JP2000126853A - Continuous casting apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel the raising of meniscus point in a mold with the increase of drawing speed and to prevent the dispersion of variation of the meniscus point causing to the stop of operation by arranging guide rolls so as to pass though the recessed part on the surface of a cast slab when the meniscus point in the mold changes from the higher state to the lower state than a target level. SOLUTION: The guide rolls 3 for supporting the cast slab, with which the solidified shell can be formed from the portion in contact with the mold 1 to the inner part, are arranged below the mold 1. In the arrangement thereof in the case of using Lk, for the distance to the k-th guide roll 3(k) in the casting direction from a prescribed position in the mold and Lk+1 for the distance to the (k+1)-th guide roll 3(k+1) in the casting direction from the prescribed position in the mold, the ratio of the length (d) which divides the distance (Lk+1-Lk) from the k-th guide roll to (k+1)-th guide roll with an integer (m), and the distance L3, i.e., L3/d is made to be (n+α). Wherein, when (n) is an integer, 0<=α<=0.25 or 0.75<=α<1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a guide roll for supporting a slab obtained by pouring a molten metal (molten metal) into a mold below the mold so as to suppress a variation in the position of a meniscus in the mold. To a continuous casting apparatus.

[0002]

2. Description of the Related Art In the operation of a continuous casting apparatus, it is very important to suppress the fluctuation of the position of the meniscus in the mold in the mold from the viewpoint of both stabilizing the operation and improving the product quality. The reason is that when the position of the meniscus in the mold fluctuates greatly, the molten metal overflows from the mold and hinders the operation, and the synthetic slag called powder that covers the molten metal surface is rolled into the surface layer of the slab. It became a subcutaneous defect on the slab surface, and became a flaw after rolling, resulting in deterioration of product quality.

FIG. 8 is a schematic view showing a conventional continuous casting apparatus. In the figure, reference numeral 1 denotes a mold having upper and lower openings, which is water-cooled. An immersion nozzle for injecting the molten metal is arranged above the mold 1, and a pinch roll 4 is arranged below the mold 1. Further, the guide rolls 3 are arranged below the cast rolls at equal intervals so as to form a pair.

[0004] Various theories have been proposed for the cause of the variation of the position of the meniscus in the mold in the mold.
In Japanese Patent Publication No. 4-65742, in a continuous casting apparatus, when a solidified shell thickness of a slab and a molten steel static pressure which is a force for expanding outward are constant, a bulging amount generated between adjacent guide rolls. Does not change, but in the slab at the start of casting and at the end of casting, the amount of expansion due to the static pressure of the molten metal fluctuates periodically with time, resulting in "unsteady bulging", and the same period as this , The position of the meniscus in the mold fluctuates. In addition, it is pointed out that the fluctuation of the position of the meniscus in the mold due to "unsteady bulging" tends to occur when the guide rolls are arranged at equal intervals in the casting direction.

FIG. 9 is a schematic view showing a continuous casting apparatus in Japanese Patent Publication No. 4-65742. As shown in the drawing, the guide rolls 3 are alternately arranged so as to be asymmetrical with respect to the slab in order to prevent a change in the position of the meniscus in the mold due to “unsteady bulging”. As a result, the time for moving between the specific guide rolls and the fluctuation cycle of the position of the meniscus in the mold do not match, preventing the occurrence of "unsteady bulging" and suppressing the fluctuation of the position of the meniscus in the mold. .

[0006]

However, in addition to the above-mentioned "unsteady bulging", there is a phenomenon that the time required for the slab to move between the specific guide rolls and the fluctuation period of the position of the meniscus in the mold are made equal. Exists. FIG. 10 is an explanatory view of a mechanism in which the position of the meniscus in the mold fluctuates due to the surface dent of the slab. As shown in the figure, in the mold meniscus where solidification starts at the earliest stage, first, at the timing when the position of the meniscus in the mold is lowered, the solidified shell falls down to the molten metal side, and a gap is formed between the mold and the solidified shell. When the position of the meniscus in the mold is lowered, the molten metal is poured to a target level set for keeping the position of the meniscus in the mold constant, so that the powder in the upper layer of the molten metal with the rise of the position of the meniscus in the mold is raised. Layers rise. At this time, the powder penetrates into the gap to form a dent.

