Page 188 - Tribology in Machine Design

Friction, lubrication and wear in lower kinematic pairs 173

Coning of the rotating interface element occurs as a result of wear or by
thermal pressure or mechanical forces. Depending on the type of pressuriz-
ation (that is internal or external) coning may enhance the hydrostatic
effects or give instability with a diverging leakage flow path. The
thermoelastically generated nodes can determine the leakage gap in seals so
that greater axial pressures on the sealing interface may increase leakage
flow. With moving points of contact and subsequent cooling, the worn
nodes become recesses and a progressive alteration of the seal interface
geometry occurs. There does not seem to be a predictable method of using
the features described above to achieve lubricant film formation. The effects
can be minimized by the proper selection of interface materials.
Recently reported investigations have mostly concentrated on isolated
modes of seal face lubrication. The fact that many modes may be
functioning and interacting in the operation of seals has not been
questioned, but simplifying assumptions are essential in achieving tractable
analyses. To utilize those research studies in a design for service requires
that the modes identified be considered with respect to interactions and
designed into a seal configuration that can have industrial applications.
Analytical appraisal of dynamic behaviour like that associated with
angular misalignment can provide a significant step towards integration.
Experimental determinations will be required to document the interactions
in seal face lubrication and supplement further analytical design.

References to Chapter 4 1. C. E. Wilson and W. Michels. Mechanism - Design Oriented Kinematics.
Chicago, III: American Technical Society, 1969.
2. Belt Conveyors for Bulk Materials. Conveyor Equipment Manufacturers
Association. Boston, Mass.: Cahners Publishing Co., 1966.
3. V. M. Faires. Design of Machine Elements. New York: The Macmillan
Company, 1965.
4. J. Gagne. Torque capacity and design of cone and disc clutches. Mach. Des., 24
(12) (1953), 182.
5. P. Black. Mechanics of Machines. Elmsford, New York: Pergamon Press, 1967.
6. H. S. Rothbart. Mechanical Design and Systems Handbook. New York:
McGraw-Hill, 1964.
7. J. N. Goodier. The distribution of load on the thread of screws. J. Appl. Mech.,
Trans. ASME, 62 (1940), 000.
8. E. T. Jagger. The role of seals and packings in the exclusion of contaminants.
Proc. Instn Mech. Engrs, 182 (3A) (1967), 434.
9. C. M. White and D. F. Denny. The Sealing Mechanism of Flexible Packings.
London: His Majesty's Stationary Office, 1947.