JPH06240332A - Method for refining molten metal and bottom blowing tuyere for refining molten metal - Google Patents

Abstract

(57) [Summary] [Purpose] When refining molten metal by utilizing the reaction occurring at the interface between gas and molten metal, the reaction rate can be increased to shorten refining time and improve productivity. Provided is a metal refining method and a bottom-blown tuyere therefor. When a molten metal is refined in a molten metal refining vessel while stirring with a bottom-blown gas, the shape of the gas outlet is annular and the ratio R of the inner diameter R of the annular ring and the radial width r of the annular ring is R. It is characterized in that the bottom-blowing gas is agitated by a bottom-blowing tuyere where / r is 10 or more. [Effects] According to the present invention, generated bubbles are miniaturized, the reaction interface area between the gas and the metal is increased, and the residence time of the bubbles is also increased, so that refining of molten metal can be performed in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for refining molten metal and a bottom blowing tuyere therefor.

[0002]

2. Description of the Related Art When refining molten metal by utilizing a gas-liquid reaction, for example, when decarburizing molten steel in a low carbon region, carbon in molten steel is combined with oxygen in molten steel and CO It becomes a gas and escapes from the gas-liquid interface. In refining utilizing the reaction at such a gas-liquid interface,
By blowing gas from the bottom of the container to increase the gas-liquid interface area, the reaction can be promoted and the processing time can be shortened.

Conventionally, a method of blowing gas into molten steel has been disclosed in, for example, Japanese Patent Laid-Open No. 2-217412 or Japanese Patent Laid-Open No. 3-6.
As disclosed in Japanese Patent No. 1316, a method is known in which an inert gas is blown into the molten steel in a decompression / vacuum tank, and a certain effect can be expected in improving the decarburization rate. At that time, the gas is blown from a porous plug or a circular tube nozzle. When the blowing gas flow rates are the same, the smaller the bubble diameter that is blown, the larger the gas-liquid reaction interfacial area and the shorter the refining reaction time.

Since the bubble diameter depends on the blowing nozzle diameter, it is necessary to make the nozzle diameter as small as possible in order to make the bubbles small. In that case, however, the blowing flow rate per nozzle is limited, so that the same flow rate is maintained. A large number of nozzles are required to secure it. As such a bottom blowing tuyere, a CB tuyere in which thin tubes are gathered is known, but in this case, the distance between the nozzles is short and the air bubbles coalesce, so that small air bubbles are not generated. In order to secure a distance between nozzles that prevents bubbles from merging, a large number of tuyere with one thin tube nozzle must be installed in the refining container, and the cost of tuyere brick, tuyere sleeve brick, etc. Increase. Also,
Even when using a porous plug, even if each pore is small, the distance between the pores is still extremely small, and the wettability between the molten metal and the plug is poor, so the gas spreads on the plug surface and coalesces bubbles. And still small bubbles are not generated.

[0005]

DISCLOSURE OF THE INVENTION According to the present invention, when refining a molten metal while blowing gas, small bubbles are generated to increase the gas-metal interface area, accelerate the refining reaction rate, and increase the treatment time. It is an object of the present invention to provide a method for refining molten metal for shortening the temperature and a bottom-blown tuyere therefor.

[0006]

The subject matter of the present invention is as follows. (1) When refining molten metal while stirring with a bottom-blown gas in a molten metal refining vessel, the gas outlet shape is annular, and the ratio R of the inner diameter R of the annular ring and the radial width r of the annular ring A method for refining molten metal, characterized in that bottom blowing gas stirring is performed by a bottom blowing tuyere having an / r of 10 or more.

(2) A bottom blowing tuyere for molten metal refining in which the gas outlet shape is an annular shape and the ratio R / r of the inner diameter R of the annular ring and the radial width r of the annular ring is 10 or more. The feature of the present invention resides in that the gas outlet shape of the bottom blown tuyere is annular and the ratio R / r of the inner diameter R of the annular ring and the radial width r of the annular ring is defined as described above. Thus, the diameter of generated bubbles can be reduced without decreasing the gas flow rate per nozzle,
This is because the metal interfacial area is increased and the reaction occurring at the gas-liquid interface can be made to proceed faster than before.

