JP5293012B2 - Molten metal continuous casting apparatus and molten metal continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a machine and a method for continuously casting molten metal, which prevent adhesion of nonmetallic inclusions to the inside of a continuous casting nozzle. <P>SOLUTION: A sliding nozzle 1 having two movable plates (3a, 3b) oscillating along fixed plates 2 is used. Among the portions in openings 4 of the fixed plates 2, portions which are not covered with the two movable plates 3, become a runner 5 through which molten metal passes. The position of the runner in the openings of the fixed plates is oscillated by oscillating the two movable plates 3. Thereby, the flow of the molten metal in a cylindrical inner hole 16 is periodically moved from one end to the other end of the cylindrical inner hole 16, so that the portion of the flow where the flow rate of the molten metal is constantly kept low becomes inexistent. Thus, adhesion of nonmetallic inclusions to the cylindrical inner hole 16 of an immersion nozzle is reduced. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a continuous casting apparatus and a continuous casting method capable of preventing adhesion of non-metallic inclusions into a continuous casting nozzle in continuous casting of molten metal, particularly molten steel.

  In the continuous casting of molten metal, the molten metal that has been refined is accommodated in a ladle and further transferred to a tundish. A continuous casting nozzle is installed at the bottom of the tundish, and the molten metal in the tundish is injected into the mold via the continuous casting nozzle. The molten steel in the mold forms a solidified shell by the primary cooling by the mold, and then the solidification is promoted by the secondary cooling by the water spray from the cooling nozzle laid on the support segment installed under the mold. Manufacture pieces.

  In order to adjust the amount of molten metal to be injected through the continuous casting nozzle, the continuous casting nozzle is provided with a sliding nozzle or stopper, and the injection of molten metal is controlled by opening and closing these. In general, when a sliding nozzle is used, the controllability of the molten metal injection amount is superior to that of a stopper. When a sliding nozzle is used, the continuous casting nozzle has a divided structure including an upper nozzle, a sliding nozzle, a lower nozzle, and an immersion nozzle.

Among the continuous casting nozzles, particularly non-metallic inclusions such as Al ₂ O ₃ suspended in the molten metal are likely to adhere to the portion of the immersion nozzle that is immersed in the molten metal in the mold. This is remarkable when casting Al killed steel having a high Al content. Of the inner wall of the immersion nozzle, non-metallic inclusions are likely to be deposited on the portion corresponding to the vicinity of the molten metal meniscus in the mold or near the molten metal discharge port at the tip of the immersion nozzle. If non-metallic inclusions accumulate on the inner wall of the nozzle, the flow of molten metal is hindered and casting becomes difficult. Moreover, if non-metallic inclusions adhere to the inner wall of the nozzle, the controllability of the injection amount following the fluctuation of the molten metal surface height in the mold deteriorates, and the continuous casting flux that covers the molten metal in the mold (Powder for continuous casting) is entrained in the molten metal, and a part thereof is trapped by the solidified shell of the molten metal, which may become a starting point of defects.

  Usually, an inert gas such as argon gas is blown into a continuous casting nozzle to reduce adhesion of non-metallic inclusions to the inner wall of the continuous casting nozzle. Although this reduces the adhesion of non-metallic inclusions, the effect is not sufficient, and the blown inert gas is trapped in the slab as bubbles, which may cause bubble defects.

Patent Document 1 discloses a technique for reducing the adhesion of non-metallic inclusions on the inner wall of a continuous casting nozzle by blowing the inert gas into the continuous casting nozzle while increasing or decreasing the back pressure or flow rate of the inert gas. It is disclosed. Thereby, the molten steel flow flowing down the immersion nozzle is disturbed, and the stagnation in the immersion nozzle is eliminated, so that the adhesion of Al ₂ O _{3 on} the inner wall of the immersion nozzle can be efficiently prevented.

  The sliding nozzle is usually composed of one or two fixed plates and one movable plate. Both the fixed plate and the movable plate have openings through which molten metal flows. By sliding the movable plate, the area of the overlapping portion (runner) of the opening of the fixed plate and the movable plate is adjusted, and the flow rate of the molten metal is adjusted. When the opening area of the runner is narrowed, the runner opening is located at the end of the opening of the fixed plate.

