JP4445404B2 - Continuous casting method for molten steel - Google Patents

Description

The present invention relates to a method for continuously casting molten steel using a preheated immersion nozzle.

Conventionally, in a continuous casting method, molten steel is once supplied to a tundish, and after pouring the molten steel into a mold through an immersion nozzle, the molten steel is cooled to produce a slab. In the pouring of the mold, since the molten steel having a high temperature of 1450 to 1530 ° C. suddenly comes into contact with the immersion nozzle, the immersion nozzle is subjected to a rapid heat load, causing problems such as generation of cracks and breakage. Therefore, an immersion nozzle preheated with a gas burner or the like is installed in the tundish to reduce the heat load during pouring.

However, the preheating of the immersion nozzle usually requires a large space, and it has to be preheated far away from the tundish. In this case, in the process of transporting from the preheating place to the tundish, and in the process of attaching the immersion nozzle to the tundish, it is said that the temperature of the immersion nozzle is lowered and the relaxation of the thermal load during pouring is sufficiently eliminated. The situation is difficult.

As countermeasures, for example, Patent Document 1 and Patent Document 2 disclose an immersion nozzle in which a part or all of the immersion nozzle is formed of conductive ceramics, and the immersion nozzle is cast while directly generating heat by an induction coil during casting. ing. Further, in Patent Document 3, a side wall of a traveling carriage provided with an immersion nozzle handling device for automatically replacing the immersion nozzle is provided with a heat retaining box for keeping the preheated immersion nozzle warm, and the replacement place while keeping the immersion nozzle warm. A heat retaining box of an immersion nozzle handling device that conveys the air to the surface is disclosed.

JP-A-1-205858 JP 2002-336842 A JP-A-10-249514

However, in the inventions of Patent Documents 1 and 2, since induction heating is performed during continuous casting, there is a problem that an installation place for the induction coil is required between the tundish and the mold. Moreover, in invention of patent document 3, although the temperature to the replacement | exchange place of an immersion nozzle can be performed, there existed a problem that the temperature of an immersion nozzle fell in the attachment process to a tundish. Further, in the inventions of Patent Documents 1 to 3, the discharge port of the immersion nozzle is always open, and the temperature of the immersion nozzle is lowered by the air entering and exiting the discharge port of the immersion nozzle installed in the tundish. There was a problem that it was difficult to reduce the heat load.

This invention is made | formed in view of this situation, and it aims at providing the continuous casting method of the molten steel which can prevent the temperature fall of an immersion nozzle and can relieve the thermal shock of an immersion nozzle.

The continuous casting method for molten steel according to the first aspect of the present invention is characterized in that a cylindrical immersion nozzle provided with a discharge port on the lower side surface and closed at the bottom is attached to a tundish of a continuous casting machine, and the immersion nozzle is used as a mold. A molten steel continuous casting method in which molten steel in the tundish is poured into the mold through the immersion nozzle,
Before or after the immersion nozzle is preheated, or after the immersion nozzle is preheated , a heat insulating material is wrapped so as to cover the discharge port of the immersion nozzle, or a cap-shaped heat insulating material is provided so as to cover from the lower end of the immersion nozzle to the slag line portion. It is attached to prevent heat dissipation, and the heat insulating material is dissolved and disappeared by the molten steel supplied to the immersion nozzle during use.

In the continuous casting method of molten steel according to the first invention, the heat insulating material is a material that dissolves and disappears by molten steel at, for example, about 1450 to 1530 ° C., and does not deteriorate the quality of the slab even when mixed with molten steel For example, kao wool, asbestos cloth, fireproof glass cotton, etc. can be used, and it is formed in a sheet shape or a cap shape. The heat insulating material covers at least the outlet of the immersion nozzle, preferably covers from the lower part of the immersion nozzle to the slag line portion, and more preferably covers the entire immersion nozzle.
In the molten steel continuous casting method according to the first aspect of the present invention, for example, when the immersion nozzle is preheated by a flame by a burner, the flame is discharged when the burner is inserted into the immersion nozzle from the top of the immersion nozzle. When the burner is ejected from the outlet and the burner is inserted from the discharge port below the immersion nozzle, the discharge port is opened, and therefore a heat insulating material is attached after preheating. Further, for example, when the immersion nozzle is preheated by induction heating, the heat insulating material can be attached both before and after preheating.

