This paper presents experimental performance characteristics of fixed-geometry hydrodynamic thrust bearings machined to different helical taper depths. 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. These characteristic performance indicators have not previously been observed experimentally for unidirectional fixed-geometry hydrodynamic thrust bearings with helically tapered pads. An experimental test rig was developed by re-purposing a horizontal milling machine capable of subjecting the test bearings to speeds up to 1,265 rpm and axial loads up to 250 lbf (1,112 N). Under various combinations of constant speed, load, and lubrication supply conditions, the steady-state oil-film pressure distribution across the bearing pad and active friction torque are measured. The effects of variable taper-depth on hydrodynamic pressure distribution and friction torque are compared and discussed.

Tapered-land hydrodynamic thrust bearings require taper depths of approximately 20–100 μm to operate efficiently within the hydrodynamic regime. Machining the tapers in traditionally manufactured bearings increase production time and costs. The thermo-mechanical analysis presented in this work shows that the utilization of composite laminas in place of taper machining may be used to provide taper formation in hydrodynamic bearings by exploiting the thermal expansion produced from frictional heating. Thermal expansion of three different carbon/epoxy composite layups (AS-4/3501-6, IM7/3501-6, T-300/3501-6) was analyzed using ABAQUS/CAE composite module. The analysis shows that the composites provide bidirectional taper depths of 24.25 μm, 23.7 μm, and 22.27 μm while being subjected to in-service film pressures and temperatures.

This research presents a newly developed hydrodynamic test rig for experimental testing of hydrodynamic thrust bearings. In this study, the test rig applies thrust loads up to 500 lbf at rotational speeds up to 6,000 rpm. Three fixed geometry hydrodynamic thrust bearings with eight identical helically tapered thrust pads made of cast aluminum alloy have each been machined such that the depth of their tapered surface at the leading edge is 0.0005″, 0.0015″, and 0.0025″ with all other geometrical features held constant. The test rig includes an oil conditioning system which supplies a constant flow of ISO 32 motor oil to the test bearing at 40°C. An integrated sensor system includes an eddy current sensor to measure the minimum oil film thickness, a friction torque moment arm with load cell to measure power loss, K-type thermocouples to measure bearing temperature, pressure transducers to measure oil film pressure distribution, and load cells to measure the applied thrust force. The test rig also introduces a novel bearing alignment system used to ensure precise alignment of the bearing and runner during operation based on pressure feedback from individual thrust pads. Results obtained from this experiment are used to compare the effect of taper geometry on active performance of the test bearings considered. Trends in performance observed are related to the trends predicted analytically by the Reynolds equation.

This work investigates the use of carbon fiber filled polyamide filament as feedstock material for fused filament fabrication of hydrodynamic tapered-land thrust bearings. Experimental analysis was conducted on fused filament fabricated carbon fiber filled polyamide samples to obtain elastic properties and thermal expansion coefficients along the longitudinal and transverse directions with respect to the print orientation. Single bearing pads were modeled using the obtained mechanical properties and were then analyzed under in-service bearing operating pressures and temperatures. Thermo-mechanical analysis conducted in ABAQUS/CAE shows that taper geometry forms on both [0,90] and [0,0,90] print orientations with depths of 174 μm and 260 μm as a result of thermal expansion occurring from the heat load produced during hydrodynamic bearing operation.

Fixed-geometry hydrodynamic thrust bearings rely on convergent geometry on the bearing face in the direction of relative motion to develop and maintain hydrodynamic pressure. Machining the convergent taper feature onto the bearing using traditional manufacturing processes can prove to be a difficult process due to the small magnitude of taper depth necessary for proper bearing performance. The work presented here investigates three different types of carbon fibers (AS-4/IM7/T-300) in an epoxy (3501-6) matrix for composite lamina formulation in taper-land composite thrust bearings as a means of controlling taper depth via thermal expansion so that favorable bearing functionality is maintained during load fluctuation without the need for traditional machining processes to create the taper. Thermal expansion of specific composite laminate formulation is analyzed using the ABAQUS/CAE composite module. The thermo-mechanical analysis shows that under realistic in-service temperature conditions resulting from bearing friction-torque, the thermal expansion of composite tapered-land thrust bearings expand to provide physical surface gradient magnitudes of 0.09504 mm, 0.08987 mm and 0.08829 mm that are capable of producing hydrodynamic pressure.