JP2002283016A - Heating device for molten steel in tundish using plasma torch - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress instability of plasma arc caused by slag entering during continuous casting, and at the same time, to prevent local overheating of molten steel and perform uniform heating, The present invention provides a heating device for molten steel in a tundish using a plasma torch that can reduce the cost of refractory by suppressing erosion of refractory and the like and increase the heating efficiency. A pouring port (18) for molten steel (11), a pair of plasma torch insertion ports (15, 16), and a lid (14) including a heating chamber (13).
And a pair of plasma torches 24 and 25 that are held by a lifting device above the plasma torch insertion ports 15 and 16 and inserted into the tundish 12.
The upper dam 2 in which the lower part is immersed in the molten steel 11 between the pouring port 18 of the molten steel 11 in the tundish 12 and the heating chamber 13 in the molten steel heating apparatus 10 to which the cords 27 and 28 are connected.
2 and a tundish 12 just below the heating chamber 13.
Is provided with a porous plug 20 for blowing an inert gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing molten steel in a tundish using a plasma torch capable of preventing instability of a plasma arc caused by slag entering during continuous casting and improving the heating efficiency of the molten steel. It relates to a heating device.

[0002]

2. Description of the Related Art Conventionally, cast slabs are prepared by pouring molten steel from a tundish into a mold, cooling by a mold and cooling by water spray from a support segment, and completely solidifying the molten steel, and then using a pinch roll. Manufactured by continuous drawing. In this continuous casting, after the middle stage of casting,
As the casting time elapses, the temperature of the molten steel decreases by about 0.2 to 0.5 ° C./min due to heat radiation from the ladle or the like, and the temperature of the molten steel poured into the tundish becomes lower than the target temperature.
Then, during the casting, the immersion nozzle formed at the bottom of the tundish is clogged, causing problems such as interruption of the casting operation and deterioration of the quality of the slab due to fluctuations in the molten metal level in the mold. As a countermeasure, as described in JP-A-61-229451, a flow path of molten steel is formed inside a tundish, and an induction heating device is arranged so as to surround the flow path. By heating the molten steel by Joule heat by energizing the heating device, the temperature drop corresponding to the heat dissipation is compensated. Furthermore, as described in Japanese Patent Publication No. 4-52599, one plasma torch is attached to a part of the lid of the tundish, and a heating chamber is provided so as to surround the plasma torch. The lower end of the side wall of the heating chamber surrounding the torch is immersed in molten steel to partition the heating chamber from the surroundings, and the plasma torch provided in this heating chamber is energized by using an electrode provided outside, so that the plasma is generated. A method of heating a molten steel by forming a plasma arc on the surface of the molten steel from a torch has been performed.

[0003]

However, in the method for heating molten steel described in Japanese Patent Application Laid-Open No. 61-229451, the flow path of molten steel is formed inside the tundish, so that the structure of the tundish is complicated. Therefore, it is difficult to construct the refractory lining of the tundish, and the construction cost increases. Moreover, since the coil of the induction heating device is arranged so as to surround the flow path of molten steel, when a refractory constituting the flow path is cracked or melted, an accident such as an accident that a metal is inserted into the coil may occur. An electrical short-circuit accident or the like due to dew condensation or the like is caused, and there is a problem in stably heating the molten steel. Furthermore, 4-5
According to the method described in Japanese Patent No. 2599, the atmosphere of the heating chamber can be stably maintained, so that the plasma arc formed on the surface of the molten steel from the plasma torch can be stabilized. Is heated for a long time, and the temperature becomes extremely high, and the heating efficiency of the molten steel in the entire tundish decreases. Moreover, since the heating of molten steel is mainly based on heat using radiant heat from the heating chamber, if the heating chamber is completely partitioned from the inside of the tundish, the temperature of the heating chamber rises sharply and the refractory lining heats up. Or the plasma arc heat causes rapid melting and shortens the life of the heating chamber. In addition, the reduction in the life of the heating chamber has a problem that the life itself of the molten steel heating device using the plasma torch is reduced.

