Gas up-blowing nozzle and continuous casting method

Abstract

Provided are a gas up-blowing nozzle capable of preventing gas leakage and a continuous casting method using the gas up-blowing nozzle. The gas up-blowing nozzle is provided with a refractory material (1) comprising a gas permeable material (1B), a metal shell (2) surrounding the periphery of the refractory material (1), and an upper end metal shell (3) extending inwards from the upper end of the metal shell (2), and the upper end of a sealing mortar part (4) between the refractory material (1) and the metal shell (2) is covered by the upper end metal shell (3). In the continuous casting method, the gas up-blowing nozzle is arranged at the bottom of a tundish, and molten steel is injected from the tundish to a casting mold through the gas up-blowing nozzle while inert gas is blown into the gas permeable material.

Description

Technical Field

[0001] The present invention relates to a gas upward blowing nozzle which is arranged at the bottom of a tundish and used at a high temperature, and a continuous casting method using the gas upward blowing nozzle. Background Art

[0002] In the past, during the continuous casting of molten steel, inclusions such as alumina (Al2O3) in the molten steel adhered to and accumulated on the inner wall of the gas blowing nozzle used, and nozzle clogging often occurred. If nozzle clogging occurs, the clogging material will peel off during the injection of molten steel and mix into the cast sheet, or the molten steel in the nozzle will flow unevenly due to the clogging, which will cause quality problems of the cast sheet.

[0003] As a countermeasure to prevent nozzle clogging, inert gas is blown from the nozzle to achieve floating separation of inclusions, thereby preventing inclusions from adhering to the nozzle and clogging. Gas blowing using a continuous casting nozzle is usually performed through an upper nozzle, a sliding plate, and an immersion nozzle connected to the lower part of the tundish.

[0004] Gas blowing using a gas blowing nozzle sometimes uses air holes that penetrate porous gas-permeable materials or refractory materials. Figure 4 As shown in (a), when a porous permeable material is used, it is mostly composed of a refractory material 1 that combines a non-permeable material 1A and a permeable material 1B. Moreover, the periphery of the gas blowing nozzle 100 is kept airtight by the metal shell 2. The inert gas is introduced via an inert gas introduction pipe 6 arranged at the lower side of the gas blowing nozzle 100. A part of the inert gas is introduced into the upper permeable material 1B part through the gas flow path, i.e., the gas pool 5, arranged between the refractory periphery of the non-permeable material 1A and the metal shell 2. Moreover, it is blown into the molten steel flow flowing down the through hole 11 of the gas blowing nozzle 100. In addition, the remaining part of the inert gas is blown into the molten steel flow flowing down the through hole 11 of the gas blowing nozzle 100 through the permeable material 1B at the bottom. At this time, there is a concern that gas may leak from the outer periphery of the refractory material 1 of the gas blowing nozzle 100 and the metal shell 2 without blowing a specified amount of inert gas into the molten steel flow flowing down in the gas blowing nozzle. Therefore, the outer periphery of the refractory material 1A of the non-permeable material 1A and the metal shell 2 are bonded by a sealing mortar portion 4, etc., to suppress gas leakage.

[0005] On the other hand, the sealing performance between the metal shell 2 and the refractory material 1 provided at the periphery has always been a problem. For example, if the sealing between the metal shell 2 and the refractory material 1 is impaired, the inert gas leaks through the periphery of the refractory material 1 and leaks from the tundish laying part into the molten steel. Therefore, the amount of inert gas to be blown into the molten steel through the through hole 11 of the gas blowing nozzle 100 cannot be sufficiently ensured. The cast piece cast in this state does not meet the standard.

[0006] Figure 4 (b) is to Figure 4 FIG. 1 is a schematic diagram showing an enlarged view of the double-dashed line portion B in (a), i.e., the vicinity of the upper end of the gas upward blowing nozzle 100. Figure 4 (b) shows a situation where the upper end of the metal shell 2 opens due to thermal deformation (indicated by an arrow). If continuous casting is repeated, the metal shell 2 of the upper nozzle becomes high temperature due to heat conduction from the molten steel, and will expand thermally. At this time, the upper nozzle is pushed open to set the slurry 10, and the upper end of the metal shell 2 opens in a manner away from the refractory material 1 as shown by the arrow. If the shell 2 is deformed like this, a gap is generated between the sealing slurry part 4 and the metal shell 2. Gas leakage is easily generated through this gap. The reason for the leakage of inert gas is that, as described above, a gap is generated between the metal shell 2 and the refractory material 1, and a leakage path is formed based on the decrease in the sealing of the sealing slurry part 4. In addition, the occurrence of gas leakage can be grasped by detecting changes in the gas blowing pressure (back pressure). If gas leakage occurs, the back pressure decreases. Therefore, the following structure is constructed: when gas blowing is performed during continuous casting, the back pressure of the blown gas is monitored, and when the back pressure decreases, it is determined to be abnormal.

