Sign up Calendar Latest Topics Donate
 
 
 


Reply
  Author   Comment  
Batman

Avatar / Picture

Sr. Member
Registered:
Posts: 88
Reply with quote  #1 
We know of the greasing frequency/interval and greasing quantities.
But for how long regreasing would be permitted?
There are motors which do not have an 'exhaust' hole for the excess grease to be expelled so the greases added should go somewhere, right?
One cannot keep packing in grease at each regreasing. What's the practice?
Am I explaining myself? 


RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,533
Reply with quote  #2 
Greasing motor bearings with the recommended amounts at the intervals specified by the manufacturer should not be a problem.  But that seems to rarely be done.  Either they are greased too much and too often, or not at all.  I have heard "stories" of windings being coated with grease and failing, but I've never actually seen that with my own eyes.  I have one customer that put auto-lubricators on a motor and they go through a full charge every 6 months or so (too much, and I've told them so).  Much of the grease at the inboard bearing seems to liquifiy and run out the seal (oil puddles up under the drive end of the motor) -- I have no idea where the grease in the outboard bearing goes.  But it doesn't seem to be a problem and the motors have run trouble-free for years.  

I would recommend following -- but not exceeding -- the manufacturers recommendations.

__________________
"The trend is your friend"
MarkL

Avatar / Picture

Sr. Member
Registered:
Posts: 902
Reply with quote  #3 
I tend to point customers to using an ultrasound instrument, and checking them monthly and greasing on noise quality. I grease motors on some contracts using the analyser as a guide.
Big Al

Sr. Member
Registered:
Posts: 93
Reply with quote  #4 
I've wondered about this myself. I have actually witnessed one case of a motor failure where the windings were coated with grease. Unfortunately I've no idea how long the motor had been in service or what the greasing frequency/amount was.

We tend to follow the manufacturer's recommendations, but if I suspect a bearing fault then I may request a little extra. When this happens, I usually accompany the lube guys with an ultrasonic instrument and add grease one shot at a time. When I hear the grease hit the bearing then we stop greasing and carry on with the normal lubrication schedule.

So far, this works for us.
Beatnik

Sr. Member / Supporter
Registered:
Posts: 183
Reply with quote  #5 
It's a big mess really.

Most of our new motors are TECO Westinghouse, their recommended amounts are enormous. 300 grams (10.5 oz) for a 6326 P.26 https://www.tecowestinghouse.com/Manuals/TWMC%20O&M%20MANUAL_5000%20frames%20plus.pdf

SKF have 2 formulas: 0.002DB if the replenishment is made directly in the bearing (W33 bearing) and 0.005DB if it's from the side. For a 6326 it will be 81grams or 32grams. What change depending on the speed/utilisation is the intervals of re-lubrication.

FAG will make you calculate the interval and based on this this amount will change. IF it's weekly 0.002DB, monthly 0.003DB, yearly 0.004DB. see P.37-38. http://mountingmanager.schaeffler.com/library/library.pdf.wl81.115.e.pdf  On page 38 you will find the method to calculate the total space in your bearing if you worry about that.



Some companies will tell you to grease 2s/2z bearings, some will tell you not to. Most companies will tell you to fill up completely very slow bearings, but will also tell you to add up new grease...
electricpete

Sr. Member
Registered:
Posts: 510
Reply with quote  #6 

I agree, it's a mess. Some rambling thoughts...

 

There is a theory that 80% of the grease is oil and it is somehow consumed (to vapor) over time when the machine runs and grease temperature is elevated.    At best that theory applies only to the hot / agitated grease within the bearing, not in the housing which tends to be cooler and stagnant … if you go back in and look at the grease in the housing at various times before full you see the initial grease pack and globs from relub… no evidence that it is shrinking in any way.  

 

There are a variety of configurations related to greasing.  A few motors have flow-through design but most do not.  Some shielded, double shielded, open.  If single shielded, the bearing manufactuerer (SKF) will tell you to put the shield toward the outboard cavity for metering the grease, while most electricians would put it toward the winding to help avoid grease going to winding in event of eventual (inevitable?) overgreasing. Sometimes there's an inner cap between bearing and winding, but not on cheap motors.  Different OEMs provide different cavity size for a given bearing.   Yet we tend to want a cookie-cutter approach to greasing where we can figure out the quantity/frequency just knowing the speed and the size, without knowing the details.

 

So, let's say cavity does end up full, what then?  One good practice is to run the motor for 30 minutes to 2 hours with grease plug removed (or grease relief fitting installed) after grease in order to give the grease room to expel as it expands.  That at least minimizes (but not eliminates) the potential for the cavity getting so full that the bearing is unable to move the grease away from the ball path (assuming the grease is not caked dried to the point nothing can move). 

