Atomization of viscous melts

Specific melt types have high viscosity and comparably low surface tension. Therefore, conventional twin-fluid atomization of these viscous melts for powder production often results not in spherical particles but in a great amount of fiber material In this investigation, viscous mineral melts are atomized in a pilot plant by means of hot gases for spherical particle granulation. Experimental results show that on almost fiber-free product (97% spherical powder) can be obtained. Usually, the atomization process is controlled by the gas pressure only (here before the expansion in the atomizer nozzle). For constant atomization pressure the mass median diameter of the powder yield decreases with increasing atomization gas temperature. Numerical simulations of the gas flow field in the atomizer vicinity support the analysis of the melt fragmentation process by obtaining the gas temperature distribution and the gas flow, conditions within the atomization process. Simulations for different atomizer nozzle designs and several operating conditions have been realized. From the discussion of the experimental results together with the results of the simulations, the relevant shear process between the melt jet and the atomization gas, characterized by the Reynolds number, can be determined as the main driving mechanism of the atomization and spheroidization process.