JPH07284890A - Hot continuous operation of tundish for continuous casting - Google Patents

Abstract

PURPOSE:To smoothly discharge the remaining molten steel and the remaining molten steel slab in a tundish and to prevent the increase of inclusion in a cast slab even if this tundish is used in the following new casting. CONSTITUTION:After completing the casting of molten steel, the tundish is shifted to the discharging position of the remaining molten steel and the remaining molten steel slag. Then, just before starting tilting of the tundish, a shut-off valve of a non-oxidizing gas device 13 provided with an upper cover 12 is opened and the non-oxidizing gas is blown into the tundish 3 to make the inside of the tundish the non-oxidizing atmosphere, and the remaining molten steel and the remaining molten steel slag are discharged from a discharging hole 4. The flow rte of the non-oxidizing gas is made to be discharging quantity or more to the volumes of the remaining molten steel and the remaining molten steel slag. After discharging, a movable cover 5 is closed and the inside of the tundish in the tilting condition is held to the non-oxidizing gas atmosphere. Successively, the tundish is tilted, and after returning back to the normal state, a tundish car is shifted and positioned to above the mold and the new casting is started.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot continuous operation method for a tundish for continuous casting (hereinafter referred to as "tundish").

[0002]

2. Description of the Related Art In this type of tundish operating method, molten steel is generally poured into a tundish from a molten steel ladle, and while flowing through the tundish, the steel slag mixed with the molten steel is floated and separated, and is provided at the bottom of the tundish. Molten steel is injected into the mold through a molten steel injection dipping nozzle having an opening / closing device.

After closing the opening / closing device and completing the above casting,
The tundish is cooled to solidify the residual molten steel and the residual molten steel slag remaining in the tundish (these are collectively referred to as the residue, unless otherwise specified hereafter) and taken out of the system. Next, the refractory surface of the inner wall of the tundish is coated with a new refractory, for example, a spraying agent or mortar, which is then heated for the next casting.

In this way, after each casting, the residue remaining in the tundish is cooled and removed, and the inner wall is coated with a new refractory material. This is because when treating molten steel, there is a risk that steel and slag adhering to the inner wall and the like will mix with the molten steel and be cast in the mold, causing defects in inclusions. That is, the steel on the surface of the inner wall is oxidized by the atmosphere, and the steel slag is caught and causes defects of inclusions. Further, the refractory wall such as the spraying agent and the mortar in the tundish may melt and fail to withstand the next casting.

However, the process of repeating the cooling of the tundish, the removal of steel and steel slag, and the coating of a new refractory on the inner wall after each casting as described above is performed in terms of heat energy and the original refractory material. Problems are also included on a unit basis, and methods for solving these problems are being investigated.

[0006] For example, in Japanese Unexamined Patent Publication No. 1-107949, after the casting is completed, the tundish is tilted and a residue in the tundish is discharged from an outlet provided between the upper part of the tundish and the lid of the tundish. After discharging
A method of melting steel and slag adhering to the inside of the tundish with a preheating gas and oxygen gas, re-discharging from the discharge port, then waiting while preheating the inside of the tundish, and using this tundish for the next casting Is disclosed.

In Japanese Utility Model Laid-Open No. 5-9741 a tundish is tilted after casting of a starting charge, and the residue in the tundish is discharged from a discharge port provided at an upper edge of the tundish. In the continuous casting device for reusing the tundish, the tundish is provided with a lid, and the lid is provided with a gas injection means including a burner or tuyere, and the tundish is covered with the lid by the gas injection means. There is disclosed a continuous casting tundish in which an inert gas or a pressurized gas for cleaning is jetted toward a discharge port in a state and the discharge port can be cleaned from the inside of the tundish toward the outside. On the other hand, during the casting operation, only the inert gas is made to flow from the gas ejection means, and acts as a seal gas that makes the space between the molten steel and the tundish lid in the tundish an unoxidized atmosphere and as a gas for cooling the gas ejection means. I can do it.