  According to Patent Document 2, when the opening area of the runner is small, the molten metal flow flowing in the immersion nozzle is deviated with respect to the center of the nozzle hole, and the discharge port flow rate of the immersion nozzle is not uniform and the flow direction is not uniform. It is said that stability and the like will be difficult to control the flow rate, and that the inclusion of non-metallic inclusions in the product will be promoted. Therefore, in this document, the movable plate in the sliding nozzle of the continuous casting nozzle is divided into two parts, the center of the runner opening formed by the opening of the fixed plate and the two movable plates, and the continuous casting nozzle. The center of the inner wall is made coincident to prevent the continuous casting nozzle and the molten metal in the mold from drifting.

JP 2007-237246 A JP-A-5-277678

  With respect to the problem of non-metallic inclusions adhering to the molten metal flow path of the continuous casting nozzle, a sufficient effect cannot be obtained simply by blowing an inert gas into the nozzle. Moreover, since the blown inert gas is trapped in the slab as bubbles, it also causes bubble defects. The same applies to the invention described in Patent Document 1.

  The invention described in Patent Document 2 is not intended to prevent non-metallic inclusions from adhering to the continuous casting nozzle, and, as with conventional nozzles, non-metallic inclusions are attached to the nozzle. Problems occur.

  An object of the present invention is to provide a molten metal continuous casting apparatus and a molten metal continuous casting method capable of preventing adhesion of non-metallic inclusions into a continuous casting nozzle.

  In the case of a continuous casting nozzle that uses a sliding nozzle to adjust the flow rate of the molten metal, as shown in FIG. 9, the continuous casting nozzle is composed of an upper nozzle 13, a sliding nozzle 1, a lower nozzle 14, and an immersion nozzle 15. It becomes. The immersion nozzle 15 has a bottomed cylindrical shape and usually has two discharge ports 17 below. Here, the inner space of the cylinder is referred to as a cylindrical inner hole 16. When the behavior of the molten metal in the cylindrical inner hole 16 of the immersion nozzle 15 during continuous casting is investigated, at least as long as non-metallic inclusions adhere to the cylindrical inner hole 16 and the discharge port 17 of the immersion nozzle, As shown in FIG. 9B, the molten metal is filled up to a position slightly higher than the surface of the molten metal 18 in the mold (herein referred to as “first meniscus 19”). Here, the uppermost portion of the portion filled with the molten metal is referred to as a second meniscus 20 here. On the upper side of the second meniscus 20, the molten metal that has passed through the opening of the sliding nozzle 1 is falling in the cylindrical inner hole, and below the second meniscus 20 is a molten metal filled region 21. When adhesion of non-metallic inclusions to the cylindrical inner hole 16 and the discharge port 17 of the immersion nozzle increases, the pressure loss at the time of molten metal circulation increases, so that the second meniscus rises, as shown in FIG. The inside of the cylindrical hole including the sliding nozzle portion becomes a molten metal filled region 21.

  As described above, when the opening area of the runner 5 of the sliding nozzle 1 is narrowed, the runner 5 is located at the end of the opening 4 of the fixed plate 2 (FIGS. 9B and 9C). )). When the molten metal falls from the sliding nozzle 1 to the second meniscus 20 in the cylindrical inner hole of the immersion nozzle 15 and enters the molten metal full region 21 from the second meniscus 20, the runway 5 of the sliding nozzle is It flows in at the end on the open side (hereinafter referred to as “downstream side 22”). As a result, in the molten metal filling region 21 below the second meniscus in the cylindrical inner hole, the molten metal flow rate is low on the side where the molten metal flow enters (downflow side 22), whereas the molten metal flow is fast. On the opposite side (hereinafter referred to as “flowing opposite side 23”), the phenomenon that the molten metal flow rate becomes slow occurs.

  As a result of investigating the non-metallic inclusion adhesion state in the cylindrical inner hole of the immersion nozzle, there is little non-metallic inclusion adhesion on the downstream side 22 of the cylindrical inner hole, and more non-metallic inclusion adhesion on the opposite flow side 23. Turned out to be.

