JP2020104139A - Twin drum type continuous casting apparatus and twin drum type continuous casting method - Google Patents

Abstract

To prevent overshooting of a molten metal surface between twin drums during the initial stage of a casting process in a twin drum type continuous casting apparatus and a twin drum type continuous casting method.SOLUTION: A twin drum type continuous casting apparatus 1 comprises: a first tundish 10; a second tundish 20 that temporarily stores a molten metal injected from the first tundish 10; a twin drum type strip caster 30 that has a pair of drums rotated in opposing directions and forms a basin between the pair of drums to carry out continuous casting by injecting the molten metal between the pair of drums from the second tundish 20; and a flowrate controller 40 that controls the throughput V1 of the molten metal injected from the first tundish 10 to the second tundish 20 so that the height H of the molten metal surface of the second tundish 20 can be a prescribed value. The throughput V2 of the molten metal injected from the second tundish 20 to the twin drum type strip caster 30 is determined on the basis of the height H of the molten metal surface of the second tundish 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a twin-drum type continuous casting device and a twin-drum type continuous casting method.

Twin-drum type continuous casting is a technique for directly casting molten metal into thin plate-shaped slabs (strips). The twin-drum type continuous casting device used in this casting technique continuously melts molten metal (for example, molten steel) stored between a pair of rotating drums (twin drums) in a drum nip while solidifying it to continuously cast strip. To do. According to the twin-drum type continuous casting method using this twin-drum type continuous casting device, it is possible to cast a near net shape material and omit the hot rolling step. Further, according to the twin-drum type continuous casting method, improvement in material properties due to rapid solidification is expected.

As such a twin-drum type continuous casting device, for example, in Non-Patent Document 1, in order to control solidification in a short time and overcome an excessive heat load applied to a mold, a tundish (large There is disclosed a strip caster in which a small tundish (Transition Piece: TP) is arranged directly below a tundish. In Non-Patent Document 1, TP is said to play the role of reducing the iron static pressure of molten steel and making the flow distribution in the width direction of the casting roll uniform.

Further, for example, in Patent Document 1, thin cast continuous casting in which molten metal injected from a large tundish into a small tundish through a sliding nozzle overflows from the small tundish and is cast by a belt type continuous casting machine. In the method, it is disclosed that the amount of hot water supplied from the large tundish to the small tundish is controlled, and the drawing speed is constantly controlled. That is, this casting method is characterized in that the molten metal overflows by controlling the molten metal surface level of the small tundish.

Further, for example, in Patent Document 2, in a continuous casting method using a twin belt caster, a gate is provided in a hot water supply port opened on a tundish side wall on the caster side, and the hot water in the caster and the tundish on the caster side is provided. According to the surface level, it is disclosed that the opening/closing amount of the nozzle of the tundish (upper tundish) arranged on the upper part of the gate and the tundish on the caster side is adjusted to control the level of the molten metal in the caster at a constant level. ing.

In addition, for example, Patent Document 3 discloses a twin roll type continuous casting machine in which a pressure chamber for gas-pressurizing the surface of the molten metal for casting is formed between the twin rolls and the tundish. Further, in this casting machine, the pressurization type may be formed from the lower end of the tundish toward the upper surface of the roll and the upper part of the side dam, and the tundish has a flow regulating nozzle for tapping at the bottom. It is also disclosed that a lower hot water storage part having a relatively small bottom area may be formed in the upper part of the nozzle, and an upper hot water storage part having a relatively large bottom area may be formed in the upper part of the lower hot water storage part.

JP-A-60-203351 JP 61-014059 A JP-A-02-127946

Toshio Matsushita, 3 others, IHI Technical Report, Ishikawajima Harima Heavy Industries, Ltd., Vol. 48 No. 2 (2008-6)

By the way, according to the study by the present inventors, in the conventional twin-drum type continuous casting apparatus, when the operation of the apparatus is started, at the beginning of the casting process (particularly immediately after the start of casting), It was found that a phenomenon called a so-called overshoot occurs, in which the level of the molten metal greatly exceeds (is penetrated) the ideal way of rising the molten metal.

When this overshoot occurs, the level of the molten metal in the basin between the twin drums rises to a level higher than the targeted molten metal level. As a result, there is a problem that the metal is stretched on the wall surface of the pool where the level is higher than the intended level and the scum weir installed inside the pool. In some cases, the molten metal may overflow from the twin drums (overflow).

However, the problem that the molten metal surface level of the molten metal pool between the twin drums overshoots at the initial stage of the casting process has not been examined in Non-Patent Document 1 and Patent Documents 1 to 3 above. Thus, up to now, in the twin-drum type continuous casting apparatus and the twin-drum type continuous casting method, a means for preventing overshoot at the initial stage of the casting process has not been proposed.

The present invention has been made in view of the above circumstances, and in a twin-drum type continuous casting apparatus and a twin-drum type continuous casting method, prevents overshoot of the molten metal surface of the pool between the twin drums at the initial stage of the casting process. The purpose is to do.

MEANS TO SOLVE THE PROBLEM this invention which solves the said subject WHEREIN: The 1st tundish which temporarily stores a molten metal, the 2nd tundish which temporarily stores the molten metal injected from the said 1st tundish, and it rotates to mutually opposite direction. A twin-drum type strip caster for continuous casting, which has a pair of drums and forms a molten metal pool between the pair of drums by continuously injecting molten metal from the second tundish between the pair of drums. A flow rate control device for controlling the throughput V1 of the molten metal injected from the first tundish into the second tundish so that the height H of the molten metal surface of the second tundish becomes a predetermined value. It is characterized in that the throughput V2 of the molten metal injected from the second tundish into the twin-drum type strip caster is determined by the height H of the molten metal surface of the second tundish.

According to the present invention, by providing the second tundish and injecting the molten metal from the second tundish into the twin-drum type strip caster, the injection speed of the molten metal from the second tundish into the twin-drum type strip caster is It becomes proportional to the height H of the molten metal surface of the second tundish. Therefore, at the start of casting, the molten metal level of the second tundish gradually rises, and no sudden pouring occurs from the beginning of the casting process. It is possible to prevent overshoot at the beginning of the process.

The twin-drum type continuous casting apparatus is provided at a bottom portion of the first tundish, and has a first nozzle for injecting the molten metal in the first tundish into the second tundish and an upper portion in the second tundish. And a second nozzle that is provided at the bottom of the discharge section and that injects the molten metal in the discharge section into the twin-drum type strip caster. The first nozzle may be installed such that the bottom of the first nozzle is a melting wall and the outlet of the first nozzle is located at a position lower than the upper end of the weir in the charging part.

The twin-drum type continuous casting apparatus is inert to at least a cover member that shuts off a space from a bottom portion of the second tundish to a surface of the molten metal injected between the pair of drums to the outside air and an inside of the cover member. An inert gas supply device for supplying gas may be further provided.

In the twin-drum type continuous casting apparatus, the predetermined value is the molten metal surface in the second tundish when the throughput V3 ^* of the molten metal from the twin-drum type strip caster in the steady casting state becomes equal to the throughput V2. May have a height H ^* .

