Acoustic Emission testing

Rotating machinery fault diagnosis

Update time：2008-03-26 16:21　　　 Viewed：次

The power industry at home and at abroad have paid special attention to the monitoring of steam turbine vibration and friction. However, since having no means of monitoring friction, power plants mainly monitor vibration and attempt to use the change of the vibration table indicating value to monitor friction indirectly, many turbine equipped with vibration monitoring instrument have occurred a lot of serious friction accidents, but the indicating value of the vibration table doesn't change or the change is tiny, so it is necessary to look for a way to directly monitor the steam turbine dynamic and static friction. According to the features of friction signal, we introduce principle and method of monitoring steam turbine dynamic and static friction by acoustic emission signal.

Metal grid work on the surface will change when metal rubs. In this process, the energy it released would be released in the form of elastic wave and acoustic emission is produced.

In actual artifacts, acoustic emission wave transmission is much more complex than the ideal medium transmission. The acoustic emission signal from turbine’s dynamic and static friction spreads through blade, impeller, shaft, whose medium is limited thickness plate. In the process of transmission, the wave reflects on the two interface and every reflection produce mode conversion , so transmission like this has complicated characteristic. Therefore, it is very difficult to deal with transition phenomenon like acoustic emission wave. Roughly speaking, tracing apparent velocity of the wave is similar to that of shear wave velocity.

For characterization parameters of acoustic emission signal, acoustic emission rate is commonly used in general engineering. Set a certain threshold voltage, ringing waveform than the threshold voltage of rectangular pulse formation, counting the ringing pulse number, ringing count per unit time is called acoustic emission ringing count rate, hereinafter referred to as acoustic emission rate.

Besides, there are many characterization parameters, such as amplitude, amplitude distribution, RMS characterization parameters voltage, energy, and energy distribution.
(Editor：admin)

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