Page 75 - Tribology in Machine Design

62 Tribology in machine design

so that

and

If p' denotes the load per unit of projected area of the bearing surface and N
is the speed in r.p.s. then P — 2p'r and V — 2nrN, so that

In using these expressions care must be taken to ensure that the units are
consistent.

Numerical example
A journal and complete bearing, of nominal diameter 100mm and length
100mm, operates with a clearance of c = 0.05 mm. The speed of rotation is
600r.p.m. and jU=20cP. Determine:
(i) the frictional moment when rotating without load;
(ii) the maximum permissible load and specific pressure (i.e. load per unit
of projected area of bearing surface) knowing that the eccentricity
ratio e/c must not exceed 0.4;
(iii) the frictional moment under load.

Solution
The virtual coefficient of friction when e/c = 0.4 is 1.1 (c/r) and the load per
unit length is

(i) when rotating without load, eqn (2.128) will apply, namely