JP2020131198A - Protective refractory for induction heating coil and electromagnetic induction heating method - Google Patents

Abstract

To provide a protective refractory for an induction heating coil, the protective refractory preventing coil damage and insulation plate drop-off that occur when inserting and removing an inner coil that is heated by electromagnetic induction from an inner peripheral side of an immersion nozzle, the protective refractory also having excellent durability even after repeated high-temperature preheating and having facilitated replaceability, and also to provide an electromagnetic induction heating method using the same.SOLUTION: A protective refractory 8 for protecting an induction heating coil (inner coil 33) of an apparatus that preheats, by electromagnetic induction heating, an immersion nozzle 5 for continuous casting of molten metal, includes a sleeve 41 for covering a shaft part and a tip part of the induction heating coil 33, the sleeve 41 being formed by integrally molding alumina fibers.SELECTED DRAWING: Figure 3

Description

The present invention relates to a protective refractory for an induction heating coil and an electromagnetic induction heating method in an electromagnetic induction heating device used for preheating a dipping nozzle used in continuous casting of molten metal.

Conventionally, in a metal such as steel, a continuous casting method is known in which a molten metal is continuously cooled and solidified to form a slab having a predetermined shape. In the continuous casting method, the molten metal is injected from the tundish into the mold via the immersion nozzle.

The immersion nozzle is attached to the bottom of the tundish and is configured to discharge the molten metal in the tundish into the mold from the discharge port at the bottom of the nozzle. This immersion nozzle is used with the lower end immersed in the molten metal in the mold to prevent the injected molten metal from scattering and to prevent the injected molten metal from coming into contact with the atmosphere for oxidation. It is suppressing. In addition, since the immersion nozzle can be injected in a rectified state, impurities such as slag and non-metal inclusions floating in the molten metal are prevented from being caught in the molten metal, and the quality of the slab is improved. At the same time, the stability of operation can be ensured. The immersion nozzle is formed of a refractory material having excellent corrosion resistance to molten metal, and for example, an AG nozzle or a ZCG nozzle is used.

In the casting process, if the temperature of the immersion nozzle is low, the immersion nozzle will crack or block at the beginning of casting when the injection of molten metal is started, and the flow of molten metal will be disturbed and the slag will not float sufficiently. May occur, such as a decrease in the value. On the other hand, by preheating the immersion nozzle, it is conceivable to reduce the temperature difference generated in the immersion nozzle when the injection of the molten metal is started and prevent the occurrence of a defect.

As a preheating method for the immersion nozzle, a method of blowing combustion gas with, for example, a burner has been conventionally practiced. However, when preheating with gas, it is difficult to heat the entire immersion nozzle evenly, and the preheating temperature varies depending on the part of the immersion nozzle, and stress is caused by the difference in thermal expansion due to the temperature difference. Cracks may occur. Further, in the case of preheating with a burner, there is a problem that heating takes a long time and can be heated only up to about 800 ° C. If the heating temperature is insufficient, nozzle clogging is likely to occur due to the adhesion of the refractory compound (Al ₂ O ₃ ) to the inner hole of the immersion nozzle at the initial stage of casting.

Therefore, as a method capable of uniformly heating the immersion nozzle and completing preheating to a desired temperature in a short time, for example, Patent Document 1 discloses that a high frequency induction heating method is adopted. In this heating method, the induction heating device includes an outer coil that heats from the outer peripheral side of the immersion nozzle and an inner coil that is inserted into the inner hole of the immersion nozzle and heats from the inner peripheral side.

JP-A-2007-326110

However, in the induction heating device composed of the outer coil and the inner coil as described in Patent Document 1, when the inner coil is inserted and removed, the inner coil comes into contact with the antioxidant adhering to the inner hole of the immersion nozzle. It often happened that the coils were damaged or the insulating plate used for preventing sparks fell off between the coils, and the heating device could not be used continuously.

In addition, when the circumference of the inner coil is protected by an amorphous refractory as a countermeasure, the amorphous refractory is vulnerable to thermal shock due to repeated high-temperature heating, and once a crack occurs, the crack grows from there and a chip occurs. Not only that, there is a problem that repairs at the field level are difficult.

Therefore, the present invention prevents the coil from being damaged and the insulating plate from falling off when the inner coil is heated by electromagnetic induction from the inner peripheral side of the immersion nozzle, and has excellent durability against repeated high-temperature preheating. It is an object of the present invention to provide a protective refractory of an induction heating coil that can be easily replaced, and an electromagnetic induction heating method using the same.