[0008]

However, the above-mentioned JP-A-1-107949 and Japanese Utility Model Application Laid-Open No. 5-9741.
The technique disclosed in the publication has the following problems.

In the technique disclosed in Japanese Patent Application Laid-Open No. 1-107949, the heating amount must be a sufficient heating amount for the steel and the slag to reach their melting points. However, it is difficult to determine whether or not the amount of heat is sufficient, and in the case of insufficient heat, these steels and slags do not melt and remain in the tundish. Further, if the inner wall has irregularities due to melting or the like of the refractory of the tundish inner wall, even if all the steel and the steel slag are melted, they are not discharged and remain in the recesses.

In this case, the steel is iron oxide, and the iron content present in the steel slag is also in an oxidized state. Therefore, if the tundish is subjected to the next casting in this state, the oxidized steel or slag and the newly injected molten steel react with Al, Ti or other elements having a high oxygen affinity to cause Al ₂ O 3. Oxides such as ₃ and TiO ₂ are generated, and these are the origin of non-metallic inclusions in the molten steel.

In the technique disclosed in Japanese Utility Model Laid-Open No. 5-9741 O _{2 in the} tundish is discharged as the residue is discharged.
The gas or {O ₂ + CO} gas is filled. for that reason,
If the inner wall of the tundish is uneven due to melting of refractory, the steel and slag are not discharged, the remaining steel is oxidized and becomes iron oxide, and the iron content in the remaining slag is also oxidized. become. If the tundish is subjected to the next casting in this state, these become the origin of the non-metallic inclusions in the molten steel, as described above. In addition, since the discharge port is always open here, the inert gas and the like are diffused from the discharge port not only during casting but also during standby until the next casting, which is an economical problem.

The present invention is intended to solve the above-mentioned problems, and when the tundish for continuous casting is continuously hot-operated, the residue in the tundish is smoothly discharged and the tundish is smoothly discharged. Provides a hot continuous operation method for a continuous casting tundish that can prevent the increase of slab inclusions due to the steel and slag remaining in the tundish even when used for the next new casting of molten steel. The purpose is to

[0013]

The above object can be achieved by the following.

The present invention relates to a tundish hot continuous operation method in which a discharge port is provided at the upper edge and an immersion nozzle for injecting molten steel having an opening / closing device is provided at the bottom, and the tundish is provided with a gas blowing device. With a top lid,
The outlet is provided with a closing lid, and molten steel is injected into the tundish from a molten steel ladle, and after the molten steel is cast into the mold through the dipping nozzle, the openings other than the outlet are closed and non-oxidized in the tundish. A non-oxidizing gas is blown from the gas blowing device into a non-oxidizing gas atmosphere, and when the tundish is tilted to discharge the residue from the discharge port, the non-oxidizing gas is discharged at a flow rate higher than the discharge flow rate of the volume of the residue. Residue is discharged while blowing into the tundish, then the outlet is closed with the closing lid, the inside of the tundish is kept in a non-oxidizing gas atmosphere, and the tundish is restarted. It is a hot continuous operation method for tundish for continuous casting, which is characterized by receiving an order for molten steel from

[0015]

In the present invention, the tundish is moved to the residue discharge position by the tundish car after casting molten steel into the mold through the immersion nozzle. Therefore, the tundish is closed at openings other than the discharge port, and a non-oxidizing gas is blown into the tundish from a gas blowing device provided on the upper lid to create a non-oxidizing gas atmosphere. The tundish is tilted and the residue is drained.

During the discharge of the residue, it is necessary to make the charging flow rate of the non-oxidizing gas equal to or higher than the discharge flow rate of the volume of the residue. This is to prevent outside air from entering as much as the space created as a substitute for the residue in the tundish. The discharge flow rate (R) of the volume of the above residue is obtained by the equation (1).

[0017]

[Equation 1]

The charging flow rate of the non-oxidizing gas is set to be equal to or higher than the discharge flow rate of the volume of the residue calculated according to the above.

