JPH08164453A - Twin belt type continuous casting method and casting machine therefor - Google Patents

Abstract

PURPOSE: To stably cast a good quality cast slab by periodically varying the moving speed of one pair of belts forming a mold within a specific range. CONSTITUTION: When molten steel 2 stores in a tundish 1, a sliding nozzle 3 is operated and the molten steel 2 is poured into the mold 9 formed with pair of endless rotational belts 7a, 7b and one pair of moving short side blocks 8a, 8b through an immersion nozzle 4. In a power circuit of a driving motor 17 of one pair of belts 7a, 7b, a driving motor 18 of the moving short side block and a driving motor 19 of supporting rolls below the mold, a current control device periodically varying the rotation speed of the motor by means of the control of an arithmetic unit 20. Then, the moving speed of one pair of belts 7a, 7b is periodically varied (accelerated on decelerated) within ±5-±100% to the casting speed to develop solidified shell. By this method, the uneven solidification is mitigated and the development of crack can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin belt type steel continuous casting method and a continuous casting machine used as a continuous casting method for steel (carbon steel, stainless steel, etc.) in the field of steel production.

[0002]

2. Description of the Related Art In recent years, in the field of continuous casting of iron and steel, there has been an increasing demand for reducing the thickness of slabs and increasing the speed of casting. To meet this demand, for example, a pair of endlessly moving molds is used. Development of a twin-belt continuous casting method using a belt and a pair of moving short-side blocks that move endlessly is in progress.

In the twin-belt continuous casting machine used here, for example, as shown in FIG. 3, molten steel s is supplied to a tundish d, and when the molten steel is accumulated in the tundish to some extent, it is installed in the tundish. The sliding nozzle c is operated to inject molten steel through the injection nozzle e, between the two pulleys pa and pb and the tension adjusting pulley pc whose position is controlled by a tension control device, and a pair of belts endlessly rotationally moved. A mold m formed by a pair of moving short side blocks ca (cb) consisting of ba, bb and a large number of copper blocks that move endlessly at both side ends of the pair of belts.
Inject into

The belts ba and bb form the long side of the mold m, and the back surface of the position contacting the molten steel is formed by a plurality of fin rolls f arranged in a cooling box w through which cooling water flows. It is supported and cooled. In addition, a moving short side block ca composed of a large number of copper blocks
(Cb) forms the short side of the mold m, and is connected to a chain (not shown) that moves endlessly (not shown).
And is configured to be movable along a guide rail (not shown).

The molten steel s is cooled in the mold m, removed of heat and solidified, and is sandwiched and pulled out by a support roll r arranged below the mold m, and is carried out as a thin cast slab sc. ing. (Reference technology: JP-A-60-1523)
47 publication). In the continuous casting method using this twin-belt continuous casting machine, non-uniformity of the solidified shell is likely to occur, which may cause cracks in the slab.

Conventionally, as a method for eliminating the unevenness of the solidified shell, a method has been proposed in which unevenness is formed on the belt or a ceramic coating is applied to gently cool the molten steel to alleviate the uneven cooling rate. There is. However, in these methods, it is necessary to form unevenness and a ceramic coating layer on the belt, and in order to maintain its function,
It is necessary to frequently perform repair processing or belt replacement.
Further, it is hard to say that the evaluation can be sufficiently performed because the productivity is lowered in addition to the costs of forming, repairing and belt replacement.

[0007]

SUMMARY OF THE INVENTION The present invention effectively eliminates uneven solidification without forming unevenness on a belt forming a mold or a moving short side block or coating to prevent slab cracking. A twin-belt type continuous casting method and a twin-belt type continuous casting machine capable of preventing the same are provided.

[0008]

The first invention of the present invention is as follows:
A pair of belts that move endlessly in synchronization with the casting speed,
In a twin-belt type continuous casting method performed using a mold formed with a pair of moving short side blocks composed of a plurality of blocks, the moving speed of the pair of belts forming the mold is ± 5 ± ± with respect to the casting speed. The twin-belt continuous casting method is characterized in that a solidified shell is generated by cyclically changing (accelerating-decelerating) within a range of 100%.

