Application of an Envelope Technique in the Detection of Ball Bearing Defects in a Laboratory Experiment

To judge the diagnostic capabilities of a envelope technique Bearcon signature Carl Schenck AG, Germany artificially damaged ball-bearings SKF 6207 were run under oil lubrication at different radial loads and speeds in a laboratory experiment. Respectively outer race, inner race and ball damages of different sizes were introduced by spark erosion and the response of the measuring system was analysed. The results showed, that vibration spectrum components of outer race defects showed up in the envelope spectra of undamaged bearings and that detectability of defects was primarily limited by the speed of the bearing, sometimes the automatic scaling facility of the analyser was a limiting factor. Inner race and ball defects showed the well known effects of load modulation in the defect-contact zone, which can become dominant in the envelope spectra at high loads and speeds. This phenomenon could be confirmed by computer simulation. The detection of ball-damage was hampered by the fact, that over rolling of the defect in purely radially loaded bearings takes place incidentally. This draw back could be mitigated by applying a trigger-technique to the envelope signal.