Development of High Speed Machine Tool Main Spindle Using Liquid-Gas Two Layer Film Hydrostatic Bearing

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In the first fiscal year:(1) Before designing, the two problems of sealing and exhausting the oil supplied into the bearing surface and preventing oil intrusion into the air supply holes were solved by means of vacuum pump and design of the exit shape of air holes, respectively.(2) The new model of main bearing of grinder hydrostatically lubricated by liquid-gas two layer film was designed being based on the numerical calculation of the static bearing performance and considering the above mentioned method, and was manufactured.In the last fiscal year:(3) The static performance of this bearing model was estimated by the experiments. The experimental results were in good agreement with the results of the calculation for the design.(4) The anti-seizure performance against over load due to the existence of the oil film was evaluated. The results are shown as follows:(a) The bearing stiffness increases abruptly when the shaft contacts on the oil film at large eccentricity, and thus the thin oil film is effective to prevent bearing damages against over load.(b) The oil film thickness under over load is scarcely affected by the flow rate of supplied oil, and consequently a little oil flow rate is sufficient to prevent bearing damages with in the limit of the existence of the oil film layer.(5) It is concluded that the application feasibility of this new type of bearing for machine tools is demonstrated in spite of the structure complexity because it takes advantages of avoiding seizure at over loading which is a weak point of gas bearing as well as of low friction in gas bearing.