While the guide roll 3 passes through the dents formed as described above, the rolling friction of the guide roll 3 increases, and the resistance to pulling out of the slab increases.
Although the increase in the resistance decreases the speed of drawing the slab, the pinch roll 4 is controlled so as to keep the speed of drawing the slab constant, so that the torque of the pinch roll 4 is adjusted to balance the increase in the resistance. Increase.

After the dents pass through the surface of the slab just below the guide roll 3, the rolling friction of the guide roll 3 decreases, and the resistance to pulling out the slab sharply decreases.
However, since the drawing torque of the pinch roll 4 is still increased, the drawing speed is temporarily increased. At this time, the position of the meniscus in the mold is changed from a high state to a low state at the same time as the solidification is performed on the molten metal side. The shell falls down to create a gap, into which the powder layer flows and a new dent is formed.

As a result of observing the variation of the position of the meniscus in the mold in detail, the inventor of the present application has found that the distance L _k from the meniscus in the mold to the k-th guide roll, the variation period T of the position of the meniscus in the mold, and the casting time. when showing the relationship between the distance that a dent occurs in the slab surface by the following equation (1) by variation of the position of the mold in the meniscus represented using write speed _{Vc, L k / (Vc ×} T) = n + α where , N is an integer (1) If 0.25 <α <0.75, when the position of the meniscus in the mold transitions from a high state to a low state, the drawing speed of the pinch roll and the casting speed are reduced. It has been found that the fluctuation width of the position of the meniscus in the mold is increased due to the increase in the drawing speed of the cast slab due to the imbalance with the drawing resistance of the slab.

Further, when α = 0.5 in the equation (1), since the speed at which the meniscus in the mold descends at the highest speed, the speed at which the slab is drawn out increases most.
It was found that the variation of the position of the meniscus in the mold was promoted most.

The inventor of the present application further proposes that, for example, a k-th guide roll and an adjacent guide roll have an integer m times the interval (Vc × T) at which dents occur, as represented by the following equation (2). When the interval D between the adjacent guide rolls matches, D = m × Vc × T (2) Since the drawing resistance of the slab increases simultaneously between the adjacent guide rolls, the adjacent guides Roll spacing D
Where d = D / m, which is a length obtained by dividing the number of dents m formed on the surface of the mold by the following equation (3), L _k / d = n + α , N is an integer (3) When 0.25 <α <0.75, the fluctuation width of the position of the meniscus in the mold in the period T increases, and a new dent is formed on the surface of the slab at the interval d. Therefore, it has been found that the fluctuation of the meniscus position in the period T is promoted repeatedly.

As described above, in the continuous casting apparatus, when the time during which the dents pass through the surface of the slab and the cycle at which the position of the meniscus in the mold fluctuates coincide with each other, no matter where the guide roll is arranged, While large dents are formed on the surface of the piece, fluctuations in the position of the meniscus in the mold, the slab withdrawal resistance, and the slab withdrawal speed diverge, which not only deteriorates the product quality but also may lead to a shutdown. Had been a problem.

The present invention has been made based on the above findings.
Yes, its purpose is from the meniscus in the mold
Distance to the k-th guide roll (where k is a natural number)
L_kAnd the (k + 1) th guide line from the meniscus in the mold
Distance L_{k + 1}And the k-th guide law
(K + 1) th guide roll (L
_{k + 1}-L_k) From the k-th guide roll to (k + 1)
Divided by the number m of dents existing up to the th guide roll
Length d and distance L_kAnd the distance L _{k + 1}Passing
And L_kIn both cases, the fractional part α is 0.25 <α <
Position the guide roll so that it does not reach 0.75
The position of the meniscus in the mold to the target level
When the guide roll changes to a lower state,
The position of the meniscus in the mold, passing just below the surface dent
When the resistance changes from low to high
By taking advantage of the fact that the drag decreases and the drawing speed of the slab increases
To cancel the rise of the meniscus position in the mold.
To reduce the cost of operation without increasing equipment costs.
It is possible to prevent the variation of the meniscus position in the mold from diverging.
It is an object of the present invention to provide a continuous casting apparatus capable of performing the above functions.

