JPH01129924A - Method and apparatus for refining molten metal - Google Patents

Abstract

PURPOSE:To rapidly and stably execute flux refining without any fear of damage of refractory by adjusting positional relation of an axis of a refining vessel to an axis of a rotating magnetic field and subjecting a refining agent to contacting and mixing with molten metal and coagulating and separating contained impurities. CONSTITUTION:Circular flow is given to the molten metal 4 charged in the refining vessel 1 and by bringing the molten metal 4 into contact and mixing with the refining agent (refining flux) 5, the molten metal 4 is refined. In this case, at the time of promoting the contact and mixture with the molten metal 4 and the flux 5, the circular flow is given to the molten metal 4 under shifting condition of the axis of this vessel 1 from the axis of the rotating magnetic field center. On the other hand, at the time of coagulating and separating the flux 5 after containing impurities of P, S, O, etc., in the molten metal 4, the circular flow is given to the molten metal 4 under almost coinciding condition of the axis of this vessel 1 and the axis of the rotating magnetic field. By this method, the flux 5 containing the above impurities can be surely separated, and a high purity and high class steel can be industrially and stably produced at low cost.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention promotes contact and mixing of the smelting flux and the molten metal when refining the molten metal contained in a refining vessel by rotary stirring, thereby reducing the amount of the molten metal in the metal. The present invention relates to a refining method and apparatus that is effective for quickly reducing impurity elements to a high purity range and that significantly improves the life of refractory refining vessels.

<Conventional technology> Improvements in molten metal refining technology are strongly desired as the need for removing impurities from steel materials increases, and in particular, there is a strong demand for further improvements in technology for obtaining ultra-low P, ultra-low S, and ultra-low 0 steel. .

Conventionally, impurities such as P-3.0 have been removed by reaction with refining flux or adsorption to the flux, but in order to remove them to the utmost limit, it is necessary to contact and mix the flux and molten metal. A common method is to apply stirring force to promote this.

Since the object is a high-temperature melt, mechanical stirring, which is used in the chemical industry, is difficult, and bubble stirring is generally used. However, in the case of bubble stirring, there is a problem in that if an attempt is made to improve the stirring power, the splash when the bubbles separate from the molten metal increases, making operation difficult.

On the other hand, the method of stirring molten metal by applying electromagnetic force avoids the problem of splashing caused by air bubbles, allows the application of a large stirring force, and is used in various recent processes.

For example, Japanese Patent Application Laid-Open No. 53-1022 uses electromagnetic stirring force to contact and mix flux and molten metal.
Publication No. 12 describes a method in which a horizontal rotating flow is generated in molten metal by a rotating magnetic field, and refining flux is introduced into the depressions on the surface of the molten metal that are formed at that time, and furthermore, a method is described in which a baffle plate is installed to promote flux refining. What should be done is disclosed.

The inventors studied the above-mentioned technology in detail and found that with simple rotational stirring, the refining flux only remains at the bottom of the depression on the metal surface caused by the swirling flow of the molten metal, and does not exhibit a sufficient refining effect. In addition, stirring using a baffle plate that disturbs the direction of the horizontal rotational flow of molten metal can improve contact and mixing with the refining flux compared to simple rotary stirring, but this baffle plate usually Because it is made of refractory material, it can be damaged by contact with flux when not being stirred, and its life can be shortened due to severe thermal shock caused by rapid contact with molten metal when rotational stirring is started. The property damage is not only limited to the baffle plate, but due to the turbulence of the tg steel flow induced by the presence of the baffle plate, there is also significant damage to the refractory of the refining vessel near where the baffle plate is installed, and there is a problem with the life of the vessel. It was big.

Further, if the rotational stirring is continued, flux or nonmetallic inclusions are re-incorporated due to the action of the baffle plate, resulting in insufficient separation after refining.

<Problems to be Solved by the Invention> The present invention solves the conventional problems that occur when refining molten metal by rotary stirring, promotes contact mixing with the refining flux, and furthermore, the present invention solves the conventional problems that occur when refining molten metal by rotary stirring. The present invention has been made in order to provide a refining method and an apparatus therefor that are advantageous for rapid agglomeration and separation of flux and that significantly improve the lifespan of refractory refractories in refining vessels.

Means for Solving the Problems〉 As a result of intensive research into the refining of molten metal, the present inventors have succeeded in ensuring sufficient contact and mixing between the molten metal and the refining flux when necessary, and eliminating the need for such contact and mixing. In such cases, a molten metal container housed in a rotating magnetic field generator is used as a method to reduce the contact and mixing of molten metal and smelting flux, and also to avoid the problem of damage to refractories caused by the presence of baffles. We have discovered the superiority of a method in which a cart that can be moved to any position (back and forth, left and right) is installed on a pedestal, and based on this knowledge, we have developed the present invention.

