JP3693028B2 - Preheating device for tundish for continuous casting and its preheating method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a preheating of a continuous casting tundish, which is located between a transfer container and a casting mold of a continuous casting facility and preheats a continuous casting tundish having a role of a molten steel using a burner before casting. The present invention relates to an apparatus and a preheating method thereof.
[0002]
[Prior art]
In continuous casting of molten metal, a tundish as an intermediate container is provided between a molten metal transport container such as a ladle and a continuous casting mold so that a predetermined depth is provided in the tundish during casting. In general, casting is performed under stable conditions in a state where the molten metal is held.
[0003]
And when pouring high temperature molten metal into the tundish, the purpose is to minimize the temperature drop of the molten metal and prevent the occurrence of cracks due to the thermal expansion of the tundish-lined refractory that forms the inner wall of the tundish Therefore, preheating the tundish-lined refractory is performed. This is what is called tundish preheating.
[0004]
In the preheating of the tundish, in order to achieve the above-mentioned purpose, the tundish-lined refractory just before casting is usually set to about 1000 ° C. at its surface temperature. Preheating using a burner using fuel such as LPG or LPG is performed.
[0005]
[Problems to be solved by the invention]
By the way, in an actual continuous casting operation, the time from the start of preheating to the start of casting may not be as scheduled, and the preheating time may be changed halfway.
For example, when the upper process such as a refining process for preparing the molten metal to be cast is delayed by adjusting the component and temperature of the molten metal, the preheating of the tundish must be extended. In such a case, if the preheating is continued and extended as it is, the temperature of the tundish will rise too much, causing the problem of melting the quality improvement jig installed in the tundish. End up.
[0006]
In addition, when the preparation of tundish is delayed and the preheating start time is delayed from the schedule, it is necessary to perform preheating with an extremely increased burner heat load in order to meet the scheduled casting start time. In such a case, the same problem may occur. Here, the burner heat load is controlled by the fuel input speed to the burner.
On the other hand, in recent years, since it has become possible to increase the number of times of casting with the same tundish, there is room for preheating the new tundish. For this reason, it has become more important to save energy and reduce CO ₂ emissions by reducing the amount of fuel input throughout the preheating time rather than rapidly preheating the tundish in a short time. In addition, if the tundish is heated rapidly in a short time, the above-described problems also occur. However, conventional tundish preheating has not responded to such demands.
[0007]
Therefore, the present invention has been made in view of such a problem, and it is possible to keep the tundish temperature from rising excessively while continuously minimizing the amount of input fuel throughout the preheating time. An object of the present invention is to provide a preheating device for a casting tundish and a preheating method thereof.
[0008]
[Means for Solving the Problems]
In order to solve the above problem, a continuous casting tundish preheating apparatus according to claim 1 is a continuous casting in which a tundish lined refractory constituting an inner wall of a continuous casting tundish is preheated by a burner. The tundish preheating device includes a fuel input amount control means for controlling the amount of fuel input to the burner so that the cross-sectional average temperature of the tundish-lined refractory is in the range of 280 to 310 ° C. It is characterized by that.
[0009]
A continuous casting tundish preheating apparatus according to a second aspect of the invention is the continuous casting tundish preheating apparatus according to the first aspect of the invention, wherein the fuel input amount control means is responsive to a preheating time. And controlling so that the amount of fuel input to the burner is minimized.
A method for preheating a tundish for continuous casting according to a third aspect of the invention is a method for preheating a tundish for continuous casting in which a tundish-lined refractory constituting the inner wall of the tundish for continuous casting is preheated by a burner. The fuel input amount to the burner is adjusted so that the cross-sectional average temperature of the tundish-lined refractory is in the range of 280 to 310 ° C.
[0010]
A continuous casting tundish preheating method according to a fourth aspect of the present invention is the continuous casting tundish preheating method according to the third aspect of the present invention, wherein fuel is input to the burner according to the preheating time. The amount is adjusted to the minimum.
Here, when the molten metal is poured into the tundish for continuous casting, the temperature of the molten metal drops due to the heat being taken away by the tundish-lined refractory. When the temperature drop of the molten metal becomes large, the molten metal flowing out from the tundish for continuous casting may fall below the temperature of the molten metal required in the mold. That is, when the initial temperature of the tundish-lined refractory is lower than a predetermined temperature, the molten metal flowing out of the tundish falls below the temperature of the molten metal required in the mold due to the temperature drop. For this reason, in the inventions according to claims 1 and 3, the lower limit of the predetermined temperature is 280 ° C.
