Effect of real longitudinal surface roughness on lubrication film formation within line elastohydrodynamic contact

In many applications (e.g. roller, barrel or needle bearings) surface features exhibit longitudinal alignment to the direction of motion. These features are produced by surface finishing techniques in the circumferential direction and are associated with line or very wide elliptical contact geometries. In such a case, the contact length in the direction of motion is considerably shorter comparing its width and the effect of a longitudinal roughness could significantly influence the lubrication film formation. Recent experimental studies have indicated less severe effect of a longitudinal roughness on lubrication film formation in the comparisons with that observed with transversely orientated roughness caused by the inlet perturbation. Nevertheless, these experimental studies have been focused on the behaviour of artificially produced asperities within a circular contact. The quantitative experimental study of longitudinal real surface roughness within a line contact has not been realized yet. That is why, in this study, the line contact formed between a steel tapered roller and glass disc is observed within an optical test rig and the effects of real surface roughness on lubrication film formation are studied. Experiments carried out under pure rolling conditions have shown that the depth is the key parameter that influences the effect on the film thickness. If the roughness features are shallow, the lubrication film shape within the contact follows the shape of the surface closely. However, the groove having only about 800 nm in depth divided the line contact into two parts that behave as two separate line contacts. Such an effect can increase the risk of the wear of rubbing surfaces as the lubrication film thickness between the real machine components can be significantly lower than expected.     

Numerical analysis of non-Newtonian TEHL line contact problem based on real-coded genetic algorithm

This paper presents a new simple numerical method to solve the non-Newtonian thermal elastohydrodynamic lubrication (TEHL) line contact problem based on real-coded genetic algorithm (RGA). To solve the line contact TEHL problem by means of RGA, the initial population producing method is deeply investigated, an appropriate grid partition method is proposed and an appropriate evolutional computation technology is determined. Finally, the fitness evaluation function and the iterative stop qualifications are put forward. The algorithm is examined by some examples, and the results are compared with empirical solutions. The study shows that the application of RGA in the numerical analysis of the TEHL line contact problem is feasible, reliable and sufficiently accurate.     

Numerical analysis of grease thermal elastohydrodynamic lubrication problems using the Herschel-Bulkley model

Grease thermal elastohydrodynamic lubrication (TEHL) problems of line contacts are analysed numerically. The effects of temperature and rheological parameters on grease TEHL are investigated using the Herschel-Bulkley model as a rheological model of greases. The pressure distribution, the shape of grease film, mean film temperature and surface temperature of solid wall in line contacts are obtained. It is found that thermal effects on the minimum film thickness become remarkable at high rolling speeds. The effect of yield stress of the Herschel-Bulkley model on minimum film thickness is negligible, while the flow index and viscosity parameter have significant effects on minimum film thickness.     

Parametric elastohydrodynamic study of a linear contact applied to SiC lubricated with a low‐viscosity fluid

Ceramic materials are often used in tribological applications because of their good mechanical properties. Silicon carbide (SiC) has a low density, high Young's modulus, high corrosion resistance, and very low friction in water. It is a very good candidate for replacing waterproof oil‐lubricated bearings in water pumps and for applications when water is used as a lubricant. In such applications the SiC dissolves very slowly in water to form silicilic acid. After running in, journal and bearing surfaces look like mirrors with very low roughness and very small friction coefficient. This paper reports on a parametric study to model the cylinder—plane configuration, which is then utilised in the specific case of SiC in water. The study was carried out in order to reduce the number of parameters and to ensure good precision of the results. The numerical model is applied to an SiC contact with a very low‐viscosity lubricant (water) using elastohydrodynamic (EHD) conditions. Multigrid techniques for the Reynolds equation and multilevel, multi‐integration methods for the elasticity equations are used to solve the EHD problem. These results are given in non‐dimensional form using the Moes parameters M and L for several velocities and loads. Comparison is made between the two‐ and three‐dimensional cases in order to assess the effects for the cylinder ends.     