In order to solve the above problem, the present invention is a refractory material that protects the induction heating coil of an apparatus that preheats the immersion nozzle used in continuous casting of molten metal by electromagnetic induction heating, and the shaft portion of the induction heating coil. Provided is a protective refractory for an induction heating coil, which has a sleeve covering the tip and the sleeve, which is formed by integrally molding an alumina fiber.

A hole may be formed in the lid portion of the sleeve that covers the tip end portion of the induction heating coil.

In addition to the sleeve, it may have a top plate that covers the upper end of the immersion nozzle. In that case, the top plate may be provided with a ventilation groove that serves as a passage for water vapor generated in the sleeve. Further, the base end of the sleeve may have a collar portion that can be locked to the top plate. Further, the surfaces of the top plate and the collar portion may be subjected to a curing treatment with a chemical containing alumina and silica.

A groove may be formed on the outer circumference of the sleeve. A carbon-based, boron nitride-based, or alumina-based release agent may be applied to the surface of the sleeve. The sleeve may be pre-baked at 1000 ° C. or higher.

Further, the present invention is a method of preheating a dipping nozzle used in continuous casting of molten metal by electromagnetic induction heating, and an inner coil for electromagnetic induction heating from the inner hole side of the dipping nozzle is used for the induction heating coil. Provided is an electromagnetic induction heating method, which comprises covering with a protective refractory, inserting the immersion nozzle into an inner hole, and electromagnetically inducing heating the immersion nozzle.

A protective sheet made of an alumina-based refractory may be wrapped around the sleeve of the protective refractory for the induction heating coil. In that case, it is preferable that the protective sheet has heat resistance that melts during continuous casting of the molten metal and does not melt during preheating of the immersion nozzle.

According to the present invention, the protective refractory prevents the coil from being damaged and the insulating plate from falling off when the induction heating coil is inserted into and removed from the immersion nozzle, and can withstand repeated use of high temperature preheating a plurality of times. Moreover, if the protective refractory is damaged, it can be easily replaced at the site. Therefore, the high temperature preheating of the immersion nozzle can be efficiently performed.

It is a figure which shows the outline of the structure of the continuous casting machine. It is sectional drawing which shows the state which installed the immersion nozzle in the induction heating apparatus which used the protection refractory for an induction heating coil which concerns on embodiment of this invention. It is sectional drawing of the protection refractory which concerns on embodiment of this invention. FIG. 3 is a partial cross-sectional view of a protective refractory according to different embodiments of the present invention. It is an exploded perspective view of the protection refractory which concerns on embodiment of this invention. It is sectional drawing which shows the example of the groove formed in the sleeve.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals to omit duplicate description.

FIG. 1 shows an outline of the configuration of a continuous steel casting machine as an example of a continuous casting machine in which a dipping nozzle is used. The continuous casting machine 1 continuously cools and solidifies the molten steel 10 to form a steel ingot having a predetermined shape. The continuous casting machine 1 includes a ladle 2, a long nozzle 3, a tundish 4, a plurality of immersion nozzles 5, and a plurality of molds 6. In FIG. 1, only one immersion nozzle 5 and one mold 6 are shown.

The ladle 2 is a heat-resistant container in which the molten steel 10 is first housed in continuous casting, and an injection port 11 is provided on the bottom surface. The long nozzle 3 is attached to the injection port 11 of the ladle 2 and is configured to discharge the molten steel 10 housed inside the ladle 2 into the tundish 4 from the opening 12 at the lower end.

The tundish 4 is a heat-resistant container arranged below the long nozzle 3 and accommodating the molten steel 10 injected from the ladle 2 via the long nozzle 3. A plurality of injection ports 13 are formed on the bottom surface of the tundish 4 corresponding to each mold 6, and inside the injection port 13, a flow rate adjustment for adjusting the flow rate of the molten steel 10 flowing out from the injection port 13 is performed. A machine (not shown) is provided. With such a tundish 4, the molten steel 10 from the ladle 2 is rectified, and the molten steel 10 is distributed to each mold 6 in a predetermined amount.

