R. S. GREGORY
Manager, Research and Development
Kingsbury, Inc., Philadelphia, Pa.
Mem. ASME
Significance
THE significant contribution of this paper is the publication
of experimentally measured values of bearing power loss
and pad temperatures under variable load, speed, and oil flow.
The operating conditions range from laminar to turbulent, and
information of this nature for this popular bearing-type has been
heretofore unavailable to designers and analysts.
Introduction
This paper presents the initial results of a current research
program investigating the performance of a standard 10 ½ in.
Kingsbury double thrust bearing operating at shaft speeds in
excess of 15,000 surface ft per min. A petroleum-based, light
turbine oil with a viscosity of 150 SUS at 100 deg F was used as a
lubricant for all test work. During the course of this experimental
study, shaft speeds ranged from 4000 to 11,000 rpm, and
bearing loading was varied from "no load" to 400 psi, based upon
a bearing area of 55.1 sq in. The tests were performed in a new
research and development facility recently constructed to investigate all aspects of high speed bearing performance.
The results reported in "this paper are considered incomplete
since additional testing is currently under way at still higher
shaft speeds. These additional data will be published at some
future time. However, it was felt that information on the critical
laminar to turbulent transition region would be of particular value
if presented now. Several interesting examples of bearing power
loss in the transitional region are discussed in this text. Moreover,
the considerable effect of a variable oil supply rate on both bearing power loss and bearing temperature is described in detail. This paper is intended solely to present new test data as a
contribution to understanding the phenomenon of turbulence in
bearings. Analysis and theoretical predictions are postponed
until the entire series of tests are complete.
Most, if not all experimental work in the field of bearing turbulence
has been performed on single element thrust bearings.
It was felt that testing of a double thrust bearing would be more
truly representative of actual machine applications. The double
thrust bearing consists of a loaded, or "active," thrust bearing
designed to absorb the thrust load imposed by the parent machine.
On the other side of the shaft collar is the slack-side, or "inactive,"
thrust bearing which serves to carry any transient loads that
possibly might develop in the other direction. The two bearings
(loaded and slack) that comprise the double thrust bearing undergoing
test are identical in design and size. One of the single
element thrust bearings utilized to assemble the double thrust
bearing is shown in Fig. 1. It is a conventional design with standard
dimensions and centrally pivoted pads.
During the course of normal machine operation, the loaded
bearing absorbs the imposed thrust load and operates with a relatively
thin film thickness, on t.he order of 0.001 in. or less. Under
this condition, the slack side bearing operates with only the internally
generated hydrodynamic load due to collar rotation, and
experiences a large film thickness, equivalent to the hot end play
of the bearing installation less the film thickness of the loaded
bearing. For the test bearing, this slack side film thickness is
on the order of 0.017 in. or more. Using one critical value of
Reynolds number (as discussed below) for the criterion of transition
into the turbulent regime, it can easily be shown that the
slack side bearing will encounter turbulence at a much lower
shaft speed than a loaded bearing, owing to its thicker film thickness.
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