The molten steel continuous casting method according to the second invention is the molten steel continuous casting method according to the first invention, wherein a consumable heater is attached to the heat insulating material at least in a portion covering the discharge port.
In the continuous casting method of molten steel according to the second invention, the consumable heater is melted away by molten steel at, for example, about 1450 to 1530 ° C., and does not deteriorate the quality of the slab even when mixed with molten steel. Formed of material.

According to a third aspect of the present invention, there is provided a continuous casting method of molten steel according to the second aspect of the present invention, wherein the consumable heater is an electric resistance wire, and the electric resistance wire is located inside the heat insulating material. , Inside or outside.

In the continuous casting method of molten steel according to claims 1 to 3 , since the discharge port of the submerged nozzle is covered with a heat insulating material to prevent heat dissipation, it is kept on standby during the mounting operation to the sliding nozzle and in the mold. The temperature of the submerged nozzle is prevented from lowering, and the temperature is not lowered due to the flow of air from the outlet of the submerged nozzle. The entire nozzle is maintained at a high temperature, reducing the thermal shock to the submerged nozzle during pouring. It is possible to prevent the occurrence of cracks and cracks due to uneven heat. Moreover, since a heat insulating material melt | dissolves and lose | disappears with molten steel, it can pour hot water with a heat insulating material mounted | worn, and a temperature fall becomes difficult to occur. Furthermore, since the immersion nozzle is kept at a high temperature until the time of use by the heat insulating material, the strength of the immersion nozzle and the resistance to melting damage can be improved, and the immersion nozzle can be made compact. By making the immersion nozzle compact, a gap between the immersion nozzle and the mold can be secured, and surface defects of the slab can be prevented. Furthermore, since the heat insulating material is attached to the discharge port of the immersion nozzle before or after preheating the immersion nozzle, it is possible to prevent a temperature drop of the immersion nozzle.

In particular, in the continuous casting method for molten steel according to claim 2, since a consumable heater is attached to at least a portion covering the discharge port of the heat insulating material, the discharge port of the immersion nozzle can be heated to about the temperature of the molten steel, The thermal shock caused by pouring can be reduced.
In the method for continuously casting molten steel according to claim 3, the consumable heater is an electric resistance wire, and the electric resistance wire is provided inside, inside, or outside the heat insulating material, so that the apparatus is simple. In addition, the cost is low .

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory view of a continuous casting facility to which a molten steel continuous casting method according to an embodiment of the present invention is applied, and FIG. 2 is an explanatory view of a heat insulating material according to a modification of the continuous casting facility.

With reference to FIG. 1, the continuous casting equipment 10 to which the continuous casting method of the molten steel which concerns on one embodiment of this invention is applied is demonstrated.
The continuous casting equipment (which constitutes a part of a continuous casting machine) 10 is a mold 13 that is formed by using molten steel at approximately 1500 to 1530 ° C. supplied into a tundish 11 from a ladle (not shown) through a submerged nozzle 12 for continuous casting. It is a device that pours hot water into.

The immersion nozzle 12 has a substantially cylindrical shape with a closed bottom, and is provided with a pouring port 16 into which molten steel is poured into an upper portion and two discharge ports 17 formed in a lower side surface. A sheet-like kao wool 18, which is an example of a heat insulating material, is wound around the discharge port 17 of the immersion nozzle 12. In addition, a consumable heater (hereinafter also simply referred to as “heater heater”) 19 composed of a nichrome wire (trade name), which is an example of an electrothermal resistance wire, is disposed in the inside of the Khao wool 18 and is supplied from a power source (not shown). Electricity is supplied to the heater 19 to heat the heater 19. In addition, it is not necessary to arrange an electric resistance wire such as a nichrome wire on a heat insulating material such as kao wool. The immersion nozzle 12 is preheated to about 1000 to 1400 ° C., for example, by an induction heating preheating device (not shown) in a state where the kao wool 18 and the heater 19 are wound. 11 is pressed against a sliding nozzle 15 provided at the lower part of 11 and fixed to the tundish 11.

