JP2000204421A - Gas-stirring of molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for shortening uniform mixing time by effectively stirring the whole molten metal in a ladle more than the conventional method, in the case of stirring the whole molten metal with gas for stirring by dipping an immersion tube for charging an adjusting material for adjusting a component in the molten metal under atmospheric pressure. SOLUTION: In a ladle refining by dipping the immersion tube for charging the adjusting material for adjusting the component into the molten metal and blowing and stirring the gas into the molten metal from the lower part, the diameter (d) of the immersion tube satisfies an inequality I and the position of a gas blowing nozzle for stirring is made to the center part of the immersion tube, and further, an eccentric quantity X of the center in the diameter direction of the immersion tube to the center in the diameter direction of the ladle satisfies an inequality II. The inequality I: 1.2.2h.tan(θ/2)<=d<=2.0.2h.tan(θ/2). The inequality II: d/2<=X<=D/2-h.tan(θ/2), wherein, h: blowing depth of the gas for stirring from the lower end of the immersion tube, θ: widening angle of rising gas bubbles and D: diameter of the ladle.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for agitating molten metal gas in ladle refining of molten metal.

[0002]

2. Description of the Related Art As a method for adjusting the composition of a molten metal, an immersion tube is immersed in a molten metal stored in a ladle, and a stirring gas is blown from below the immersion tube while a substance for adjusting the component is injected from above the immersion tube. There is a ladle refining method for pouring into molten metal.
When the molten metal is molten steel, for example, Japanese Unexamined Patent Publication No.
A method disclosed in Japanese Patent Publication No. 14 has been proposed.

In this method, as shown in FIG. 2A, the expansion of a plume (bubble bubble region) formed by blowing a stirring gas 6 from below the dip tube 4 is taken into consideration.
The center of the ladle 1 and the center of the ladle 1 are made to coincide with each other, and the blowing position of the stirring gas 6 is eccentric with respect to the center of the ladle 1 by the range Y shown in the following formula (3). h · tan (θ / 2) ≦ Y ≦ d / 2−h · tan (θ / 2) (3) where d: diameter of immersion tube

[0004] This method is effective for a vacuum refining reaction in which the degassing reaction in the molten metal is promoted by reducing the pressure inside the immersion tube while adjusting the components. That is, when the inside of the immersion tube 4 is depressurized as shown in FIG. 2A, the upper surface of the molten metal 2 in the immersion tube 4 rises as compared with the outside of the immersion tube 4.
An upward flow is generated in the molten metal 2 inside the immersion tube 4, and a larger upward flow of the molten metal 2 is generated in the immersion tube 4 by the synergistic effect with the blowing stirring gas 6 from below the immersion tube 4, and the molten metal 2 flows out of the immersion tube 4. This is because the agitated flow 7 of the molten metal 2 that flows out is generated. Further, in the vacuum refining apparatus, in order to efficiently perform the degassing reaction, the reaction area of the upper surface of the molten metal 2 in the immersion pipe 4 must be increased, and the immersion pipe diameter D with respect to the ladle diameter d needs to be increased. . However, when the conventional method is applied to a refining apparatus under normal pressure where the degassing reaction effect is small, stirring of the component adjusting substance cannot be sufficiently performed.

That is, when the ratio of the diameter d of the immersion tube to the diameter D of the ladle is increased while the inside of the immersion tube is under normal pressure as described in Japanese Patent Application Laid-Open No. In the example of JP-A-113114, when the ratio of the area of the stirring plume on the upper surface of the molten metal 2 in the immersion tube 4 to the cross-sectional area of the immersion tube 4 is reduced to about 0.03), FIG.
As shown in (b), although the upward flow generated by the stirring gas 6 flows from the upper surface of the molten metal 2 toward the inner wall of the immersion tube, it decelerates before colliding with the inner wall of the immersion tube due to the large diameter of the immersion tube. As a result, the descending flow after the collision is further decelerated, so that a flow for stirring the entire molten metal 2 in the ladle cannot be obtained. As described above, when the present method is applied under normal pressure, there is a problem that it takes time to uniformly mix the entire molten metal 2 in the ladle.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to immerse a dip tube into which a substance for adjusting the composition of a molten metal is introduced under normal pressure and stir the molten metal with a stirring gas. Effectively agitating the entire molten metal in the pot,
It is an object of the present invention to provide a method for shortening the uniform mixing time.

[0007]

The present inventor has repeatedly conducted detailed examinations and detailed experiments on the means for achieving the object, and as a result, the main object of the present invention is to mix and stir the molten metal under normal pressure. In the refining equipment, it was found that the above-mentioned problems could be solved by appropriately setting the stirring gas injection position while minimizing the immersion pipe diameter, and completed the present invention. .

