Measurement of Temperature and Load Versus Bearing Displacement in a Thrust Foil Bearing: Differences Between Light Load and High Load Operation

This paper presents a test rig for evaluation of gas thrust foil bearings (GTFBs) and details measurements of load capacity conducted with a commercial GTFB comprising a single 360 deg, 0.127 mm thick top foil divided into six continuous arc segments with a formed taper of 0.102 mm. Coated with Teflon®, the top foil rests on a stack of shims above six underspring structures, each comprising three strips of bump foils, 0.102 mm thick. Measurements include the applied static load and break-away torque, rotor speed, bearing axial displacements at three locations 120 deg apart, the flow of a cooling stream, and temperatures in and out of the bearing. Static load tests produce the underspring deformation and a dry-sliding friction coefficient f ∼ 0.12. The underspring is rather flexible though quickly hardening for specific load (P*) > 25 kN/m² to reach an ultimate deformation of ∼0.320 mm. Measurements at 30 krpm (OD surface speed = 111 m/s) and increasing static loads produce bearing displacements that parallel the displacements without shaft rotation. Most importantly, the difference between displacements approaches ∼0.060 mm for P* > 45 kN/m². The test bearing operated safely to P* = 90 kN/m² and failed at P* = 120 kN/m². When heavily loaded, the GTFB is significantly stiffer than when lightly loaded. Designed for easiness of installation and operation, the test bearing demonstrated a stable and repeatable performance with likely a uniform gap or film thickness even for the largest loads applied.