Experiences in a New Degassing Concept

Abstract

Rotary impeller degassing, or rotary degassing for short, is a well-established practice for removing hydrogen from molten aluminum alloys. The principle behind rotary degassing is to disseminate inert or active gasses within the aluminum melt. The dissolved hydrogen seeks to equilibrate with the purge gas bubbles, which rise to the melt surface, carrying hydrogen out of the melt and into the atmosphere. Issues with hydrogen control when degassing become exaggerated when a process requires an intermediate level of hydrogen. This is common when controlled amounts of hydrogen within a melt can help offset the problematic volumetric contraction observed when pouring the same casting with a hydrogen-depleted melt. In applications where discernible amounts of hydrogen are desired, "best in class" aluminum foundries typically complete a full degassing cycle and then try to add controlled amounts of hydrogen via mixed gas additions.