Temperature measurement of debris particles in EHL contacts

Abstract

Dents caused by entrained debris are now the main cause of fatigue failure in rolling element bearings. It is therefore important to be able to understand and predict the deformation behaviour of particles in elastohydrodynamic contacts. This paper describes a new method to study debris entrainment. This uses a sensitive infrared microscope to map the temperature of a contact between a steel ball and coated sapphire disc as lubricant dispersed with bearing dust is entrained. Full-field thermal maps were acquired at a sufficient rate to monitor the deformation of a single particle on its journey through the contact. Under the low-speed, high-sliding conditions studied, the temperature rise increases from when the particle is trapped by the inlet to reach a peak near the contact centre, where shearing is a maximum. Under these conditions, temperature rises are typically of the order of 10C, which is significantly lower than has been predicted theoretically. Even lower temperature rises were observed under pure rolling conditions, since minimal shearing occurs. Experimental results are also compared with existing models used to predict particle behaviour. Measured radiation distributions confirm qualitatively the ductile particle deformation mechanisms originally proposed by Hamer et al.