Establishment of lubrication diagnostic technique with ultrasonic method

将超声波技术应用于球轴承寿命试验中的异常检测。超声波脉冲从安装在轴承座外部的压电式振动器进入轴承座。这些脉冲部分地从轴承的外壳和外圈之间的界面反射。由于固-固接触和与中间气体或液体接触之间的声阻抗不同，回波的强度取决于在界面上形成的实际接触面积，它可以用作局部接触压力的测量。当在正常情况下运行的轴承的载荷范围内确定时，经过滤波的回波脉冲的强度会产生与滚珠通道相对应的平滑的、接近正弦的峰值。然而，磨屑等固体颗粒侵入滚珠和滚道之间的滚动面会导致局部接触压力的突然上升，而滚动面上形成的缺陷则会导致滚动面的突然下降。实验结果表明，这些“事件”是通过超声波技术检测到的，而且，当累计旋转次数达到轴承总寿命的80%时，这些事件在一定时期内的强度或持续时间的简单总和开始增加。这表明有可能及早发现球轴承中的异常，这些异常会由于表面裂纹而导致疲劳故障。

An ultrasonic technique is applied for detection of abnormalities in a ball bearing in its life test. Ultrasonic wave pulses are entered into a bearing housing from a piezoelectric vibrator attached to the outside of the housing. Those pulses are partially reflected from the interface between the housing and the outer ring of the bearing. Because of the different acoustic impedance between the solid-to-solid contact and the contact with an intervening gas or liquid layer, the intensity of the echo depends on the real contact area formed at the interface, and it can be used as a measure of the local contact pressure. When determined in the loading zone ofthe bearing which is running in a normal condition, the intensity of the filtered echo pulses produces smooth, nearly sinusoidal peaks corresponding to passages of the balls. However, invasion of a solid particle like wear debris to the rolling surface between a ball and either of the raceways causes a sudden rise of the local contact pressure, while a flaw formed on their rolling surface causes its sudden drop. The experimental results show these "events" are detected by the ultrasonic technique, and, further, a simple sum of the intensity or of the time duration of those events over a certain period starts to increase when the cumulative number of revolution reaches, typically, 80% of the total bearing life. This indicates the possibility of the early detection of abnormalities in ball bearings which lead to fatigue failure due to surface-originated cracks.