[0007] In order to suppress the gas leakage as described above, various improvements have been made. For example, in the technology disclosed in patent documents 1 and 2, a thermally expansive mortar is used to fill the gap between the metal shell and the air-permeable material caused by the thermal expansion of the metal shell. According to the above patent documents, for the thermal expansion coefficient, the metal shell is usually large and the refractory is small. Due to the heating during the use of the nozzle, the expansion of the metal shell is larger than the outer periphery of the nozzle refractory, forming a gap between the outer periphery of the nozzle refractory and the metal shell, thereby leaking gas. As a countermeasure to this, an expansive 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 shell can be suppressed by increasing the restraining force. According to Patent Document 3, a flexible fire-resistant sealing material is arranged on the outer periphery of the metal shell, thereby restraining the deformation of the metal shell due to thermal expansion by the fire-resistant sealing material, thereby suppressing thermal deformation. In addition, in Patent Document 4, the restraining force of the metal shell is increased by installing spiral fins on the outer periphery of the metal shell.

[0009] Patent Document 1: Japanese Patent Application Publication No. 2011-256079

[0010] Patent Document 2: Japanese Patent Application Publication No. 2006-175482

[0011] Patent Document 3: Japanese Patent Application Publication No. 2016-36811

[0012] Patent Document 4: Japanese Patent Application Publication No. 2017-94386

[0013] However, the above-mentioned conventional technology has the following problems.

[0014] That is, in the technologies disclosed in Patent Documents 1 and 2, even if the thermal expansion coefficient is increased, the thermal expansion amount of the mortar between the metal shell and the air-permeable material has a limit. If the metal shell expands more than the expansion amount of the mortar, there is a problem that the gas leakage between the metal shell and the refractory material cannot be completely prevented. In addition, as in Patent Document 2, if a foaming material is used to increase the thermal expansion coefficient of the mortar, the density of the mortar itself decreases, and there is a problem that the sealing performance decreases.

[0015] In addition, in the technologies disclosed in Patent Documents 3 and 4, the method of physically suppressing the thermal expansion of the metal shell by increasing the restraining force of the metal shell also has the following problems. For the method of winding a flexible refractory seal around the outer periphery of the metal shell as in Patent Document 3, the part wound with the refractory seal material can be expected to reduce the thermal deformation of the metal shell, but other parts cannot suppress thermal expansion. In addition, if the refractory seal is wound as a whole, the adhesion between the upper nozzle and the surrounding large bricks decreases, and the upper nozzle moves up and down, so there is a concern that the risk of steel leakage increases. Therefore, it is difficult to say that it is sufficient as a gas leakage suppression method. If it is a method of setting fins on the outer periphery of the metal shell as in Patent Document 4, it can be expected to reduce the thermal deformation of the entire metal shell. However, when the upper nozzle is set in the surrounding large bricks, if the size is made so that the fins are in contact with the large bricks, there is a concern that the large bricks themselves will be damaged. 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 fin is designed to be smaller than the inner diameter of the large brick, the effect of improving the strength becomes smaller, and there is a problem that the thermal expansion of the metal shell cannot be completely suppressed. Summary of the invention

[0016] The present invention solves the above-mentioned existing problems and aims to provide a technology capable of preventing gas leakage when inert gas is blown into the gas blowing nozzle during continuous casting of molten steel. Here, gas leakage refers to the inert gas flowing out from between the metal shell and the refractory material provided on the periphery of the gas blowing nozzle to the part other than the permeable material.

[0017] The gas upward blowing nozzle involved in the present invention, which advantageously solves the above-mentioned problems, is characterized in that it comprises: a refractory material (1) including a gas-permeable material (1B); and a metal shell (2) surrounding the outer periphery of the refractory material (1), the gas upward blowing nozzle having an upper end metal shell (3) extending inward from the upper end of the metal shell (2), and the upper end of the sealing slurry part (4) between the refractory material (1) and the metal shell (2) is covered by the upper end metal shell (3).

