Diagnostics of gear units

Vibration diagnostics is one of the most important tasks of gear inspection (GI), defect detection and evaluation of a residual life under the actual operating conditions or under the conditions maximum similar to the actual ones.

This example illustrates usability of a vibroacoustic analyzer ZET017-U8 for controlling performance of gearing. Applicability of vibroacoustic methods for diagnostics of the test equipment designed to inspect damages of the gear wheels under the fatigue test conditions is illustrated with the example of experimental gear’s operation.

Each gear unit measurements and diagnostics scheme has its own features and modes of mechanisms’ operation. For detailed understanding of the occurring processes, it is necessary to use various measurement channels coming from various sensors. The vibration acceleration sensors (vibration pickups) are installed as close as possible to an area of gear units. It is advisable to install them in the longitudinal and transverse directions of rotation axis. The reference vibration pickups are mounted on the bearing supports of drive mechanism, service engines, and pumps. A microphone is mounted near the area of controlled gear units. The RPM sensor may be installed on one of the drive shafts. In addition to these parameters, temperature (thermocouple element or thermoresistor), pressure (pressure sensor), mechanical stress (strain sensor), voltage, frequency and phase of the supply mains may be monitored as well, if necessary.

The tests are carried out under the conditions, when a large number of different mechanisms operate creating acoustic, vibration and electromagnetic noise. The main task of applying different methods of signal analysis is the possibility to extract a “useful” signal of the tested unit against the interfering factors.

Diagnostics can be performed in the following ways:

• based on spectrum of vibration signal;
• based on ultra narrow-band spectrum;
• based on co-spectrum characteristics;
• based on inter-correlation characteristics;
• based on spectrum of envelope curve;
• based on order normalization.

The analyzer ZET 017-U8 allows simultaneously running several programs of signal analysis and display. This enables to create various complexes for testing, systems of controlling and monitoring the condition of gear units. The combined application of several programs allows carrying out the tests in non-steady-state conditions — on speed-up and running-out of the gear pair.