  When the movable plate 3 of the sliding nozzle is one, the same side always becomes the flow-down side 22 when narrowing the opening area of the runner (FIGS. 9B and 9C). On the other hand, if the number of the movable plates 3 is two, as shown in FIG. 1, the downstream side 22 is moved to one end (see FIG. 1 (a)) to the other end (FIG. 1 (c)). As a result, for the part on the opposite side 23 of the flow down during the injection and the non-metallic inclusions began to adhere, the movable plate is then swung to change the part from the flow down side 23 to the flow down side 22, It has been found that non-metallic inclusions that have started to adhere can be removed and non-metallic inclusions can be prevented from adhering into the cylindrical bore of the immersion nozzle.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
(1) A continuous casting apparatus having a fixed plate 2 having an opening with a cross-sectional area S ₀ and a sliding nozzle 1 having two movable plates (3a, 3b) sliding along the fixed plate. A movable plate driving device 6 for driving a single movable plate, and a portion of the opening 4 of the fixed plate 2 that is not covered by the two movable plates 3 becomes a runner 5 through which molten metal passes, The runner area S ₁ is 50% or less of the cross-sectional area S ₀ of the fixed plate opening , and the movable plate driving device 6 suppresses the fluctuation of the runner area S ₁ within ± 5%, and the two movable plates 3 is swung, and the position of the runner in the opening is swung. At least the area ratio of 80% or more of the opening 4 of the fixed plate 2 passes through the molten metal at least once every 10 seconds. It becomes the runway 5 A continuous casting apparatus for molten metal, characterized in that the two movable plates 3 are swung as described above.
(2) In the movable plate driving device 6, the runner area S ₁ when the amount of molten metal passing, that is, the throughput is constant, increases to a range of 1.25 times or more and 2 times or less of the initial runner area S _{10 at} the start of casting. In this case, the molten metal continuous casting apparatus according to the above (1), wherein the swinging of the two movable plates 3 is started.
(3) A continuous casting method using a sliding plate 1 having a fixed plate 2 having an opening 4 having a cross-sectional area S ₀ and two movable plates (3a, 3b) sliding along the fixed plate 2. The portion of the opening 4 of the fixed plate 2 that is not covered by the two movable plates 3 becomes the runner 5 through which the molten metal passes, and the runner area S ₁ is the cross section of the fixed plate opening S _0. The runner position in the opening is swung by swinging the two movable plates 3 while suppressing the fluctuation of the runner area S ₁ to be within ± 5%. Is to swing the two movable plates 3 so that at least a portion of the opening 4 of the fixed plate 2 having an area ratio of 80% or more becomes a runner 5 through which molten metal passes at least once every 10 seconds. Continuous casting of molten metal Manufacturing method.
(4) When the molten metal passage amount, that is, the runner area S ₁ when the throughput is constant, increases to a range of 1.25 times or more and 2 times or less the initial runner area S _{10 at} the start of casting, 2. The molten metal continuous casting method according to (3) above, wherein the movable plate 3 starts to swing.

  According to the continuous casting apparatus and continuous casting method of the molten metal using the sliding nozzle of the present invention, the sliding nozzle has two movable plates, and the runner position in the opening is determined by swinging the two movable plates. Because it oscillates, there is no part where the flow rate of the molten metal is constantly kept low in the molten metal flow in the cylindrical hole of the immersion nozzle, reducing non-metallic inclusions adhering to the cylindrical hole of the immersion nozzle It became possible to do.

  Using molten steel as the molten metal, a numerical simulation was performed on the flow state of the molten steel in the immersion nozzle of the continuous casting nozzle. The molten steel flow that has passed through the runner 5 formed by the fixed plate opening 4 of the sliding nozzle 1 and the opening of the movable plate 3 falls freely in the cylindrical inner hole of the immersion nozzle 15 (FIG. 9B). In the cylindrical inner hole of the immersion nozzle 15, the molten steel is filled below the second meniscus 20 to become a molten metal filled region 21, and there is a molten steel flow that freely falls from above. The height of the second meniscus 20 is slightly higher than the molten steel surface (first meniscus 19) in the mold. When the non-metallic inclusions adhere to the continuous casting nozzle, the second meniscus 20 rises, and finally the position up to the sliding nozzle 1 becomes the molten metal-filled region 21 (FIG. 9C).

  In the conventional sliding nozzle 1 composed of the fixed plate 2 and one movable plate 3, the area of the overlapping portion (runner channel 5) of the opening of the fixed plate 2 and the movable plate 3 is adjusted. When the opening area of the runner is narrowed, the runner 5 is positioned at the end of the opening 4 of the fixed plate as shown in FIG. 9B. The molten steel flow flowing downward from the runner 5 descends vertically and joins the molten metal full region 21 at the position of the second meniscus 20. The position where the molten steel flows join is not the center of the cylindrical inner hole 16 but the side where the runner 5 of the sliding nozzle is open (downstream side 22). As a result of the numerical simulation, in the molten metal filling region 21 below the second meniscus 20, the molten steel flow velocity becomes non-uniform in the radial direction of the cylindrical inner hole 16, and the molten steel flow velocity is fast on the downstream side 22, which is about 1 m / sec. On the other hand, it was found that the molten steel flow rate is slow on the opposite flow side 23, which is only about 0.05 m / sec.

