ANDREW M. MIKULA, (Member, STLE)
Kingsbury, Inc.
Philadelphia, PA 19154
This paper compares various shoe materials and analyzes their
influence on the thermal performance of tilting-pad (shoe) equalizing
thrust bearings. The paper presents experimental data on 267
mm (lO ½ inch) O.D. bearings, operating at shaft speeds up to
14000 RPM with loads ranging up to 4.83 MPa (700 PSI).
The data presented demonstrates the effect of shoe construction
material on bearing operating babbitt temperature.
Introduction
Tin or lead based (>80 percent) babbitt normally used
on the working surface of thrust bearing pads, or "shoes",
loses its tensile and compressive strength at elevated temperatures
and is subject to creep (1), which places a fundamental
limitation on bearing operation. Therefore, babbitt
operating temperatures are routinely monitored as an
important yet convenient means of assessing bearing risk
(2). Providing that a sufficient oil film is developed and
maintained, elevated babbitt temperatures are the result of
high sliding velocities. The options available to reduce elevated
babbitt operating temperatures resulting from the
oil film shear rate are limited, and the trade-offs can adversely
affect other areas of bearing performance.
Velocity related elevated babbitt temperatures can be reduced
either by lowering the heat generated in the oil film
or improving the conduction of that heat away from the
babbitt by using a backing material with greater thermal
conductivity. Pivot location (3), lubricant supply method (1),
(4), (5), and lubricant supply temperatures (4) have been
shown to be effective in reducing oil film heat generation.
The purpose of this paper is to provide the information
necessary to evaluate the effect of thermal conduction on babbitt operating temperature, based upon actual performance data.
The effect of thermal conduction was evaluated on a tilting-pad,
equalizing, double thrust bearing arrangement. The
tests were conducted with a light turbine oil which had a
viscosity of 0.027 Pa·s @ 37.8°C and 0.005 Pa·s @ 98.9°C
(150 SSU @ 1OO°F and 43 SSU @ 210°F-ISO VG 32). The
temperature-viscosity curve for this lubricant can be found
in Ref. (6). The lubricant supply temperature for all tests
was held constant at 46.6°C (115°F). The shaft speed ranged
from 4000 RPM to 14000 RPM, and the load ranged from
a "no-load" condition to 4.83 MPa (700 PSI) in increments
of 0 .345 MPa (50 PSI).
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