JPH0241747A - Leading tube for molten metal - Google Patents

Abstract

PURPOSE:To drastically reduce frequency of nozzle clogging by arranging one or more spiral steps on inner wall in the nozzle for continuous casting and gradually reducing cross sectional area of molten metal flowing passage from inlet side to outlet side. CONSTITUTION:In the nozzle cross section in the case of three for the number of spirals, the spiral steps 2 are arranged in the inner face of a nozzle main tube part 1 and the molten metal flowing passage 4 is formed to discharge the molten metal from the discharging hole 3. By winding a plate ABC of right-angled triangle having thickness (t), height (h) and length (l) of the base as tubular from a while aligning the base AB, one piece of the spiral is obtd. The (n) pieces of the spirals are obtd. similarly. The strong circular movement is given to molten steel flow at the inlet of the nozzle and since sp. gr. of Al2O3 inclusion produced at the time of deoxidizing the molten steel is smaller than the sp. gr. of the molten steel, the Al2O3 inclusion is separated from the nozzle wall with centripetal force during circulation in the nozzle. Further, by strong circular flow, the boundary layer in the vicinity of the nozzle wall is broken, and washing effect is developed. In such a manner, the frequency of the nozzle clogging can be drastically reduced.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a continuous casting nozzle used, for example, when injecting molten steel from a ladle to a tundish or from a tundish to a mold. This prevents nozzle constriction or blockage.

<Prior Art> In general, molten metal casting nozzles, especially tandate nozzles used when continuously casting molten steel, use Metal A!, which is used for deoxidizing molten steel. When the content of AlzCh in the steel becomes 0.02% or more, the deoxidation product AlzCh adheres to the nozzle and precipitates, resulting in a phenomenon of constriction.

This phenomenon is also commonly observed during ingot formation, but it has not been a major problem because the diameter of the ladle nozzle is large and oxygen lancing of the ladle nozzle is easy. However, during continuous casting, especially when casting is carried out using a submerged nozzle, the constriction of the Kundeitssch nozzle can lead to interruptions in the casting operation in the history of low steel flow rates, leading to a decrease in workability and casting yield. was.

Therefore, many countermeasures have been taken to prevent nozzle constriction. For example, by injecting Ar gas into the nozzle from the nozzle wall to create a gas barrier between the molten steel and the nozzle, and separating the molten steel from the nozzle inner wall, nozzle constriction can be prevented. Measures to prevent AIto's from depositing and adhering to the nozzle, such as applying heat insulating material to the outside of the nozzle to maintain the nozzle temperature at a high temperature, or heating molten steel using an induction coil installed around the nozzle. has been taken.

However, in the former case, it is difficult to accurately create a gas diaphragm against fluctuations in the flow rate of molten steel during casting work, and there are disadvantages such as an increase in the equipment cost of the static blowing system and the nozzle unit price due to the use of a special nozzle. there were.

Furthermore, in the latter case, the amount of work required to install the heat insulating material increases, the running varnish must be increased, etc., and the current situation is that no remarkable effect has been achieved in preventing stenosis.

Furthermore, the method of induction heating molten steel requires high heating equipment costs;
is hardly ever adopted.

Furthermore, apart from the above-mentioned measures against nozzle constriction, methods for preventing nozzle clogging by swirling molten steel within the nozzle have recently been proposed, as disclosed in Japanese Patent Laid-Open No. 54-125134 and Japanese Patent Laid-Open No. 57-1.
This is proposed in Japanese Patent No. 30745.

However, in the former case, the spiral groove is installed only on the nozzle inlet side, so the flow path length is not long enough to give sufficient swirling flow to the molten steel, and because the molten steel flow velocity is high, the spiral groove is Because the flow would separate and the flow path resistance would increase, it was almost impossible to create a swirling flow.

In addition, in the latter method, a spiral groove or projection is provided on the inner wall surface of the immersion nozzle, but in this method, when the angle of the spiral is large, the flow velocity of molten steel in the immersion nozzle is high. The flow will separate, the flow path resistance will increase, and sufficient swirling flow will not be obtained.
On the other hand, when the angle was set to an angle such that the slope did not separate, there was almost no swirling component, and a sufficient swirling flow could not be obtained.

<Problems to be Solved by the Invention> The present invention solves the problems of the existing technology as described above, namely, increased equipment costs, increased running costs, and 1) prevention of nozzle constriction without causing any increase in the amount of work. This paper proposes a continuous casting nozzle that utilizes the swirling flow that can be produced.

<Means for solving the problem> The present invention provides one or more spiral steps 2 on the inner wall, and has a portion in which the cross-sectional area of the molten metal channel 4 is gradually reduced from the inlet side to the outlet side. This is a molten metal guide tube characterized by the following.

<Function> Before explaining the present invention, let us first consider the type of constriction in the tandate nozzle for continuous casting.

The first is the type in which AlzOx, which is generated during deoxidation of molten steel, is deposited on the nozzle surface.

The second type is the type in which molten steel solidifies and adheres to the nozzle surface.

The third type is a type in which a mixture of Atz (h) and molten steel adheres to the nozzle surface.

