JPH02165851A - Submerged nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To make molten steel stream in a mold in a state of commutation and to prevent involving of powder by making bottom part in a submerged nozzle for supplying the molten metal the recessed hemispherical state and forming upper edge of a molten steel discharging hole to the arc-state from inside of the nozzle toward the outlet. CONSTITUTION:The molten steel discharged from a tundish is allowed to flow down in the submerged nozzle 2 and discharged into a mold from discharging holes 2a, 2b at right and left sides. Then, the bottom part 2d in the nozzle 2 is made to the recessed hemi-spherical state and the upper edges 2e in the discharging holes 2a, 2b are formed to the arc-state from the inside of the nozzle 2 toward the outlet. Further, at the time of using (r) for radius of this nozzle 2, R1 for radius of hemi-spherical face at the bottom part 2d, D for the depth thereof and R2 for radius of arc at the upper edge of the discharging hole, they are made to R>r, D<r/2 and R2 = about (0.9-1.1) r. By this method, the molten steel flow speed discharged from the nozzle 2 is made uniform, and the flow rates from the discharging holes 2a, 2b at right and left sides are made to equal, and eddy and excessive rising flow are not developed and the involving of the powder is eliminated and the quality of a cast slab is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an immersed nozzle for hot water supply used in continuous casting, and more particularly to an immersed nozzle for rectifying a flow of molten steel discharged from the nozzle.

(Prior Art) In the continuous casting method, molten metal (hereinafter referred to as molten steel for steel casting) is injected into a mold from a tundish through an immersion nozzle.

Figure 1 shows this state.
The molten steel 1 discharged from the immersion nozzle 2 (not shown) flows down the immersion nozzle 2 and is discharged into the mold 3 from the left and right discharge ports (2a, 2b). Was it spit out? 811Il collides with the short side of the mold 3 and is divided into an upward flow 1a and a downward flow 1b. At this time, if the upward flow 1a is too large, the powder 4 on the meniscus will be drawn into the molten steel, reducing the quality of the slab.

Therefore, in the past, as shown in FIG. As shown in Fig. 3, the bottom 2d of the immersion nozzle 2 is formed in a concave shape, and the molten metal flowing down inside the immersion nozzle 2 collides with the concave part of the bottom, so that the flow of molten steel flowing out from the discharge port is made gentle; Measures are taken to prevent powder from being drawn in, such as by making the nozzle outlet into a vertically elongated oval or rectangle to ensure a uniform flow rate of molten steel.

However, each of the above methods has the following problems.

In other words, the above-mentioned method (2) of setting the nozzle discharge angle θ downward or deepening the nozzle position is effective in the early stage of casting, but in the latter half of casting, A 1 zOs etc. adhere to the inner wall of the nozzle and the discharge port. Then, the flow of molten steel changes and the effect is lost. Furthermore, if the downward flow 1b is too large, it prevents inclusions from floating and actually deteriorates the quality. In the submerged nozzle 2 having a concave portion in the bottom portion 2d of (2), the third
As shown in the figure, abnormal turbulence occurs within the nozzle and the flow from the discharge ports (2a, 2b) becomes unstable, so that the effect of preventing powder entrainment is small. In addition, the nozzle that averages the flow velocity distribution of molten steel described in (1) is effective when the discharge amount is small, but when the discharge amount becomes large as in the case of high-speed casting, the flow velocity distribution becomes disordered and becomes ineffective.

(Problems to be Solved by the Invention) An object of the present invention is to provide an immersion nozzle that rectifies the mold solid solution 'w4iJi and prevents powder from being drawn in, in order to solve the problems of conventional immersion nozzles. .

(Means for Solving the Problem) It is known that powder entrainment that occurs during continuous casting is mainly due to the following causes.

(1) As shown in FIG. 4, as the flow velocity directly below the meniscus increases, the powder entrainment index increases. The entrainment index is a numerical value that indicates the frequency of occurrence of entrainment, organized by flow velocity directly below the meniscus.

(2) The flow velocity directly below the meniscus is determined by the maximum discharge velocity from the nozzle.

(3) Fig. 5(a) and Fig. 5~) (A in Fig. 5(a)
- As shown in the arrow view A), the entrainment of the powder 4 is caused not only by the excessive upward flow but also by the vortex 5 generated in the vicinity of the nozzle 2. The vortex 5 is generated due to the speed difference between the left upward flow 1aL and the right upward flow law just below the meniscus.

