ◽  
Central Difference ◽  
Integration Algorithm ◽  
Wide Range ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Thermal Ehl

One of the most time-consuming routines in thermal EHL problem is the calculation of the surface temperature integral. Combining the multigrid technique and the Newton-Raphson method, a modified multilevel, multi-integration algorithm for this integral is developed that can reduce the computational complexity from O (n2) to O (n ln n) for the thermal EHL problem of rolling/sliding line contacts. The employed standard central difference approximation to the coupled Reynolds and energy equations can yield the maximum difference of mass flow flux within one percent. Effects of dimensionless load, dimensionless materials parameter, slip ratio, and thermal loading parameter on the minimum film thickness are investigated. Correlation formula of thermal reduction factor for the minimum film thickness is derived for a wide range of slip ratios, loads, thermal loading parameters, and materials parameters.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts

1991 ◽  
Vol 113 (3) ◽  
pp. 481-491 ◽  
Author(s):  
H. Salehizadeh ◽  
N. Saka
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Shear Stresses ◽  
Hertz Contact ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Heavy Loads

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.

New equations for enhanced film thickness in line contacts under pressurized ambient conditions

2016 ◽  
Vol 231 (5) ◽  
pp. 616-622 ◽  
Author(s):  
Niraj Kumar ◽  
Punit Kumar
Keyword(s):  
Film Thickness ◽  
Ambient Pressure ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Ambient Conditions ◽  
Alternative Approach ◽  
Film Forming ◽  
Highly Sensitive ◽  
Minimum Film Thickness ◽  
Line Contacts

An elastohydrodynamic lubrication model is proposed for line contacts under pressurized ambient conditions often encountered in hydraulic pumps, submarine machinery and many other submerged systems. It has been demonstrated that the film forming behavior under such conditions is essentially different from that in conventional elastohydrodynamic lubrication contacts. The numerical simulation results are regressed to develop new central and minimum film thickness equations for Newtonian fluids as functions of ambient pressure, speed, load, and material parameters. An alternative approach is also discussed which involves the use of existing film thickness formulas with ambient viscosity and pressure–viscosity coefficient pertaining to the desired pressure range. A film thickness enhancement of more than 100% over conventional elastohydrodynamic lubrication case is observed. This enhancement is shown to be highly sensitive to the pressure–viscosity coefficient. Besides, the effect of shear-thinning behavior is also investigated and it is found to lower the film thickness enhancement, especially at high ambient pressures.

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