What are the prominent problems in the tundish
At present, there are many problems in the tundish used in China, especially in the tundish used for billet caster. The specific performance is as follows:
(1) The shape of tundish cavity is unreasonable. Due to the unreasonable shape of the inner cavity, the flow of molten steel in the tundish is unreasonable and the residence time is short, which can not purify the molten steel. The distance from the drop point of the large ladle injection into the tundish to the tundish nozzle is short, or the distance from each nozzle is too different; The volume at the drop point of the ladle is too small, resulting in serious steel slag mixing and lining scouring, affecting the service life of the tundish and polluting the molten steel.
(2) The capacity of tundish is small and the depth of molten pool is shallow, so it is not suitable for high-speed caster. The molten steel stays in the tundish for a short time, which makes it difficult to purify the molten steel and remove inclusions; It is difficult to maintain constant casting speed when changing the package; During pouring, the steel slag in the tundish is agitated seriously, which makes it difficult to float the inclusions and easy to enter the mold, especially when changing the tundish.
(3) The position of tundish nozzle is not properly designed, especially the nozzle on both sides is too close to the two sides, which is easy to cause unsmooth pouring of the two side nozzles.
(4) The tundish nozzle control device is too thin and unreliable, which makes it difficult to accurately control the flow of molten steel, making it difficult to stabilize the liquid level of the mold and often causing out of control accidents.
(5) The large deformation of tundish and the problems of design and manufacturing accuracy result in insufficient centering accuracy of multiple water outlets.
(6) The lifting device of tundish is ineffective, and most of them can not be lifted, which brings difficulties to the continuous casting process and causes many defects of the slab.
(7) The distance from the bottom of tundish to the upper mouth of crystallizer is improperly selected. Most of the distance is too high, which makes it difficult to align the nozzle, and also makes the nozzle too long, which increases the refractory consumption per ton of steel nozzle.
(8) Insufficient attention has been paid to the quick change technology of submerged nozzle.
The above tundish can only be used at low casting speed, which is not suitable for the requirements of high casting speed. Modern tundish should not only adapt to the conditions of constant speed casting at high drawing speed, high steel throughput and strength, and intense agitation in the tundish, but also play the role of purifying molten steel and removing inclusions. The specific measures adopted include:
(1) Optimize the shape of the inner cavity of the tundish, make the liquid steel flow reasonably in the tundish, expand the volume of the large ladle at the drop point of the tundish and optimize the distance from the drop point of the large ladle to each water inlet under the condition of adapting to the high pulling speed;
(2) Tundish with large capacity deep melting bath;
(3) Prevent deformation of tundish shell;
(4) Adopt firm and reliable tundish nozzle control device;
(5) Adopt reliable tundish lifting device under load;
(6) Optimize the distance from the tundish to the upper mouth of the crystallizer.