KR20140017175A - Method for stabilizing meniscus in continuous casting - Google Patents

Abstract

The present invention relates to a method for stabilizing a level of molten steel in a continuous casting process by controlling a factor causing level fluctuation of the molten steel, the method comprising: a step of measuring and calculating a discharge rate of the molten steel flowing out from a tundish; a step of measuring the immersion depth of an immersion nozzle inside a mold in real time; a step of calculating a stabilization index of the level of the molten steel by using the calculated discharge rate of the molten steel, the immersion depth of the immersion nozzle and the width of the mold stored in advance; and a step of controlling the discharge rate of the molten steel by using a stopper, in case the stabilization index of the level of the molten steel is over a stabilization reference of the level of the molten steel by comparing the calculated stabilization index of the level of the molten steel with the predetermined stabilization reference of the molten steel. [Reference numerals] (AA) START; (BB) END; (S110) Measure the width of a mold; (S120) Calculate a discharge rate of molten steel; (S130) Measure the immersion depth of an immersion nozzle; (S140) Calculate a stabilization index of the level of the molten steel by using the calculated discharge rate of the molten steel, the immersion depth of the immersion nozzle and the width of the mold; (S150) Compare the calculated stabilization index of the level of the molten steel with a predetermined stabilization reference of the molten steel; (S160) Control the discharge rate of the molten steel by using a stopper, in case the stabilization index of the level of the molten steel is over the stabilization reference of the level of the molten steel

Description

[0001] METHOD FOR STABILIZING MENISCUS IN CONTINUOUS CASTING [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for stabilizing a hot surface in a continuous casting process, and more particularly to a method for stabilizing a hot surface in a continuous casting process by controlling factors that cause hot surface fluctuation.

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. It includes a plurality of pinch rolls.

In other words, the molten steel tapping out of the ladle and tundish is formed as 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. It is made of slabs (Slab), Bloom (Bloom), Billet (Billet) and the like having a predetermined shape.

Related Prior Art Korean Patent Publication No. 2002-0034062 (published on May 05, 2002, entitled " Method for stabilizing a hot-wall surface in continuous casting) is available.

The present invention provides a method for stabilizing a hot water surface in a continuous casting process which numerically calculates a variation according to factors causing melt flow unevenness generated in a mold and compares it with a reference stabilization index to stably maintain a molten steel flow .

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

According to another aspect of the present invention, there is provided a method of stabilizing a hot surface in a continuous casting process, comprising: measuring and calculating a discharge amount of molten steel flowing out from a tundish to a mold; Measuring in real time the immersion depth of the immersion nozzle immersed in the mold; Calculating the stabilization index of the hot water surface using the calculated amount of molten steel, the immersion depth of the immersion nozzle, and the pre-stored mold width; And controlling the discharge amount of the molten steel by using the stopper if the bath surface stabilization index is higher than the bath surface stabilization standard by comparing the bath surface stabilization index calculated in the above with the preset bath surface stabilization standard.

Specifically, the hot-dip stabilization index can be obtained by the following relational expression.

Relation

At this time, A ₀ represents the amount of molten steel discharged (Ton / min), A ₁ represents the width of the mold (m), and A ₂ represents the immersion depth (m) of the immersion nozzle.

In addition, the bath surface stabilization standard may be less than 30.

In addition, the depth of the immersion nozzle may represent the distance from the hot water surface in the mold to the upper end of the discharge port.

As described above,

According to the present invention, it is possible to maintain the flow of the bath surface at the stabilization index of the bath surface at all times by controlling the factors that cause the bath surface fluctuation, and it is possible to prevent defects of the main body caused by the vortex and unsteadiness generated in the bath surface.

Further, the present invention can numerically express the stability of the hot-dippered surface, thereby facilitating management.

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.
Fig. 2 is a view showing vortex and instability generated in the mold.
3 is a flowchart illustrating a method of stabilizing a hot water surface in a continuous casting process according to an embodiment of the present invention.
4 is a graph showing the relationship between the mold width and the vortex using a numerical model in which the mold is reduced.
5 is a graph showing the relationship between the water inflow and the vortex using a numerical model in which the mold is reduced.
FIG. 6 is a graph showing the relationship between the immersion depth of the immersion nozzle and the vortex using a numerical model in which the mold is reduced.
Fig. 7 is a graph showing the relationship between the tangential stabilization index and occurrence of surface inclusion defects.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components are denoted by the same reference symbols whenever 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.

Referring to FIG. 1, the continuous casting machine may include a ladle 10, a tundish 20, a mold 30, secondary cooling tables 60 and 65, and a pinch roll 70.

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 surface of the mold 30. 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, as well as lubrication of the mold 30 and the solidification shell 81, as well as to prevent oxidation and nitriding of the molten metal in the mold 30, to keep warm, and to the surface of the molten metal. It also performs the function of absorption of 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, 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 control of the flow of the molten steel M through the immersion nozzle 25 may be performed by 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 pulls the front end portion 83 of the completely cast solid cast steel 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.

Here, when the molten steel M in the tundish 20 is caused to flow into the mold 30 by the immersion nozzle 25 extending into the mold 30, when the molten steel inflow amount is increased as shown in FIG. 2, 25) Due to the size of the discharge port, the flow rate of the molten steel at the discharge port is accelerated, thereby causing irregular flow of molten steel in the mold 30, which causes fluctuation of the molten metal surface to cause the mold powder slag applied to the upper surface of the molten metal to flow into molten steel, Or the molten steel is unstable, thereby deteriorating the quality of the cast steel.

