METAL-POWDER PRODUCTION BY CENTRIFUGAL ATOMIZATION

A new atomizer has been designed and constructed of the centrifugal disc type. A liquid metal stream leaving the tundish enters the centre of the disc and is atomized by centrifugal force. Droplets formed fly in air and then enter a water vortex barrier 5cm thick. The wafer barrier is 10cm away from the disc. Solidification is partially in air and partially in water. Lead, aluminium and 8640 steel have been atomized Atomization and material parameters investigated were: (1) disc shape (flat, cup shaped and vaned) and size, (2) liquid metals (different densities and melting temperatures), (3) liquid metal superheat (varying viscosity and surface tension), (4) disc speed (15,000rpm (1570rad/s) to 25,000rpm (2618rad/s) and (5) liquid metal flowrate. The characteristics of the powders produced were examined by various techniques. The shape of the steel powders was spherical and that of aluminium and lead powders was irregular Mean powder size is dependent on the atomizing parameters, and is about 100 mu m. Microhardness of the steel powder is 1045 HV, which has a supercooled martensitic structure. Of the three different disc geometries, the performance of the vaned disc was much better than that of the others. The powders produced were finer; and the efficiency and production rate were much higher than with the other disc shapes