Degassing & Flux Injection
Hydrogen gas can build up in molten aluminum and result in gas holes in the final casting. To remove this gas, a degassing unit is used to inject an inert gas to grab the hydrogen and bring it to the surface. This can be done with a graphite tube or rotating shaft. The rotating shaft is far more efficient. At the end of the shaft is a rotor to break the inert gas into very fine bubbles.
Molten aluminum oxidizes quickly. In order to remove these oxides, foundries use fluxes to grab the oxide and bring it to the surface. This can be done manually. However, flux injection is far more efficient. Often the flux is carried through the graphite degassing shaft to the bottom of the melting vessel. The flux and oxide are brought to the surface by the rising bubbles and can be skimmed off as ash.