JPH04314813A - Apparatus for removing non-metallic inclusion in molten metal - Google Patents

Abstract

PURPOSE:To easily separate and remove non-metallic inclusions in molten steel from the molten steel by charging the molten steel into a refractory vessel, giving horizontal rotating flow to this and aggregating, floating up and separating included impurities with centrifugal force. CONSTITUTION:Into a tundish composed of a rotrating vessel 1 and a float-up vessel divided with a partition wall 5, the molten steel 7 is poured from an inlet 3 and the horizontal rotating flow is given by rotating or shifting magnetic field device 2. The non-metallic inclusions in the molten sheet 7 are aggregated, separated and floated up on parabollic eddy flow with this rotating flow. In this case, the rotating vessel horizontally rotating the molten steel and the float-up vessel connected with this and providign flow-out hole and floating up the non-metallic inclusion in the molten steel, are partitioned with a refractory-made wall 5, and by arragning a communicating hole at position, where projected spectrum from molten steel flow-in point in the rotating flow spectrum to direction directed to flow-out point does not have direction to the flow-out point with the wall face, between the rotating vessel and the float-up vessel, a large part of the non-metallic inclusions in the molten steel are removed and cleaned.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for separating and removing nonmetallic inclusions from molten metal.

0002

BACKGROUND OF THE INVENTION Among the manufacturing techniques for high-grade thin steel sheets, the removal of non-metallic inclusions during the molten steel stage is a technique that greatly affects the defective rate of products. Recent trends in molten steel cleaning technology include (
1) Larger intermediate container (hereinafter referred to as tundish) between the ladle and mold in continuous casting.By extending the residence time of molten steel in the tundish, inclusions are expected to be separated by floating. (2) A multi-stage weir is installed in the tundish to control the path of molten steel and also to extend the residence time of the molten steel in the tundish. (3) Flow control of molten steel flow in the mold by changing the shape of the immersion nozzle discharge hole Prevents mold powder from being entrained in the mold due to the flow of molten steel from the nozzle discharge hole. etc.

[0003] However, these methods do not provide sufficient quality improvement effects, and the quality is particularly problematic during unsteady pouring, which is called pot change. Therefore,
As a countermeasure, Japanese Patent Application Publication No. 58-22317, Japanese Patent Application Publication No. 5
As disclosed in Japanese Patent No. 5-107743, there is a method in which molten steel is turned into a horizontally rotating flow to float inclusions. These methods apply centrifugal force to molten metal and nonmetallic inclusions through horizontal rotation, and the difference in specific gravity collects the nonmetallic inclusions at the center of rotation, promoting collision, adsorption, and agglomeration, thereby separating them. It is. This technology can improve the separation effect of inclusions compared to the methods of simply extending the residence time or controlling the passage of molten steel in the tundish. This is considered to be effective in that the dish can be significantly downsized.

However, this method also has the following problems.

(1) When molten steel is rotated horizontally, the outer periphery of the molten steel swells in a parabolic shape due to centrifugal force, and the height of the swell is proportional to the radius and the square of the rotation speed, so an increase in the radius will increase the equipment height. In addition, a large electromagnetic coil is required to horizontally rotate all of the molten steel, which increases equipment costs, which is not practical.

(2) Although reducing the radius of rotation is preferable in terms of equipment, if the tundish capacity is reduced, the molten steel buffer function for realizing ladle exchange will no longer be fulfilled.

(3) At the same time, air oxidation of the upper surface of the molten metal due to air entrainment caused by the rotational flow and erosion of the refractory proceed, and the number of nonmetallic inclusions generated in the container increases rapidly, resulting in large-sized Non-metallic inclusions flow out. As a countermeasure for this, it is necessary to use an expensive refractory material with excellent abrasion resistance over the entire container, and to seal the entire container with gas or the like, which increases costs.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and aims to provide a method for separating and removing non-metallic inclusions in molten metal in an effective and economical manner. The present invention aims to provide a device for removing non-metallic inclusions.

[0009]

[Means for solving the problem] When molten metal is horizontally rotated at high rotational speed, large stirring energy causes not only the centrifugal effect of nonmetallic inclusions but also the coalescence of nonmetallic inclusions.
Coagulation occurs and nonmetallic inclusions become coarse. This effect makes it possible to enlarge small nonmetallic inclusions that normally could not be separated by flotation.