[0018] In addition, the gas blowing nozzle involved in the present invention can become the following more preferred solution mechanism:

[0019] (a) the extension length of the upper metal shell (3) is greater than the thickness of the joint between the metal shell (2) and the large brick (8),

[0020] (b) The extended front end of the upper metal shell (3) is within a range covered by being clamped by the flat top end of the refractory material (1) and the upper refractory material (9) of the upper nozzle.

[0021] The continuous casting method involved in the present invention which advantageously solves the above-mentioned problems is characterized in that any one of the above-mentioned gas blowing nozzles is arranged at the bottom of the tundish, and while blowing inert gas into the above-mentioned permeable material, molten steel is injected from the tundish into the mold through the above-mentioned gas blowing nozzle.

[0022] The gas upward blowing nozzle involved in the present invention is constructed as described above, so that the following effects can be obtained. That is, the gas upward blowing nozzle is formed by a refractory material including a gas-permeable material and a metal shell having an upper metal shell. Even if a gap is generated in the joint between the refractory material and the metal shell due to thermal deformation of the metal shell, the upper metal shell configured in a manner to cover the joint at the top of the upper nozzle also plays a role in physically cutting off the leakage path of the gas. By doing so, gas leakage can be prevented. In addition, the continuous casting method involved in the present invention injects molten steel from the tundish into the mold via the above-mentioned gas upward blowing nozzle, so that continuous casting can be performed without leakage, and the quality of the cast sheet can be well maintained. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a longitudinal sectional view of the gas upward blowing nozzle which concerns on one embodiment of this invention.

[0024] Figure 2 (a) is a schematic cross-sectional view showing the gas upward blowing nozzle of the above embodiment being installed in the tundish. Figure 2 (b) is a partial enlarged cross-sectional view of portion A.

[0025] Figure 3This is a conceptual cross-sectional view showing a state in which a metal shell of the gas upward blowing nozzle according to the above embodiment is thermally expanded.

[0026] Figure 4 (a) is a simplified cross-sectional view of a conventional gas blowing nozzle installed in a tundish. Figure 4 (b) is a partially enlarged cross-sectional view of the B portion, and is a conceptual cross-sectional view showing a state of thermal expansion of the metal shell.

[0027] Figure 5 This is a graph evaluating the gas leakage condition when continuous casting is performed using the gas upward blowing nozzle of the above-mentioned embodiment by comparison with a conventional example. DETAILED DESCRIPTION

[0028] The following is a detailed description of the embodiments of the present invention. In addition, the drawings are schematic and may differ from the actual ones. In addition, the following embodiments illustrate the devices and methods for implementing the technical ideas of the present invention, and do not limit the structures to the following contents. That is, the technical ideas of the present invention can be modified in various ways within the technical scope described in the scope of the application.

[0029] Figure 1 1 is a diagram showing a longitudinal section of a gas blowing nozzle according to an embodiment of the present invention. The refractory material 1 inside the gas blowing nozzle 100 has a through hole 11 for molten steel to flow along the rotation axis (symmetry axis) CL, and is in the shape of a hollow thick-walled rotating body. The through hole 11 expands upward into a morning glory shape. There is a flat portion at the top (upper end) of the refractory material 1. In addition, at Figure 1 In the example of , the non-permeable material 1A and the permeable material 1B are combined. The permeable material 1B can be arranged at any position. Gas can be blown into the molten steel passing through the through hole 11 from the position where the permeable material 1B is arranged. The non-permeable material 1A can also be arranged at any position. Figure 1 As shown, when it is desired to split from the upper and lower parts to carry out gas blowing, the non-permeable material 1A is configured at the boundary of the permeable material 1B, thereby enabling separate blowing. In addition, when there is no need to carry out separate blowing of gas, there is no problem even if the refractory material 1 is formed as a structure in which all the permeable materials 1B are used.

[0030] The supply path of the inert gas to the gas permeable material 1B is constructed as follows. First, the inert gas is introduced into the gas blowing nozzle 100 through the inert gas introduction pipe 6. Then, the inert gas reaches the gas permeable material 1B through the gas pool 5 provided between the refractory material 1 and the substantially cylindrical metal shell 2 covering the outer periphery of the refractory material 1. Figure 1In the example of FIG. 1 , the gas pool 5 is provided between the refractory material 1 and the metal shell 2, but a slit can also be provided in the refractory material 1 to form the gas pool 5. However, in this embodiment, as shown in FIG. Figure 1 In this way, the structure in which the gas pool 5 is provided between the refractory material 1 and the metal shell 2 can enjoy its effect more obviously.

