SKF - Rolling Bearings

Friction
Starting torque
The starting torque of a rolling bearing is
defined as the frictional moment that must be
overcome by the bearing to start rotating.
Therefore, only the sliding frictional moment
and the frictional moment of seals, if applied,
must be taken into consideration. At an ambient
temperature of 20 to 30 °C (70 to 85 °F),
the starting torque can be calculated using
M start = M sl + M seal
where
M start = starting frictional moment [Nmm]
M sl = sliding frictional moment [Nmm]
M seal = frictional moment of the seals [Nmm]
However, the starting torque can be considerably
higher for roller bearings with a large
contact angle. It can be up to four times higher
for tapered roller bearings in the 313, 322 B,
323 B and T7FC series, and up to eight times
higher for spherical roller thrust bearings.
Power loss and bearing
temperature
The power loss in a bearing as a result of bearing
friction can be estimated using
N R = 1,05 ¥ 10 –4 M n
where
N R = power loss [W]
M = total frictional moment of
the bearing [Nmm]
n = rotational speed [r/min]
The cooling factor W s is defined as the heat
being removed from the bearing per degree of
temperature difference between the bearing
and ambient. If the value of W s is known, a
rough estimate of the temperature increase in
the bearing can be obtained using
DT = N R /W s
where
DT = temperature increase [°C]
N R = power loss [W]
W s = cooling factor [W/°C]
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