  And when the state of inclusion attachment of the immersion nozzle used in actual continuous casting was investigated, among the inner walls of the cylindrical inner hole 16, there was little non-metallic inclusion attachment on the flow-down side 22, and on the flow-flow opposite side 23 It was found that there were many nonmetallic inclusions.

  Next, as shown in FIGS. 1 to 4, the numerical simulation was similarly performed with two movable plates 3. FIG. 3 is a diagram showing the position of the movable plate and the open / close state of the runner. 3A shows a runner fully closed state, FIG. 3B shows a runner half-open state, and FIG. 3C shows a runner fully opened state.

The position of the movable plate 3 is determined so that the portion of the opening 4 of the fixed plate 2 that is not covered by the two movable plates (3a, 3b) becomes the runner 5 through which the molten metal passes. while the area S ₁ of is held constant, and to perform the sliding reciprocating in conjunction with two movable plates 3. This movement is hereinafter referred to as “rocking”. In the example shown in FIGS. 1 and 2, the runner 5 is first positioned at the left end of the fixed plate opening 4 (FIGS. 1A and 2C), and then moved to the center of the fixed plate opening 4 (FIG. 1). 1 (b) and FIG. 2 (d)), and then move to the left end of the fixed plate opening 4 (FIG. 1 (c) and FIG. 2 (e)). Further, the movable plate is reversed, and the runner 5 returns to the position shown in FIGS. 1B and 2D, FIGS. 1A and 2C, and this reciprocating motion is repeated. As the movable plate 3 swings, the runner 5 reciprocates between one end and the other end of the opening 4 of the fixed plate. This movement is called swinging the runner position. FIG. 1 shows a case where the second meniscus 20 is present at a position close to the height of the first meniscus 19 in the mold, whereas FIG. The case where all 16 become the molten metal filling area | region 21 is shown.

A numerical simulation was performed on the flow state of the molten steel in the immersion nozzle under the condition that the runner position was swung by swinging the two movable plates 3 while keeping the runner area S ₁ constant. As a result, at a certain moment, one end in the radial direction of the cylindrical inner hole 16 becomes the flow-down side 22 and the molten steel flow velocity is fast, and the other end becomes the flow-opposite side 23 and the molten steel flow velocity becomes slow, but constant. After a lapse of time, the end portion where the flow-down side 22 is located is replaced, and the molten steel flow velocity is reduced at a portion where the molten steel flow velocity is high, and conversely, the molten steel flow velocity is increased at a portion where the molten steel flow velocity is slow. In this way, it has been found that there is no region where the molten steel flow rate remains consistently slow.

Therefore, in actual continuous casting of molten steel, the movable plate 3 is made into two pieces, and the two movable plates 3 are swung, so that the runner position is swung while keeping the runner area S ₁ constant. . As a result, it became clear that non-metallic inclusion adhesion to the inner wall of the cylindrical inner hole of the immersion nozzle was greatly reduced. Since there is no region where the molten steel flow rate remains consistently slow, it is presumed that the adhesion of non-metallic inclusions was hindered.

When the runner area S ₁ fluctuates greatly when the movable plate 3 swings, the molten metal injection amount (ton / hour) from the sliding nozzle 1 fluctuates, and the molten metal level in the mold (first meniscus 19). ), And the continuous casting flux (powder for continuous casting) covering the surface of the molten metal in the mold is entrained in the molten metal, and a part is captured by the solidified shell of the molten metal, which becomes the base point of the defect. Therefore, it is not preferable. In order to prevent such a problem from occurring, it is preferable to keep the runner area S ₁ constant. However, if the fluctuation margin of the runner area S ₁ is within ± 5%, casting can be performed without any problem. Therefore, in the present invention, the variation of the runner area S ₁ is controlled within ± 5%.

