The electrolytic aluminum liquid directly produces cast-rolled coils, although it can save costs and reduce consumption. However, compared with remelted aluminum ingots, the excessively high proportion of electrolytic aluminum liquid will directly lead to problems such as high hydrogen content, high slag content, high alkali metal content, and coarse grain size of cast-rolled slabs. Therefore, the aluminium melt refining and grain size refinement are the difficulties that must be solved in the direct production of cast-rolled coils using electrolytic aluminum liquid.
In addition to the chemical composition, the internal quality is mainly grain size, gas and slag inclusion. In addition to the ratio of electrolytic aluminum liquid and solid material that will affect the internal quality of the cast-rolled plate, the aluminium melt refining is the key.
Before the furnace is poured, the molten aluminum is sprayed for refining, so that the gas and slag in the molten aluminum have enough time to float from the lower part of the molten pool to the surface of the molten aluminum, and then the slag is removed. The refining time is 20 min~25 min, the amount of refining agent is 3 kg/t, and it is allowed to stand for 20 min after refining. In the powder spraying refining process, the refining agent should be sprayed evenly into the aluminum liquid and the purity of nitrogen should be ensured. The purity of nitrogen can be controlled above 99.9995%.
An online degassing filtering system is adopted between the holding furnace and the front box. The system uses a graphite rotor in the degassing box, so that nitrogen can re-refine the aluminum liquid in the degassing box, and take out the slag and gas. The plate filtering unit is used to filter the inclusions in the molten aluminum. After passing through the online processing system, the hydrogen content in the molten aluminum can be controlled within 0.12 mL/(100 gAl), and more than 90% of the slag content above 5um can be filtered out. It provides billets with good internal quality for cast-rolled coils.