Since the Khao wool 18 is melted at about 1200 ° C. and the heater 19 is melted at about 1500 ° C., these are melted by the molten steel and finally disappear. Moreover, since the quantity of the kao wool 18 and the heater 19 is small with respect to molten steel, the molten steel supplied to the casting_mold | template 13 is not contaminated, and the fall of the quality of the molten steel in the casting_mold | template 13 can be prevented.
In addition, instead of disposing the heater 19 on the kao wool 18 and covering the discharge port 17 to the immersion nozzle 12, a cap-like heat insulating material 20 formed of heat-resistant glass cotton, for example, as shown in FIG. 2 is attached. You can also. The heat insulating material 20 covers the discharge port 17 of the immersion nozzle 12 and is formed so as to cover from the lower end of the immersion nozzle 12 to the thick slag line portion 21 provided in the center of the immersion nozzle 12. As a result, the thermal shock caused by the molten steel supplied into the immersion nozzle 12 and substantially filled up to the slag line portion 21 can be mitigated.

Next, a method for continuously casting molten steel using the continuous casting facility 10 will be described.
After winding the kao wool 18 embedded in the heater 19 so that the discharge port 17 may be covered under the immersion nozzle 12, the immersion nozzle 12 is heated to about 1000-1400 degreeC with an induction heating preheating apparatus. At this time, an electric current may be passed through the heater 19 to generate heat, and the immersion nozzle 12 may be further heated. After the immersion nozzle 12 is heated by the induction heating preheating device, the immersion nozzle 12 is attached to the gripping device 14 while being heated by the heater 19. Further, while the immersion nozzle 12 is heated by the heater 19, the immersion nozzle 12 is pressed against the sliding nozzle 15 provided below the tundish 11 by the gripping device 14, and the immersion nozzle 12 is fixed to the tundish 11 and installed in the mold 13. To do.

Below the mold 13, a dummy bar 22 is installed to prevent the molten steel from leaking and to solidify the molten steel and pull out a cast piece. Molten steel of about 1500 to 1530 ° C. is supplied from the ladle into the tundish 11 and poured into the mold 13 through the immersion nozzle 12. At this time, the Khao wool 18 and the heater 19 are melted and mixed with the molten steel. However, since the amount of the Khao wool 18 and the heater 19 is small relative to the molten steel, the molten steel supplied to the mold 13 is contaminated. Therefore, the quality of the molten steel in the mold 13 can be prevented from being deteriorated, and the immersion nozzle 12 can be heated until the molten steel is supplied. Therefore, the temperature difference between the molten steel and the immersion nozzle 12 can be reduced, and Cracks and breakage can be prevented.

Next, examples carried out for confirming the effects of the present invention will be described. Here, FIG. 3 is a graph showing the damage occurrence index of the preheated immersion nozzle, and FIG. 4 is a graph showing the cost reduction index of the preheated immersion nozzle.

After preheating the immersion nozzle, the gripping device is pressed against the sliding nozzle provided at the lower part of the tundish, fixed to the tundish, and about 1500 to 1530 ° C. supplied into the tundish after about 10 minutes from the end of heating. The molten steel was poured into a mold through an immersion nozzle to continuously cast the molten steel, and the occurrence of cracks and breakage of the immersion nozzle was confirmed.

As Example 1, kao wool in which a nichrome wire was embedded was wound around the discharge port of the immersion nozzle, and the immersion nozzle was heated to 1400 ° C. by an induction heating preheating device. As Example 2, a cap-shaped heat insulating material formed of heat-resistant glass cotton was attached to the discharge port of the immersion nozzle, and the immersion nozzle was heated to 1400 ° C. by an induction heating preheating device. As Comparative Example 1, the immersion nozzle was heated to 1400 ° C. by an induction heating preheating device without attaching a heat insulating material. As Comparative Example 2, the immersion nozzle was heated to 1150 ° C. by a burner heating preheating device without attaching a heat insulating material.

