JP2720692B2 - High-speed casting end method in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method for a continuous casting machine in which a molten metal in a tundish is continuously cast into cast pieces.

[0002]

2. Prior Art and Problems to be Solved by the Invention
Conventionally, this type of casting termination method is disclosed in
No. 4056, the casting end control method, and JP-A-62-203652
In general, a method for ending a casting operation of a steel strip casting apparatus and an apparatus for performing the method, an automatic stop method in a continuous casting machine disclosed in JP-A-62-244848, and the like are known. The above is referred to as Conventional Method 1.

[0003] In these methods, first, the casting speed is appropriately reduced by a predetermined deceleration pattern in accordance with the remaining steel weight or the remaining steel level in the tundish before the casting is completed, and a predetermined small amount of the casting is left in the tundish. Stop casting, leaving molten steel. Next, after the pouring is stopped, a coolant (metal particles, metal pieces, water, etc.) is poured into the last end of the residual molten steel in the tundish, the so-called bottom portion, and after the solidification by the coolant, the so-called bottom processing operation is performed. After that (see FIG. 6), the drawing speed is appropriately increased to perform the drawing (see FIG. 7).

[0004] However, in the method of the conventional method 1, productivity and quality are lowered at the end of casting.

As a countermeasure for this, the applicant has previously disclosed a method of controlling the end of high-speed casting in continuous casting (Japanese Patent Application No. 3-22170).
2) is invented. This is referred to as Conventional Method 2.

In this method, the casting speed reduction work and the bottom processing work before the casting is completed are abolished, the casting is finished while the normal casting speed is maintained, and the cast piece is pulled out (see FIG. 8). In addition, the solidification of the bottom portion by this method is performed by the secondary cooling water immediately below the mold, and leakage of steel from the bottom portion is prevented by optimizing the amount of the cooling water and the pattern of increasing the drawing speed after the casting is completed.

However, the conventional method 2 is different from the conventional method 1 described above.
Although it has largely solved the problems of productivity and quality, the prevention of steel leakage at the bottom is not yet complete.

In the conventional method 2, the solidification is promoted by the secondary cooling water immediately below the mold in order to prevent the steel leakage at the bottom. Further, if the amount of the secondary cooling water is too large, it enters into the molten powder or the molten steel and causes a steam explosion. Therefore, it is necessary to control the flow rate to an appropriate value.

However, since the solidification of the bottom portion is affected by the temperature of the molten steel and the temperature of the cooling water, it is difficult to control the flow rate when these conditions change. As a result,
Insufficient solidification of the bottom part increases the risk of bottom steel leakage.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and has as its object to improve the productivity and quality and to increase the safety in continuous casting in which the safety against steel leakage at the bottom can be enhanced. It is to provide a method of finishing casting.

[0011]

The features of the method of the present invention are as follows.
As shown in FIG. 1, a plurality of cavities 14 having a hierarchical structure are formed in which a bottom portion of molten steel in a mold (not shown) is partitioned by several solidified layers 13. As a result, even if blow-up due to squeezing out of unsolidified molten steel occurs, it is blocked by the solidified layer 13 and does not lead to steel leakage (see FIG. 2). In order to form a bottom having such a hierarchical structure, the following means is used.

First, as shown in FIG. 3A, the thickness of the powder in the mold 2 at the end of the casting is set to be equal to or less than X mm. Thereby, heat dissipation from the unsolidified molten steel surface in the bottom portion becomes large, and the surface is easily solidified.

Next, as shown in FIG. 3 (B), when the casting is completed and the slab starts to be drawn out, the unsolidified molten steel level in the bottom portion due to solidification shrinkage starts to decrease. This solidification of molten steel
Since the process proceeds from the solidification shell 15, the entire surface of the molten metal does not solidify while the molten metal surface is continuously decreasing.

Here, as shown in FIG. 3 (C), when stress is applied to the slab 4 to squeeze out molten steel in an amount that balances the solidification shrinkage, the molten metal surface stagnates and solidifies over the entire molten metal surface. Progresses to the solidified layer
Form 13. The time required for forming the solidified layer 13 is 10 to
It is about 100 seconds. Then, when the stress is relaxed, FIG.
As shown in (D), the level starts to fall again.

After that, when a stress is again applied to the slab 4 after the molten metal surface drops by a predetermined amount, a new solidified layer 13 is formed below the first solidified layer 13 as shown in FIG. The cavities 14 are formed and separated by the two solidified layers 13, 13.

