JP2002194421A - Degassing treating method and molten steel stirring apparatus in simple degassing facility for molten steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain flowing speed of molten steel to inner wall surface, etc., of a vacuum vessel to be remarkably lower than that in the conventional vessel especially without needing the blowing of inert gas. SOLUTION: In a degassing treating method for a simple molten steel degassing facility performing the degassing of the molten steel with the vacuum vessel by dipping an immersion tube at the lower end of the vacuum vessel into the molten steel in a refining vessel, an impeller is arranged at the bottom of the above refining vessel and the flow of the molten steel in the above vacuum vessel is caused from the center part to the outside in the radius direction with the impeller by circling the refining vessel, and the vertical circulating flow is caused with this flow to perform the degassing in the molten steel in the refining vessel 1 by making the negative pressure in the vacuum vessel by a vacuum source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for degassing molten steel in a smelting vessel, which can efficiently stir the molten steel for dehydrogenation and denitrification of the molten steel in the smelting vessel. The degassing efficiency can be increased and the degassing processing time can be shortened.

[0002]

2. Description of the Related Art As a method for degassing molten steel in a refining vessel, there are a method using a jet flow method (Japanese Patent Application Laid-Open No. 56-123320) and a method using a molten steel stirring method (Japanese Patent Application Laid-Open No.
3-140029, JP-A-63-183119). The present invention is based on the molten steel stirring method of the above-mentioned conventional degassing treatment method. In the molten steel stirring method, an inert gas is blown into molten steel pulled into a vacuum tank to generate an upward flow, and the upward flow is generated. Degassing is performed in the same vacuum chamber, and an example thereof is disclosed in Japanese Patent Application Laid-Open No. 63-1400.
No. 29) is as shown in FIG.
This is referred to as “prior art 1”). In the above prior art 1, the immersion pipe (the lower end is opened) 5 at the lower end of the vacuum tank 4 is immersed in the molten steel 2 in the refining vessel (specifically, a ladle) 1 to below the slag layer 3. An electromagnetic stirring device 8 is arranged on the outer periphery of the lower portion of the vacuum chamber 4. Further, a pair of nozzles n facing the immersion pipe 5 is provided, and a gas supply pipe 9 is connected to the nozzle n. In addition, an alloy storage layer 7 is provided at the upper end of the vacuum tank 4 and a pressurizing / depressurizing pipe 6 is connected. The pressurizing / depressurizing pipe 6 is connected to a vacuum source to make the inside of the vacuum tank 4 negative pressure, and the level of the molten steel 2 in the refining vessel 1 is pulled up into the vacuum tank 4. To generate a swirling flow. At this time, a large amount of argon gas is blown from a nozzle n connected to the gas supply pipe 9 to perform a degassing process. This applies a strong swirling flow to the molten steel in the vacuum chamber 4 and alternately switches the pressurizing / depressurizing pipe 6 between a vacuum source and a pressurizing source to repeatedly reduce and increase the pressure in the vacuum chamber 4 (for example, The pressure of the molten steel in the vacuum tank 4 is moved up and down to agitate the molten steel in the refining vessel. FIG. 2 shows another conventional technique. In this apparatus, two immersion tubes 25a and 25b are provided in a lower portion 24a of a vacuum tank 24, and an inert gas (argon gas) is blown into the immersion tube 25a with the molten steel pulled up to the lower portion 24a in the vacuum tank 24. By generating an ascending flow in the pipe 25a and refluxing it from the other immersion pipe 25b to the refining vessel 1, a vertical circulating flow is generated and degassing is performed with this circulating flow (hereinafter referred to as "conventional"). Technology 2).

