KR101193850B1 - Method for detecting dropping alien substance of submerged entry nozzle and continuous casting method using the same - Google Patents

Method for detecting dropping alien substance of submerged entry nozzle and continuous casting method using the same Download PDF

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KR101193850B1
KR101193850B1 KR20100062405A KR20100062405A KR101193850B1 KR 101193850 B1 KR101193850 B1 KR 101193850B1 KR 20100062405 A KR20100062405 A KR 20100062405A KR 20100062405 A KR20100062405 A KR 20100062405A KR 101193850 B1 KR101193850 B1 KR 101193850B1
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South Korea
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height
immersion nozzle
blockage
index
blockage index
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KR20100062405A
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Korean (ko)
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KR20120001828A (en
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권효중
문홍길
장진수
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현대제철 주식회사
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Abstract

The present invention includes the steps of obtaining a first height of the stopper for the amount of molten steel discharged through the immersion nozzle in the steady state in the tundish; Acquiring a second height which is a height of a stopper for discharging the molten steel in the state in which the immersion nozzle is blocked; Obtaining a blockage index of the immersion nozzle using the first height and the second height; Obtaining a difference value obtained by subtracting the blockage index of the second time point from the blockage index of the first time point, wherein the first time point is earlier than the second time point; When the difference value is a positive real number greater than a predetermined value, it relates to a method for detecting inclusion dropout of the immersion nozzle, and a continuous casting method related thereto comprising the step of determining that the inclusion of the immersion nozzle has dropped.

Description

METHODS FOR DETECTING DROPPING ALIEN SUBSTANCE OF SUBMERGED ENTRY NOZZLE AND CONTINUOUS CASTING METHOD USING THE SAME}

The present invention relates to a method for detecting inclusion dropout of an immersion nozzle in a continuous casting and a continuous casting method relating thereto.

In general, a continuous casting machine is a facility for producing slabs of a constant size by receiving a molten steel produced in a steelmaking furnace and transferred to a ladle in a tundish and then supplying it as a mold for a continuous casting machine.

The continuous casting machine includes a ladle for storing molten steel, a continuous casting machine mold for cooling the tundish and the molten steel discharged from the tundish to form a casting having a predetermined shape, and a casting formed in the mold connected to the mold. It includes a plurality of pinch roller to move.

In other words, the molten steel tapping out of the ladle and tundish is formed of a slab (Slab) or bloom (Bloom), billet (Billet) having a predetermined width and thickness in the mold and is transferred through the pinch roller.

The present invention is to propose a method for increasing the productivity of continuous casting by detecting the dropping point of inclusions formed in the immersion nozzle in continuous casting.

In order to solve the above problems, an embodiment of the present invention, the inclusion drop detection method of the immersion nozzle, obtaining a first height of the stopper for the amount of molten steel discharged through the immersion nozzle in the steady state in the tundish; Acquiring a second height which is a height of a stopper for discharging the molten steel in the state in which the immersion nozzle is blocked; Using the first height and the second height, obtaining a blockage index of the immersion nozzle by the following formula; Obtaining a difference value obtained by subtracting the blockage index of the second time point detected after a predetermined time has elapsed from the blockage index of the first time point; And determining that the inclusion of the immersion nozzle is dropped if the difference is a positive number greater than a predetermined value, wherein the predetermined value may be 0.1 or more and 1.0.
[Equation 2]
C (blocking index) = 1-H 0 / H
H 0 : 1st height (mm)
H: 2nd height (mm)

According to an aspect of an embodiment of the present invention, the first height may be obtained by the following [Formula 1].

[Equation 1]

H 0 [mm] = discharge rate [ton / min] × a + b

H 0 is the first height, a is a constant set to 7.01 and b to 3.74.

delete

delete

delete

delete

delete

According to one embodiment of the present invention, the blockage index difference value can be obtained by the following [Equation 3].

