Gap on Nozzle and Rolls Control in Aluminum Casting and Rolling

Increase the gap on nozzle and rolls, optimize the nozzle flow pattern, help eliminate the longitudinal streak defects, and improve the surface quality of the cast-rolled strip.

Gap on Nozzle and Rolls

The surface features of the longitudinal stripes are defects that run through the entire length of the cast-rolled sheet. The longitudinal stripes are bright bands, sometimes deep. The longitudinal stripe will form a corresponding stripe in the circumferential direction on the surface of the casting roll, which must be polished with sandpaper in production. Longitudinal stripes cannot be eliminated on the surface of the foil. When the longitudinal stripes are serious, bright and dark stripes appear on the surface of the foil, which seriously affects the surface quality and product grade of the foil.

By increasing the gap on nozzle and rolls, and optimizing the nozzle flow pattern, the longitudinal stripes on the cast-rolled plate surface are reduced or eliminated. The size of the caster tip and nozzle gap has a great influence on the generation of longitudinal stripes. In normal production, due to the assembly error of the nozzle or the poor quality of the nozzle, the gap between the nozzle rollers is too small or partially uneven, and the nozzle is ground after the roller and the nozzle contact. Inclusions such as powders and aluminum slag during the casting and rolling process will accumulate at the outer front end of the mouthpiece. When the aluminum liquid passes through, the crystallization conditions here are significantly different from the crystallization conditions at other places. An obvious structural difference is formed on the surface of the rolled coil due to different crystallization conditions. If this difference is serious, it will produce sliver defects, if it is slight, longitudinal stripes will appear. After the longitudinal stripes are generated, stripes will be printed on the same position of the roll. And gradually form a small, uneven sticky aluminum strip along the circumference of the roll. Due to the interaction between the roll and the cast-rolled coil, the longitudinal stripes are difficult to eliminate online, sometimes running through the full length.

On the basis of adjusting other process parameters, the gap between the nozzle rolls was increased, and the test proved that there are almost no stripes on the surface of the cast-rolled billet, the longitudinal stripes are well controlled, the surface quality of the blank has been greatly improved, but the gap between the nozzle rolls is too large At this time, the oxide film at the gap between the nozzle rolls is easy to crack and roll to the plate surface, forming oxide film folding defects. In severe cases, the oxide film ruptures and causes aluminum to return. Therefore, it is necessary to be cautious to increase the gap between the nozzle rolls.

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