JP7700732B2 - Gas blowing nozzle and continuous casting method - Google Patents

Description

The present invention relates to a gas blowing nozzle that is installed at the bottom of a tundish and used in hot conditions, and a continuous casting method using the same.

Conventionally, in the continuous casting of molten steel, inclusions such as alumina (Al ₂ O ₃ ) in the molten steel adhere to and accumulate on the inner wall of the gas blowing nozzle used, often causing nozzle clogging. When nozzle clogging occurs, the clogging material may come off during the injection of the molten steel and be mixed into the slab, or the clogging may cause a drift in the molten steel in the nozzle, resulting in quality problems in the slab.

As a measure to prevent nozzle clogging, inert gas is blown into the nozzle to float and separate the inclusions, preventing them from adhering to the nozzle and clogging it. Gas blowing in continuous casting nozzles is generally performed by an upper nozzle installed in the tundish, a sliding plate, and a submerged nozzle connected to its lower part.

For gas blowing with the gas blowing nozzle, a porous gas-permeable material or a vent hole penetrating a refractory may be used. As shown in FIG. 4(a), when a porous gas-permeable material is used, the refractory material 1 is often composed of 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. An inert gas is introduced through an inert gas introduction pipe 6 installed at the lower side of the gas blowing nozzle 100. A part of the inert gas is introduced into the upper gas permeable material 1B part through a gas flow path provided between the outer periphery of the refractory of the gas non-permeable material 1A and the metal case 2, that is, through a gas pool 5. Then, it is blown into the molten steel flow flowing down through the through hole 11 of the gas blowing nozzle 100. The remaining part of the inert gas is blown into the molten steel flowing down through the through hole 11 of the gas blowing nozzle 100 through the lower gas permeable material 1B. At this time, there is a concern that gas may leak from between the outer periphery of the refractory material 1 of the gas blowing nozzle 100 and the metal case 2, preventing a predetermined amount of inert gas from being blown into the molten steel flowing down inside the gas blowing nozzle. Therefore, the outer periphery of the refractory material 1A made of gas-impermeable material is bonded to the metal case 2 by a sealing mortar portion 4 or the like to suppress gas leakage.

On the other hand, there has been a problem in the past with regard to the sealing performance between the metal case 2 provided on the outer periphery and the refractory material 1. For example, if the sealing performance between the metal case 2 and the refractory material 1 is impaired, the inert gas leaks through the outer periphery of the refractory material 1 and leaks into the molten steel from the bottom of the tundish. As a result, the amount of inert gas to be blown into the molten steel passing through the through hole 11 of the gas blowing nozzle 100 is not sufficiently secured. A cast piece cast under such a condition will be out of specification.

FIG. 4(b) is a schematic diagram showing an enlarged view of the area B of FIG. 4(a) , i.e., the upper end of the gas blowing upper nozzle 100. FIG. 4(b) shows the state in which the upper end of the metal case 2 has opened due to thermal deformation (indicated by the arrow). When continuous casting is repeated, the metal case 2 of the upper nozzle becomes hot due to heat transfer from the molten steel, and thermally expands. 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 part 4 and the metal case 2. Gas leakage is likely to occur through this gap. The inert gas leakage phenomenon is caused by the occurrence of a gap between the metal case 2 and the refractory material 1 as described above, which reduces the sealing ability of the seal mortar part 4 and forms a leak path. The occurrence of gas leakage can be grasped by detecting the change in the gas blowing pressure (back pressure). When gas leakage occurs, the back pressure decreases. For this reason, when gas is blown during continuous casting, a system is established in which the back pressure of the blown gas is monitored and a drop in back pressure is detected as an abnormality.

In order to prevent the above-mentioned gas leaks, various improvements have been made in the past. For example, the technology disclosed in Patent Documents 1 and 2 uses thermally expandable mortar to fill the gap that occurs between the metal case and the gas-permeable material due to the thermal expansion of the metal case. According to these patent documents, the thermal expansion coefficient is generally large for metal cases and small for refractory materials. When the nozzle is in use, heating causes the metal case to expand more than the outer periphery of the nozzle refractory, creating a gap between the outer periphery of the nozzle refractory and the metal case, through which gas leaks. As a countermeasure to this, an expansive mortar is used to prevent gas leaks.

Furthermore, the technologies disclosed in Patent Documents 3 and 4 suppress the thermal expansion of the metal case by improving the restraining force. According to Patent Document 3, by arranging a flexible fireproof sealant around the outer periphery of the metal case, the fireproof sealant restrains the metal case from deforming due to thermal expansion, suppressing thermal deformation. Also, in Patent Document 4, the restraining force of the metal case is increased by attaching a spiral fin to the outer periphery of the metal case.

