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Hello all. I’m chasing some information pertaining to bearing lubrication. In our lube routes we with have a percentage of machines that are online due to duty cycles or turnarounds. I heard from a couple of people that you should not grease bearings in rotating equipment when they are offline as it may lead to bearing skidding ?. I can understand that the bearing would receive better lubricant when the bearing is rotating, but surely some lube is better them none?
Any feedback with either the positives or negatives in greasing offline bearings would be greatly appreciated.


thanks in advanced

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Some thoughts about lube while running vs secured:

According to traditional wisdom, OEM documentation should be consulted since there may be varying configurations. I can’t argue with that although it’s not always practical and most facilities (like ours) tend to develop a generic lub procedure applying to all their motors.

I have heard a few people/articles say that certain motors are susceptible to pumping grease through tight annular clearances if grease is added while running. And it leads to a concern that grease can end up in the winding. I’d think that is not a concern where the cavity that is replenished is located on the side of the bearing away from the winding.

There can be a personnel hazards in lubricating while running (how close do you have to get to moving parts both to access inlet fitting and drain fitting).

At our plant, we lubricate all motors while shut down due to concerns about personnel safety which trump all the other considerations.

quote:
I heard from a couple of people that you should not grease bearings in rotating equipment when they are offline as it may lead to bearing skidding

Yes. Skidding may occur during startup if machine was lubricated during shutdown. In a simple viewpoint, skidding occurs when the friction force which tends to retard roller motion exceeds the traction force which tends to keep them going. Friction force can be larger if grease is cool (ever start) and has not redistributed following lubrication. Sometimes you may hear a relatively-constant pitch (*) screech when you start a machine (typically about 1 second)... I believe this is skidding. (* if the pitch of the screech is continuously increasing in frequency during start, then it’s not skidding, but something else). Skidding may be occuring even if you don't hear it.

Momentary skidding during start is not ideal but also not catastrophic.
RM
Also there are certain aspect of lub procedure that are tied to lub while running or lube while secured.

We just add a fixed amount at a fixed interval and it works fine lubing while secured.

Some people monitor ultrasound or vib while adding to determine correct amount, obviously requires machine running.

I think there may be some people in the world that add until grease comes out of the drain. I cringe at the thought but I have heard people say that. I don't think I'd do it myself, but it may be more suitable to do it when the machine is running.
RM
John,

I like the Perma-lube (or other manufacturer) route on motors myself also. We stopped all bearing failures on DC motors on a dragline by going to the auto luber. I think we had them set for 3 months discharge, and on the bigger motors we made a Christmas tree of lubers. However, some of the ones today do not build enough pressure to push the lube through a piece of 1/8" pipe nipple. If you go the auto luber canister route, buy a couple and run an experiment to make sure they will build pressure enough to push the grease through how ever long a pipe or hose you need. I've seen two or three different ones that won't. Wink
RM
We have ABB motor that recommends greasing only in operation near 300 rpm min., kinda like Pete said, refer to OEM if they have specifics in the manual. Motor or not. We grease manualy, some motor(<10hp) amount is in teaspoons so you do the math. We also must follow LOTO to perform service, but the above motor is safely accessable, and as also noted in other post, it is fed from remote zerk and grease tubes.
RM
quote:
Originally posted by electricpete:
Dave - is that like putting multiple positive displacement pumps in parallel? Does that affect the feed rate?

A general question - does the grease cavity fill up faster with automatic greasers?.... or is the total addition rate per time roughly the same as typical recommendations for manual greasing?


EP,
Yes, it would be a similiar setup. You're after volume. We made "Christmas Trees" from either pipe 90's or crosses (4 way), depending on how many canisters you needed for the cavity. As billw says, depending on frame size, as I'm sure you're well aware, some of the cavities take much more than others. Some of the old DC motors had pretty good size cavities, much bigger than the ones I fool with now, and being in the application they were in (sitting on a dragline getting their guts wrung out each day) we used a little more grease than you would use in the power plant.
As far as the cavity filling up quicker, I'm not sure. We lost a few motors to electrical shorts, and following the motors to the shop I never saw nor was told of any that had excess grease in the stator.
We used the "Permalube" product that had the pill in the top that you dropped into the liquid (base?) to generate a gas and pressure. Now that was many years ago (mid 80's) and we didn't have trouble with the canisters discharging their contents. I've seen several places run tests (I just did a month ago at a customer site) whereby you turn these new ones on with the flashing red light and set them for a month discharge. Lay them in a box and forget about them. I screwed an 1/8" X 6" nipple on two of them. We tested 4, I've seen as many as 12 tested at a time. The "hit and miss" as to whether they discharged their contents in a month or two months was disturbing to me. The ones I screwed the nipple on did not discharge more than a thimble full. It possibly went 1/2" down the pipe and both quit. We left ours for two months set on 1 month discharge.
This seemingly lack of reliability to do what you pay a pretty good price for them to do has turned me off of them.
I urge customers to manually grease if it is at all possible. If I have to go by and check the cansiter to ensure it is operating as it is supposed to, then I may as well grease it by hand and ensure it got the right amount at the right time.

D
RM
Timely discussion guys...I have an application of >100 electric motors that would be best lubed only once...on their annual PM schedule. I'm looking for a cost effective auto-greasing product that will dispense over 12 months (reliably)...any input as to real life reliability would be welcome...I've read/heard all the sales pitches and "it seems that they all work 100% of the time"...I'd like to set half my motors up with the auto-greaser and run a trial for a year. Thanks for any input.
RM
RJ,

Can you screw them right into the motors, or do you have to plumb them in?
I recommend doing a test as I've said above. Contact all the manufacturers of the products and see if they will give you 2 or 3 of their canisters. If not give, then for miniscule price. Tell them what you're doing. Set them for a month, and lay them in a box. If you have something that shakes continuosly, lay them on that (At one plant, the engineer found that when they discharged in the box, they had trouble on the exuipment that was shaking.
If you are going to have to plumb them in, screw a nipple the size you're going to use on at least one of each model and turn them on. You can go ahead and fill the nipple from a grease gun if someone thinks that will make a difference. Try them your self in the box. If they work, you're off and running. If some don't, I wouldn't fool with them no matter what the salesman came up with. I think you may find the simplest works the best.

D
RM
Out of curiosity I googled the cansiters and found several. The perma's I used are still there, but they say they only generate 58 psi through gas generated pressure. The Electrolubers I most recently saw tested say they generate up to 200 psi through dispensing the lube by a small screw conveyor. I didn't read much about the canisters when I was at my customers site, but after reading about them, I like the way they are supposed to work. The customer and I had talked about what a good one would be (mechanical positive displacement would be great, refillable with whatever grease you wanted, more options than the standard 1,3,6,12 month) and this one seems to have those capabilities. I now wonder if the little motors didn't work. 2 of the 4 did not put out anything. We had them all set the same, to empty in 1 month. 2 months later, only 2 of them were close to being empty. All were blinking.
Dang, I like the concept too, always have.

D
RM

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