[0031] The inert gas reaching the gas pool 5 needs to be completely blown into the molten steel through the permeable material 1B. The leakage of the inert gas from a portion other than the permeable material 1B to the outside of the gas blowing nozzle 100 is called gas leakage. If a gas leakage occurs, a sufficient amount of inert gas will not be supplied to the molten steel in the hollow portion of the gas blowing nozzle 100. Therefore, a sufficient effect of improving the cleanliness of the molten steel cannot be obtained. As a result, the cast sheet may have quality problems. In order to prevent such gas leakage, a sealing slurry portion 4 is arranged between the refractory material 1 and the metal shell 2. The sealing slurry portion 4 fills the gap outside the gas pool 5 between the refractory material 1 and the metal shell 2. The sealing slurry portion 4 serves to prevent the inert gas from leaking out of the gas blowing nozzle 100.

[0032] Figure 2 (a) shows a schematic diagram of the gas blowing nozzle 100 of the present embodiment when it is set in the tundish. The gas blowing nozzle 100 is surrounded by the tundish iron sheet 7, the large bricks 8, and the upper nozzle upper refractory material 9. The gas blowing nozzle 100 is constrained by the surrounding materials. The upper nozzle setting mortar 10 is arranged at the joint between the large bricks 8 and the metal shell 2, and a gap is not left. The restraining force on the gas blowing nozzle 100 is ensured by the bonding force with the large bricks 8, the upper nozzle setting mortar 10 and the metal shell 2.

[0033] Will Figure 2 The upper end of the gas blowing nozzle 100 surrounded by the double-dashed line portion A in (a) is enlarged and Figure 2 (b) is shown. In the present embodiment, there is an upper metal shell 3 extending inward from the upper end of the metal shell 2. The upper end of the sealing mortar portion 4 (joint portion) between the refractory material 1 and the metal shell 2 is covered by the upper metal shell 3. The connection between the upper periphery of the metal shell 2 and the upper metal shell 3 is, for example, welding or riveting, or the metal shell 2 and the upper metal shell 3 may be integrally formed by deep drawing or the like. In addition, the upper metal shell 3 is preferably in the shape of a circular ring along the flat portion of the top of the refractory material 1. The upper metal shell 3 is arranged at the upper end of the gas blowing nozzle 100, and the upper metal shell 3 is connected to the metal shell 2 at the outer periphery of the upper nozzle without a gap. By doing so, even if the metal shell 2 is thermally deformed, gas leakage from the joint between the refractory material 1 and the metal shell 2 can be suppressed. That is, even if thermal deformation occurs, Figure 3As shown in the thermal deformation (indicated by arrows), the upper metal shell 3 and the sealing mortar part 4 will also block the gas leakage path generated in the joint between the refractory material 1 and the metal shell 2, and can physically cut off the gas leakage path. At this time, the maximum length of the metal shell 2 opened due to thermal deformation depends on the thickness of the joint between the metal shell 2 and the large brick 8. Therefore, in order to have the effect of preventing gas leakage even if the metal shell 2 produces the maximum thermal deformation, it is preferred that the extension length of the upper metal shell 3 is greater than the thickness of the joint between the metal shell 2 and the large brick 8. In addition, if the upper metal shell 3 is in direct contact with the molten steel, it will melt and cannot maintain its shape. Therefore, it is preferred that the maximum extension length of the upper metal shell 3 is also controlled within the range covered by the flat top of the refractory material 1 of the gas blowing nozzle and the upper refractory material 9 of the upper nozzle. Here, the extension length of the upper metal shell 3 is the length in the radial direction in the cylindrical coordinate system with the rotation axis CL as the center axis.

[0034] The refractory material 1 is, for example, a high-alumina material, and the metal shell 2 and the upper metal shell 3 are made of metal, for example, carbon steel, alloy steel, stainless steel, cast steel, cast iron, titanium and titanium alloys are preferably used. The sealing mortar portion 4 and the upper nozzle setting mortar 10 can be used by adjusting the high-alumina water-mixed mortar to a suitable consistency. The thickness of the joint between the metal shell (2) and the large brick (8) is about 1 to 5 mm. The range of the gas blowing nozzle 100 sandwiched by the flat top of the refractory material 1 and the upper refractory material 9 of the upper nozzle is about 5 to 20 mm in length in the radial direction from the rotation axis CL.

