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.
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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