JP 2011-256079 A JP 2006-175482 A JP 2016-36811 A JP 2017-94386 A

However, the above-mentioned conventional techniques have the following problems.
That is, in the techniques 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 amount of thermal expansion of the mortar. If the metal case expands beyond the amount of expansion of the mortar, there is a problem that gas leakage between the metal case and the fireproof material cannot be completely prevented. In addition, if a foaming material is used to improve the thermal expansion coefficient of the mortar as in Patent Document 2, there is a problem that the density of the mortar itself decreases, and the sealing ability decreases.

In addition, the techniques disclosed in Patent Documents 3 and 4, which physically suppress the thermal expansion of the metal case by improving the binding force of the metal case, have the following problems. The method of wrapping a flexible fireproof 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 in the part wrapped with the fireproof sealant, but cannot suppress the expansion in other parts. In addition, if the fireproof seal is wrapped around the entire case, the adhesion between the upper nozzle and the surrounding mass bricks will decrease, and the upper nozzle will move up and down, which may increase the risk of steel leakage. Therefore, it is difficult to say that this is a sufficient method of suppressing gas leaks. The method of installing fins on the outer periphery of the metal case as in Patent Document 4 is expected to reduce the thermal deformation of the entire metal case. However, if the dimensions are such that the fins come into contact with the mass bricks when the upper nozzle is set into the surrounding mass bricks, the mass bricks themselves may be damaged. Therefore, there is a problem that the insertion work 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 mass brick, the effect of improving strength is reduced, and there is an issue that it is not possible to completely prevent the thermal expansion of the metal case.

The present invention aims to solve the above-mentioned problems of the conventional art and to provide a technique capable of preventing the occurrence of gas leakage when injecting an inert gas from a gas blowing nozzle into molten steel during continuous casting of molten steel. Here, gas leakage refers to the leakage of inert gas from between a metal case provided on the outer periphery of the gas blowing nozzle and a refractory material to a portion other than the gas-permeable material.

The gas-blowing nozzle of the present invention, which advantageously solves the above problems, comprises 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 is characterized in that it has an upper end metal case (3) extending inward from the upper end of the metal case (2), and the upper end of a sealing mortar portion (4) between the refractory material (1) and the metal case (2) is covered by the upper end metal case (3).

The gas blowing nozzle according to the present invention is as follows:
(a) 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 mass brick (8) ;
(b) the extended tip of the upper end metal case (3) is within a range that is covered and concealed by being sandwiched between the flat top end of the refractory material (1) and the upper nozzle upper refractory material (9);
This may be a more preferable solution.

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

The gas-blowing nozzle according to the present invention is configured as described above, and therefore can provide the following effects. That is, the gas-blowing nozzle is formed of a refractory material including a gas-permeable material and a metal case having an upper metal case. Even if a gap occurs in the joint between the refractory material and the metal case due to thermal deformation of the metal case, the upper metal case arranged to cover the joint at the top end of the upper nozzle physically blocks the gas leakage path. This makes it possible to prevent gas leakage. In addition, the continuous casting method according to the present invention injects molten steel from the tundish into the mold through the gas-blowing nozzle, so that continuous casting can be performed without gas leakage and the quality of the cast piece can be maintained at a good level.

FIG. 2 is a vertical cross-sectional view of a gas blowing up nozzle according to one embodiment of the present invention. FIG. 2A is a schematic cross-sectional view of the gas blowing nozzle of the above embodiment installed in a tundish, and FIG. 2B is a partially enlarged cross-sectional view of part A thereof. FIG. 4 is a conceptual cross-sectional view showing a state in which a metal case of the gas blowing up nozzle of the embodiment is thermally expanded. FIG. 2A is a schematic cross-sectional view of a conventional gas blowing nozzle installed in a tundish, and FIG. 2B is a partially enlarged cross-sectional view of part B thereof, which is a conceptual cross-sectional view showing the state in which the metal case is thermally expanded. 1 is a graph showing an evaluation of the state of gas leakage when continuous casting is performed using the gas blowing nozzle of the above embodiment in comparison with a conventional example.

