Development of New Gas Atomizer Nozzle System for the Production of Fine Metal Powder used in Power Metallurgy

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In the gas atomization method, the molten metal is atomized by supersonic free jets. However, the breakup process of the melted metal droplet is not known and the industrial atomizer system is designed through the empirical consideration. The aims of the present research are to clarify the breakup process with the laser-based new diagnostic method, to develop the supersonic nozzle with a special exit shape and also to establish the method for numerically predicting the detailed structure of supersonic jets. The following results are obtained.(1) To observe the breakup process of the water droplet, the novel method is developed. This uses the THG of the Nd : YAG laser (wavelength 355 nm). The inline laser holography system with this ultraviolet laser is constructed and tested with the standard particle with known diameter, and the accuracy of 10% is obtained.(2) To check the effect of the exit shape of a supersonic orifice on the breakup' of a water droplet, the orifice is made that has 50 micron-wire stretched over the diametrical direction of the orifice. It is found from the holography measurements that this wired-orifice produces water particles with the diameter 10 to 20% smaller than the normal orifice. We believe from this experiment that the droplet size is controllable by changing the exit shape of the orifice or nozzle.(3) To clarify the detailed structure of the supersonic free jets, the TVD scheme is developed for solving the Euler equations, and the jets with the ratio of stagnation to ambient pressure of up to 1500 are calculated. This scheme is extended to calculated with the boundary fitted grid to increase the accuracy. The three-dimensional calculation scheme is also developed.