What are the purification technologies in the casting of copper castings
The copper liquid sucked from the electrolytic cell contains various impurities, so it needs to be purified before casting. In the industry, purification methods such as clarification, flux, and gas are mainly used, and some try directional solidification and filtration methods for purification.
Flux purification Flux purification uses the flux added to the copper liquid to form a large number of fine droplets, so that the oxides in the copper liquid are wetted, absorbed 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 salt with low melting point, low density, low surface tension, high activity, and strong adsorption capacity for oxidation slag. When in use, 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 finished, take out the iron cage and let it stand for 5-10 minutes. Remove the surface scum to cast. If necessary, the flux can also be removed on the surface to cover it.
2. Gas purification Gas purification is a main primary copper purification method. The gas used is chlorine, nitrogen or a mixture of chlorine and nitrogen.
(1) Chlorine purification. In the past, the active gas chlorine was used as a purifying agent (chlorination method). In the chlorination method, when chlorine is passed into the copper liquid, a lot of abnormally fine AlCl3 and bubbles are generated, which are fully mixed in the copper liquid. The hydrogen dissolved in the copper liquid and some mechanical inclusions are adsorbed on the AlCl3 bubbles and are discharged as the AlCl3 bubbles rise to the surface of the copper liquid. When chlorine gas is introduced, some elements that are more negative than copper can be chlorinated, such as calcium, sodium, magnesium, etc., which are separated by the generation of corresponding chlorides due to the introduction of chlorine gas. Therefore, the chlorination method is a very effective method for purification of original copper. The amount of chlorine gas is 500-700g per ton of copper. However, because oxygen is poisonous and expensive, in order to avoid air pollution and reduce the cost of copper ingot production, the modern copper industry has gradually abolished the chlorination method and changed it to inert gas- -Nitrogen purification method.
(2) Nitrogen purification method. Also known as the smokeless continuous purification method, copper oxide balls (418mm) are used as the filter medium. N2 is directly passed into the copper liquid. The copper liquid is continuously fed into the purification furnace, passes through the copper oxide ball filter layer, and is flushed by nitrogen, so the non-metallic inclusions and dissolved hydrogen in the copper liquid are removed, and then continuously discharged, so that the fine nitrogen bubbles are evenly distributed Play a purifying role in the treated copper liquid. Nitrogen has no pollution to the atmosphere and has a large purification capacity. It can process 200~600kg copper liquid per minute, and the copper loss caused by the purification process is relatively reduced, so it is now widely used. But it is not as capable of removing calcium, sodium and magnesium in copper liquid as chlorine gas.
(3) Mixed gas purification method. A mixture of chlorine and nitrogen is used to purify the copper liquid. Its role is to remove hydrogen and separate oxides on the one hand, and remove some metal impurities (such as magnesium) in copper on the other. The commonly used composition is 90% nitrogen + 10% chlorine . There are also 10% chlorine + 10% carbon dioxide + 80% nitrogen. This effect is better, carbon dioxide can diffuse chlorine and nitrogen well, which can shorten the operation time.