JPH02187240A - Submerged nozzle for high speed continuous casting - Google Patents

Abstract

PURPOSE:To obtain a cast slab having high quality by having rectangular opening part sideward for each discharging hole and having the specific relations of distance between upper and lower discharging holes, length of the mold, position and throughput in the nozzle for the submerged nozzle providing one pair of the discharging holes at upper and lower parts in both sides to axis of the nozzle body. CONSTITUTION:In order to execute high speed continuous casting, which the throughout becomes more than the prescribed quantity, the four-holes types submerged nozzle, which the max. discharging flow speed thereof does not become large even if the discharging flow speed of the molten steel is increased but the uniform flow speed distribution is obtd., is effective. However, in such a four-holes type submerged nozzle, the distance X from upper end of the upper discharging holes 2a to the molten steel surface is necessary to short and develops involving of mold powder. Each of the discharging holes 2, 3 at upper and lower parts in the four-holes submerged nozzle is made to the rectangular opening shape sideward and has the specific relation between the distance (l) between the opening holes, the length L of the mold, the distance Z from upper end of the mold to the meniscus and 1/4 of the throughput for the four-holes nozzles. By this method, even if the throughput of the molten metal is high, the cast slab having high quality without entrapment of the mold powder can be obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention has a throughput of 3.5 g:, /+min.
The present invention relates to an immersion nozzle suitable for use in the above-described high-speed continuous casting.

(Conventional technology) Conventionally, in continuous casting, immersion was used to feed molten steel into the mold without reoxidizing it, to promote the levitation of inclusions brought into the mold, and to prevent breakout when drawing slabs. Although nozzles have been used,
Here, for example, the discharge flow rate of molten steel is set to 2 to 3 tons using a two-hole immersion nozzle.

When trying to improve productivity by increasing the speed from 4.0 to 6.0'/min to 4.0 to 6.0'/min, mold powder is unavoidably dragged into the molten steel, resulting in a significant drop in the cleanliness of the molten steel. Ta.

The entrainment of mold powder is caused by the fact that the flow velocity at the discharge port of the immersion nozzle is highest at the lower end, while it shows a negative flow velocity distribution at the upper end, resulting in an uneven flow velocity distribution above and below the discharge port (Fig. 3(a)), and as a prior document related to this, Japanese Patent Application Laid-Open No. 1983-150
No. 756 discloses a technique for changing the discharge angle of a nozzle according to the discharge flow rate of molten steel, and Japanese Patent Application Laid-Open No. 49-65328
Each of the publications discloses a technique for reducing the discharge speed of molten steel by increasing the cross-sectional area of the nozzle outlet.

(Problem to be solved by the invention) By the way, when changing the discharge angle of the immersion nozzle according to the discharge flow rate of molten steel, there is an advantage of suppressing the entrainment of mold powder, but on the other hand, it is completely expected that inclusions in the mold will float. On the other hand, when enlarging the nozzle outlet, the distance from the outlet to the meniscus becomes shorter, so entrainment of mold powder by the flow of molten steel must be avoided. sea bream.

Some attempts have been made to address the above problem by making the immersion depth of the nozzle deeper than before, but in this case, there is a high risk of breakout because the flow of molten steel is below the mold.

It is an object of the present invention to propose a new immersion nozzle that can realize high-speed continuous casting with a throughput of 3.5 tons/min or more without degrading the cleanliness of the molten steel injected into the mold.

(Means for Solving the Problems) The present invention provides an immersion nozzle equipped with a pair of upper and lower discharge ports sandwiching the axis of the nozzle body on the left and right sides, in which each discharge port has a horizontally long opening shape, and the upper and lower discharge ports each have a horizontally elongated opening shape. Opening distance l between exits
However, the mold length is 4-hole nozzle throughput Y4,
This immersion nozzle for high-speed continuous casting is characterized in that the distance Z from the upper end of the mold to the meniscus satisfies N<L-Z64ya 370.

FIG. 1 schematically shows an enlarged vertical cross section of the immersion nozzle according to the present invention, particularly at the tip, and in the figure 1 indicates the nozzle body;
2 is a main discharge port, 3 is a lower discharge port, and the main discharge port 2 and the lower discharge port 3 both have a horizontally long opening shape as shown in FIG. The distance from the upper end of 2 to the lower end of lower discharge port 3) is the mold length, throughbutt y4 in a 4-hole nozzle, and distance Z from the upper end of the mold to the meniscus, f<L-Z-64y
, becomes -370.

(Function) In order to perform high-speed continuous casting with a throughput of 3.5 g/min or more, as shown in Figure 3(b), even if the discharge flow rate of molten steel is increased, the maximum discharge flow rate of the nozzle must be 4. A uniform flow velocity distribution can be obtained without increasing the flow rate.
It is extremely effective to use a hole-type submerged nozzle.

