KR101277707B1 - Method for decreasing pin-hole defect in continuous casting process - Google Patents

Abstract

The present invention relates to a method for reducing pinhole defects in the playing process that predicts pinhole defects according to operating factors in the playing process to reduce pinhole defects. The method includes a plurality of operations including casting width, molten steel injection, immersion depth of the immersion nozzle, and argon gas injection. Storing the data on the printing factor, and calculating a collision depth from the hot water surface to a point when molten steel discharged from the immersion nozzle collides with the inner wall of the mold by using the plurality of operating factors stored above; Comparing the collision depth calculated from the set reference depth with each other, and determining whether the collision depth is more than the set reference depth, and if the collision depth is more than the set reference depth, the casting width currently casting to reduce the pinhole defect At least one of the immersion depth of the immersion nozzle and the amount of argon gas injected through the immersion nozzle Variable controlling one or more.

Description

METHOOD FOR DECREASING PIN-HOLE DEFECT IN CONTINUOUS CASTING PROCESS}

The present invention relates to pinhole defect reduction, and more particularly, to a pinhole defect reduction method in a playing process for predicting the pinhole defect level according to an operation factor in the playing process to reduce the pinhole defect.

In general, a continuous casting machine is a facility for producing cast steel of a certain size by receiving a molten steel produced in a steelmaking furnace and transferred to a ladle (Tundish) and then supplied to a continuous casting machine mold.

The continuous casting machine includes a ladle for storing molten steel, a playing mold for cooling the tundish and the molten steel discharged from the tundish for the first time to form a casting cast having a predetermined shape, and the casting cast formed in the mold connected to the mold. And a plurality of pinch rolls. The molten steel tapping out of the ladle and tundish is formed into a cast piece having a predetermined width, thickness and shape in a mold and is transferred through a pinch roll, and the cast piece transferred through the pinch roll is cut by a cutter to have a predetermined shape. It is made of slabs or slabs such as Bloom and Billet.

An object of the present invention is to calculate the crash depth in the mold using a variety of operating factors, including casting width, molten steel injection amount, dipping depth of the immersion nozzle and argon gas injection amount, and predict the pinhole defects through the calculated collision depth to determine the collision depth The present invention relates to a method for reducing pinhole defects in a playing process that can reduce the degree of occurrence of pinhole defects.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above.

Pinhole defect reduction method of the present invention for realizing the above object, the step of storing data for various operating factors including the casting width, molten steel injection amount, the immersion depth of the immersion nozzle and the argon gas injection amount; Calculating the depth of impact from the hot water surface to the point when molten steel discharged from the immersion nozzle collides with the mold inner wall using the various operation factors stored above; Comparing the collision depth calculated above with the set reference depth and determining whether the collision depth is greater than or equal to the set reference depth; And if the collision depth is greater than or equal to a predetermined reference depth, variably controlling at least one of the immersion depth of the immersion nozzle and the amount of argon gas injected through the immersion nozzle according to the casting width currently being cast to reduce pinhole defects. It may include.

The variable control may include determining whether a casting width currently being cast is greater than or equal to a predetermined reference width when the collision depth is equal to or greater than a predetermined reference depth; And determining that the casting width is less than the set reference width, so that the immersion depth of the immersion nozzle is reduced or the amount of argon gas injection through the immersion nozzle is increased.

The variable control may include determining whether a casting width currently being cast is greater than or equal to a predetermined reference width when the collision depth is equal to or greater than a predetermined reference depth; And when the casting width is greater than or equal to the set reference width, the immersion depth of the immersion nozzle may be controlled and the amount of argon gas injected through the immersion nozzle may be increased.

The set reference depth may be 550 mm.