Then, such steps (FIGS. 3A, 3B,
By repeating (C), (D), and (E) several times, a plurality of cavities 14 having a hierarchical structure partitioned by the solidified layer 13 can be formed inside the bottom portion.

The stress is applied to the slab 4 mechanically, for example, by a roll pressing force. Alternatively, heat contraction by secondary cooling spray control is used. Further, there is use of electromagnetic force.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for ending high speed casting in continuous casting according to the present invention will be described with reference to the illustrated embodiment.

First, a control device for performing the high-speed casting end method of the present invention will be described. Control device 1 (see FIG. 5)
Is a spray nozzle 5 for injecting secondary cooling water to the slab 4
A speed control unit 7 for sending an operation signal (roll pressing force and rotation speed) to the driving roll 6, a secondary cooling water control unit 8 for controlling a flow rate of the secondary cooling water to each spray nozzle 5,
A process computer 9 for sending control signals to the speed control unit 7 and the secondary cooling water control unit 8 based on the input value of the drawing length of the slab 4 is provided. In FIG. 5, reference numeral 2 denotes a mold, reference numeral 3 denotes a guide roll, reference numeral 10 denotes a tundish, reference numeral 11 denotes molten powder, and reference numeral 12 denotes molten steel.

Next, the control device 1 having such a configuration will be described.
The time when the method of ending high-speed casting according to the present invention will be described with reference to FIG.

First, the amount of the secondary cooling water to the spray nozzle 5 after the casting is completed, and the drawing speed and the drawing length S ₁ by the driving roll 6 are tracked by the process computer 9, and the position of the cast piece 4 and each part of the cast piece are tracked. The shell thickness, solidification shrinkage, and the level of the molten metal are estimated.

Next, when the level of the molten metal falls to a predetermined level by the process computer 9, a reduction of an amount balanced with the solidification shrinkage is applied in consideration of the slab shell deformation resistance and the static iron pressure. Thus, the pressing pressure of the driving roll 6 is controlled. If the pressing pressure falls within a range of ± 15% of the solidification shrinkage, the molten metal surface solidifies and a predetermined effect is obtained.

These operations, that is, the operation of stagnation of the molten metal surface due to the application of stress by the driving roll 6 and the operation of lowering the molten metal surface due to the release of the applied stress are repeated several times (FIG. 3A,
(See (B), (C), (D), and (E)), and the inside of the bottom portion may have a hierarchical structure in which a plurality of cavities 14 partitioned by a solidified layer 13 are formed.

[0024]

According to the high-speed casting end method of the present invention, the occurrence of steel leakage at the bottom of the molten steel in the mold can be reduced without impairing the productivity and quality advantages of the above-mentioned conventional method 2. As shown in FIG. 4, it can be prevented almost completely.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a bottom portion formed by the high-speed casting end method of the present invention.

FIG. 2 is a schematic view showing a state in which blowing of unsolidified molten steel is prevented by a bottom portion formed by the high-speed casting end method of the present invention.

FIG. 3 is a schematic process diagram showing a solidification formation state of a bottom portion by the high-speed casting end method of the present invention.

FIG. 4 is a graph comparing the frequency of occurrence of steel leakage between the method of the present invention and the conventional method.

FIG. 5 is a schematic diagram showing a control device for performing the high-speed casting end method of the present invention.

FIG. 6 is a schematic view showing a conventional bottom processing operation.

FIG. 7 is a graph showing a casting speed pattern in a conventional method.

FIG. 8 is a graph showing a casting speed pattern in a conventional method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Control device, 2 ... Mold, 3 ... Guide roll, 4 ... Slab,
5: spray nozzle, 6: drive roll, 7: speed control unit, 8: secondary cooling water control unit, 9: process computer, 10: tundish, 11: molten powder, 12: molten steel, 13: solidified layer, 14 ... hollow, 15 ... solidified shell.

Claims (1)

(57) [Claims] At the end of casting of a continuous casting machine for casting a molten metal in a tundish to form a slab, the casting speed is reduced and stopped, and a processing operation of a bottom portion, which is the last end of the slab, is performed. When casting is finished while maintaining the normal casting speed and the slab is pulled out , stress
Stagnation due to stress and low surface due to release of stress
Control the solidification position by repeating the following operation several times
To high-speed casting termination method of continuous casting, characterized in that to form a hierarchical structure having a plurality of cavities partitioned by solidified layer inside the bottom portion.