Sign up Calendar Latest Topics Donate
 
 
 


Reply
  Author   Comment   Page 1 of 3      1   2   3   Next
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,607
Reply with quote  #1 
We hear this a lot. I’ve seen a couple of posts on LinkedIn about this lately. A couple of people stated flatly that over-greasing is the main cause of failed bearings. But this all seems anecdotal to me. I’ve never seen data or a case study that proves this.

Sure a bearing that’s over-greased will run hot, but will it actually fail from the heat? I’ve heard it compared to “running through mud” but if it’s hot, the grease is going to be considerably thinner, right? I cab see where there is a legitimate concern where very high speeds are concerned, but aren’t those bearings typically oil lubricated?

In 30 years I’ve never seen a failed bearing that I was certain failed from over lubrication. Oh, I’ve seen bearings that failed that were in fact over lubricated. But I’ve seen more bearings that were routinely over lubricated that ran for many, many years.

My theory is that over-lubrication is often a band-aid applied to a bearing that is noisy, or is failing, or that has a history of failing, but due to causes unrelated to over-lubrication. When the failed bearing is pulled apart, of course there’s grease everywhere, so “it failed from over-lubrication.”

What do you think? Have you ever seen actual verifiable evidence of failure due to over-lubrication?

__________________
"The trend is your friend"
John from PA

Sr. Member
Registered:
Posts: 815
Reply with quote  #2 
Quote:
Originally Posted by RustyCas
We hear this a lot. I’ve seen a couple of posts on LinkedIn about this lately. A couple of people stated flatly that over-greasing is the main cause of failed bearings.


I would not agree that over greasing it is the main (emphasize “main”) cause of failure nor would most bearing manufacturers. I believe most bearing manufacturers feel that improper installation procedures are a major reason for bearing failure. I have always found installation procedures a difficult sell however, even when a gearbox (for example) had run for 5 years trouble free, but on replacing a bearing the user then gets repeated failures every three months. With the passage of us old-timers, all too often we are replaced with a generation that lacks “uncommon” sense.
Shurafa2

Sr. Member
Registered:
Posts: 78
Reply with quote  #3 
Rusty,

I tend to agree with you based on my limited experience.

Is over greasing a good practice? For sure, no.

Is over greasing detrimental as explained on the lubrication literature? My experience does not support that.

I think some of these conclusions are overgeneralized or taken out of context. Most of us heard about these statistics or similar to them:

"Researchers and manufacturers agree that the primary cause of friction and mechanical wear is poor lubrication. In fact, studies have shown that improper lubrication leads to 43 percent of mechanical failures, 54 percent of bearing failures, 50 percent of roller bearing damage and 70 percent of equipment failures."  https://www.machinerylubrication.com/Read/30589/common-lubrication-misconceptions

Where I work, we do our best to have good lubrication but by no means what we do is perfect. Having said that, the failure rates associated with lubrication is by far less than these figures. But again, my world is small and I could be totally wrong as on many occasions.

Regards- Ali M. Al-Shurafa


 
Alex

Avatar / Picture

Sr. Member
Registered:
Posts: 142
Reply with quote  #4 
I believe that over-lubrication CAN cause bearing failure because of overheating. The evidence could be the specific surface colour at the bearing taken out being still greased. Yes sure, there can be other causes of overheating, but I am thinking about a machine that normally hasn't got some overload or other issues before. 
It is true that more temperature brings the viscosity change but everything has its limits. One thing to consider is ˝running through mud˝ as you said when rolling elements loose their basic function, the other thing is heat transfer / cooling that can be significantly reduced in case of over-lubrication.
One thing I have experienced is that most of the over-greased problems come soon after startup, with cold grease which viscosity doesn't change in a second. A couple thousands of rotation cycles with elements sliding instead of rolling + high temperature and here comes the failure. 

But per my experience I would never say this is the main cause of failed bearings. Very far from that. It rarely happens and needs very specific conditions and some bad luck.
OLi

Sr. Member
Registered:
Posts: 1,519
Reply with quote  #5 
I have a case I refered to previously, a aux diesel generator like 1MW in one of 5 sister ships that caught fire, after that crew was seriously worried, installed monitoring including bearing temp monitoring etc. and called a consultant as the bearing failures still was like 2-3 times a year and no sister ship was near as bad. So we checked balancing and made a smaller unrelated trim, at the time the fancy laser fixtures was not around so I mounted a number of laser pointers and painted dots from cold to full operation, no impressive movement. Searching further the trends of bearing temp was real strange, suddenly at unrelated points in time temp got sky high and decayed repeatedly. So I wrote a report advicing the time lock to the door of the grease gun and use of the grease and grease interval of the best sistership. result was that no bearing was swapped until the next mandatory 5-6 year service interval for the generator so going from 5-6 months bearing swap to 5-6 years was pretty good. So yes I firmly believe you repeatedly can grease your bearings to failure if you work on it. In this case the crew was so upset by the fire that at any instance real or not of sound, temp, feeling etc they gave the bearings a shot of grease "just to be safe" since they had monitoring they got alarms and swapped bearings in time. Why it failed at first in fire? Well during the building all machinery was standing key side for several years as building was delayed and all bearings on all generators eventually was swapped prematurely the first years of operation since they were corroded and if you have no tool no hand temp monitoring and not even a yellow handle analyzer and likely don't even care, you have a fire eventually if you are unlucky or you actually have it comming. In a similar application it was found "no balls left inside" bearing fail that showed as a significant unbalance as it was drive shaft coupled. So yes I am convinced, if you work on it you can kill bearings with grease. But it is not the main reason, bad mounting is way more common.....
__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
dnk