According to the present invention as described above, pinhole defects of the cast pieces by determining the degree of pinhole defects through the impact depth, and controlling the collision depth through the immersion depth of the immersion nozzle and the argon gas injection amount when the pinhole defects exceeds the reference value It is possible to manufacture a product having excellent surface quality by reducing the.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.
2 is a view showing a pinhole defect reducing apparatus according to the present invention.
3 is a view showing argon gas supplied to a mold through an immersion nozzle.
4 is a diagram illustrating a pinhole defect for each steel type.
5 is a view showing the immersion depth of the immersion nozzle according to the height of the tundish.
6 is a view showing the relationship between the pinhole defect index and the depth of impact by casting width.
7 is a flowchart illustrating a process of reducing pinhole defects according to an embodiment of the present invention.
8 is a view showing various operating factors for the calculation of the collision depth.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements in the figures are denoted by the same reference numerals wherever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a conceptual diagram showing a continuous casting machine according to an embodiment of the present invention mainly on the flow of molten steel.

Continuous casting is a casting process in which a molten metal is continuously cast into a bottomless mold while continuously drawing a steel ingot or steel ingot. Continuous casting is used to manufacture slabs, blooms and billets, which are mainly rolled materials, and long products of simple cross-section such as square, rectangle, and circle.

The shape of a continuous casting machine is classified into a vertical type and a vertical bending type. In Fig. 1, a vertical bending type is illustrated.

1, the continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, a secondary cooling stand 60 and 65, a pinch roll 70, and a cutter 90 have.

The tundish 20 is a container that receives the molten metal from the ladle 10 and supplies the molten metal to the mold 30. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic 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 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. In the case of manufacturing the slab, the mold 30 includes a pair of barriers and a pair of end walls connecting the barriers. Here, the end wall has a smaller area than the barrier. The walls of the mold 30, mainly short walls, may be rotated away from or close to each other to have a certain level of taper. This taper is set to compensate for the shrinkage due to the 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 is formed such that a solidified shell or a solidified shell 81 is formed so as to maintain the shape of the casting pluck pulled out from the mold 30 and to prevent the molten metal from being hardly outflowed from flowing out. . The water-cooling structure includes a method using a copper tube, a method of water-cooling the copper block, and a method of assembling a copper tube 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. Lubricant is used to reduce friction between the mold 30 and the solidification shell 81 and prevent burning during oscillation. As the lubricant, there is oil to be sprayed 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 and the lubrication of the mold 30 and the solidification shell 81 as well as the prevention of oxidation and oxidation of molten metal in the mold 30, It also functions to absorb the emerging nonmetallic inclusions. A powder feeder 50 is installed to feed the powder into the mold 30. The portion of the powder feeder 50 for discharging the powder is directed to the inlet of the mold 30.

The secondary cooling zones 60 and 65 further cool the molten steel primarily cooled in the mold 30. The primary cooled molten steel is directly cooled by the spraying means 65 for spraying water while being maintained by the support roll 60 so that the coagulation angle is not deformed. The solidification of the cast steel is mostly made by the secondary cooling.

The drawing device adopts a multidrive method using a pair of pinch rolls 70 and the like so as to pull out the cast pieces 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 continuous casting machine configured as described above allows the molten steel M accommodated in the ladle 10 to flow into the tundish 20. For this flow, the ladle 10 is provided with a shroud nozzle 15 extending toward the tundish 20. The shroud nozzle 15 extends into the molten steel in the tundish 20 so that the molten steel M is not exposed to the air to be oxidized and nitrided.

The molten steel M in the tundish 20 is caused to flow into the mold 30 by the submerged entry nozzle 25 extending into the mold 30. The immersion nozzle 25 is disposed at the center of the mold 30 so that the flow of the molten steel M discharged from both the discharge ports of the immersion nozzle 25 can be made symmetrical. The start, the discharge speed and the interruption of the discharge of the molten steel M through the immersion nozzle 25 are determined by a stopper 21 provided on the tundish 20 in correspondence with the immersion nozzle 25. Specifically, the stopper 21 can be vertically moved along the same line as that of the immersion nozzle 25 so as to open and close the inlet of the immersion nozzle 25. The control of the flow of the molten steel M through the immersion nozzle 25 may use a slide gate method different from the stopper method. The slide gate controls the discharge flow rate of the molten steel (M) through the immersion nozzle (25) while the plate material slides horizontally in the tundish (20).

Molten steel (M) in the mold (30) starts to solidify from a portion in contact with the wall surface of the mold (30). This is because the periphery of the molten steel M is liable to lose heat by the water-cooled mold 30. The rear portion along the casting direction of the cast slab 80 is formed into a shape in which the non-solidified molten steel 82 is wrapped in the solidifying shell 81 by the method in which the peripheral portion first coagulates.

