Page 218 - Tribology in Machine Design

Sliding-element bearings 203

performance is determined by the combination of both factors, some
method is required to predict the temperature and film parameters at other
than the basic design point.
A strong relationship between temperature rise and eccentricity is quite
obvious and the short bearing theory can be used to establish it. Then,
knowing the eccentricity, the actual operating temperature can be pre-
dicted. If the result of eqn (5.64) does not relate precisely to a conveniently
available oil then an oil having a higher viscosity at the estimated
temperature must be selected. This, however, will cause the bearing to
operate at a non-optimum eccentricity ratio, the temperature rise will
change, and with it the viscosity. Some process of iteration is again
necessary and the suggested procedure is illustrated in Fig. 5.23.
The method outlined above is best illustrated by a practical example. It is
1
assumed that a shaft 0.25m in diameter and rotating at 42rads~ is
3
required to support a load of 38 000N. A clearance ratio of 10" and L/D
ratio of 1/2 can be assumed. Then from eqn (5.64)

Figure 5.23