(4) As the casting speed increases, the difference in flow rates from the left and right discharge ports increases.

The present inventors conducted further studies based on the above facts, and as a result, they obtained the following knowledge.

(a) Powder entrainment will not occur unless the flow of molten steel in the mold is uneven.

[Yes]) In order to make the left and right discharge speeds equal, the turbulence of the molten steel in the nozzle near the discharge port should be minimized and the discharge flow should be rectified.

(C) The above (a) can be realized by appropriately shaping the bottom and discharge port of the immersion nozzle.

This invention was made based on the above findings,
The gist of the product is ``It is an immersion nozzle for hot water supply used in continuous casting, and the bottom of the nozzle has a full hemispherical shape, and the upper edge of the molten steel discharge port is formed in an arc shape from the inside to the exit. ``Immersion nozzle for continuous casting''.

(Function) Hereinafter, the continuous casting immersion nozzle of the present invention will be explained with reference to the drawings.

FIG. 6 (al is a diagram showing a vertical cross section of the immersion nozzle of the present invention) As shown in FIG.
and 2b. The bottom portion 2d of the nozzle has a concave hemispherical shape, and the upper edge 2e of the discharge port is formed in an arc shape from the inside of the nozzle to the exit.

By the way, it is desirable that the hemispherical surface of the nozzle bottom 2d and the circular arc of the upper edge 2e of the discharge port be properly formed.The radius R1 of the bottom hemispherical surface is equal to or larger than the radius r of the molten steel flow passage, and its depth D is preferably 172 or less of the radius r of the molten steel flow passage. If the radius R1 of the bottom hemispherical surface is smaller than the nozzle radius r, proper rectification will not be possible, and the depth D is larger than the radius r1/2 of the flow passage. This is because it does not have a rectifying effect.

The radius R2 of the arc of the upper edge of the discharge port is preferably 0.9 to 1.1 times the radius r of the molten steel flow passage 2C. If the radius R2 of the arc is less than 0.9 times the radius r of the flow passage, there is no rectifying effect on the flow of molten steel. On the other hand, if the radius Rt exceeds 1.1 times the radius of the flow passage, the thickness of the nozzle at the discharge port becomes thinner, and the volume increases quickly, shortening the life of the nozzle.

Next, the rectification effect of the immersion nozzle of the present invention will be explained.

FIG. 6(b) (BB sectional view of FIG. 6(a)) shows the flow state of molten steel in the nozzle. The molten steel flow that has passed through the sliding nozzle 6 is distorted in an S-shape and flows down in the flow passage 2c of the immersion nozzle as shown in the figure. However, since the nozzle bottom 2d is formed in a hemispherical shape,
The molten steel 1 that has flowed down reverses itself inside the nozzle again and rises, and collides with and mixes with the molten steel that is flowing down, so that the flow is suppressed. After that, it is discharged from the discharge ports, but since the upper edges 2e of the discharge ports (2a, 2b) are formed in an arc shape, the same amount is discharged from both outlets, and the flow is gently rectified.

(Example 1) Using water instead of molten steel, the flow velocity at the discharge port of the nozzle of the present invention and the conventional nozzle shown in FIG. 1 was investigated. This test is based on the idea that the calculated average flow velocity value is compared with the actual value measured using a water model, and that the closer the value is to the calculated value, the more averaged it is. FIG. 7(a) is a local cross-sectional view of one discharge port 2a of the nozzle 2 used in this test, and six points a and b at 0% indicate flow velocity measurement points. The results are shown in FIG. 7(b). The line (a) in FIG. 7 is the average flow velocity value calculated by the following formula.

V-Q/2A Here, ■ is the average discharge speed, Q is the discharge amount, and 2A is the area of both discharge ports.

In FIG. 7(c), the sound is the flow velocity at point a of the nozzle of the present invention, . is the flow velocity at point b, ■ is 0 point, and ◆ is the flow velocity at point d.

Further, Δ is the flow velocity at point a of the conventional nozzle, and 050 and ◇ are the flow velocity at point b, point 0, and point d, respectively. From this figure, the flow velocity in the case of the nozzle of the present invention was determined by calculation (a
) line, indicating that it is averaged and rectified. On the other hand, the flow velocity of conventional nozzles varies widely,
It can be seen that the flow is turbulent.