Further, during casting, the runner area S ₁ is determined according to the passing amount of molten steel determined from the mold cross-sectional area and the casting speed, that is, the throughput M. Further, the runner area S ₁ changes when the throughput is kept constant due to the fluctuation of the non-metallic inclusion adhesion state in the immersion nozzle. When the opening area of the fixed plate opening 4 is S ₀ as shown in FIG. 2B, the runner area S ₁ is 0.9 of the fixed plate opening cross-sectional area S ₀ due to the large throughput. When the ratio is larger than twice, the flow rate of the molten metal can be kept high on the inner wall of the immersion nozzle, so that non-metallic inclusions hardly adhere to the inner wall of the immersion nozzle. In addition, when the runner area S ₁ becomes larger than 0.9 times the fixed plate opening cross-sectional area S ₀ due to adhesion of non-metallic inclusions, the effect of swinging the runner position is little. Absent. Further, when the runner area S ₁ is smaller than 0.2 times the cross-sectional area S ₀ of the fixed plate opening, the flow rate of the molten metal is kept low on the inner wall of the immersion nozzle, and the non-metallic inclusions on the inner wall of the immersion nozzle are maintained. Although there is concern about adhesion, there is no such operation mode in the first place. That is, the present invention is applied in the range where the runner area S ₁ is 0.2 to 0.9 times the cross-sectional area S ₀ of the fixed plate opening.

  In the present invention, the non-metallic inclusions are prevented from adhering by swinging the position of the runner 5 through which the molten metal of the sliding nozzle passes. It becomes impossible to prevent the adhesion of objects sufficiently. In the present invention, the two movable plates are swung so that at least a portion of the fixed plate opening having an area ratio of 80% or more becomes a runway through which the molten metal passes at least once every 10 seconds. Adhesion of nonmetallic inclusions to the inner wall of the immersion nozzle can be sufficiently suppressed in the entire area of the inner wall of the nozzle. Even if a part where the flow rate of the molten metal is locally low on the inner wall of the immersion nozzle occurs and a small amount of non-metallic inclusions are attached, the molten metal may flow in the part at least once every 10 seconds. Since the flow velocity changes and the velocity increases, a small amount of non-metallic inclusions attached to the inner wall separate from the inner wall of the immersion nozzle due to the shearing force received by the flow of the molten metal. Accordingly, this can further reduce the adhesion of non-metallic inclusions to the inner wall of the immersion nozzle and prevent the deterioration of productivity.

Here, even if the movable plate 3 is swung, if there are many portions of the opening 4 of the fixed plate that do not become the runner 5 through which the molten metal passes, the effect of the present invention can be sufficiently exerted. I can't. This is because a portion of the molten metal pool below the second meniscus 20 where the molten metal flow rate is always kept low is generated in a portion that does not become the runner 5 through which the molten metal passes. In FIG. 7, (a) shows the runner 5 at the left end position, and (b) shows the runner 5 at the right end position. The hatched portion in FIG. 7C shows the portion of the opening 4 of the fixed plate that becomes the runner 5 by swinging, and the area thereof is S ₂ here. In the present invention, the two movable plates 3 are swung so that at least a portion of the opening 4 of the fixed plate 2 having an area ratio of 80% or more becomes a runner 5 through which molten metal passes at least once every 10 seconds. This is preferable. Since the portion with the area ratio of 80% or more (the hatched portion in FIG. 7 (c) has the area S ₂ ) becomes the runner 5 through which the molten metal passes, there is sufficient portion where the molten metal flow rate is always kept low. The adhesion of non-metallic inclusions to the inner wall of the immersion nozzle can be sufficiently prevented.

  The movable plate 3 of the present invention may be oscillated at all times during continuous casting, but it is more preferable that the oscillating plate 3 is oscillated only when the oscillation is necessary.

Even if the runner area S ₁ is kept constant due to adhesion of non-metallic inclusions to the inner wall of the immersion nozzle during casting, the amount of molten metal passing through the immersion nozzle, that is, the throughput M is reduced. Alternatively, in order to keep the throughput M constant, the runner area S ₁ must be increased.

In the present invention, while the amount of molten metal passing, that is, when the throughput is constant, the runner area S ₁ is less than 1.25 times the initial runner area S _{10 at} the start of casting, nonmetallic inclusions are present on the inner wall of the immersion nozzle. Since it is not adhered or slightly adhered, the movable nozzle 3 does not have to be oscillated. Since the runner area S ₁ when the throughput is constant is 1.25 times or more and 2 times or less of the initial runner area S _{10 at} the start of casting, it is considered that non-metallic inclusions have progressed to some extent. It is preferable that the movable nozzle 3 is swung. At the time when the adhesion of the non-metallic inclusion has progressed to this extent, the non-metallic inclusion has adhered to the portion that was on the opposite side 23 while the movable nozzle 3 was not rocked. Owing to the rocking movement, the portion that was the opposite flow-down side 23 is periodically changed to the flow-down side 22 and the molten metal flow rate is increased, so that the adhering non-metallic inclusions can be removed well.