Among these causes, types 1 and 3 frequently cause operational problems due to nozzle constriction.

In other words, the current flow of molten steel in the Kundeinsch nozzle is a laminar flow along the nozzle wall, which forms a so-called laminar boundary layer near the nozzle wall where the molten steel flow velocity is extremely slow. There is a temperature boundary layer in the low temperature range where heat is dominantly removed by heat conduction from the flow toward the nozzle wall.

Furthermore, since Al2O3 inclusions in the molten steel in the current nozzle are uniformly distributed in the radial direction of the nozzle, Al2O, which is a high melting point substance, remains in a high concentration near the nozzle wall. Coupled with the existence of a boundary layer of low flow rate and low temperature, this results in promoting the deposition of Ah03 or Alz(h) and the molten steel mixture on the nozzle wall.

However, when the present invention is applied to the current nozzle, it is possible to impart a strong swirling motion to the molten steel flow at the inlet of the tundish nozzle, and the following effects become noticeable. First, because the specific gravity of Al2O3 inclusions (3.8 to 4.0) is smaller than the specific gravity of molten steel (6.8 to 7.0), centripetal force causes the center of the nozzle to move closer to the nozzle wall than the nozzle wall due to the centripetal force during rotation in the nozzle. It is to be separated towards.

Second, the strong swirling flow destroys the boundary layer near the nozzle wall, producing an effect as if it were being cleaned.

Due to the above two effects, A! near the nozzle wall! 203
By being able to significantly reduce the temperature by 11 degrees and virtually eliminating the low temperature range, the constriction of the tundish nozzle was significantly improved, and the complete casting rate during continuous casting was able to be improved.

It goes without saying that this can significantly improve nozzle narrowing not only due to Alz03 inclusions, but also nozzle narrowing due to solidification of molten steel due to the second effect.

Next, the nozzle structure of the present invention that can impart strong swirling motion to the molten steel flow will be described in detail.

The nozzle structure of the present invention can be easily understood if considered as follows.

That is, the thickness t, height, and base length I as shown in Figure 2.
A right triangular plate ABC is wound into a tube shape with the base AB aligned from 8 (the difference in shape created by this is t). The cross-sectional view and conceptual diagram of the nozzle thus made are shown in Figures 3 and 4. As shown in the figure.

In addition, if there is one spiral (n: a positive integer), the bases of n right triangular plates are aligned, and the length of the circumference of the nozzle is 1
The shape is made by shifting the pieces by a distance of /n, overlapping them, and rolling them into a tubular shape in the same way.

FIG. 1 shows an example of a cross-sectional view of an immersion nozzle according to the present invention in which the number of spirals is three (n=3).

By the way, if the helical angle θ is too small, the flow path resistance increases and the flow tends to separate, whereas if it is too large, a 4-minute swirling component cannot be obtained.

Therefore, approximately 45°≦θ≦75° is a suitable range.

Furthermore, if the step N,) of the spiral is too small, it will not be possible to provide sufficient turning force, so it is preferably 1 mm or more.

Moreover, the number of helices (n) is more effective when there are several helices than one. This is because a uniform swirling force can be applied to the entire inner surface of the nozzle. If a strong swirling flow is generated in the molten steel passage by the above-mentioned means, it is not necessary to gradually reduce the cross-sectional area from the inlet to the outlet; for example, there may be some parallel portions near the inlet and outlet.

<Example> Fig. 5 shows a comparison between the amount of alumina deposited when the present invention is applied to a two-hole immersion nozzle made of alumina graphite between the tundish and the mold and the amount of deposited on a conventional nozzle. The casting conditions in this case are low-order Al killed steel at a melting temperature (superheat 1-) of 30°C and a casting speed of 4 tons/*ln per nozzle to produce 920 tons.
Cast. The nozzle has 3 spirals, the angle of the spirals is 60°, and the height difference between the spirals is 3 mm. Note that the conventional nozzle is only provided with a protrusion having an arcuate cross section of 3 mm, and there is no step, and other conditions are almost the same.

<Effects of the Invention> As described above in detail, the molten metal flow in the nozzle can be sufficiently swirled, so the frequency of nozzle clogging can be drastically reduced to approximately 1/3 compared to the prior art. Ta.

Although the present invention has been described with respect to a vertical continuous casting nozzle for injecting molten steel, the same anti-occlusion effect can be achieved in horizontal continuous casting or in a guide pipe connecting molten metal holding containers vertically and horizontally.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a nozzle with three spirals according to the present invention, FIG. 2 is an explanatory diagram for forming the shape of the helical nozzle, and FIG. 3 is a cross-sectional view of a nozzle with one spiral according to the present invention. FIG. 4 is a conceptual diagram of a nozzle having one spiral according to the present invention, and FIG. 5 is a graph showing the ratio of alumina deposition thickness between the conventional nozzle and the nozzle of the present invention. 1... Nozzle main pipe part, 2... Spiral step, 3
...Discharge hole, 4... Molten metal channel.

Claims (1)

[Claims] A molten metal guide pipe characterized by having one or more spiral steps on the inner wall and a portion where the cross-sectional area of the molten metal flow path is gradually reduced from the inlet side to the outlet side.