 

We could (should) decide what to do based on observations during greasing and post-grease run. If there is evidence cavity is full, what to do?  If we are confident based on knowledge of machine construction that excess grease will not enter the winding, we might make the argument that no action is required provided we monitor the machine with vibration at a sufficient interval to detect bearing degradation (from overgreasing) early enough.  But we are not always confident in knowing whether the grease will get in the winding or whether we will be able to detect problem arising from overgrease so we may want to be more proactive depending on the situation. I tend to think high (D*N) bearings are most sensitive to overfilling. So I'm more worried about full grease cavities on 2-pole motors and especially as the bearing size gets in the heighborhood of 6313.    If it is a critical motor with high D*N and evidence of overfilled cavity, I sometimes request the bearings be changed to address the situation.  I guess we could disassemble and just clean grease from cavity of endbell without changing the bearings, but then we haven't reset the clock on our bearings, and we might also risk contamination of the grease in the bearing, depending on construction.

Shoveldr

Member / Supporter
Registered:
Posts: 69
Reply with quote  #7 

I was at a plant where they discovered they were have a lot of failures due to over greasing.  Their brilliant solution was to go to double sealed "greased for life" bearings and stop any greasing.

That eliminated the over greasing issues, but when they started their vibration program they couldn't do anything about the lubrication issues they were finding except track them to failure.

MarkL

Avatar / Picture

Sr. Member
Registered:
Posts: 902
Reply with quote  #8 
Yeah I've a few like that, went to a site this morning with a direct drive motor in a AHu we tracked last one deterioration and the changed bearings on motor last week during shut down as per recommendation. Test today and mde bearing is showing higher than expected gE (envelope) and as they are sealed no pint in advising guy to grease them.
Big Al

Sr. Member
Registered:
Posts: 93
Reply with quote  #9 
As a user of Emonitor, I've added the lubrication method of each bearing (grease nipple, auto-pot, SFL, oil filled, etc) in the Location pane. This means that it gets displayed in the legend at the bottom of the plot screen and I can consider this during analysis. Hence, I won't ask someone to grease a sealed-for-life bearing, or I can ask for auto-pots to be checked out for operation, etc. It's a nice-to-have addition, but you have to keep it updated when kit gets changed.
Batman

Avatar / Picture

Sr. Member
Registered:
Posts: 88
Reply with quote  #10 
Thanks to all of you who have contributed.

It seems there is'nt one fast and good rule but lots of valuable insights and practical experience.
VibGuy~5

Member
Registered:
Posts: 69
Reply with quote  #11 

We look at the calculated grease quantity (using 0.005), but so far we’ve found that this is usually between 2 and 4 times the recommended nameplate grease quantity.

We grease using a grease caddy and look for decreasing dB until we hit an inflection point and the dBs start to rise again, but if we hit the recommended nameplate grease quantity, then we stop regardless and just continue to trend on vibration and ultrasonics. The grams per stroke of each grease gun has been calculated in the workshop by greasing 10 strokes onto a balance scale and then averaging-although this is greasing to atmosphere and would likely change when greasing under pressure-it’s the best we can do at the moment.

The unknown for new motors is whether the greasing standpipe has been primed, although this can be calculated if you estimate the diameter and measure distance between the zerk and the OD of the bearing (once the density of the grease is on the tube, or you can weigh).

I’ve seen motors returned with a couple of tubes of grease in the windings-not pretty. Usually done be enthusiastic apprentices that want to control the temperature of the motor by adding more grease. I’ve also opened up bearings that haven’t been greased. All that’s left is oxidized, varnished (i.e. black) grease, which I would say is mostly thickener-the base oil will flash off as the hydrocarbon chains are broken down.

It’s a tricky one to get right, but it helps if you’re in the one place all the time and not in a different plant/state/country

Aro

Member
Registered:
Posts: 1
Reply with quote  #12 
From my experience. Do not be afraid of where is grease going when you relubricate. Open bearing (not RS or ZZ) are designer for relubrication. We call it loss lubrication. This loss is very small. In the construction of electromotor behind bearing is usualy nilos ring (part that prevent of moving grease from bearing to other parts of machine). 

2RS and ZZ bearings we do not relubricate, they are designed to withstand the whole bearing lifetime with initial bearing filling. 

Sometimes on electromotors are labels with ifnormation about lubrication intervals and amounts. I recomend it to recalculate it to exact type of bearing. You can use SKF software dial set, or other techniques. Each brands of bearings sometimes differ from each other in design of bearing. 

For me as a vibration analysts best method how much and when to lubricate bearing is via vibration analysis measuring. I think it is best method, because u can "hear" from bearing when bearing is not properly lubricated, or when you are lubricating it, when it is enough lubricated, and I can tell you that maybe 40 % of cases when we had service action label info was different than the actual needs of bearing. For this method u can use any type of vibration monitoring equipment, I saw this method with Adash A4910 Lubri. It is interesting to hear and see how values of vibration and sound changes during lubrication and recommend for every technician to experience it, because it is interesting moment.

I wish you best luck and I hope I helped a bit in your question. 

Martin Šimončič
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.