[0003] In both the prior art 1 and the prior art 2 described above, an inert gas is blown and an ascending force is used to generate an ascending flow in the molten steel. However, in order to secure a required degassing efficiency, a large amount of inert gas is required. It is necessary to blow in an inert gas.
Moreover, in the prior art 1, the molten steel in the refining vessel 1 is moved up and down in the vacuum tank 4 to agitate the molten steel, but the degree of vacuum in the vacuum tank 4 is greatly reduced in a short time while performing degassing. (For example, even if the molten steel level in the vacuum chamber 4 is raised from 0 m to 1 m in 10 seconds, the degree of vacuum change is extremely large during this period), and the equipment for this is not very large. Not get. In the above-mentioned prior art 2, the molten steel in the smelting vessel 1 is stirred and degassed by the upward flow of the inert gas. However, since the two immersion tubes 25a and 25b are immersed, this immersion is performed. The inner diameter of the tube must be small (for example, the inner diameter d is 500 to 800 mm, and the outer diameter D is 1000 to 1000).
1300 mm). On the other hand, in order to secure a circulation flow rate necessary for performing degassing at a predetermined efficiency, the flow velocity of the upward flow has to be considerably increased. For this purpose, the dip tube 25
Since the inner surfaces of a and 25b are worn early due to friction with molten steel, durability is poor.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention is directed to a scouring vessel without increasing the flow rate of molten steel in the vacuum chamber to the wall surface of the vacuum chamber by actively stirring the molten steel in the vacuum chamber vertically. An object of the present invention is to devise a method of stirring molten steel so that the stirring and degassing functions of molten steel can be improved.

[0005]

[Measures taken to solve the problem]

[MEANS FOR SOLVING PROBLEMS] A solution 1 for solving the above-mentioned problem is a degassing treatment in a molten steel simple degassing facility in which a dipping pipe at a lower end of a vacuum tank is immersed in molten steel in a refining vessel and the molten steel is degassed by the vacuum tank. Based on the method, it is composed of the following (a) and (b). (A) An impeller is provided at the bottom of the smelting vessel, and the smelting vessel is swirled to generate a flow of molten steel from the center to the outside in the radial direction. (B) The immersion pipe of the vacuum tank is immersed shallowly in the vessel. The vacuum chamber is set to a negative pressure by a vacuum source, and a vertical flow is created in the molten steel by the rotation of the impeller and the vacuum in the vacuum chamber, and a vertical circulating flow is caused to stir the molten steel. In addition, the above-mentioned "Immerse the dip tube of the vacuum tank shallowly in the container"
Means that the immersion depth is about 2/3 that of the prior art.

[0006]

When the smelting vessel provided with an impeller at the bottom is swirled, the impeller causes molten steel at the bottom of the smelting vessel to flow radially outward from the center, hit the inner wall of the smelting vessel, and rise along the inner wall. It is pulled up by the vacuum in the vacuum chamber to the dip tube, descends again from the center, and flows radially outward along the bottom of the smelting vessel. Since the molten steel in the immersion pipe is actively stirred vertically by the vertical circulation flow, degassing is efficiently performed by the high degree of vacuum in the vacuum chamber. Since the circulating flow stirs the entire molten steel in the refining vessel, degassing of the entire molten steel in the refining vessel is promoted evenly. Also, since the vacuum chamber is maintained at a substantially constant degree of vacuum, the degassing efficiency in each stage is lower than in systems that vary the pressure in the vacuum chamber to move the molten steel level up and down. Are better. Further, since the inner diameter of the immersion pipe is about twice as large as that of the prior art 2, the circulating flow rate required to secure the required vertical circulating flow rate is 1/4 to 1 of the circulating flow rate in the prior art 2. Therefore, wear of the inner wall surface of the immersion pipe due to the upward flow of molten steel is extremely small.

[0007]

[Embodiment 1] In this embodiment 1, the smelting vessel has a swirling speed of 10 times / min or less, and a flow rate of 0.1 to 10 mm / min for molten steel in a vacuum chamber.
A vertical circulating flow of 0.2 m / sec was produced.

With the rotation of the smelting vessel, the molten steel is circulated vertically by the impeller at the bottom of the smelting vessel.
By generating a vertical circulating flow of about 0.2 m / sec, the degassing efficiency is reduced while the flow velocity of the molten steel in the vacuum chamber with respect to the inner surface of the vacuum chamber is suppressed to such an extent that the abrasion of the inner surface is suppressed. It can be as high as possible.