The immersion nozzle 5 is attached to the injection port 13 of the tundish 4, and the molten steel 10 in the tundish 4 is injected into the mold 6 via the immersion nozzle 5. The immersion nozzle 5 includes a nozzle body 21 and a holder 22 that is attached to the lower part of the injection port 13 and holds the upper end portion of the nozzle body 21. The nozzle body 21 is formed in a substantially cylindrical shape, and a discharge port 23 is provided near the lower end. The discharge port 23 may be provided at two or four places on the side surface near the lower end by closing the lower end of the nozzle body 21, or may be provided at the lower end of the nozzle body. Absent. With such a nozzle body 21, the molten steel 10 flowing in from the upper end opening of the immersion nozzle 5 is discharged into the mold 6 through the discharge port 23. The nozzle body 21 is made of a refractory material, is preheated by a high-frequency induction heating device described later, and is used in a state where the lower end side is immersed in the molten steel 10 in the mold 6.

The mold 6 is a water-cooled mold provided below the immersion nozzle 5. The inside of the mold 6 has a predetermined cross-sectional shape, and the molten steel 10 from the tundish 4 is continuously injected into the mold 6 via the immersion nozzle 5. Then, the molten steel 10 in the mold 6 is cooled, and a solidified shell is formed and grown from the inner peripheral surface side in the mold 6, and the solidified steel is formed. Further, below the mold 6, a roller (not shown) for continuously pulling out the steel formed in the mold 6 from the lower opening of the mold 6 and a cutting machine for cutting the continuously extended steel to a predetermined length. Etc. are provided. In this way, a steel ingot having a predetermined shape such as a plate shape or a rod shape is formed.

As described above, the immersion nozzle 5 used in the continuous casting machine 1 as described above is used after being preheated in order to reduce the temperature difference generated when the injection of the molten steel 10 is started. Next, a heating device for preheating the immersion nozzle 5 will be described with reference to FIG. FIG. 2 is a cross-sectional view showing a state in which the immersion nozzle 5 is installed in the heating device.

As shown in FIG. 2, the heating device 7 for heating the immersion nozzle 5 by high-frequency induction heating includes a heat-resistant container 31, an outer coil 32, an inner coil 33, and an induced current application device 9. Further, water for cooling is supplied to the inside of each of the outer coil 32 and the inner coil 33 via a pipe (not shown).

The outer coil 32 is an induction heating coil that is arranged on the outer periphery of the immersion nozzle 5 and heats from the outer periphery of the immersion nozzle 5. The outer coil 32 is housed inside the heat-resistant container 31, and the side of the dipping nozzle 5 is housed inside the outer coil 32 from the lower end of the nozzle body 21. The inner coil 33 is an induction heating coil that is inserted into the inner hole 24 of the immersion nozzle 5 and heats from the inner peripheral portion of the immersion nozzle 5, and is configured to be insertable into the inner hole 24 from the upper opening of the nozzle body 21. A high-frequency induced current is applied to the outer coil 32 and the inner coil 33 from the induced current applying device 9, respectively.

The inner coil 33 is inserted into the inner hole 24 of the immersion nozzle 5. An insulating plate 34 is arranged between the inner coils 33 in order to prevent sparks. Then, when the inner coil 33 is taken in and out of the inner hole 24 of the immersion nozzle 5, the inner coil 33 and the insulating plate 34 may be damaged or fall off due to contact with an antioxidant or the like adhering to the inner hole 24. A protective refractory 8 is attached around the inner coil 33 to prevent it.

Next, the protective refractory for the induction heating coil 8 according to the embodiment of the present invention will be described with reference to FIGS. 3 to 5.

The protective refractory 8 for the induction heating coil is attached so as to surround the outer periphery of the inner coil 33 that heats the immersion nozzle 5 from the inner peripheral side. As shown in FIG. 3, the protective refractory 8 according to the present embodiment has a sleeve 41 and a top plate 42. When the immersion nozzle 5 used for continuous casting of steel is preheated, the protective refractory 8 withstands a preheating temperature of about 1200 ° C. to 1300 ° C. and has heat impact resistance to withstand repeated temperature differences between the preheating temperature and room temperature. It is necessary to have. Further, the inner coil 33 is provided with an insulating plate 34 for preventing sparks between the coils (see FIG. 2), and is required to have a heat insulating property corresponding to the heat resistance of the insulating plate 34. As a material satisfying these conditions, alumina fiber is used as a main raw material and molded using a binder or the like. Alumina has durability against high temperatures, and fiber products have excellent thermal shock resistance.