On the other hand, when the runner area S ₁ when the throughput is constant is expanded to more than twice the initial runner area S _{10 at} the start of casting, the non-metallic inclusions adhere to the inner wall of the immersion nozzle, and the movable plate is It is difficult to detach the non-metallic inclusion from the inner wall of the immersion nozzle even if it is swung.

Therefore, when the runner area S ₁ when the amount of molten metal passing, that is, the throughput is constant, increases to a range of 1.25 times to 2 times the initial runner area S _{10 at} the start of casting, the two movable It is better to start the rocking of the plate.

The molten metal continuous casting apparatus of the present invention has a movable plate driving device 6 for driving two movable plates (3a, 3b). As shown in FIG. 8, the movable plate drive device 6 includes a control device 7 and a drive mechanism 8, and the drive mechanism 8 drives the movable plate 3 based on a command from the control device 7. An air cylinder or a hydraulic cylinder can be used as the drive mechanism 8. The movable plate driving device 6 performs operation control for swinging the two movable plates 3 while suppressing the fluctuation of the runner area S ₁ within ± 5%. Further, control is performed to swing the two movable plates 3 so that at least a part of the fixed plate opening 4 having an area ratio of 80% or more becomes a runner through which the molten metal passes at least once every 10 seconds. Furthermore, when the runner area S ₁ when the amount of molten metal passed, that is, the throughput is constant, increases to a range of 1.25 times or more and 2 times or less of the initial runner area S _{10 at} the start of casting, the two movable sheets Control to start rocking the plate.

  In the sliding nozzle 1 applied in the present invention, the two movable plates 3 can be configured such that the two movable plates (3a, 3b) do not overlap as shown in FIGS. In this case, the runway 5 is a space formed by the gap 10 formed between the two movable plates (3a, 3b) and the opening 4 of the fixed plate. When the two movable plates come into contact with each other, the gap 10 disappears (FIG. 3A), and the runner 5 is closed.

  Further, as shown in FIGS. 5 and 6, the two movable plates (3a, 3b) can be overlapped. In this case, as shown in FIG. 6C, the movable plate openings (11a, 11b) are provided in the two movable plates (3a, 3b), respectively. A space formed by the movable plate opening 11 of the two movable plates and the opening 4 of the fixed plate is a runner 5. FIG. 6D shows a case where a runner 5 is formed at the left end of the fixed plate opening 4, and FIG. 6E shows a case where the runner 5 is formed at the center of the fixed plate opening 4.

  The sliding direction of the movable plate 3 may be either the thickness direction of the mold or the width direction of the mold.

  The present invention was applied when continuously casting low-carbon Al-killed steel using a steel slab continuous casting apparatus having a ladle molten steel amount of 350 tons. The continuous casting apparatus is a 2-strand slab continuous casting apparatus, and the slab thickness is 250 mm. As the continuous casting nozzle 12, a nozzle composed of an upper nozzle 13, a sliding nozzle 1, a lower nozzle 14, and an immersion nozzle 15 was used. The submerged nozzle 15 is made of a bottomed cylindrical alumina graphite refractory, has an inner diameter of φ70 mm, and has two discharge ports 17 on the lower side. No inert gas is blown into the continuous casting nozzle.

As the sliding nozzle 1, the one shown in FIG. 6 was used. Two fixed plates 2 and two movable plates 3 are provided. The fixed plate 2 has a circular opening 4, and the sectional area S ₀ of the opening 4 is 3850 mm ² . The movable plate drive device 6 that drives the two movable plates 3 includes a drive mechanism 8 that uses an air cylinder and a control device 7 that controls the movement of the drive mechanism 8. The direction in which the movable plate 3 slides is the mold thickness direction.

Casting was started at the casting speed shown in Table 1, using the width shown in Table 1 as the mold width. The runner area S ₁ is adjusted by the movable plate driving device 6 to achieve a target casting speed. The runner area at the start of casting was defined as S ₁₀ , and the S ₁₀ / S ₀ ratio performance is shown in “Casting initial runner area ratio” in Table 1.

