Gas injection nozzle and continuous casting method

Abstract

To provide a gas blowing upper nozzle which can prevent gas leak, and a continuous casting method using the same.SOLUTION: A gas blowing upper nozzle comprises a refractory material (1) containing a gas permeable material (1B) and a metal case (2) surrounding an outer periphery of the refractory material (1), and has an upper end metal case (3) which extends to an inner side from an upper end part of the metal case (2). In the gas blowing upper nozzle, an upper end of a seal mortar part (4) the rectory material (1) and the metal case (2) is covered with the upper end metal case (3). A continuous casting method installs the gas blowing upper nozzle at bottom of a tundish, and pours a molten steel into a casting mold from the tundish via the gas blowing upper nozzle while blowing an inert gas into the gas permeable material.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas blowing nozzle provided at the bottom of a tundish and used in a hot state, and a continuous casting method using the same. [Background technology]

[0002] Conventionally, in the continuous casting of molten steel, inclusions such as alumina (Al2O3) in the molten steel adhere to and accumulate on the inner wall of the gas blowing nozzle, often causing nozzle clogging. When nozzle clogging occurs, the clogging material may break off during the injection of molten steel and mix into the slab, or the clogging may cause an uneven flow of molten steel in the nozzle, causing problems with the quality of the slab.

[0003] As a measure to prevent nozzle clogging, inert gas is blown into the nozzle. and then , floating of inclusions aim at separation , to the nozzle of inclusions Adhesion and Blockage of Continuous casting nozzle the gas blowing in this This is generally done using an upper nozzle installed in a tundish, a sliding plate and an immersion nozzle connected to its lower part.

[0004] For gas blowing with the gas blowing nozzle, porous gas permeable material and refractory In some cases, a through hole is used. As shown in FIG. 4(a), when a porous gas-permeable material is used, it is often made of a fireproof material 1 that is a combination of a gas non-permeable material 1A and a gas permeable material 1B. The outer periphery of the gas blowing nozzle 100 is kept airtight by a metal case 2. The inert gas is blown into the gas blowing nozzle 100. sideways The inert gas is introduced through an inert gas introduction pipe 6 installed at the bottom. A part of the inert gas flows through a gas flow passage provided between the outer periphery of the refractory material 1A made of gas impermeable material and the metal case 2. that is Gas Pool No. 5 Then, the gas is introduced into the upper gas-permeable material 1B through the through hole of the gas blowing nozzle 100.11 is blown into the molten steel flow flowing downward. The remaining part of the inert gas passes through the gas-permeable material 1B at the lower part and into the through-hole of the gas lift nozzle 100 11 is blown into the molten steel flow flowing downward. At this time, there is a concern that gas may leak between the outer periphery of the refractory material 1 of the gas lift nozzle 100 and the metal case 2 and a predetermined quantity of inert gas may not be blown into the molten steel flow flowing through the inside of the gas lift nozzle. Therefore, the seal mortar part 4 etc. adheres the space between the outer periphery of the refractory of the gas-impermeable material 1A and the metal case 2, suppressing gas leakage.

[0005] On the other hand, the sealing performance between the metal case 2 provided on the outer periphery and the refractory material 1 has been a problem conventionally. For example, if the seal between the metal case 2 and the refractory material 1 is inhibited, the inert gas leaks through the outer periphery of the refractory material 1 and leaks into the molten steel from the tundish laying part. Therefore, the amount of inert gas to be blown into the molten steel passing through the through-hole 11 of the gas lift nozzle 100 cannot be sufficiently ensured. The slab cast in such a state will be out of specification.

