A study of contaminated lubricants concerning wear, rheological properties and sample withdrawal

Abstract: The wear of a machine, whether it is due to fatigue or abrasive wear, will add contaminants, in the form of particulates, to the system in question. Since a total breakdown of the machine can be rather costly, one wants to be able to foresee breakdowns and increase the machine life. Follow-up checks of machines are often performed to enable one to detect an increase in wear, and thereby replace the machine or remove it for service. This licentiate thesis mainly deals with the problems associated with contamination control and sample withdrawal. A survey of where and how to take a representative sample is performed using Stokes' law and the migration of spheres in a channel. Some different techniques to measure the contamination are also presented, together with their advantages and disadvantages. Sampling routines for proper sample withdrawal are included. The thesis also includes some field aspects concerning the influence of particles and the wear of grease-lubricated rolling element bearings.