Further, the present invention is a twin-drum type continuous casting method using the twin-drum type continuous casting apparatus described above, wherein the molten metal throughput V3 ^* from the twin-drum type strip caster in the steady casting state is the throughput V2. When the height H ^* of the molten metal surface in the second tundish when they are equal to each other is predetermined, the height of the molten metal surface in the second tundish from the start of operation of the twin-drum type continuous casting device is the height H. ^In the period until reaching ^* , the molten metal is injected from the first tundish to the second tundish at the throughput V1 which is larger than the throughput V2, and the pair of drum drum type casters is operated from the start of operation. During the period until the level of the molten metal poured between the drums reaches the planned level angle θ ^* , the throughput V3 of the molten metal from the twin-drum strip caster is smaller than the throughput V2. It is characterized by casting.

According to the present invention, by providing the second tundish and injecting the molten metal from the second tundish into the twin-drum strip caster, the pouring speed of the molten metal from the second tundish into the twin-drum strip caster is It becomes proportional to the 1/2 power of the height of the molten metal surface of the second tundish. Therefore, at the start of casting, the molten metal level of the second tundish gradually rises, and no sudden pouring occurs from the beginning of the casting process. It is possible to prevent overshoot at the beginning of the process.

A steady casting state in which the throughput V3 of the molten metal from the twin-drum type strip caster in the twin-drum type continuous casting method is constant, in other words, the peripheral speed of the drum is constant and the height H of the molten surface in the second tundish is constant. When H is equal to H ^*, when the molten metal surface angle θ of the molten metal injected between the pair of drums is θ<θ ^* , the flow rate control device causes the second tank The throughput V1 is adjusted so that the height H of the molten metal surface in the dish is higher than the height H ^*, and the molten metal surface angle θ of the molten metal injected between the pair of drums is θ> In the case of θ ^*, the flow rate control device may adjust the throughput V1 so that the height H of the molten metal surface in the second tundish is lower than the height H ^* . Here, the throughput means the mass flow rate (kg/min) of the molten metal (for example, molten steel) or the slab.

According to the present invention, in the twin-drum type continuous casting apparatus and the twin-drum type continuous casting method, it is possible to prevent the overshoot of the molten metal surface of the molten metal pool between the twin drums in the initial stage of the casting process.

It is a schematic diagram which shows the structure of the twin drum type continuous casting apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows an example of the control method in the twin drum type continuous casting method which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the structure of the 2nd tundish of the twin drum type continuous casting apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram for demonstrating the function of the scum weir provided in a general twin drum type strip caster. It is explanatory drawing which shows an example of the control method in the twin-drum type continuous casting method which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows an example of a structure of the cover member and inert gas supply apparatus of the twin drum type continuous casting apparatus which concerns on 3rd Embodiment of this invention. It is a schematic diagram which shows the other example of a structure of the cover member and inert gas supply apparatus of the twin drum type continuous casting apparatus which concerns on 3rd Embodiment of this invention. 6 is a graph showing the relationship between the molten metal throughput V3 from the twin-drum type strip caster and the height H of the molten metal surface in the second tundish in the example of the present invention. It is a graph which shows the simulation result of the molten metal surface level between twin drums by the twin drum type continuous casting method in the Example of this invention. It is explanatory drawing which shows the overshoot phenomenon of the molten metal surface of the molten metal pool part between twin drums in the initial stage of a casting process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, elements having substantially the same functional configuration are designated by the same reference numerals, and duplicate description will be omitted.

[Examination of the cause of overshoot and its preventive measures]
As described above, in the conventional twin-drum type continuous casting apparatus, when the operation of the apparatus is started, overshoot occurs at the beginning of the casting process. Here, the cause of occurrence of overshoot will be described with reference to FIG.

First, as an ideal way of raising the molten metal level between twin drums, as shown by the solid line in FIG. 10, the target molten metal is mainly determined by the stability and productivity of the molten metal flow in the molten metal pool between twin drums. The level is gradually increased until the surface level θ ^* (for example, the surface angle θ=40 degrees) is reached, and after reaching the target surface level, the level is kept constant. On the other hand, in order to improve the productivity of twin-drum type continuous casting, it is required that the level of the molten metal between the twin-drums reaches the target level of molten metal as soon as possible. For that purpose, it is desirable to make the flow rate of the molten metal injected between the twin drums large at the initial stage of the casting process (particularly immediately after the start of casting). In this case, even if the molten metal flow rate is narrowed (limited) when the molten metal level between the twin drums approaches the target molten metal level, the flow rate of the molten metal is large, and therefore a very steep control (time constant (Short control), and the rising speed of the molten metal level between the twin drums does not immediately decrease (low responsiveness to the adjustment of the molten metal flow rate). As a result, the actual molten metal level between the twin drums greatly exceeds the ideal rising direction of the molten metal (the curve shown by the solid line in FIG. 10) and the overshoot (see FIG. 10), as shown by the broken line in FIG. (See the circled part of)) occurs. Also, when controlling the flow rate of the molten metal between the twin drums via a stopper, the stopper is in the closed state at the start of pouring the molten metal from the ladle to the tundish, and when the molten metal has accumulated in the tundish. Open up. Immediately before opening the stopper, the bare metal is in tension in the tundish.To wash away the bare metal, the stopper must be fully opened immediately after opening the stopper. The flow rate of the molten metal injected between the drums increases at the beginning of the casting process. Therefore, similarly to the above, it is difficult to control the flow rate of the molten metal and overshoot occurs.

Therefore, as a result of diligent studies, the inventors of the present invention provided a second tundish in the subsequent stage (lower part) of the first tundish into which molten metal was poured from a ladle (not shown), and provided a second tundish from the first tundish. By controlling the throughput of the molten metal injected into the two tundish so that the height H of the molten metal surface of the second tundish becomes a predetermined value, a gentle flow rate control of the molten metal injected between the twin drums ( It was found that control with a long time constant) is possible, and based on this finding, a method for preventing overshoot at the initial stage of the casting process was conceived.

[First Embodiment]
Hereinafter, the twin-drum type continuous casting apparatus and the twin-drum type continuous casting method using the apparatus according to the first embodiment of the present invention made based on the above-described knowledge will be described in detail.

(Twin drum continuous casting machine)
First, the configuration of a twin-drum type continuous casting apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of a twin-drum type continuous casting apparatus 1 according to this embodiment.

As shown in FIG. 1, a twin-drum type continuous casting apparatus 1 according to the present embodiment includes a large tundish 10 as an example of a first tundish according to the present embodiment and a second tundish according to the present embodiment. A small tundish 20 as an example, a twin-drum type strip caster 30 (hereinafter, abbreviated as “twin-drum caster 30”), a flow rate control device 40, and a molten metal level detection device 50 are provided.

