Failure Analysis of Fatigue Fracture on the Outer Ring of a Cylindrical Roller Bearing in an Air Blower Motor

In order to identify the causes of a fracture incident that occurred on the outer ring of a cylindrical roller bearing within an air blower motor, diverse characterization analyses were conducted in this study. Metallurgical structures and chemical compositions of the bearing’s matrix materials were inspected by metallographic microscope and photoelectric direct reading spectrometer. Scanning electron microscope and energy dispersive spectroscope were applied to detect the microscopic morphologies and micro-area compositions on the fracture surfaces and contact surfaces. The compositions and thermal properties of the lubrication medium, the grease, were also examined. Analysis results revealed that interaction between dry friction and impact both led by the degraded grease due to decomposition and oxidation at elevated temperatures, which resulted in serious wear of the outer ring and the cage, was the main cause that originated and propagated the fatigue cracks on the corners of the outer ring, and eventually resulted in the fracture. Finally, countermeasures and suggestions have been proposed.