A second aspect of the present invention is a continuous casting machine used for implementing the first aspect of the invention, in which the rotation of the drive motor is controlled by an arithmetic unit in the power supply circuit of the drive motor of the pair of belts forming the mold. The current control device and the drive motor are connected via an inverter by disposing a current control device for periodically varying the speed.

A third aspect of the present invention is a twin-belt type method that uses a mold formed of a pair of belts that move endlessly in synchronism with the casting speed and a pair of moving short-side blocks composed of a plurality of blocks. In the continuous casting method, the moving speeds of the pair of belts and the pair of moving short side blocks forming the mold are cyclically changed (acceleration-deceleration) within ± 5 to ± 100% of the casting speed, A twin-belt continuous casting method characterized by producing a solidified shell.

A fourth aspect of the present invention is a twin-belt type continuous casting machine according to the third aspect of the present invention, in which a pair of belts forming a mold and a pair of moving short side blocks have respective driving motor power supply circuits provided with arithmetic units. The current control device and the drive motor are connected via an inverter by arranging a current control device for periodically varying the rotation speed of the drive motor under the control of 1.

A fifth aspect of the present invention is a twin-belt continuous method using a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. In the casting method, the moving speed of the pair of belts forming the mold and the peripheral speed of the slab supporting roll below the mold are periodically changed within a range of ± 5 to ± 100% with respect to the casting speed (acceleration-deceleration). The twin belt type continuous casting method is characterized in that a solidified shell is generated by the above.

A sixth aspect of the present invention is a twin-belt type continuous casting machine according to the fifth aspect of the present invention, in which a pair of belts forming the mold and the power supply circuits of the drive motors of the slab support rolls under the mold are operated. A twin-belt continuous system characterized in that the current control device and the drive motor are connected via an inverter by disposing a current control device for periodically varying the rotation speed of the drive motor under the control of the device. Casting machine.

A seventh aspect of the present invention is a twin-belt continuous method using a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. In the casting method, the moving speed of the pair of belts and the pair of moving short side blocks forming the mold and the peripheral speed of the slab supporting roll below the mold are ± 5 with respect to the casting speed.
The twin-belt continuous casting method is characterized in that a solidified shell is generated by cyclically changing (accelerating-decelerating) within a range of ± 100%.

An eighth aspect of the present invention is a continuous casting machine for carrying out the seventh aspect of the invention, in which the power supply circuits for the pair of belts forming the mold, the movable short side block, and the drive motors for the slab support rolls below the mold are provided. The current control device and the drive motor are connected via an inverter by arranging a current control device for periodically varying the rotation speed of the drive motor under the control of the arithmetic device.

[0016]

According to the present invention, in the twin-belt type continuous casting machine, the driving speed of the belt forming the mold, the moving short side block, and the slab supporting roll under the mold is periodically changed to periodically change the meniscus shape at the solidification starting point. By changing it, the same effect as the mold oscillation in the fixed mold type continuous casting machine can be produced. by this,
It is possible to eliminate natural solidification unevenness, prevent cracking of the slab, and stably cast a slab with good quality.

The present invention will be described in more detail below. It is known that the slab cracks in the twin-belt continuous casting method occur due to uneven solidification. Such a phenomenon is a common phenomenon also in well-known fixed mold type continuous casting and the like, and in this type of continuous casting, a vibration device is attached to the mold and the entire mold is supplied while supplying lubricating powder. By vibrating up and down, the so-called mold oscillation effect is used to eliminate this unevenness of the solidified shell.

However, in twin belt type continuous casting,
Because a moving mold different from the fixed mold type continuous casting machine is used, it is difficult to vibrate the mold vertically due to its structure, and this cannot be directly applied to the twin belt type continuous casting. The inventor et al.
We examined how to obtain the same effect as oscillation.

As a result, a pair of belts forming the mold,
A pair of moving short-side blocks, the peripheral speed of the slab support roll of the lower part of the mold in the vicinity of the casting speed, by changing the cycle (acceleration-deceleration), the same effect as the mold vibration in the fixed mold type continuous casting Has come to the knowledge that
As a result of further studies, the present invention has been completed.