As the pinch roll 70 (FIG. 1) pulls the tip portion 83 of the completely cast solid cast piece 80, the unsolidified molten steel 82 moves together with the solidified shell 81 in the casting direction. The non-solidified molten steel (82) is cooled by the spraying means (65) for spraying the cooling water in the up-shifting process. This causes the thickness of the non-solidified molten steel (82) to gradually decrease in the cast steel (80). When the cast steel 80 reaches one point 85, the cast steel 80 is filled with the solidification shell 81 of the entire thickness. The solidification casting 80 having been solidified is cut to a predetermined size at the cutting point 91 and is divided into a slab P such as a slab or the like.

2 is a view showing a pinhole defect reduction apparatus in the playing process according to an embodiment of the present invention, the pinhole defect reduction apparatus 100 is a memory 110, input unit 120, display unit 130, height adjusting unit ( 140, an argon injection unit 150, and a controller 160.

The memory 110 stores data on various operating factors including casting width, molten steel injection amount, immersion depth of the immersion nozzle 25, and argon gas injection amount. Herein, the operation factors may include not only casting width, molten steel injection amount, immersion depth of the immersion nozzle, and argon gas injection amount, but also the diameter of the discharge port 26 of the immersion nozzle 25 and the discharge angle of the immersion nozzle 25 and the discharge angle of the molten steel. It may further include data.

The input unit 120 is configured to receive data on various operation factors from the outside.

The display unit 130 may display the collision depth calculated according to the control of the controller 160 and the predicted pinhole defect degree according to a character or a graph. Of course, the memory 110 may store data on the degree of pinhole defects corresponding to the depth of collision.

The height adjusting unit 140 may be configured by a hydraulic cylinder that is operated under the control of the controller 160 to move the tundish 20 up and down, thereby adjusting the immersion depth of the immersion nozzle 25. The height of the tundish 20 is indirectly checking the immersion depth of the immersion nozzle 25 through the height of the tundish 20 at the interval between the top surface of the mold 30 and the bottom surface of the tundish 20. It is possible.

The argon injection unit 150 is operated under the control of the controller 160 to adjust the amount of argon gas injected into the immersion nozzle 25. Non-metallic inclusions exist in the molten steel temporarily stored in the tundish 20, so that when the molten steel is transferred to the mold, the non-metallic inclusions adhere to the refractory inner wall of the immersion nozzle 25, thereby preventing casting. do.

In order to prevent such clogging, Argon gas, which is an inert gas, is continuously injected as shown in FIG. 3. The blown argon gas forms a bubble or a bubble film to flow along the inner wall of the immersion nozzle 25 or bubbles to collect and move non-metallic inclusions to reduce clogging. However, since the amount of argon gas injected into the immersion nozzle 25 is not small, fine argon bubbles mixed into the mold through the immersion nozzle 25 move together with the molten steel. Some are floated and removed by the surface, but some remain in the molten steel and remain in the produced cast pieces or are collected in the solidification layer to cause pinhole defects in the produced cast pieces 80 as shown in FIG. 4. In particular, as shown in FIG. 4, the ultra low carbon steel has a deeper depth of the oscillation mark (OSM) and the hook generated by the mold oscillation in the initial solidification layer in the mold than the low carbon steel, and bubbles are collected by the hook. Since it is easier than other steel grades, pinhole defects are likely to occur.

The controller 160 calculates the collision depth from the hot water surface to the point when the molten steel discharged from the immersion nozzle 25 collides with the mold inner wall using various operation factors stored in the memory 110, and the calculated collision When the depth is greater than or equal to the set reference depth, at least one of the immersion depth of the immersion nozzle 25 and the amount of argon gas injected through the immersion nozzle 25 is variably controlled according to the casting width in order to reduce pinhole defects.

