What's the normal operating temperature of bearings? 2

[etgbccc2003]

Dear All,

I have very little knowledge on bearings and would like to understand the above.

Anyone kindly advice?

Thanks.

 

[electricpete]

Normal is tough to answer. You haven't defined the type of bearing or the application.

For sleeve bearings, often alarm is set at 180-190F and shutdown is set at 200-210F metal temperature.

For antifriction bearings, the following requirements are given in IEEE841 (severe duty electric motors):

"When direct coupled, the stabilized bearing temperature rise at rated load shall not exceed 45 °C
(50 °C on two-pole motors) as measured by a thermometer or thermocouple on the surface of the
bearing housing as close to the outer race as possible."

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[israelkk]

electricpete:

This is not quite accurate.

For ball bearings used in electric motors for Aerospace and Military use the temperatures of the motor can go as high as 180 C (336 F). The lubrication should be suitable for such temperatures, the metal parts of the bearing are not affected by such temperatures.

 

[electricpete]

israelkk - You are not even close to accurate because you did not read my post. I said that normal was tough to define, meaning I did not intend to offer any normal value (don't you agree that "normal" depends on the application?)

For sleeve bearings I gave some typical alarm and shutdown values, used at out plant.

For anti-friction bearings I gave a quote from a standard. (I never said anything about damage). If you think my quote from the standard is inaccurate thatn you have not read the standard.

If you are saying that 180C is normal for all applications of rolling bearings in electric motors you are off your rocker.

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[diamondjim]

Normal operating temperatures is probably
from 0 degrees to 280 degrees. For applications
beyond or below, they are not normal and require
special grease, seals, etc.
If you are asking what is normal for the different
applications, you are asking a different question.
If you know the answer, why ask?

 

[electricpete]

Another data point: For sleeve bearings EASA Large Electric Motor Handbook suggests the following:
"Normal" - 80C
Alarm 90C
Shutdown 100C

When you apply a temperature limit also give consideration to where is the temperature being monitored.



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[electricpete]

I would like to add it is a complex and perhaps somewhat controversial subject. I take no exception to anyone's opinion other than someone who throws around phrases like "not quite accurate" in response to a factual statement on the content of a standard.

Diamondjim - you say up to 280 I assume it is F.

NLGI Group 1 General Purpose grease has a temperature range up to 250F doesn't it? That would seem to argue 250F as an max upper limit for actual bearing metal temperature. If temperature may be monitored on housing we have to reduce our limit another 15F or so to account for limitations of our monitoring.

In our plant housing temperatures on most motor bearings are 130F or below. Occasionally after greasing some go to 180F or even 200F. If anything ever remained at these levels 180F-200F by housing I would be concerned (my opinion).


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[jet1749]

As is often the case, an innoccuous question can give rise to an extended thread of discussion. Whilst interesting in itself, this sometimes doesn't really answer the question asked. Each answers according to his own area of expertise. So no right and no wrong answer. its only possible to really answer in general terms to a no-specific question. Whats really needed is information on a specific type and class of bearing and a particular set of circumstances. With this I am sure everyone can make a considered contribution, and perhaps learn a little also! Until or unless the information is forthcoming then its perhaps better for etgbccc2003 to consult a bearing reference book such as supplied by the major bearing manufacturers such as SKF and others, and get a little more insight.

 

[rnd2]

jet1749, I beg to differ.
I strongly disagree with the statement "so there is no right or wrong answer".
Electripete offers and promotes considered and accurate opinions that are pertinent to his area of expertise as well as to the subject matter. If he does not know he always asks why.
Take some time and look at his track record. It cannot be faulted.
I am a grumpy Australian and have never met Electripete who I think is American. I sure like the way he handles himself in the many discussions he has participated in.
etgbccc2003 probaby has learned a lot from his post.
Maybe to stay out of the kitchen

 

[electricpete]

Thanks for the kind words rnd. I enjoy your posts as well.

My apologies to all - I did not exactly handle myself well in earlier comments. All comments should be welcome and respected.

