Vibration analysis on test stands

Vibration analysis on test stands

Problem

During the end-of-line testing of electric motors, assembly errors as well as the bearing and balancing condition are to be determined.

Solution

Example

Following series production of electric motors, an EOL test is carried out to check all technical specifications. The scope of tests carried out to date is to be extended to include a vibration test. In the course of a test measurement, different fault patterns were prepared on engines of different sizes and designs. This made it possible to determine a parameter set for the determination of definite characteristics for vibration monitoring. This includes the following errors:

Unbalance state:

The vibration velocity on a frequency range of 10 ... 1000 Hz was selected. Thus, the oscillations at speed (= unbalance state) are reliably detected. Permissible limit values are taken from DIN ISO 60034-14, depending on the motor power / size.

Bearing Condition:

Damaged bearings generate typical signatures of the damaged bearing component in the envelope spectrum. Bearing damage can thus be detected by the presence of lines in the envelope curve spectrum. The limit values are determined individually according to bearing type.

Missing Bearing:

If, in the course of production, a bearing was not assembled, this can be proven in the envelope spectrum. The lines are noticeable at rotational speed and higher orders.

Damage to bearing seal ring:

If the sealing ring of the bearing has been damaged during assembly, it can be detected by envelope analysis. The cage frequency and its multiples are clearly visible.

 

VibroMatrix is used as the measuring system for monitoring. The listed monitoring features were implemented in a specially configured setup. This does not only allow a general recognition of errors on the test object, but also the underlying error is directly named, so that a targeted rework can be carried out.