Tribology and Lubricants

Korean Tribology Society (한국트라이볼로지학회)
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Testing of Load Capacity of a Foil Thrust Bearing

  • Kim, Choong Hyun (Center for Bionics, Bionics Research Institute, Korea Institute of Science and Technology) ;
  • Park, Jisu (Center for Bionics, Bionics Research Institute, Korea Institute of Science and Technology)
  • Received : 2018.10.03
  • Accepted : 2018.11.28
  • Published : 2018.12.31
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Abstract

In this study, the performance of foil thrust bearings was investigated by performing bearing take-off and load capacity tests, using an in-house designed and manufactured vertical bearing test rig. The mean take-off rotational speed and maximum load capacity of the bearing specimen were ~18,000 rpm and ~80 kPa, respectively. The vertical bearing test rig was observed to yield higher coefficients of friction and frictional torques than a horizontal bearing test rig under identical test conditions. This was a result of its structural characteristics, in that the bearing specimen is placed atop the thrust runner, which keeps it from being separated from the runner after the bearing take-off. In addition, bearing take-off was observed at a higher runner rotational speed as this structure keeps air from flowing between the top foil and runner surfaces, which requires a higher runner speed. The parallel alignment between the bearing specimen and runner surfaces can be maintained within a certain range more easily in a vertical test rig than in a horizontal test rig. Because of these advantages, Korean Industrial Standard, KS B 2060, recommends a vertical bearing test rig as the standard test device for foil thrust bearings.

Keywords

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Fig. 1. Test rig for performance testing of foil thrust bearing: 1 - loading plate, 2 - load cell, 3 - loading shaft, 4 - mounting disk for bearing specimen, 5 - thermocouple for measuring air temperature, 6 - thermocouple for measuring bump foil surface temperature, 7 - runner, 8 - electric motor, 9 - driving shaft, 10 - bearing specimen.

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Fig. 1. Test rig for performance testing of foil thrust bearing: 1 - loading plate, 2 - load cell, 3 - loading shaft, 4 - mounting disk for bearing specimen, 5 - thermocouple for measuring air temperature, 6 - thermocouple for measuring bump foil surface temperature, 7 - runner, 8 - electric motor, 9 - driving shaft, 10 - bearing specimen.

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Fig. 2. Schematic of foil thrust bearing: 1 - bump foil, 2 - top foil, 3 - bearing plate, 4 - inner radius of top foil, 5 - outer radius of top foil, 6 - runner, 7 - air film, 8 - bump height, 9 - welding point, 10 - thermocouple for measuring bump foil surface temperature, 11- thermocouple for measuring air temperature, 12 - bearing plate, 13 - bump foil, 14 - top foil.

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Fig. 2. Schematic of foil thrust bearing: 1 - bump foil, 2 - top foil, 3 - bearing plate, 4 - inner radius of top foil, 5 - outer radius of top foil, 6 - runner, 7 - air film, 8 - bump height, 9 - welding point, 10 - thermocouple for measuring bump foil surface temperature, 11- thermocouple for measuring air temperature, 12 - bearing plate, 13 - bump foil, 14 - top foil.

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Fig. 3. Take-off test with runner speed up to 25,000rpm.

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Fig. 3. Take-off test with runner speed up to 25,000rpm.

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Fig. 4. Comparison of torque variations between foil thrust bearings: (a) start-up torque (b) bearing torque.

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Fig. 4. Comparison of torque variations between foil thrust bearings: (a) start-up torque (b) bearing torque.

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Fig. 5. Variation of torque vs runner speed up to 25,000 rpm: averaged torque values of start-stop test from 501 to 2,000 cycles.

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Fig. 5. Variation of torque vs runner speed up to 25,000 rpm: averaged torque values of start-stop test from 501 to 2,000 cycles.

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Fig. 6. Typical bearing test data during load capacity test under 25,000 rpm runner rotational speed: (a) load, (b) torque, and (c) temperature.

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Fig. 6. Typical bearing test data during load capacity test under 25,000 rpm runner rotational speed: (a) load, (b) torque, and (c) temperature.

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Fig. 7. Torque vs load during load capacity test under 25,000 rpm runner rotational speed.

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Fig. 7. Torque vs load during load capacity test under 25,000 rpm runner rotational speed.

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Fig. 8. Bearing specimen after load capacity test.

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Fig. 8. Bearing specimen after load capacity test.

Table 1. Specification of bearing specimen

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Table 1. Specification of bearing specimen

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References

  1. Army Research Laboratory, "A Foil Thrust Bearing Test Rig for Evaluation of High Temperature Performance and Durability," ARL-MR-0692, April 2008.
  2. Dykas, B. D., "Factors Influencing the Performance of Foil Gas Thrust Bearings for Oil-Free Turbomachinery Applications," Thesis for the degree of Doctor of Philosophy, Case Western Reserve University, May, 2006.
  3. Stahl, B. J., "Thermal Stability and Performance of Foil Thrust Bearings," Thesis for the degree of Master of Science, Case Western Reserve University, May 2012.
  4. Kim et al., "Experimental study on the load carrying performance and driving torque of gas foil thrust bearings," J. Korean Soc. Tribol. Lubr. Eng., Vol. 31, No. 4, pp. 141-147, 2015. https://doi.org/10.9725/kstle.2015.31.4.141
  5. KS B 2060:2016, "Hydrodynamic Oilless Plain Bearing - Foil Thrust Bearing - Evaluation of Static Load Capacity, Friction Coefficient and Lifetime," December 2016.