JP2783484B2 - Twin drum continuous casting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-drum continuous casting method and apparatus for continuously casting a thin plate from a molten metal such as molten steel, and more particularly, to a drum in a case where foreign matter is caught between the drums. And a device for implementing the method.

[0002]

2. Description of the Related Art JP-A-55-100852 discloses that
The rolling reaction force acting on the water-cooled casting roll is detected by a load cell, etc., and the number of revolutions of the water-cooled casting roll is adjusted according to the magnitude of the reaction force to constantly control the rolling reaction force within a certain safe range. A direct rolling continuous casting method is disclosed which stabilizes the operation by preventing overload from acting on the roll and continuously casts a slab of stable quality.

In Japanese Patent Publication No. 47-48774, the thickness of a sheet coming out from between a pair of rolls is detected by a pickup, and when the thickness of the sheet increases, the rotation speed of the roll increases. In the opposite case, a continuous metal plate manufacturing method is described in which the thickness of the plate is kept at a predetermined value by controlling the rotation speed to decrease.

In these conventional examples, the magnitude of the reaction force acting on the roll or the thickness of the slab is detected, and the thickness is adjusted by controlling the number of rotations of the roll. As shown in FIG. 5, as shown in FIG. 5, a reaction force acting on the support portion of the roll is detected by a load detector such as a load cell, and the value is compared with a set value so that the reaction force deviation becomes zero. By operating the servo cylinder supporting the roll bearings in a manner such as proportional control and proportional integral control, and finely adjusting the position of one roll with respect to the other roll, the reaction force, that is, the rolling force It is common to control.

[0005]

SUMMARY OF THE INVENTION In continuous casting,
A so-called hot band that can be made into a slab may cause slab breakage. A hot band is a phenomenon in which foreign matter such as shards of refractory is intruded into the solidified shell during casting, and the thickness of the slab temporarily increases in that part. This is a high-temperature portion that appears in a strip shape on the slab as a result of the instantaneous reduction of the rolling force on the slab.

When a slab portion that has caught foreign matter passes through the gap between the pair of drums, as shown in FIG. 4A, the pair of drums is deformed due to slight elastic deformation of the drum and the portion supporting the drum. The instantaneous gap increases instantaneously, and the reaction force at the support portion of the drum also increases as indicated by b.
Since the rolling force of the drum at that time acts intensively on the foreign matter biting portion and does not act on the entire area of the slab in the width direction, heat removal of the slab in that portion, that is, cooling is deteriorated. The temperature rises and a hot band is formed.

[0007] Foreign matter, such as ingots and refractory debris, may fall between the drums.
When passing through the gap (closest point), the gap of the drum when passing
And the reaction force of the drum sharply increases.
After a short time, the gap between the drums quickly returns to the original state (reduced)
And the reaction force of the drum suddenly returns to the original value (reduced).
A little). However, the reaction force acting on the drum support was detected.
Then, the drum gap is proportionally controlled by the detected signal.
When controlling, the control operation to be tend to bring said reaction force increases as b in FIG. 4 the setting value, supports because the drum is run at a specific time lag in the control unit and drive mechanism The bearing retreats, and as shown in FIG. 4c, the gap of the drum that has begun to return widens again along the way . As a result, the gap between the drums changes in such a manner that there are peaks such as a and c and a constriction e having a depth d therebetween.

Immediately after the foreign matter passes through the gap between the drums ,
Originally, the reaction force is suddenly returning to the original value
Because ring, bearing moves backward gap for supporting the drum by the control unit at this point rather open as shown in c of FIG. 4 again
Then, the reaction force becomes excessively lower than the original value and becomes considerably lower than the set value . This state is called “pressure loss”
I'm calling This pressure release only state, the pressure decreases with respect to the slab of the drum, the temperature of the heat removal is worsening slab of the slab is high due to the drum no longer, temperature <br/> of the hot band immediately after section slab Cause it to increase. Slab breakage due to hot band
It is going on hot parts of the slab and the thickness variation portion of the slab corresponding to the constricted portion e as described above, and corresponds to the pressure immediately after omission portion f.

[0009] When the slab exits the gap between the drums and is guided toward the coiler, tension acts on the slab,
The slab is easily broken at the weak point formed in the slab such as a hot band, and if it breaks, not only will the continuous casting operation be interrupted, but also a large amount of time and materials will be wasted on repair work. become. Therefore, the present invention
An object of the present invention is to solve the problems of slab breakage due to a hot band and variation in slab thickness in a twin-drum thin sheet continuous casting method and an apparatus for implementing the method.