The present invention has been made in view of such circumstances, and suppresses the instability of a plasma arc caused by slag entering during continuous casting, and at the same time, prevents local overheating of molten steel to achieve uniformity. The purpose of the present invention is to provide a heating device for molten steel in a tundish using a plasma torch, which can perform appropriate heating, suppress erosion of refractory in a heating chamber or the like, reduce refractory cost, and increase heating efficiency. And

[0005]

According to the present invention, there is provided an apparatus for heating molten steel in a tundish using a plasma torch according to the present invention, which has a pouring port for molten steel and a pair of plasma torch insertion ports. A lid covering a tundish having a molten steel heating chamber on the insertion port side, and a pair of plasma torches inserted into the tundish from the plasma torch insertion port held by a lifting device above the plasma torch insertion port; Further comprising a heating device for heating molten steel in which a cord of a heating device is connected to the plasma torch, wherein a lower part is immersed in the molten steel between the pouring port of the molten steel in the tundish and the heating chamber. And a porous plug for blowing an inert gas into the tundish immediately below the heating chamber is provided. As a result, when pouring molten steel from the long nozzle inserted into the pouring port,
The upper dam prevents the slag accompanying the molten steel from flowing into the heating chamber, and the slag accumulated in the heating chamber is eliminated around the heating chamber by the molten steel flow accompanying the floating of the inert gas blown from the porous plug. An exposed surface of the molten steel is formed, and a plasma arc can be stably generated using the exposed surface of the molten steel. Furthermore, the formation of the molten steel flow can prevent the occurrence of local overheating of the molten steel by supplying new unheated molten steel in the vicinity of the ignition point of the plasma arc, thereby effectively reducing the radiant heat from the heating chamber. To increase the heating efficiency of the molten steel, suppress the erosion of the refractory in the heating chamber or the like, reduce the cost of the refractory, and increase the heating efficiency.

Here, the inert gas is preferably argon gas. Thereby, since the molten steel is brought into contact with the argon gas, the oxidation of the molten steel can be suppressed, the generation of inclusions can be suppressed, and the argon gas atmosphere in the heating chamber can be increased to stabilize the formation of a plasma arc.

Further, the argon gas amount is set to 1 to 20 NL.
/ Min is more preferable. The slag covering the surface of the molten steel is removed by the molten steel flow to generate an exposed surface of the molten steel, the disturbance of the molten steel surface due to the blown argon gas is suppressed, and a plasma arc can be more stably formed on the exposed surface. Here, when the amount of the argon gas is less than 1 NL (normal liter) / minute, the formation of the molten steel flow due to the floating of the argon gas is weakened, and the removal of the slag is also deteriorated, so that the exposed surface of the molten steel is formed. And ignition failure of the plasma arc occurs. 20 NL of argon gas
If the rate exceeds / min, when the argon gas is released from the surface of the molten steel, the surface of the molten steel is disturbed, and the plasma arc becomes unstable or causes a splash in the heating chamber.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. FIG. 1 is an overall view of a heating device for molten steel in a tundish using a plasma torch according to one embodiment of the present invention. As shown in FIG. 1, a heating device 10 for molten steel in a tundish using a plasma torch according to one embodiment of the present invention is an example of a tundish 12 for storing molten steel 11 and a pouring port for molten steel 11. Nozzle hole 1
8 and an anode torch 24 and a cathode torch 25, which are examples of a pair of plasma torches, and plasma torch insertion ports (hereinafter, simply referred to as insertion ports) 15 and 16, and the molten steel 11 is provided on the insertion ports 15 and 16 side. A heating chamber 13 is provided (in this embodiment, the insertion ports 15 and 16 are provided in the heating chamber 13).
A lid 14 covering the tundish 12 and molten steel 11 in the tundish 12 through the insertion openings 15 and 16.
And a plasma device 17 for heating the substrate. Further, the tundish 12 has a long nozzle 19 for supplying molten steel 11 (not shown) into the tundish 12 via a ladle from a nozzle hole 18 provided in the lid 14 and a rising flow in the molten steel 11 of the heating chamber 13. For this purpose, a porous plug 20 communicating with a pressure source of argon gas that blows an argon gas, which is an example of an inert gas, into the tundish 12 immediately below the heating chamber 13 and a molten steel 11 that has passed through the heating chamber 13 are not shown in the mold. And a nozzle 21 for pouring the molten metal. A tundish 12 is provided between the heating chamber 13 and the nozzle hole 18 of the molten steel 11 in which the long nozzle 19 is disposed.
An upper weir 22 made of a refractory material is disposed perpendicular to the flow direction of the molten steel 11 and is in contact with both inner sides of the tundish 12. The upper end of the upper weir 22 is in contact with the inside of the lid 14, and the lower part is immersed in the molten steel 11 to block the slag 23 existing above the molten steel 11, and the molten steel 11 passes below the upper weir 22. It is arranged so that it can pass. Further, the plasma device 17 has an anode torch 24 and a cathode torch 25 provided with an argon gas blowing hole for forming a plasma gas from around an electrode (not shown).
Since the cords 27 and 28 of the power supply device 26 are connected to 5, the anode torch 24 and the cathode torch 25 are electrically connected to the power supply device 26 by the cords 27 and 28. The anode torch 24 and the cathode torch 25
And the heating device 26 are placed and held on an elevating device (not shown) above the insertion ports 15 and 16, so that the anode torch 24 and the cathode torch 25 are tanned from the insertion ports 15 and 16 provided in the heating chamber 13. Insertion and retraction of the dish 12 can be performed freely.

