The process and operation process of removing gas, inclusions and harmful elements from the melt to obtain pure aluminum liquid is called refining. Some people call it purification. There are many refining methods for aluminum alloy, which can be divided into three types according to refining position: pre refining before furnace (such as ladle refining), in furnace refining, on-line degassing refining or continuous refining outside furnace. It can be divided into adsorption refining and non adsorption refining.
Pretreatment before furnace mainly refers to the refining methods for aluminum alloy before adding into aluminum melting furnace. At present, many manufacturers of aluminum and aluminum alloy products at home and abroad use electrolytic aluminum liquid as raw material. Although electrolytic aluminum liquid can greatly reduce the burden and melting time and save energy, there are many characteristics in the melt, such as more hydrogen content, more inclusions, less active crystal nucleus, and high temperature of aluminum melt. It is very easy to cause metallurgical defects of casting billet, such as porosity, slag inclusion, coarse grains, etc., which have adverse effects on the quality of final products.
In order to ensure the purity of raw materials, it is necessary to purify the electrolytic aluminum liquid in advance. At present, the common method is that inert gas or refining agent (generally aluminum fluoride powder) is directly injected into aluminum ladle through rotor or steel pipe to refine it, so as to reduce the content of hydrogen, alumina and alkali metal in aluminum melt. Furnace treatment mainly refers to purification of aluminum melt in aluminum melting furnace or holding furnace.
Aluminum and aluminum alloy melt in the furnace is usually refined after the alloy composition adjustment is completed. The refining process mainly includes purging brick refining in furnace, mixed gas blowing, inert gas flux mixed blowing (introduced from furnace top or side wall or furnace door through rotor or pipe) to further remove hydrogen, inclusions and alkali metals in aluminum melt. Off furnace on-line treatment mainly refers to the treatment of aluminum and aluminum alloy melt from aluminum melting furnace or holding furnace to casting equipment.
After on-line treatment, the melt will directly enter the casting equipment. Therefore, this part of aluminum and aluminum melt treatment is the most important, and also the most intensive place for various aluminum melt treatment technologies.