The sleeve 41 covering the shaft portion and the tip portion of the inner coil 33 has a lid portion 411 at the tip portion, a body portion 412, and a flange portion 413 at the base end, which are formed by integrally molding alumina fibers. There is. When the lid portion 411 and the body portion 412 are separated, when the antioxidant 61 adhering to the inner hole of the immersion nozzle 5 swells, it comes into contact with the sleeve 41, and the sleeve 41 is welded to the antioxidant. When the inner coil 33 is removed from the immersion nozzle 5 after the preheating is completed, the adhesive portion between the lid portion 411 and the body portion 412 may break. Therefore, the sleeve 41 is integrally molded. Further, by providing the flange portion 413, it can be placed on the top plate 42 to prevent the sleeve 41 from falling from the top plate 42. The thickness of the sleeve 41 is not particularly limited, but is preferably about several mm, so that sufficient strength is ensured and the distance between the immersion nozzle 5 and the inner coil 33 is within an allowable range. It is preferable that the outer diameter of the body portion 412 of the sleeve 41 is designed so as to secure a gap such that the antioxidant 61 adhering to the inner hole of the immersion nozzle 5 and the sleeve 41 do not come into contact with each other.

The top plate 42 covering the upper end of the immersion nozzle 5 has an opening 421 formed in the center, and after the body portion 412 of the sleeve 41 is inserted through the lid portion 411 into the opening 421, the collar portion 413 is locked to the upper surface of the top plate 42. It is supposed to be done. The thickness of the top plate 42 is preferably about 8 mm, for example. The collar portion 413 is not limited to a shape that is bent at a right angle from the body portion 412 as shown in FIG. 3, and may have a tapered shape as shown in FIG. 4, for example.

Further, as shown in FIG. 5, a hole 414 may be formed in the lid portion 411 of the sleeve 41, or a ventilation groove 422 may be provided in the top plate. These are provided for ventilation for releasing the water vapor generated in the sleeve 41 when the inner coil 33 is damaged and the cooling water leaks. Either one of the holes 414 and the ventilation groove 422 may be provided, or both may be provided.

As shown in FIG. 6, it is preferable to form a groove 43 on the outer periphery of the body portion 412 of the sleeve 41. The number and size of the grooves 43 are not limited to the example shown in FIG. 6, and are formed, for example, in a direction along the longitudinal direction or in an oblique direction with respect to the longitudinal direction. By forming the groove 43 on the surface of the sleeve 41 in this way, the occurrence of cracks can be further suppressed.

Further, the surface of the sleeve 41 may be cured with a chemical containing alumina and silica. Alternatively, only the flange portion 413 of the sleeve 41 and the top plate 42 may be cured. Further, a carbon-based, boron nitride-based, or alumina-based release agent may be applied to the surface of the sleeve 41.

Further, the sleeve 41 may be pre-baked at a temperature (about 1000 ° C.) or higher at which the organic binder burns out and the inorganic binder exhibits strength, and at a temperature lower than the operating temperature of the sleeve 41. If the pre-baking is not performed, the binder component in the sleeve 41 may volatilize and emit smoke during the initial heating, but if this is acceptable, the pre-baking may not be performed.

It should be noted that the sleeve 41 and the top plate 42 are not adhered so that when one of them is damaged, only the damaged one needs to be replaced, and the stress acting on one of them is less likely to affect the other. Is preferable.

When preheating the immersion nozzle 5 used in the continuous casting machine 1, as shown in FIG. 2, the immersion nozzle 5 is charged in the outer coil 32 of the refractory container 31 in which the outer coil 32 is housed, and the above-mentioned protection is provided. The inner coil 33 to which the refractory material 8 is attached is inserted to an appropriate position in the inner hole 24 of the immersion nozzle 5. When inserting the inner coil 33, it is preferable to wind, for example, a protective sheet made of an alumina-based refractory obtained by molding alumina and silica into a sheet around the sleeve 41 of the protective refractory 8.

The protective sheet is provided so that the sleeve 41 is not damaged even if the protective refractory 8 and the antioxidant adhering to the inner hole 24 of the immersion nozzle 5 are rubbed when the inner coil 33 is taken in and out of the immersion nozzle 5. is there. Even if this protective sheet remains inside the immersion nozzle 5 after the inner coil 33 is removed, it melts during casting and withstands the preheating temperature (about 1200 ° C to 1300 ° C) of the immersion nozzle 5. It shall have heat resistance. By wrapping such a protective sheet, it is possible to prevent damage to the sleeve 41 when the inner coil 33 is inserted and removed without applying a release agent to the sleeve 41.