Next, an apparatus 10 for heating molten steel in a tundish using a plasma torch according to one embodiment of the present invention.
Will be described. The supply of the molten steel 11 from the long nozzle 19 into the tundish 12 is started. Along with the supply of the molten steel 11, the slag 23
Mixed in. Since the molten steel 11 in the tundish 12 is small in the initial stage of the supply start of the molten steel 11, the slag 2
A part of 3 passes through the lower end of the upper weir 22 and enters the heating chamber 13. However, the amount of molten steel 11 in the tundish 12 is 1
At the point of time exceeding 5 tons, the lower end of the upper weir 22 is immersed in the molten steel 11. As a result, the slag 23 that has entered the tundish 12 cannot enter the heating chamber 13 due to the upper weir 22. And molten steel 11 in tundish 12
At a time of 40 tons, the supply of the molten steel 11 from the long nozzle 19 and the pouring of the molten metal into the mold from the nozzle 21 are continuously performed. At this time, the molten steel 11 of the tundish 12
Pouring into tundish 12 is performed so as to always maintain 40 tons. This pouring is done from a ladle to a long nozzle 1
9, the amount of molten steel 11 supplied through the
When the temperature exceeds half of the ton), the temperature of the molten steel 11 supplied into the tundish 12 becomes lower than the target temperature due to heat radiation of the ladle, the long nozzle 19 and the like.

[0010] Therefore, the lifting device is operated to activate the heating chamber 13.
The anode torch 24 and the cathode torch 25 are inserted into the tundish 12 from the insertion ports 15 and 16 provided in the
At a position 100 to 500 mm above the surface of the molten steel 11,
The anode torch 24 and the cathode torch 25 are held so that the tips thereof come in contact with each other. Then, a flow of argon gas is formed from the outlets of the anode torch 24 and the cathode torch 25 toward the surface of the molten steel 11, and at the same time, the anode torch 24 and the cathode torch 25 are supplied from the charging device 26 to the anode torch 24 and the cathode torch 25.
A current of 0 to 5000 amps is passed to ionize the argon gas to generate a plasma arc. in this way,
Since a plasma arc is generated between the anode torch 24 and the surface of the molten steel 11 and a plasma arc is also formed between the surface of the molten steel 11 and the cathode torch 25, the molten steel 11 is heated by the heat and radiation heat of the plasma arc. At this time, since the amount of the slag 23a flowing into the heating chamber 13 is suppressed by the upper weir 22, the thickness of the slag in the heating chamber 13 can be reduced to within 10 mm. Of the plasma arc to improve the ignition of molten steel 11
A plasma arc can be formed stably.

