JPH01215448A - Submerged nozzle for continuous casting - Google Patents

Abstract

PURPOSE:To restrain sticking and growth of inclusion to inner wall of a nozzle and to prevent the development of fault caused by oxide inclusion by specifying distance between upper end of molten metal inlet side of discharging hole and upper end of gas flow outlet. CONSTITUTION:The gas flow outlet 12 shifted at 90 deg. from two discharging holes 2 in the submerged nozzle and arranged at the position, where the distance between the upper end of the molten metal inlet side of the discharging hole 2 and the upper end of the gas flow outlet 12 is in the range of 0 to +100mm to height direction, is arranged. By this method, without developing the surface fault of slag inclusion, blow hole, etc., the sticking of alumina to the inner wall of the submerged nozzle is prevented.

Description

Detailed Description of the Invention [Field of Industrial Application] This invention relates to an immersed nozzle that suppresses the adhesion and growth of inclusions on the inner wall of the immersed nozzle and prevents defects caused by oxide inclusions in continuous casting. It is something.

[Prior Art] The adhesion of inclusions to the inner wall of the immersion nozzle during continuous casting increases over time, not only limiting the operating time but also causing the deoxidation products in the molten steel, which are several microns in size, to become coarse. Often leads to product defects.

The material of the immersed nozzle has a great effect on adhesion to the inner wall of the immersed nozzle.For example, fused silica immersed nozzles rarely have inclusions attached, but fused silica immersed nozzles have less inclusions, such as Mn in steel. It reacts and melts, which tends to cause operational troubles and also poses problems to the quality of slabs.

Therefore, in general continuous casting of aluminum quilt steel, an immersion nozzle made of alumina graphite or a combination of alumina graphite and zirconia is used. When using an alumina-graphite immersion nozzle, the attachment, sintering, and growth of oxide inclusions progress rapidly. is suppressed. Furthermore, recently, materials for immersion nozzles have been studied. For example, 20 to 30% 5i02 is mixed into alumina graphite as a countermeasure against thermal shock at the start of casting, but under the strongly reducing atmosphere at the time of casting, 5i02(s) + C (s) −=SiO(g) +
The material of the immersion nozzle is SiO□, which becomes CO(g) and gasifies Si, which becomes an oxygen supply source into the steel, generates inclusions, and may induce the adhesion and growth of inclusions.
Replaced with SiC and carbon. Regarding zirconia immersion nozzles, recently, zirconia immersion nozzles are often used for the following reasons: (1) low thermal conductivity, (2) deoxidation products are difficult to adhere to, etc. FIG. 6 is a cross-sectional view of the conventional submerged nozzle 1 passing through the center of two discharge holes 2, (a) is a plane cutaway view of the submerged nozzle 1 passing through the center of the two discharge holes 2, and (b) is the sixth A vertical cross-sectional view (A-A') of the immersion nozzle 1 passing through the center of the two discharge holes 2 in (A) of the figure.
, (c) is a vertical cross-sectional view (B-B') in a direction perpendicular to the vertical cross-sectional view (A-A') of the submerged nozzle 1 passing through the center of the two discharge holes 2 in (b) of FIG. .

