It is known that molten metals such as aluminum include high levels of oxide and/or nitride fragments, which have a negative effect on the solidification of certain alloys. The molten or liquefied form of aluminum also attracts the formation and absorption of hydrogen in molten aluminum. Hydrogen is precipitated in the form of pores during the solidification of the aluminum alloy and is harmful to the mechanical properties of the solid alloy. Degassing is an effective method to reduce the porosity caused by hydrogen. The degassing process in aluminum is essential to remove dissolved hydrogen and non-metallic content from molten metal before casting to achieve the best quality.
A mixture of inert gas (such as argon or nitrogen) and a reactive gas (such as chlorine or hydrogen fluoride sulfur) is introduced into the molten aluminum to collect hydrogen and wet solid impurities. The gas mixture bubbles up to the surface along with hydrogen and oxide impurities.
Molten aluminum may also require flux degassing treatment to introduce refining agents into the molten metal. Flux degassing is a process in which powdered or granular salt mixtures such as chloride or fluoride are introduced into molten aluminum via a carrier gas such as nitrogen or argon. Salt flux can be introduced by rotating degassing equipment.
The rotary degassing device includes a central hollow shaft attached to the rotor, which is inserted into the molten aluminum pool and rotated so that the salt flux travels along the hollow shaft and is dispersed in the molten aluminum through orifices in the rotor. The aluminum alloy liquid continuously enters the degassing device, and the nitrogen is continuously blown in. Through the degassing process in aluminum, the purpose of purifying the aluminum alloy liquid is realized.
The rotary degassing device uses the nitrogen blown into the aluminum alloy melt to be crushed by the rotating silicon nitride rotor, forming a large number of diffusion bubbles, so that the aluminum alloy liquid and nitrogen are fully contacted in the processing tank.
According to the principle of pressure difference and surface adsorption, the bubbles absorb the hydrogen in the melt and adsorb the oxidized slag (the collision is larger, the radial interception is smaller). Slag forms on the surface of the melt. The aluminum alloy melt flows from the outlet of the degassing device (located in the lower part of the dirt) to the casting machine.