The present invention provides: (1) Storing molten metal in a refining container, imparting a swirling flow to the molten metal in the container, and bringing the molten metal and a refining agent into contact and mixing to refine the molten metal. To promote contact and mixing with the refining agent, a swirling flow is applied to the molten metal with the center of the container being offset from the center of the rotating magnetic field, while the molten metal is refined after containing impurities. A molten metal refining method characterized by applying a swirling flow to the molten metal with the center of the container almost completely centered around the rotating magnetic field when coagulating and separating the refining agent; A rotating magnetic field generating coil for imparting a swirling flow to the molten metal is arranged around the outer periphery of the container, and the coil or/and
A molten metal refining apparatus is characterized in that it is provided with a horizontally movable pedestal on which the container is mounted.

Coagulating and separating the refining flux means that when the refining vessel is located at the center of the rotating magnetic field generator, the centripetal force generated by the horizontal rotational flow of molten metal causes the flux with low density to gather at the center of the metal bath surface. and the flux, and significantly improve the cleanliness of the molten metal.

<Function> In the present invention, as described above, when a cart capable of moving a mental container of molten metal within a rotating magnetic field generator is installed on a frame and the refining of molten metal is promoted, the refining container is rotated. Mixing and stirring are performed while being offset from the center of the magnetic field, and when the refining flux mixed and dispersed in the molten metal is quickly coagulated and separated, the refining vessel is positioned at the center of the rotating magnetic field while rotating and stirring is performed. This method and apparatus significantly reduce damage to the refractory of the refining vessel by appropriately changing the degree of deflection of the refining vessel.

The present invention was derived from studies regarding the behavior of refining flux on molten metal under swirling flow operation caused by a rotating magnetic field. In other words, in order to compensate for the insufficient contact and mixing of the refining flux and molten metal in the case of a symmetrical arrangement in which the refining vessel is placed in the center of the rotating magnetic field generating device and gives a swirling flow to the molten metal, the molten metal swirling flow is This was obtained from the results of the study as a method of applying an asymmetrical force.

Inside the rotating magnetic field generating coil 3 with an inner diameter of 2.0 m, a refractory material 2 is constructed on the inner surface of the iron skin made of non-magnetic steel, and the inner diameter is 1 m.
A refining container 1 with a height of 2.0 m was accommodated.

On the other hand, a pedestal 6 is installed below the rotating magnetic field generating coil, and a cart 8 with built-in rotatable wheels is mounted on the pedestal, and a refining container is mounted on it. By adjusting the stroke of each air cylinder 7, which can be operated freely, the refining container carrying cart can be moved to any position.

Prior to implementation, the following experiments were conducted to investigate the rotation of molten metal.

First, as shown in Figure 1, when the container is offset from the center of the rotating magnetic field coil and the same input power as before is applied, the rotational state of the molten metal is measured. The speed was 50 to 60 rpm on the far side, and 40 to 50 rpm on the far side, and the difference in height of the bath surface was 20 to 251.

When the refining agent was added under these conditions, the refining agent disappeared from the bath surface.

Second, as shown in Fig. 2, when the container is placed at the center of the rotating magnetic field coil and the same input power is applied as before, the rotation speed of the present invention and the conventional one is compared to 20 to 25 rpm and 25 rpm.
Although there was a slight decrease in rotational speed of ~30 rpm, it did not affect the coagulation and separation effect of impurities.

<Example> The molten metal has a component equivalent to API-X-70, and the inner diameter is 10
A smelting vessel having a diameter of 1,400 nm and a diameter of 1,400 nm contained a melt of 15.0 nm. This molten steel is given horizontal rotation by a rotating magnetic field generator (inner diameter 1700 mm, height 2300 m) and refining flux (70 to 80% Cab) is applied to the molten steel.
-20 to 30% CaFz) and 50 rpta
Rotating magnetic field stirring to generate a swirling flow was performed for 4 to 5 minutes to perform deoxidation and desulfurization reduction treatments.