[Formula 3]

Blockage Index Difference = Cl n -Min (Cl n +1 : Cl n +90 )

Cl n : Blockage index value at n seconds

Min (Cl n +1 : Cl n +90 ): Minimum blockage index between n + 1 and n + 90 seconds

n: seconds (sec)

Cl: blockage index

delete

In another embodiment of the present invention, a continuous casting method includes: obtaining a first blockage index indicating a degree of blockage at a first time point with respect to an immersion nozzle used in a continuous casting process; Obtaining a second blockage index indicating a degree of blockage of the immersion nozzle at a second time point, which is a set time point after the first time point; And if the difference value obtained by subtracting the second blockage index from the first blockage index is a positive number greater than a predetermined value, determining that the inclusions of the immersion nozzle have been dropped, and scarfing or downgrading the slab accordingly. The predetermined value is 0.1 or more and 1.0, and the first blockage index and the second blockage index can be obtained by the following equation.
[Equation 2]
C (blocking index) = 1-H 0 / H
H 0 : 1st height (mm)
H: 2nd height (mm)

delete

delete

According to one embodiment of the present invention, in the continuous casting, when the molten steel is discharged into the mold, it is possible to detect the dropping time of the inclusions formed in the immersion nozzle. At this time, the slab manufactured is able to prevent the process cost and defects that may occur due to the input into the post-process, it is possible to expect cost reduction and quality improvement effect.

1 is a side view showing a continuous casting machine according to an embodiment of the present invention.
Figure 2 is a conceptual diagram for explaining the continuous caster of Figure 1 centered on the flow of molten steel (M).
Figure 3 is a graph showing the relationship between the height of the stopper and the discharge amount of the molten steel in the steady state associated with one embodiment of the present invention.
Figure 4 is a graph showing the weight of the ladle, the weight of the tundish, the casting speed, the blockage index, and the blockage change rate ratio over time associated with one embodiment of the present invention.
5 is a flowchart illustrating a inclusion drop detection method of an immersion nozzle according to an embodiment of the present invention.
6 is a flowchart illustrating a continuous casting method using the inclusion drop detection method of the immersion nozzle according to an embodiment of the present invention.

Hereinafter, the inclusion drop detection method and the continuous casting method of the immersion nozzle according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the present specification, different embodiments are given the same or similar reference numerals for the same or similar configurations, and the description is replaced with the first description.

Continuous casting is a casting method in which a casting or steel ingot is continuously extracted while solidifying molten metal in a mold without a bottom. Continuous casting is used to manufacture simple products such as squares, rectangles, circles, and other simple cross-sections, and slab, bloom and billets, which are mainly for rolling.

The type of continuous casting machine is classified into vertical type, vertical bending type, vertical axis difference bending type, curved type and horizontal type. 1 and 2 illustrate a curved shape.

1 is a side view showing a continuous casting machine related to an embodiment of the present invention.

Referring to this drawing, the continuous casting machine may include a tundish 20, a mold 30, secondary cooling tables 60 and 65, a pinch roll 70, and a cutter 90.

The tundish 20 is a container that receives molten metal from the ladle 10 and supplies molten metal to the mold 30. Ladle 10 is provided in a pair, alternately receives molten steel to supply to the tundish 20. In the tundish 20, the molten metal supply rate is adjusted to the mold 30, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the non-metallic inclusions are separated.

The mold 30 is typically made of water-cooled copper and allows the molten steel to be primary cooled. The mold 30 forms a hollow portion in which molten steel is accommodated as a pair of structurally facing faces are opened. In manufacturing the slab, the mold 30 comprises a pair of barriers and a pair of end walls connecting the barriers. Here, the short wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated to move away from or close to each other to have a certain level of taper. This taper is set to compensate for shrinkage caused by solidification of the molten steel M in the mold 30. The degree of solidification of the molten steel (M) will vary depending on the carbon content, the type of powder (steel cold Vs slow cooling), casting speed and the like depending on the steel type.

The mold 30 has a strong solidification angle or solidifying shell 81 (see FIG. 2) so that the casting extracted from the mold 30 maintains its shape and does not leak molten metal which is still less solidified. It serves to form. The water cooling structure includes a method of using a copper pipe, a method of drilling a water cooling groove in the copper block, and a method of assembling a copper pipe having a water cooling groove.

The mold 30 is oscillated by the oscillator 40 to prevent the molten steel from sticking to the wall of the mold. Lubricants are used to reduce friction between the mold 30 and the casting during oscillation and to prevent burning. Lubricants include splattered flat oil and powder added to the molten metal surface in the mold 30. The powder is added to the molten metal in the mold 30 to become slag, as well as the lubrication of the mold 30 and the casting, as well as the oxidation and nitriding prevention and thermal insulation of the molten metal in the mold 30, and the non-metal inclusions on the surface of the molten metal. It also performs the function of absorption. In order to inject the powder into the mold 30, a powder feeder 50 is installed. The part for discharging the powder of the powder feeder 50 faces the inlet of the mold 30.

