R. S. GREGORY
Manager, Research and Development
Kingsbury, Inc., Philadelphia, Pa.
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.
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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