Posted on behalf of Robert Allen,

I have some large DC motors used in wind tunnels for automotive testing. The maintenance manual requires grease flushes every year. These motors are mounted inside the wind tunnel and to removing the motors to get to the bearings will incur a lot of down time and additionally 100’s of thousands of dollars for rigging equipment. Someone suggested we get hot oil flush equipment to do this. I was wondering if through your travels you have encountered anything like this.

Robert Allen, CSE, FMA

It seems to me that the person who wrote the maintenance manual did not give too much thought to the welfare of the end user of the DC motor. It is very easy to put something on the paper; it is much harder to actually do it.
I fail to understand why should such a flush be done at all. A regular, documented greasing program will maintain fresh grease in the bearing without any hot flushes for the life of the bearing. And I would think that the author of the manual would come to the same conclusion in a hurry if he were responsible for the operation of the motor.
jank

This message has been edited. Last edited by: jank,

I agree. We have thousands of greased bearing motors in a wide range of sizes at our plant and none of them demand that kind of regimen.

But it does depend to a certain extent on the application/conditions. A very large high speed bearing operating continuously might demand very frequent grease addition which may fill the housing rapidly (and will be less tolerant of a full housing since it is high speed and probably already running hot)

We can make some guesses about if and why this motor would require such special care if we knew:
1 - Motor speed
2 - Bearing part number
3 - Duty cycle (continuous or a few hours a day or a few hours a week)
4 - Ambient temperature
5 - What is the greasing regimen. How often add and how much?
6 - Any special conditions. Abnormally high load, environmental contamination threat, etc.

I have occasionally heard people suggest various approaches to flush out at least a portion of the old grease without disassembling the motor when the housing becomes full after many years of greasing (a low speed/small bearing will probably tolerate the full housing but a high-speed large bearing won't). I've heard people suggest pressurized air or hot oil. At work I think I have a hardcopy "procedure" for this that was passed out by a speaker at a seminar once. Will check on Monday.