The aluminum liquid sucked out of the electrolytic tank for 6061 aluminum rods contains various impurities, so it needs to be purified before casting. In industry, purification methods such as clarification, flux, and gas are mainly used, and some attempts are made to use directional solidification and filtration methods for purification.
1. Flux purification is to use the flux added to the aluminum liquid to form a large number of fine droplets, so that the oxides in the aluminum liquid are wetted, adsorbed and dissolved by these droplets, forming new droplets and rising to the surface. After cooling, the scum is formed and removed. . The flux used for purification is composed of salts with low melting point, low density, low surface tension, high activity, and strong adsorption capacity for oxidized slag. When using, first put a small piece of flux into the iron cage, then insert it into the bottom of the mixing furnace and stir it back and forth. After the flux is completely melted, take out the iron cage and let it rest for 5 to 10 minutes. Remove the surface scum and you can cast it. If necessary, the flux can also be removed on the surface to cover it.
2. Gas purification is a main 6061 aluminum rod purification method. The gas used is chlorine, nitrogen or chlorine-nitrogen mixed gas.
(1) Chlorine gas purification. In the past, active gas chlorine was used as a purification agent (chlorination method). In the chlorination method, when chlorine gas is passed into the aluminum liquid, a lot of extremely fine AlCl3 and bubbles are generated, which are fully mixed in the aluminum liquid. The hydrogen dissolved in the aluminum liquid and some mechanical inclusions are adsorbed on the AlCl3 bubbles, and are discharged as the AlCl3 bubbles rise to the surface of the aluminum liquid. When chlorine gas is introduced, certain elements that are more electronegative than 6061 aluminum rods can be chlorinated. For example, calcium, sodium, magnesium, etc. are all generated by the introduction of chlorine gas and corresponding chlorides can be separated. Therefore, the chlorination method is a very effective method for purifying primary aluminum. The dosage of chlorine gas is 500-700g per ton of aluminum. However, because oxygen is toxic and relatively precious, in order to avoid air pollution and reduce the cost of aluminum ingot production, the chlorination method has been gradually abandoned in the modern aluminum industry and replaced by inert gas - -Nitrogen purification method.
(2) Nitrogen purification method. Also known as smokeless continuous purification method, alumina balls (418mm) are used as filter media. N2 is directly passed into the aluminum liquid. The aluminum liquid is continuously fed into the purification furnace, passes through the alumina ball filter layer, and is flushed with nitrogen. As a result, non-metallic inclusions and dissolved hydrogen in the aluminum liquid are removed, and then continuously discharged, so that fine nitrogen bubbles are evenly distributed. It plays a purifying role in the treated aluminum liquid. Nitrogen has no pollution to the atmosphere and has a large purification capacity. It can process 200~600kg of aluminum liquid per minute. The amount of aluminum loss caused during the purification process is relatively reduced, so it is now widely used. But it is not as capable as chlorine in removing calcium, sodium and magnesium in liquid aluminum.
(3) Mixed gas purification method. A mixture of chlorine and nitrogen is used to purify aluminum liquid. The function of 6061 aluminum rod is to remove hydrogen and separate oxides on the one hand, and to remove certain metal impurities (such as magnesium) in aluminum on the other hand. The commonly used composition is 90% nitrogen + 10 % chlorine. There are also 10% chlorine + 10% carbon dioxide + 80% nitrogen. This has a better effect. Carbon dioxide can diffuse chlorine and nitrogen very well, which can shorten the operation time.
