I'm loking for general information on electric motors. When motors are found to be over-lubricated, is it mostly the non-drive end (nde) or the drive end (de) that seems to be the culprit?

Or, is it split between both ends?

Just curious,
Wally

Wally
I owned a electric motor shop for year. And made a lot of money off of over greased motor bearings.

The outboard bearing in the motor was over greased the most. Because it was the smaller bearing in the motor and was greased just like the bigger bearing on the drive end.

The big question is how much grease to put in and how do you know that the grease is going into the bearing not on to the stator.

I know that people are going to say pull the plug on the end bell and the old grease will come out. But this seem to be a flaw in most motors.

Greg Gorham

I apologize if this gets off-course, but it seems that most motor manufacturers use a polyurea based grease. Is it the best suited for the job?? Greg, being in the motor repair business, what type of grease did you usually use when repairing motors, and how many customers supplied their own grease for motors you were repairing for them? Did you ask your customers if they had a grease preference for you to use?? Thanks for the in-sights.

quote:

Originally posted by Greg Gorham:
Wally

I know that people are going to say pull the plug on the end bell and the old grease will come out. But this seem to be a flaw in most motors.

Greg,

As far as I know, if you do the above and let the drain plug stay off for about 20 min while motor is running in order to let the excess grease out, the bearing will recieve the exact amount of lube it needs.

So what is in your view specifically flawed in this approach and what do you recommend? Please mention what type of bearing you apply your procedure for: open, single, double shielded.

Penman,
Every bearing manufacturer that I know of recommends a polyurea grease for motor bearings. Everyone recommended Chevron SRI for years, and this was the grease that SKF and others packed their bearings with when they shipped them. Recent advances in lubrication have caused most of the bearing manufactures (and motor manufacturers) to switch to Exxon's Polyrex EM (the EM is for Electric Motor). This is still a polyurea and is compatible with SRI. If you buy double shielded or sealed bearings, chances are it has Polyrex EM inside it, unless it was ordered special for a particular environment. Polyurea greases are particularly well suited to the typical loads, temperatures, and environment that exists inside a electricl motor bearing. Lithium and moly based lubricants have strenghts in other area's, and are more commonly found in pillow block bearings. Polyurea is not compatible with anything else except some rare calcium and sodium based greases, so don't mix!

quote:

Originally posted by David_G:

quote:

Originally posted by Greg Gorham:
Wally

I know that people are going to say pull the plug on the end bell and the old grease will come out. But this seem to be a flaw in most motors.

Greg,

If you do the above and let the drain plug stay out for about 20 min while motor is running in order to let the excess grease out, the bearing will recieve the exact amount of lube it needs.

So what is in your view specifically flawed in this approach and what do you recommend? Please mention what type of bearing you apply your procedure for: open, single, double shielded.

David
The 20 min. rule is what a lot of people go by. But if you can just take the plug out for a few days and see if more grease comes out. I'll bet that it does.

I have some companys leave the plug out all the time because when the motor heats up the grease does come out. It's better to have the old grease come out the grease plug hole than on to the stator. If the grease tube is full of old grease and it should be. What is going to get past the old grease and back in to the bearing?

The outboard bearing in motors must move when the rotor heats up. This will push the old grease out the grease plug hole. And you can see it when you walk by the motor.

This does not work with ALL MOTORS and app. But if you don't let the grease out it will go some place you don't want it to go.

Greasing a motor the right way is more work than what most people want to do. The Old grease does not get eaten up by the bearing you will have to deal with the old grease at some point

quote:

Originally posted by penman39:
I apologize if this gets off-course, but it seems that most motor manufacturers use a polyurea based grease. Is it the best suited for the job?? Greg, being in the motor repair business, what type of grease did you usually use when repairing motors, and how many customers supplied their own grease for motors you were repairing for them? Did you ask your customers if they had a grease preference for you to use?? Thanks for the in-sights.

penman39
Polyurea pased grease is good. Yes some customers did supplied their own grease. It would cost them more if we had to pull a shield on a bearing and regrease them. And no we did not put the shield back on. You take the risk of damaging the shield but that seemed to be okay with them. Or they would supply the bearing.

we have aprox 1000 motors. we use the polyrex em grease. we also use the 20 min rule for the draining of the old grease. It concerns me when after 20 min no old grease is discharged. this is often the case. what goes in must come out or stay within the motor contaminating it. do you just hope the grease gets where it is supposed to or is there a way to determine that without ripping the motor apart?

