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.

On the Negative Influence of Roller-End Axial Profiling on Friction in Thermal Elastohydrodynamic Lubricated Finite Line Contacts

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
W. Habchi
Keyword(s):  
Fatigue Life ◽  
Elastohydrodynamic Lubrication ◽  
Element Model ◽  
Negative Influence ◽  
Frictional Behavior ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Negative Effect ◽  
Finite Line ◽  
Reducing Stress

Abstract This paper presents a finite element model for the solution of thermal elastohydrodynamic lubrication in finite line contacts, including edge effects. The model is used to investigate the influence of roller-end axial profiling on the frictional behavior of such contacts. Roller-end profiling in finite line contacts has always been used to enhance fatigue life by increasing lubricant minimum film thickness and reducing stress concentration at roller ends. The influence on friction on the other hand has often been overlooked in the literature. The current work reveals that roller-end profiling has a negative effect on friction. In fact, it turns out that the improvement in fatigue life comes at the expense of increased friction.

Influence of Roller-End Axial Profiling Type on Lubrication Performance in Thermal Elastohydrodynamic Finite Line Contacts

2021 ◽  
Vol 144 (1) ◽  
Author(s):  
W. Habchi
Keyword(s):  
Finite Element ◽  
Film Thickness ◽  
Lubricant Film ◽  
Lubricant Film Thickness ◽  
Reference Case ◽  
Pressure Buildup ◽  
Lubrication Performance ◽  
Frictional Dissipation ◽  
Line Contacts ◽  
Finite Line

Abstract This study presents a finite-element-based numerical investigation of the influence of roller-end axial profiling type on the lubrication performance of thermal elastohydrodynamic finite line contacts. Performance is evaluated with respect to the reference case of straight rollers. The two most commonly used profiling types (i.e., dub-off and logarithmic) are compared under similar profiling length and height. It is found that a logarithmic profile outperforms a dub-off one by all accounts (i.e., frictional dissipation, lubricant film thickness, pressure buildup, and temperature rise), unless an extremely steep logarithmic shape is adopted. In the latter case, lubricant film thickness and pressure buildup may end up being negatively affected.

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.

Elastohydrodynamic lubrication of coated finite line contacts

2017 ◽  
Vol 232 (9) ◽  
pp. 1077-1092 ◽  
Author(s):  
Shivam S Alakhramsing ◽  
Matthijn B de Rooij ◽  
Dirk J Schipper ◽  
Mark van Drogen
Keyword(s):  
Mechanical Properties ◽  
Film Thickness ◽  
Surface Profile ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Maximum Pressure ◽  
Lubrication Performance ◽  
Line Contacts ◽  
Finite Line ◽  
Axial Surface

In this work, a finite element-based model is presented that simulates elastohydrodynamic lubrication in coated finite line contacts. Using this model, the film thickness and pressure distributions, between a straight roller with rounded edges on a plate, were analyzed. The model was successfully validated against representative results reported in literature. Parameter studies were conducted to study the influence of varying operating conditions, axial surface profile parameters and coating mechanical properties on the overall elastohydrodynamic lubrication behavior of the contact. It was found that in contrast with typical elastohydrodynamic lubrication behavior, the maximum pressure and minimum film thickness, which are located at the rear of the contact, are largely influenced by variations in load. Results also reveal that axial surface profile parameters and coating mechanical properties may act as amplifiers to the effect of load on pressure and film thickness distribution and can thus, if smartly chosen, significantly enhance lubrication performance.

The Elastohydrodynamic Lubrication of Heavily Loaded Contacts

1977 ◽  
Vol 19 (4) ◽  
pp. 149-156 ◽  
Author(s):  
C. J. Hooke
Keyword(s):  
Analytical Solution ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Dimensional Parameter ◽  
Effect Of Pressure ◽  
General Line ◽  
Minimum Film Thickness ◽  
Line Contacts

An analytical solution is presented to the problem of the lubrication of highly deformed contacts, including the effect of pressure on viscosity. It is shown that the character of the lubrication process depends on the value of a single non-dimensional parameter, and that for each value of this parameter there is a unique non-dimensional value for minimum film thickness. Results are presented for general line contacts and for cylindrical contacts.

