The purification of the aluminium ingot casting
From various impurity is contained in liquid aluminum electrolyzer suck out, so the casting needs to be cleaned before. Industry mainly clarify, flux and gas purification methods, also some trial directional solidification purification and filtering methods.
1. Flux and flux purification is to use the join flux form a large number of small droplets of liquid aluminum, the aluminum oxide by these droplets of liquid moisture adsorption and dissolution, the formation of new liquid drop rises to the surface, formation scum removal after cooling. Purification with flux choose low melting point, low density, surface tension and large activity, the oxidation slag has strong adsorption ability of salt. , when using small flux first into the cage, then insert the hybrid furnace bottom agitation, back and forth to take it out of the flux change their cages, rest 5 ~ 10 min. Remove scum on the surface of casting. Also can according to need to flux on the surface of the cover effect.
2. Gas purification gas purification is a major aluminium purification method, the chlorine gas is chlorine, nitrogen or nitrogen gas mixture.
(1) the chlorine gas purification. Before adopting reactive gas chlorine as cleaning agent (LvHuaFa). In LvHuaFa, chlorine gas flux into the aluminum liquid generated within the many abnormal small AlCl3, bubbles, fully mixing in liquid aluminum. Of hydrogen dissolved in liquid aluminum and some mechanical adsorption on AlCl3 bubbles, inclusions and with AlCl3 bubbles rise to the surface of liquid aluminum and discharge. Ventilation with chlorine can also make some more electronegative than aluminum chloride, elements such as calcium, sodium, magnesium, etc. Generate the corresponding chloride by ventilation with chlorine gas, to separate. So LvHuaFa aluminium purification is a very effective method. Chlorine dosage of 500-700 - g per ton aluminum. But because chlorine is toxic and is more valuable, in order to avoid the air is pollution and reduce the cost of
aluminum production, therefore, in the modern aluminum industry has gradually removed LvHuaFa into inert gas, nitrogen gas purification method.
(2) nitrogen purification method is also called smokeless continuous purification method, using alumina ball (418 mm) as filter medium. N2 directly into the liquid aluminum. Liquid aluminum into purification furnace, continuously through the alumina ball filter layer, and nitrogen flushing, and non-metallic inclusions in aluminum liquid and to remove dissolved hydrogen, then continuous discharge, making slight nitrogen bubbles evenly distributed in the play the role of purification in the treatment of liquid aluminum. Nitrogen gas of atmospheric pollution, and purification capacity is big, can handle 200 ~ 200 kg per minute liquid aluminum, aluminum yield loss caused by the purification process is relatively reduced, therefore, is widely used now. But it is not like chlorine can remove liquid aluminum calcium, sodium, magnesium.
(3) the mixed gas purification method. A mixture of chlorine and nitrogen gas is used to purify the aluminum liquid, the effect is on the one hand to take off hydrogen oxide and separation, on the other hand to eliminate some metal impurities in the aluminium (e.g., magnesium), the composition of the commonly used 90% nitrogen + 10% chlorine. There are 10% + 10% co2 + 80% n2 chlorine. Such effect is better, carbon dioxide can spread the chlorine and nitrogen is very good, can shorten the operation time.
