鋼球の衝突音の研究

抄録

The character of the impact sound, one of the main causes of machinery noise, is examined by using two steel balls colliding with each other.
First, the mechanism of the production of impulsive sounds of two steel balls collision is studied theoretically and also it is ascertained experimentally by using steel balls of various diameters which are used for ball bearings.
According to H. Hertz theory, the contact time is proportional to the (-1/5) power of relative collision velocity. Therefore, the average acceleration of each sphere becomes proportional to the (6/5) power of the collision velocity. On the other hand, the sound pressure at a point of space is proportional to the acceleration of the moving surface of sound source. Hence, the maximum value of sound pulse becomes proportional to the (6/5) power of the collision velocity.
The free vibration of the steel ball excited by the collision is studied by using a small transducer of piezoelectric material attached to one of the two balls, and the period of this vibration is found to be so short that the intensity of the sound produced by the free vibration becomes small to be negligible compared with that of the impact sound.
The dynamical characteristics of the microphones used for catching the sound pulses are examined fully to obtain the correct analysis of the records of the sound pulses obtained by the microphones.
Lastly, the impact sound character of the oblique collision of steel balls is studied, and it is found that the effect of the parallel component of the velocity to the center line becomes large on the impact sound and that of the right angle component becomes small to be neglected respectively.