After the immersion nozzle 5 is attached to the heating device 7, a high-frequency induced current is applied, and the immersion nozzle 5 is preheated to a predetermined temperature by the outer coil 32 and the inner coil 33 by an electromagnetic induction heating method.

As described above, according to the protected refractory 8 according to the present embodiment, the durability of the protected refractory 8 itself is improved, and by protecting the inner coil 33 with the protected refractory 8, the protected refractory 8 and The inner coil 33 can withstand repeated preheating of the immersion nozzle 5. Further, by making the protective refractory 8 an integrally molded product instead of an amorphous refractory, it can be easily replaced at the site when it is damaged.

Further, the present invention is used for electromagnetic induction heating of the immersion nozzle 5, and since high temperature and uniform heating can be performed in a short time, the inner hole 24 of the immersion nozzle 5 is compared with the preheating by gas. Adhesion of bare metal can be reduced and blockage can be suppressed. Therefore, it is possible to omit the oxygen cleaning work that has been conventionally performed as a countermeasure against clogging of the immersion nozzle 5. In addition, the casting yield is improved, and the quality of the slab can be improved.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention also includes them. It is understood that it belongs to.

As shown in Table 1, an offline test was conducted as an example of the present invention. Test No. In No. 3, the sleeve was pre-baked at 1200 ° C. for 2 hours.

The result is that it has good durability under any condition, and by forming a groove 43 on the surface of the sleeve 41 or attaching two protective sheets on top of each other, cracks in the protective refractory 8 can be further suppressed. The result was that the number of durability was increased.

The present invention can be applied to protect an inner coil that is charged into the inner hole of a refractory and heated from the inside when a refractory such as a dipping nozzle used in continuous casting of molten metal is preheated.

1 Continuous casting machine 2 Ladle 3 Long nozzle 4 Tandish 5 Immersion nozzle 6 Mold 7 Heating device 8 Protective refractory 9 Inductive current application device 10 Molten steel 11, 13 Injection port 12 Opening 21 Nozzle body 22 Holder 23 Discharge port 24 Hole 31 Heat-resistant container 32 Outer coil 33 Inner coil 34 Insulation plate 41 Sleeve 42 Top plate 43 Groove 411 Lid 412 Body 413 Nozzle 414 Hole 422 Ventilation groove

Claims (12)

A refractory that protects the induction heating coil of a device that preheats the immersion nozzle used in continuous casting of molten metal by electromagnetic induction heating.
A protective refractory for an induction heating coil, which has a sleeve that covers a shaft portion and a tip portion of the induction heating coil, and the sleeve is formed by integrally molding an alumina fiber. The protective refractory for an induction heating coil according to claim 1, wherein a hole is formed in a lid portion of the sleeve that covers the tip end portion of the induction heating coil. The protective refractory for an induction heating coil according to any one of claims 1 or 2, further comprising a top plate covering the upper end of the immersion nozzle in addition to the sleeve. The protective refractory for an induction heating coil according to claim 3, wherein the top plate is provided with a ventilation groove that serves as a passage for water vapor generated in the sleeve. The protective refractory for an induction heating coil according to any one of claims 3 or 4, wherein a collar portion that can be locked to the top plate is provided at the base end of the sleeve. The protective refractory for an induction heating coil according to claim 5, wherein the surface of the top plate and the collar portion is subjected to a hardening treatment with a chemical containing alumina and silica. The protective refractory for an induction heating coil according to any one of claims 1 to 6, wherein a groove is formed on the outer periphery of the sleeve. The protection for an induction heating coil according to any one of claims 1 to 7, wherein a carbon-based, boron nitride-based, or alumina-based release agent is applied to the surface of the sleeve. Refractory. The protective refractory for an induction heating coil according to any one of claims 1 to 8, wherein the sleeve is pre-baked at 1000 ° C. or higher. A method of preheating a dipping nozzle used in continuous casting of molten metal by electromagnetic induction heating.
The inner coil for electromagnetic induction heating from the inner peripheral side of the immersion nozzle is covered with the protective fireproof material for the induction heating coil according to any one of claims 1 to 9, and inserted into the inner hole of the immersion nozzle. An electromagnetic induction heating method comprising electromagnetic induction heating of the immersion nozzle. The electromagnetic induction heating method according to claim 10, wherein a protective sheet made of an alumina-based refractory is wound around the sleeve of the protective refractory for the induction heating coil. The electromagnetic induction heating method according to claim 11, wherein the protective sheet has heat resistance that melts during continuous casting of the molten metal and does not melt during preheating of the immersion nozzle.

Images