The aluminium melting flux should be thoroughly dried beforehand, so as to remove the moisture, which can improve the refining effect and prevent explosion accidents when the flux is added to the molten aluminum. The chloride flux has high hygroscopicity. The flux must be dried carefully before use. The removal of adsorbed water and crystal water can improve the refining effect.
Usually, the main components of aluminum casting fluxes are chloride and fluoride. Chloride flux can wet oxide and melt well, and adding fluoride to chloride flux can improve the refining ability of flux.
The reason why fluoride improves the refining capacity is that it increases the interfacial tension between the flux and the melt, and enhances the adsorption of the flux to the oxide; the other is that the fluoride has a higher reactivity with the aluminum melt. Surface-active reaction products such as aluminum fluoride gas and liquid sodium are formed on the oxide interface, which promotes the elimination of oxides. When only treated with chloride, only a small amount of gaseous product of aluminum chloride is produced, so the refining effect is not as good as that with fluoride.
The aluminium melting flux refining operations are carried out in accordance with the regulations. The refining temperature should be controlled at the upper limit of the casting temperature to improve the refining effect. The amount of flux should be sufficient. For products with higher internal purity requirements, the amount can be larger, and the usage amount is generally 4-5 kg/t metal. For general products, the usage amount is 2-3 kg/t metal. After the refining is completed, the slag is removed immediately, and then the covering flux is sprinkled and left standing. The standing time varies depending on the product. For important products, the standing time should not be less than 30 minutes, and the general product should be no less than 15 minutes.