[0014]

According to a first aspect of the present invention, there is provided a continuous casting apparatus in which a slab obtained by pouring a molten metal into a mold is supported by a plurality of guide rolls from below the mold.
In a continuous casting apparatus that is continuously manufactured by drawing with a pinch roll below the guide roll, the guide roll is separated from a predetermined position in the mold by a distance L _k from a predetermined position in the mold to a k-th guide roll. (k + 1) -th guide a distance L _{k + 1} up roll, k-th from the guide roll (k + 1) -th guide distance to the roll (L _{k + 1} -L k) the length divided by the integer m d And the distance L _k
Where L _k / d = n + α, where n is an integer, 0 ≦ α ≦ 0.25 or
It is provided at a position where 0.75 ≦ α <1.

In the present invention, the predetermined position in the mold is set as a target level at which the meniscus in the mold should be located in order to control the position of the meniscus in the mold, and the position of the meniscus in the mold is transiently changed from a high state to a low state. When the guide roll is arranged so that the dent passes directly under the guide roll when changing to the timing, after the dent has passed, the timing at which the drawing speed temporarily increases as the pull-out resistance decreases and the mold The timing at which the position of the inner meniscus rises can be matched, and as a result, the rise of the position of the meniscus in the mold can be canceled by the drawing speed, so the position of the meniscus in the mold due to the dent formed on the surface of the slab. Can be suppressed.

Specifically, the distance from the meniscus in the mold to the k-th guide roll is L _k , and the distance from a predetermined position in the mold to the (k + 1) -th guide roll is L _{k + 1.}
Then, a ratio between a length d obtained by dividing a distance (L _{k + 1} −L _k ) from the k-th guide roll to the (k + 1) -th guide roll by an integer m and the distance L _k is _obtained .

In this case, d is an interval at which dents are formed on the surface of the slab, and is a product of the fluctuation period T of the position of the meniscus in the mold and the drawing speed Vc of the slab. 0 ≦ α ≦ 0.25 or 0.75 ≦ α <1
By arranging the guide rolls so that, between adjacent guide rolls, when the position of the meniscus in the mold changes from a high state to a low state transiently, a dent formed on the surface of the slab immediately below the guide rolls Will pass through.

Thus, when the position of the meniscus in the mold changes from a low state to a high state, the drawing speed is temporarily increased to cancel the rise in the position of the meniscus in the mold. The variation of the position of the meniscus in the mold can be suppressed.

[0019]

Embodiments of the present invention will be specifically described below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic diagram showing a continuous casting apparatus according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes a mold having upper and lower openings. Above the mold 1, an immersion nozzle 2 is provided, which is controlled to inject the molten metal until the meniscus in the slab is at the target level. The mold 1 is water-cooled by a cooling device to form a solidified shell from a portion of the molten metal that comes into contact with the inner wall of the mold 1. A guide roll 3 is arranged below the casting mold 1 and pulls the casting from the casting mold 1 while supporting the casting to form a solidified shell while sandwiching the casting. A pinch roll 4 is provided below the guide roll 3, and is controlled so that the speed of drawing the slab is constant.

When the distance from the meniscus in the mold to the k-th guide roll 3 (k) is L _k , the guide roll 3 is (k + 1) from the k-th guide roll 3 (k).
Distance (L _{k + 1} −) to the third guide roll 3 (k + 1)
(L _k ) divided by an integer m and the distance L _k so as to satisfy the following equation (4). L _k / d = n + α (4) where n is an integer and 0 ≦ α ≦ 0.25 or 0.
75 ≦ α <1

FIG. 2 is a schematic diagram showing the arrangement of the first to fifth guide rolls in the continuous casting apparatus according to the first embodiment of the present invention. In the figure, the guide rolls 3 are arranged such that the distance from the meniscus in the mold to the first guide roll 301 is 900 mm, and the first guide roll 301 and thereafter are arranged at equal intervals of 300 mm in the drawing direction of the slab. is there. Thus, for example, the distance L ₅ = 21 from the meniscus in the mold to the fifth guide roll 305
For 00 mm and a distance of 300 mm from the fourth guide roll 304 to the fifth guide roll 305, assuming that the slab withdrawal speed Vc = 1.0 m / min and the fluctuation period T of the position of the meniscus in the mold is 4.5 sec. The distance d between the dents formed on the surface of the slab is 75 mm
Becomes

