Effects of couple stresses and surface roughness on the film thickness of heavily loaded rollers

Abstract

Purpose

This paper aims to study the effects of couple stresses and surface roughness on the minimum film thickness of heavily loaded rollers and to discuss these by following Grubin's approach and Crook's approximations.

Design/methodology/approach

A generalised form of Reynolds equation for rough surfaces with lubricant as couple stress fluid is derived. This equation is then used to study the combined effect of couple stresses and surface roughness on the roller bearings under heavily loaded conditions. EHD minimum film thickness expressions is obtained by following Grubin's approach and Crook's approximation and it is studied numerically.

Findings

It is found that, as the chain length of the additive molecules increases, the elastohydrodynamic minimum film thickness increases. Also, as the mean height of roughness asperities increases, the elastohydrodynamic minimum film thickness increases for the transversal roughness and it decreases in the case of longitudinal roughness.

Research limitations/implications

These effects are studied theoretically by the mathematical equations in heavily loaded roller bearings.

Practical implications

Reduction of the film thickness in the EHD lubrication between the rollers can be compensated by the use of lubricants containing additives of molecules of size. As a result the bearing performance can be improved.

Originality/value

This research paper provides a closed form of the expressions for the bearings in EHD lubrication and is studied with regard to couple stress parameter. This paper helps to manufacture better bearings.

Citation

Raghavendra Rao, R. and Raja Sekhar, K. (2007), "Effects of couple stresses and surface roughness on the film thickness of heavily loaded rollers", Industrial Lubrication and Tribology, Vol. 59 No. 6, pp. 285-296. https://doi.org/10.1108/00368790710820883