[0008]

The operation of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing the shape of tuyere, FIG. 2 is an explanatory view of an example of decarburization of molten steel in the low carbon region using the tuyere, and FIG. 3 is an enlarged view of a portion of FIG. 2A. As shown in FIG. 1, by using a cylindrical nozzle 2 inside a tuyere brick 1, the shape of the gas outlet is annular. When this tuyere is installed at the bottom of the refining vessel 4 for the molten metal 5 as shown in FIG. 2 and Ar gas is blown into it, the bubbles 3 are melted by being defined by the width of the ring at the nozzle outlet as shown in FIG. It is blown into metal. Therefore,
Compared to a single pipe nozzle having the same nozzle outlet area, the bubbles generated at the same gas amount are much smaller. However, the ratio R / r of the inner diameter R of the annulus and the radial width r of the annulus is 10
When it is less than the above, the bubbles coalesce immediately above the annular exit, as shown in FIG. 4, and the effect of making the bubbles finer decreases. Carbon and oxygen in the molten steel react with each other on the surface of the Ar bubbles blown into the molten metal to form CO gas and the decarburization reaction proceeds, but the reaction interface area increases as the Ar bubbles become smaller. Further, as the bubbles are smaller, the floating speed of the bubbles is also reduced, so that the molten steel residence time of the bubbles is increased. For the above two reasons, the total decarburization reaction rate increases as the bubbles become smaller when the blowing gas flow rates are the same.

For the above reasons, it becomes possible to carry out the refining of the molten metal by utilizing the reaction occurring at the interface between the gas and the metal in a shorter processing time than before.

[0010]

EXAMPLE A decarburization experiment of low carbon molten steel was conducted using a cylindrical refining vessel having an inner diameter of 1.1 m and having a bottom blowing stirring function. The nozzle annular part of the tuyere had an inner diameter of 30 mm and a radial width of 1 mm. In the experiment, the C concentration was 290
It carried out using the molten steel adjusted to -310 ppm. Molten steel weight is 6 t, Ar gas blowing amount is 150 Nl / min,
The refining time was 10 minutes. After the start of refining, a metal sample was taken every 2 minutes and C analysis was performed. FIG. 5 shows the change with time of the C concentration in the molten steel during this experiment. As a comparison, FIG. 5 also shows changes over time in the C concentration when a tuyere having a circular tube nozzle with an inner diameter of 8 mm having substantially the same nozzle outlet cross-sectional area is used. It was confirmed that the refining method according to the present invention took less time to reach a certain C concentration.

Further, the cross-sectional area of the nozzle outlet is constant,
FIG. 6 shows the C concentration after 10 minutes under the same experimental conditions as above when R / r was set to 5, 10, 15, and 30. R / r
It was confirmed that by setting 10 to 10 or more, a low C concentration was obtained in each case.

[0012]

According to the present invention, the refining time utilizing the reaction occurring at the gas-metal interface can be shortened and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view of a tuyere in which a nozzle outlet shape is annular.

FIG. 2 is an explanatory view of an example in which the present invention is applied to a refining vessel for decarburizing molten steel by blowing Ar gas from the bottom.

FIG. 3 is an enlarged explanatory view of a portion A of FIG.

FIG. 4 is a diagram showing the behavior of bubbles when Ar gas is blown in using a nozzle having an R / r of less than 10.

FIG. 5 is a graph showing changes in C concentration in molten steel during a decarburization experiment.

FIG. 6 is a diagram showing the ultimate C concentration during a decarburization experiment when R / r was changed.

[Explanation of symbols]

 1: Tuyere brick 2: Annular nozzle 3: Bubbles 4: Refining vessel 5: Molten metal

Claims (2)

[Claims] 1. When refining a molten metal in a molten metal refining vessel while stirring with a bottom-blown gas, the gas outlet shape is annular, and the inner diameter R of the annular ring and the radial width r of the annular ring A method for refining molten metal, characterized in that bottom-blowing gas stirring is performed by a bottom-blowing tuyere having a ratio R / r of 10 or more. 2. The gas outlet shape is an annular shape, and the inner diameter R of the annular shape.
Bottom blown tuyere for molten metal refining, wherein the ratio R / r between the radial width r of the ring and the radial width r is 10 or more.