Nozzle

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Nozzle

This entry is compiled and applied by "popular science China" Science Encyclopedia

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Nozzle refers to the joint of the frame and parts formed by the factory when casting the model. Also known as the "soup gate" (gate), which means the flow of liquid material into and out of the heat. The structure parameters of Sen determine the flow field characteristics of molten steel in mold to a great extent. Therefore, it is an economical and efficient way to obtain reasonable flow field of molten steel by optimizing Sen structure parameters.

introduce

In order to improve production efficiency and reduce production cost, the development and application of high casting speed technology is imperative. But in the continuous casting process, the increase of casting speed will increase the instability and asymmetry of the flow field in the mold, and then lead to quality problems such as mold flux involvement and surface defects, and even lead to breakout.

The structure parameters of Sen determine the flow field characteristics of molten steel in mold to a great extent. Therefore, it is an economical and efficient way to obtain reasonable flow field of molten steel by optimizing Sen structure parameters.

Sen structure optimization is mainly realized by optimizing the exit angle, bottom shape, exit area and shape. For the optimization of Sen nozzle outlet angle and bottom shape, previous researchers have carried out in-depth research through water model test: under the conventional casting speed, the circular nozzle with nozzle angle of 25 ° and flat bottom and diameter of 40mm is the best for reducing the probability of longitudinal crack on slab surface and slag inclusion; under the high casting speed, the nozzle with upper and lower angle of 15 ° and bottom shape of concave bottom is the best . In the study of nozzle outlet area and outlet shape, the predecessors mainly used the numerical simulation method to explore, and reached the following conclusion: Gupta divided the flow into "spinning jet" and "rotating jet" The research shows that the total area of the outlet is larger than the inner area, so as to reserve a certain space for alumina nodulation, but the liquid steel is usually only transported from Sen The results show that the lower end of the outlet flows out, while the upper end produces a negative flow area, and the molten steel flows back into Sen; Bai et al. Think that the velocity and negative flow area of the square outlet are the largest, which is easy to cause the flow field asymmetry, while the negative flow area and the rotation angle of the rectangular outlet are the smallest; Najjar thinks that under the same outlet area, the circular outlet will produce more vortex flow than the rectangular outlet, and the square outlet will produce more vortex flow The turbulence intensity of the stream is higher than that of the stream

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Related impacts

Influence of nozzle outlet shape on surface velocity

The influence of nozzle outlet shape on average surface velocity was investigated when the steel flux was 3.20 and 4.48 T / min. It can be found that the surface velocity increases first and then decreases from the center of the nozzle to the narrow surface, and the surface velocity of different outlet shapes from small to large is in the order of ellipse < rectangle < square, which is consistent with the effect of outlet shape on the average wave height. At high casting speed, the maximum surface velocities of elliptical, rectangular and square nozzles reach 0.33, 0.38 and 0.42 M / s respectively. Kubota research considers that the condition of no slag entrapment is that the surface velocity is less than 0.4m/s. In order to reduce the occurrence of slag entrapment in the actual production process, it should be ensured that the surface velocity is less than the critical surface velocity of slag entrapment. Therefore, in the high casting speed production, the elliptical or rectangular nozzle can reduce the possibility of mold flux entrapment, so as to improve the surface quality of slab and subsequent rolling plate.

Effect of nozzle exit shape on velocity distribution of strand

At low and high speed, the velocity distribution of the stream at the exit of ellipse, rectangle and square is analyzed, and the left and right exit are established in the same coordinate system. The velocity distribution map can only show the velocity distribution in the central part of the measuring point because the actual boundary conditions are not clear. At the same time, the symmetry degree of flow velocity at the left and right sides of the nozzle with different outlet shapes is also: ellipse < rectangle < square.

Under the high speed of 4.48t/min, the vertical expansion angle of free flow strand under different nozzle outlet shapes follows the rule of ellipse, rectangle and square, and the flow strand at ellipse outlet is "rotating flow strand", while the flow strand at rectangle and square outlet is "smooth flow strand". This is similar to the experimental conclusion of Najjar. This rule is also followed at low drawing speed of 3.20t/min.