The following is a detailed description of the embodiments of the present invention. Note that the drawings are schematic and may differ from the actual product. The following embodiments are illustrative of devices and methods for embodying the technical ideas of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

FIG. 1 is a diagram showing a vertical cross 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 through which molten steel flows along a rotation axis (axis of symmetry) CL, and is in the shape of a hollow, thick-walled body of revolution. The through hole 11 spreads upward in a morning glory shape. The top end (upper end) of the refractory material 1 has a flat part. In the example of FIG. 1, the nozzle is configured by a combination of a gas non-permeable material 1A and a gas permeable material 1B. The gas 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 gas permeable material 1B is arranged. The gas non-permeable material 1A can also be arranged at any position. When it is desired to perform gas blowing by dividing it into two places, upper and lower, as shown in FIG. 1, the gas non-permeable material 1A can be arranged at the boundary of the gas permeable material 1B, thereby making it possible to perform blowing separately. In addition, when there is no particular need to blow separately the gas, there is no problem in having a structure in which the entire refractory material 1 is made of the gas permeable material 1B.

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 by the inert gas introduction pipe 6. The inert gas then passes through the gas pool 5 provided between the fireproof material 1 and the approximately cylindrical metal case 2 that covers the outer periphery of the fireproof material 1, and reaches the gas-permeable material 1B. In the example of FIG. 1, the gas pool 5 is provided between the fireproof material 1 and the metal case 2, but the gas pool 5 can also be configured by providing a slit in the fireproof material 1. However, in this embodiment, the effect can be more pronounced with a structure in which the gas pool 5 is provided between the fireproof material 1 and the metal case 2 as shown in FIG. 1.

It is necessary that all of the inert gas that reaches the gas pool 5 passes through the gas-permeable material 1B and is blown into the molten steel. The leakage of the inert gas from the gas blowing nozzle 100 from a portion other than the gas-permeable material 1B is called a gas leak. When a gas leak occurs, a sufficient amount of the inert gas is not supplied to the molten steel in the hollow portion of the gas blowing nozzle 100. Therefore, a sufficient effect on improving the cleanliness of the molten steel cannot be obtained. As a result, a quality problem may occur in the cast slab. In order to prevent such a gas leak, a seal mortar portion 4 is disposed between the refractory material 1 and the metal case 2. The seal mortar portion 4 fills the gap between the refractory material 1 and the metal case 2 other than the gas pool 5. The seal mortar portion 4 plays a role of preventing the inert gas from leaking out of the gas blowing nozzle 100.

2(a) is a schematic diagram of the gas blowing up nozzle 100 of this embodiment set in a tundish. The gas blowing up nozzle 100 is surrounded by the tundish iron shell 7, mass bricks 8, and upper nozzle upper refractory material 9. The gas blowing up nozzle 100 is restrained by the surrounding materials. Upper nozzle set mortar 10 is placed in the joint between the mass bricks 8 and the metal case 2 to prevent any gaps from being formed. The restraining force on the gas blowing up nozzle 100 is guaranteed by the adhesive forces between the mass bricks 8, upper nozzle set mortar 10, and the metal case 2 .

FIG. 2B shows an enlarged view of the upper end of the gas blowing nozzle 100 surrounded by the two-dot chain line A in FIG. 2A. In this embodiment, the upper end metal case 3 extends inward from the upper end of the metal case 2. The seal mortar portion 4 (joint portion) between the refractory material 1 and the metal case 2 is covered by the upper end metal case 3. The connection between the upper end outer periphery of the metal case 2 and the upper end metal case 3 may be, for example, by welding or crimping, or the metal case 2 and the upper end metal case 3 may be integrally formed by drawing. In addition, it is preferable that the upper end metal case 3 is annular along the flat portion of the top end of the refractory material 1. The upper end metal case 3 is disposed at the upper end of the gas blowing nozzle 100, and the upper end metal case 3 and the metal case 2 on the outer periphery of the upper nozzle are connected without any gaps. In this way, even if the metal case 2 is thermally deformed, 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 an arrow) as shown in FIG. 3 occurs, the upper end metal case 3 and the seal mortar part 4 block the gas leakage path occurring in the joint between the refractory material 1 and the metal case 2, and the gas leakage path can be physically blocked. In this case, the limit length that the metal case 2 opens due to thermal deformation depends on the joint thickness between the metal case 2 and the mass brick 8. Therefore, in order to have the effect of preventing gas leakage even if the metal case 2 undergoes 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 mass brick 8. Furthermore, if the upper end metal case 3 comes into direct contact with molten steel, it melts and cannot maintain its shape . Therefore, it is preferable that the extension length of the upper end metal case 3 is within a range that is covered by being sandwiched between the flat top end of the refractory material 1 of the gas blowing upper nozzle and the upper nozzle upper refractory material 9. Here, the extension length of the upper end metal case 3 is the radial length in a cylindrical coordinate system with the rotation axis CL as the central axis.