The large tundish 10 temporarily stores the molten metal injected from a ladle (not shown). A first nozzle 11 is provided at the bottom of the large tundish 10. The molten metal stored in the large tundish 10 is poured into the small tundish 20 from the first nozzle 11. The first nozzle 11 is provided with an actuator 12 as a flow rate adjusting device that adjusts the flow rate of the hot water so as to flow through the first nozzle 11. The actuator 12 injects the large tundish 10 into the small tundish 20. The throughput V1 of the molten metal is adjusted. The actuator 12 can be appropriately selected from a stopper type and a gate type. As a relative comparison, the stopper type is structurally simple, but the opening characteristics (relationship between stopper movement amount and flow rate change amount) are large, and problems such as damage to the stopper itself may occur. .. The gate type has a slightly complicated structure, but the operation is stable. These methods may be selected in consideration of the characteristics of each factory and facility.

The small tundish 20 temporarily stores the molten metal injected from the large tundish 10 through the first nozzle 11. A second nozzle 21 is provided at the bottom of the small tundish 20. The molten metal stored in the small tundish 20 is injected from the second nozzle 21 into the molten metal pool 30 a between the pair of drums (twin drums) 31 of the twin drum caster 30. Here, in the present embodiment, the second nozzle 21 is not provided with a flow rate adjusting device like the first nozzle 11, and the throughput V2 of the molten metal injected from the small tundish 20 into the twin-drum caster 30 is , H of the surface of the molten metal of the small tundish 20. The height H of the molten metal surface of the small tundish 20 is, as shown in FIG. 1, the molten metal discharge port opening on the side surface of the tip end portion (end portion on the outlet side of the molten metal) 21a of the second nozzle 21. It means the height of the molten metal level 2TDP (for example, molten steel head) of the molten metal stored in the small tundish 20 from the center.

The twin-drum caster 30 has a pair of drums (twin-drums) 31 and 31 that rotate in mutually opposite directions. The molten metal poured from the small tundish 20 into the pool 30 a between the pair of drums 31 and 31. Continuous casting. In the twin-drum caster 30, the molten metal is injected between a pair of rotating drums (twin-drums) 31, 31, and heat is removed from the surface of each drum 31 to form a solidified shell on the surface of each drum 31. The two solidified shells are pressure-bonded at the point where the distance between the twin drums 31, 31 is the smallest to form one cast piece (strip).

The drum 31, which is the main part of the twin-drum caster 30, has little thermal deformation due to heating due to contact with the molten metal, does not undergo fatigue fracture by repeated heating and cooling, and has stable thermal conditions for solidifying the molten metal. Is required. In order to satisfy such conditions, it is preferable that the drum 31 has, for example, a three-layer structure of stainless steel-copper alloy-nickel plating, and a cooling water channel is provided inside.

The flow rate control device 40 controls the throughput V1 of the molten metal injected from the large tundish 10 into the small tundish 20 so that the height H of the molten metal surface of the small tundish 20 becomes a predetermined value. For example, the flow rate control device 40 adjusts the throughput V1 by controlling the actuator 12 so that the height H of the molten metal surface of the small tundish 20 can be kept constant at a predetermined value. As described above, in the present embodiment, the first nozzle of the large tundish 10 is provided with the flow rate adjusting device (actuator 12), but the second nozzle of the small tundish 20 is provided with the flow rate adjusting device. However, the throughput V1 of the molten metal from the first nozzle is controlled so that the height H of the molten metal surface of the small tundish 20 is constant at a predetermined value, so that the throughput V2 of the molten metal from the second nozzle is That is, the flow rate of the molten metal injected from the small tundish 20 into the twin drum casters 30 is determined only by the height H of the molten metal surface of the small tundish 20.

Here, the predetermined value is such that the throughput V3 ^* in the steady casting state where the throughput V3 of the molten metal from the twin-drum casters 30 is constant (the state where the throughput is the capacity value) is equal to the throughput V2 from the second nozzle 21. It is preferable that the height H ^* of the surface of the molten metal in the small tundish 20 is (when V3 ^* =V2).

As a method for measuring the height H of the molten metal in the small tundish 20, for example, the weight of the small tundish 20 is measured and estimated from the measured value (for example, the changed weight of the small tundish 20 is small tundish. 20) and a method of directly measuring the melt level 2TDP of the small tundish 20 using a laser displacement meter, but the method is not limited to these. ..

The molten metal level detection device 50 detects the molten metal level WSP of the molten metal pool 30a between the twin drums 31, 31 of the twin drum caster 30. The specific structure of the molten metal level detecting device 50 is not particularly limited, but may be, for example, a molten metal level meter having an image pickup means such as a CCD camera. As shown in FIG. 1, the molten metal level WSP is the molten metal angle with respect to the drum 31 (in the cross section shown in FIG. 1, the central angle of the circular arc connecting the molten metal surface and the contact portion of the drum 31 and the drum nip portion N) θ. It is expressed by. For example, the molten metal level detection device 50 constantly measures the molten metal angle θ of the molten metal level WSP, and when it is detected that the molten metal angle θ is θ>θ ^* or θ<θ ^* , the flow rate control is performed. The detection result is transmitted to the device 40. The flow rate control device 40 receiving the detection result controls the throughput V2 from the small tundish 20 by adjusting the height H of the molten metal surface of the small tundish 20 so that θ=θ ^* .

As described above, according to the twin-drum type continuous casting apparatus 1 according to the present embodiment, the small tundish 20 is provided, and the outlet of the second nozzle 21 is directly connected to the molten metal pool 30a of the twin-drum caster 30. The pouring speed of the molten metal from the small tundish 20 to the twin drum casters 30 becomes proportional to the height H of the molten metal surface of the small tundish 20 to the power of 1/2. Therefore, at the start of casting, the molten metal level 2TDP of the small tundish 20 gradually rises, and sudden molten metal does not occur from the beginning of the casting process. Therefore, the molten metal level between the twin drums 31, 31 of the twin drum caster 30 is not increased. It is possible to prevent the WSP from overshooting early in the casting process.

Further, in the steady casting state (during continuous casting operation), the small tundish 20 is injected into the twin-drum caster 30 by controlling the flow rate control device 40 so that the level 2TDP of the small tundish 20 becomes constant. The molten metal throughput V2 is also kept constant. Therefore, it becomes easier than the flow rate control in the twin drum type continuous casting apparatus having only the large tundish 10 (only a single tundish) in the related art, and a stable casting process can be carried out.

(Twin drum continuous casting method)
Next, the flow of the twin-drum type continuous casting method according to the present embodiment, which is performed by operating the twin-drum type continuous casting apparatus 1 according to the present embodiment having the above-described configuration, will be described with reference to FIG. 2. To do. FIG. 2 is an explanatory diagram showing an example of a control method in the twin-drum type continuous casting method according to the present embodiment.

The twin-drum type continuous casting method according to this embodiment satisfies at least the following three conditions <condition 1> to <condition 3>.

<Condition 1>
The melt surface in the small tundish 20 when the throughput V3 ^* of the molten metal from the twin drum casters 30 in the steady casting state is equal to the throughput V2 from the small tundish 20 to the twin drum casters 30 (V3 ^* =V2). The height H ^* is defined in advance (hereinafter, the value in the steady casting state is marked with a superscript *, for example, represented as V3 ^* , H ^*, etc.).

