Study On The Nozzles Used In High-Throughput Continuous Cast-rolling Of Aluminium Alloy Plate And Strip

High throughput continuous cast-rolling of aluminium alloy plate and strip is established on the basis of horizontal continuous casting. It is a new production technology with high efficiency, short process and low energy consumption. Electrolytic aluminum melt go through high throughput continuous cast-rolling mill and hot rolling mill, direct molding for 2 mm to 8 mm slab. In this process, the circulation of the aluminum melt is very high, up to 50t/h. The nozzles is the key components which sent the aluminum melt into high throughput continuous cast-rolling mill directly. The selection of its material and structure are very important. At present, the nozzles used on the casting production line all needs to import, the high price is the main reason for the aluminum plate’s cost can’t reduce; In addition, the structure of nozzles is fixed, which can’t be unable to adjust and control according to the production situation. It is easy to block in the course of producing aluminum alloy which containing a high percentage of Mg alloy. The only solution of this problem is shuting down the mill and changing the nozzles. This process is not only wasting a lot of manpower, but also greatly reducing the production efficiency. Therefore, studies on the material and structure of the nozzles casting nozzles has important significance for the analysis of the nozzles plugging mechanism and the localization of the high flux of continuous cast-rolling nozzles.In this paper, we studied on the material and structure of the nozzles. In terms of material analysis, we taked up research of the import nozzles used in high throughput continuous cast-rolling from the appearance shape, microstrucrure and performance of the organization systematically. At the same time, we selected four types of domestic nozzles used in Twin-roll continuous cast-rolling for comparison. Analysising the same and difference between the domestic and imported and discussing the feasibility of localization for the nozzles used in the high throughput continuous cast-rolling casting. In terms of structure analysis, the main analysis is the two structures used in the high flux continuous cast-rolling.Through calculating simulation, we simulated the flow of the melt in the cavity of the nozzles and analysied the flowing discipline;Finally, combined with two factors of the cast nozzles material and structure,we made a inference of the mechanism about the nozzles which used for producing the aluminum alloy containing a high percentage of Mg, then we verified it.Through the analysis of the nozzles materials, we found that the nozzles made in China and abroad had a small difference in terms of shape and microstructure and the production technology of them were very close to. So the feasibility of localization about the nozzles used in high flux of continuous cast-rolling was high. The main differences of casting nozzles materials made in China and abroad was the use of fiber, the silicate fiber used in imported casting nozzles was crystalline structure but the chinese was subcrystalline structure The refractoriness and service life of crystalline fibres were significantly better than that of amorphous fibers. Therefore, import casting nozzles in the heat preservation performance and service life are better than domestic casting nozzlesBy means of modelling the nozzles use in high throughput continuous cast-rolling and making computer simulation, we found that the state of the flow of the melt in the cavity was turbulent flow, and the flow state of each part are not the same. In general it can be divided into three parts:Near the center of mold, the flow field had fast speed and relatively stable condition; Near the cavity wall, the flow field had low speed and stable condition; In the middle part, the flow field had medium speed and the state is complicated. Through analysis exit speed curve, we found that the exit velocity of the ends of the casting nozzles was significantly higher than the exit velocity of the middle part.The casting speed, casting slab width and the surface roughness of inner cavity of the nozzles had significant impact on the flow field of casting melt in the nozzles. With the increasing of casting speed, the turbulent state of the melt in the cavity became more complicated; With increasing of the casting width, the out speed of the casting nozzle outlet edge and middle had the more wide gap; As surface roughness of the nozzles cavity increasing, the near wall region steady flows was broken, instead, the turbulence became complexed, compounded and hanged the slag phenomenon.Through thermodynamic calculation, dynamics analysis of the casting mouth jam, SEM and XRD analysis of the casting mouth slag layer and combining with casting nozzle material and flowing discipline of the flow in the nozzles cavity, it is concluded that the reasons about the nozzles blockage mechanism during the production process of the high content of Mg-Al alloy strip. We think that the Mg in melt is constantly making response with the material of the casting nozzles in the process of production, and small inclusions in the melt can be deposited in surface, then it would change the melt flow field and temperature field in the cavity when the deposition reached a certain degree,;Finally the melt solidify in the middle, causing the cavity blocked.