[0035] In a continuous casting method as another embodiment of the present invention, Figure 2 As shown, the gas blowing nozzle 100 of the above embodiment is arranged at the bottom of the tundish. Then, the inert gas introduced from the inert gas inlet pipe 6 flows into the molten steel flowing down the through hole 11 through the permeable material 1B. In addition to the gas blowing nozzle 100, the molten steel in the tundish is also injected into the mold through the sliding nozzle and the immersion nozzle as needed. By using the gas blowing nozzle 100 of the above embodiment for continuous casting, gas leakage caused by deformation caused by thermal expansion of the metal shell 2 of the gas blowing nozzle 100 can be prevented even in the case of continuous casting. The range of the upper metal shell 3 covering the top of the gas blowing nozzle 100 needs to be covered in a manner that the joint between the refractory material 1 and the metal shell 2, that is, the sealing slurry part 4, is not exposed to the outside despite the thermal deformation of the metal shell 2. By configuring like this, gas leakage can be prevented.

[0036] Will Figure 1 and Figure 2 The present embodiment shown and Figure 4The conventional gas blowing nozzle shown in FIG. 1 is set at the bottom of the tundish for continuous casting and the presence or absence of gas leakage is evaluated by the back pressure of the inert gas blown into the gas blowing nozzle. Figure 5 As shown. Whether a gas leakage has occurred can be determined by monitoring the back pressure of the inert gas connected to the gas blowing nozzle. That is, when the inert gas is normally blown into the molten steel from the permeable material 1B, the back pressure of the inert gas bears the resistance pressure of the molten steel static pressure and the ventilation resistance of the permeable material 1B, and the resistance pressure is expressed as the back pressure. However, in the case of gas leakage, at least the ventilation resistance of the permeable material 1B is not generated, so the back pressure decreases. Therefore, as a judgment of whether a gas leakage has occurred, it is judged based on whether the back pressure decreases, and the effect of this embodiment and the existing gas blowing nozzle is verified.

[0037] Here, the back pressure threshold used in the judgment is affected by the casting equipment and the degree of operation, so it needs to be optimized in each continuous casting machine. In the continuous casting machine that performed this judgment, the situation in which the back pressure dropped by about 30% compared with the stable back pressure was called back pressure drop. Figure 5 As shown, when the conventional gas blowing nozzle (conventional example: N=1012) is used, the back pressure drop occurs at a rate of 0.018. On the other hand, by applying the present embodiment (inventive example: N=107), the back pressure drop, that is, the occurrence of gas leakage, can be suppressed.

[0038] Industrial Applicability

[0039] According to the gas blowing nozzle and continuous casting method of the present invention, continuous casting can be performed while blowing the injected inert gas into molten steel without leakage, so the quality of the cast piece can be well maintained, and it is industrially useful.

[0040] Description of Reference Numerals

[0041] 100…gas upward blowing nozzle (upper nozzle); 1…refractory material; 1A…non-permeable material; 1B…permeable material; 2…metal shell; 3…upper metal shell; 4…sealed slurry part; 5…gas pool (gas flow path); 6…inert gas inlet pipe; 7…intermediate iron sheet; 8…large brick; 9…refractory material on the upper part of the upper nozzle; 10…slurry for setting the upper nozzle; 11…through hole; CL…rotation axis (symmetry axis).

Claims

1. A gas blowing nozzle, characterized in that: have: Refractory materials (1), including gas permeable materials (1B); and A metal shell (2) surrounds the outer periphery of the refractory material (1). The gas upward blowing nozzle comprises an upper metal shell (3) extending inward from the upper end of the metal shell (2). The upper end of the sealing mortar portion (4) between the refractory material (1) and the metal shell (2) is covered by the upper metal shell (3).

2. The gas upward blowing nozzle according to claim 1, characterized in that: The extension length of the upper metal shell (3) is greater than the thickness of the joint between the metal shell (2) and the large brick (8).

3. The gas upward blowing nozzle according to claim 2, characterized in that: The extended front end of the upper metal shell (3) is within a range covered by being clamped by the flat top end of the refractory material (1) and the upper refractory material (9) of the upper nozzle.

4. A continuous casting method, characterized in that: The gas upward blowing nozzle according to any one of claims 1 to 3 is arranged at the bottom of the tundish, and while blowing an inert gas into the permeable material, molten steel is injected from the tundish into the mold through the gas upward blowing nozzle.

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