[0006] Figure 4(b) is an enlarged schematic view of the two-dot chain line part B in Figure 4(a) that is, near the upper end of the gas blowing-up nozzle 100 showing the state where the upper end of the metal case 2 is opened due to thermal deformation (indicated by the arrow). When continuous casting is repeated, the metal case 2 of the upper nozzle becomes hot and thermally expands due to heat transfer from the molten steel. At that time, the upper nozzle set mortar 10 is pushed aside, and the upper end of the metal case 2 opens away from the refractory material 1 as shown by the arrow. When the metal case 2 is deformed in this way, a gap is generated between the seal mortar is. In Fig. 4(b), 4 and the metal case 2. Gas leakage is likely to occur through this gap. The inert gas leakage phenomenon occurs when a gap is generated between the metal case 2 and the refractory material 1 as described above, and the seal mortar part 4 and the metal case 2, and gas leakage is likely to occur through this gap. The inert gas leakage phenomenon occurs when a gap is generated between the metal case 2 and the refractory material 1 as described above, and the seal mortar partIt is caused by the sealing performance being reduced by 4 and a leakage path being formed. The occurrence of gas leakage can be grasped by detecting a change in the pressure (back pressure) of the gas blowing. When gas leakage occurs, the back pressure decreases. Therefore, when performing gas blowing during continuous casting, a mechanism is constructed to monitor the back pressure of the blown gas and determine it as abnormal when the back pressure decreases.

[0007] In order to suppress gas leakage as described above, various improvements have been made conventionally. For example, in the technologies disclosed in Patent Documents 1 and 2, a heat-expandable mortar is used to fill the gap generated between the metal case and the gas-permeable material due to the thermal expansion of the metal case. According to these patent documents, the coefficient of thermal expansion is generally large for the metal case and small for the refractory. Due to the heating during nozzle use, the expansion of the metal case becomes larger than that of the outer periphery of the nozzle refractory, creating a gap between the outer periphery of the nozzle refractory and the metal case, and gas leaks from there. As a countermeasure for this, an expandable mortar is used to suppress gas leakage.

[0008] Furthermore, in the technologies disclosed in Patent Documents 3 and 4, the thermal expansion of the metal case is suppressed by improving the restraining force. According to Patent Document 3, by disposing a flexible refractory sealing material on the outer peripheral portion of the metal case, the deformation of the metal case due to thermal expansion is restrained by the refractory sealing material, suppressing thermal deformation. Also, in Patent Document 4, the restraining force of the metal case is increased by attaching spiral fins to the outer peripheral portion of the metal case.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the above prior art has the following problems. That is, in the technologies disclosed in Patent Documents 1 and 2, even if the thermal expansion coefficient of the mortar between the metal case and the gas-permeable material is improved, there is a limit to the thermal expansion amount of the mortar. If the metal case expands more than the expansion amount of the mortar, there is a problem that gas leakage between the metal case and the refractory material cannot be completely prevented. Further, as in Patent Document 2, when a foaming material is used to improve the thermal expansion coefficient of the mortar, the density of the mortar itself decreases, and there is a problem of reducing the sealing property.

[0011] In addition, in the technologies disclosed in Patent Documents 3 and 4, the method of physically suppressing the thermal expansion of the metal case by improving the restraining force of the metal case also has the following problems. The method of winding a flexible refractory seal around the outer periphery of the metal case as in Patent Document 3 is expected to reduce the thermal deformation of the metal case at the portion where the refractory seal material is wound, but the expansion cannot be suppressed at other portions. Further, if the refractory seal is wound around the whole, the adhesiveness between the upper nozzle and the surrounding masonry bricks decreases, and the upper nozzle may shift up and down, increasing the risk of steel leakage. Therefore, it is hard to say that it is sufficient as a gas leakage suppression method. In the case of the method of installing fins on the outer periphery of the metal case as in Patent Document 4, an effect of reducing the thermal deformation of the whole metal case can be expected. However, if the fins are sized such that they come into contact with the masonry bricks during the operation of setting the upper nozzle into the surrounding masonry bricks, there is a risk of damaging the masonry bricks themselves. Therefore, there is a problem that the insertion operation of the upper nozzle itself becomes difficult. On the other hand, if the outer diameter of the fins is designed to be smaller than the inner diameter of the masonry bricks, the effect of improving the strength becomes small, and there is a problem that the thermal expansion of the metal case cannot be completely suppressed.

[0012] The present invention solves the above-described conventional problems and provides continuous casting of molten steel In the process of blowing the inert gas from the gas blowing-up nozzle into the molten steel in the part, a technology that can prevent gas leakage and aims to achieve this. Here, gas leakage means that the inert gas flows out from the part other than the gas-permeable material between the metal case provided on the outer periphery of the gas blowing-up nozzle and the refractory material.