[0011]
Further, if the tundish-lined refractory exceeds a predetermined temperature during preheating, the jig provided in the continuous casting tundish will be damaged. For this reason, in the first and third aspects of the invention, the upper limit of the predetermined temperature is set to 310 ° C.
And in invention of Claim 1 and 3, it implement | achieves by controlling the injection | throwing-in amount of the fuel to a burner so that the cross-sectional average temperature of a tundish lining refractory may become the range of 280-310 degreeC. . Here, the cross-sectional average temperature is, for example, a temperature obtained by averaging temperatures in the cross-sectional direction of the tundish-lined refractory.
[0012]
Further, in the inventions according to claims 2 and 4, while controlling the preheated tundish-lined refractory so as to have a predetermined temperature, the fuel is supplied to the burner which is the basis of the control. The amount is made variable according to the preheating time so as to be minimum.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a tundish equipped with a tundish preheating control device of the present invention.
A tundish (tundish for continuous casting) 10 has a structure in which a tundish main body 13 in which a tundish-lined refractory 12 is lined on the inner surface of an iron skin 11 is covered with a lid 14. Further, the tundish 10 is provided with an upper nozzle 15 at the bottom of the tundish main body 13, and a sliding nozzle 16 is disposed below the upper nozzle 15.
[0014]
The tundish preheating device 20 is equipped with a burner 21, a flow rate adjusting unit 22 and a control device 23 as a tundish preheating control device. And when preheating the tundish 10, the preheating burner 21 is arrange | positioned facing the opening part 17 provided in the lid | cover 14. As shown in FIG. Here, the preheating burner 21 is supplied with fuel through a flow rate adjusting unit 22, and the flow rate adjusting unit 22 is controlled by a control device 23 in the amount of fuel supply or fuel input.
[0015]
For example, the flow control unit 22 is, for example, a flow control valve, and the control device 23 controls the fuel supply rate or the fuel input amount by adjusting the opening degree of the flow control valve and controlling the fuel supply speed. ing.
Here, the amount of fuel input refers to the total amount of fuel input within the preheating time. Further, the flow rate control unit 22 and the control device 23 constitute fuel input amount control means for controlling the amount of fuel input to the preheating burner 21 so that the cross-sectional average temperature of the tundish lining refractory 12 becomes a predetermined temperature. ing.
[0016]
In such a configuration, the tundish preheating control device controls the fuel supplied or supplied to the preheating burner 21 by adjusting the flow rate adjusting unit 22 by the control device 23, and the tundish lining refractory by the preheating burner 21. 12 is heated.
The control by the control device 23 is performed such that the fuel input amount is minimized while the cross-sectional average temperature of the tundish-lined refractory 12 is set to a predetermined temperature. Here, the reason why the average cross-sectional temperature is used is that the average cross-sectional temperature is an indicator of the heat capacity of the tundish-lined refractory 12, and the tundish lining after the temperature drop when molten metal is poured. This is because the temperature of the refractory 12 varies depending on the cross-sectional average temperature. The cross-sectional average temperature is a temperature obtained by averaging the temperatures in the cross-sectional direction of the tundish-lined refractory 12.
[0017]
Specifically, the control device 23 realizes the control by adjusting the flow rate adjusting unit 22 (or the burner heat load) according to the preheating time. Here, the predetermined temperature is 280 ° C. to 310 ° C., and this temperature range is determined for the following reason.
The lower limit temperature is set to 280 ° C. for the following reason.
[0018]
First, the cross-sectional average temperature of the tundish-lined refractory 12 is obtained by calculation, and when the molten metal is poured into the tundish 10 from the state where the cross-sectional average temperature is at a certain temperature, the tundish-lined lining is formed from the molten metal. The amount of heat lost to the refractory 12 was calculated, and the temperature drop of the molten metal was estimated.
On the other hand, in order to judge whether or not the temperature drop of the molten steel in the tundish 10 is acceptable, the temperature in the ladle is assumed to be 1580 ° C. assuming normal operation using molten steel as the molten metal. Conditions were set on the assumption that when the molten steel temperature required in the mold was 1520 ° C to 1540 ° C, the operation was possible without any obstacles.
