JP2712920B2 - High speed casting end control 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 end control method for a continuous casting machine in which a molten metal in a tundish is continuously cast into cast pieces.

[0002]

2. Description of the Related Art Conventionally, a casting end control method of this type is disclosed in Japanese Patent Application Laid-Open No. 62-124056,
Japanese Patent Application Laid-Open No. 62-203652 discloses a method for ending a casting operation of a steel strip casting apparatus, an apparatus for performing the method,
An automatic stop method in a continuous casting machine disclosed in 44848 is generally known.

[0003] In order to prevent leakage of steel from the last end portion (bottommost portion) of the slab at the end of casting or during the drawing of the slab after the casting, these are firstly used in a tundish before the end of casting. Depending on the remaining steel weight or level,
The casting speed is appropriately reduced according to a predetermined speed reduction pattern, and the casting is stopped while leaving a predetermined small amount of molten steel in the tundish. Next, after the casting is stopped, after the coolant (metal particles, metal pieces, water, etc.) is introduced into the bottommost portion and solidified, after the so-called bottom processing operation (see FIG. 9), the drawing speed is appropriately increased. (See Fig. 10).

[0004]

However, in the conventional casting end control method described above, the casting speed is reduced before the end of casting, so that the productivity of the continuous casting machine is reduced and the tundish residual steel casting is performed. As the time becomes longer, the temperature of the residual molten steel decreases greatly, and the quality of the final slab deteriorates. Further, as described above, since the bottom processing operation is required, the work load is large, and the quality of the final slab deteriorates due to the mixing of the coolant, and the cost of purchasing the coolant is increased.

Further, in order to stop the casting during the bottom processing operation, the slab bulging between the rolls in the continuous casting machine increases, and after the start of the drawing, the unsolidified molten steel in the slab is squeezed out, and the molten steel leaks from the bottommost portion. May be. Moreover, at the end of casting, the temperature of the slab in the continuous casting machine decreases,
It is disadvantageous when hot charging hot rolling or performing direct roll.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to eliminate casting slowdown work and bottom processing work before completion of casting, to improve the productivity of a continuous casting machine and to improve the quality of cast slabs. It is an object of the present invention to provide a high-speed casting end control method capable of reducing fragmentation and work load.

[0007]

The feature of the present invention is that, by optimizing the control of the secondary cooling water immediately below the mold and optimizing the pattern of increasing the drawing speed after the casting is completed,
This is to make it possible to abolish the casting speed reduction work and the bottom processing work before the end of casting, which were essential for preventing steel leakage from the bottommost part.

According to the termination control method of the present invention, the casting is terminated at the normal casting speed (V ₀ ) without reducing or stopping the casting speed before the completion of the casting.
11). As a result, the casting time of the remaining steel in the tundish can be reduced, and the effect of improving the productivity and suppressing the temperature decrease of the remaining molten steel can be obtained. For example, V ₀ = 2.0, V ₁ = 1.2,
Under the conditions of V ₂ = 0.5, V ₄ = 0.3 m / min, and W ₀ = 35, W
_{1 = 20, W 2 = 10} , W 3 = W 4 = the condition of 5 ton, 220
When casting a × 1000 mm slab with two strands, the tundish residual steel casting time is reduced by 9 minutes, and at this time, the temperature drop of the residual molten steel in the tundish is reduced by 15 ° C. (see FIG. 12).

Next, the solidification of the lowermost portion is performed by the secondary cooling water just below the mold without performing the bottom treatment after the casting. This makes it possible to improve the quality deterioration and work load due to the introduction of the cold material in the bottom processing operation. On the other hand, when the bottom portion solidification is performed with the secondary cooling water just below the mold, the amount of secondary cooling water not only promotes cooling of the bottom portion, but also allows cooling water to enter molten powder and molten steel, and Flow rate Q ₁ that does not cause
To control.

[0010] To explain the control of the secondary cooling water Specifically, the spray nozzle is between S ₀ to S ₁ to the position S ₁ where the outermost bottom portion is sufficiently solidified from the mold bottom S ₀ (see FIG. 11) ( from FIG. 1), to control the flow rate of cooling water to the top-bottom portion Q _1.

[0011] lowest bottom position (pull-out length) the top-bottom portion after solidification completion reached S _1, the secondary cooling water to the Q ₀ of the constant region and the same amount (see FIG. 13), and the withdrawal speed of the predetermined V
_The speed is increased up to ₅ at an acceleration a ₀ (see FIG. 11). This acceleration a ₀ is used to squeeze molten steel due to a change in the slab bulging amount between rolls at the time of speed increase, and to prevent leakage of steel at the bottommost portion,
It must be less than or equal to a predetermined value. Note After withdrawal speed reaches V _5, as in the end a conventional casting, pulled out from the slab continuous casting machine.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high-speed casting end control method in continuous casting according to the present invention will be described below with reference to the illustrated embodiment.