Film Thickness and Rolling Resistance in Starved Elastohydrodynamic Lubrication of Point Contacts With Reflow

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Takashi Nogi
Keyword(s):  
Boundary Condition ◽  
Film Thickness ◽  
Numerical Study ◽  
Critical Role ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Resistance ◽  
Point Contacts ◽  
Rolling Bearings ◽  
Wear Life ◽  
Minimum Film Thickness

Elastohydrodynamic lubrication (EHL) film thickness and rolling resistance play a critical role in determining friction, wear, life, and other tribological characteristics of rolling bearings. Although film thickness formulas are widely used and experimentally verified, accurate prediction of the film thickness is still difficult under starved conditions. This paper presents a numerical study of starved EHL point contacts using a nonuniform inlet film thickness obtained from a modified Coyne–Elrod boundary condition. An experimental verification of the numerical results is also presented. Based on the results of a parametric study, inlet distance formulas are obtained as a function of the initial film thickness, the fully flooded central film thickness, and the capillary number. By using the inlet distance formulas and the Hamrock–Dowson formulas, the central film thickness, the minimum film thickness, and the viscous rolling resistance can be calculated.

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.

Transient elastohydrodynamic lubrication analysis of spur gears running-in considering effects of solid particles and surface roughness

2016 ◽  
Vol 68 (2) ◽  
pp. 183-190 ◽  
Author(s):  
Xingbao Huang ◽  
Youqiang Wang
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Solid Particles ◽  
Maximum Pressure ◽  
Spur Gears ◽  
Content Type ◽  
Lubrication Performance ◽  
Minimum Film Thickness ◽  
Variant Effect

Purpose – This paper aims to investigate the mechanism of spur gears running-in and to solve the lubrication problems of teeth running-in. Design/methodology/approach – The elastohydrodynamic lubrication (EHL) model considering solid particles was established by applying multi-grid and multiple-grid integration methods to the numerical solution. Findings – In the region where debris settle, transient pressure increases sharply, and a noticeable increase in the running-in load causes a remarkable increase in both the centre and maximum pressures and a slight increase in the minimum film thickness. Roughness wavelength makes a considerable difference to the minimum film thickness at double-to-single tooth transient. A considerable increase in rotation velocity can cause a remarkable reduction in both the centre and maximum pressures but an amazing increase in the minimum film thickness. The effects of roughness amplitude on the maximum pressure are considerably distinct. Research limitations/implications – Research on EHL of spur gears in the running-in process considering solid particles, surface roughness and time-variant effect is meaningful to practical gears running-in. Thermal effect can be included in the next study. Practical implications – The analysis results can be applied to predict and improve lubrication performance of the meshing teeth. Social implications – The aim is to reduce gears’ manufacture and running-in costs and improve economic performance. Originality/value – The EHL model that considers solid particles was established. The Reynolds equation was deduced taking the effects of solid particles into account. The EHL of spur gears running-in was investigated considering the time-variant effect, surface roughness, running-in load and rotation speed.

Thermal Elastohydrodynamic Lubrication of Heavily Loaded Line Contacts—An Efficient Inlet Zone Analysis

1998 ◽  
Vol 120 (1) ◽  
pp. 119-125 ◽  
Author(s):  
Mihir K. Ghosh ◽  
Raj K. Pandey
Keyword(s):  
Film Thickness ◽  
Thermal Loading ◽  
Elastohydrodynamic Lubrication ◽  
Thermal Reduction ◽  
Reduction Factor ◽  
Computationally Efficient ◽  
Rolling Velocity ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Inlet Zone

An inlet zone analysis of TEHD lubrication of heavily loaded line contacts has been done using a computationally efficient and accurate numerical method based on Lobatto quadrature developed by Elrod and Brewe (1986). The results under extremely heavy conditions of dimensionless load W = 5.2*10−4 (pH = 2.0 GPa) and dimensionless rolling velocity U = 2.0*10−10(50 m/s) are presented. Significant reduction in thermal reduction factor (film thickness) at high rolling speeds relative to isothermal conditions have been observed. The results of the present work have been compared with the results of Wilson and Sheu (1983) and Hsu and Lee (1994). A correction formula of the thermal reduction factor for the minimum film thickness has been derived for a range of thermal loading parameters, loads, and slip ratios.

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