Advice for Greasing Electric Motor Bearings

Noria Corporation

"What are your thoughts on greasing motor bearings on acceleration/demodulated vibration levels as opposed to a schedule dictated by a running hours counter on the motor's control panel? I have an end user insisting on the latter despite my findings of high vibration."

Greasing electric motor bearings doesn't have to be tricky or based on someone's gut feeling. Simply tracking runtime on a motor and greasing on a predefined routine is largely guesswork and can lead to overextended greasing intervals, which puts the bearing in starvation mode.

It could also result in greasing far too frequently, which in turn prematurely fills the bearing cavity with grease and increases the risk of damaging the bearing shields and introducing grease into the motor's windings.

Using some type of feedback mechanism is highly recommended, especially if the motor is operating in a critical process. Several different technologies can help identify the optimum greasing interval, including vibration analysis, thermography, ultrasound monitoring and grease sampling. Each has associated strengths and weaknesses and should be selected based on the parameters of the motor's operating conditions and environment.

A simple cross-check of the motor's size, speed and position will enable you to approximate how often to grease the bearings, but this will not account for all the variables you would expect to find in these applications. Vibration analysis can help with this by actively monitoring the bearing's condition. Although you will be able to see some of the impact of the grease's oil loss, extensive monitoring and a trained eye are usually required to detect fluctuations.

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Consider ultrasound to help fine-tune your greasing frequency. Ultrasound can monitor lubricant degradation with more finesse than other technologies. This type of monitoring allows you to not only know when the bearing needs grease but also can indicate when you should stop adding grease during the application process.

Most of the other technologies don't have the capability to provide reliable, real-time information on the greasing frequency and the volume to be pushed into the bearing.

Thermography has been used with sporadic success. The problem with utilizing temperature as a gauge for greasing is that it lags real-time action. The feedback comes much slower, and there will be an increase in temperature as you are applying grease.

This elevated temperature may dissipate quickly or take days to drop back to normal levels. You can then lose much of the data you were hoping to monitor for accurate greasing.

Grease analysis is gaining in popularity. While it is not real-time monitoring, you can check the grease's rate of degradation and adjust your greasing intervals accordingly. This technology also allows you to track bearing degradation by capturing wear debris in the sample.

Overall, many different technologies can be used for greasing electric motor bearings. Regardless of the method you choose, it is important to validate and fine-tune your current frequencies for lubrication activities. 

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