[0010]

According to the present invention, as a means for solving the above-mentioned problems, a thin plate is formed by using a device provided with a pair of drums which are internally cooled and driven to rotate in opposite directions at the same rotational speed. In a method of detecting a reaction force acting on the drum support portion during continuous casting and controlling the gap of the drum by a control system including proportional control based on the detected signal, a total value of the detected reaction forces is provided. Is divided by the drum width, that is, the set value (P ₀ ) of the reaction force per drum width, that is, the line contact rolling force, is set to ₁ to 25 kg / mm, and the upper limit value (P ₀ + ΔP ₀ ) to the set value (P ₀ ). ) Is set, and the upper limit value (P ₀ + Δ) of the detected values (P) of the line contact rolling force is set.
The detected value (P) exceeding P ₀ ) is the upper limit value (P ₀ + Δ
P ₀ ) as well as the upper limit (P
₀ + [Delta] P ₀₎ of the ([Delta] P ₀₎ to provide _{0.1P 0 kg / mm ≦ ΔP 0} ≦ 0.2P 0 kg / mm satisfying twin drum type thin plate continuous casting method characterized by the.

[0011]

[0012]

[Function] A limiter for detecting a reaction force acting on a drum supporting portion and dividing a total of the detected values by a drum width, that is, a linear contact reduction force per drum width, to a predetermined upper limit value or less. As a result, the operation of the rolling force control becomes slower and the depth of the constriction in the change characteristic of the drum gap becomes smaller. In addition, the reaction force of the drum supporting portion does not greatly decrease even when pressure is released, the stable rolling force on the slab is maintained, and the slab cooling (heat removal) performance of the drum is deteriorated. Is prevented, and it can be prevented that the temperature of the hot band becomes abnormally high and the slab breaks.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a twin-drum type thin plate (steel plate in the embodiment) continuous casting apparatus 1 embodying the present invention. While being cooled by such a cooling medium, they are rotationally driven in opposite directions (directions of arrows) at the same rotational speed by a drive mechanism (not shown). The twin-drum thin-sheet continuous casting apparatus 1 includes a pair of bearings 6, 6 and 7 that rotatably support both ends of the shafts 4 and 5 of the drums 2 and 3, respectively.
7 (FIG. 1 shows only the bearings 6 and 7 on one end side of the shafts 4 and 5; the same applies hereinafter) and a common frame 8 (the phantom line) supporting those bearings 6, 6 and 7, 7. ), And hydraulic servo cylinders 9, 9 respectively provided between the bearings 7, 7 and the frame 8 to determine the positions of the bearings 7, 7, and a load (reaction force) acting on the bearings 6, 6. ) Are provided with load detectors (load cells) 10 and 10 provided between the frame and the frame 8 to detect the load.

The distance between the drums 2 and 3 is determined by the hydraulic cylinder 9,
Although determined by the positions of the bearings 7 determined by 9, the size of the interval and the rotation speed of the drum are the main factors that determine the thickness of the cast slab to be continuously cast. In the upper part of the gap between the drums 2 and 3, there is formed a pool 11 whose side is partitioned by a side weir (not shown). A nozzle of a tundish (not shown) extends into the pool 11 and molten steel ( Generally, molten metal (metal) is supplied into the pool 11. Hot water pool part 1
The molten steel supplied in 1 is cooled where it is in contact with the surfaces of the drums 2 and 3, solidifies to form a shell 12, and the drums 2 and 3 are driven to rotate in the directions of the arrows, thereby causing the drums 2 and 3 to rotate. Through the narrowest gap between 3
Upon receiving the rolling force, the strip 13 becomes a strip-shaped cast piece 13 and is continuously fed downward. The fed slab 13 is further cooled while being guided by a pinch roller or the like (not shown) and finally wound up by a coiler. When continuous casting is performed, the drum 3 is pressed and supported toward the drum 2 by the hydraulic cylinders 9, 9, whereby the slab 13 (shell 12) sandwiched between the drums 2, 3 exerts a rolling reduction force. Acts, and the load detectors 10 detect a reaction force having a magnitude corresponding to the rolling force.

