July 16, 2015 By Kay Cabaniss
AC motors require relatively little maintenance, however, reliability maintenance is critical to achieving long, reliable motor life. This type of maintenance pertains to both mechanical and electrical considerations. Studies indicate that more than 50% of motors fail due to mechanical reasons. To prevent mechanical failures, special preventive precautions should be taken around bearing lubrication and motor cleaning.
A majority of motor failures are related to bearing failures, and a major cause of bearing failures is inadequate lubrication. Bearing life is directly proportional to lubricant life, so it’s important to remember that all non-sealed bearings require re-lubrication during their entire service life.
95% of the motor population is lubricated with grease, while the remainder use oil. How much of each to use is not an exact science, it’s more of an art depending on operating conditions and the environment. Consider these factors when lubricating your motor’s bearings:
The manufacturer’s recommended lubrication procedures.
Motor service conditions, such has environment, temperature, and operating hours.
The proper amount of lubricant based on bearing size and type.
Grease compatibility. When mixing different greases, incompatibility is evident when soupiness or hardening occurs.
Best practices for lubrication frequency and volume can be found the motor instruction manual. It is important to identify the appropriate environment and bearing type to extend the motor life. Taking a few minutes to acquaint your maintenance staff with the proper procedures will result in longer motor life and less downtime.
We also recommend the following best practices when the time comes to re-grease.
1.STOP the motor, unplug it, and re-lubricate it while it’s still warm
2.Clean the grease inlet fitting
3.Remove the grease drain plug if installed
4.Add the recommended volume of fresh grease using a hand operated grease gun
5.Plug the motor back in and run it for 2 hours with the grease drain open to allow for grease purging
6.Replace the grease drain plug
Dirty motors run much hotter than clean ones due to a reduction in effective cooling properties. A motor that is not properly ventilated is more likely to overheat, leading to early motor failure. So it’s important to inspect your motors at regular intervals to ensure the ventilation openings are clear. We recommend 500 hours of operation or every 3 months, whichever happens first.
1.Check the interior and exterior of the motor to ensure they are free of dirt, oil, grease, water, etc. Oily vapor, paper pulp, textile and lint can accumulate and block motor ventilation.
2.Check ventilation filters and clean or replace as necessary.
3.Perform a dielectric check test periodically to ensure that the integrity of the winding insulation has been maintained. Record the readings, and immediately investigate any significant decrease in insulation resistance.
4.Check all electrical connectors to be sure they are tight.
Properly lubricating non-sealed bearings and keeping the motor clean, both inside and outside, are simple preventive maintenance steps that will enhance the mechanical life of your motor. Determining the right schedule for your environment and operating conditions is critical to the success of the maintenance program you design.