Here, the height H of the molten metal surface in the small tundish 20 and the throughput V2 from the small tundish 20 to the twin-drum casters 30 have the relationship of the following expression (1). Note that the pressure loss coefficient k of the second nozzle 21 is a value of 3 to 4, but these values are determined in advance by experiments.
V2=S×k(2gH) ^1/2 (1)
V2: Throughput of twin-drum caster 30 in steady casting state S: Cross-sectional area of second nozzle 21 (outlet area)
g: Gravitational acceleration k: Pressure loss coefficient of the second nozzle 21

Therefore, prior to the operation of the twin-drum type continuous casting apparatus 1, the height H ^* of the molten metal surface (melt level 2TDP) of the small tundish 20 that can obtain the throughput V3 ^* of the twin-drum caster 30 in the steady casting state is obtained in advance. Keep it. This height H ^* can be obtained by the following equation (2) based on the above equation (1).
H ^* =(V3 ^* /kS) ² /(2g)... (2)

<Condition 2>
As shown in the uppermost chart and the second chart from the top in FIG. 2, the height of the molten metal surface in the small tundish 20 from the start of operation of the twin-drum type continuous casting apparatus 1 (time t ₁ ) is the height in the steady state. During the period (period I) until reaching H ^* (time t ₃ ), the molten metal is injected from the large tundish 10 to the small tundish 20 at a throughput V1 (V1>V2) larger than the throughput V2. The actuator 12 is controlled by the flow rate control device 40. The reason V1>V2 is to store the molten metal in the small tundish 20.

<Condition 3>
Top of Figure 2, as shown in the third row and the lowermost chart from the top, from the operation of the twin drum caster 30 (rotation of the twin drum 31, 31) start (time _{t 2),} during twin drum 31 In the period (period II) until the molten metal surface level WSP of the molten metal injected into the molten metal pool portion 30a reaches the planned molten metal surface angle θ ^* (for example, θ ^* =40 degrees) (time t ₄ ). The casting is performed at a throughput V3 (V2>V3) of the molten metal from the twin-drum caster 30 that is smaller than the throughput V2. The reason V2>V3 is to store the molten metal in the molten metal pool 30a between the twin drums 31 of the twin drum caster 30.

Next, a specific example of the twin-drum type continuous casting method according to this embodiment will be described with reference to FIG.

<Step S ₀ >
First, as shown in the uppermost chart of FIG. 2, injection of molten metal (for example, molten steel) from a ladle (not shown) into the large tundish 10 is started (time t ₀ ). When the amount of molten metal in the large tundish 10 reaches a predetermined value (time t ₁ ), the actuator 12 (eg, tundish stopper) is opened, and the large tundish 10 passes through the first nozzle 11 to the small tundish. The molten metal starts to be injected into the inside of 20 at the throughput V1. The throughput V1 (flow rate of the molten metal in the first nozzle 11) at this time is adjusted by the flow rate control device 40 to be the same value as the throughput V3 ^* of the twin-drum caster 30 in the steady state. The value of the throughput V3 ^* is set in advance.

After the start of pouring the molten metal into the small tundish 20, as shown in the second chart from the top of FIG. 2, the level 2TDP of the small tundish 20 starts to rise, and as a result, in the small tundish 20. The height H of the molten metal surface also begins to increase.

<Step S ₁ >
At the same time as the molten metal is poured from the large tundish 10 into the small tundish 20, the molten metal is poured from the small tundish 20 through the second nozzle 21 between the twin drums 31 and 31 of the twin drum caster 30 at the throughput V2. As shown in the chart at the bottom of FIG. 2, the molten metal level WSP of the molten metal pool 30a starts to rise (the molten metal angle θ starts to increase). At this time, as described above, during the period (time period I) from time t ₁ until the height of the molten metal surface in the small tundish 20 reaches the height H ^* in the steady state (time t ₃ ), the throughput V1 However, the actuator 12 is controlled by the flow rate control device 40 so as to be larger than the throughput V2 (see Condition 2 above).

<Step _S 2>
Next, as shown in the third and bottom charts from the top of FIG. 2, the molten metal level WSP of the molten metal pool 30a between the twin drums 31 is set to a predetermined molten metal angle θ ₀ (for example, 15° (Time t ₂ ), the twin drums 31, 31 are started to rotate, and strip casting is started. The rotation speeds of the twin drums 31, 31 are increased by a predetermined acceleration as shown in the third chart from the top of FIG. 2, and when the target rotation speed V ^* is reached, the rotation speed value is maintained. To do.

Further, as described above, from the start of casting of strip (time t _2), molten metal surface level WSP of molten metal injected into the hot water reservoir portion 30a between twin drum 31 and 31, the molten metal surface angle was scheduled theta ^{* (e.g.} , Θ ^* =40 degrees (time t ₄ ), the strip is cast at a throughput V3 (V3<V2) smaller than the throughput V2 (see Condition 3 above). At this time, the throughput V3 of the twin-drum caster 30 is determined by the rotation speeds of the twin-drums 31, 31 and the level WSP of the molten metal pool 30a. Here, the relationship between the rotational speeds of the twin drums 31 and 31, the level WSP of the molten metal pool 30a, and the throughput V3 will be described in detail below.

In a strip casting machine such as the twin-drum type continuous casting apparatus 1, the strip plate thickness (twice the solidification shell thickness) is, as shown in the following equation (3), half the solidification time of the molten metal. Proportional.
^{_{d = k 1 (t) 1/2}} ··· (3)
d: Strip plate thickness t: Melt solidification time k ₁ : Coefficient (value specific to twin-drum caster 30)

Further, since the solidification time of the molten metal is equal to the time during which the molten metal contacts each drum 31, it can be expressed as the following formula (4), assuming that the diameter of the drum 31 is constant.
t=k ₂ (θ/V) (4)
k ₂ : coefficient θ: molten metal level WSP (arc angle display)
V: rotational speed of twin drums 31, 31

Therefore, the plate thickness d of the strip has a relationship represented by the following expression (5).
d=k ₃ (θ/V) ^1/2 (5)
k ₃ : coefficient

From the above formula (5), in order to obtain the strip with the target plate thickness d, the ratio between the molten metal surface level WSP in the molten metal pool 30a and the rotation speeds of the twin drums 31, 31 may be kept constant. Actually, from the stability of maintaining the molten metal level WSP, a value of 40° to 50° is determined as the molten metal level angle θ of the molten metal level WSP, and the twin drum 31 is set in accordance with the determined molten metal level WSP. The rotation speed of 31 will be determined.

Next, if the width of the twin drums 31, 31 is constant (naturally, the density is also constant), the throughput V3 has a relationship as in the following expression (6).
V3 = k ₄ × V × d
= K ₅ ×(θ×V) ^1/2 (6)
k ₄ , k ₅ : coefficient

If the molten metal surface angle θ is increased by n times, the rotation speed V of the twin drums 31, 31 is also increased by n times in order to obtain the same plate thickness d, and as a result, the throughput V3 is increased by n times. .. That is, the higher the level of WSP, the higher the productivity of twin-drum type continuous casting.