For example, the controller 160 controls the immersion depth of the immersion nozzle 25 to be reduced or the amount of argon gas injection through the immersion nozzle 25 when the casting width is less than the set reference width when the calculated collision depth is greater than or equal to the set reference depth. Will be controlled to increase. In addition, the controller 160 controls the immersion depth of the immersion nozzle 25 to be reduced and the argon gas through the immersion nozzle 25 when the casting width is greater than the set reference width when the calculated collision depth is equal to or greater than the set reference depth. It is controlled to increase the injection amount. The reference depth set above may be 550 mm, and the reference width may be set to a value between 1400 mm and less than 1600 mm, but is preferably about 1500 mm.

The controller 160 controls the argon injection unit 150 to increase the argon gas when the calculated collision depth is greater than or equal to the set reference depth, or to increase the height of the tundish 20 by controlling the height adjusting unit 140. To control. Here, when the height of the tundish 20 is increased, the immersion depth of the immersion nozzle 25 is lowered as shown in FIG. 5. That is, if the height of the tundish 20 is known, the immersion depth of the immersion nozzle 25 may be indirectly confirmed, for example, as shown in Table 1 below. Table 1 is only an example for better understanding, and may be changed according to the width and thickness of the slab to be cast, and the casting speed.

Tundish  Height Immersion Depth of Immersion Nozzle One 63 mm 172 mm 2 55mm 180 mm 3 49 mm 186 mm 4 44 mm 191 mm 5 40mm 195 mm

In Table 1, the height of the tundish means the maximum height of the tundish at each casting speed, which means that the height of the tundish at the corresponding casting speed should not exceed the maximum height. The immersion depth of the immersion nozzle 25 is a distance from the hot water surface to the upper end of the discharge port 26 of the immersion nozzle 25 as a value converted using the height of the tundish. As the height of the tundish 20 increases, the immersion depth of the immersion nozzle 25 becomes shallow, and as the height of the tundish 20 decreases, the immersion depth of the immersion nozzle 25 becomes deep.

As described above, the pinhole defect reduction apparatus 100 collides with the mold inner wall by ejecting the molten steel discharged from the immersion nozzle 25 using various operation factors including casting width, molten steel injection amount, immersion depth of the immersion nozzle 25, and argon gas injection amount. By calculating the depth of impact from the floor to the point at which it occurs, it is possible to indirectly predict the occurrence of pinhole defects in the final product.

For example, when the casting width is less than 1400mm, as shown in Figure 6, the pinhole defect index is less than 0.1, no problem. However, when the casting width is more than 1400mm, the pinhole defect index is more than 0.1, and the impact depth at that time is more than 550mm. . In addition, when the casting width was more than 1600mm, the pinhole defect index was more than 0.3, which was serious, and the impact depth at that time was about 580mm. In other words, it was found that the pinhole defect index and the collision depth were related to the casting width. If the pinhole defect index is '0.1' or less, there is no problem with the product. If the pinhole defect index is '0.1' or more, the product sale may be a problem, so quality control is required.

Therefore, in the present invention, when the casting width is approximately 1400mm, by calculating the collision depth from the hot water surface to the point when the molten steel discharged from the immersion nozzle 25 collides with the mold inner wall, by appropriately managing the collision depth, To reduce pinhole defects.

7 is a flowchart illustrating a process of reducing pinhole defects in a playing process according to an embodiment of the present invention, with reference to the accompanying drawings.

First, the controller 160 receives or transmits data on various operating factors including the casting width, the molten steel injection amount, the immersion depth of the immersion nozzle 25, and the argon gas injection amount through the input unit 120, and stores the data in the memory 110. It is made (S11). The operating factors include not only casting width, molten steel injection amount, immersion depth of immersion nozzle 25 and argon gas injection amount, but also diameter of discharge port 26 of immersion nozzle 25 and discharge angle of immersion nozzle 25 and discharge angle of molten steel. It may further include data about.

The controller 160 calculates the collision depth from the hot water surface to the point when the molten steel discharged from the immersion nozzle 25 collides with the mold short side by using various operation factors stored in the memory 110 (S12). . Here, the collision depth means the collision depth from the hot water surface to the point when the molten steel discharged through the discharge port 26 of the immersion nozzle 25 hit the mold short side as shown in FIG. Molten steel bubbles have a greater chance of being trapped in the coagulation shell and need to be addressed.