As shown in Table 1, the temperature of the immersion nozzle at the start of casting (after preheating and after about 10 minutes) was 1200 ° C. and 1150 ° C. in Examples 1 and 2, respectively, and 950 ° C. in Comparative Examples 1 and 2, respectively. It can be seen that the temperature drop of the submerged nozzle can be suppressed by the molten steel continuous casting method of the present invention.

As shown in FIG. 3, when the incidence of cracks and breakage of the immersion nozzle in Comparative Example 2 was 1, Examples 1 and 2 were 0.01, and Comparative Example 1 was 0.5. This is because the heating with the immersion nozzle by induction heating can heat the immersion nozzle to a higher temperature compared to the heating with the burner, and the surface can be heated more uniformly, so that the thermal stress is reduced, and further, the immersion nozzle is further heated. It is understood that when the nozzle outlet is covered with a heat insulating material and kept warm or heated, the temperature drop is suppressed, and cracks and breakage did not occur.

As shown in FIG. 4, according to Examples 1 and 2 and Comparative Examples 1 and 2, the reduction index of the cost of the immersion nozzle calculated from the extension of the life of the immersion nozzle by preventing cracking and breakage of the preheated immersion nozzle is Comparative Example 2 was taken as 1, and in Examples 1 and 2, it was 0.5, and in Comparative Example 1, it was 0.8. In Examples 1 and 2, it is understood that since the incidence of cracks and breakage is low, the life of the immersion nozzle can be extended and the cost can be reduced.

The present invention is not limited to the above-described embodiment, and can be changed without changing the gist of the present invention. For example, a part or all of the above-described embodiment and modification examples are combined. Thus, the case of constituting the molten steel continuous casting method of the present invention is also included in the scope of the right of the present invention.
For example, in the method for continuously casting molten steel according to the above-described embodiment, the immersion nozzle is heated by the induction heating preheating device in a state where a heat insulating material is attached to the immersion nozzle, but may be heated by a burner. In this case, a heat insulating material is attached after heating. Even when an induction heating preheating device is used, a heat insulating material may be attached after heating. As the heat insulating material, khao wool and refractory glass cotton were used. the use of asbestos cloth or the like is also possible. Moreover, although the electrothermal resistance wire is provided inside the heat insulating material, it may be provided inside or outside the heat insulating material.

It is explanatory drawing of the continuous casting installation to which the continuous casting method of the molten steel which concerns on one embodiment of this invention is applied. It is explanatory drawing of the heat insulating material which concerns on the modification of the same continuous casting installation. It is a graph which shows the breakage generation | occurrence | production index | exponent of the preheated immersion nozzle. It is a graph which shows the cost reduction index | exponent of the preheated immersion nozzle.

Explanation of symbols

10: continuous casting equipment, 11: tundish, 12: immersion nozzle, 13: mold, 14: gripping device, 15: sliding nozzle, 16: pouring port, 17: discharge port, 18: Khao wool 19: consumable heater, 20: heat insulating material, 21: slag line part, 22: dummy bar

Claims (3)

A cylindrical immersion nozzle provided with a discharge port on the lower side and closed at the bottom is attached to the tundish of a continuous casting machine, and the immersion nozzle is placed in a mold, and the molten steel in the tundish is passed through the immersion nozzle. A continuous casting method of molten steel poured into the mold,
Before or after the immersion nozzle is preheated, or after the immersion nozzle is preheated , a heat insulating material is wrapped so as to cover the discharge port of the immersion nozzle, or a cap-shaped heat insulating material is provided so as to cover from the lower end of the immersion nozzle to the slag line portion. A method for continuous casting of molten steel, characterized in that the heat insulating material is melted and disappeared by the molten steel supplied to the submerged nozzle during use to prevent heat dissipation. 2. The molten steel continuous casting method according to claim 1, wherein a consumable heater is attached to the heat insulating material at least in a portion covering the discharge port. The continuous casting method for molten steel according to claim 2, wherein the consumable heater is an electric resistance wire, and the electric resistance wire is provided inside, inside, or outside the heat insulating material. A continuous casting method for molten steel.

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