The secondary cooling zones 60 and 65 further cool the molten steel that has been primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spray 65 spraying water while maintaining the solidification angle by the support roll 60 so as not to deform. Casting solidification is mostly achieved by the secondary cooling.

The drawing device adopts a multidrive method using a plurality of sets of pinch rolls 70 and the like so that the casting can be taken out without slipping. The pinch roll 70 pulls the solidified tip of the molten steel in the casting direction, thereby allowing the molten steel passing through the mold 30 to continuously move in the casting direction.

The cutter 90 is formed to cut continuously produced castings to a constant size. As the cutter 90, a gas torch, a hydraulic shear, or the like can be employed.

FIG. 2 is a conceptual view illustrating the continuous casting machine of FIG. 1 based on the flow of molten steel M. Referring to FIG.

Referring to this figure, the molten steel (M) is to flow to the tundish 20 in the state accommodated in the ladle (10). For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends to be immersed in the molten steel in the tundish 20 so that the molten steel M is not exposed to air and oxidized and nitrided. The case where molten steel M is exposed to air due to breakage of shroud nozzle 15 is called open casting.

The molten steel M in the tundish 20 flows into the mold 30 by a submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed in the center of the mold 30 so that the flow of molten steel M discharged from both discharge ports of the immersion nozzle 25 can be symmetrical. The start, discharge speed, and stop of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 installed in the tundish 20 corresponding to the immersion nozzle 25. Specifically, the stopper 21 may be vertically moved along the same line as the immersion nozzle 25 to open and close the inlet of the immersion nozzle 25.

The molten steel M in the mold 30 starts to solidify from the part in contact with the wall surface of the mold 30. This is because heat is more likely to be lost by the mold 30 in which the periphery is cooled rather than the center of the molten steel M. The rear portion along the casting direction of the strand 80 is formed by the non-solidified molten steel 82 being wrapped around the solidified shell 81 in which the molten steel M is solidified by the method in which the peripheral portion first solidifies.

As the pinch roll 70 (FIG. 1) pulls the tip portion 83 of the fully solidified strand 80, the unsolidified molten steel 82 moves together with the solidified shell 81 in the casting direction. The uncondensed molten steel 82 is cooled by the spray 65 for spraying cooling water in the course of the above movement. This causes the thickness of the uncooled steel (82) in the strand (80) to gradually decrease. When the strand 80 reaches a point 85, the strand 80 is filled with the solidification shell 81 in its entire thickness. The solidified strand 80 is cut to a predetermined size at the cutting point 91 and divided into a product P such as a slab.

Here, when the height of the stopper 21 rises in the discharge of the molten steel M discharged from the tundish 20 to the mold 30, the discharge amount of the molten steel M is determined according to the rising degree. By the way, when molten steel is Ca untreated steel, the fused material, such as alumina, adheres to the inner wall of the immersion nozzle 25, and a clogging phenomenon arises in the immersion nozzle 25 by this adhesion. If clogging occurs in the immersion nozzle 25, in order to inject a certain amount of molten steel (M) into the mold 30, it is necessary to raise the height of the stopper 21.

By using this principle, the reference height of the stopper 21, that is, the discharge amount of the molten steel M discharged from the immersion nozzle 25 in the normal state and the actual height of the stopper 21 for discharging the reference amount of molten steel are determined. The degree of clogging of the immersion nozzle 25 can be estimated. The degree of blockage is defined as a blockage index, and this blockage index can be obtained by using the height of the stopper as described above. In addition, the blockage index may be obtained in consideration of the influence of the flow rate of argon gas Ar introduced into the immersion nozzle and the tundish residue.

In this detailed description, for the sake of simplicity, a method of obtaining a blockage index according to the stopper height will be described in detail with reference to FIG. 3. It is to be understood that the present invention is not limited thereto and that the blockage index of the immersion nozzle can be obtained by various methods as described above. That is, the blockage index may be obtained based on the amount of argon gas Ar introduced into the immersion nozzle.

Hereinafter, a method of obtaining the blockage index through the stopper height will be described in detail with reference to FIGS. 3 and 4.

3 is a graph of the discharge amount and the height of the stopper in the immersion nozzle in the steady state. The vertical axis is the height of the stopper (mm), and the horizontal axis is the discharge amount per minute (ton / min) of the molten steel (M). As shown, the height of the stopper 21 and the discharge amount of the molten steel have a relation of linear function, and the relation is as follows.