As conceptually shown in FIGS. 1 and 2, the reaction force detected by the load detector 10 (a value obtained by adding the reaction forces detected by the two load detectors 10; Since the reaction force per drum width divided by the drum width is equal to the line contact reduction force per drum width, in the following description, simply referred to as the reaction force, refers to the reaction force per drum width, that is, the line contact reduction force ) Is input to, for example, an electronic control device 16 and is set by a limiter circuit 17 provided in the control device 16 to an upper limit value that is set to a positive side higher than the set value of the reaction force. Limited to: Therefore,
Even if a detected value of a large reaction force is input to the limiter circuit 17, the portion exceeding the upper limit is cut off, so that in the case of a large reaction force range equal to or more than the upper limit , the upper limit is output. Control with high responsiveness such as proportional control is performed by a signal whose magnitude is limited to the upper limit value through the limiter circuit 17.

The control device 16 generates a control signal in this manner, and thereby automatically operates a control valve (not shown) to finely adjust the hydraulic pressure sent to the hydraulic cylinder 9. If the detected value of the reaction force is equal to or less than the upper limit value of the limiter circuit 17, the reaction force control is operated as it is, and the hydraulic cylinder 9 moves the drum 3 via the bearing 7 in the forward and backward directions with respect to the drum 2. As a result, the drum gap changes, so that drums 2 and 3
If the rotation speed of the slab is constant, the slab 1
The rolling force 3 and the thickness of the slab vary depending on the size of the drum gap. On the other hand, the reaction force control does not work for the reaction force deviation exceeding the upper limit value , that is,
Because they are recognized as the upper limit value, the upper limit to the slow control state operating range becomes narrow reaction force control is set to a value close to the set value of the reaction force.

Therefore, by adjusting the upper limit value of the limiter circuit 17 and limiting the maximum value of the passing reaction force signal, the depth d of the constricted portion in FIG.
Can be made small to obtain a smooth shape with almost no constriction in the change in the drum gap as shown in FIG.
The control device 1 which attempts to reduce the reaction force deviation
6, the actual reaction force value (detected value) does not drop below the set value, and the shell 12
Can be prevented from abnormally decreasing the rolling force of the drums 2 and 3 with respect to the temperature of the slab 13, and as a result,
It is possible to avoid slab breakage due to the hot band.

Table 1 shows the results of experiments in which the set value (P ₀ ) of the reaction force of the drum and (ΔP ₀ ) of the upper limit value (P ₀ + ΔP ₀ ) are variously changed. Cases 3-1, 3-2, 4-3, and 5-2 correspond to the present invention .
2 ) which corresponds to the embodiment of 3 ), 3-3, 4-1, 4
The present invention also covers -2, 4-4, 5-1 and 5-3, but satisfies claim 1 only.
1-3, 2, and 6 are comparative examples that do not meet the purpose of the present invention. The common experimental conditions were as follows: drums 2 and 3 had a drum diameter of 1200 mm, a drum width of 800 mm,
Casting speed 80m / min, thickness of slab 13 2.5m
m. In Table 1, the hot band has a difference of 0.6 mm or more in the value of the drum gap.

[0019]

[Table 1]

As can be seen from Table 1, even if the set value of the reaction force of the drum is simply increased, the reaction force at the time of pressure release increases, and the probability of slab breakage due to the hot band decreases. However, since the depth d of the constricted portion e (see FIG. 4) cannot be reduced, no slab break due to the hot band could be eliminated. However, by adjusting the set value ( upper limit value ) of the reaction force deviation limiter, the controllability against the sudden rise of the reaction force when the foreign matter is caught is slowed, and the depth d of the constricted portion e is reduced. In addition, it was found that by reducing the amount of reduction in the rolling force at the time of pressure release, it was possible to eliminate slab breakage due to the hot band.

FIG. 6 shows the set value (P ₀ ) of the reaction force and the upper limit value (P ₀ + ΔP ₀ ) of the reaction force based on the experimental results.
(P ₀ ) shows the probability of slab breakage in the hot band. Case 2 does not satisfy the requirement of Claim 1 because the reaction force set value (P ₀ ) is as low as less than 1 kgmm, and has a high probability of slab breakage. In case 4-1, the probability of slab breakage is low,
Value (ΔP ₀ ) is too small and the controllability of the reaction force is poor . Cases 3-3, 4-4, and 5-3 satisfy the requirements of claim 1, and thus have a lower probability of slab breakage than the comparative example.
Although the following effect is obtained , the probability does not become 0% because the requirement of claim 2 is not satisfied. In case 6, the probability of hot band breakage is 0%, but since the set value of the reaction force ( P ₀ ) is too large, there is a problem that the roll surface is worn out a lot, which is inconvenient. From the above, the range in which stable operation can be performed with the probability of slab breakage being 0% is expressed by the following two equations. _{1kg / mm ≦ P 0 ≦ 25kg} / mm 0.1 P 0 kg / mm ≦ ΔP 0 ≦ 0.2P 0 kg / mm However, P _0: reaction force setting value (line contact pressure force per drum width (kg / Mm)) P ₀ + ΔP ₀ : Upper limit of reaction force (Line contact reduction force per drum width (kg / mm)) P: Detected reaction force (Line contact reduction force per drum width (kg / mm) )