Dear Fred F:

Please find two articles on electric motor lubrication in the motors section of reliabilityweb.com. The process is the standard motor manufacturer recommended practice for greasing motors.

In general, if you use the proper amount of grease, it may not be ejected from the bearing housing. It depends on the fill within the bearing housing, the mechanics involved (type of 'pumping action') and the release of pressure.

If you grease the motor while it is running (something that is actually not recommended, in virtually all cases), the action between the bearing and shaft surfaces acts to 'pump' grease into the motor, itself.

Greasing Motors Part 1: http://www.reliabilityweb.com/art04/greasing_motors.htm

Greasing Motors Part 2: http://www.reliabilityweb.com/art04/greasing_motors_2.htm

The articles were combined into one article for several magazine articles, of which several motor manufacturers requested rights to copy them for customer training.

I hope you find them helpful.

Sincerely,
Howard

Howard,

By keeping adding grease at certain intervals and amount, even with relief plug removed for 40 min, may eventually result later on in time in a condition when bearing cavity will become full although bearing had expelled extra grease from its own internals.

Do you think it is normal for a bearing (either open or shielded) to operate under those conditions? It is known that OEMs supply new motors with grease filled only at 30-50% of bearing cavity. Same question is valid for pillow block bearings and other types as well.

Thanks,
David

How many of you use ultrsonics to help aide in determining re-greasing intervals and amounts? I have found this to be a very useful in helping determine amount and frequency for most bearings. It will definitely help reduce the risk of over lubrication.

David:

It is expected that the grease will flow (settle) and some will exit. The main thing about leaving the grease plug open for the cited time period is to a) Ensure that pressure does not build when the grease and bearing housing/components heat up and cause excessive grease to enter the motor enclosure; b) The temperature (and other operating forces) will allow some of the grease to exit through the grease plug.

The main thing is to ensure that the 'soap,' or oil medium, does not come between the operating surfaces for an extended period. This will close the tolerances, which should be 3-5 mils, and increase friction, heat and wear.

Back to the point: Yes, original manufacture and repair practice is to ensure that the grease cavity is filled 1/3 to 2/3. Part of the reason is that it is not normal practice to leave the grease plug open during the 30 minute (minimum)test run and leaves room for expansion/movement. The cavity will eventually fill more, with regular greasing, but operating for 30-60 minutes with the plug removed will allow for expansion and expulsion of excess grease.

Sherman:

Interesting point. However, I would recommend that you check with the bearing manufacturer concerning their acceptance of warranty when ultrasonics is used. There is presently an ongoing debate between a number of bearing manufacturers and ultrasonic lubrication equipment manufacturers. (By the way, as an amusing point, one of the manufacturers that do not warranty bearings lubed in this fasion, actually sell an ultrasonic lube system).

At this point, there does not appear to be any conclusive evidence, supporting either opinion of the impact on bearing reliability due to ultrasonic lubrication, in the form of independent testing.

I have my own concerns on ultrasonic lubrication that stems from a combination of design and field service experience. Those can be found in the articles I cited earlier in this string.

Howard,

The way I interpret your statement is that there is no risk of overlubrication (assuming an open or single shilded bearing) as long as plug is removed for an hour. Also, having cavity full is not a problem as long as soap is not present on the operating surfaces of a bearing.

If that is correct, why do you and the rest of the world recommend just a predetermined amount of grease depending on bearing size instead of adding grease until it begins exiting from the plug?

