How to degas is an important problem for molten aluminum refining. If the gas in the aluminum liquid is not removed in time, pores will be formed during solidification, which will affect the performance and deep processing of aluminum products.
Moisture: it comes from furnace gas, inadequately dried charge, refining agent, covering agent, modifier, under-dried furnace lining, crucible and paint on tools, and residual water on crucible, tools and charge The solvent, the water vapor reacts with aluminum as: 2AL+3H2O→AL2O3+6H to produce hydrogen, which enters the aluminum liquid in an atomic state.
The greasy dirt comes from the furnace charge and tools with grease. The grease reacts with aluminum to generate hydrogen.
There are water-containing corrosion products on the charge. To reduce the absorption of gas by the aluminum alloy liquid, the alloy raw materials should be properly stored to prevent moisture. Fully preheat and dry before use; the smelting crucible and tools should be fully preheated to remove moisture before use. In order to remove the gas in the aluminum alloy liquid, all the aluminum alloy liquid must be degassed and refined before pouring.
How to Degas?
Nitrogen refining method (also known as inert gas degassing method) Basic principle: Nitrogen enters the bottom of the molten aluminum through a certain process device. When the nitrogen floats up from the bottom of the molten aluminum in the form of bubbles, it will There is a hydrogen partial pressure difference at the contacting interface, and the hydrogen partial pressure in the bubble is very low. When the hydrogen partial pressure tends to balance, the hydrogen in the alloy liquid continuously enters the bubble. When the bubble rises to the liquid surface, Hydrogen then escapes into the atmosphere, and while the bubbles are rising, they simultaneously adsorb the oxidized slag and its fixed impurities and make them float to the liquid surface together. The inert gas should be condensed and dehydrated before use to prevent moisture from entering the aluminum liquid. If the refining quality is good, the pores must be less.