ANDREW M. MIKULA, (Member, STLE)
Philadelphia, PA 19154
This paper compares various shoe materials and analyzes their influence on the thermal performance of tilting-pad (shoe) equalizing thrust bearings. The paper presents experimental data on 267 mm (lO ½ inch) O.D. bearings, operating at shaft speeds up to 14000 RPM with loads ranging up to 4.83 MPa (700 PSI). The data presented demonstrates the effect of shoe construction material on bearing operating babbitt temperature.
Tin or lead based (>80 percent) babbitt normally used on the working surface of thrust bearing pads, or "shoes", loses its tensile and compressive strength at elevated temperatures and is subject to creep (1), which places a fundamental limitation on bearing operation. Therefore, babbitt operating temperatures are routinely monitored as an important yet convenient means of assessing bearing risk (2). Providing that a sufficient oil film is developed and maintained, elevated babbitt temperatures are the result of high sliding velocities. The options available to reduce elevated babbitt operating temperatures resulting from the oil film shear rate are limited, and the trade-offs can adversely affect other areas of bearing performance.
Velocity related elevated babbitt temperatures can be reduced either by lowering the heat generated in the oil film or improving the conduction of that heat away from the babbitt by using a backing material with greater thermal conductivity. Pivot location (3), lubricant supply method (1), (4), (5), and lubricant supply temperatures (4) have been shown to be effective in reducing oil film heat generation. The purpose of this paper is to provide the information necessary to evaluate the effect of thermal conduction on babbitt operating temperature, based upon actual performance data.
The effect of thermal conduction was evaluated on a tilting-pad, equalizing, double thrust bearing arrangement. The tests were conducted with a light turbine oil which had a viscosity of 0.027 Pa·s @ 37.8°C and 0.005 Pa·s @ 98.9°C (150 SSU @ 1OO°F and 43 SSU @ 210°F-ISO VG 32). The temperature-viscosity curve for this lubricant can be found in Ref. (6). The lubricant supply temperature for all tests was held constant at 46.6°C (115°F). The shaft speed ranged from 4000 RPM to 14000 RPM, and the load ranged from a "no-load" condition to 4.83 MPa (700 PSI) in increments of 0 .345 MPa (50 PSI).
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