Aluminum rod casting purification technology

[China Aluminum Industry Network] 6061 Aluminum rod Absorbed from the electrolytic bath contains a variety of impurities in the liquid, so need to be cleaned before casting. In the industry, purification methods such as fining, fluxing, and gas purification are mainly used, and directional solidification and filtration methods are also used for purification.

1. flux purification flux purification is the use of flux added to the aluminum liquid to form a large number of fine droplets, so that the oxides in the aluminum liquid are wetted by the droplets to adsorb and dissolve, forming new droplets to the surface and cooling to form a float Slag removed. The flux used for purification is composed of salt with low melting point, low density, small surface tension, high activity, and strong adsorption capacity for oxidized slag. When using, firstly put a small amount of flux into the iron cage, and then insert it into the bottom of the mixing furnace to stir. After the fluxing is completed, remove the iron cage, and stand still for 5~10min. Remove the surface scum and cast it. The flux can also be withdrawn on the surface as needed to provide coverage.

2. Gas purification Gas purification is a major 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 scavenger (chlorination method). In the chlorination process, when chlorine gas is introduced into the aluminum liquid, many abnormally fine AlCl3 and bubbles are generated and sufficiently mixed in the aluminum liquid. Hydrogen dissolved in the molten aluminum, as well as some mechanical inclusions, are adsorbed on the AlCl3 bubbles, and are discharged as the AlCl3 bubbles rise to the surface of the aluminum liquid. Chlorine can also be used to chlorinate certain elements that are more negative than 6061 aluminum rods. For example, calcium, sodium, magnesium, etc., can be separated by chlorine gas. Therefore, the chlorination method is a very effective primary aluminum purification method. The amount of chlorine gas is 500-700g per ton of aluminum. However, because oxygen is poisonous and expensive, in order to avoid air pollution and reduce the cost of aluminum ingot production, the chlorination process has gradually been replaced in the modern aluminum industry with inert gas— - Nitrogen purification method.

(2) Nitrogen purification method. Also known as smokeless continuous purification method, alumina ball (418mm) is used as the filter media. N2 directly into the liquid aluminum. The molten aluminum is continuously fed into the purifier, passes through the alumina ball filter, and is flushed with nitrogen. The non-metallic inclusions and dissolved hydrogen in the molten aluminum are then removed and continuously discharged, so that the fine nitrogen bubbles are evenly distributed. In the treatment of aluminum liquid play a role in purification. Nitrogen has no pollution to the atmosphere, and has a large amount of purification treatment. It can handle 200-600 kg of aluminum liquid per minute. The loss of aluminum caused by the purification process is relatively reduced, so it is widely used now. However, unlike chlorine, it does not remove calcium, sodium, and magnesium from aluminum.

(3) Mixed gas purification method. Using a mixture of chlorine and nitrogen to purify the aluminum liquid, the 6061 aluminum rod removes hydrogen and separates oxides on the one hand, and removes certain metallic impurities (such as magnesium) from 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 works better. Carbon dioxide can spread chlorine and nitrogen well, reducing operating time.