After starting casting, the movable plate 3 starts to swing from a predetermined timing. When the movable plate 3 is swung, the movable plate driving device 6 drives the movable plate 3 so as to keep the runner area S ₁ constant. The fluctuation of the runner area S ₁ can be kept within ± 5%. The runway area fluctuation results are shown in “Runway area fluctuation” in Table 1. Further, by adjusting the swing range of the movable plate 3, the area ratio (S ₂ / S ₀ ) of the portion that becomes the runner by the swing of the runner 5 in the opening 4 of the fixed plate is adjusted. The results of the area ratio of the portion that becomes the runner are shown in Table 1, “Area ratio of the opening that becomes the runway”. Further, by adjusting the swing period of the movable plate 3, it is adjusted at least once every second that the portion that becomes a runner by swinging the runner 5 becomes a runner. This frequency coincides with the swing period of the movable plate. The results are shown in “Frequency of runners in openings” in Table 1.

Table 1 shows a ratio (S ₁ / S ₁₀ ) between the runner area S ₁ at the time when the swing of the movable plate 3 is started and the runner area S ₁₀ at the start of casting. In the example indicated as S ₁ / S ₁₀ = 1.0, it means that the rocking is performed from the start of casting. For the other examples, casting was performed while maintaining the casting speed constant without swinging at the start of casting. When non-metallic inclusions adhere to the continuous casting nozzle, control is performed to increase the runner area S _{1 in} order to maintain the casting speed. As a result, the swing of the movable plate was started when S ₁ / S ₁₀ reached a predetermined value (the value shown in “ratio of S ₁ and S ₁₀ at the start of swing” in Table 1).

  After the casting in the tundish was completed, the adhesion amount of non-metallic inclusions adhered in the continuous casting nozzle was evaluated. Table 1 shows the evaluation values of the adhesion thickness evaluated with the adhesion amount of Comparative Example 3 in Table 1 as 1. Moreover, the cast slab was hot-rolled and cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.9 mm, and the number of ridges (hege, sliver) per unit length of the steel sheet was evaluated. Table 1 shows the evaluation values obtained by evaluating the number of wrinkles in Comparative Example 2 in Table 1 as 1.

In Examples 1 to 9 and Reference Examples 3, 4 , and 6 in Table 1, the movable nozzle started to swing from the start of casting. Of these, in Reference Example 4, the oscillation cycle was intentionally set to 12 seconds, so the frequency of the runner in the opening was once every 12 seconds, and in Reference Example 6, the oscillation amplitude was intended. By making it small, the area ratio which becomes a runner in the opening was set to 75%. As a result, for Reference Example 4 and Reference Example 6, Examples 1 , 2 , 5 , 7 to 9 (all of the ratio of the area of the opening that becomes a runner and the frequency of the runner that becomes a runner of the present invention) In comparison with (range), the inclusion adhesion thickness slightly increased, and the defect occurrence rate in the cold-rolled steel sheet slightly increased, and the quality evaluation result was “good but slightly inferior”. In Example 9, the fluctuation of the runner area S ₁ during rocking was intentionally increased to ± 5% which is the upper limit of the present invention, but the quality evaluation result was good.

In Examples 10 to 13 and Reference Examples 14 to 17 , the movable nozzle was not oscillated at the start of casting, non-metallic inclusions adhered to the continuous casting nozzle, and the runner area S ₁ increased. The swinging of the movable nozzle was started after S ₁ / S ₁₀ reached a predetermined value. S ₁ / S ₁₀ at the start of swinging was changed to 1.18, 1.25, 2, and 2.5. In Reference Examples 14 to 17, the oscillation cycle was 12 seconds, and the frequency of the runner in the opening was once every 12 seconds. Although the quality evaluation decreases as S ₁ / S ₁₀ at the start of oscillation increases, the quality evaluation is “good but slightly inferior” if S ₁ / S ₁₀ is in the range of 1.25 to 2. It is a good range. In addition, the effect of not starting oscillation from the start of casting can reduce wear due to oscillation of the movable plate 3 and eliminates the need to always guarantee precise control of the movable plate drive device 6. I was able to get it.

In Comparative Example 1, since the mold width was wide and the casting speed was high, the casting initial runner area ratio S ₁₀ / S ₀ was as large as 0.95, which was outside the scope of the present invention. Since the flow rate of molten steel in the continuous casting nozzle was high from the beginning of casting, the quality evaluation result was good despite no rocking.

In Comparative Example 2, although the casting initial runner area ratio S ₁₀ / S ₀ was 0.5 and was within the scope of the present invention, no swinging was performed. As a result, both the non-metallic inclusion adhesion in the continuous casting nozzle and the failure occurrence rate in the cold-rolled steel sheet were the worst results.

