Page 198 - Tribology in Machine Design

Sliding-element bearings 183

and

Flat plates of other shapes are not solved so readily. If the length is much
greater than the width, it may be treated as a case of unidirectional flow, as
was done for the hydrostatic bearing. For a square plate with sides of length
D (see Fig. 5.9) the average pressure can be taken as 4/3 of that on a circular
plate of diameter D, to allow for the increased length of path of the corners.
Thus

Figure 5.9

The action of the fluctuating loads on cylindrical bearing films is more
difficult to analyse. Squeeze-film action is important in cushioning and
maintaining a film in linkage bearings such as those joining the connecting
rods and pistons in a reciprocating engine. Here, the small oscillatory
motion does not persist long enough in one direction to develop a
hydrodynamic film.

5.4. Thrust bearings Thrust bearing action depends on the existence of a converging gap
between a specially shaped or tilted pad and a supporting flat surface of a
collar. The relative sliding motion will force oil between the interacting
surfaces and develop a load-supporting pressure. In Fig. 5.10, the surface
velocities are Ui and U 2. With constant viscosity \i and with 8h/dz=Q,
Reynolds' equation, eqn (5.7), becomes

This complete equation has not been solved analytically, but numerical
analysis and digital computers may be used for solving particular cases. It is

Figure 5.10