Experimental investigation on double-impulse phenomenon of hybrid ceramic ball bearing with outer race spall

Spall is a major fault type in rolling element bearings, which can produce specific vibration signals viz. double impulses. Previous reports indicated that the double impulses consist of two parts, the step response and the impulse response, which can be observed in the vibration generated by a spalled ball bearing. A step and an impulse responses will occur when a rolling element is entering and exiting the spall zone, respectively. Precise measurement of the space between the two parts can be employed to estimate the length of the spall zone along the rotating direction, and provide a possibility to evaluate the remaining useful life (RUL) of faulty bearings under running conditions. However, all the previous works are only concerned with the metal ball bearings. The double-impulse phenomenon generated by faulty hybrid ceramic ball bearings is rarely reported. To address this issue, the double-impulse phenomenon of hybrid ceramic ball bearings with different spall lengths on their outer races will be investigated in this paper. The pre-whitening, kurtogram and squared envelop are employed to extract the two events (the entry and the exit) from the picked vibration. Experimental results indicate that the hybrid ceramic ball bearing with an outer race spall can generate shaper double-impulse phenomenon than that from the faulty metal bearings with almost the same outer race spall length.