FIG. 1 is a conceptual explanatory view showing an example of periodic fluctuation of the moving speed of the belt in the present invention. Regarding the changing conditions of the belt moving speeds Vb to Vc, the casting speed Va
It is desirable to periodically accelerate and decelerate within a range of ± 5 to ± 100%. If acceleration / deceleration exceeds this range, a large tensile force or compression force acts on the solidified shell, causing breakage of the solidified shell to cause slab cracking, or buckling to deteriorate the surface quality. To do.

The acceleration-deceleration cycle time T is 0.1
A range of up to 2.0 sec is preferred. Below 0.1 sec,
Not only is it difficult to ensure controllability of periodic fluctuations,
The mold oscillation effect is not fully expressed. Further, if it is 2.0 seconds or more, the mold oscillation effect is not sufficiently exhibited, and the solidification unevenness cannot be sufficiently eliminated. The waveform of the periodic fluctuation is not limited to the sine waveform shown in FIG. It may be a rectangular waveform, an arbitrary waveform, or the like.

[0022]

【Example】

Example 1 An example of the present invention will be described below. Figure 2
(A)-(b) shows the outline of the twin belt type continuous casting machine which implemented this invention. In this twin-belt type continuous casting machine, the molten steel 2 is supplied to the tundish 1, and when the molten steel 2 is accumulated in the tundish 1 to some extent, the tundish 1
The sliding nozzle 3 installed at the position is operated so that the molten steel 2 is wound between the drive pulley 5a, the driven pulley 5b, and the tension adjusting pulley 5c position-controlled by the tension control device 6 through the dipping nozzle 4 to endlessly rotate. It is poured into a mold 9 formed by a pair of moving short-side blocks 8a, 8b consisting of a pair of moving belts 7a, 7b and a large number of blocks that move endlessly at both ends of the pair of belts.

The belts 7a and 7b form the long sides of the mold 9, and the back surface at the position in contact with the molten steel is constructed so as to be cooled by the cooling water flowing in the cooling box 10, and The pair of movable short side blocks 8a and 8b form the short side of the mold 9, and are connected to the chain 12 that moves endlessly by the drive wheel 11 via a connecting link (not shown) and to the guide rail 13. It is configured so as to move along and be cooled by a cooling device 14 arranged along the moving path during the moving process and come into contact with molten steel. The molten steel 2 is cooled by a mold 9 and is heat-removed to be solidified, and is sandwiched and pulled out by a support roll 15 arranged below the mold 9, and is carried out as a thin cast piece 16.

Drive motor 1 for a pair of belts 7a, 7b
7. In the power supply circuits of the drive motor 18 for the moving short side block and the drive motor 19 for the support rolls at the lower part of the mold, a current controller 21 for periodically varying the rotation speed of each drive motor is controlled by the arithmetic unit 20. Arrange,
As a result, the current control device and each of the drive motors are connected via the inverter 22.

The arithmetic unit 20 is connected to a casting speed and a setter 23 in which a current control condition for periodically varying the rotational speed of each drive motor is set in accordance with the casting speed, and each computing device 20 is connected to a setter 23 according to the casting speed. The fluctuation pattern of the current supplied to the drive motor is calculated, and a command signal is transmitted to the current control device 21, where the current is controlled and each inverter 2 is controlled.
The rotation of each drive motor is periodically changed via 2a to 22c.

In this example, the moving speeds of the pair of belts and the pair of moving short side blocks and the peripheral speed of the supporting rolls are cyclically changed according to the casting speed, and the rotation conditions of these drive motors are set. It is set in the container 23.
Here, the current control condition is set so that the moving speed of the belt and the moving short side block and the peripheral speed of the support roll can be equalized.

By using the twin-belt type continuous casting machine of the present invention thus constructed, the moving speed condition of the belt and the moving short side block, the peripheral speed condition of the supporting roll, and the fluctuation period (cycle time) are changed. , Continuous casting of thin slabs of low carbon steel was carried out.