Since d = 300/4 = 75 mm, the ratio of L ₅ to d is 2100/75 = 2
8, which satisfies α = 0 in equation (4). In addition to this, when α is obtained by the same procedure for the tenth guide roll and the twentieth guide roll, α becomes 0, so that 0 ≦ α ≦ 0.25 or
In addition to satisfying 0.75 ≦ α <1, the guide roll is arranged so as to pass through the dent formed on the surface of the slab at the timing when the position of the meniscus in the mold reaches the lowest point. Therefore, it is possible to suppress the variation of the position of the meniscus in the mold, which has occurred at the period d / Vc of the position of the meniscus in the mold.

(Embodiment 2) FIG. 3 shows an embodiment of the present invention.
It is a schematic diagram which shows the continuous casting apparatus by the form 2. In the figure
And the guide roll also casts from the meniscus in the mold.
(K + 1) th guide roll 3 (k + 1)
Distance L at_{K + 1}To determine the k-th guide roll
Distance L to 3 (k)_k(5), (6) and
And (7). L_k/ (L_{k + 1}-L_k) = N + α₁ (5) where n is an integer and 0 ≦ α₁≦ 0.25 or
0.75 ≦ α₁<1 and L_k/ ｛(L_{k + 1}-L_k) / 2｝ = n + α_Two (6) where n is an integer and 0 ≦ α_Two≦ 0.25 or
0.75 ≦ α_Two<1 and L_k/ ｛(L_{k + 1}-L_k) / 3｝ = n + α_Three (7) where n is an integer and 0 ≦ α_Three≦ 0.25 or
0.75 ≦ α_Three<1 In the example of Table 1, α₁= 0 and
0 <α_Two<0.02 or 0.98 <α _Two≦ 1 and 0
<Α_Three<0.02 or 0.98 <α_ThreeSatisfies ≦ 1
Are arranged as follows.

[0024]

[Table 1]

FIG. 4 is a schematic diagram showing the arrangement of the tenth to fourteenth guide rolls in the continuous casting apparatus according to the second embodiment of the present invention. In the figure, the tenth guide roll 310 is located at a position 3600 mm away from the meniscus in the mold. The distance between the guide rolls is 10 mm, the distance between the 11th guide rolls 310 and 311 is 300 mm,
The distance between the first and twelfth guide rolls 311 and 312 is 2
78.5 mm, 12th and 13th guide rolls 312,
The distance between 313 is 321.5 mm and the distance between the thirteenth and fourteenth guide rolls 313 and 314 is 300 mm, respectively. For example, for the eleventh and twelfth guide rolls 311, 312, L ₁₂ = 417 from Table 1.
Assuming that 8.5 mm and L ₁₁ = 3900 mm, the equation (5) gives 15.003, and α ₁ = 0.

In addition, the 18th guide roll and 36
Th when obtaining the alpha ₁ in the same procedure for the guide rolls, both become zero. Further, from equations (6) and (7), α
_{When both 2} and α ₃ are obtained, 0 <α ₂ <0.02 or 0.98 <α ₂ ≦ 1 and 0 <α ₃ <0.02 or 0.98 <α ₃ ≦ 1 Meets Thus,
Since the guide rolls are arranged so as to pass through the dents on the surface of the slab at the timing when the position of the meniscus in the mold reaches the lowest point, fluctuations in the position of the meniscus in the mold can be suppressed.

FIG. 5 is a graph showing the results of an experimental operation of the continuous casting apparatus according to the second embodiment of the present invention. With the continuous casting apparatus of the present invention, the drawing speed of the slab is 1.0 m /
As a result, the position of the meniscus in the mold fluctuated about 3 mm from the target level, but there was almost no fluctuation in the slab withdrawal resistance and the mold withdrawal speed. Indicates that the process was completed.