[0019]

EXAMPLES Examples of the present invention will be described in detail below. FIG. 1 is a diagram showing a state immediately after starting the tilting by moving the tundish to a residue discharge position after completion of casting of molten steel from the tundish to the mold in the present invention, and FIG. 2 is a tundish at the discharge position. FIG. 3 is a diagram showing a state in which the lid is tilted, and FIG. 3 is a diagram showing a state in which the blocking lid is closed after the residue is discharged and the tilting is still performed.

In the figure, 3 is a tundish, which is provided with a residue discharge port 4 having a closing lid 5 and a molten steel injection port 6 having an opening / closing device 7 for injecting molten steel into a mold. The tundish 3 is provided with a tilting device 19, and includes a support point 19a having a function as an action point and a hydraulic cylinder 19b for moving the support point 19a up and down.
Reference numeral 31 is an operating mechanism of the hydraulic cylinder 19b.

Further, the tundish 3 is provided with a shaft 29 having a function as a tilting shaft at the time of tilting on both side surfaces on the discharge port side and engaged with a bearing 30 of the tundish car. The tilting device is not limited to this, and a known device such as a wire rope or a trunnion can be used. Reference numeral 13 is a non-oxidizing gas blowing device, which is connected to a non-oxidizing gas pipe of a tundish car and blows non-oxidizing gas into the tundish 3 to create a non-oxidizing gas atmosphere.

In this embodiment, Ar gas was used as the non-oxidizing gas, but N ₂ or the like may be used. The discharge port 4 and the molten steel receiving port 15 are closed at the time when the molten steel injection from the molten steel ladle into the tundish is completed, and the temperature measurement / sampling port 16 is opened only when necessary for temperature measurement and sampling, and the others are always closed. There is.

In FIG. 1, the tundish 3 is provided with a molten steel receiving port 15 and a temperature measuring / sampling port 16 other than the discharge port 4 by driving pneumatic cylinders 14 and 14, respectively, to move the movable lid 1.
7 and 18 are moved and closed.

Next, the tundish 3 is tilted through a tilting device 19 provided outside the bottom of the tundish 3. Before starting tilting, the closing lid 5 is opened via the pneumatic cylinder 14a, the shutoff valve 20 of the non-oxidizing gas blowing device 13 provided on the upper lid 12 is opened, and the non-oxidizing gas is blown into the tundish 3. After that, tilting is started. The charging flow rate of the non-oxidizing gas is set to be equal to or higher than the discharge flow rate of the volume of the residue, and the discharge flow rate is obtained by the above-mentioned formula (1). 1a is residual molten steel and 1b is residual molten steel slag.

In FIG. 2, the residue is discharged from the discharge port 4 to the pan 26 by tilting the tundish 3. During discharge of the residue, the non-oxidizing gas is continuously blown into the tundish 3 from the non-oxidizing gas blowing device 13, and the non-oxidizing gas atmosphere is maintained in the tundish 3 during this period. The non-oxidizing gas continues to be fed in while the closing lid 5 is opened.

FIG. 3 is a view showing a state in which the movable lid 5 is closed by the pneumatic cylinder 14a after the residue is discharged by the tilting of the tundish 3, and the tilting is continued. After discharging the residue, the tundish 3 closes the discharge port 4 with a lid 5.
The tundish is kept in a non-oxidizing gas atmosphere.

Next, after returning the tundish to a normal state, the tundish car 21 is moved by the tundish moving device 28 and positioned on the mold. In the above-described operation, data is input to the control device 23, and the next step is accurately instructed based on the data, and the operation is performed.

FIG. 4 is a view showing a casting state in the tundish according to the present invention. In FIG. 4, reference numeral 2 denotes a molten steel pot provided with a molten steel injection port 10 having a long nozzle 11 for injecting the molten steel 1 into the tundish 3. Molten steel 1 from molten steel ladle 2 through long nozzle 11 tundish 3
Is injected into.

In the tundish 3, the molten steel 1 and the molten steel slag 1c are completely separated, the molten steel 1 is cast into the mold 9 through the immersion nozzle 8, and the slab 25 is pulled out from the mold 9. Reference numeral 24 is a guide roll.