一个表面带单粗糙峰的线接触时变微弹流润滑数值分析

通过数值求解研究了一个固体表面的单粗糙峰对两固体形成的线接触时变弹流润滑区压力、膜厚分布曲线的影响。结果表明：粗糙峰的出现，使其对应位置上的压力、膜厚发生急剧变化；粗糙峰的移动，对压力和膜厚的变化、固体表面的凹陷现象以及Hertz接触区的出口颈缩均有不同的影响；另外，压力峰和油膜形状随着粗糙峰幅值和半波长的变化而变化。结果亦表明：准稳态解比时变解过高地估计粗糙峰对压力和膜厚的影响。     

Analysis of the thermal elastohydrodynamic lubrication of a finite line contact

A complete numerical solution for the thermal elastohydrodynamic lubrication (EHL) problem of a finite line contact between an infinite plane and an axially profiled cylindrical roller is obtained. The pressure profile and the film shape in the middle part of the roller are very different from those at the ends. However, the finite line contact results in the middle part of the roller are nearly the same as those of the corresponding infinite line contact. It is revealed that, in a finite line contact, the maximum pressure, the highest film temperature and the minimum film thickness all occur at the end regions of the roller. A comparison is made between isothermal and thermal solutions of a finite line contact. In addition, variations in the minimum film thickness, the maximum pressure and the highest temperature with the dimensionless velocity parameter, the slide/roll ratio and the radius of the end profiles of the roller are discussed.     

An analysis of heat transfer in the thin-layer transducer used for the measurements of EHD contact parameters

Thin-layer transducers, which are mainly used for the measurement of the EHD contact parameters, have to be attached to an isolating layer separating it from the steel roller. The isolating layer, made of SiO_x or Al₂O_3, disturbs heat flow in relation to the real contact. This paper presents a solution for the system of two heat conduction equations for a two-layer body: SiO_x-steel. The boundary conditions reflect the real situation during the measurements carried out by means of these transducers. The solution was obtained for an assumed temperature distribution of the isolating layer surface. Computation results for two different temperature distributions of the surface and for various values of the SiO_x-layer thickness are also presented.     

Temperature rise due to sliding in rolling/sliding elastohydrodynamic lubrication line contacts: an efficient numerical analysis for contact zone temperatures

An efficient numerical method based on Lobatto quadrature analysis is adopted for a rigorous analysis of temperature in elastohydrodynamic lubrication (EHL) line contacts. Temperature distributions are calculated for maximum Hertzian pressures and rolling speeds varying between 0.5 to 2.0 GPa and 1 to 30 m/s, respectively. Significant mid-film temperature and surface temperature increases have been observed at higher rolling speeds with an increase in loads and slip ratios. Results have been compared with the results of Manton, S. M., O'Donoghue, J. P. and Cameron, A., Temperatures at lubricated rolling/sliding contacts. Proceedings of the Institution of Mechanical Engineers, 1967–68, 182(417), 813–824. An empirical equation is presented for the prediction of non-dimensional maximum mid-film temperature in the contact zone in terms of the dimensionless thermal loading parameter Q, dimensionless load W and slip S, as:

     

A non-symmetric discretization formula for the numerical solution of elasto-hydrodynamic lubrication circular contact problem

The control volume method has been employed to obtain an appropriate discretization scheme for the numerical solution of the two-dimensional Reynolds equation. A non-symmetric discretization formula has been developed and incorporated into the author's computer program. The lubricant film thickness distribution for a typical configuration of the EHL circular contact has been solved as a benchmark. Results are presented. Convergence behavior is investigated using different density of grids for computations. A comparison with the finite difference-based formula is presented. Dependence of results on the grid density is reduced in comparison with results obtained using the finite difference formula. On conclusion, an additional discussion on the discretization of the Reynolds equation is presented and further recommendations are given.     

弹流润滑高速角接触球轴承旋滚比分析

为了提高主轴轴承的高速性能,提出弹流润滑高速角接触球轴承的数学计算与分析模型.针对实际生产工况建立弹流润滑高速角接触球轴承分析计算模型.并将弹流润滑高速角接触球轴承的旋转打滑分析转化为旋滚比的分析.通过计算与分析,得出弹流润滑高速角接触球轴承在不同工作条件下或选用不同轴承参数时,轴承旋滚比的变化规律及旋滚比与各参数之间的关系.为实际生产中高速角接触轴承的选择使用和轴承的参数优化设计提供了理论依据,并为机床高速主轴用支撑轴承的设计与优化提供分析计算模型.