However, in the case where two or more ladles are exchanged and a plurality of charges are cast using the same tundish 12 while continuous casting is performed, etc., the long nozzle 19 is replaced each time the ladles are exchanged. Since the supply of the molten steel 11 cannot be performed, the amount of the molten steel 11 in the tundish 12 fluctuates.
In some cases, the amount of the molten steel 11 may be less than 15 tons.
The slag 23 passes through the lower end of 2 and enters the heating chamber 13 to increase the slag 23a. And every time the ladle is replaced,
The amount of the slag 23 mixed into the tundish 12 is increased, and penetration of the slag 23 is promoted. This slug 23a
Increases, the electric resistance between the molten steel 11 and the anode torch 24 and the cathode torch 25 increases, the plasma arc of the anode torch 24 and the cathode torch 25 becomes unstable, and the radiant heat in the heating chamber 13 is transmitted to the molten steel 11. And the heating efficiency of the molten steel 11 decreases. On the other hand, molten steel 11 heated by plasma arc heat, radiant heat, etc.
A stagnation portion (a portion where the flow of molten steel is slow) is generated in the stagnation portion, and the molten steel 11 in the stagnation portion near the ignition point of the plasma arc is overheated, or the temperature locally increases, resulting in so-called uneven heating. Further, the local overheating causes a decrease in the heating efficiency of the entire molten steel 11 and abrasion of the refractory lining of the heating chamber 13, and the life of the heating device 10 is greatly reduced.

Accordingly, the porous plugs 20 provided at the bottom of the tundish 12 under the projection of the heating chamber 13 are 1-2
By blowing argon gas at 0 NL / min, the molten steel flow shown in the drawing can be formed in the molten steel 11 in the heating chamber 13, and the slag 23 a is brought to the periphery of the side wall in the heating chamber 13. As a result, the surface of the molten steel 11 immediately below the tips of the anode torch 24 and the cathode torch 25 is exposed, and the electrical resistance between the molten steel 11 and the anode torch 24, and the electrical resistance between the molten steel 11 and the cathode torch 25 can be reduced, and the plasma arc can be stabilized. Can be formed. In particular, in the case of the direct current type anode torch 24 and cathode torch 25, the molten steel 11
Since the plasma arc is formed directly on the substrate, the effect of stabilizing the plasma arc is greater than in the case of the AC type, and more favorable results can be obtained. Furthermore, an exposed surface is formed in the molten steel 11 below the heating chamber 13 with the rise of the blown argon gas, so that the radiant heat in the heating chamber 13 can be efficiently transmitted to the molten steel 11, and the heating of the molten steel 11 can be performed. Efficiency can be improved. Moreover, since new unheated molten steel 11 can be supplied to the heating surface, overheating and unbalanced heat can be suppressed, and the molten steel 11 can be brought to a uniform temperature. By suppressing this overheating, there is no abnormal temperature rise of the molten steel 11, and the temperature rise of the refractory lining the heating chamber 13 can be suppressed,
It is also possible to prevent the lining refractory from being melted and prolong the life of the heating device 10. Further, by providing the upper weir 22, the inside of the heating chamber 13 is shut off from outside air (oxygen) entering through the nozzle hole 18 of the long nozzle 19, and the oxygen concentration in the heating chamber 13 is reduced to 1.0% by weight or less. Thus, an increase in electric resistance can be suppressed and the plasma arc can be further stabilized.

The molten steel 11 thus heated is poured into a mold via a nozzle 21, solidified by cooling by the mold and water sprinkling from a support segment arranged downstream of the mold, and becomes a slab in a subsequent process. Conveyed.