[Equation 1]

H 0 = Discharge amount × a + b

H 0 : Stopper height in steady state immersion nozzle (mm), a and b are constants, a is 7.01 and b is 3.74.

Discharge amount: ton / min

If nozzle clogging occurs under a constant molten steel discharge amount, the height of the stopper is raised to compensate for the decrease in the opening area of the immersion nozzle 25. In consideration of this phenomenon, the nozzle clogging index is determined by Equation 2.

[Equation 2]

Cl (blocking index) = 1-H 0 / H

H 0 : Height of the stopper in the normal immersion nozzle (mm)

H: Height of stopper in immersion nozzle in blocked state (mm)

The blockage index thus obtained is obtained over time, and the dropping point of the inclusions formed in the immersion nozzle can be detected through the distribution of the blockage index. That is, if the blockage index at the first time point and the blockage index at the second time point are obtained, and the difference value is a positive real number larger than a predetermined value, it is determined that the inclusions of the immersion nozzle are dropped. Here, the difference value may be obtained by Equation 3 below.

[Equation 3]

Blockage Index Difference = Cl n -Min (Cl n +1 : Cl n +90 )

Cl n : Blockage index value at n seconds (blockage index at the first time point)

Min (Cl n +1 : Cl n +90 ): The lowest blockage index between n + 1 and n + 90 seconds (blockage index at the second time point)

n: seconds (sec)

4 is a graph showing the weight of the ladle, the weight of the tundish, the casting speed, the blockage index, and the blockage change rate ratio over time.

In Fig. 4, reference numeral (a) denotes a line for the amount of molten steel of the ladle over time, reference numeral (b) denotes a line for the amount of molten steel of the tundish over time, and reference numeral (c) corresponds to the time It is a line about casting speed (that is, the meaning of discharge amount of molten steel), and (D) is a line about the blockage index with time.

As shown, the clogging index of the immersion nozzle generally rises over time. However, at some point A, the value of the blockage index rapidly decreases. This point is when the inclusion of the immersion nozzle is dropped. Therefore, it can be seen that after this point, the address speed returns to normal speed again (see line (c)).

5 is a flowchart illustrating a method for detecting inclusions of an immersion nozzle according to an embodiment of the present invention.

As shown, first, the first height of the stopper with respect to the amount of molten steel discharged through the immersion nozzle in the steady state in the tundish is obtained (S1). Since the first height acquisition has been described with reference to FIG. 3, description thereof will be omitted. Then, the continuous casting process is actually carried out to obtain a second height which is the height of the stopper for discharging the molten steel amount during the actual process, that is, the immersion nozzle is blocked (S3). Using the first height and the second height, the blockage index of the immersion nozzle is obtained by [Equation 2] (S5). Since the blockage index has been described above, detailed description thereof will be omitted. A difference value obtained by subtracting the blockage index at the second time point detected after a predetermined time has elapsed from the blockage index at the first time point is obtained. The first time point is earlier than the second time point (S7). If the difference is a positive real number larger than a predetermined value, it is determined that the inclusions of the immersion nozzle are dropped (S9). The predetermined value is 0.1 or more and 1.0 here. That is, as shown in Figure 4, even if there is no dropout of the inclusions, the difference value of the blockage index may be a positive real number at a fine value according to the discharge degree of the molten steel. In order to prevent such an error, the predetermined value is preferably 0.1 or more. In addition, the difference value may not be greater than 1.0. Therefore, the predetermined value is limited from 0.1 to 1.0.

According to one embodiment of the present invention having the above-described configuration, it is possible to detect the dropping point of the inclusions formed in the immersion nozzle. At this time, the slab manufactured is able to prevent the process cost and defects that may occur due to the input into the post-process, it is possible to expect cost reduction and quality improvement effect.

6 is a flowchart illustrating a continuous casting method using the inclusion drop detection method of the immersion nozzle according to an embodiment of the present invention.

