Thermal resistance of ball bearings (rotating)
Thermal resistance of ball bearings (rotating)
(OP)
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
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





RE: Thermal resistance of ball bearings (rotating)
RE: Thermal resistance of ball bearings (rotating)
Is this what you are interested in? If so you should be able to find the file somewhere on www.fag.com I think. I tried to cut/paste from the pdf file but it may not work perfectly. I didn't spend too much time because I'm not sure this is what you're looking for. Let me know if you wnat more clarification of what is in the document. (I may be able to put it in a better format)
The heat flow QR generated by the
bearing is calculated from the frictional
moment M [N mm] (section 1.2) and the
speed n [min –1 ].
QR = 1.047 · 10 –4 · n · M [W]
The heat flow QL dissipated to the en-vironment
is calculated from the differ-ence
[K] between bearing temperature t
and ambient temperature tu , the size of
the heat transfer surfaces (2 dm · ??· B)
and the heat flow density qLB customarily
assumed for normal operating conditions
(fig. 19) as well as the cooling factor Kt .
For heat dissipation conditions found in
the usual plummer block housings,
Kt = 1, for cases where the heat dissipa-tion
is better or worse, see below.
QL = qLB · [(t–tu )/50] · Kt · 2 · 10 –3 · dm · ??· B [W]
qLB [kW/m 2 ] rated heat flow density,
see diagram, fig. 19
dm [mm] (D + d)/2
B [mm] bearing width
Kt cooling factor
= 0.5 for poor heat dissipation
(warm environment,
external heating)
= 1 for normal heat dissipation
(self-contained bearing
housing)
= 2.5 for very good heat dissipa-tion
(relative wind)
With oil circulation lubrication, the
oil dissipates an additional share of the
heat. The dissipated heat flow Qöl is the
result of the inlet temperature tE and the
outlet temperature tA , the density r and
the specific heat capacity c of the oil as
well as the amount of oil m [cm 3 /min].
The density usually amounts to 0.86 to
0.93 kg/dm 3 , whereas the specific entro-py
c – depending on the oil type – is
between 1.7 and 2.4 kJ/(kg . K).,
QÖl = m · r · c · (tA – tE )/60 [W]
For a standard mineral oil with
r = 0.89 kg/dm3 and
c = 2 kJ/(kg . K) the following simplified
equation is used:
QÖl = 30 · VÖl · (tA – tE ) [W]
where
Völ amount of oil flowing through the
bearing [l/min]
The bearing temperature t can be
calculated as follows
QR = QL + QÖl [W]
=====================================
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RE: Thermal resistance of ball bearings (rotating)
Greetings,
dirkschiller
RE: Thermal resistance of ball bearings (rotating)
RE: Thermal resistance of ball bearings (rotating)
thanks for sharing your experience. I agree the problem with a rotating bearing is somewhat complicated. It must be some kind of transport effect either via the ball material close to the surface of the ball or via the oil film on the ball. The reason I have to know this in detail is that the bearing is running under vacuum, which means no air conduction or convection. Radiation I can calculate, so the only remaining unknown factor is the friction and thermal conductivity of the bearing.
Regards,
dirkschiller
RE: Thermal resistance of ball bearings (rotating)
RE: Thermal resistance of ball bearings (rotating)
http://www.bearingspecialists.com/software.asp
I don't know how far he has progressed with the program - maybe not as far as his web site suggests, but you might want to talk to him, since bearing heat generation and its effects on surrounding structures is one of his consulting specialties. There is an old finite difference mainframe program called SHABERTH, which may actually now be in the public domain, and his intent was to supplant that with his more up to date approach. Of course, bearing manufacturers have their own proprietary software for this sort of thing.