Page 137 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs 123

and

Case C. Journal rotating in a bush under ideal conditions of wear
Let us be assumed that the journal remains circular and unworn and that,
after the running-in process, any further wear in the bush reduces the metal
in such a way that vertical descent is uniform at all angles. The volume of
metal worn away at different angles is proportional to the energy expanded
in overcoming friction, so that the pressure will vary over the bearing
surface. For vertical displacement,.(5, the thickness worn away at angle 0 is
(5sin0, where 5 is constant (Fig. 4.27).
Hence, since frictional resistance per unit area is proportional to the
intensity of normal pressure p, and the relative velocity of sliding over the
Figure 4.27 circle of radius r is constant, it follows that:

Summarizing the results of the above three cases

virtual coefficient, /'=/ in a loose bearing,
= 1.57/in a new well-fitted bearing,
= 1.275/in a well-worn bearing.

4.9.1. Axially loaded bearings
Figure 4.28 shows a thrust block or pivot designed on the principle of
uniform displacement outlined in case C. In other words, we have the case
of a journal rotating in a bush under ideal conditions of wear.