DeCamillo S, Manager of Research and Development
Kingsbury, Inc., 10385 Drummond Road, Philadelphia, PA, 19154 U.S.A.
The hydrodynamic bearing is an extraordinary device. There are 3000 mm diameter bearings supporting loads of 7 MPa at less then one rpm and 30 mm bearings supporting rotors that operate at tens of thousands of rpm. And more, these bearings can run for decades with little or no wear. Unfortunately, there are also an extraordinary number of factors that can affect and cause bearing problems. Lubricant contamination, misalignment, and other adverse operating conditions degrade thermal performance. Vibration must also be considered as the bearing contributes to system dynamics. Failures can be devastating and so it is important to share knowledge on these subjects. Many researchers have provided valuable theory, experiments and models regarding bearing behavior under adverse and unusual operating conditions. This paper contributes four cases of unusual behavior that have been encountered in high-speed turbomachinery where few references were found in literature, and towards which Kingsbury has devoted effort and time in tests and studies.
The first case addresses offset pivot journal bearings. Pad temperatures are reduced by offsetting the pivot. However, some machines can experience reverse rotation under temporary or adverse conditions. Tests were performed to determine if offset pads can accommodate reverse rotation without damage. The other three cases are different in that the unusual behavior occurred at conditions that would typically be considered normal. The phenomena include low amplitude broadband radial vibration, sub-synchronous axial vibration, and high thrust bearing temperatures under low loads. These cases were reported in working machinery and caused sufficient concern to stop production. Laboratory tests were able to duplicate these phenomena, which allowed investigation and design of a solution for all three cases. Results are presented with some theory, hypothesis, or discussion. The intention is that this information will be of value to researchers and other personnel involved with design and prediction of hydrodynamic bearings in high-speed turbomachinery.
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