Fracture Analysis of Roller Bearing in Closing Buffer of 220 kV Circuit Braker
The roller bearing in the closing buffer of a 220 kV circuit braker fractured during the closing operation.In this paper,the fracture morphology of the roller bearing was observed by stereomicroscope and scanning electron microscope(SEM).The chemical composition of the outer surface of the roller bearing was analyzed by X-ray fluorescence spectroscopy.The hardness of the outer surface,the center of the cross section and the inner surface of the bearing was measured by hardness tester.The microstructure of the bearing was analyzed by optical microscope(OM).The impact process of the roller bearing was simulated by finite element simulation software.The results show that the main reason for the fracture of the roller bearing of the closing buffer is that the surface hardness of the bearing is high and the hardness of the cross section center is low after carburizing and quenching heat treatment,resulting in a hard and brittle surface and poor impact toughness of the center.When impacted by the cams,the surface of the bearing is broken and the internal plastic deformation occurs,resulting in the locking of the cams,the bearing and the roller.The action load of the mechanism is completely loaded on the locking bearing shell,and finally the whole bearing is broken.
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