FIG. 7 shows the relationship between the slab neck depth (mm) and the reaction force per drum width (kg / mm) of the reaction force at the time of pressure release based on the experimental results in Table 1 as in FIG. 5 shows a high probability of slab breakage in the hot band portion. Since the shaded region where the probability of slab breakage is 0 is within the range suitable for the purpose of the present invention, the conditions for realizing this in the continuous casting machine used in the experiment are the depth d of the constricted portion e and the pressure drop. It was confirmed that the reaction force (F) per drum width obtained by dividing the reaction force at that time by the drum width was as follows. F ≧ 1 (kg / mm) d ≦ 0.5 (mm) d ≦ 0.022 × F−0.022 where d: slab squeeze depth (mm) F: reaction force at pressure release (line contact per drum width) Rolling force (k
g / mm))

[0023]

According to the present invention, even when foreign matter is caught in the operating state of the twin-drum type thin plate continuous casting apparatus, there is no danger of forming a high-temperature hot band and causing slab breakage. The operation of continuous casting can be continued, and a large loss due to cut slab can be prevented.

[Brief description of the drawings]

FIG. 1 is a front view showing a twin-drum thin sheet continuous casting apparatus for carrying out the present invention.

FIG. 2 is a diagram conceptually showing a relevant portion of a control device for implementing the present invention.

FIG. 3 is a characteristic diagram showing the operation of the embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the operation of a conventional example.

FIG. 5 is a diagram conceptually showing a relevant portion of a conventional control device.

FIG. 6 is a table showing the result of examining the probability of slab breakage in a hot band portion.

FIG. 7 is a table showing the results of examining the probability of slab breakage in a hot band portion.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Twin drum type continuous thin-plate casting apparatus 2, 3 ... Drum 4, 5 ... Shaft 6, 7 ... Bearing 8 ... Frame 9 ... Hydraulic cylinder 10 ... Load detector 11 ... Pool hole 12 ... Shell 13 ... Cast piece 16 ... Control device 17: Limiter circuit

Continued on front page (72) Inventor Yasuhiro Yamagami 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division (72) Inventor Hideki Oka 3434 Shimada, Oji, Hikari-shi, Yamaguchi Prefecture Nippon Steel Corporation (72) Inventor Hidenori Hattori 4-62 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. 22 Hiroshima Works, Mitsubishi Heavy Industries, Ltd. (56) References JP-A-59-193740 (JP, A) JP-A-61-103651 (JP, A) JP-A-62-223482 (JP, A) 1-192449 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 11/00-11/22

Claims (1)

(57) [Claims] 1. A reaction force acting on a drum supporting portion when a thin plate is continuously cast using a device provided with a pair of drums which are internally cooled and driven to rotate in opposite directions at the same rotation speed. In the method of controlling the gap of the drum by the proportional control based on the detected signal, the set value (P ₀ ) of the reaction force per drum width obtained by dividing the total value of the detected reaction force by the drum width is 1 to 25 kg / mm and an upper limit (P ₀ + ΔP ₀ ) with respect to the set value (P ₀ ) of the reaction force, and the upper limit (P ₀ +
The detected value (P) of the reaction force exceeding ΔP ₀ ) is the upper limit value (P ₀
+ ΔP ₀ ) as well as the upper limit value
(P ₀ + ΔP ₀ ) wherein (ΔP ₀ ) satisfies the following condition . 0.1 P ₀ kg / mm ≦ ΔP ₀ ≦ 0.2 P ₀ kg / mm, where P _{0 is} the set value of the reaction force (the linear contact reduction force per drum width (kg / mm)) P ₀ + ΔP _{0 is the} reaction force Upper limit value (Line contact reduction force per drum width (kg / mm)) P: Reaction force detection value (Line contact reduction force per drum width (kg / mm))