Operating conditions Steel type: Low carbon steel {Ingredient composition (% by weight) is shown in Table 1} Casting temperature: 1530 to 1570 ° C Slab size: thickness 75 mm x width 1300 mm Belt material: carbon steel Size: thickness 1 mm x width 1500mm Moving speed: Against casting speed ±% Moving short side block Material: Copper Dimensions: Thickness 75mm x Width 100mm x Length 80mm Moving speed: Against casting speed ±% Support roll diameter: 130mm Peripheral speed: Against casting speed ±%

The occurrence of cracks in the slab obtained in this example was compared with that in the comparative example, which is outside the scope of the present invention, and the moving speed and moving short side of the belt (having a ceramic coating on the surface). Table 2 shows the case in which the moving speed of the block (copper block) and the peripheral speed of the support roll are not changed periodically, and the conventional case is used.

[0030]

[Table 1]

[0031]

[Table 2]

As shown in Table 2, the moving speeds of the belts 7a and 7b, the moving speeds of the moving short side blocks 8a and 8b, and the peripheral speed of the support roll 15 are ± 5% to ± with respect to the casting speed.
Examples (1) to (1) of the present invention in which the period is changed in the range of 40%
No cracking was observed in the cast slab 16 according to (7).

Example (8) in which the moving speed of the belt and the moving speed of the moving short side block were changed by ± 40% with respect to the casting speed, and only the moving speed of the belt was ± 40% with respect to the casting speed. In Example (9) in which the cycle was varied within the range, extremely slight slab cracking was observed. In Examples (10) to (11) in which the moving speed of the belt, the moving speed of the moving short side block, and the peripheral speed of the support roll were periodically changed within a range of ± 80% to ± 100% with respect to the casting speed,
Occurrence of slight slab cracking was observed.

The moving speed of the belt, the moving speed of the moving short side block, and the peripheral speed of the support roll are ± 2 with respect to the casting speed.
In Comparative Example (12) in which the cycle was varied within the range of%, the improvement effect was not remarkable as compared with the conventional example, and the occurrence of slab cracking was recognized. Further, in Comparative Example (13) in which the moving speed of the belt and the moving short side block and the peripheral speed of the support roll were periodically changed within a range of ± 120%, occurrence of slab cracking similar to that of the conventional example (14) was observed. .

From the above, it is not always essential to periodically vary the peripheral velocity of the support roll in the region where the period variation width with respect to the casting speed is ± 5% to ± 40%. However, in a region where the moving speed of the belt and the moving short side block is ± 40% or more of the casting speed, when only the moving speed of the belt or the belt and the moving short side block is periodically changed, slab cracking occurs. It tends to be easier to do. Therefore, in such a region, it is more preferable that the moving speed of the belt and the moving short-side block and the peripheral speed of the support roll are cyclically changed synchronously.

The belt, the moving speed of the moving short side block, and the peripheral speed of the supporting roll are ± 100 with respect to the casting speed.
When the cycle is changed in the range of% or more and in the range of ± 2% or less, as in the case of the conventional example (14) in which the moving speed of the belt, the moving short side block, and the peripheral speed of the supporting roll are not changed, the slab cracks However, it was confirmed that there was no improvement effect from this viewpoint.

The cycle time is shown here as being fixed at 0.5 sec, but if it is within the range of 0.5 to 2.0 sec under the general casting operating conditions, it is the same as the conventional example. It has been confirmed that a sufficient improvement effect can be obtained. The present invention can also be applied to the case of using a belt having irregularities, a coated belt, or a moving short side to obtain an effect.

[0038]

According to the present invention, in the twin-belt type continuous casting method, the mold oscillation is performed by periodically changing (accelerating-decelerating) the moving speed of the belt forming the mold and the moving short side block in the vicinity of the casting speed. The effect can be obtained, unevenness of solidification can be alleviated, cracking can be prevented, and a slab of good quality can be stably cast.

[Brief description of drawings]

FIG. 1 is a conceptual explanatory diagram of a periodic fluctuation of a belt moving speed applied in twin belt type continuous casting.