As shown in FIG. 6, first, a first blockage index indicating a blockage degree at a first time point is obtained for the immersion nozzle used in the continuous casting process (S11). Next, a second blockage index indicating a degree of blockage of the immersion nozzle at a second point in time after the first point in time is obtained (S13). As described above, the blockage indices are represented by Equation 2 according to the height of the stopper. ] Or the amount of argon gas introduced into the immersion nozzle. When the difference value obtained by subtracting the second blockage index from the first blockage index is a positive real number larger than a predetermined value, it is determined that the inclusions in the immersion nozzle are dropped, and the slab is thus scarfed or downgraded. The predetermined value is 0.1 or more and 1.0 here. That is, as shown in Figure 4, even if there is no dropout of the inclusions, the difference value of the blockage index may be a positive real number at a fine value according to the discharge degree of the molten steel. In order to prevent such an error, the predetermined value is preferably 0.1 or more. In addition, the difference value may not be greater than 1.0. Therefore, the predetermined value may be set from 0.1 to 1.0. If the difference value obtained by subtracting the second blockage index from the first blockage index is less than or equal to the predetermined value, it is determined that dropouts do not occur and normal operation is maintained (S15).

According to one embodiment of the present invention, in the continuous casting, when the molten steel is discharged into the mold, the dropping point of the inclusions formed in the immersion nozzle is detected and, accordingly, the slab containing the inclusions is scarfed or down. By graded, process costs and defects can be prevented in advance, resulting in cost reduction and quality improvement.

10: ladle 15: shroud nozzle
20: tundish 25: immersion nozzle
30: mold 40: mold oscillator
50: powder feeder 51: powder layer
52: liquid fluidized bed 53: lubricating layer
60: support roll 65: spray
70: pinch roll 80: strand
81: solidified shell 82: unsolidified molten steel
83: tip 85: solidification completion point
87: oscillation mark 88: bulging area

Claims (8)

Obtaining a first height of the stopper for the amount of molten steel discharged through the immersion nozzle in a steady state in a tundish;
Acquiring a second height which is a height of a stopper for discharging the molten steel in the state in which the immersion nozzle is blocked;
Using the first height and the second height, obtaining a blockage index of the immersion nozzle by the following formula;
Obtaining a difference value obtained by subtracting the blockage index of the second time point detected after a predetermined time has elapsed from the blockage index of the first time point; And
And determining that the inclusions of the immersion nozzle are dropped if the difference value is a positive real number greater than a predetermined value, wherein the predetermined value is 0.1 or more to 1.0.
Equation
C (blocking index) = 1-H 0 / H
H 0 : 1st height (mm)
H: 2nd height (mm)
The method of claim 1,
And the first height is obtained by the following equation.
H 0 [mm] = discharge amount [ton / min] × a + b
H 0 is the first height, a is a constant set to 7.01 and b to 3.74.
delete The method of claim 1,
The clogging index difference value is obtained by the following equation, the inclusion drop detection method of the immersion nozzle.
Blockage Index Difference = Cl n -Min (Cl n + 1 : Cl n + 90 )
Cl n : Blockage index value at n seconds
Min (Cl n + 1 : Cl n + 90 ): Minimum blockage index between n + 1 and n + 90 seconds
n: seconds (sec).
Cl: blockage index
delete Obtaining a first blockage index indicating a degree of blockage at a first time point for the immersion nozzle used in the continuous casting process;
Obtaining a second blockage index indicating a degree of blockage of the immersion nozzle at a second time point, which is a set time point after the first time point; And
If the difference between the first blockage index minus the second blockage index is a positive real number larger than the predetermined value, the inclusion of the immersion nozzle is determined to fall off, and thus the step of scarfing or downgrading the slab accordingly, The predetermined value is 0.1 or more and 1.0, wherein the first blockage index and the second blockage index is obtained by the following formula.
Equation
C (blocking index) = 1-H 0 / H
H 0 : 1st height (mm)
H: 2nd height (mm)

delete delete
KR20100062405A 2010-06-30 2010-06-30 Method for detecting dropping alien substance of submerged entry nozzle and continuous casting method using the same KR101193850B1 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101505156B1 (en) * 2013-04-30 2015-03-23 현대제철 주식회사 Continuous casting method

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101400035B1 (en) * 2012-01-31 2014-06-27 현대제철 주식회사 Method for producing high quality slab
KR101400042B1 (en) * 2012-04-26 2014-05-30 현대제철 주식회사 Method for producing high quality slab

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6224848A (en) 1985-07-23 1987-02-02 Kawasaki Steel Corp Automatic stopping method for continuous casting machine

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6224848A (en) 1985-07-23 1987-02-02 Kawasaki Steel Corp Automatic stopping method for continuous casting machine

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101505156B1 (en) * 2013-04-30 2015-03-23 현대제철 주식회사 Continuous casting method

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