[0008]

[MEANS FOR SOLVING PROBLEMS] A solution 2 for solving the above-mentioned problem is that molten steel in a refining vessel is immersed shallowly in a dip tube at the lower end of a vacuum tank having a lower end opened, and the vacuum tank is depressurized and degassed. Assuming a degassing device in a simple degassing facility,
It is constituted by the following (a) and (b). (B) the refining vessel is rotatably supported by a thrust bearing, and is rotated by a driving device;
(B) An impeller is provided at the bottom of the refining vessel.

[0009]

According to the second aspect of the present invention, the degassing method of the first aspect can be effectively implemented.

[0010]

[Embodiment 1] In Embodiment 1, a thrust bearing is provided on a carrier of a bogie, a refining vessel (specifically, a ladle) is pivotably supported by the thrust bearing, and the thrust bearing is rotationally driven by a driving device. That's what we did.

The immersion tube can be immersed shallowly in the molten steel in the smelting vessel while the smelting vessel is mounted on the trolley, and the smelting vessel can be turned on the trolley. Can be done

[0011]

Embodiment 2 In Embodiment 2, a speed reducer and a drive motor are provided below a thrust bearing that supports the refining vessel, and a ring gear of the thrust bearing is driven by a drive pinion of the speed reducer. .

Since the speed reducer and the drive motor are provided below the thrust bearing, and the thrust bearing is directly driven to rotate by this, the mechanism of the driving device for turning the scouring vessel can be simplified.

[0012]

Embodiment 3 Embodiment 3 is that an insulating plate is interposed on the upper surface of the thrust bearing.

[Action] The bottom outer surface of the scouring vessel is heated to a high temperature,
Since the heat insulating plate (for example, a porous ceramic plate or the like) is interposed between the upper surface of the thrust bearing and the thrust bearing, a thermal effect on the driving device disposed below the thrust bearing is reduced.

[0013]

Next, an embodiment will be described with reference to the drawings. This embodiment is an example in which molten steel is degassed using a ladle (refining vessel) 1 having a capacity of 200 tons, and a flange joint 1 is provided at the lower end of a main body 11 of a vacuum chamber 10.
The dip tube 13 is detachably attached by 2 and the upper end of the main body 11 is connected to the upper part 15 via the flange joint 14. The upper part 15 communicates with a vacuum source, and has a lance hole 16 at its upper end.
7 is inserted to be able to move up and down in a sealed state.
The provision of the lance 17 is conventionally known in a degassing apparatus, but the lower end of the lance 17 reaches just above the molten steel level in the immersion pipe 13 below the vacuum chamber 10. The immersion tube 13 is manufactured by projecting a rib material from an iron core material 13x inward and outward in the radial direction, laminating a cement layer 13y so as to wrap the rib, firing and hardening the cement layer 13y, and has an inner diameter of It is a cylindrical body having an outer diameter of 2500 mm and an outer diameter of 3500 mm. A trolley 20 for transporting the ladle 1
A thrust bearing (slewing bearing) 23 is provided on a carrier 21 of the vehicle. Therefore, when ladle 1 is placed on trolley 20, ladle 1
Is rotatably supported by a thrust bearing 23. A drive motor 24 is interposed between the thrust bearing 23 and the loading platform 21. The drive motor 24 drives the ring gear 22 provided on the upper plate of the thrust bearing via a speed reducer (built in the drive motor in this example). I try to drive. Thereby, the ladle 1 is driven at a speed of 10 times / min. With 200 tons of molten steel placed in the ladle 1 and placed on the carrier 21 of the trolley 20, the vacuum tank 10 is lowered to immerse the dip tube 13 from the level of the molten steel in the ladle 1 to a depth of about 1000 mm. At this time, the inside of the vacuum chamber 10 is sucked at a high vacuum (for example, approximately 0.05 Torr) by a vacuum source, and the molten steel level is raised to a height of 1100 to 1400 mm therein, and this state is continuously maintained. Ladle 1 in this state
Is turned 10 times per minute, the impeller 1a at the bottom of the ladle
As a result, a vertical circulating flow having a flow velocity of about 0.2 m / sec is generated in the molten steel in the vacuum chamber 10 and is stirred in the vertical direction. This circulating flow reaches the bottom of the ladle 1 and circulates from the bottom to the top of the molten steel in the vacuum chamber 10.