In Comparative Example 3, although the movable nozzle was oscillated, the control of the movable nozzle driving device was intentionally changed to increase the variation of the runner area S ₁ during oscillation to ± 7%. As a result, the incidence of rejection in cold-rolled steel sheets increased. As the runner area S ₁ fluctuates greatly, the flow rate of molten steel discharged from the nozzle for continuous casting fluctuates, which fluctuates the surface position of the molten steel in the mold, inducing powder entrainment and increasing non-metallic inclusions in the slab It is estimated that

It is a fragmentary sectional view showing one form of the present invention, and (a), (b), and (c) show the case where the runway is located in the left side, the center, and the right side, respectively. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining this invention, (a) is an exploded sectional view of the nozzle for continuous casting, (b) is a figure explaining a fixed plate, (c) (d) (e) is a figure, respectively. A situation corresponding to 1 (a), (b) and (c) is shown in which a runner is formed by the overlap of the opening of the fixed plate and the movable plate. It is a fragmentary sectional view showing one form of the present invention, (a) shows a runner fully closed state, (b) shows a runner half-opened state, and (c) shows a runner fully opened state. It is a fragmentary sectional view showing one form of the present invention, and (a), (b), and (c) show the case where the runway is located in the left side, the center, and the right side, respectively. It is a fragmentary sectional view showing one form of the present invention, and (a), (b), and (c) show the case where the runway is located in the left side, the center, and the right side, respectively. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining this invention, (a) is a decomposition | disassembly sectional drawing of the nozzle for continuous casting, (b) is a figure explaining a stationary plate, (c) demonstrates two movable plates. (D) and (e) respectively correspond to (a) and (b) of FIG. 5 and show a situation in which a runner is formed by the overlap of the opening of the fixed plate and the movable plate. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic explaining this invention, (a) (b) shows the condition where a runway is located in the left end and the right end, respectively, (c) demonstrates the site | part used as a runner in the opening part of a fixed plate. FIG. It is sectional drawing which shows the nozzle for continuous casting of this invention. It is a fragmentary sectional view showing the conventional nozzle for continuous casting, (a) shows a runner fully closed state, and (b) and (c) show a runner half open state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sliding nozzle 2 Fixed plate 3 Movable plate 4 Opening part 5 Runway 6 Movable plate drive device 7 Control apparatus 8 Drive mechanism 9 Tundish 10 Gap 11 Movable plate opening part 12 Continuous casting nozzle 13 Upper nozzle 14 Lower nozzle 15 Immersion nozzle 16 Cylinder inner hole 17 Discharge port 18 Molten metal 19 in mold 1st meniscus 20 2nd meniscus 21 Molten metal filling area 22 Flowing side 23 Flowing opposite side

Claims (4)

A continuous casting apparatus having a fixed plate having an opening with a cross-sectional area S ₀ and a sliding nozzle having two movable plates sliding along the fixed plate, and driving the two movable plates The portion of the opening of the fixed plate that is not covered by the two movable plates is a runner through which the molten metal passes, and the runner area S ₁ is equal to the sectional area S ₀ of the fixed plate opening . 50% or less, and the movable plate drive device swings the runner position in the opening by swinging the two movable plates while keeping the fluctuation of the runner area S ₁ within ± 5%. The swinging is performed by swinging the two movable plates so that at least a portion of the fixed plate opening having an area ratio of 80% or more becomes a runner through which molten metal passes at least once every 10 seconds. A continuous casting apparatus for molten metal, characterized in that The movable plate driving device is configured such that when the molten metal passage amount, that is, the throughput is constant, the runner area S ₁ increases to a range of 1.25 times or more and 2 times or less the casting start initial runner area S _10. 2. The molten metal continuous casting apparatus according to claim 1, wherein swinging of the two movable plates is started. A continuous casting method using a fixed plate having an opening with a cross-sectional area S ₀ and a sliding nozzle having two movable plates sliding along the fixed plate, and two of the openings of the fixed plate the portion not covered by the movable plate becomes runner passing of molten metal, the runner area S ₁ is 50% or less of the fixed plate opening sectional area S _0, the variation of the runner area S ₁ The runner position in the opening is oscillated by oscillating the two movable plates while keeping it within ± 5%, and the oscillating position is at least 10% of the area of the fixed plate opening having an area ratio of 80% or more. A method for continuously casting molten metal, characterized in that two movable plates are swung so as to form a runner through which molten metal passes once or more per second. When the molten metal passage amount, that is, the runner area S ₁ when the throughput is constant, increases to a range of 1.25 times to 2 times the initial runner area S _{10 at} the start of casting, the two movable plates 4. The molten metal continuous casting method according to claim 3, wherein rocking is started.

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