Since the molten steel slag 1c floats on the molten steel 1 to form a layer in the tundish 3, a non-oxidizing gas atmosphere is not required in the tundish. Therefore, casting is performed in the atmosphere.

FIG. 5 is a flow chart showing an example of the present invention, and the procedure (step: SP) of the present invention will be described with reference to FIG.

In SP1, after the completion of discharging the residue, the tread of the tundish with all the openings closed is measured by the load cell 22 on the tundish car 21. This is used to weigh the residue in the tundish.

In SP2, the molten steel receiving port 15 is opened to inject the molten steel 1 from the molten steel ladle 2, and the long nozzle 11 is inserted into the tundish 3 from the molten steel receiving port 15.

In SP3, the molten steel ladle 2 to the long nozzle 11
The molten steel 1 is injected through the mold, and when the predetermined height is reached, the opening / closing device 7 is opened, the molten steel 1 is injected into the mold 9 through the immersion nozzle 8, and casting is started. When the casting is started, the blowing of the non-oxidizing gas into the tundish 3 is stopped.

At SP4, when the injection of the molten steel 1 from the molten steel ladle 2 is completed, the volume of the molten steel slag 1c floating above the molten steel 1 in the tundish 3 is determined (hereinafter, the residual molten steel slag 1
b)), the depth of the layer of the residual molten steel slag 1b is measured from the temperature measuring / sampling port 16, and the volume is obtained.

In SP5, the mold 9 from the tundish 3
The injection of the molten steel 1 into the container closes the switchgear 7, and ends.
In order to prevent the residual molten steel slag 1b from being mixed, a part of the molten steel is treated as the residual molten steel 1a in the tundish 3.

At SP6, the molten steel ladle 2 and the long nozzle 11 connected thereto are pulled up from the tundish 3.

At SP7, all openings are closed to prepare for blowing non-oxidizing gas. At SP8, the shutoff valve 20 of the non-oxidizing gas blowing device 13 is opened to blow the non-oxidizing gas into the tundish 3 to make the inside of the tundish 3 a non-oxidizing gas atmosphere. The confirmation of the non-oxidizing gas atmosphere is performed by detecting the gas in the vicinity of the inside of the exhaust port 4 and confirming the presence or absence of oxygen.

At SP9, the tundish 3 is moved by the tundish car 21 from the position above the mold 9 to the position for discharging the residue.

In SP10, the weight of the tundish 3 including the residue is measured by the load cell 22.

At SP11, the weight of the residue is calculated by the difference between the weight of the tundish measured at SP10 and the tare of the tundish at SP1, and the volume of the residual molten steel slag 1b measured at SP4 is used to calculate the residual molten steel 1a. The volume is calculated. From these values, the discharge flow rate of the volume of the residue is calculated by the above-mentioned formula (1).

At SP12, at the same time when the opening / closing lid 5 of the discharge port 4 is opened, a higher non-oxidizing gas charging flow rate is set from the calculated discharge flow rate of the residual volume at SP11.
It is loaded into the tundish.

At SP13, the tundish 3 is tilted by the tilting device 19. At SP14, the residue is discharged to the pan 26 according to SP13.

At SP15, the completion of the discharge of the residue to the pan 26 is visually confirmed after the elapse of a predetermined time with a 90 ° tilt, and the discharge is completed.

At SP16, the outlet 4 is closed by the closing lid 5. In SP17, a non-oxidizing gas is blown into the tundish 3 to maintain the inside of the tundish 3 in a non-oxidizing gas atmosphere.

At SP18, the tundish 3 is double rotated by the tilting device 19 to bring it into a normal state.

At SP19, the tundish car 21 is moved by the tundish moving device 28 to set the tundish 3 on the mold 9. These steps are precisely instructed by the control device 23 and are repeatedly executed.

