Page 201 - Tribology in Machine Design

186 Tribology in machine design

thus,

and frictional horsepower = Tco = 6.32 x 78.54=496.4 W%0.5 kW.
Referring to the footstep bearing discussed in the above example, if

then, regarding the bearing as a flat pivot
frictional torque T=\fpAr^.
Equating this value of T to that given by eqn (5.26)

i.e.

or

5.4.2. The effect of the pressure gradient in the direction of motion
In the early, simple types of thrust bearing, difficulty was experienced in
maintaining the film thickness. By the introduction of a pressure gradient in
the direction of motion, i.e. circumferentially in a pivot or collar-type
bearing, a much higher maximum pressure is attained between the surfaces,
v and the load that can be carried is greatly increased.
Michell (in Australia and Kingsbury in the USA, working indepen-
dently) was the first to give a complete solution for the flow of a lubricant
between inclined plane surfaces. He designed a novel thrust bearing based
on his theoretical work. The results are important and may be illustrated by
considering the simple slider bearing in which the film thickness varies in a
linear manner in the direction of motion (Fig. 5.11). Here the slider moves
with uniform velocity V and is separated from the bearing or pad by the
lubricant, flow being maintained by the motion of the slider. The inlet and
outlet ends are assumed filled with the lubricant at zero gauge pressure.
Let B=the breadth of the bearing in the direction of motion and consider
Figure 5.11 the unit length in a direction perpendicular to the velocity V. Leakage is