Observations of the size of damages or wear particles, and fluctuations of the ball load are useful for the quantitative evaluation of operational abnormalities in a ball bearing. An ultrasonic technique was therefore attempted for use as a semi-quantitative measurement method. Ultrasonic wave pulses were directed into a bearing housing from an ultrasonic probe attached to the outside of the housing. The pulse waves were partially reflected from the interface between the housing and the outer ring of the bearing. Semi-quantitative evaluation of abnormalities becomes possible on the basis of observations of the magnitude and frequency of the echo height fluctuation. Diagnosis of bearing abnormalities was performed based on the evaluation of size, fluctuation velocity and mode of echo height fluctuation. The measurement of a model indentation with 0.3 mm width added to the inner ring and quantitative evaluation of the growth of an indentation were demonstrated.
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