Page 155 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs 141

or, resisting torque

(Hi) Block pivoted at one extremity
Figure 4.43 shows a brake block or shoe pivoted at or near one extremity of
the arc of contact. For a new well-fitted surface, the pressure distribution
may be approximately uniform. Wear of the friction lining material will,
however, occur more readily at the free end of the shoe, since the hinge may
be regarded as being at a constant distance from the centre 0.
Taking the radius through the pivot centre as representing the position
0=0, let (5 = the angular movement of the shoe corresponding to a given
condition of wear.
xz = movement at position 0 = 2asin^0<>
and
normal wear at position 0 = 2asin^0cos^0<!>
= c)asin0.
Hence, pa is proportional to da sin 0 or
Figure 4.43

In this case, eqns (4.109) to (4.112) will apply, and so

Expanding the term cos(/? — 0) and integrating, this becomes

For the angle ft we have from eqn (4.110)

Again, expanding sin(/? — 0) and integrating