The alumina adhesion thickness 4 on the inner wall side 3 of the molten metal flow path 4 after use of the immersion nozzle 1 is 40 mm from the upper end of the discharge hole 2 of the immersion nozzle 1.
mm longitudinal cross-sectional view A-A' and perpendicular vertical cross-sectional view B-B''
It was measured with The results of using alumina graphite and zirconia as materials for the immersion nozzle 1 will be explained. FIG. 7 is a graph showing the relationship between casting time and alumina deposition thickness on the inner wall side of the molten metal flow path after using the immersion nozzle. O mark and Δ
The mark is an alumina graphite nozzle, and the * and mu marks are zirconia nozzles. The marks ◯ and * are longitudinal cross-sectional views of the immersion nozzle 1 taken along the line AA', and the marks Δ and the marks ``mu'' are the longitudinal cross-sectional views taken along the line BB' of the immersion nozzle 1. FIG. 8 is a graph showing the relationship between the flow velocity inside the nozzle and the alumina deposition thickness on the inner wall side of the molten metal flow path after using the immersion nozzle. The flow velocity in the pipe shown here is the average flow velocity obtained by dividing the amount of molten metal passing (n (/see)) by the internal cross-sectional area of the immersion nozzle (m2). 'The alumina deposition thickness decreases due to the increase in the flow velocity in the pipe, but the vertical cross-sectional view B-
In B', there is no clear correlation between the flow velocity in the pipe and the alumina deposition thickness.The reason for this is that although the amount of molten metal passing through increases and the flow velocity in the pipe naturally increases, the vertical cross-sectional view of the submerged nozzle 1 B-B In the downstream area of the molten metal, there is a deceleration region near the wall due to a rapid cross-sectional change caused by the discharge hole, and since a slight increase in the amount of molten metal passing through does not cause a change in flow velocity, alumina in the molten metal is discharged from the flow and enters the deceleration region. This is because they entered the soil and grew attached there. FIG. 9 is a graph showing the relationship between the amount of argon gas blown from the top of the immersion nozzle and the alumina deposition thickness. As is clear from FIGS. 7, 8, and 9, in the longitudinal section view A-A' of the discharge hole 2 of the immersion nozzle 1, the material of the immersion nozzle 1 is made of zirconia, and the molten metal inside the immersion nozzle 1 is The alumina deposition thickness is reduced by increasing the flow rate and increasing the amount of argon gas blown from the top of the immersion nozzle.
Then, even if the material of the immersion nozzle 1 is changed to zirconia, the flow rate of the molten metal in the immersion nozzle 1 is increased, and the amount of argon gas blown from the top of the immersion nozzle is increased, the alumina deposition thickness is not reduced much. Unexpected defects often occur in products.

Figure 10 is a cross-sectional view of a conventional submerged nozzle that passes through the center of two discharge holes 2, with a slit nozzle installed at the bottom.
(A) is a plan cutaway view of the immersed nozzle passing through the center of the two discharge holes, and (B) is a vertical cross-sectional view (A-A') of the immersion nozzle passing through the center of the two discharge holes in (A) of FIG. ), (c) are vertical cross-sectional views (B--) in the direction perpendicular to the vertical cross-sectional view (A-A') of the submerged nozzle passing through the center of the two discharge holes in (b) of FIG.
It is a figure showing B'). As a countermeasure against this problem, a method has been adopted in which argon gas is blown into the molten metal through a slit nozzle 16 from the entire bottom 11 of the immersion nozzle 1 as shown in FIG.

[Problems to be Solved by the Invention] However, in this method, the alumina deposition thickness on the vertical cross section (B-B') of the submerged nozzle 1 passing through the center of both ridge holes 2 decreases; A large amount of argon gas is required to uniformly blow argon gas into a wide area. In addition, it is also necessary to blow argon gas from the top of the immersion nozzle 1 as described above (if blowing is not carried out, alumina deposition will progress at the top of the immersion nozzle 1),
The blowing amount is 6 to 1 ONi/win for each, and a total of 12 to 20 NJI/win is required. If the amount of argon gas blown is too large, surface defects such as cracks and blows will occur in the slab. 1st
Figure 1 shows an example in which a porous body is installed at the molten steel inlet in the upper tundish of the immersion nozzle 1 and argon gas is blown into the tundish. FIG. 3 is a graph showing the relationship between the amount of argon gas blown into the molten metal and the number of blows on the surface of the slab during casting. As is clear from this figure, the number of blows increases in proportion to the amount of argon gas blown. The amount of argon gas blowing is 5tll/
When the temperature is less than 100%, alumina adheres to the inside of the immersion nozzle 1 during casting, causing the nozzle to become clogged. This invention was made in view of the above circumstances. The purpose is to prevent alumina from adhering inside a submerged nozzle without increasing surface defects.

[Means and effects for solving the problems] The immersion nozzle for continuous casting of the present invention injects the molten metal in the tundish into the mold. and a gas outlet provided at a position in the height direction where the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is 0 to +100 mm, and a gas flow passage connected to the gas outlet. and a gas supply means for supplying gas to the gas flow path.

Then, adjust the total gas injection amount to 5 to 1ONρ/ff.
90 mm from the two discharge holes of the immersion nozzle without changing from 1 inch.
The gas outlet is provided at a position in the height direction such that the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is 0 to +100 mm. The reason for limiting the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is that the alumina deposition thickness increases if it is less than 0 mm or more than 100 m+a. As a result, the shape of the slab,
It is possible to prevent alumina from adhering to the inner wall of the immersion nozzle without causing surface defects such as blows.