[0019]
In determining whether or not the temperature drop of the molten steel in the tundish 10 is acceptable, a result that the molten steel temperature drop becomes large when the cross-sectional average temperature of the tundish-lined refractory 12 is less than 280 ° C. is obtained. It was found that the temperature of the molten steel flowing out from the steel was lower than the temperature required in the mold. That is, when the cross-sectional average temperature of the tundish-lined refractory 12 is less than 280 ° C., when molten steel having a temperature in the ladle of 1580 ° C. to 1600 ° C. is poured into the tundish 10, the molten steel temperature required in the mold Was 1520 ° C to 1540 ° C, whereas the temperature of the molten steel was found to be lower than that temperature.
[0020]
If casting is performed at such an average cross-sectional temperature, the tundish nozzle (upper nozzle 15) for supplying molten steel from the tundish 10 into the mold, the sliding nozzle 16 connected below it, or the immersion nozzle, etc. As a result, the molten steel is solidified and casting becomes impossible.
Therefore, in order to avoid such a situation, the cross-sectional average temperature of the tundish-lined refractory 12 is set to 280 ° C. or higher.
[0021]
On the other hand, the upper limit temperature is set to 310 ° C. for the following reason.
When the cross-sectional average temperature of the tundish-lined refractory 12 exceeds 310 ° C., the atmosphere temperature in the tundish 10 becomes extremely high, and a jig provided in the tundish 10, for example, a tundish stopper, has a high temperature. The possibility of erosion or welding with the tundish nozzle increases. Here, the tundish stopper is used to prevent the molten steel from entering and solidifying into the tundish nozzle until a predetermined amount of molten steel is accumulated after the molten steel is supplied from the ladle into the tundish 10. This device closes the tundish nozzle.
[0022]
Thus, in order to prevent the jig provided in the tundish 10 from being damaged, the cross-sectional average temperature of the tundish-lined refractory 12 is set to 310 ° C. or lower.
For the reasons described above, the cross-sectional average temperature of the tundish-lined refractory 12 is set to 280 ° C to 310 ° C.
[0023]
And the control apparatus 23 is controlling so that the fuel injection amount to the preheating burner 21 used for the preheating may become the minimum, maintaining such a predetermined temperature range within preheating time. Specifically, the control device 23 performs the control using a characteristic table (or table).
The characteristic table is obtained, for example, by heat transfer calculation. For example, as shown in FIG. 2, the fuel input amount to the preheating burner 21 (total input amount) with the burner heat load as a parameter (solid line in the figure) is shown. ) And the average refractory cross-sectional temperature, which is the cross-sectional average temperature of the tundish-lined refractory 12 at the end of preheating, as the average burner heat load (35%, 42%, 47%, 60% in the figure) It is the characteristic table | surface which can be obtained when changing. FIG. 2 is obtained by calculation for various cases in which the amount of input fuel is changed based on the current preheating pattern. Here, the average burner heat load means a heat load obtained by averaging all burners when preheating is performed using a plurality of burners as in the illustrated example. Moreover, the amount of input fuel based on the current preheating pattern is a relative value described as the average burner heat load in the figure.
[0024]
According to FIG. 2, if the preheating time (broken line in the figure) and the average burner heat load (solid line in the figure) are determined, the cross-sectional average temperature of the tundish-lined refractory 12 and the case as the intersection are The required fuel input can be obtained. As an example, when the burner heat load is 42% and the preheating time is 120 minutes, the cross-sectional average temperature of the tundish-lined refractory 12 is about 300 ° C., and the fuel input at that time is 735 Nm ^3. become.
[0025]
The control device 23 uses the relationship shown in FIG. 2 to select an average burner heat load at which the intersection with the preheating time is in the temperature range of 280 to 310 ° C. and the fuel input amount is minimized. The flow rate adjusting unit 22 is adjusted so that the selected average burner heat load is selected, and the flow rate of the fuel supplied to the preheating burner 21 (specifically, the fuel supply speed) is adjusted.
[0026]
For example, taking the relationship shown in FIG. 2 as an example, when the preheating time is 110 minutes, the average burner heat load is 42% and 47% in the range of 280 to 310 ° C. In this case, the fuel input amount is smaller when the average burner heat load is 42%. In such a case, the control device 23 adjusts the flow rate adjusting unit 22 so that the average burner heat load is 42%. And adjust the fuel flow rate.
[0027]
Further, when the preheating time needs to be changed during the preheating of the tundish 10, the control device 23 determines that the cross-sectional average temperature of the tundish lining refractory 12 is in accordance with the preheating time. Control is performed so that the amount of fuel input is minimized while maintaining a predetermined temperature.