In the twin-drum type continuous casting method described above, the height H of the molten metal surface (melt level 2TDP) of the small tundish 20 at the start of injecting the molten metal from the large tundish 10 to the small tundish 20 is an initial specified value at the maximum. The flow rate control device 40 controls the actuator 12 so that the height H ^* becomes H ^* , which causes the molten metal level WSP of the molten metal pool 30a of the twin-drum caster 30 to overflow (the molten metal from between the twin-drums 31 and 31). There is no danger.

Note that the control by the flow rate control device 40 is a very gradual control (time constant of the time constant because the increase/decrease in the flow rate of the molten metal in the actuator 12 does not directly increase or decrease the flow rate in the twin-drum caster 30). (Long control), stable control of the molten metal level WSP is possible without using an expensive control device having high response as the flow rate control device 40.

Further, since the height H of the molten metal surface (melt level 2TDP) in the small tundish 20 immediately after the start of casting is the height H ^* which is the initial specified value at the maximum, the small tundish 20 moves to the twin-drum caster 30. Throughput V2 does not significantly exceed the throughput V3 of the twin drum caster 30. Therefore, the molten metal level WSP between the twin drums 31 does not overshoot immediately after the start of casting.

<Step S ₄ >
In the steady casting state in which the throughput V3 of the molten metal from the twin-drum casters 30 is constant, the flow rate control device 40 controls the actuator 12 as follows to adjust the throughput V1.

For example, assuming that the height H of the molten metal surface (melt level 2TDP) of the small tundish 20 becomes a predetermined height H ^* , that is, the throughput V2 becomes equal to the throughput V1, the twin drums 31, 31 After the acceleration is completed, the rotation speed of the twin drums 31, 31 reaches a steady state (becomes the rotation speed V ^* ), and the molten metal level WSP of the molten metal pool 30a of the twin drum caster 30 is stabilized at the molten metal angle θ*. In a period (period III) after the time (time t4), the height H of the molten metal surface in the small tundish 20 is the initial prescribed value H ^* (for example, in the embodiment described below, The flow rate control device 40 controls the actuator 12 so that the height H of the molten steel head from the tip of the nozzle is 500 mm.

Specifically, in the period III, when the melt surface level WSP (melt surface angle θ) of the molten metal injected between the twin drums 31, 31 is θ<θ ^* , the flow rate control device 40 causes the small tank. The throughput V1 is adjusted so that the height H of the molten metal surface in the dish 20 is higher than the height H ^* . On the other hand, when the molten metal surface angle θ of the molten metal injected between the twin drums 31, 31 is θ>θ ^* , the flow control device 40 determines that the height H of the molten metal surface in the small tundish 20 is large. , The throughput V1 is adjusted to be lower than the height H ^* . That is, in the period III, if the molten metal level WSP deviates from the planned molten metal angle θ ^* (for example, 40 degrees), the flow rate control device 40 controls the actuator 12 so that the inside of the small tundish 20 is controlled. By increasing or decreasing the height H of the target molten metal surface (molten steel head), that is, adjusting the height H ^* in the steady casting state to the height H ^* ' (≠H ^* ), the molten metal level WSP So that the surface angle is θ ^* . For example, as shown in the lowermost chart of FIG. 2, in the period after time t5, when the molten metal surface angle θ of the molten metal level WSP is θ<θ ^* , the second chart from the top of FIG. As shown in, the height H of the molten metal surface in the small tundish 20 is adjusted to the height H ^* ' (H ^* '>H ^* ). On the other hand, in the period after time t5, when the melt surface angle θ of the melt surface level WSP is θ>θ ^* , the height H of the melt surface in the small tundish 20 is changed to the height H ^* ′(H ^* Adjust to'<H ^* ).

As described above, according to the twin-drum type continuous casting method according to the present embodiment, the molten metal level 2TDP of the small tundish 20 gradually increases from the start of the operation of the twin-drum type continuous casting apparatus 1, and the casting process Since the rapid pouring does not occur from the initial stage of, the overshoot in the initial stage of the casting process of the molten metal level WSP between the twin drums 31, 31 can be prevented. Further, in the steady casting state, the molten metal level 2TDP of the small tundish 20 is controlled to be constant, that is, the height H of the molten metal surface of the small tundish 20 is maintained at the height H* in the steady casting state. By controlling, by injecting the molten metal from the large tundish directly into the twin drum caster 30 and adjusting the opening degree of the nozzle provided at the bottom of the large tundish, as in the conventional twin drum type strip casting machine. Stable casting can be achieved as compared with the method of controlling the flow rate (throughput) to the twin-drum casters 30.

[Second Embodiment]
Next, a twin-drum type continuous casting apparatus according to the second embodiment of the present invention and a twin-drum type continuous casting method using this apparatus will be described in detail. The twin-drum type continuous casting apparatus 2 according to the present embodiment is different from the twin-drum type continuous casting apparatus 1 according to the first embodiment described above in the configuration of the second tundish 20. Hereinafter, the twin-drum type continuous casting apparatus according to this embodiment and the twin-drum type continuous casting method using this apparatus will be described focusing on the points different from the first embodiment.

(Twin drum continuous casting machine)
Hereinafter, the configuration of the twin-drum type continuous casting apparatus according to the second embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 is a schematic diagram showing the configuration of the second tundish 20 of the twin-drum type continuous casting apparatus 2 according to this embodiment. FIG. 4 is a schematic diagram for explaining the function of the scum weir 32 provided in a general twin-drum strip caster.

As shown in FIG. 3, the twin-drum type continuous casting apparatus 2 according to the present embodiment is provided at the bottom of the large tundish 10 to reduce the molten metal in the large tundish 10 in the same manner as in the first embodiment described above. In addition to having the first nozzle 11 for injecting into the tundish 20, unlike the first embodiment, a weir 22 is further provided in the small tundish 20. The weir 22 divides the inside of the small tundish 20 into a charging chamber 20a and a discharging chamber 20b. The charging chamber 20a is an example of a charging unit according to the present embodiment, and is a portion of the small tundish 20 into which the molten metal is charged from the large tundish 10 via the first nozzle 11. The discharge chamber 20b is an example of the discharge unit according to the present embodiment, and is a portion of the small tundish 20 where the molten metal is discharged from the small tundish 20 to the twin-drum casters 30 via the second nozzle 21. is there. The charging chamber 20a and the discharging chamber 20b communicate with each other at the top. That is, the weir 22 is not provided above the small tundish 20 in which the input chamber 20a and the discharge chamber 20b communicate with each other. The reason for this is that when the weir 22 is provided up to the upper part of the small tundish 20, the following problems may occur. First, when a problem occurs in the flow rate control from the first nozzle 11 by the flow rate control device 40 and the inflow of the molten metal into the charging chamber 20a increases, the molten metal does not flow from the charging chamber 20a to the discharging chamber 20b. The molten metal overflows from the chamber 20a at an earlier timing. Secondly, when the melting wall 23 is melted, the molten metal may overflow from the charging chamber 20a. In order to reduce these problems, in the present embodiment, the height of the weir 22 is made lower than the wall around the small tundish 20, so that the charging chamber 20a and the discharge chamber 20b communicate with each other at the upper part of the small tundish 20. I am trying to do it. If the timing at which the molten metal overflows from the charging chamber 20a is delayed a little later, measures such as emergency closing of the first nozzle 11 become effective. The second nozzle 21 according to the present embodiment is provided at the bottom of the discharge chamber 20b and injects the molten metal in the discharge chamber 20 into the twin-drum caster 30.

