JPH06172879A - Method for generating bubbles in molten metal - Google Patents

Abstract

PURPOSE:To generate fine bubbles in a molten metal by controlling the size of bubbles formed in the molten metal by blowing a gas. CONSTITUTION:The bubbles 9 are generated in the molten metal 2 by blowing the gas G into the molten metal 2. In this method, the diameter of bubbles 9 generated, by blowing the gas G through the gas blowing nozzle 3 is controlled by heating a part where the bubbles 9 are generated. Thus, gaseous components such as hydrogen, nitrogen and impurities such as carbon, non metallic inclusions in the molten metal 2 can be efficiently removed by the fine bubbles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bubble generating method which makes it possible to miniaturize bubbles generated in a molten metal.

[0002]

2. Description of the Related Art Gas bubbles are blown into a molten metal as a means for removing gas components such as hydrogen and nitrogen, carbon and non-metallic inclusions in the molten metal. It is effective to blow fine bubbles in order to actively perform the removal effect by blowing bubbles. As a means for forming fine bubbles, a static magnetic field and an alternating current, which are applied in a horizontal direction and are orthogonal to each other, as shown in Japanese Patent Publication No. 30456/1993, are used to apply a varying electromagnetic force to a molten metal. A method has been proposed in which the apparent pressure that acts on the surface of a porous body that is generated and blows gas is varied.

[0003]

[Problems to be Solved by the Invention] Japanese Patent Publication No.
In the method disclosed in the publication, it is necessary to widely apply a static magnetic field and an alternating current in the molten steel height direction in order to change the apparent pressure. The cost is high. In addition, when applied to a large container such as a ladle, the gap between the magnetic pole and the electrode becomes large, and therefore a device for generating a strong magnetic field is required to obtain the effect because the magnetic field is attenuated, and the current is The path through which the current flows becomes unstable, making it difficult to obtain a stable effect. Furthermore, for example, when applied to a channel such as a tundish in continuous casting, either the electrode or the magnetic pole must be installed in the direction perpendicular to the channel wall, and it must be installed so as to block the channel. It is difficult to apply because it must be done. Therefore, there is a need for a method that is low in cost and easy to apply to large containers and flow paths.

[0004]

In order to solve the above problems, the present invention provides: 1. In a method of blowing gas into a molten metal to generate bubbles in the molten metal, heating a portion where bubbles are generated. A method of generating bubbles in molten metal, characterized in that the diameter of the bubbles generated by the above is controlled, and a nozzle or a porous body for blowing gas to heat the bubble generating part is constituted by a conductive resistor, The present invention relates to a method for generating bubbles in a molten metal, which is characterized by applying electricity.

[0005]

FIG. 1 shows an embodiment of the present invention. Molten steel 2 in ladle 1
When the refractory nozzle 3 is installed at the bottom and gas G is blown, bubbles 9 are generated in the molten steel from the nozzle. The nozzle is heated by the heater 7 installed around the nozzle. When such a heater is provided, the gas expands inside the nozzle. By doing so, the flow rate of the gas supply source does not change, but the gas flow rate from the nozzle apparently increases, and the frequency of bubble generation increases. Since the expansion of gas increases as the temperature rises, it becomes possible to control the bubble diameter by changing the heating temperature and changing the bubble separation interval.

As a heating method, in addition to the method of installing a heater near the nozzle as in the above method, there is a method of directly heating the nozzle by energizing it as a conductive resistor. By generating heat from the nozzle itself, the gas at the tip of the nozzle can be efficiently heated, which is effective. Therefore, when applied to molten steel, it is desirable that the nozzle is made of a graphite-based or zirconium boride-based conductive refractory. The means for blowing gas may be a single-tube or multi-tube nozzle or a porous refractory material.

[0007]

【Example】

(Embodiment 1) An embodiment of the present invention is shown in FIG. 300 kg
Ladle 1 of molten steel 2 whose bottom is 15 cm square and whose height is 20 cm
Nozzle 3 made of refractory and having an outer diameter of 1.0 cm was installed at the bottom, and gas G was blown thereinto. The nozzle was heated by an electric heater 7 installed around the nozzle at the bottom of the ladle. The results are shown in Table 1, and the bubbles 9 are formed depending on the heating temperature.
It was observed that the diameter of the was changed.

Example 2 In FIG. 1, a graphite refractory was used as the material of the nozzle 3, and a power source was connected to this nozzle to pass an alternating current. The results are shown in Table 1. The heating efficiency was better than in Example 1, and the bubble diameter could be controlled.

(Embodiment 3) An embodiment in which the present invention is applied to a flow path is shown in FIG. In a tundish 12 having a width of 40 cm and a depth of 80 cm in continuous casting of steel, molten steel 2 of low carbon aluminum killed steel injected from a ladle 1 through a long nozzle 13 was cast from a dipping nozzle 14 into a mold 15.
A nozzle 3 made of a graphite refractory having an outer diameter of 1.0 cm and having an electrode 6 embedded in the bottom of the tundish 12 was installed, and a gas G was blown therein. Electrode 6'inserted in molten steel
An alternating current was passed through the nozzle 3 at the bottom of the tundish 12 to heat it by energization. The results are shown in Table 1, and it was observed that the diameter of the bubble 9 changed depending on the current value.

Comparative Example A comparative example is shown in FIG. 300k
Molten steel 2 of g was filled in a ladle 1, a refractory nozzle 3 having an outer diameter of 1.0 cm was installed at the bottom, and gas G was blown therein. The width of the side wall of the ladle is 1.5 times the diameter of the nozzle and the height is 10
A pair of permanent magnets 4 and 5 having a size of 1 cm are installed so that the N pole and the S pole face each other. An alternating current with a frequency of 30 to 60 Hz was applied to the molten steel by the electrodes 10 and 11 having the same width and height as the magnets, which were installed on the side wall surface of the ladle so that the current could flow perpendicularly to the magnetic field generated by this magnet. Shed The results are also shown in Table 1, and the air bubbles 9 are generated according to the frequency of the current.
Although it was observed that the diameter of the particles changed, the effect was not observed when the magnetic field was weak or when the current density was low.

[0011]

[Table 1]

[0012]

According to the present invention, fine bubbles can be blown into the molten metal, and the fine bubbles produced by the present invention cause gas components such as hydrogen and nitrogen in the molten metal, carbon, and non-metallic inclusions. It is possible to efficiently remove impurities such as.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention,

FIG. 2 is a diagram showing an embodiment in which the present invention is applied to a flow channel,

FIG. 3 is an explanatory diagram showing a comparative example.

[Explanation of symbols]

 1 Ladle 2 Molten Steel 3 Nozzle 4 Magnetic Field Generator 5 Magnetic Field Generator 6 Electrode 6'electrode 7 Heater 8 AC Power Supply 9 Bubble G Gas 10 Electrode 11 Electrode 12 Tundish 13 Long Nozzle 14 Immersion Nozzle 15 Mold

Claims (2)

[Claims] 1. A method of blowing gas into a molten metal to generate bubbles in the molten metal, wherein the diameter of the bubbles generated is controlled by heating a portion where the bubbles are generated. How to generate bubbles inside. 2. A nozzle for blowing gas or a porous body is constituted by a conductive resistor for heating the bubble generating portion,
The method for generating bubbles in a molten metal according to claim 1, characterized in that electricity is applied.