The first step is to promote flux-metal contact and mixing.
As shown in FIG. 8
It was installed at a location where the strength of the magnetic field applied to the steel was asymmetrically introduced into the molten steel in the refining vessel. Next? g fil In order to coagulate and separate the flux after containing all the metal particles, the refining vessel was placed in the center of the rotating magnetic field generator as shown in Figs. 2 and 4, and CL + = 150 no.
) While applying a horizontal rotating flow of 20 rpm symmetrically to the molten steel, the flux containing impurities dispersed in i8 E was collected at the center of the metal bath surface by centripetal force, suppressing the reaction between the metal and the flux. As a result, the molten steel reaches S'
It was confirmed that impurity elements were reduced, with an a degree value of 3 ppm and an ofjA degree value of 5 ppm or less. Conventional simple rotary stirring (
Fig. 5 shows a comparison of the case where the rotational strength applied to the molten steel is applied symmetrically to the molten steel. In addition, in the case of the refining vessel and the coil gap L+-150 mm, the case of LI=200 mm was shown as Comparative Example 1 and Comparative Example 2, respectively, but in this example, the reaction rate capacity coefficient Ks of the desulfurization reaction was 0.4 to 0. .6
m1n"' is obtained and the Ks value of Comparative Example 1 is 0.08 to 0.1
A value about 5 times higher than that of 3m1n-' was obtained. This is because the strength of the magnetic field applied to the molten steel becomes non-uniform in the circumferential direction of the molten metal, resulting in the asymmetrical flow of the molten metal which causes the refining flux to roll into the bath.

By the way, if the swirling flow of molten metal is a steady and symmetrical flow, the problem of damage to the refractory due to the 111 collision of the molten metal flow to the refractory can be avoided, but if the swirling flow of molten metal is made asymmetrical, Local damage to the container refractories in areas where the flow velocity of the swirling molten metal flow is high or where the flow velocity changes rapidly is unavoidable.

However, as shown in Figure 4, which shows the positional relationship between the refining container and the rotating magnetic field generating device from the top, the installation position of the refining container can be adjusted 360 degrees in the circumferential direction using an air cylinder.
Damage to refractories can be reduced by sequentially changing the degree of
It is completely solved by averaging over its inner surface. Alternatively, by disposing a rotary plate on a pedestal and placing the refining vessel on it, the installation position of the vessel can be changed depending on the situation of damage to the refractory.

That is, for example, in order to reduce S from 0.003% to 0.0003%, the refining vessel is moved from the center of the rotating magnetic field generator and desulfurization treatment is performed for 4 to 5 minutes. It was about one injection at the University of Agriculture, and if the refractory was damaged when the swirling flow of molten steel was disturbed using a conventional baffle plate, the refractory had to be repaired every few tens of heats.

On the other hand, the true nature is that the refining container is inside the rotating magnetic field generator.
By changing the pitch to 45 degrees within a range of 60 degrees, it has become possible to substantially increase the life of the refractory by more than 10 times.

As shown in the above examples, the present invention provides a convenient means for achieving high purity refining with a significantly large reaction capacity coefficient while maintaining a stable refractory life.

<Effects of the Invention> By adopting the present invention, faster flux refining can be carried out than before without worrying about damage to refractories, and high-purity high-grade steel can be produced industrially at low cost and stably. Became.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram when refining flux by making the refining container eccentric from the rotating magnetic field generating coil, Figure 2 is an explanatory diagram when coagulating and separating flux, and 3rd Vl corresponds to Figure 1. FIG. 4 is an equipment layout diagram corresponding to FIG. 2, and FIG. 5 is a graph of desulfurization reaction rate capacity coefficients for Examples and Comparative Examples. DESCRIPTION OF SYMBOLS 1... Refining container, 2... Refractory, 3... Rotating magnetic field generating coil, 4... Molten metal, 5... Refining flux, 6
... Frame, 7... Air cylinder, 8
... Cart, A-A... Center line of smelting container, B-B... Center line of magnetic field generating coil, L+, Lx...
- Distance between the rotating magnetic field generating coil and the refining vessel. Patent applicant Kawa*! ! Tetsu Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In refining the molten metal by storing the molten metal in a refining container, applying a swirling flow to the molten metal in the container, and bringing the molten metal and a refining agent into contact and mixing, When promoting contact and mixing between the molten metal and the refining agent, a swirling flow is applied to the molten metal with the center of the container being offset from the center of the rotating magnetic field, while impurities in the molten metal are removed. A method for refining molten metal, characterized in that when agglomerating and separating the refining agent, a swirling flow is applied to the molten metal with the center of the container substantially aligned with the center of a rotating magnetic field. 2. A rotating magnetic field generating coil for imparting a swirling flow to the molten metal in the refining container is arranged around the outer periphery of the container, and a horizontally movable pedestal is provided on which the coil and/or the container is mounted. Characteristic molten metal refining equipment.