First, a control device for performing the high-speed casting end control method of the present invention will be described. The control device 1 (see FIG. 1) includes a spray nozzle 5 for injecting secondary cooling water to the slab 4 and a driving roll 6. Speed control unit 7 that sends an operation signal to
A secondary cooling water control unit 8 for controlling the flow rate of the secondary cooling water to each spray nozzle 5, a speed control unit 7 and a secondary cooling water control unit 8 based on the input value of the drawing length of the slab 4 And a process computer 9 for sending a control signal to the computer. In FIG. 1, reference numeral 10 denotes a tundish, 11 denotes a molten powder, 12 denotes molten steel, and 4a denotes a slab shell.

Next, an embodiment in which the control device 1 is used to perform the high-speed casting end control method of the present invention will be described. First, the secondary cooling water flow rate to the spray nozzle 5 after the casting is completed,
In order to control the drawing speed by the driving roll 6, the drawing length at the lowest position was tracked by the process computer 9, and this was determined in advance.
The spray water is between pulling length S ₀ to S ₁ to Q _1, also S ₁ after control by Q ₀ in the secondary cooling water control unit 8. Further casting speed, as held at a velocity V ₀ which end casting until withdrawal length 0～S _1, is accelerated at S ₁ since the acceleration a ₀ to a predetermined drawing speed V _5,
The speed is controlled by the speed control unit 7.

Here, as specific numerical values, S ₀ is the distance from the meniscus to the lower end of the mold, and S ₁ is S ₁ ≧ V
₀ (m / min) × 1 (min) = V ₀ (m), Q ₁ is spray water amount ≧ 0.1 l / kgsteel (total water amount between S _{0 and} S ₁ ), and spray water collision force on the slab surface ≦ 250g / cm ² , Q ₀ is the same amount of spray water as during normal casting, a ₀ is acceleration ≦ 0.5m / min
And

The reasons for limiting the numerical values of S ₁ , Q ₁ and a ₀ are as follows:
If S ₁ and a ₀ are outside the above range, the rate of steel leakage from the bottommost portion during drawing becomes high (see FIGS. 2 and 3), and the amount of secondary cooling water from the spray nozzle becomes In the following cases, the rate of occurrence of steel leakage from the bottommost portion during drawing becomes high. However, when the secondary cooling water collision force from the spray nozzle is equal to or more than the above value, water enters into the unsolidified powder slag or molten steel at the bottom and causes a steam explosion, so it is performed from the viewpoint of operation and safety. No (see FIGS. 4 and 5).

Of course, according to the method for controlling the end of high-speed casting of the present invention, the amount of cooling water from the spray nozzle and the drawing speed are controlled so as to fall within the above-mentioned conditions while the operator checks the drawing length without using a computer or the like. But it is possible.

[0018]

As described above, according to the high-speed casting end control method of the present invention, the frequency of occurrence of steel leakage at the bottommost portion can be reduced to about 1/5 of the conventional frequency (see FIG. 6). In addition, the temperature of the slab in the continuous casting machine at the end of casting can be improved by about 50 ° C. (see FIG. 7). Furthermore, the quality of the slab in the bottom material can be significantly improved (see FIG. 8). In addition, the productivity of the continuous casting machine can be improved, the material cost of the coolant can be reduced, and the effect of omitting the bottom processing operation can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a control device for performing a high-speed casting end control method in continuous casting according to the present invention.

FIG. 2 is a table showing the rate of occurrence of steel leakage at the bottommost portion with respect to the drawing length.

FIG. 3 is a table showing the rate of occurrence of steel leakage at the bottommost portion with respect to the acceleration of the casting speed.

FIG. 4 is a table showing the rate of occurrence of steel leakage at the bottom portion with respect to the amount of secondary cooling water.

FIG. 5 is a table showing the frequency of occurrence of steam explosions with respect to the secondary cooling water collision force from a spray nozzle.

FIG. 6 is a table showing a comparison of the frequency of occurrence of steel leakage at the bottom portion between the method of the present invention and the conventional method.

FIG. 7 is a chart showing a comparison of slab temperature between the method of the present invention and the conventional method.

FIG. 8 is a table showing a comparison of the occurrence rate of material flaws in the lowermost material lower process step between the method of the present invention and the conventional method.

FIG. 9 is a schematic perspective view showing a bottommost processing operation.

FIG. 10 is a graph showing a casting speed pattern in a conventional method.

FIG. 11 is a graph showing a casting speed pattern in the method of the present invention.

FIG. 12 is a table showing a comparison of molten steel temperature between the method of the present invention and the conventional method.

FIG. 13 is a graph showing the amount of secondary cooling water in the present invention.

[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.

Claims (1)

(57) [Claims] 1. At the end of casting of a continuous casting machine that casts molten metal in a tundish into cast slabs, the casting speed is maintained at a normal casting speed V ₀ without reducing or stopping the casting speed and performing bottom processing work. while the cast finished the, of the slab
When the rear end exits the mold, the secondary cooling water just below the mold
The water volume Q ₀ of the end can be sufficiently solidified at the end and
Water volume Q enough to prevent cooling water from entering the unsolidified portion
_{To 1} and solidification of the rear end is complete.
Predetermined amount of water with back to Q _0, the withdrawal speed from V ₀
Fast casting termination control method in a continuous casting, characterized by accelerated to the speed V ₅ of the.