The present invention will be specifically described. In the above method, the tundish was moved to the residue discharge position with a tundish car after the casting into the mold was completed. Here, it was confirmed that 1.2 tons of residual molten steel slag 1b and 3 tons of residual molten steel 1a remained at the end of casting.
Further, the tilt angular velocity ω = 0.5 rpm, and at this time θ _i = 30
Since we have confirmed that θ _e = 90 degrees,
From the equation (1), R = 0.0475 m ³ / sec is obtained. Therefore, Ar gas was charged at a flow rate of 0.05 m ³ / sec.
Table 1 shows the chemical composition ranges of the steels cast by the conventional method as a comparative example of the present embodiment and comparative examples, and Table 2 shows the casting conditions.

[0049]

[Table 1]

[0050]

[Table 2]

The degree of inclusions in the slab in the early stage of casting, which was cast by the continuous hot working method of the tundish according to the present invention, and the degree of inclusions in the slab in the early stage of casting, which was cast by the conventional method, were determined by the infrared absorption method. It was evaluated by measuring the total oxygen content. The result is shown in FIG.

In the conventional method, since the steel and the steel slag adhered to the inner wall of the tundish are oxidized, Al of the molten steel component at the initial stage of casting was oxidized and a large amount of inclusions were generated. It is considered that the total oxygen concentration in the steel increased. On the other hand, the slab according to the present invention does not show an increase in the total oxygen concentration in the steel at the initial stage of casting as seen in the conventional method,
A good slab with few inclusions was obtained.

[0053]

As described above, according to the present invention, when the tundish for continuous casting is continuously hot-operated, the residue in the tundish is smoothly discharged, and Even when it is used for casting molten steel in a mold, it is possible to prevent an increase in slab inclusions due to the residue.

[Brief description of drawings]

FIG. 1 is a diagram showing a state before discharge of a residual molten steel and a residual molten steel slag showing an embodiment of the present invention.

FIG. 2 is a diagram showing a state at the time of discharging a residual molten steel and a residual molten steel slag showing an embodiment of the present invention.

FIG. 3 is a diagram showing a state at the end of discharging the residual molten steel and the residual molten steel slag showing an embodiment of the present invention.

FIG. 4 is a diagram showing a cast state in a tundish according to the present invention.

FIG. 5 is a flowchart of the present invention.

FIG. 6 is a graph showing total oxygen (w) in steel of a slab according to an embodiment of the present invention.
It is a figure which shows the state of (t%) compared with the conventional method.

[Explanation of symbols]

 1 Molten Steel 1a Residual Molten Steel 1b Residual Molten Steel Slag 1c Molten Steel Slag 2 Molten Steel Pan 3 Tundish 4 Discharge Port 5 Closing Lid 6 Molten Steel Inlet 7 Opening / closing Device 8 Immersion Nozzle 9 Mold 10 Molten Steel Injecting Port 11 Long Nozzle 12 Upper Lid 15 Gas Injecting Device Molten Steel Ordering Port 16 Temperature Measuring / Sampling Port 17, 18 Movable Lid 19 Tilt Device 29 Tilt Shaft 30 Bearing

Claims (1)

[Claims] 1. A tundish hot continuous operation method in which a discharge port is provided at an upper edge portion and a molten steel injection dip nozzle having an opening / closing device is provided at a bottom portion, wherein the tundish is provided with a gas blowing device. In addition to providing a closing lid on the discharge port, after pouring molten steel into the tundish from a molten steel ladle and casting molten steel into a mold through a dipping nozzle, the tundish is closed by closing the openings other than the discharging port. A non-oxidizing gas is blown into the inside from the gas blowing device to form a non-oxidizing gas atmosphere, and when the tundish is tilted to discharge the residual molten steel and the residual molten steel slag from the discharge port, the residual molten steel and the residual molten steel slag are The residual molten steel and residual molten steel slag are discharged while blowing the non-oxidizing gas into the tundish at a flow rate higher than the volume discharge flow rate, and then the discharge port is closed with a closing lid, and the inside of the tundish is filled with the non-oxidizing gas atmosphere. A hot continuous operation method for a tundish for continuous casting, which is characterized by holding the atmosphere and returning to the tundish and receiving an order for molten steel from a new molten steel ladle.