Page 157 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs 143

and for zero wear at one extremity

In every case the retarding couple on the flywheel is

Numerical example
A brake shoe, placed symmetrically in a drum of 305 mm diameter and
pivoted on a fixed fulcrum £, has a lining which makes contact with the
drum over an arc as shown in Fig. 4.44. When the shoe is operated by the
force F, the normal pressure at position 0 is p =0.53 sin0MPa. If the
coefficient of friction between the lining and the drum is 0.2 and the width of
the lining is 38 mm, find the braking torque required. If the resultant R of
the normal pressure intensity p is inclined at an angle /? to the position
0 = 0, discuss with the aid of diagrams the equilibrium of the shoe when the
direction of rotation is (a) clockwise and (b) anticlockwise.

Solution
Applying eqn (4.127), the braking torque is given by

Since R is the resultant of the normal pressure intensity, p, the angle /? i
given by

Figure 4.44