(Example 2) As described above, when the left and right discharge speeds are different, a vortex is generated near the meniscus and the powder is drawn in.

Therefore, in this example, a water model was used to investigate the flow rate of water discharged from the discharge ports on both sides. Note that the nozzle used in Example 1 was used.

The results are shown in FIG. 8. In Figure 0, * indicates the case of the nozzle of the present invention, and O indicates the case of the conventional nozzle.

From this figure, it can be seen that in the case of the nozzle of the present invention, there is almost no difference in flow velocity from the left and right discharge ports, but in the conventional nozzle, there is a considerable difference in flow velocity.

(Example 3) A water model test was conducted using various submerged nozzles as described below, and the frequency of powder entrainment due to vortices and upward flow was investigated.

The nozzles used were a conventional nozzle (type A) with a discharge angle θ of 20 degrees as shown in Figure 2, a conventional nozzle (type D) with a discharge angle of 30 degrees, and a nozzle with a concave bottom as shown in Figure 3. The conventional nozzle (C type) formed and the nozzle of the present invention (D type) shown in FIG.

The test results are shown in Figure 9. In the figure, ○ indicates powder entrainment due to vortices, and . indicates entrainment due to upward flow. As is clear from the figure, all conventional nozzles have a high frequency of powder entrainment due to vortices and upward flow. However, in the case of the nozzle of the present invention, it is extremely low.

(Example 4) When a slab was cast using the A-D type nozzle used in Example 3, and a cold rolled steel plate was manufactured from this slab,
The incidence of Sulper flaws caused by powder appearing on the surface was investigated.

The results are shown in FIG. 10, and the numbers in parentheses in the figure are the number of slabs that were investigated.

As can be seen from this figure, the D-type nozzle of the present invention has a much lower incidence of surface flaws than the conventional A to C-type nozzles.

(Example 5) Spalling (
We investigated the incidence of microscopic cracks that occur on the surface of the refractories that make up the nozzle.

The results are shown in FIG. From this, it can be seen that the nozzle of the present invention (D type) has an extremely low incidence of spalling and has excellent spalling resistance compared to the conventional nozzle (A-C type).

(Effect of the invention) As explained above, if the immersion nozzle of the present invention is used,
The flow rate of the molten steel discharged from the nozzle is made uniform, and the flow rate from the left and right discharge ports is also equal, so that eddies and excessive upward flow do not occur.As a result, powder is not dragged in, and the quality of the slab is improved.

[Brief explanation of the drawing]

Figure 1 shows the state in which the molten steel flow discharged from the immersion nozzle circulates inside the mold. Figure 2 shows the state in which the molten steel flow discharged from the immersion nozzle circulates in the mold. 1 Figure 3 is a diagram of a submerged nozzle with a recess formed at the bottom. Figure 4 is a diagram showing the relationship between the flow velocity just below the meniscus and the powder entrainment index. Figure 5 (a) @ shows the rise in the left and right sides. Figure 6(a) is a diagram showing a vertical cross section of the immersion nozzle of the present invention; Figure 61) is a cross section taken along line B-B in Figure 6(a). FIG. 7(a) is a diagram showing the flow state of molten steel in the nozzle.
Figure 7 (b) is a diagram showing the measurement points of the discharge outlet in the water model test, Figure 7 (b) is a diagram showing the relationship between the calculated average flow velocity value and the actual value measured in the water model test, and Figure 8 is the water model test. FIG. 9 is a diagram showing the frequency of powder entrainment in the nozzle of the present invention and the conventional nozzle in a water model test. FIG. FIG. 11 is a diagram showing the incidence of surface flaws when a conventional nozzle is used in actual operation, and FIG. 11 is a diagram showing the incidence of spalling between the nozzle of the present invention and the conventional nozzle used in actual operation. 1 is the molten steel, 1a is the upward flow, lb is the downward flow, 2 is the immersion nozzle, 2a, 2b are the discharge ports, 2c is the downstream passage, 2d is the bottom of the nozzle, 2e is the upper edge of the discharge port, 3 is the mold, 4 is the powder , 5 is a vortex, and 6 is a sliding nozzle.

Claims (1)

[Claims] A immersion nozzle for hot water supply used in continuous casting,
1. An immersion nozzle for continuous casting, characterized in that the bottom of the nozzle has a concave hemispherical shape, and the upper edge of the molten steel discharge port is formed in an arc shape from the inside of the nozzle to the exit.