• Title/Summary/Keyword: mating ball

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Rotor Coastdown and Acceleration Performances of High-speed Motors Supported on Ball Bearings and Gas Foil Bearings (볼 베어링 및 가스 포일 베어링으로 지지되는 고속 전동기의 회전체 관성정지 및 가속 성능 연구)

  • Mun, HyeongWook;Seo, JungHwa;Kim, TaeHo
    • Tribology and Lubricants
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    • v.35 no.2
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    • pp.123-131
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    • 2019
  • This study characterizes the coastdown performances of two small electric motors supported on high-speed ball bearings (BBs) and gas foil bearings (GFBs), and it predicts their acceleration performances. The two motors have identical permanent magnetic rotors and mating stators. However, the shaft of the GFBs has a larger mass and polar/transverse moments of inertia than that of the BBs. Motor coastdown tests demonstrate that the rotor speed decreases linearly with the BBs and nonlinearly with the GFBs. A simple model for the BBs predicts a constant drag torque and linear decay of speed with time. The test data validate the model predictions. For the GFBs, the hydrodynamic lubrication model predictions reveal that the drag torque increases linearly with speed, and the speed decreases exponentially with time. The predictions agree very well with the test data in the speed range of 100-30 krpm. The boundary lubrication model predicts a constant drag torque and linear decay of speed with time. The predictions agree well with the test data below 15 krpm. Mixed lubrication occurs in the speed range of 30-15 krpm. Rotor acceleration performances are predicted based on the characteristics of deceleration performances. The GFBs require more time to reach 100,000 krpm than the BBs because of their larger shaft polar moment of inertia. However, predictions for the assumed identical polar moment of inertia reveal that the GFBs have a nearly identical acceleration performance to that of the BBs with a motor torque greater than $0.03N{\cdot}m$.

A Study on the Failure Mode of the Rolling Bearing with Defective Balls

  • Hyun, J.S.;Park, T.J.
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 2002.10b
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    • pp.305-306
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    • 2002
  • In this paper, the endurance life of the rolling bearings with defective balls and their failure (flaking) phenomena are presented. It was found that the lives of ball bearings with defective balls were shorter than that of calculated L10 life as well as that of normal bearings in spite of the using standard bearing components. Although the bearings were assembled with defective balls, whereas the other parts were qualified new ones, the main failures were occurred on the inner ring raceways. Moreover, the failures were on the center of the groove curvature and the severity of failure is similar to the order of initial defect depth of the balls. These shows that the defects on the bearings can affect the life of tribologically contacted mating parts.

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