Means for Solving the Problems

[0013] The gas blowing-up nozzle according to the present invention that advantageously solves the above problems includes a refractory material (1) containing a gas-permeable material (1B), and a metal case (2) surrounding the outer periphery of the refractory material (1), and has an upper-end metal case (3) extending inward from the upper-end portion of the metal case (2), and the sealing mortar part (4) upper end between the refractory material (1) and the metal case (2) is covered by the upper-end metal case (3).

[0014] In addition, regarding the present invention The gas blowing-up nozzle (a) it is a more preferable solution means that the extension length of the upper-end metal case (3) is equal to or greater than the joint thickness between the metal case (2) and the masonry brick (8). 、 (b) The extended tip of the upper end metal case (3) is within the covered range by being sandwiched between the flat top end of the refractory material (1) and the upper nozzle upper refractory material (9). etc This can be a more preferable solution means.

[0015] The continuous casting method according to the present invention that advantageously solves the above problems is characterized in that any of the above gas blowing-up nozzles is installed at the bottom of the tundish, and while blowing an inert gas into the gas-permeable material, molten steel is injected from the tundish into the mold through the gas blowing-up nozzle.

Effects of the Invention

[0016] Since the gas blowing-up nozzle according to the present invention is configured as described above, the following effects can be obtained. That is, the gas blowing-up nozzle is formed by a refractory material containing a gas-permeable material and a metal case having an upper-end metal case. Even if a gap is generated at the joint between the refractory material and the metal case due to thermal deformation of the metal case, the upper-end metal case arranged so as to cover the joint at the top end of the upper nozzle physically blocks the gas leakage path. By doing so, gas leakage can be prevented. Further, in the continuous casting method according to the present invention, molten steel is injected from the tundish into the mold through the above gas blowing-up nozzle, so that continuous casting can be performed without gas leakage and the quality of the cast slab can be maintained well.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the embodiments of the present invention will be described in detail. Note that the drawings are schematic and may differ from the actual ones. Furthermore, the following embodiments are merely examples of devices and methods for embodying the technical idea of ​​the present invention, and are not intended to limit the configuration to the following. In other words, the technical idea of ​​the present invention can be modified in various ways within the technical scope described in the claims.

[0019] 1 is a diagram showing a vertical cross section of a gas blowing up nozzle according to one embodiment of the present invention. The refractory material 1 inside the gas blowing up nozzle 100 has through holes through which molten steel flows along a rotation axis (axis of symmetry) CL. 11 The through hole has a hollow, thick-walled shape. 11 The refractory material 1 has a flat portion at the top (upper end). In the example of FIG. 1, the refractory material 1 is made up of a combination of a gas non-permeable material 1A and a gas permeable material 1B. The gas permeable material 1B can be placed at any position. The through holes 1B are arranged in a direction perpendicular to the gas permeable material 1A. 11 Gas can be injected into the molten steel passing through the gas passage. The gas non-permeable material 1A can also be placed at any position. When it is desired to perform gas injection from two separate locations, top and bottom, as shown in Figure 1, it is possible to perform gas injection by placing the gas non-permeable material 1A at the boundary of the gas permeable material 1B. is not In this case, there is no problem in constructing the structure in which the entire fire-resistant material 1 is made of the gas-permeable material 1B.

[0020] The supply path of the inert gas to the gas-permeable material 1B is configured as follows. First, the inert gas is introduced into the gas blowing nozzle 100 through the inert gas introduction pipe 6. Then, it passes through the gas pool 5 provided between the refractory material 1 and the substantially cylindrical metal case 2 that covers the outer periphery of the refractory material 1 and reaches the gas-permeable material 1B. In the example of FIG. 1, the gas pool 5 is provided between the refractory material 1 and the metal case 2, but a slit can also be provided in the refractory material 1 to form the gas pool 5. However, in this embodiment, the structure with the gas pool 5 provided between the refractory material 1 and the metal case 2 as shown in FIG. 1 can enjoy the effect more significantly.