Further, the bottom of the weir 22 is a melting wall 23. In order for the melting wall 23 to hold the wall for a short time and then melt, it is necessary that the material of the melting wall 23 has a melting point similar to that of the metal to be cast. Therefore, the melting wall 23 is preferably formed of the same metal as the metal to be cast. For example, when the metal to be cast is steel, the melting wall 23 is formed of an iron plate. When the metal to be cast is aluminum, the melting wall 23 is formed of an aluminum plate. The melting wall 23 melts after several seconds (for example, 2 to 3 seconds) have elapsed since the molten metal was poured from the large tundish 10 into the small tundish 20. The reason why the melting wall 23 is provided below the weir 22 is that by slightly delaying the time during which the molten metal flows into the discharge chamber 20b, inclusions such as scum generated by the oxidation of the molten metal components are added to the upper portion of the charging chamber 20a. This is for floating the clean molten metal into the discharge chamber 20b and injecting the clean molten metal into the twin-drum casters 30. Further, by providing the melting wall 23, it is possible to prevent clogging of the discharge hole at the outlet of the second nozzle 21 due to the generated inclusions.

Further, according to the present embodiment, by providing the weir 22 and the melting wall 23 in the small tundish 20, clean molten metal is injected from the discharge chamber 20b of the small tundish 20 into the hot water pool portion 30a of the twin drum caster 30. To be done. Therefore, as shown in FIG. 4, the scum weir 32 provided in the hot water pool portion 30a between the twin drums 31 of the twin drum type caster 30 of the related art can be omitted. The scum weir 32 blocks the flow of the molten metal injected from the nozzle 24 into the hot water pool portion 30a to the hot water pool portion 30a as shown by an arrow in FIG. 4, and scum (metal oxide) floating on the hot water surface is generated. This is to prevent the slab from being caught. When the scum weir 32 is provided, the metal may spread on the molten metal surface between the scum weir 32 and the nozzle 24, or between the scum weir 32 and the side weir (not shown), so that the normal This is one of the factors that hinder the detection of the molten metal level. In the present embodiment, since the scum weir 32 can be omitted, it is possible to prevent the metal surface of the molten metal pool of the molten metal pool 30a from being crusted, and as a result, it is possible to maintain a normal molten metal level detection and to perform stable operation. The molten steel is supplied to the pool 30a. As a result, the inclusion of inclusions such as scum is significantly reduced, so that the quality of the cast piece (strip) cast by the twin-drum caster 30 according to the present embodiment is improved.

In addition, in the present embodiment, the outlet of the first nozzle 11 is opened in the charging chamber 20a, and the first nozzle 11 is arranged so that the outlet of the first nozzle 11 is located at a position lower than the upper end of the weir 22 in the charging chamber 20a. The nozzle 11 is installed. This is to prevent the molten metal containing the inclusions injected from the first nozzle 11 from directly flowing into the discharge chamber 20b.

Furthermore, the level 2TDP of the molten metal in the small tundish 20 required to define the height H that determines the flow rate (throughput V2) of the molten metal from the small tundish 20 is determined by the position of the outlet of the second nozzle 21 and the weir 22. Design so that it is between the top position. This is to prevent inclusions such as scum (oxide) floating on the molten metal surface of the charging chamber 20a from flowing into the discharge chamber 20b side from the upper part of the weir 22.

(Twin drum continuous casting method)
Next, the flow of the twin-drum type continuous casting method according to the present embodiment, which is performed by operating the twin-drum type continuous casting apparatus 2 according to the present embodiment having the above-described configuration, will be described with reference to FIG. 5. To do. FIG. 5: is explanatory drawing which shows an example of the control method in the twin drum type continuous casting method which concerns on this embodiment.

It is similar to the first embodiment that the twin-drum type continuous casting method according to the present embodiment satisfies at least the three conditions <Condition 1> to <Condition 3> described above. Below, based on FIG. 5, among the specific examples of the twin-drum type continuous casting method according to the present embodiment, the points different from the first embodiment will be described.

<Step S ₀ >
In step S ₀ , similarly to the first embodiment, pouring of molten metal from the ladle (not shown) into the large tundish 10 is started (time t ₀ ), and the amount of molten metal in the large tundish 10 reaches a predetermined value. (Time t ₁ ), the actuator 12 is opened, and the molten metal is started to be injected from the large tundish 10 into the small tundish 20 via the first nozzle 11 at the throughput V1. In the present embodiment, at this time, as shown in the second chart from the top of FIG. 5, first, the molten metal surface of the charging chamber 20a of the small tundish 20 starts to rise (at this point, the discharge chamber 20b is discharged). Is not flowing in).

<Step S ₁ >
A few seconds after the molten metal starts to be poured into the small tundish 20 (usually 2 to 3 seconds), the melting wall 23 (for example, an iron plate) provided below the weir 22 in the small tundish 20 melts ( Time t ₁ '). Simultaneously with the melting of the melting wall 23, the molten metal starts to flow from the charging chamber 20a to the discharging chamber 20b, and the molten metal level 2TDP of the charging chamber 20a and the discharging chamber 20b becomes almost instant. Further, the molten metal is poured between the twin drums 31 and 31 at the throughput V2 via the second nozzle 21 provided at the bottom of the discharge chamber 20b, and the molten metal level WSP of the molten metal pool 30a of the twin drum caster 30 rises. To start. At this time, during the period (period I) from time t ₁ until the height of the molten metal surface in the small tundish 20 reaches the height H ^* in the steady state (time t ₃ ), the throughput V1 is higher than the throughput V2. Controlling the actuator 12 by the flow rate control device 40 so as to increase is also the same as in the first embodiment.

Since Step S ₂ or less is the same as in the first embodiment, a detailed description thereof is omitted.

(Operation and effect of the second embodiment)
According to the present embodiment, by providing the weir 22 and the melting wall 23 in the small tundish 20, the path of the flow of the molten metal becomes longer, so that the floating of inclusions such as scum in the charging chamber 20a is promoted. it can. As a result, the scum weir 32, which is conventionally provided between the twin drums 31 of the twin drum caster 30, can be omitted. As a result, skinning (forming a film of scum on the surface of the molten metal) generated on the molten metal surface of the pool 30a is reduced, stable operation is possible, and inclusion of inclusions such as scum is reduced. However, since defects on the surface of the slab due to inclusions are reduced, the quality of the slab (strip) is improved.

