Oil-air lubrication is an effective lubrication method for the high-speed spindle of machine tools. However, the rate of oil supply to the bearing fluctuates markedly due to intermittent oil supply from the oil-air mixing valves. In this study, a new oil-air mixing apparatus is developed by applying a piezoelectric nozzle which has been used to the printing head of ink-jet printers. By using the piezoelectric nozzle instead of the conventional mixing valve, fluctuation of the oil supply is successfully controlled. Further, it becomes possible to attach the oil-air mixing equipment in the vicinity of the bearings. The oil supply rate can be, therefore, quickly changed in response to changes in the running condition of the bearing.
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