There are two cases where it is necessary to change the preheating time, in which case it is necessary to complete the preheating in a shorter time than scheduled and in which case it is necessary to extend the preheating.
[0028]
First, a case where preheating must be completed in a shorter time than planned will be described. Here, when preheating must be completed in a shorter time than planned, the upper process such as a refining process for preparing the molten metal to be cast by adjusting the components and temperature of the molten metal is accelerated. Is mentioned.
In this way, if the preheating must be completed in a shorter time than planned, after the necessity of changing the preheating time becomes clear, the tundish 10 must be heated at a higher heating rate than planned. No longer. In this case, of course, it is necessary to increase the average burner heat load.
[0029]
Even in such a case, the control device 12 sets the average burner heat load so that the cross-sectional average temperature of the tundish-lined refractory 12 satisfies the range of 280 ° C. to 310 ° C. and becomes the minimum fuel input amount. Yes. For example, there is an option of increasing the average burner heat load from 42% to 60% or 100%. In such a case, the cross section of the tundish-lined refractory 12 is used. The average burner heat load is such that the average temperature satisfies the range of 280 ° C. to 310 ° C. and the minimum fuel input amount.
[0030]
Here, for example, FIG. 2 shows the relationship between the average burner heat load, the refractory cross-sectional average temperature, and the preheating time. Based on FIG. 2, the relationship between the preheating time and the refractory average temperature is shown. Consider FIG. 3, which is shown with attention. In FIG. 3, the inclination indicates the rate of heat increase. For example, as described above, when the preheating time is changed, the average burner heat that falls within the range of the refractory cross-sectional average temperature of 280 to 310 ° C. within the allowable preheating time using the relationship shown in FIG. Load.
[0031]
Further, since the refractory cross-sectional average temperature has an allowable range of 30 ° C. as described above, the average burner heat load also has an allowable range. Therefore, also in this case, which average burner heat load is selected is set to the average burner heat load that minimizes the fuel input amount using the relationship shown in FIG.
On the other hand, a case opposite to the above-described case, that is, a case where preheating has to be extended due to a delay in processing of the upper process will be described.
[0032]
In this case, after the necessity of changing the preheating time becomes clear, there is no problem even if the tundish 10 is heated at a heating rate slower than planned, so that the average burner heat load can be reduced. Become. Also in this case, the average burner heat load satisfying the range of the average cross-sectional temperature of the tundish-lined refractory 12 during preheating as a constraint condition is 280 to 310 ° C.
[0033]
For example, using the relationship shown in FIG. 3, the average burner heat load that falls within the range of the refractory cross-sectional average temperature of 280 to 310 ° C. within the allowable preheating time is set in the same manner as described above. Also in this case, the average burner heat load that minimizes the fuel input amount is set using the relationship shown in FIG.
The tundish preheating control apparatus having the above-described configuration maintains the predetermined temperature range (280 ° C. to 310 ° C.) of the refractory cross-sectional average temperature within the preheating time, and the amount of fuel input to the preheating burner 21. Is preheated so that the tundish-lined refractory 12 is minimized. Further, the tundish preheating control device realizes preheating under the same restrictions according to the preheating time even when the preheating time is changed.
[0034]
As a result, the tundish preheating control device prevents the temperature of the tundish 10 from rising too much and melts the jig installed in the tundish 10 for quality improvement, and further preheats. By reducing the amount of fuel input throughout the entire time, energy savings and CO ₂ emissions have been reduced. Further, even when the preheating time is changed, the tundish preheating control device can obtain such an effect.
[0035]
In the above-described embodiment, the case of controlling using FIG. 2 and FIG. 3 has been described, but it is needless to say that the present invention is not limited to this. Control may be performed using another relationship or a characteristic table, or a necessary value may be obtained by calculation in real time, and control may be performed based on the value.
[0036]
【Example】
The case where the present invention is applied to the preheating of a tundish having a molten steel holding capacity of 75 tons will be described in comparison with the conventional technique. The tundish was preheated with a burner using C gas (coke oven gas (4300 kcal / Nm ³ )) as fuel.
[0037]
(In the case of conventional technology)
The tundish was preheated uniformly on the basis of a preheating standard where the standard preheating time for tundish was 120 minutes and the burner heat load was 45%.
