R. S. Gregory, Manager, Research & Dev.
Kingsbury, Inc., Philadelphia, Pa. 19154
Assoc. Mem. ASME
Several recent technical papers have discussed the advantages of various designs of thrust
bearings by comparing the power losses of the different type bearings. However, great care
must be exercised to ensure that the comparisons are fair. There are many external factors
that influence loss, such as oil flowrate, clearance, supply temperature and so on. Unless
compensation for these external factors is included in the analysis, the power loss
comparisons may be misleading. This paper attempts to show both qualitatively and
quantitatively the influence that various external factors have on bearing power loss. It
has been determined experimentally that oil flowrate adjustment can vary power loss by
as much as 150 percent. The choice of radial or tangential discharge can reduce power loss
by 60 percent, while the actual size of the discharge can influence power loss by 50 percent.
Varying the bearing end play has little effect on measured power loss.
Introduction
It is often necessary to compare dissimilar types of thrust bearings
for the purpose of evaluating competitive designs and determining
which is superior from the standpoint of performance. Due to the
energy crisis, power losses are now of paramount importance in any
such comparison-especially for high shaft speed applications above
3600 rpm. As a first approach, this paper will be limited to a thorough
discussion of comparative power loss values. While the significance
of other bearing factors, such as turbulence, equalization, temperature, and so on, are not to be denied, it is felt that each is a complex
topic in its own right, deserving individual treatment in depth. Hence
the focus on power loss in this paper.
In many instances, comparison of published (or vendor-supplied)
data on different bearings is complicated by the fundamental differences
between installations and operating conditions. These differences
are magnified as the size of the bearings and shaft speeds
increase into areas where little data are available. Often the significance
of an oil drain configuration is overlooked in the haste to
"compare apples with oranges" and match numbers. Another criticism
is that too little descriptive information is used to qualify published
data. For example, stipulation of a bearing power loss level normally
includes the lubricant viscosity, bearing load and shaft rpm for that
one data point. But the inlet oil temperature, oil flowrate, discharge
configuration and end play should also be included for the sake of
accuracy.
In order to demonstrate these principles, the approach used in this
paper is to take one, standard, bearing design and perform every
conceivable test on it to show clearly the broad range of power loss
values attainable from that one basic design. The different tests
performed will involve manipulation of external parameters only there
will be no change in the basic thrust bearing design. Each test
is treated independently, and it should be clearly understood that if
several design improvements are employed at the same time, the individual
beneficial effects resulting from each are not necessarily
cumulative. By reporting the effect of each parameter separately, it
is hoped that this paper will demonstrate both the need for full disclosure
of pertinent details, as well as the versatility of a proven,
standard, bearing design.
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