Bearing damage FTF
Increased wear due to incorrect lubrication
For the correct functioning and an optimized durability of a rolling element bearing, lubrication is from the upmost importance. Too little lubrication caused friction, wear and high temperatures. Too much or over lubrication can however also lead to increased bearing temperatures because of its insulating properties. These high temperatures can on their turn cause degradation or complete disappearance of the lubricant.
Damaged bearing retainer
For the incineration process of raw and household refuse, many fans and blowers are used. Some of these fans are critical to the process. Malfunctions should be avoided at all times. For an optimized maintenance planning and in order to increase the reliability and availability, the most critical pumps and fans are monitored in a 3-monthly condition monitoring program. The critical machinery is besides the vibration measurements also visually and audibly monitored by the plants personnel in weekly inspection routes.
During a scheduled lubrication of the bearings of a large electric motor of one of the critical fans, the maintenance technician notices a soft metallic sound. After the application of the necessary lubricant the sound disappears directly. When the technician walked past the fan a short while later he once again notices the metallic sound. In order to determine the cause of the sound Van Geffen VMS directly performs an additional vibration measurement. Analysis of the "normal" spectral measurement hardly showed any abnormalities. However the use of more specialized analysis technologies does show a very high frequency modulation of the fundamental train frequency. The responsible production and maintenance personnel were directly notified since a damaged bearing retainer can cause a bearing to fail very suddenly and very quickly.
In order to prevent a sudden failure and large consequential losses it is decided to shut down the fan outside the planned outage and to replace the bearing. Bearing damage analysis on the exchanged bearing showed large lumps of clotted and hardened lubricant. The clotting and hardening of the lubricant is most probably caused by the usage of different kinds of lubricant in one bearing. Mixing different kinds of lubricants can cause chemical reactions degrading or complete loss of the lubricating properties.
The bearing damage analysis performed by Van Geffen VMS showed that due to the absence of lubrication the rolling elements had been rubbing into the brass retainer. This rubbing had caused the retainer to wear and sag over the rolling elements enabling the retainer to contact the inner or outer ring of the bearing. If this bearing was not replaced at this moment, it would almost certainly have lead to a soon and complete failure of the bearing. The large clearances that occur when a retainer breaks would also cause extensive damage to the electric motor and the coupling.