Why is degassing necessary during aluminum scrap smelting

1. Types and functional differences of rotary furnaces

Aluminum ash rotary kiln: This type of rotary furnace is mainly used for calcining solid aluminum ash, which decomposes harmful substances (such as aluminum nitride and salt flux residues) in the aluminum ash at high temperatures. The core of its process is the oxidation reaction of solid materials rather than the purification of liquid metal. Since the processing object is solid waste residue rather than molten aluminum liquid, there is no need to perform degassing operation on liquid aluminum.

Rotary furnace for melting: If the rotary furnace is used for scrap aluminum melting (such as a tilting aluminum melting furnace), degassing is still required. At this time, the aluminum liquid in the furnace needs to be sprayed with inert gas (such as argon) through graphite rotors or refined with refining agents to remove hydrogen and inclusions.

2. The process objective determines whether to remove gas

Aluminum ash treatment process: The core goal of aluminum ash rotary kiln is to achieve harmless treatment of hazardous waste and resource recovery (such as extracting alumina), rather than producing casting grade aluminum materials. This process focuses on chemical decomposition rather than physical purification, so there is no need to introduce degassing step 3.

Smelting process: If a rotary furnace is used for smelting recycled aluminum (such as producing aluminum ingots or die castings), degassing is necessary. Untreated aluminum liquid containing hydrogen gas and oxides can cause porosity and decreased strength in castings, and purification can be achieved through techniques such as rotary blowing and vacuum degassing.

3. Technological substitution effect

Some rotary furnaces may integrate pre-treatment functions, such as directly decomposing some volatile impurities through high-temperature oxidation during the calcination stage, thereby reducing the degassing pressure during subsequent melting. However, this process is still not equivalent to traditional smelting and degassing, and cannot completely replace the refining process.

In summary, whether rotary furnaces require degassing depends on their specific application scenarios: rotary kilns used for solid aluminum ash treatment do not require degassing; However, the rotary furnace used for liquid aluminum melting still requires refining equipment (such as graphite rotor degassing machines) to remove gases and inclusions