[0021] All of the inert gas that reaches the gas pool 5 needs to pass through the gas-permeable material 1B and be blown into the molten steel. The leakage of the inert gas from a part other than the gas-permeable material 1B to the outside of the gas blowing nozzle 100 is called gas leakage. When gas leakage occurs, a sufficient amount of inert gas cannot be supplied to the molten steel in the hollow part of the gas blowing nozzle 100. Therefore, a sufficient effect on improving the cleanliness of the molten steel cannot be obtained. As a result, quality problems may occur in the cast slab. To prevent such gas leakage, seal mortar part 4 is arranged between the refractory material 1 and the metal case 2. Seal mortar part 4 fills the gaps other than the gas pool 5 between the refractory material 1 and the metal case 2. Seal mortar part 4 plays a role in preventing the inert gas from leaking out of the gas blowing nozzle 100.

[0022] A schematic diagram when the gas blowing nozzle 100 of this embodiment is set in the tundish is shown in FIG. 2(a). The periphery of the gas blowing nozzle 100 is surrounded by the tundish steel shell 7, masons 8, and the upper nozzle upper refractory material 9. The gas blowing nozzle 100 is restricted by the surrounding materials. The upper nozzle setting mortar 10 is arranged at the joint between the masons 8 and the metal case 2 to prevent gaps. The restraining force on the gas blowing nozzle 100 is from the masons 8, the upper nozzle setting mortar 10, and the metal case2 It is guaranteed by the adhesive force with

[0023] The upper end portion of the gas blowing nozzle 100 surrounded by the two-dot chain line portion A in Fig. 2(a) is enlarged and shown in Fig. 2(b). In this embodiment, it has an upper end metal case 3 that extends inward from the upper end portion of the metal case 2. The sealing mortar part 4 (joint portion) is configured to be covered by the upper end metal case 3. The connection between the outer periphery of the upper end of the metal case 2 and the upper end metal case 3 may be, for example, welding or caulking, or the metal case 2 and the upper end metal case 3 may be integrally formed by drawing or the like. Also, the upper end metal case 3 is preferably an annular shape along the flat portion at the top end of the refractory material 1. The upper end metal case 3 is arranged at the upper end portion of the gas blowing nozzle 100, and the space between the upper end metal case 3 and the metal case 2 on the outer periphery of the upper nozzle is in a state of being connected without a gap. By doing so, even if thermal deformation occurs in the metal case 2, gas leakage from the joint between the refractory material 1 and the metal case 2 can be suppressed. That is, even if thermal deformation (indicated by the arrow) as shown in Fig. 3 occurs, the gas leakage path generated at the joint between the refractory material 1 and the metal case 2 is blocked by the upper end metal case 3 and the sealing mortar part 4, and the gas leakage path can be physically blocked. At this time, the limit length at which the metal case 2 opens due to thermal deformation depends on the joint thickness between the metal case 2 and the masonry brick 8. Therefore, in order to have the effect of preventing gas leakage even when the metal case 2 undergoes the maximum thermal deformation, it is preferable that the extension length of the upper end metal case 3 is equal to or greater than the joint thickness between the metal case 2 and the masonry brick 8. Also, since the upper end metal case 3 will melt and its shape cannot be maintained when it comes into direct contact with the molten steel part therefore, it is preferable that the extension length of the upper end metal case 3 is within the range covered by being sandwiched between the flat top end of the refractory material 1 of the gas blowing nozzle and the upper nozzle upper refractory material 9 at most. Here, the extension length of the upper end metal case 3 is the length in the radial direction in the cylindrical coordinate system with the rotation axis CL as the central axis.

[0024] The refractory material 1 is, for example, a high-alumina-based material, and the metal case 2 and the upper-end metal case 3 are metallic, and for example, carbon steel, alloy steel, stainless steel, cast steel, cast iron, titanium, and titanium alloys are preferably used. The sealing mortar part The seal mortar 4 and the upper nozzle set mortar 10 can be used by adjusting a watered mortar of high-alumina quality to an appropriate consistency, for example. The joint thickness between the metal case (2) and the masu bricks (8) is about 1 to 5 mm. The range sandwiched between the flat top end of the refractory material 1 of the gas blow-up nozzle 100 and the upper nozzle upper refractory material 9 is about 5 to 20 mm in the radial length from the rotation axis CL.

