A New Vacuum Degassing Process For Molten Aluminum

Molten aluminum reacts with the water vapor to form hydrogen which can dissolve in the aluminum melt and be released during the solidification of casting as a harmful gas, resulting in porosity in the casting. There have been quite a few methods of degassing molten aluminum in industry. However, the hydrogen content will increase with the increasing of the time even if the effective degassing has been carried out carefully. In order to keep a low hydrogen content all the time during the continual pouring (such as the case in low pressure die casting, high pressure casting and permanent gravity casting), a patented degassing method is investigated. A porous refractory absorber that is connected with a vacuum system is immersed in the molten aluminum. The vacuum is started inside the porous absorber and the dissolved hydrogen atom will diffuse towards the absorber. In this way, the hydrogen in the melt is removed through the vacuum system. The absorber is made of mullite and of porous structure. It is permeable with gas but can’t be penetrated by the molten aluminum. RPT experiment (Reduced Pressure Test) and density test were conducted to evaluate effectiveness of the new method. The experiments indicate that use of the absorber can improve the metallurgical quality of the melt