[Embodiments] Examples of the present invention will be described below with reference to the attached drawings.

FIG. 1 is a cross-sectional view of a submerged nozzle according to an embodiment of the present invention, (a) is a plan cross-sectional view including two gas outlets for blowing argon, and (b) is a cross-sectional view of the two immersion nozzles in (a) of FIG. A vertical cross-sectional view (A-A') of the submerged nozzle passing through the center of the discharge hole, (C) is a longitudinal cross-sectional view (A-A') of the submerged nozzle passing through the center of the two discharge holes in (B) of FIG. ) vertical cross-sectional view (B
-B'). 1 is a submerged nozzle, 2 is a discharge hole, 11 is a bottom of the submerged nozzle, 12 is a gas outlet, 13 is a gas flow path, 14 is a gas supply pipe, and 15 is a gas supply means.

The discharge hole 2 of the submerged nozzle 1 is round and pool-shaped at the bottom of the submerged nozzle. The immersion nozzle 1 is made of refractory material and has two opposing discharge holes 2 installed in its lower part. Here, argon gas from the gas supply means 15 is introduced into the gas flow passage 13 through the gas supply connection pipe 14, and the argon gas is further discharged from the gas outlet 12 connected to the gas flow passage 13.

(Example 1) Molten metal is supplied from a tundish (not shown) to an immersion nozzle 1, and a mold (not shown) is supplied from two opposing discharge holes 2.
injected into the body. When argon gas is supplied from the gas supply means 15 at a rate of about 2Njl/ff1in, it is introduced into the gas flow passage 13 through the gas supply connection pipe 14, and further connected to the gas outlet 12. 2 of the inner inner wall of the immersion nozzle 1
The gas is blown into the molten metal from the gas outlet 12 in the form of bubbles.

At this time, 5 to 8 fl/min of argon is blown from the tundish inlet to the conventional argon blowing position in order to prevent alumina from being thickly deposited on the inner wall of the immersion nozzle 1 over the top. Since the total flow rate of argon blown into the molten metal through the nozzle is 5 to 101111 I/min, as shown in Fig. 8, the number of blows on the slab surface does not increase, and the thickness of alumina adhesion near the gas outlet 12 can be prevented. .

The range of the gas outlet 12 is 30 mm x - 100 am. The diameter of the discharge hole is 80IIlfflΦ.

The blowing position of the gas outlet 12 was set at the same level as the upper end of the gas outlet 12 of the nozzle and the upper end of the discharge hole 2.

As a result, the alumina deposition thickness was reduced to 1/3.

(Example 2) Next, the relationship between the alumina adhesion thickness was investigated by changing the blowing position of the gas outlet. The distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet was changed in the height direction from -30 to +150 mm. FIG. 2 is a sectional view of the submerged nozzle showing the level at which the blowing position of the gas outlet has been changed. In <a), the distance between the upper end of the gas outlet 12 of the nozzle and the upper end of the discharge hole 2 is 30 mm downward;
In b), the upper end of the nozzle gas outlet 12 and the upper end of the discharge hole 2 are at the same level, and in (C), the upper end of the nozzle gas outlet 12 and the upper end of the discharge hole 2 are separated upward by 30 mm. In (d), the distance between the upper end of the gas outlet 12 of the nozzle and the upper end of the discharge hole 2 is 100 mm upward, and (e) shows the upper end of the nozzle gas outlet 12 and the discharge hole 2.
The distance from the upper end of the figure is 150 mm upward.

FIG. 3 is a graph showing the relationship between the difference in the blowing position of the gas outlet shown in FIG. 2 and the alumina deposition thickness. As is clear from this figure, the alumina deposition thickness is small when the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is in the range of -0 to +100+ m in the height direction.

