Electrostatic wear monitoring of rolling element bearings

Research and development work at the University of Southampton using an electrostatic condition monitoring system developed by Smiths Aerospace Information Systems has shown that electrostatic charge signals can be used to detect the onset of wear in lubricated tribo-contacts. Preliminary investigations have already demonstrated the viability of this system when tested on a laboratory-based pin-on-disc rig, a reciprocating laboratory wear rig and in an FZG gear scuffing rig. These preliminary experiments have indicated several charging mechanisms may be involved, namely—tribo-charging, localised surface charge variations, exo-emissions and debris generation. The electrostatic monitoring system has now been implemented on a taper-roller bearing test rig. The electrostatic system employed comprises three wear-site sensors (WSS) and an oil-line sensor (OLS). The WSS are mounted close to the bearing in order to monitor the earliest stages of component surface breakdown and wear, whereas the OLS is placed in the re-circulation oil-line to monitor debris generated and transported from the deteriorating component. For the present tests, taper-roller bearing wear was monitored using electrostatic sensors as well as vibration and lubricant temperature measurements; also two additional oil-line monitoring devices, supplied by Macom Technology Ltd., using Eddy current technology and ferromagnetism to sense debris entrained in the lubricant recirculating system were employed. The experimental data shows that the electrostatic monitoring systems detected bearing deterioration up to 4 h prior to complete failure (seizure) during a seeded fault test. The electrostatic wear-site and oil-line sensors detected changes in charge that coincided with increases in vibration, temperature and debris generation detected by the two Macom units