Characterization of Embedded Debris Particles on Crankshaft Bearings 2024-01-2594

Crankshaft bearings function to maintain the lubrication oil films needed to support crankshaft journals in hydrodynamic regime of rotation. Discontinuous oil films will cause the journal-bearing couple to be in a mixed or boundary lubrication condition, or even a bearing seizure or a spun bearing. This condition may further force the crankshaft to break and an engine shutdown. Spun bearings have been identified to be one of the top reasons in field returned engines. Excessive investigations have found large, embedded hard debris particles on the bearings are inevitably the culprit of destroying continuity of the oil films. Those particles, in particular the suspicious steel residues, in the sizes of hundreds of micrometers, are large enough to cause oil film to break, but rather fine and challenging for materials engineers to characterize their metallurgical features. This article presents the methodology and steps of debris analyses on bearings at different stages of engine build. Common and advanced materials characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), have been employed to evaluate the appearance, size, composition, characteristic spectrum, and even microstructure, microhardness of the deleterious particles embedded on the failed bearings. The successful characterization of the troublesome particle material has made it practical in the relevant component manufacturing process for cleanliness improvement. Advantages and shortcomings of the analytical technique are also commentated.