[0014]

As described above, according to the present invention, an impeller is provided at the bottom of a smelting vessel, and the smelting vessel is turned to generate a vertical circulating flow in molten steel in the smelting vessel by the impeller. Since the degassing is promoted by the circulating flow, it is not necessary to blow an inert gas, and the flow rate of the molten steel to the inner wall surface of the vacuum chamber 10 can be suppressed significantly lower than that of the conventional one. Therefore, wear damage to the refractory wall surface due to friction with molten steel can be reduced, and the durability thereof can be significantly improved. In addition, since the refining vessel is swirled and a vertical circulating flow is generated in the molten steel by the impeller at the bottom of the smelting vessel, a device for generating a vertical circulating flow is relatively simple,
The manufacturing cost of the degassing apparatus and the operating cost of the degassing apparatus can be significantly reduced as compared with those described in the prior arts 1 and 2.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a conventional degassing apparatus.

FIG. 2 is a schematic sectional view of another conventional degassing apparatus.

FIG. 3A is a schematic cross-sectional view of the embodiment, and FIG. 3B is an AA view of FIG.

4A is an AA view of FIG. 3, and FIG. 4B is a longitudinal sectional view of a main part of FIG.

[Explanation of symbols]

 1: Ladle (refining vessel) 1a: Impeller 10: Vacuum tank 11: Main body of vacuum tank 12, 14: Flange joint 13: Immersion pipe 13x: Iron core material 13y: Cement layer 15: Upper part of vacuum tank 16: Lance hole 17: lance 20: bogie 21: bogie carrier 22: ring gear 23: thrust bearing 24: drive motor

Claims (6)

[Claims] In a degassing method in a molten steel simple degassing apparatus for immersing a dipping pipe at a lower end of a vacuum tank in molten steel in a refining vessel and degassing the molten steel by the vacuum vessel, an impeller is provided at the bottom of the refining vessel. The smelting vessel is swirled to create a flow from the center to the outside in the molten steel, the immersion tube of the vacuum vessel is immersed shallowly in the vessel, the vacuum vessel is set to a negative pressure by a vacuum source, and the rotation of the impeller and the vacuum A degassing method in which a vertical flow is created in molten steel by a vacuum in the tank, and a vertical circulating flow is created to agitate the molten steel. 2. The method according to claim 1, wherein the smelting vessel has a swirling speed of not more than 10 times / minute, and a vertical circulating flow having a flow velocity of 0.1 to 0.2 m / sec is generated in the molten steel in the vacuum chamber. Gas treatment method. 3. A degassing treatment apparatus in a simple degassing equipment for molten steel in which a dipping tube at a lower end of a vacuum tank having a lower end opened shallowly immersed in molten steel in a refining vessel to depressurize and degas the vacuum tank. A molten steel stirring device in a simple molten steel degassing facility, wherein the refining vessel is rotatably supported by a thrust bearing, and the refining vessel is pivotally driven by a driving device, and an impeller is provided at a bottom of the refining vessel. 4. The molten steel stirring device according to claim 3, wherein a thrust bearing is provided on a carrier of the bogie, the refining vessel is pivotably supported by the thrust bearing, and the thrust bearing is rotationally driven by a driving device. 5. The molten steel stirring device according to claim 4, wherein a speed reducer and a drive motor are provided below the thrust bearing supporting the refining vessel, and a ring gear of the thrust bearing is driven by a drive pinion of the speed reducer. 6. A molten steel stirrer according to claim 3, wherein a heat insulating plate is interposed on the upper surface of the thrust bearing.