Aerostatic journal bearings with porous tilting pads enable shaft support with minute drag power losses. To date archival information on the static and dynamic load performance of this bearing type is scant. Thus, the paper presents measurements conducted with an air lubricated bearing with diameter D = 102 mm and comprising four tilting pads made of porous carbon-graphite, each with length L = 76 mm. Two nested Belleville washers resting on spherical pivots support each pad. Under increasing static loads (W), measurements include shaft eccentricity and attitude angle, pad temperature and pad tilt displacements. As the air supply pressure into the bearing pads increases, so does the bearing aerostatic specific load (W/(LD)) that reaches 58% of the pressure drop (supply-ambient). Upon operation with shaft speed up to 9 krpm (48 m/s surface speed), and to avoid contact, the load capacity reaches 43% of the aerostatic load. Supplied with air at 7.8 bar(a),&nbsp;the bearing carried static loads (W) up to 1,330 N (specific load ~172 kPa) at 6 krpm and 922 N (~117 kPa) at 9 krpm. At an operating temperature of ~ 35°C and air supply pressure of 7.8 bar(a), the test bearing static stiffness is independent of both shaft speed and static load and equals KS = 13.1 MN/m, just 63% of the washers’ stiffness KP = 20.6 MN/m.During operation with shaft speed at 6 krpm/9 krpm and up to 115 kPa/101 kPa specific load, dynamic load experiments with excitation frequencies up to 342 Hz show the test bearing supplied with air at 6.8 bar(a) has frequency independent stiffness (K) and damping (C) coefficients. For rotor speeds equaling 0, 6 and 9 krpm, the bearing stiffness (KXX ~ KYY) increases with static load and ranges from 13.6 MN/m to 32.7 MN/m, whereas the direct damping (CXX ~CYY) is as large as 5.8 kN∙s/m (though having a large experimental uncertainty). The test bearing produces insignificant cross-coupled force coefficients.The test externally pressurized porous gas bearing reached its intended load capacity, demonstrated a dynamically stable operation, and produced significant force coefficients mainly affected by the pads’ pivot supports (the Belleville washers) and the magnitude of air supply pressurization.&nbsp;

Measurements of Static and Dynamic Load Performance  of a 102 Mm Carbon-Graphite Porous Surface Tilting-Pad  Gas Journal Bearing

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2021/volume/84898

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