FIG. 6 shows a conventional continuous casting apparatus.
It is the schematic diagram which showed arrangement | positioning of the 14th to 14th guide roll. In the figure, the tenth guide roll 31
0 is located at a distance of 3787.5 mm from the meniscus in the mold. The intervals of the eleventh guide roll 311, the twelfth guide roll 312, the thirteenth guide roll 313, and the fourteenth guide roll 314 are each 30.
0 mm, and the guide roll withdrawal speed Vc =
1.0 m / min, the interval d = 75 mm of the dent formed on the surface of the slab expressed by the product of the variation period T of the position of the meniscus in the mold = 4.5 sec. .5.

FIG. 7 is a graph showing the results of an experimental operation of a conventional continuous casting apparatus. As a result of manufacturing a slab at a drawing speed of 1.0 m / min with a conventional continuous casting apparatus, the position of the meniscus in the mold was raised and lowered about 10 mm from the target level in a cycle of 4.5 seconds 20 minutes after the start of casting. It was way. Thereafter, the fluctuation range further increased, and after 30 minutes from the start of casting, the fluctuation range became 20 mm above and below the target level. In addition, since the fluctuations in the slab withdrawal resistance and the slab withdrawal speed also increased in the period of 4.5 seconds, even in some guide rolls, 0.25 <α <0.7 in equation (1).
5 satisfies that the position of the meniscus in the mold fluctuates at a period corresponding to an integer 1 / m of the interval between the guide rolls 3.

[0030]

As described in detail above, in the present invention, the distance L _k from the predetermined position in the mold to the k-th guide roll, and the distance L _k from the predetermined position in the mold to the (k + 1) -th guide roll. the distance L _{k + 1, k-th} from the guide roll to the (k + 1) -th guide roll distance (L
_{k + 1−} L _k ) divided by an integer m and the distance L _k , the fractional part α is 0 ≦ α ≦ 0.25 or 0.75 ≦ α <1. Arrange guide rolls so that With this, when the position of the meniscus in the mold is changed from a state in which the position of the meniscus in the mold is low, since the dent of the surface of the slab passes immediately below the guide roll when the position of the meniscus in the mold transitions from a high state to a low state transiently. By using the fact that the drawing resistance decreases and the drawing speed temporarily increases when changing to a high state, it is possible to cancel the rise in the position of the meniscus in the mold and suppress the fluctuation of the position of the meniscus in the mold. it can. In addition to preventing the occurrence of defects that cause deterioration of product quality due to the indentation of the slab surface and the powder entrained on the molten metal surface, it also prevents fluctuations in the position of the meniscus in the mold resulting in the shutdown of the operation such as overflow of the molten metal from the mold. The present invention has excellent effects, for example, because it can prevent divergence, thereby enabling stable operation.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a continuous casting device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing the arrangement of first to fifth guide rolls in Embodiment 1 of the continuous casting apparatus of the present invention.

FIG. 3 is a schematic diagram showing a continuous casting device according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing an arrangement of tenth to fourteenth guide rolls in a continuous casting apparatus according to a second embodiment of the present invention.

FIG. 5 is a graph showing the results of an experimental operation of the continuous casting apparatus of the present invention.

FIG. 6 is a schematic diagram showing the arrangement of tenth to fourteenth guide rolls in a conventional continuous casting apparatus.

FIG. 7 is a graph showing the results of an experimental operation of a conventional continuous casting apparatus.

FIG. 8 is a schematic view showing a conventional continuous casting apparatus.

FIG. 9 is a schematic view showing a continuous casting apparatus disclosed in Japanese Patent Publication No. 4-65742.

FIG. 10 is an explanatory diagram of a mechanism in which the position of a meniscus in a mold fluctuates due to a surface dent of a slab.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 Guide roll 4 Pinch roll

Claims (1)

[Claims] 1. A slab obtained by pouring a molten metal into a mold is continuously produced by being drawn by a pinch roll below the guide roll while being supported by a plurality of guide rolls below the mold. in the continuous casting apparatus, wherein the guide roll, the distance L _k from a predetermined position within said mold to k-th guide roll, distance from a predetermined position in said mold until the (k + 1) -th guide roll L _{k + 1,} and a k-th guide distance from the roll to the (k + 1) -th guide roll (L k _{+ 1} -L _k) the length divided by the integer m d, the ratio of the distance L _k, L _k / D = n + α where n is an integer, 0 ≦ α ≦ 0.25 or
A continuous casting apparatus provided at a position satisfying 0.75 ≦ α <1.