Thanks,
David

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

There are alot of people greasing double shielded and sealed bearings causing alot of failures. There is no way that either of these bearings will get greased and the grease will end up either damaging your bearing or finding its way inside the motor winding. Food for thought.

David:

Pardon the delay. Enjoying my first vacation in years.

If you 'purge-grease' a bearing, then you are in danger of over-lubricating the bearing. The reason has to do with the viscosity of the grease. It takes a long time for the grease to actually move through the bearing, even at higher temperatures. If you start by filling the grease cavity, then there is nowhere for the 'soap' to go, other than into the bearing surfaces.

The 'soap' is actually the medium that carries the actual lubricant, oil.

By adding a little at a time, you are providing new lubricant (oil) to the bearing, while allowing the medium to move through the bearing without putting too much pressure (increased friction) on the contact surfaces.

Does that help? I would be happy to provide a longer explanation as an attachment, otherwise.

Howard

Mike:

You are absolutely right. Another problem, that many might not realize, is that some manufacturers may have grease fittings on motors that are not greaseable (ie: shields or seals on bearings). This primarily occurs in smaller motors that are 'mass-produced' such that the housings are pulled from an assembly line stock.

Used to run into this a lot in the motor repair industry. Best way is to either:

1. Ask to ensure that the bearings are greasable or non-greasable when a motor is purchased or repaired;
2. Obtain the model and serial number and contact the nearest authorized distributor.

Lubrication of rotating machinery is one of the most important components of a motor maintenance and management program, but one of the least understood and most dominated by mis-information.

Howard

quote:

Originally posted by MotorDoc:


If you start by filling the grease cavity, then there is nowhere for the 'soap' to go, other than into the bearing surfaces.

By adding a little at a time, you are providing new lubricant (oil) to the bearing, while allowing the medium to move through the bearing without putting too much pressure (increased friction) on the contact surfaces.

Howard,

Thanks a lot for your reply. Where confusion may be coming from is due to wrong understanding on my behalf of the mechanism the oil gets dispensed into the bearing internals once grease gets into the cavity.

Are you saying that grease (oil+soap) gets into the bearing internals from the cavity and then soap gets expelled back into the free portion of the cavity? Does having some soap in the races become the factor creating heat? If this is correct then, I think, having full cavity may impede the process of expulsion, although, by having an open drain, won't stop it.

So, again is "purge-greasing" that bad? In real life there is no way to control the amount of cavity not filled by grease.This is further aggrevated by the fact that recommended amount of grease to be added is greately affected by the environement. As a result, after several cylcles of re-lubrication a bearing most likely ends up either having 0% or 100% of cavity volume full.

David

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

My opinion fwiw. Greasing is never perfect and not an exact science. Overlubrication is a hazard no matter what technique you use, but I recommend what the bearing manufacturers recommend - add a little at a time.

By adding a little at a time, you have no real concern for overgreasing until the cavity gets full. Even then, if you are successful at purgin excess grease after greasing, you won't have a problem.

By trying to add to a new motor until grease comes out, you probably fill up the cavity right off the bat. Now you are immediatelyl dependendent on the successful purging of excess grease which can be difficult to accomplish.

So why even bother trying to add until grease comes out. You don't need to get rid of the old grease, just add a little bit of new grease to provide fresh oil. I can see there is a small advantage in adding until grease comes out that you are less likely to develop hardened plugs of grease that may obstruct successful purging when it becomes necessary. But I think this small advantage is outweighed by the disadvantage of filling up the cavity faster.

That is correct.

By the way, I owe Terry O a few articles. I think another one on greasing that will cover the specific issue of what happens in purging over adding a bit at a time (until the cavity is full) is an excellent topic. It will also be easier to explain than in short snippets.

Also, will post a copy on this string. Give me a week.

FYI: the 'soap' or medium is actually just an oil 'sponge,' it is not actually the lubricant. You do not want the medium actually in the moving parts of the bearing, that is when friction increases along with bearing damage. There is actually a number of physical processes that are occuring that draw the oil from the grease, as needed, which will be explained in the paper.

Howard