FIG. 2 is a schematic explanatory view showing an embodiment of a twin belt type continuous casting machine to which the present invention is applied, in which (a) is a side sectional schematic explanatory view,
FIG. 6B is a schematic cross-sectional view taken along the line Aa-Ab of FIG.

FIG. 3 is a side sectional schematic explanatory view showing an example of a conventionally known twin belt type continuous casting machine.

[Explanation of symbols]

 1 Tundish 2 Molten Steel 3 Sliding Nozzle 4 Immersion Nozzle 5a, 5b Pulley 5c Tension Adjusting Pulley 6 Tension Control Device 7a, 7b Belt 8a, 8b Moving Short Side Block 9 Mold 10 Cooling Box 11 Drive Wheel 12 Chain 13 Guide Rail 14 Cooling Device 15 Support Roll 16 Thin Slab 16s Solidified Shell 17 Drive Motor (For Belt) 18 Drive Motor (For Moving Short Side Block) 19 Drive Motor (For Support Roll) 20 Computing Device 21 Current Control Device 22a, 22b, 22c Inverter 23 Setting vessel

Claims (8)

[Claims] 1. A twin-belt continuous casting method, which uses a mold formed of a pair of belts that move endlessly in synchronization with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks, A twin belt characterized in that a moving speed of a pair of belts forming a mold is periodically changed (accelerated-decelerated) within a range of ± 5 to ± 100% with respect to a casting speed to generate a solidified shell. Type continuous casting method. 2. A twin-belt continuous casting machine having a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. By disposing a current control device for periodically varying the rotation speed of the drive motor under the control of the arithmetic device in the power supply circuit of the drive motor for the pair of belts to be formed, the current control device and the drive motor are connected to the inverter. A twin-belt continuous casting machine characterized by being connected via. 3. A twin-belt continuous casting method using a mold formed of a pair of belts that move endlessly in synchronization with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. Periodic fluctuation of the moving speed of the pair of belts forming the mold and the pair of moving short side blocks within the range of ± 5% to ± 100% of the casting speed (acceleration-deceleration)
A twin-belt continuous casting method, characterized in that a solidified shell is produced. 4. A twin-belt continuous casting machine having a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. In the power supply circuit of each drive motor of the pair of belts and the pair of moving short side blocks to be formed,
A twin-belt type wherein the current control device and the drive motor are connected via an inverter by arranging a current control device for periodically varying the rotation speed of the drive motor under the control of a computing device. Continuous casting machine. 5. A twin-belt continuous casting method, which uses a mold formed of a pair of belts that move endlessly in synchronization with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks, The moving speed of the pair of belts forming the mold and the peripheral speed of the slab supporting roll under the mold are cyclically changed (accelerated-decelerated) within ± 5 to ± 100% of the casting speed to solidify. A twin-belt continuous casting method characterized by producing a shell. 6. A twin-belt continuous casting machine having a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. By providing a current control device for cyclically varying the rotation speed of the drive motor under the control of an arithmetic unit in the power supply circuit of each drive motor for the pair of belts to be formed and the slab support roll under the mold, A twin-belt continuous casting machine, characterized in that a current control device and the drive motor are connected via an inverter. 7. A twin-belt continuous casting method using a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short side blocks composed of a plurality of blocks, The moving speed of the pair of belts forming the mold and the pair of moving short side blocks and the peripheral speed of the slab support roll under the mold are ± 5% to ± 100% of the casting speed.
A twin-belt continuous casting method, characterized in that the solidified shell is generated by cyclically changing (accelerating-decelerating) within the range. 8. A twin-belt continuous casting machine having a mold formed of a pair of belts that move endlessly in synchronism with a casting speed and a pair of moving short-side blocks composed of a plurality of blocks. A pair of belts to be formed, a movable short side block, and a power supply circuit for each drive motor of the slab support roll under the mold are provided with a current control device for periodically varying the rotation speed of the drive motor under the control of an arithmetic unit. By doing so, a twin-belt continuous casting machine characterized in that the current control device and the drive motor are connected via an inverter.