Here, the gist of the present invention is that, as shown in FIG. 1, a dip tube is immersed in a ladle containing molten metal, and a substance for adjusting a component of the molten metal is introduced into the dip tube. When performing ladle refining while stirring the molten metal by blowing a stirring gas from a nozzle installed below the dip tube below the ladle, the dip tube diameter d satisfies the condition of the following formula (4),
And the agitating gas injection position is at the center of the immersion pipe radial direction,
Further, there is provided a gas stirring method for molten metal, wherein an eccentric amount X of a center of a ladle in a radial direction with respect to a center of a ladle in a radial direction satisfies a condition of the following formula (5). 1.2.2htan (θ / 2) ≦ d ≦ 2.0.2.htan (θ / 2) (4) d / 2 ≦ X ≦ D / 2-htan (θ / 2). (5) where, h: depth of gas blowing for stirring from the lower end of immersion tube θ: spread angle of rising bubble D: ladle diameter

[0009]

Next, an embodiment of the present invention will be described in detail. In the following example, molten steel will be described as an example of molten metal based on FIG. As shown in FIG. 1, an immersion pipe 4 for introducing a substance 3 for component adjustment to be introduced into molten steel is immersed in molten steel 2 accommodated in a ladle 1, and is immersed in a lower part of the ladle 1 under the immersion pipe 4. A stirring gas injection nozzle 5 is installed, and a ladle refining is performed under normal pressure while blowing the stirring gas 6 and stirring the molten steel 2.

The stirring gas 6 gradually spreads while rising inside the molten steel 2. When the divergence angle is θ and the depth from the lower end of the immersion pipe 4 to the blowing point of the stirring gas injection nozzle 5 is h, the plume of the stirring gas 6 reaching the lower end of the immersion pipe 4 has a radius h.・ It has a spread of tan (θ / 2). That is, in order for the stirring gas 6 not to flow out of the immersion tube 4, the diameter d of the immersion tube 4 needs to be 2 h · tan (θ / 2) or more, and it is necessary to satisfy the following expression (6). 2h · tan (θ / 2) ≦ d. (6)

In this case, the immersion tube 4 is stirred by the stirring gas 6.
In order for the molten steel 2 flowing into the ladle 1 to immediately flow out of the dipping tube 4 and effectively generate the molten steel flow 7 descending into the ladle 1, the dipping tube 4 has a diameter d and a height position at the lower end of the dipping tube 4. Ideally, the plume diameter of the reached stirring gas 6 should be the same value. Therefore, the above equation (6) becomes the following equation (7). d = 2h · tan (θ / 2). (7)

Further, as described above, in order to minimize the diameter of the immersion pipe 4 while completely accommodating the plume in the immersion pipe 4, it is necessary to consider the geometrical positional relationship and to examine the center of the immersion pipe 4 in the radial direction. It is necessary to provide a stirring gas 6 injection point immediately below.

However, fluctuations in plume diameter and plume generation position are unavoidable due to instability in the flow rate, pressure, and nozzle state of the molten steel flow 7 and the stirring gas 6, and as a result, the apparent plume diameter increases and the immersion pipe 4 It is necessary to appropriately select the diameter d of the immersion tube 4 that can completely accommodate the plume therein. Therefore, the diameter d of the immersion tube 4 is changed and the ladle 1
Investigation of the time τ (hereinafter referred to as “homogeneous mixing time”) from the start of the addition of the component adjusting material to the molten steel 2 in the ladle to the complete mixing into the molten steel 2 in the ladle 1, revealed that in order to shorten the uniform mixing time, Has to be in the range of the expression (8). 1.2.2 h · tan (θ / 2) ≦ d ≦ 2.0 · 2h · tan (θ / 2) (8)

Next, a method of arranging the position of the stirring gas injection nozzle 5 with respect to the center of the ladle 1 in the radial direction (= the center of the dip tube 4 in the radial direction) will be described. In the present invention, in order to efficiently stir the entire ladle 1 including the above-described mixing in the immersion tube 4, the center of the immersion tube 4 in the radial direction, that is, the stirring gas injection nozzle 5
The position needs to be arranged with the eccentric amount X with respect to the center of the ladle 1. This is because, as shown in FIG. 3, when the position of the stirring gas injection nozzle 5 is decentered, the molten steel flow 7 flowing out of the immersion pipe 4 by the ladle 1 side wall becomes difficult to be dispersed toward the ladle 1 side wall. As a result, the one-way annular flow in the entire ladle 1 is likely to occur. However, as shown in FIG.
Is too large, the plume of the stirring gas 6 comes into contact with the side wall of the ladle 1, and the plume cannot be reliably covered with the immersion pipe 4. From the above results, the eccentric amount X at the position of the stirring gas injection nozzle 5 with respect to the center of the ladle 1 in the radial direction needs to be within the range of the following equation (9). d / 2 ≦ X ≦ D / 2−h · tan (θ / 2). (9) However, depending on the value of the diameter d of the immersion tube 4 in the above formula (8), when the immersion tube 4 comes into contact with the wall of the ladle 1 even if the eccentric amount X is within the range of the above formula (9). X such that the immersion tube 4 does not contact
Value.

