Simple Solutions That Work! Issue 6

Dynamic systems may be driven externally by motors mounted above the melt in the simpler cases, or may be sophisticated systems designed to receive “dirty” aluminum at one end and deliver clean metal at the other. Dynamic systems are usually designed to “shear” the bubbles, which is generally accepted as an enhancement in the cleansing process. In either case, large numbers of small bubbles and long service life are the desired properties of an ideal system. It may be reasonable to suggest that bubble efficiency and component attributes are the main criteria in degasser design. A review of these criteria follows: Static Systems Static systems can be defined as those embedded in the floor of an aluminum containment vessel. The components are often called spargers or porous plugs. Conventional design is predominantly a truncated ceramic cone, the top flush with the metal- furnace floor interface, and the bottom connected to “plumbing” for introduction of the cleansing gas. BUBBLE REQUIREMENTS COMPONENT REQUIREMENTS Small Not attacked by aluminum Many of them Do not oxidize at air-metal interface Reach entire melt Not attacked by treatment gases Flow easily controlled Easily installed and maintained Reasonable strength Of these criteria, small initial bubble size may represent the single greatest opportunity for optimization, as most of the others have multiple approaches. Advanced ceramic material takes this property to a new level. A unique process allows the production of ceramic bodies with a continuous pore network. The average pore size is in the order of five microns, about ten percent that of conventional ceramics, including those currently used in “porous plugs” or “spargers.” In addition, the permeability can be manipulated to allow gas flow levels compatible with most degassing requirements. This small pore size not only creates tiny initial bubbles in a melt, but also greatly reduces any metal penetration into the ceramic, significantly extending its life. Additionally, the tiny bubble size results in reduced usage of gas. Special non-wetting agents further diminish aluminum attack. The process is independent of any specific material, allowing options in terms of strength, oxidation resistance, erosion resistance, etc. Figure 2 Micropore Distribution in Refractories Figure 1 Figure 3 Static Degasser/Spargers/Porous Plugs Our degassing ceramic transcends the static/dynamic gap. It may be the ideal material for both approaches, and in fact, may allow a transition in the current rotary degassing art. With the current design, the ceramic is encased in a metal shell. This is necessary because otherwise there would be significant gas loss through side and bottom. The metal shell also facilitates attachment of the piping continued ❱❱ Contact: PHILIP GEERS [email protected] 29