In Fig. 8, y is a vertical distance m with the outlet of the immersion nozzle discharge port 26 as the origin, and x is a horizontal distance m with the outlet of the immersion nozzle discharge port 26 as the origin. Collision depth (D) can be obtained by the following equations (1) to (3).

Equation 1

Here, h is the distance m from the hot water surface to the upper end of the discharge port 26 of the immersion nozzle 25, and w is the width m of the long side of the mold. y is obtained by the following equation (2).

Equation 2

는 침지노즐 토출구(26)의 토출각(degree)이고, a1 내지 d2는 상수이다. G_i는 아래 수학식 3에 의해 구해진다.Where Q _L is the molten steel injection rate per unit time (m ³ / sec), Q _g is the argon gas injection amount per unit time (Nm ³ / sec), S is the diameter (m) of the immersion nozzle discharge port 26,

Is the discharge angle of the immersion nozzle discharge port 26, and a1 to d2 are constants. G _i is obtained by the following equation.

Equation 3

는 상수이다.here,

Is a constant.

That is, the collision distance of Formula (1) was calculated | required based on the y value in the locus x = W / 2 position of the molten steel discharge stream obtained from Formula (2). Equation 2 is obtained by performing a multiple regression analysis on the trajectory of the molten steel discharge flow in the numerical model experiment on the trajectory of the molten steel discharge flow.

The collision depth may be calculated using the above Equations 1 to 3.

Meanwhile, the constants may be determined as shown in Table 2 below. Such constant values are only examples, and may be changed according to operational conditions.

Table 2

When the collision depth is calculated using Equations 1 to 3, the controller 160 compares the calculated collision depth with a reference depth set in the memory 110 to determine whether the collision depth is greater than or equal to the set reference depth. (S13, S14). Here, the reference depth may be approximately 550 mm as a result of FIG. 6.

The controller 160 controls the immersion depth of the immersion nozzle 25 or argon injection according to the casting width currently being cast by controlling the height adjusting unit 140 to reduce pinhole defects when the collision depth is greater than or equal to the set reference depth. The amount of argon gas injected through the immersion nozzle 25 through the unit 150 is controlled. If the collision depth is less than the set reference depth, the continuous casting process may be performed with various set operation factors (S15). Of course, if the operator changes, the collision depth will be recalculated.

In detail, when the collision depth is equal to or greater than the set reference depth (S14), the controller 160 compares the casting width currently being cast with the set reference width, and determines whether the casting width is greater than or equal to the reference width (S16). As a result of the determination, if the casting width is equal to or greater than the set reference width, the controller 160 controls the height adjusting unit 140 to control the immersion depth of the immersion nozzle 25 and simultaneously controls the argon injection unit 150 to immerse it. Argon gas injection through the nozzle 25 is controlled to increase (S17). When the immersion depth of the immersion nozzle 25 is reduced, the collision depth is lowered, and when the argon gas injection amount is increased, the collision depth is lowered by bending to the hot water surface by buoyancy. Here, the reference width may be determined between 1400mm and 1600mm, but may preferably be 1500mm.

On the other hand, if the determination result is that the casting width is less than the set reference width, the controller 160 controls the height adjusting unit 140 to control the immersion depth of the immersion nozzle 25 or to control the argon injection unit 150 Argon gas injection through the immersion nozzle 25 is controlled to increase (S18). When the casting width is less than the set reference width, the pinhole defect index can be reduced below the reference value as shown in Table 3 below by controlling only one of the immersion depth or the argon gas injection amount, and the control order may follow the set priority.

TABLE 3

In Table 3, Examples 1 to 3 show the change of the collision depth according to the change of the immersion depth, the argon injection amount and the discharge angle (angle of the immersion nozzle discharge port) when the casting width is 1.4. Example 5 shows the change of the collision depth according to the simultaneous change of the immersion depth and the argon gas injection amount, and the change of the discharge angle (angle of the immersion nozzle discharge port). When the discharge angle of the immersion nozzle 25 is changed as shown in Table 1, the impact depth is decreased the most when the immersion depth or the argon gas injection amount is changed. However, the change of the discharge angle of the immersion nozzle 25 is not possible during the operation, it is difficult to apply during operation because it requires a new production of the immersion nozzle (25). Therefore, in order to adjust the collision depth during operation, it is preferable to change the immersion depth or the argon gas injection amount of the immersion nozzle 25. Here, the immersion depth is preferably adjusted within the range of 0.14 to 0.20 in operation, the argon gas injection amount is preferably less than 9 used. In case of excessive use of argon gas, fluctuations in the water surface may increase, and the quality of the product may be deteriorated.