The refractory material 1 is, for example, a high alumina 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, titanium alloy, etc. are preferably used. The sealing mortar part 4 and the upper nozzle set mortar 10 can be, for example, high alumina water-mixed mortar adjusted to an appropriate consistency. The joint thickness between the metal case (2) and the mass brick (8) is about 1 to 5 mm. The range sandwiched between the flat top end of the refractory material 1 of the gas blowing upper nozzle 100 and the upper nozzle upper refractory material 9 is about 5 to 20 mm in radial length from the rotation axis CL.

In a continuous casting method according to another embodiment of the present invention, the gas blowing nozzle 100 according to the above embodiment is installed at the bottom of a tundish as shown in FIG. 2. Then, an inert gas introduced from an inert gas introduction pipe 6 is flowed through the gas-permeable material 1B into the molten steel flowing down through the through holes. The molten steel in the tundish is injected into the mold through the gas blowing nozzle 100, as well as a sliding nozzle or a submerged nozzle, as necessary. By using the gas blowing nozzle 100 according to the above embodiment for continuous casting, gas leakage caused by deformation due to thermal expansion of the metal case 2 of the gas blowing nozzle 100 can be prevented even in the case of continuous casting. The range in which the upper end metal case 3 covers the top end of the gas blowing nozzle 100 must be covered so that the seal mortar portion 4 , which is the joint between the refractory material 1 and the metal case 2, is not exposed to the outside despite the thermal deformation of the metal case 2. By configuring in this way, gas leakage can be prevented.

The present embodiment shown in Fig. 1 and Fig. 2 and the conventional gas blowing nozzle shown in Fig. 4 were installed at the bottom of the tundish, and continuous casting was performed. The results of evaluating the presence or absence of gas leakage based on the back pressure of the inert gas blown into the gas blowing nozzle are shown in Fig. 5. Whether or not a gas leakage has occurred can be determined by monitoring the back pressure of the inert gas being conducted to the gas blowing nozzle. In other words, when the inert gas is normally blown into the molten steel from the gas-permeable material 1B, the back pressure of the inert gas is subjected to a combined resistance pressure of the molten steel static pressure and the airflow resistance of the gas-permeable material 1B, and this resistance pressure appears as a back pressure. However, when a gas leakage has occurred, at least the airflow resistance of the gas-permeable material 1B is no longer generated, so the back pressure decreases. Therefore, whether or not a gas leakage has occurred is determined by the presence or absence of a decrease in back pressure, and the effectiveness of the present embodiment and the conventional gas blowing nozzle was verified.

The back pressure threshold used in the judgment depends on the casting equipment and the operating rate, and therefore needs to be optimized for each individual continuous caster. In the continuous caster used in the judgment, a back pressure drop of about 30% compared to the steady back pressure was called a back pressure drop and judged. As shown in Figure 5, when a conventional gas blowing nozzle (conventional example: N = 1012) was used, the occurrence rate of back pressure drop was 0.018. On the other hand, by applying this embodiment (inventive example: N = 107), it was possible to suppress the occurrence of back pressure drop, i.e., gas leaks.

The gas blowing nozzle and continuous casting method of the present invention allow continuous casting while blowing the inert gas into the molten steel without gas leakage, which maintains good quality of the cast piece and is industrially useful.

100 Gas blowing nozzle (upper nozzle)
1 Fire-resistant material 1A Gas-non-permeable material 1B Gas-permeable material 2 Metal case 3 Upper end metal case 4 Sealing mortar part
5 Gas pool (gas flow path)
6 Inert gas introduction pipe 7 Tundish iron shell 8 Mass brick 9 Upper nozzle upper part refractory material 10 Upper nozzle set mortar
11 Through hole
CL Rotation axis (symmetric axis)

Claims (3)

A fire-resistant material (1) including a gas-permeable material (1B);
A metal case (2) surrounding the outer periphery of the fireproof material (1);
Equipped with
An upper end metal case (3) extends inwardly from an upper end of the metal case (2),
The upper end of the sealing mortar portion (4) between the fireproof material (1) and the metal case (2) is covered by the upper end metal case (3),
A gas blowing nozzle in which 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 mass brick (8) . 2. The gas blowing upper nozzle according to claim 1, wherein the extended tip of the upper end metal case (3) is within a range that is covered by being sandwiched between the flat top end of the refractory material ( 1 ) and the upper nozzle upper refractory material (9). 3. A continuous casting method comprising the steps of: installing the gas-blowing nozzle according to claim 1 or 2 at a bottom of a tundish; and injecting molten steel from the tundish into a mold through the gas-blowing nozzle while blowing an inert gas into the gas-permeable material.

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