Bearing failure
It would seem that all the necessary conditions for engine bearings to function long and reliably were met. The proper storage, maintenance, appropriate lubricant and correct installation were taken care of. And yet something strange is constantly going on: unusual noises are heard, and used grease leaks from the housing.
The reason for this can be ... electrical discharges.
EDM (Electrical Discharge Machining) is a process in which the material of the workpiece is removed as a result of electrical erosion occurring during a series of discharges between the working electrode and the surface of the workpiece immersed in a dielectric. This process enables the processing of very hard materials, such as hardened steels or cemented carbides.
This phenomenon is very desirable in metalworking, but not desirable in automation systems.
Stray electric currents travel from the motor shaft, through bearings and housing, seeking grounding. Because ball bearings are in contact with grease, discharge arches cause material erosion, deterioration of grease properties, heat release and bearing damage. This phenomenon can shorten the life of bearings to just a few months. Even those that should work trouble-free for many years. Therefore, looking for the causes of failure should start with checking the motor ground, because even very small, non-grounded voltages cause electric discharges between the bearing balls and its raceway.
How to recognize the problem?
- Initially, electrical discharges cause damage to the bearing raceways and reduce the diameter of the balls. The bearing cage is also damaged. In addition, as a result of discharges and friction, a large amount of heat is created, which leads to the degradation of the lubricating properties of the grease, additionally contaminated with metal particles. Such grease may leak from the bearing and be visible on its housing.
- When the bearing degrades and is not lubricated, even more heat is released. Also because of increasing friction. This causes increasing noise at the metal-metal interface.
- If the bearings are further damaged (or even destroyed), the engine will run unevenly and very loudly.
How to determine if motor bearings have been damaged by an electric discharge and solve the problem?
- Measure the voltage at the engine components. The presence of voltage indicates that underlying faults may be electrical discharges.
- Check the grounding and cables of the drive system for proper grounding and intact shielding of the wires. If any problems were found, they must be removed and the voltages measured again.