The expansion angle and inclination angle of the square outlet strand are the smallest, about 18 ° and 17 ° respectively. The strand is concentrated in the lower part of the outlet, while there are a lot of voids in the upper part of the nozzle outlet in the white line area, which is easy to cause the reverse flow of fluid into sen in the actual pouring process, resulting in larger negative flow area and nozzle nodulation. The spreading angle and dip angle of the rectangular exit stream are about 25 ° and 35 ° respectively, and the velocity distribution uniformity at the exit is better than that at the square exit. The expansion angle and inclination angle of the elliptical exit stream are the largest, about 39 ° and 52 ° respectively; it is a "rotating stream", the left exit stream rotates clockwise, the right exit stream rotates counterclockwise, and the rotation direction changes with time, so the stream at the exit is more dispersed, and its velocity distribution is the most uniform. Guptad research shows that because the "rotating stream" has a larger rotation angle, it is conducive to the mixing between the new high-temperature molten steel and the low-temperature molten steel in the mold, and makes the jet have a smaller velocity to impact the narrow surface, which has a smaller impact on the solidified shell, so the elliptical outlet has an advantage in actual production

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Influence of nozzle exit shape on mold flow field

Generally, the inclination angles of the three kinds of nozzles are greater than the designed inclination angle (15 °), among which the inclination angle of the elliptical nozzle is the largest, with an average of 38 ° and a deep impact depth, which results in a well-developed downward return flow, while the upward return flow is relatively weak and the liquid level is relatively calm; on the contrary, the inclination angle of the square nozzle is the smallest, with an average of 21 ° and a shallow impact depth, which results in a non-uniform flow The results show that the liquid level fluctuation is the most severe in the developed up flow; the inclination angle of the rectangular nozzle stream is in the middle, and the stream stream can form the up flow and down flow with the middle developed degree after hitting the narrow surface, and the liquid level fluctuation is also in the middle, which is consistent with the previous experimental results of average wave height and surface velocity, and also with the research results of Bai, honeyands and others. The possible reasons are as follows: when the shape of nozzle outlet changes from short and fat type to thin and high type, the guiding effect of outlet in the vertical direction becomes more and more obvious, causing the inclination angle of flow strand to increase gradually, the development degree of upward reflux to decrease, and the expansion angle of flow strand in the vertical and horizontal directions gradually increases, the flow strand becomes scattered from concentration, and the energy after impacting the narrow surface is reduced, so the free liquid is formed The turbulent kinetic energy of the surface decreases, and the surface velocity and fluctuation degree decrease.

summary

1) The results show that the liquid level fluctuation and surface velocity of the mold follow the changing rule of oval nozzle < rectangular nozzle < square nozzle when the steel flow rate is 3.20 and 4.48 T / min. at high casting speed (4.48 T / min), slag entrapment is easy to occur when the surface velocity of square nozzle is higher than the critical surface velocity of 0.4 m / s, while the surface velocity of oval nozzle and rectangular nozzle are 0.33 and 0.38 M / s respectively The probability of slag entrapment is small.

2) The results show that the spreading angle of rectangular nozzle is the smallest, the spreading angle of square nozzle is the smallest, the spreading angle of square nozzle is the largest, the spreading angle of rectangular nozzle is the middle, the spreading angle of rectangular nozzle is the largest, and the spreading angle of elliptical nozzle is the lowest The velocity distribution is uniform.

3) Elliptical nozzle has the largest inclination angle of stream, which leads to well-developed downward flow, while the upward flow is relatively weak, and the free surface is the most calm; square nozzle has the smallest inclination angle of stream, which leads to well-developed upward flow, which will lead to the fluctuation of liquid surface and the increase of surface velocity; rectangular nozzle has the middle inclination angle of stream, which can form relatively developed stream after hitting the narrow surface The activity of free surface is also in the middle when the upper and lower flow back.

4) Under the condition of high casting speed, the average wave height of the mold liquid surface is 5.5mm, the surface velocity is 0.32m/s, there is still room to improve the casting speed, and the flow velocity is evenly distributed at the outlet, so the optimal shape of the nozzle outlet is oval

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