By the way, with such a submerged nozzle, as shown in Part 4, if there is a limit to the height L of the mold, the distance from the upper end of the main discharge port 2a to the meniscus must be adjusted to avoid breakout. It was necessary to shorten X, which sometimes caused mold powder to be sucked in.

Therefore, in this invention, each of the upper and lower discharge ports in the four-hole two-immersion nozzle has a horizontally elongated opening shape, and the opening distance l of these discharge ports is f < L −Z64ya 3
70, the initial objective was advantageously achieved.

Here, the opening distance i of the upper and lower discharge ports is f<L-Z-64ya
370 because in normal continuous casting (when a two-hole immersion nozzle is used, see Figure 5), the mold powder suction index I is the distance from the top of the discharge port to the meniscus X (ffim ) and throughput yt (g>/win), x==yt X/8
It is given by 0 − (1).

Figure 6 shows the relationship between the suction index I of the mold powder and the amount of slime extracted (mg7kg).
g or less, and the suction index (■) must be 1.0 or less.

In equation (1) above, in order to accommodate various throughputs, the distance from the upper end of the discharge port to the meniscus
This can be easily addressed by changing the .

On the other hand, as is clear from FIG. 7, which shows the relationship between the distance M from the lower end of the discharge port to the lower end of the mold and the incidence of breakout, especially when the distance M from the lower end of the discharge port to the lower end of the mold is 450 mm or less, Breakouts occur frequently.

Therefore, the value of X in the immersion nozzle is 1>3'2
From X/80, it is necessary to satisfy 80 (yz -1) <X.

In the case of a 4-hole submerged nozzle, the throughput of the main discharge port 2 corresponds to y2, and the maximum discharge flow of the 4-hole submerged nozzle is approximately 0.8 times that of the 2-hole submerged nozzle (the 8
(see figure), so yt = 0.8 ya, and the above X is X>80(0,8y4-1)...
It is necessary to do (2).

Next, the opening distance for a 4-hole immersion nozzle! is the length of the mold, and from the limit of breakout occurrence, L-(X+Z+j2) > 450, where f<L
-(X+Z+450)...(3) Therefore, the aperture distance! From (2) and (3), f<L Z 64)'
4 370.

Note that the opening shape of the discharge port may be any shape as long as it satisfies the above-mentioned condition of the opening distance ρ and provides a desired discharge flow rate. Further, the discharge angle of the discharge port is preferably 15 to 45 degrees downward in order to prevent reverse flow.

(Example) The four-hole immersion nozzle shown in Figure 1 above (nozzle inner diameter d
Near 0mm, outlet shape: 4 squares (size 60 x 70mm
)), the component composition is C: 0.0018%, Mn
: 0.08%, P: 0.020%, S:
Continuous casting of 0.015% molten steel (ultra low C steel) is shown below.
The amount of slime inclusions in the molten steel and the suction index of the mold powder were investigated. For comparison, a similar investigation was conducted using a conventional two-hole type immersion nozzle and a four-hole type immersion nozzle.

The results are also shown in Table-1.

Continuous casting using the immersion nozzle according to the invention of 1997 was able to yield very good results even though the throughput of molten steel was 3.5 tons/min or more.

(Effects of the Invention) According to the present invention, even when the throughput of molten steel is increased in continuous casting, a high-quality slab can be obtained without involving mold powder or the like.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of the immersion nozzle according to the present invention, Fig. 2 is an enlarged view of the main parts of the immersion nozzle according to the invention, and Fig. 3 (a) and (b) are the two-hole type immersion nozzle and the four-hole type immersion nozzle. Figure 4 is a longitudinal cross-sectional view of a four-hole immersion nozzle, Figure 5 is a longitudinal cross-sectional view of a two-hole immersion nozzle, and Figure 6 is a diagram showing a comparison of the flow velocity distribution and discharge speed of molten steel. Figure 7 is a graph showing the relationship between the distance M from the lower end of the mold to the lower end of the discharge port and the incidence of breakout, and Figure 8 is the relationship between the maximum discharge flow of a conventional immersion nozzle and this amount. 1 is a graph comparing the maximum discharge flow of submerged nozzles according to the invention. ■... Nozzle body, 2... Upper discharge port 3...
・Lower outlet! ...Opening distance L...Mold length y4...Through butt Z of 4-hole nozzle...Distance from the upper end of the mold to the meniscus O x R d Figure 4 Figure 5 Figure 6 Fig. 7 M-fL-(z+x+1 horn Fig. 8 d (mm/sec)

Claims (1)

[Claims] 1. In a submerged nozzle equipped with a pair of upper and lower discharge ports sandwiching the axis of the nozzle body on the left and right sides, each discharge port has a horizontally elongated opening shape, and the opening distance between the upper and lower discharge ports is l. However, the mold length L (mm
), throughput y_4 (t/m
in), a distance Z (mm) from the upper end of the mold to the meniscus, which satisfies l<L-Z-64y_4-370.