STUDY OF PRIMARY BREAKUP OF MOLTEN TIN DURING POWDER PRODUCTION IN FREE-FALL CONFIGURATION

A pilot scale atomization setup is built to produce metal powder by atomizing molten tin from an annular free-fall nozzle, using high-speed nitrogen gas. The primary breakup mechanism of liquid tin is investigated using high-speed shadow imaging technique starting from the inception of the atomization process. Two different protrusions of the melt nozzle at different gas flow rates are investigated. The atomization process starts by the initiation of surface waves in varicose and sinuous modes of instability. The primary breakup of the molten liquid column is characterized by a series of bag breakup events in multiple directions and subsequent breakup of the rim. The primary breakup mechanism through bag breakup in a free-fall nozzle is very different from breakup mechanisms through "melt-sheet" formation and "umbrella breakup" reported earlier in the context of close-coupled nozzles.