Preheating was completed within the standard preheating time of 120 minutes ± 10 minutes out of 500 heat preheating, and the heat that could start casting was 485 heat, and preheating had to be completed in a time shorter than 10 minutes from the standard. Heat was 6 heat (heat with insufficient preheating time), and heat that had to be preheated for 10 minutes or longer than the standard was 9 heat (preheat extended heat).
[0038]
The result was that solidification of the molten steel occurred in the immersion nozzle in 2 heats out of the preheating time shortage heat. As a result, casting had to be stopped. Moreover, the result was that the stopper in the tundish and the tundish nozzle were welded in 3 heats of the preheating extension heat. As a result, the opening cannot be made by the stopper at the start of casting, and casting has to be stopped. In addition, the average amount of fuel input in all heats was 880 Nm ³ .
[0039]
(In the case of the present invention)
Preheating was performed using a standard preheating time of 130 minutes and a burner heat load of 35% so that the average cross-sectional temperature of the tundish-lined refractory was within a range of 280 to 310 ° C. during preheating.
Of the 400 heat preheating, the preheating was completed within the standard preheating time of 130 minutes ± 10 minutes, and the heat that was able to start casting was 388 heat, and the preheating had to be completed in a time shorter than the standard by 10 minutes or more. The heat was 4 heat (heat with insufficient preheating time), and the heat that had to be preheated for 10 minutes or longer than the standard was 8 heat (preheat extended heat).
[0040]
In the heat which changed the preheating time in the middle, the average burner heat load was changed in that case. The average burner heat load to be changed was determined using the relationship shown in FIGS. 1 and 2 so that the refractory cross-sectional average temperature was within the range of 280 to 310 ° C. and the amount of fuel input was minimized.
As a result, it was obtained that solidification of molten steel in the immersion nozzle and welding of the stopper and the tundish nozzle did not occur. Further, the amount of fuel input in all heats was 610 Nm ³ on average.
[0041]
As is apparent from the results of this embodiment, according to the present invention, the temperature of the tundish is excessively increased and the jig in the tundish is not melted, and the input fuel is further reduced throughout the preheating time. be able to.
[0042]
【The invention's effect】
As described above, according to the first and third aspects of the invention, the amount of fuel input to the burner is controlled so that the cross-sectional average temperature of the tundish-lined refractory is in the range of 280 to 310 ° C. This prevents the molten metal from flowing into the tundish from dropping below the temperature of the molten steel required in the mold, and the jig provided in the tundish for continuous casting with the molten metal. It can be prevented from being damaged, and the input fuel can be reduced throughout the preheating time.
[0043]
Further, according to the invention described in claims 2 and 4, the amount of fuel input to the burner which is the basis of the control while controlling the preheated tundish-lined refractory to a predetermined temperature. Therefore, even if the preheating time is changed in the middle, the same effects as those of the inventions of claims 1 and 3 can be obtained. it can.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a tundish preheating apparatus according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the relationship between the amount of fuel input and the average refractory cross-sectional temperature, with the average burner heat load as a parameter.
FIG. 3 is a characteristic diagram showing the relationship between the preheating time and the refractory cross-sectional average temperature, with the average burner heat load as a parameter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Tundish 11 Iron skin 12 Tundish lining refractory 13 Tundish main body 14 Lid | cover 15 Upper nozzle 16 Sliding nozzle 17 Opening part 20 Tundish preheating apparatus 21 Preheating burner 22 Flow control part 23 Control apparatus

Claims (4)

In the preheating device for the continuous casting tundish, the tundish lined refractory constituting the inner wall of the continuous casting tundish is preheated by a burner.
For continuous casting, comprising fuel input amount control means for controlling the amount of fuel input to the burner so that the cross-sectional average temperature of the tundish-lined refractory is in the range of 280 to 310 ° C. Tundish preheater. The preheating device for a continuous casting tundish according to claim 1, wherein the fuel input amount control means controls the amount of fuel input to the burner to a minimum according to a preheating time. In the preheating method of the tundish for continuous casting in which the tundish lining refractory constituting the inner wall of the tundish for continuous casting is preheated by a burner,
A method for preheating a tundish for continuous casting, characterized in that an amount of fuel input to the burner is adjusted so that a cross-sectional average temperature of the tundish-lined refractory is in a range of 280 to 310 ° C. 4. The method for preheating a continuous casting tundish according to claim 3, wherein the amount of fuel input to the burner is adjusted to a minimum according to the preheating time.

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