The aluminum casting fluxes are widely used in the aluminum purification process for small-scale aluminum casting factories or workshops. When casting outside, the inclusions are removed through the filter screen, and the effect is also very good. The flux used is generally a mixture of sodium nitrate and graphite, which utilizes the thermal decomposition of sodium nitrate and the reaction with aluminum to form nitrogen oxides or nitrogen gas to achieve the purpose of removing gas impurities.
The method of combining the continuous aluminum fluxes purification method outside the furnace with filtration and gas purification. The aluminum liquid is continuously fed into the furnace, under the protection of the flux covering layer, and flushed with nitrogen (or mixed gas). Then through the ceramic foam filter system, the purified aluminum liquid is discharged from the outlet. The advantage of this method is that it can continuously purify aluminum liquid (200-600kg per minute), nitrogen has no pollution to the environment, and has a better purification effect, and the hydrogen removal rate can reach 30%-40%.
The gas purification process is to pass bubbles of inert gas or active gas into the aluminum liquid to dissolve the dissolved gas. Inert gases such as nitrogen and argon can be used, as can active gases such as chlorine, carbon tetrachloride, and hexachloroethane. When using chlorine gas, the chlorine bubbles will form dispersed aluminum chloride bubbles through the aluminum liquid, trap the suspended solid inclusions adsorbed with hydrogen, and then float to the surface of the aluminum liquid to be removed.
At the same time, metal impurities such as lithium, potassium, calcium, sodium, and magnesium contained in the aluminum liquid can be removed due to chlorination. However, chlorine is corrosive and causes aluminum loss and environmental pollution, so it is mostly used in combination with nitrogen. The chlorine content is generally 3% to 6% (volume fraction). In addition, in order to reduce the amount of aluminum chloride discharged into the atmosphere, the method of spreading chloride flux on the aluminum surface can be used to reduce the sodium content in aluminum to less than 0.001%. This low-content sodium liquid can be used for the production of Aluminum-magnesium deformation alloy.