[0025] In the continuous casting method as another embodiment of the present invention, the gas blow-up nozzle 100 of the above embodiment is installed at the bottom of the tundish as shown in FIG. 2. Then, the inert gas introduced from the inert gas introduction pipe 6 is made to flow into the molten steel flowing down through the through holes through the gas-permeable material 1B. The molten steel in the tundish is injected into the mold through a sliding nozzle or an immersion nozzle as needed in addition to the gas blow-up nozzle 100. By continuously casting using the gas blow-up nozzle 100 of the above embodiment, even when continuously casting, gas leakage due to deformation of the metal case 2 of the gas blow-up nozzle 100 caused by thermal expansion can be prevented. The range where the upper-end metal case 3 covers the top end of the gas blow-up nozzle 100 needs to cover the sealing mortar, which is the joint between the refractory material 1 and the metal case 2, regardless of the thermal deformation of the metal case 2. Part 4 It is necessary to cover it so as not to be exposed to the outside. By configuring it in that way, gas leakage can be prevented.

[0026] The present embodiment shown in FIGS. 1 and 2 and the conventional gas injection nozzle shown in FIG. 4 were installed at the bottom of the tundish for continuous casting, and the results of evaluating the presence or absence of gas leakage by the back pressure of the inert gas blown into the gas injection nozzle are shown in FIG. 5. Whether or not gas leakage has occurred can be determined by monitoring the back pressure of the inert gas conducted to the gas injection nozzle. That is, when the inert gas is normally blown from the gas-permeable material 1B into the molten steel, the back pressure of the inert gas receives the combined resistance pressure of the static pressure of the molten steel and the ventilation resistance of the gas-permeable material 1B, and that resistance pressure appears as the back pressure. However, when gas leakage occurs, at least the ventilation resistance of the gas-permeable material 1B disappears, so the back pressure decreases. Therefore, the determination of whether or not gas leakage has occurred is made based on the presence or absence of a decrease in back pressure, and the effects of the present embodiment and the conventional gas injection nozzle were verified.

[0027] Here, the threshold value of the back pressure used for the determination depends on the casting equipment and the operating rate, so it is necessary to optimize for each individual continuous casting machine. In the continuous casting machine for which the determination was made this time, a case where the back pressure decreased by about 30% with respect to the back pressure during steady state was called a back pressure decrease and the determination was made. As shown in FIG. 5, when a conventional gas injection nozzle (conventional example: N = 1012) was used, the occurrence rate of the back pressure decrease was 0.018. On the other hand, by applying the present embodiment (invention example: N = 107), it was possible to suppress the occurrence of a back pressure decrease, that is, gas leakage.

Industrial Applicability

[0028] According to the gas injection nozzle and the continuous casting method of the present invention, continuous casting can be performed while blowing the blown inert gas into the molten steel without gas leakage, so the quality of the cast slab can be maintained well and it is industrially useful.

Explanation of Reference Numerals

[0029] 100 Gas injection nozzle (upper nozzle) 1 Refractory material 1A Gas-impermeable material 1B Gas-permeable material 2 Metal case 3 Upper metal case 4 Sealing mortar part 5 Gas pool (gas flow path) 6 Inert gas inlet pipe 7 Tundish iron sheet 8 Brick 9 Refractory material for the upper part of the upper nozzle 10 Upper nozzle setting mortar 11 through holes CL Rotation axis (symmetry axis)

Claims

1. a refractory material (1) containing a gas-permeable material (1B); a metal case (2) surrounding the outer periphery of the refractory material (1); comprising having an upper-end metal case (3) extending inward from the upper end of the metal case (2); the upper end of the sealing mortar portion (4) between the refractory material (1) and the metal case (2) is covered by the upper-end metal case (3); a gas blow-up nozzle, wherein the extension length of the upper-end metal case (3) is not less than the joint thickness between the metal case (2) and bricks (8).

2. The gas blow-up nozzle according to Claim 1, wherein the extended tip of the upper-end metal case (3) is within the range covered by being sandwiched between the flat top end of the refractory material (1) and the upper refractory material (9) of the upper nozzle.

3. A continuous casting method, wherein the gas blow-up nozzle according to Claim 1 or 2 is installed at the bottom of a tundish, and inert gas is blown into the gas-permeable material while molten steel is injected from the tundish into a mold through the gas blow-up nozzle.

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