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[etgbccc2003]

Thanks a lot.

I was asking about anti-friction motors.

 

[electricpete]

One more data point:

SKF Publication Publication 5073E "Bearing know-how for rewinders - Manual for bearing health"

"Permissible operating temperature
SKF rolling bearings can generally be operated
at temperatures up to approximately 120 °C.
However, if bearings are to be operated continuously
at temperatures in the region of 100 °C
and above it is advisable to contact SKF first.
If the operating temperature is higher than
120 °C, the bearings must be subjected to a
special heat treatment (stabilisation) so that
inadmissible changes in dimensions do not
occur as a result of structural changes in the
steel."

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[MASSEY]

...and then there is the question of 'seals' are your 'normal' bearings sealed or not. If so what type of material is the seal made of?

I would suggest you contact a reputable bearing manufacturer with your 'normal' operating conditions. And let them suggest the bearing configuration and they can then [and only then] tell you what the operating temperature range is for your 'normal' bearing.

Some of the questions you should be prepared to answer are:

what speed will brgs operate at?
how much radial load is expected?
how much axial load is expected?
is inner ring stationary relative to load or outer ring?
are brgs press fit into housing, if so, how much press?
are brgs sealed, shielded, open.
this should be enough information to ascertain 'normal' operating temperature.

Good Luck!

 

[KernOily]

This is slightly off-topic so please forgive me for posting here, but I bet you guys know the answer to this. I have searched eng-tips and have not found the answer. Is there a forum on here for reliablity/maintenance/RCM/TPR/TPM engineering?

OK so maybe not off topic... my company's specs set the upper temperature limit for shutdowns and alarms in process plant equipment with rolling-element bearings as 180°F, whether oil- or grease-lubricated.

Thanks, and sorry for the (slightly) off-topic post. Pete

Thanks!
Pete

 

[electricpete]

I think you might find a little bit of that in the mechancial/vibration forum.

There is an outstanding very active forum at the vibration/alignment/balancing forum at:

reliability-magazine.com


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[Tmoose]

If the operating temp is much over 150 F, then special seals and grease and cage materials and internal clearances may be necessary. High operating temperatures may unavoidably result from bearings in hot environments or processes.

Even if the main source of bearing temperature is heat generated by the bearing itself, sometimes the danger does not come from the operating temperature. Instead an internal problem, or inadequate or excessive lubrication, abuse or a mis-application will cause the bearing to FAIL at a relatively low housing temp. But with luck there will be a symptom of a (too) rapid temperature increase.
I have witnessed a few machine tool spindles whose bearings failed CATasrophically before the housing internal temperatures reached 130 F very close to the bearing outer races. But, the temps were climbing at 5 or 10 degrees/minute. (Yes, the temp deep within the bearing was much higher at the time of death). It was not the temperature, or even the temp rise itself that was the problem. The temp rise was merely the symptom of a problem, and resulted from the thermally induced increase in internal preload generating plenty of heat.
If we expect to keep our spindles from failing during development or operation we have to monitor rate of temp increase AND absolute temperature.

 

[electricpete]

In general (but not always) we suspect that temperature will give us fair warning of a lubrication related problem, and vibration will give us fair warning of mechanical problem such as severe spalling.

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[EnglishMuffin]

Having spent my whole career in the machine tool industry, I would like to fully concur with Tmoose, except that in my case I have witnessed a lot more than a few such failures. And as he indicates, cage materials can be an issue. Of the plastic variety, Phenolic can only stand about 220F. But I believe PEEK, which is becoming more common, can stand at least 350F.

 

[JvdWal]

For higher temperatures you can take a full ceramic bearing. Without a cage you can go til 800C.
With a cage of PEEK you can stand at least 180C

 

[volpegrigia]

The bearing speed limits are calculated with an upper threshold of 70 degrees C. This does not mean that the bearing cannot operate at higher temperature, but it indicates a somewhat "normal" operating limit. Higher than this would require addressing lubrication ssies and lubricant decay as well as (if the temperature exceeds 1150 deg. C) potential material transformation issues.