Thermal resistance of ball bearings (rotating)

[dirkschiller]

Hello all,

Im am looking for some information about the heat transfer through rotating ball bearings. This is probably a function of the bearing dimensions, the lubricant and the rotational speed.
Does anyone have an idea where to find such information?

Thanks,

Dirk

 

[Montemayor]

dirkschiller:

Are you trying to find the maximum allowable temperature for a ball bearing assembly under load? Or are you trying to study the heat flow rate into the circulating oil from the ball bearings (or the race?)?

I can see the value of the former; but why would you want to know how fast the metal parts (& which ones) of the bearing are giving up heat? If the bearing is already designed and installed (which you haven't stated), the design applications engineer already took the maximum temperature rise into consideration in the selection of the circulating oil. More importantly, the manufacturer of the ball bearing in question is in control of the empirical frictional heat generated by the bearing and the recommended oil flow required to keep it both lubricated and cooled at the same time. Therefore, you should refer directly to the manufacturer of the specific bearing and the heat rate generated should be available to you there. I wouldn't trust any body else but the actual manufacturer for this type of specific information.


Art Montemayor
Spring, TX

 

[chicopee]

Whatever rolling friction you develop w/ rotating elements would transform into more heat gain and some convective heat loss. Therefore, knowing rolling friction, bearing rotational speed referenced to raceways, and load on bearing, you can calculate frictional energy loss equating to internal heat gain minus convective heat loss by bearing. Assume proportinal gain by the mass of bearing since raceways & retainers will also increase in temperature. Expect a fair amount of assumptions until you can fine tune your equations reflecting actual conditions.

 

[MikeHalloran]

Assuming you really are interested in heat transfer _through_ a bearing, as opposed to heat generated within the bearing, ... okay, I don't know where to go for an answer.

But I can give you a little hint; once a ball bearing is running, you can't pass a small electrical current through it, at least not consistently. It appears that the balls ride on a thin film of whatever oil is present.

A long time ago, I worked on an instrument that used an AC motor driven impeller pump to circulate salt water in a loop through a high impedance sensor. The system acted as if the motor rotor was ungrounded and floating; it was. We discovered that a carbon grounding brush on the blind end of the shaft brought the system noise way down. The motor guys said, "Oh yeah, we sell lots of motors with grounding brushes; you should have asked for it."




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[25362]

You may find information in Engineering Tribology by Stachowiak and Bachelor, from the Tribology Series, 24, published by Elsevier. ISBN 0-444-89235-4.

 

[dirkschiller]

Thanks a lot guys for your suggestions. I have contacted the supplier regarding this issue. The question is really how much heat is transported from the inner bearing ring to the outer one. It seems to be not a well explored field.

Greetings,

dirkschiller

 

[IRstuff]

Probably because there isn't much heat transferred.

The contact area is so small and the the overall path is so restrictive in most systems that there are many, more signficant heat transfer paths elsewhere.

TTFN