The need is becoming more and more urgent for gas-turbine bearings to be operated safely at very high speeds. Some experiments were conducted to investigate the running performances of a deep-grooved ball bearing (type # 6206) used for gas-turbine operating with dn values ranging between 0.3 × 10^6 and 2.55 × 10^6. Test bearings were rotated by air-turbine of 8 kW at 10 × 10^4 rpm. As for the bearing load, thrust of 50 kg only was given. Turbo-oil of mineral base was used to lubricate the test bearings and the temperature of the inlet oil was varied from 30° to 130℃. Oil was supplied to the bearing by a single nozzle and the flow was varied from 0.22 to 3.0 kg/min. The retainer of the test bearing was made of brass and of outer-race riding type. The test bearings were operated successfully over the range of dn values from 0.3 × 10^6 to 2.1 × 10^6. In this range, the bearing frictional torque was found to be directly proportional to Z^<0.5>-N^<1.3>-Q^<0.25>, where Z is the viscosity of the oil at the bearing outer-race temperature, N the revolutional speed of the shaft, and Q the oil flow per unit time. When the dn value increased above 2.1 × 10^6, bearing failure often occurred, of which the limiting value (the dn value at which the bearing temperature rose rapidly or the bearing frictional torque increased suddenly) depended on oil flow. The more the oil flow, the higher was the limiting dn value. But, however much oil we might supplied to the test bearing, it could not run above dn value of 2.55 × 10^6 (85, 000 rpm). Heavy wear of the retainer occurred at its outside surface, showing the lubrication failure. It must be concluded, therefore, that the retainer locating surface is the most difficult and important lubricating area limiting the high speed rotation of a ball bearing.
<論文>高dn値における玉軸受の性能(V/STOL機用エンジンに関する研究)
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