Be it a brand new motor assembly, or one already in use, the right information on bearing protection will allow you to extend the life of the bearing up to the motor’s lifetime. Best practices can be established by taking care of the following factors.
1. Bearing Inspection
It is a good idea to cut and inspect each bearing in motors that are operated on variable frequency drives. This way, you can obtain information that will help make optimum repair and improve performance.
Inspect the following:
• Marks of Excessive Heat
• Hardened Grease
• Contamination
• Black Grease
• Grease Escaping the Bearing
As far as burnt grease is concerned, it should be understood that electrical arcs in a motor bearing would often have a hand in bringing down the lubricant quality. This happens due to the overheating of the lubricant due to the sparks. The same factor that results in the race damage in bearings.
Besides burning the grease, the electrical sparks result in the distortion of small particles from the bearings to loosen from the bearing and enter the grease. These particles become agents of abrasion.
2. EDM Inspection
Electrical discharge machining are millions of tiny electrical pits that are formed when the current moves through the motor’s bearings. In a motor, the electrical charge overcomes the dielectric of the lubrication in the bearing and moves through the inner race across the bearings. This is when EDM forms and results in bearing damage.
3. Frosting
Frosting is visible as a greyish discoloured line around the bearing race. It may also be visible on the inner and outer race. The greyish part may be a result of electrical EDM whose inspection under a microscope will show whether the line is actually EDM or something else. The likelihood of the cause being EDM is higher if the motor has been operating on a Variable Frequency Device that had no protection for bearing.
4.Fluting Damage
You can identify fluting with bare eyes as it appears with a distinctive washboard pattern. If not the naked eye then 10 x magnifications will help you identify fluting. Fluting is oftentimes thought of as mechanical bearing damage, so you should be careful when reading the pattern to detect the true nature of the problem.
The sooner you make these best practices a part of your motor inspection regime, the lesser will be the damage you see on the ball bearings of the motors.