However, when considering the high rotational speed and the buffer function when exchanging the ladle, the equipment becomes oversized due to changes in the surface shape of the molten steel due to rotation, and it is said that it is difficult to apply it to equipment on a commercial production scale. It turned out that there was a problem. Furthermore, air oxidation of the upper surface of the molten metal due to air entrainment caused by the rotational flow, melting loss of the refractory, etc. proceeded at the same time, resulting in problems that impeded cleaning of the molten metal.

Therefore, in the present invention, an apparatus for separating and removing nonmetallic inclusions in molten metal by applying a horizontal rotational flow to the molten metal includes a rotating tank for receiving molten metal and horizontally rotating it; The flotation tank, which has an outlet connected to the rotating tank and levitates non-metallic inclusions in the molten metal, is partitioned with a wall made of refractory, and the wall surface allows the rotational flow vector to flow in the direction from the molten steel inflow point to the outflow point. It has been found that it is useful to provide a communication port between the rotating tank and the flotation tank at a position where the projection vector does not have a direction toward the outflow point.

That is, by separating the rotating tank and flotation tank, it is possible to provide a buffer function for the molten metal even in unsteady situations such as when changing the ladle, without increasing the size of the rotating part, which requires high equipment cost. The separation effect of inclusions is increased by ensuring floating time, and by specifying the position of the communication port from the rotating tank to the flotation tank, the inclusions can be removed from the flow of molten metal due to rotational flow and centrifugal force. It was possible to prevent objects from flowing into the flotation tank due to a short circuit, and the effect of separating inclusions was further ensured.

That is, the present invention is an apparatus for separating and removing nonmetallic inclusions in molten metal by applying a horizontal rotational flow to the molten metal, which receives molten metal from an inlet and horizontally rotates it. a flotation tank that communicates with the rotary tank through a communication port to levitate non-metallic inclusions in the molten metal and flow out the cleaned molten metal through an outlet; On the line connecting the molten metal inlet and the molten metal outlet of the flotation tank, when the side facing the outlet is positive and the side facing the inlet is negative, the vector of the molten metal in the rotating tank in the tangential direction of the rotating tank is A device for removing non-metallic inclusions in molten metal, characterized in that a communication port between the rotating tank and the flotation tank is formed at a position where a projected vector on the line becomes 0 or negative when projected onto the line. It provides:

[0014]

[Operation] The present invention will be explained in more detail below.

An apparatus (tundish) 10 for removing nonmetallic inclusions in molten metal according to the present invention includes a rotating tank 1 and a flotation tank 2. Molten steel is injected into the rotating tank 1 from a ladle (not shown) through the inlet 3 as shown by the arrow in FIG.
The injected molten steel is preferably placed in a rotating or moving magnetic field device 4
gives horizontal rotational flow. As a result, nonmetallic inclusions in the molten steel or nonmetallic inclusions caused by melting of the refractory of the tundish 10 are separated and floated onto the parabolic vortex of the rotating tank.

The molten steel thus cleaned enters the flotation tank 2 through the communication port 6 at the bottom of the partition wall 5 between the rotating tank 1 and the flotation tank 2, and removes any remaining non-metallic particles in the molten steel left still. The objects float on the flotation tank 2 and are separated. The molten steel further purified in this way passes through the outlet 7 and enters the mold (not shown).
It is injected into a cast product.

By the way, in such a nonmetallic inclusion removal device having a rotating tank and a flotation tank, most of the nonmetallic inclusions in the molten metal that enters the rotating tank from the ladle through the inlet are removed in the rotating tank. Although the non-metallic inclusions are floated and separated from the rotating tank and then transferred to the flotation tank where they are also floated and separated, there is a need for a means to more efficiently remove non-metallic inclusions in both tanks.

The present inventors have found that in a non-metallic inclusion removal apparatus having a rotating tank and a flotation tank, where should the communication port formed in the partition between the rotating tank and the flotation tank be located to meet the above requirements? We considered whether it would be possible to satisfy the following. Figure 2 shows the progress.
-4 will be explained.

In the example shown in FIG. 2, when the molten metal is rotating in the direction of arrow a, the angle is 45° from the line L connecting the inflow point of the molten metal in the rotating tank and the outflow point of the molten metal in the flotation tank. The rotational flow vector at position A is X, and the projection vector of vector X onto the line L is X0. That is, the projection vector X0
has a direction toward the outflow point, and if this direction is positive, it means that the projection vector X0 has a positive direction.

In the example shown in FIG. 3, when the molten metal is rotating in the direction of arrow a, the position on the line L connecting the inflow point of the molten metal in the rotating tank and the outflow point of the molten metal in the flotation tank is shown. This shows that the rotational flow vector at B is Y, and the projection vector of the vector Y onto the line L is Y0. That is, it shows that the projection vector Y0 is 0.