[Third Embodiment]
Next, a twin-drum type continuous casting apparatus and a twin-drum type continuous casting method using the apparatus according to the third embodiment of the present invention will be described in detail. The twin-drum type continuous casting apparatus 3 according to the present embodiment has, in addition to the configuration of the twin-drum type continuous casting apparatus 1 according to the first embodiment described above, a hood 60 (or a hood 60A) as an example of a cover member and an inert gas. It is different from the first embodiment in that a gas supply device 70 is further provided. Hereinafter, the twin-drum type continuous casting apparatus according to the present embodiment will be described focusing on the points different from the first embodiment. Since the twin-drum type continuous casting method according to the present embodiment is the same as the twin-drum type continuous casting method according to the first embodiment, detailed description thereof will be omitted.

(Twin drum continuous casting machine)
Hereinafter, the configuration of the twin-drum type continuous casting apparatus according to the third embodiment of the present invention will be described with reference to FIGS. 6 and 7. FIG. 6 is a schematic diagram showing an example of the configuration of the cover member and the inert gas supply device of the twin-drum type continuous casting apparatus 3 according to the present embodiment. FIG. 7 is a schematic diagram showing another example of the configurations of the cover member and the inert gas supply device of the twin-drum type continuous casting apparatus 3 according to the present embodiment.

As shown in FIG. 6, the twin-drum type continuous casting device 3 according to the present embodiment has a hood 60 as an example of a cover member according to the present embodiment, in addition to the same configuration as that of the first embodiment described above. An active gas supply device 70 is further provided. The hood 60 blocks at least the space from the bottom of the small tundish 20 to the surface of the molten metal injected between the twin drums 31, 31 (the surface of the hot water pool 30a) from the outside air. The inert gas supply device 70 also supplies an inert gas into the hood 60. The inert gas is supplied from the inert gas supply device 70 into the hood 60 via an inert gas supply nozzle 71 provided so as to communicate the inside and the outside of the hood 60. As described above, according to the present embodiment, since the hood 60 and the inert gas supply device 70 are provided, it is possible to prevent the molten metal from being oxidized when pouring into the twin-drum casters 30, and thus, compared to the first embodiment. Further, the amount of inclusions such as scum generated can be reduced. As a result, the inclusion amount of inclusions such as scum into the slab can be reduced, so that a high quality slab can be obtained.

As the inert gas, for example, nitrogen gas, argon gas or the like can be used. The flow rate of the inert gas into the hood 60 is sufficient if the space surrounded by the hood 60 can be maintained at a positive pressure higher than the atmospheric pressure.

Further, for example, a brush (not shown) is provided between the hood 60 and the drum 31 at the lower end of the hood 60 (the end on the side in contact with the drum 31), and the brush is pressed against the surface of the drum 31. It may be structured. On the other hand, in order to avoid the seal between the hood 60 and the drum 31, a wider range, for example, as shown in FIG. 7, a space between the small tundish 20 and the pinch roll 90 may be covered with the hood 60A.

The twin drum type continuous casting apparatus 3 according to the present embodiment is also provided with a side weir 80. The side weir 80 is for preventing molten metal leak during casting. It goes without saying that the side dam 80 may be provided in the twin-drum type continuous casting apparatus 1 according to the first embodiment and the twin-drum type continuous casting apparatus 2 according to the second embodiment.

(Operation and effect of the third embodiment)
According to the present embodiment, by providing the hood 60 (or the hood 60A) and the inert gas supply device 70, oxidation at the time of pouring the twin drum casters 30 can be prevented, so the amount of inclusions such as scum generated. Can be reduced, and a high quality slab can be obtained.

[Comparison of operational effect and slab quality in each embodiment]
Next, the operation effect of the conventional twin-drum type continuous casting apparatus having the configuration shown in the following Table 1 and the twin-drum type continuous casting apparatuses 1, 2, and 3 according to the above-described embodiments and the obtained slab (strip) ) Compare the quality of. In Table 1, the tundish is abbreviated as TD.

In the operation of the conventional twin-drum type continuous casting apparatus, an overshoot of the molten metal surface of the molten metal pool portion 30a between the twin-drums 31, 31 occurs at the start of casting. Further, skinning occurs (metal is generated) between the scum weir 32 and the side weir 80 and between the scum weir 32 and the second nozzle 21. Further, there is a large difference between the molten metal level WSP (detected molten metal level) detected by the molten metal level detection device 50 and the actual molten metal level WSP (actual molten metal level) (detected molten metal level> actual molten metal level). The surface becomes lower than the target value, the scum weir 32 does not immerse in the molten metal pool 30a, and the scum is always caught in the molten metal surface. As for the quality of the obtained slab, there are a large number of scum-engaged parts, and the scum-engaged part causes surface cracks and scale unevenness (descaling failure). The plate thickness of the enormous metal entrainment part is thick, and holes may be partially formed.

On the other hand, in the operation of the twin-drum type continuous casting apparatuses 1, 2, and 3 according to the first to third embodiments, the overshoot of the molten metal surface of the molten metal pool portion 30a between the twin-drums 31 and 31 does not occur and is gentle. The target level WSP (level angle θ=θ ^* ) is reached. Moreover, the quality of the cast product obtained by the twin-drum type continuous casting apparatus 1 according to the first embodiment is almost excellent in quality, although the scum winding part is slightly present and scale unevenness occurs in the scum winding part. is there. The quality of the slab obtained by the twin-drum type continuous casting apparatus 2 according to the second embodiment is substantially high, although there are very few scum winding portions and scale unevenness occurs at the scum winding portions. The quality of the slab obtained by the twin-drum type continuous casting apparatus 3 (provided that the weir 22 is provided) according to the third embodiment is extremely high quality without the scum winding portion.

Although the embodiment of the present invention has been described above, the present invention is not limited to this example. It is obvious to those skilled in the art that various modifications or modifications can be conceived within the scope of the technical idea described in the claims, and of course, the technical scope of the present invention is also applicable to them. Understood to belong to.

In addition, the preferred embodiment of the present invention and the above-mentioned Non-Patent Document 1, Patent Document 1 and Patent Document 2 have a method of controlling the flow rate (throughput V2) of the molten metal from the second tundish (small tundish). different. That is, in the preferred embodiment of the present invention, the throughput V2 from the second nozzle 21 provided at the bottom of the small tundish 20 is adjusted by controlling the height H of the molten metal surface of the small tundish 20. , Non-Patent Document 1, Patent Document 1 and Patent Document 2 are different.

Moreover, in the above-mentioned Patent Document 3, there is only one tundish, and no method for adjusting the flow rate (throughput V1) to the second tundish (small tundish 20) is shown. Here, in Patent Document 3, “Also, even if the gas pressure fed into the pressurizing chamber is constant, the flow rate is adjusted so as to change the static pressure ΔH of the upper hot water storage portion 15 of the tundish 3. By adjusting the height of the molten metal surface 7 between the rolls, the thickness of the thin metal plate 10 can be made constant” (page 4, lower left). However, it differs from the preferred embodiment of the present invention in the following two points. First, Patent Document 3 is based on the assumption of a constant gas pressure in the pressurizing chamber, and is a requirement that is not necessary in the present invention. Secondly, the front stage of the tundish of Patent Document 3 is the ladle 5, and there are no two tundishes, the first tundish and the second tundish, as in the preferred embodiment of the present invention. Further, there is no suggestion to provide the second tundish (small tundish) according to the above-described embodiment.