The embodiment of the present invention has been described above.
The present invention is not limited to the above-described embodiment, and all changes in conditions without departing from the gist are within the scope of the present invention. For example, as the inert gas blown from the porous plug, nitrogen gas can be used in addition to argon gas. Further, regarding the structure of the upper weir, a weir that completely blocks molten steel flowing from the long nozzle to the heating chamber side, and a tunnel hole is provided in this weir can supply molten steel from the tunnel hole to the heating chamber.

[0015]

The apparatus for heating molten steel in a tundish using a plasma torch according to any one of claims 1 to 3 has a pouring port for molten steel and a pair of plasma torch insertion ports. A lid for covering the tundish having a heating chamber, and a pair of plasma torches, which are held by a lifting device above the insertion port and inserted into the tundish from the insertion port, further comprising a cord of a power supply device attached to the plasma torch; In a heating device for molten steel, a lower dam is immersed in molten steel between a pouring port for molten steel in a tundish and a heating chamber, and an inert gas is blown into the tundish immediately below the heating chamber. Since the plug is provided, slag that enters during continuous casting can be prevented from entering the heating chamber and the plasma arc can be stabilized, and local overheating of molten steel can be achieved. It is possible to increase the heating efficiency of the entire molten steel to prevent temperature deviation. In addition, wear of a refractory such as a heating chamber can be prevented, and the life of the heating device can be extended.

In the apparatus for heating molten steel in a tundish using a plasma torch according to the second aspect of the present invention, since the inert gas uses argon gas, deterioration of quality due to inclusions of the molten steel is suppressed, and the atmosphere in the heating chamber is kept , The formation of a plasma arc can be stabilized.

In the apparatus for heating molten steel in a tundish using a plasma torch according to the third aspect, since the amount of argon gas is set to 1 to 20 NL / min, the formation of the exposed surface of the molten steel and the disturbance of the exposed surface are prevented. By suppressing this, the formation of the plasma arc can be made more stable, and the heating efficiency of the molten steel can be greatly improved.

[Brief description of the drawings]

FIG. 1 is an overall view of an apparatus for heating molten steel in a tundish using a plasma torch according to one embodiment of the present invention.

[Explanation of symbols]

10: heating device, 11: molten steel, 12: tundish,
13: heating chamber, 14: lid, 15: insertion port, 16: insertion port, 17: plasma device, 18: nozzle hole (pouring port),
19: long nozzle, 20: porous plug, 21: nozzle, 22: upper dam, 23: slag, 23a: slag, 2
4: anode torch (plasma torch), 25: cathode torch (plasma torch), 26: power supply device, 27:
Code, 28: Code

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Ryoji Nishihara 1-1-1, Tobata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works (72) Inventor Yasuo Shigenaga Tobata-ku, Kitakyushu-shi, Fukuoka No. 1-1, New Town Nippon Steel Corporation Yawata Works (72) Inventor Sanji Asano 1-1, Tobata-cho, Tobata-ku, Kitakyushu-city, Fukuoka Prefecture F-term in Nippon Steel Corporation Yawata Works (reference) 4E014 AA01

Claims (3)

[Claims] A cover for covering a tundish having a molten steel pouring port and a pair of plasma torch insertion ports and a heating chamber for molten steel on a side of the plasma torch insertion port; A pair of plasma torches held by a lifting device and inserted into the tundish from the plasma torch insertion opening, and further comprising a heating device for molten steel in which a cord of a power supply device is connected to the plasma torch. An upper weir for immersing the lower part in the molten steel between the pouring port of the molten steel and the heating chamber, and a porous plug for blowing an inert gas into the tundish immediately below the heating chamber. A heating device for molten steel in a tundish using a plasma torch. 2. The apparatus for heating molten steel in a tundish using a plasma torch according to claim 1, wherein the inert gas uses argon gas. . 3. The apparatus for heating molten steel in a tundish using a plasma torch according to claim 2, wherein the amount of argon gas is 1 to 20 NL / min. Heating equipment.