The reason for this will be explained with reference to FIGS. 4 and 5. FIG. 4 is a cross-sectional view of a conventional submerged nozzle, (a) is a plan cross-sectional view of the submerged nozzle, and (b) is a vertical cross-sectional view taken along line xx' in (a) of FIG. In Fig. 4(a), the ○ mark indicates the flow velocity in the pipe in the direction of the discharge hole (X-X'), and the Δ mark indicates the flow velocity in the direction 90 degrees away from the discharge hole (Y-X').
Y') is the in-pipe flow velocity. The measurement points for the flow velocity in the pipe are A and E near the inner wall of the immersed nozzle, C the center of the immersed nozzle, mouth and 2 between the near the inner wall of the immersed nozzle and the center of the immersed nozzle. The straight line A-A' in FIG. 4(b) is the upper end of the discharge hole 2, and the straight line B-B' is 30 mm
At the position of mm, the straight line c-c' is 15 mm from the upper end of the discharge hole 2.
This is the 0mm position. FIG. 5 is a graph showing the relationship between the flow velocity distribution in the pipe according to the measurement position in FIG. 4. Figure 5(a) shows the flow velocity distribution in the pipe along straight line A-A' in Figure 4(b), and Figure 5(b) shows the flow velocity distribution in the pipe along straight line BB' in Figure 4(b). FIG. 5(c) shows the flow velocity distribution in the pipe along the line c-c' in FIG. 4(c). As is clear from this figure, the flow velocity in the pipe in the direction of the discharge hole (x-x') is the straight line A
-A', straight line B-B', and straight line c-c', but in a direction 90 degrees off from the discharge hole (Y-Y'
) The flow velocity distribution in the pipe becomes a flow distribution state with a deceleration region as shown in part by the dotted line in FIGS. 5(a) and 5(b). This becomes noticeable at a distance of 30 mm or less from the upper end (inner side) of the discharge hole. Above that, the flow distribution state is approximately as shown in FIG. 5(c). Therefore, cleaning the side wall by blowing gas into that area is effective in preventing alumina adhesion.

That is, when the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is in the range of -0 to +100 mm in the height direction, the alumina deposition thickness is small.

As a result, the alumina deposition thickness was reduced to 1/3 to 115 times.

[Effects of the Invention] According to the present invention, the two discharge holes in the inner wall of the immersion nozzle body are offset by 90 degrees, and the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is 0 to +100 mm. Since argon is flowed from the gas outlet provided at a position in the height direction, stagnation in that area is eliminated and the alumina deposition thickness is reduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a submerged nozzle according to an embodiment of the present invention, Fig. 2 is a sectional view of the submerged nozzle showing a changed level of the blowing position of the gas outlet, and Fig. 3 is shown in Fig. 2. A graph showing the relationship between the blowing position of the gas outlet and the alumina deposition thickness, Figure 4 is a cross-sectional view of a conventional immersion nozzle, and Figure 5 is the relationship between the flow-velocity distribution in the pipe according to the measurement position in Figure 4. Fig. 6 is a cross-sectional view of a conventional immersion nozzle passing through the center of two discharge holes, and Fig. 7 shows the relationship between casting time and alumina deposition thickness on the inner wall side of the molten metal flow path after using the immersion nozzle. Figure 8 is a graph showing the relationship between the flow velocity inside the nozzle and the alumina deposition thickness on the inner wall side of the molten metal flow path after using the immersion nozzle. A graph showing the relationship between blowing amount and alumina deposition thickness. Figure 10 is a cross-sectional view of a conventional immersion nozzle that passes through the center of two discharge holes, and a slit nozzle is installed at the bottom. Figure 11 is a cross-sectional view of a nozzle with a slit nozzle installed at the bottom. FIG. 2 is a graph diagram showing the relationship between the amount of argon gas blown into the molten metal from the molten steel inlet in the upper tundish and the number of blows on the surface of the slab. DESCRIPTION OF SYMBOLS 1... Immersed nozzle, 2... Discharge hole, 11... Bottom of immersed nozzle, 12... Gas outlet, 13... Gas flow path, 14... Gas supply connection pipe, 15... ...Gas supply means.

Claims (1)

[Claims] In the immersion nozzle that injects the molten metal in the tundish into the mold, 9
A gas outlet is connected to the gas outlet, which is offset by 0 degrees, and is provided at a position in the height direction where the distance between the upper end of the molten metal inlet side of the discharge hole and the upper end of the gas outlet is 0 to +100 mm. 1. A submerged nozzle for continuous casting, comprising: a gas flow passage; and a gas supply means for supplying gas to the gas flow passage.