In order to confirm the effects of the preferred embodiment of the present invention described above, the following twin drum type continuous casting operation simulation was performed.

The type of steel to be cast is carbon steel (C: 0.05% by mass, Si: 0.6% by mass, Mn: 1.5% by mass, Al: 0.03% by mass, and the balance is Fe and inevitable impurities. ).

The casting equipment was set up as follows.
Capacity of the first tundish (large tundish 10): 30 tons Capacity of the second tundish: 4 tons Actuator 12: Stopper type Flow rate control method: Measure the surface level of the second tundish (small tundish 20) The flow rate from the first nozzle 11 (throughput V1) was controlled by the stopper-type actuator 12 so that the measured value was the target level 2TDP.

Under the above setting conditions, V3 (=V3 ^* ) in the steady casting state was obtained in advance from the thickness d of the target cast piece (strip). As a result, V3 ^{* was} 734 kg/min. From the value of V3 ^* , the height H ^* of the molten metal surface of the second tundish in the steady state is obtained by the above-mentioned formula (2), and the value of this H ^* (=500 mm) is calculated as the molten metal of the second tundish. The initial height H of the surface was defined. In addition, k=3 was used as the pressure loss coefficient k in the following equation (2).
H ^* =(V3 ^* /kS) ² /(2g)... (2)

Here, as shown in FIG. 9, for each different pressure loss coefficient k (for example, pressure loss coefficient k=2, 3, 4, 5 in the example shown in FIG. 9), the throughput V3 and the molten metal in the second tundish are previously set. An approximate curve showing the relationship with the height H of the surface was obtained by calculation, and a molten metal discharge test was conducted prior to the casting experiment to confirm that the pressure loss coefficient k was 3.

The following conditions were adopted for the twin drum casters 30.
Casting roll diameter: 600mm
Casting roll width: 1000mm
Level of molten metal at the start of casting WSP (melting angle θ ₀ ): 15 degrees Melting level of WSP in steady state (melting angle θ ^* ): 40° Casting capacity (throughput V3 ^{* in} steady casting state): 734 kg/min (Determined from the cooling and solidifying ability of the drum 31.)

As shown in FIG. 9, the acceleration pattern at the start of rotation (at the time of start-up) of the twin drums 31, 31 in the present embodiment, as shown in FIG. The rotation speed was linearly increased to 70 mpm, and after reaching the rotation speed of 70 mpm, this rotation speed was maintained.

As a result of performing the operation simulation of twin drum type continuous casting under the above conditions, the throughput V2 from the second tundish to the twin drum casters 30, the throughput V3 from the twin drum casters 30, and the twin drums 31, FIG. 9 shows the change over time of the molten metal level WSP during 31.

As can be seen from the curve of the change over time of the molten metal level WSP in FIG. 9, overshoot of the molten metal surface of the molten metal pool 30a between the twin drums 31, 31 does not occur at the beginning of the casting process, and during steady casting. It was found that the molten metal level WSP was constant and stable continuous casting operation was possible.

INDUSTRIAL APPLICABILITY The present invention is useful in a strip casting technique for directly casting a molten metal into a thin plate-shaped slab (strip).

1, 2, 3, 3A Twin-drum type continuous casting device 10 Large tundish (first tundish)
11 First Nozzle 12 Actuator 20 Small Tundish (Second Tundish)
20a Input chamber 20b Discharge chamber 21 Second nozzle 22 Weir 23 Melting wall 30 Twin drum type strip caster 30a Hot water pool 31 Twin drum 32 Scum weir 40 Flow control device 50 Liquid level detector 60, 60A Hood (cover member)
70 Inert Gas Supply Device 71 Inert Gas Supply Nozzle 80 Side Weir 90 Pinch Roll 2TDP Second Tundish Level WSP Level between Twin Drums N Drum Nip

Claims (6)

A twin-drum type continuous casting device,
A first tundish for temporarily storing molten metal;
A second tundish for temporarily storing the molten metal injected from the first tundish;
A twin-drum type having a pair of drums rotating in opposite directions, and injecting molten metal from the second tundish between the pair of drums to form a pool of the molten metal between the pair of drums for continuous casting Strip casters,
A flow rate control device for controlling the throughput V1 of the molten metal injected from the first tundish into the second tundish such that the height H of the molten metal surface of the second tundish has a predetermined value.
Equipped with
A twin-drum continuous casting apparatus, wherein the throughput V2 of the molten metal injected from the second tundish into the twin-drum strip caster is determined by the height H of the molten metal surface of the second tundish. .. A first nozzle provided at the bottom of the first tundish for injecting the molten metal in the first tundish into the second tundish;
A weir that divides the inside of the second tundish into an input part and a discharge part that communicate with each other at the upper part;
A second nozzle provided at the bottom of the discharge part for injecting the molten metal in the discharge part into the twin-drum type strip caster;
Further equipped with,
The bottom of the weir is a melting wall,
The twin-drum type continuous casting according to claim 1, wherein the first nozzle is installed such that an outlet of the first nozzle is located at a position lower than an upper end of the weir in the charging section. apparatus. A cover member for blocking at least the space from the bottom of the second tundish to the surface of the molten metal injected between the pair of drums from the outside air;
An inert gas supply device for supplying an inert gas to the inside of the cover member,
The twin-drum type continuous casting apparatus according to claim 1 or 2, further comprising: The predetermined value is the height H ^* of the molten metal surface in the second tundish when the molten metal throughput V3 ^* from the twin-drum type strip caster in the steady casting state becomes equal to the throughput V2. The twin-drum type continuous casting apparatus according to any one of claims 1 to 3, which is characterized in that. A twin-drum type continuous casting method using the twin-drum type continuous casting apparatus according to any one of claims 1 to 4,
The height H ^* of the melt surface in the second tundish when the throughput V3 ^* of the melt from the twin-drum type strip caster in the steady casting state is equal to the throughput V2 is determined in advance,
In the period from the start of the operation of the twin-drum type continuous casting device until the height of the molten metal surface in the second tundish reaches the height H ^* , the first throughput V1 is higher than the throughput V2. Inject the molten metal from the tundish into the second tundish,
From the start of operation of the twin-drum type strip caster until the level of the molten metal poured between the pair of drums reaches the molten metal angle θ ^* when the throughput V3 ^* becomes equal to the throughput V2. During the period, the casting is performed at a throughput V3 of the molten metal from the twin-drum type strip caster smaller than the throughput V2, the twin-drum type continuous casting method. In the steady casting state where the throughput V3 of the molten metal from the twin drum type strip caster is constant
When the melt surface angle θ of the melt surface injected between the pair of drums is θ<θ ^* , the flow rate control device determines that the height H of the melt surface in the second tundish is The throughput V1 is adjusted so as to be higher than the height H ^* ,
When the molten metal surface angle θ of the molten metal injected between the pair of drums is θ>θ ^* , the flow rate control device determines that the height H of the molten metal surface in the second tundish is The twin-drum type continuous casting method according to claim 5, wherein the throughput V1 is adjusted so as to be lower than the height H ^* .

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