As described above, in the present invention, the collision depth is calculated by using various operation factors including the casting width, the molten steel injection amount, the immersion depth of the immersion nozzle 25, and the argon gas injection amount, and when the calculated collision depth is equal to or greater than the set reference depth, Accordingly, at least one of the immersion depth of the immersion nozzle 25 and the argon gas injection amount is selectively controlled. For example, when the collision depth is greater than the set reference depth and the casting width is 1.4m, the immersion depth or the argon gas injection amount may be controlled within the set priority and the set range, but the immersion depth and the argon gas injection amount may be adjusted at the same time.

Such immersion depth and argon gas injection amount is preferably configured to increase or decrease within the range of 5% to 15% compared to the current immersion depth and argon gas injection amount.

As described above, in the present invention, the degree of pinhole defects is determined through the collision depth, and when the degree of pinhole defects exceeds the reference value, the pinhole defects are reduced by controlling the collision depth through the immersion depth of the immersion nozzle 25 and the argon gas injection amount. It is possible to produce products of good surface quality.

The pinhole reduction scheme as described above is not limited to the configuration and operation manner of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: Ladle 20: Tundish
21: Stopper 25: Immersion nozzle
30: mold 51: powder layer
60: support roll 65: spray
70: pinch roll 80: performance cast
81: Solidification shell 82: Non-solidified molten steel
83: tip portion 85: solidified point
90: Cutter 91: Cutting point
100: pinhole reduction device 110: memory
120: input unit 130: display unit
140: height adjustment unit 150: argon injection unit
160:

Claims (5)

Storing data for a plurality of operating factors including casting width, molten steel injection amount, immersion depth of immersion nozzle and argon gas injection amount;
Calculating a collision depth from the hot water surface to a point when molten steel discharged from the immersion nozzle collides with the mold inner wall by using the plurality of operation factors stored above;
Comparing the collision depth calculated above with the set reference depth and determining whether the collision depth is greater than or equal to the set reference depth; And
If the collision depth is greater than or equal to the set reference depth, variably controlling at least one of the immersion depth of the immersion nozzle and the amount of argon gas injected through the immersion nozzle according to the casting width currently being cast to reduce the pinhole defect; Including,
The collision depth (D [m]) is a pinhole defect reduction method in the playing step is calculated by the following equation.
Equation

only,

Here, y is the vertical distance (m) with the outlet of the immersion nozzle discharge port as the origin, x is the horizontal distance (m) with the outlet of the immersion nozzle discharge port as the origin, and h is from the hot water surface to the top of the discharge port of the immersion nozzle. Is the distance (m), w is the width of the long side of the mold (m), Q _L is the molten steel injection amount per unit time (m ³ / sec), Q _g is the argon gas injection amount (Nm ³ / sec) per unit time, S is the diameter (m) of the immersion nozzle discharge port,

Is the discharge angle of the immersion nozzle discharge port, a1 to d2 is a constant,

Is a constant.
The method according to claim 1,
The variable control step,
Determining whether the casting width being cast is greater than or equal to the set reference width when the collision depth is equal to or greater than the set reference depth; And controlling the immersion depth of the immersion nozzle to be reduced or controlling the amount of argon gas injection through the immersion nozzle to increase when the casting width is less than the set reference width.
The method according to claim 1,
The variable control step,
Determining whether the casting width being cast is greater than or equal to the set reference width when the collision depth is equal to or greater than the set reference depth; And reducing the immersion depth of the immersion nozzle when the casting width is greater than or equal to a predetermined reference width, and at the same time, reducing the pinhole defect in the playing process of controlling the amount of argon gas injected through the immersion nozzle.
The method according to claim 1,
The set reference depth is 550mm pinhole defect reduction method in the playing process.
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