In the example shown in FIG. 4, when the molten metal is rotating in the direction of arrow a, the angle is 45° from the line L connecting the inflow point of the molten metal in the rotating tank and the outflow point of the molten metal in the flotation tank. The rotational flow vector at position C is Z, and the projection vector of vector Z onto the line L is Z0. That is, the projection vector Z0
has a direction toward the inflow point, and if this direction is negative, it means that the projection vector Z0 has a negative direction.

As described above, the projection vector of the molten metal onto the line L connecting the inflow point and the outflow point is positive (example in FIG. 2), 0 (example in FIG. 3), and negative (example in FIG. 4). When we investigated the amount of nonmetallic inclusions flowing out from the outflow port when a communication port was provided at the location, we found that the communication port was located at the location in the example of FIGS. 3 and 4 where the projection vector to line L is 0 or negative. It was found that the amount of nonmetallic inclusions flowing out from the outlet can be reduced by providing the outlet.

The reason for this is that at the position where the projection vector onto the line L is positive, there is a molten metal flow from the rotating tank to the flotation tank in the rotating tank, so that more non-metallic inclusions are present in the rotating tank. It is thought that the amount of non-metallic inclusions that flow into the flotation tank from the rotating tank and flow directly toward the outlet without being sufficiently floated is large. On the other hand, at positions where the projected vector onto line L is 0 or negative, the molten metal flow in the rotating tank has a vector in the opposite direction to the molten metal flow from the rotating tank to the flotation tank. From a perspective, the molten metal flow from the rotating tank to the flotation tank becomes a quiet flow that promotes the floating of non-metallic inclusions in the rotating tank, and also promotes the floating of non-metallic inclusions in the flotation tank.
As a result, it is thought that the amount of nonmetallic inclusions flowing out from the outlet becomes extremely small.

Therefore, in the nonmetallic inclusion removing apparatus of the present invention, a communication port between the rotating tank and the flotation tank is formed in the partition wall at a position where the projection vector onto the line L becomes 0 or negative. It goes without saying that the communication port is provided at a position closer to the bottom of the partition wall.

[0025]

EXAMPLES Next, the present invention will be specifically explained based on examples.

(Example 1) When molten steel was passed through the configuration examples shown in FIGS. 2, 3, and 4, the amount of nonmetallic inclusions discharged from the outlet was as follows.
It was confirmed that the apparatus of the present invention shown in FIGS. 3 and 4 had a small amount of nonmetallic inclusions flowing out.

[0027]

[Effects of the Invention] According to the present invention, an apparatus for effectively removing non-metallic inclusions that cause product defects such as steel plates can be manufactured without excessively increasing equipment, and furthermore, By using this device, it is possible to obtain a stable effect of nonmetallic inclusions even during unsteady situations such as when changing the ladle, thereby reducing the product defect rate and making it possible to significantly improve yield. Moreover, as a result, it has become possible to produce highly clean steel at low cost without major capital investment.

[Brief explanation of drawings]

FIG. 1 is a nonmetallic inclusion removing apparatus of the present invention having a rotating tank and a flotation tank, (a) is a plan view thereof, and (b) is a side sectional view thereof.

FIG. 2 is a schematic diagram showing the direction of force acting on molten metal in the apparatus of FIG. 1;

3 is a schematic diagram showing the direction of force acting on molten metal in the apparatus of FIG. 1. FIG.

4 is a schematic diagram showing the direction of force acting on molten metal in the apparatus of FIG. 1. FIG.

[Explanation of symbols]

1 Rotating tank 2 Flotation tank 3 Inlet 4 Rotating (moving) magnetic field generator 5 Partition wall 6 Communication port 7 Outlet

Claims (1)

[Claims] 1. An apparatus for separating and removing nonmetallic inclusions in molten metal by applying a horizontal rotational flow to molten metal, comprising: a rotating tank that receives molten metal from an inlet and horizontally rotates it; a molten metal inlet of the rotating tank, comprising a flotation tank that communicates with the rotating tank through a communication port to float non-metallic inclusions in the molten metal and flow out the cleaned molten metal through an outlet; and the molten metal outlet of the flotation tank, when the side facing the outlet is positive and the side facing the inlet is negative, the velocity vector of the molten metal in the rotating tank in the tangential direction of the rotating tank is projected onto the line. A device for removing non-metallic inclusions in molten metal, characterized in that a communication port between the rotating tank and the flotation tank is formed at a position on the line where a projection vector becomes 0 or negative when the projection vector becomes 0 or negative.