Bearing Overheating

[Cessh]

Dear All,

I'm doing an FMEA for Bearing that uses grease as the main lubrication.

I've identified several failure causes for bearing overheating (above 90 degrees Celsius):

1) Overgreasing
2) Undergreasing
3) Loose Fits
4) Loss of Lubrication (leakage)
5) Wrong Type of grease used
6) Vibration???

The assumption number 6, I want to ask:

1) in your experience, does vibration in bearing normally causes overheating?

2) In bearings, How is the vibration and heat relates to one another in the process of overheating? When the vibration goes above recommended limits, does the temperature also rises above the normal value (less than 90 degrees Celsius)? or when the bearing overheats does that mean it must also be vibrating above normal limits?

3) In what ways does vibration causes overheating? Because it is known that vibration is caused by many things such as misalignment, unbalance, mechanical looseness, etc.

Please share your thoughts regarding this.

NB: Would there be any other cause for bearing overheating other than those stated above? Excluding environmental cause and human error.

Best Regards,

 

[MachinaMan]

Hi Cessh,

Both vibration and overheating are caused by a defect. The vibration does not cause the overheating, the defect does. The symptom that is vibration will be observed earlier than the temperature increase in a ball / roller bearing. You would be able to detect the defect symptoms in the following order:

1. ultrasonic inspection
2. vibration analysis
3. oil analysis
4. temperature rise
5. audible noise
6. looseness

If you search for a bearing p-f curve, it will explain the failure in a visual manner. One that I like is included as an attachment.

Best,

RP

 

[Cessh]

We had a case in our plant, it was after regreasing of the bearing (roller bearing), when the equipment (crusher) started running, the bearing temperature (bearing #4) increases to 90 degrees celcius. I causes panic to the operation staff. We held a meeting trying to find the cause of the problem... but then just after two days of the equipment running, the temperature went back to normal around 70 degrees celcius on its own without maintenance team having to do anything.

The maintenance team said it was a normal thing and that it happens frequently like that, after greasing, the temperature went high for two days and then it goes down on its own...

Is it really normal something like this to happen? Why is it happening like this?

 

[zappedagain]

While I'm not an expert, I expect the greasing process didn't have 100% coverage or there was a contaminant in the grease, so a roller got bound/stuck and heated up. Eventually it worked loose and recovered.

What does the bearing manufacturer say about this? Is it really normal or does it indicate an improper service procedure? If the maintenance crew followed the wrong procedure then they are protecting themselves by saying the followed the normal procedure.

My $0.02,

Z

 

[Cessh]

Can you explain what do you mean by 100% coverage? How is the procedure to grease a bearing from a grease nipple so that is has 100% coverage?

 

[MikeHalloran]

Contamination in the grease or 'less than 100 pct coverage' are unlikely.

The bearing temperature excursion is a classical symptom of overgreasing, wherein the bearing acts as an inefficient pump, creating a lot of heat just moving the grease around until enough grease leaks out enough so the bearing is no longer overgreased.
The usual cause of overgreasing is pumping until grease leaks out somewhere.

Your maintenance crew should be instructed to keep track of the greasing interval, the temperature of the bearing(s) for a few days after greasing, the exact amount of grease injected (# strokes, etc.), and to keep extending the grease interval and/or reducing the amount of grease injected, for each and every bearing, until the overheating turns to a small rise in temperature.

It's not a normal thing; it's something the maintenance team has been doing wrong for a long time, and they've accepted it as normal because they keep screwing up the same way. Congratulate them on their consistency, and educate them.






Mike Halloran
Pembroke Pines, FL, USA

 

[zappedagain]

Thanks for the info, Mike! Very interesting.