FIG. 3 is a flowchart illustrating a method for stabilizing the bath surface in the continuous casting process according to an embodiment of the present invention. The method for stabilizing the bath surface of the mold is as follows. Here, FIGS. 4 to 6 show the results of experiments using a numerical model that can not be tested through a mold due to a risk factor and thus reduced.

First, the length of the used mold width is measured (S110).

As shown in FIG. 4, it can be seen that the frequency of occurrence of the vortex varies with the mold width, and the frequency of occurrence of the vortex decreases as the mold width becomes longer. Accordingly, the degree of the vortex can be grasped according to the mold width.

The mold width has a fixed mold width length until the operation is completed in the mold 30. Therefore, when the length of the mold width used for the first time is measured, the mold width length remains the same.

Next, the discharge amount of the molten steel flowing out from the tundish 20 to the mold 30 is measured and calculated (S120). At this time, the discharge amount of the molten steel is measured and monitored in real time, the discharge amount of the molten steel is related to the circumferential speed, the mold width, the thickness, and the density of the molten steel, the method of calculating the discharge amount of the molten steel is as follows.

Relationship 1

As shown in FIG. 5, the discharge rate of molten steel is higher as the discharge rate is higher. That is, it can be seen that the frequency of occurrence of the vortex can be controlled according to the discharge amount of the molten steel.

Subsequently, the immersion depth of the immersion nozzle 25 immersed in the mold 30 is measured in real time (S130). At this time, the depth of the immersion nozzle 25 represents the distance from the hot water surface in the mold 30 to the upper end of the discharge port, the immersion nozzle 25 is made of refractory and reacts with the slag layer in the mold 30 so that the time is longer Refractories may be eroded or damaged, resulting in operation accidents, so the immersion depth is adjusted step by step according to time.

In addition, when the water surface freezing occurs during operation, it is possible to increase the water surface temperature by adjusting the immersion depth of the immersion nozzle 25 low. The immersion depth of the immersion nozzle 25 may be controlled by various factors.

In the method of adjusting the immersion depth, since the immersion nozzle 25 is connected to the tundish 20, the tundish 20 is adjusted up and down so that the height of the immersion nozzle 25 is adjusted.

The immersion depth of the immersion nozzle 25 is calibrated in the performance equipment itself and the immersion depth can be known depending on the height of the tundish 20 as the molten steel in the mold 30 is always maintained at the same height . A detailed method of measuring the immersion depth of the immersion nozzle 25 is omitted.

6 is a graph showing the frequency of occurrence of the vortex according to the immersion depth of the immersion nozzle. As the immersion depth of the immersion nozzle 25 is longer, the frequency of occurrence of the vortex is lowered.

Next, the stabilization index of the hot water surface is calculated through the length of the stored mold width, the discharge amount of the molten steel calculated above, and the immersion depth of the immersion nozzle 25 (S140).

At this time, the water surface stabilization index can be obtained by the following relational formula (1).

Relation 2

At this time, A ₀ represents the amount of molten steel discharged (Ton / min), A ₁ represents the mold width (m), and A ₂ represents the immersion depth (m) of the immersion nozzle.

Here, since the discharge amount of the molten steel, the mold width, and the immersion depth of the immersion nozzle are deeply related to the flow of the bath surface, it is preferable that the bath surface stabilization column can be controlled through these controls.

Finally, the calculated hot water level stabilization index is compared with a predetermined hot water level stabilization standard (S150). If the hot water level stabilization index is higher than the hot water level stabilization standard, the amount of molten steel discharged is controlled using a stopper (S160). At this time, it is preferable that the pre-set bath surface stabilization standard is less than 30, depending on the relationship between the tangential stabilization index shown in FIG. 7 and occurrence of surface inclusion defects. That is, when the bath surface stabilization standard is less than 30, it can be seen that surface layer inclusion defects do not occur.

Therefore, the present invention controls the factors that cause the fluctuation of the bath surface, so that the bath surface can always be maintained at the standard bath surface stabilization index, and defects due to the vortex and instability caused in the bath surface can be prevented.

Further, the present invention can numerically express the stability of the hot-dippered surface, thereby facilitating management.

The method of stabilizing the melt surface in the continuous casting process is not limited to the construction and the operation 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 15: Shroud nozzle
20: Tundish 25: Immersion Nozzle
30: mold 31: left short side
35: right short side 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: performance cast
81: Solidification shell 82: Non-solidified molten steel
91: Cutting point

Claims (4)

Measuring a discharge amount of molten steel flowing from the tundish to the mold;
Measuring in real time the immersion depth of the immersion nozzle immersed in the mold;
Calculating the stabilization index of the hot water surface using the calculated amount of molten steel, the immersion depth of the immersion nozzle, and the pre-stored mold width; And
And controlling the discharge amount of the molten steel by using a stopper, by comparing the calculated water level stabilization index with a preset level of stabilization.
The method according to claim 1,
Wherein the stabilization index of the melt surface is obtained by the following relational expression.
Relation

At this time, A ₀ represents the amount of molten steel discharged (Ton / min), A ₁ represents the width of the mold (m), and A ₂ represents the immersion depth (m) of the immersion nozzle.
The method according to claim 1,
Wherein the bath surface stabilization standard is less than 30.
The method according to claim 1,
The depth of the immersion nozzle is the surface level stabilization method in the continuous casting process showing the distance from the hot water surface in the mold to the upper end of the discharge port

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