<p>This paper presents a comparison between experimental and theoretical performance characteristics of fixed-geometry hydrodynamic thrust bearings machined to different helical taper depths.&nbsp; Three aluminum alloy unidirectional hydrodynamic thrust bearings have been machined such that the depth of their sector-shaped helical taper is fixed at 0.0010” (0.0254 mm), 0.0020” (0.0508 mm), and 0.0030” (0.0762 mm) with respect to a flat section of the bearing pad located on the trailing edge.&nbsp; The test bearings are realized with CNC machining operations and the geometry of the helical taper is validated using a 0.0001” resolution dial test indicator.&nbsp; This measurement technique reveals that the taper depth across the entire leading edge of the hydrodynamic thrust pad is held within ±0.0002” of the desired depth.&nbsp; Theoretical analysis based on the Reynold’s equation states that under favorable conditions, these taper depths can produce and maintain load-supporting hydrodynamic pressure yet result in characteristically different oil-film pressure distribution profiles and magnitudes of friction torque.&nbsp; One key prediction of the Reynold’s equation suggests that when the minimum oil film thickness separating the bearing from the runner is relatively thin, bearings of shallower taper depth produce a larger maximum hydrodynamic oil film pressure while bearings of greater depth produce a smaller maximum oil film pressure.&nbsp; However, this trend is reversed when the minimum oil film thickness separating the bearing from the runner becomes greater giving bearings of a deeper taper depth the advantage in developing a larger maximum oil film pressure. These characteristic performance indicators have not previously been observed experimentally for unidirectional fixed-geometry hydrodynamic thrust bearings with helically tapered pads.&nbsp; An experimental test rig was developed by re-purposing a horizontal milling machine capable of subjecting the test bearings to speeds up to 1,350 rpm and axial loads up to 200 lbf (890 N).&nbsp; The test rig has 5 different speeds as determined by the configuration of the belt-drive system (100, 175, 365, 700, and 1350 rpm).&nbsp; Axial load is applied using a hand-operated setscrew which pushes the bearing into compression against a flat spinning runner plate.&nbsp; The loads considered in this study are 50, 100, 150, and 200 lbf (222, 445, 667, and 890 N). An oil conditioning system provides flowing lubrication oil (ISO VG32) to the test bearing at a supply pressure of 5 psi (34.5 kPa) and supply temperatures of 20˚C and 30˚C.&nbsp; Under various combinations of constant speed, load, and lubrication supply conditions, the steady-state oil-film pressure distribution across the bearing pad is measured with pressure transducers integrated into the bearing surface and friction torque is determined using a moment-arm and load cell apparatus.&nbsp; The effect of variable taper-depth on hydrodynamic pressure distribution and friction torque is compared to the trends predicted by 1D theoretical analysis based on Reynold’s equation with good agreement of results.</p>

Experimental Performance Evaluation of Fixed-Geometry Hydrodynamic Thrust Bearings With Variable Taper Depths

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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