KCF Technologies Blog

Mike on Maintenance: Grease Compatibility

In my last blog, Mike on Maintenance: Overgreasing, I included this calculation:
Where G = the amount of grease in ounces
            D = the bore diameter in inches
            B = the bearing width in inches
I posted it incorrectly, it should be:
Where G = the amount of grease in ounces
            D = the bearing diameter in inches
            B = the bearing width in inches
The metric equivalent is 0.005 instead of 0.114
Use the calculation as a logical approach to greasing electrical motors.

With the correct calculation there are a few things to consider - operating temperature, ambient temperature, wet environment, bearing mounted on vertical shaft, vibration levels. Also bearing configuration like ball bearing, roller bearing and speed of rotation. Do your homework, take time to read some machinery lubrication articles/publications.
Grease Compatibility – Please read the chart, which I’ve posted below from the Machinery Lubrication website.

Figure 1. Relative Compatibility Rating
B = Borderline C = Compatible I = Incompatible 

Note: This chart is a general guide to grease compatibility. Specific properties of greases can dictate suitability for use. Testing should be conducted to determine if greases are compatible.

Grease Compatibility is very critical to machinery health. When you see that oil seeping from your bearing and always wondered why it does that, take a look at the grease that is being used.

A couple years ago I was part of an install of vibration sensors on some new, very critical supply air fans at a huge research facility. The fans were being used to heat/cool the building during final construction phases and at that time were being maintained by the installer. I noticed oil dripping down the bearing ends of the 125 HP direct drive motor.

I looked at the motor plate to identify what the motor manufacturer specified for lubrication. It was a polyurea, NLGI #2. I then went to the contractor that was maintaining the supply fans even before the bond period begain to asked what type of grease they were using, the HVAC Superintendent said “ grease is grease” we only have one type grease on the job site !!!!
The grease they had been using was identified and was incompatible with the polyurea that the motor manufacturer specified and what was purged into the bearing from the factory when the bearing was made. To cut to the chase the contractor was made to clean and purge the wrong grease out of [12] motor inboard/outboard bearings at a significant cost to the contractor. If not caught the customer would have incurred the costs of labor and the bearing and motor life expectancy would have been shortened considerably.

So please, take time to identify what type of grease you are using, the amount of grease for individual applications, and if the bearing requires lubrication.

Next Blog – Overgreasing Preventative Measures 

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