As described above, the diameter of the immersion pipe 4 and the position of the stirring gas injection nozzle 5 are made to coincide with each other, and the stirring gas is injected into the center of the immersion pipe 4 d, the immersion pipe 4 d and the ladle 1 in the direction D. Eccentricity X at nozzle 5 position (= radial center of immersion tube 4)
By appropriately setting, the molten steel 2 in the ladle 1 can be efficiently mixed and stirred. When a lance is used as the stirring gas injection nozzle 5 as shown in FIG.
Since the blowing depth is small, the stirring gas is stirred and compared with the case where the stirring gas is blown from the bottom of the ladle 1 using a porous plug.
Although the mixing effect is reduced, the effect of the present invention can be obtained equally.

[0016]

[Example] Ladle diameter D = 4770 mm, depth h from the lower end of the immersion pipe to the porous plug installed at the bottom of the ladle as a stirring gas injection nozzle, h = 2500 mm, and 340 t of aluminum killed molten steel was used. Table 1 shows the results of the investigation of the uniform mixing time by varying the eccentric amount X of the stirring gas injection nozzle position, the eccentric amount Y of the immersion pipe radial center with respect to the ladle radial center, and the immersion pipe diameter d. It is shown in FIG. In the present embodiment, Ar was blown from the porous plug as a stirring gas at a spread angle θ of the rising bubbles of 20 ° and a flow rate of 500 NL / hr.

[0017]

[Table 1]

In Examples 1 and 2, the eccentricity X of the stirring gas injection nozzle position with respect to the center of the ladle in the radial direction and the immersion pipe diameter d are set to appropriate ranges, and the eccentricity of the center of the immersion pipe in the radial direction with respect to the center of the ladle is considered. This is an example in which the amount Y is made coincident with the eccentric amount X (X = Y). Conventional example 1 is an example in which the center in the ladle radial direction and the center in the dip tube radial direction are matched (X = 0). Comparative Examples 1 to 3 are examples in which the eccentric amounts X and Y and the immersion tube diameter d are out of the range of the present invention.
From Table 1, it was possible to shorten the uniform mixing time by setting the eccentric amounts X and Y and the immersion tube diameter d in appropriate ranges.

[0019]

According to the present invention, an immersion pipe for charging a molten metal component adjusting substance is immersed in a ladle for accommodating the molten metal under normal pressure, and the immersion pipe is placed under the immersion pipe into a stirring gas immersion pipe. In ladle refining, in which the molten metal is blown in while stirring and the molten metal is stirred, good stirring in the ladle is realized, and the amount of stirring gas used can be significantly reduced by shortening the uniform mixing time. It has become possible to enjoy a great economic effect.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the present invention.

FIG. 2 is a conceptual diagram showing the difference between reduced pressure and normal pressure in the prior art.

FIG. 3 is a schematic view of a relative position of a ladle and a dip tube and a flow of a molten metal.

Fig. 4 Relative positional relationship between plume, dip tube and ladle

FIG. 5 is a conceptual diagram when a lance is used for a gas injection nozzle for stirring.

[Explanation of symbols]

1. Ladle 2. 2. Molten steel (molten metal) 3. Substances for adjusting components to be added to molten steel Immersion tube 5. 5. Gas blowing nozzle for stirring Stirring gas 7. Molten steel flow (molten metal flow) d: diameter of immersion pipe h: height of gas injection for stirring from lower end of immersion pipe θ: spread angle of rising bubble D: ladle diameter X: gas injection for ladle diameter center Eccentricity of position Y: Eccentricity of immersion tube radial center with respect to ladle radial center τ: At uniform mixing

Continued on the front page (72) Inventor Shigenori Yakura 1 Nishinosu, Oji, Oita, Oita Prefecture Inside Nippon Steel Corporation Oita Works (72) Inventor Tsukasa Kashihara 1 Nishinosu, Oita, Oita, Oita Prefecture Nippon Steel Corporation Oita Works F term (reference) 4K001 AA10 BA04 GA18 GB05 4K013 BA16 CA02 CA21 CC04

Claims (1)

[Claims] An immersion tube for charging a molten metal component adjusting substance is immersed in a ladle for accommodating a molten metal under normal pressure so that a stirring gas flows from below the immersion tube into the immersion tube. When performing ladle refining while stirring the metal, the immersion pipe diameter d satisfies the condition of the following formula (1),
The position of the stirring gas injection nozzle is located below the center of the immersion tube, and the eccentric amount X of the center of the immersion tube in the radial direction with respect to the center of the ladle in the radial direction is defined by the following equation (2). A gas stirring method for molten metal, characterized by satisfying the following. 1.2.2htan (.theta. / 2) .ltoreq.d.2.0.2.htan (.theta. / 2) (1) d / 2.ltoreq.X.ltoreq.D / 2-htan (.theta. / 2). (2) Here, h: Depth of gas blowing for stirring from the lower end of immersion tube θ: Spread angle of rising bubble D: Ladle diameter