Member
Registered:
Posts: 52
Reply with quote  #6 
Speed is the main factor to failing bearings when over greased. A very slow speed bearing can run forever with over greasing. The higher the speed the more heat you will see from over grease. I have pulled caps from tapered roller bearing that were running hot, found housing completely full of grease. Cleaned all grease from top half of housing and put back in production. Temperatures always lowered to what I considered normal. I started checking bearing housings after losing 2 bearings from overheating.
fburgos

Sr. Member
Registered:
Posts: 463
Reply with quote  #7 
Bearing skidding due to over grease is real, right?
dnk

Member
Registered:
Posts: 52
Reply with quote  #8 
Bearing skidding can be from over grease. It can also be from to light a load on bearing. 
The worst case scenario i have seen is using roller bearings on direct coupled machines.
RustyCas

Avatar / Picture

Admin
Registered:
Posts: 1,607
Reply with quote  #9 
From what I’ve seen most industrial grease has an operating temperature of up to 250F. How often do you see bearings that run that hot? Have you seen a bearing with too much grease reach that temperature? I too have seen bearing temps increased when overfilled, but nothing close to that.
__________________
"The trend is your friend"
Barry

Avatar / Picture

Member / Supporter
Registered:
Posts: 112
Reply with quote  #10 

Rusty I agree never found evidence that over greasing killed a bearing but if a bearing is operated at seeds above what is rated for grease lube they will run hot especially roller bearings and if oil lube is used over filling will as incress bearing temps.

__________________
Barry
OLi

Sr. Member
Registered:
Posts: 1,519
Reply with quote  #11 
In the one and only example above I had monitored data in the system at 120- 150 DEG C that may have been more as it was transients and not continuous monitoring. So yes once I have seen that. It may however be the exception that proves the general rule that over greasing do not kill bearings as you rarely give it the effort or have the possibilities required to make it happen.....
__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
Alex

Avatar / Picture

Sr. Member
Registered:
Posts: 142
Reply with quote  #12 
Quote:
Originally Posted by RustyCas
From what I’ve seen most industrial grease has an operating temperature of up to 250F. How often do you see bearings that run that hot? Have you seen a bearing with too much grease reach that temperature? I too have seen bearing temps increased when overfilled, but nothing close to that.


Common bearing recommended temperatures are up to 80-100°C Bearing can fail way bellow max. grease operating temperature.
OLi

Sr. Member
Registered:
Posts: 1,519
Reply with quote  #13 
I have a case with a mill that had 120 DEG C continuously for no real reason, it may be a bit tiny for the work so it may be design, however they put a electrical fan blowing air on it as a test 10 years ago (circulating oil was to expensive) that was all needed to reduce the temp and it behaved since so the actual temp is important.
__________________
Good Vibrations since early 1950's, first patented vibrometer 1956 in the US.
http://www.vtab.se
106Bones

Member
Registered:
Posts: 35
Reply with quote  #14 
Assuming the elements are anti-friction bearings; Reasonably we would first have to define "Failure". Typically that is defined two ways, 1 by the bearings inability to attain its design service life for a given application of load and speed and 2, a bearing that failed from an event or condition after installation.

I have seen the claims of over greasing being the primary component in bearing failure, assumptive and incorrect. It is well known and long time documented that >= 45% of elements fail from events related to improper application, shipping, storage and INSTALLATION. Which would be category 1 and in my career I have found this % to be accurate.

Category 2, under greasing, assuming a correct application lube schedule, not common. It takes very little grease to lubricate, typically one is just pushing a small amount of fresh grease into a load zone after what was there was spin ejected. Open a lifetime lube bearing, not much grease it usually but the construction keeps what it has in the right zone to lubricate.


Category 1+2; Thinking you are greasing often enough or even TOO OFTEN. How can that be? Its common. Under loaded antifriction bearings require appropriate load for their application. Under loaded bearing elements skid rather than roll, SRB' are the worst, and within that skidding they eject lubricant from the load zone. Result, an underloaded bearing will be short lived and even shorter lived if not lubricated on a more frequent schedule. How can this happen with an engineered product? Within bearing application programs adjustments can be made to life factor, I dont like below 1.0 factor. By reducing the factor an application with an SRB suddenly it can appear borderline acceptable, acceptable to an OEM warranty, but short lived compared to customer expectations of 60 to 80k hours. Shaft build, cost saving OEM advantage

Category 2; Wrong or mixing greases, lazy Lube Tech will often just pump in what is in their gun GL1 in a GL2 application, Walmart wax base for chassis only in a high speed rotating application. Then when it fails they run out and fill it up with fresh grease before one of us gets there. A lot of what appears to be over greasing failure is in reality CYA greasing after the failure event.

Category 2; Good application, correct grease just over greased, doesn't cause failure but is the leading category 2 cause of bearings running hot. They may have a higher steady state temp overlubricated but not fail, they typically self purge out the seals, vent if there is one or when I pull a plug. Solution, training and supervisory observation of the lube Tech and store room supply. If all thats going out is the junk grease then its going into everything

On balance many circumstances can cause a bearing to fail either what I call category 1, category 2 or a combination of 1+2. Over greasing doesn't do it but accompanies the fault. Analogy, over greasing causes hot bearings but is smoke at the train wreck. First came the train running off its track, then the fire and then the smoke. The smoke is resultant not cause of the  wreck.  
dnk

Member
Registered:
Posts: 52
Reply with quote  #15 
I always trended temperature on all bearing i monitored. On at least 5 occasions I have seen temperature as high as 375F. We had bearings that ran continuously at 250F and higher. After losing 2 bearing for heat I wrote w.o.'s to clean bearing housings when I saw temps over 300F. I worked inhouse and these W.O. always came to me on downday. Since I couldn't stop the over greasing, that was how I solved the problem.
After cleaning housing bearing temps dropped to the 250F range.
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.