STUDY OF THE INFLUENCE OF ABRASIVE PARTICLES ON A JOURNAL BEARING WITH A SOFT COATING (PB-CU-AL) UNDER BOUNDARY LUBRICATION CONDITIONS

Some times operating conditions, namely, misalignment, overheating and the start/stop of engine generate boundary lubrication conditions increasing wear of journal bearings (JBs). Thus, debris are a consequence of wear and fatigue either from JBs or other lubricated mechanical components. Debris are commonly immersed in the oil and recirculated through the entire lubrication system interacting with all the lubricated mechanical elements and accelerating wear rate due to three-body abrasion. The aim of this work is to evaluate the effects of abrasive particles on the wear behaviour of sections of an actual JB coated with a soft alloy (Pb-Cu-Al) by replicating boundary lubrication in JBs using a micro-scale abrasion test setup. Steel balls were used to replicate the shaft counter face for the tests. Initially, the tests were carried out with a slurry prepared with distilled water and SiC micro-particles at a concentration of 20% vol. On the other hand, a SAE 10W-30 engine oil was blended with SiC micro-particles at different concentrations to replicate an engine oil contaminated with abrasive particles. The slurry was tested at 26°C while the contaminated oil was tried at two different oil temperatures (26 and 100°C). The wear scars produced were measured and analysed by optical microscopy, SEM and contact profilometry. It was found that clean oil generated higher wear than oil contaminated with SiC particles at different concentrations since a layer of SiC particles was generated on the scars by embedment of many particles in the soft coating. It acted as protective layer for the JB's coating reducing wear. However, it generated significant wear in the ball surface.