JPH04365809A - Device for removing non-metallic inclusion in molten metal - Google Patents

Abstract

PURPOSE:To stably and surely float up and remove non-metallic inclusion in a molten metal by horizontally rotating the molten metal and guiding the metal to a float-up vessel after blowing gas through a gas permeable refractory provided on a suitable position therein. CONSTITUTION:To the molten metal charged in a rotary vessel 1 from a pouring hole 3, the horizontal rotating stream is given with a horizontal rotating magnetic field from a magnetic generator 4. Further, gaseous argon is blown therein. This gas blowing is executed through the gas permeable refractory blocks 5 embedded in the bottom face until 1/4 of a radius toward a center from the inside face of side wall in the rotary vessel 1 and/or in the flank until the range of 1/4 of the molten metal surface height from the bottom part of the flank. By this method, the gaseous argon is refined with strong shearing force at the max. velocity position in the vicinity of the flank in the vessel and floated up in the molten metal for long time, and colliding efficiency with the non-metallic inclusion in the molten metal is increased. Thereafter, the molten metal is guided into the float-up vessel 2 from a flowing hole 8. Thus, the fine gas bubbles catch the non-metallic inclusions and are floated up, and the inclusions are efficiently removed and the molten metal is 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

[Prior Art] In the tundish of the continuous casting method, which is generally widely used in the production of steel, further thorough flotation separation of inclusions in the molten metal is an important technical issue that determines the quality level of the product. It is. As a conventional technique for separating non-metallic inclusions in molten metal, for example, Japanese Patent Application Laid-Open No. 58-22317 discloses a method in which molten steel in a container is horizontally rotated by a magnetic field and centrifugal force is applied to the molten steel to remove non-metallic inclusions. A method has been proposed in which the molten steel is concentrated at the center of rotation and flows out from the bottom of the container far from the center of rotation while floating the molten steel. According to this technique, nonmetallic inclusions can be easily concentrated at the center of rotation, but separation by floating them is not sufficient.

On the other hand, as a technique for promoting the floating of nonmetallic inclusions in molten metal, for example, in continuous casting of steel, weirs of various shapes are installed in the tundish to change the flow pattern of molten steel. Many methods have been proposed to promote flotation and separation of inclusions. Furthermore, a porous refractory block for forming fine air bubbles is installed on a part of the bottom of the tundish as disclosed in JP-A-57-154357, and an inert gas is blown into the tundish.
A method has been proposed that aims to further clean steel by trapping and promoting the floating of inclusions using a large number of fine bubbles. However, regarding the method of forming microbubbles through a porous refractory set on the bottom of the tundish, the key to improving the cleaning effect is to improve the contact efficiency between the microbubbles and molten steel. The technique disclosed in the publication is insufficient in this respect, and lacks the effect of cleaning molten steel.

[0004] Japanese Patent Laid-Open No. 2-55649 discloses that in order to improve the contact efficiency, a permeable refractory block is buried in the entire width of the bottom of the tundish, an overflow weir is provided on the upstream side of the block, and a tunnel weir is provided on the downstream side. A method has been proposed in which the ratio of the length of the permeable refractory block to the average molten steel flow rate is 1.0 minutes or more to ensure sufficient contact time between microbubbles and molten steel. However, with this method, as the casting speed increases, the length of the air-permeable refractory block naturally needs to be increased, resulting in a correspondingly larger tundish, which contributes to an increase in equipment and refractory costs, making it unrealistic. .

Furthermore, if the length of the air-permeable refractory block is increased, the range in which the surface of the molten steel is disturbed by floating air bubbles increases, and the surface of the molten steel is coated with the aim of trapping air entrainment and floating inclusions. This caused a problem in that the product quality deteriorated significantly due to the increase in foreign inclusions due to the inclusion of flux, etc.

[0006]

[Problems to be Solved by the Invention] The present invention improves a technique for removing nonmetallic inclusions by receiving molten metal and horizontally rotating it in a rotating tank, and by using microbubbles to float the nonmetallic inclusions. It is an object of the present invention to provide an apparatus for removing non-metallic inclusions from molten metal.

[0007]

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

However, when considering the high rotational speed and the buffer function when replacing the ladle, the height of the equipment increases due to changes in the surface shape of the molten steel due to rotation, making it difficult to apply to existing equipment due to equipment constraints. , it was found that there was a problem of high construction costs. Therefore, in the present invention, we investigated a method that does not require high rotational speeds and still achieves the same effect as when high rotational speeds are used.We found that by using inert gas injection in combination, even at low rotational speeds, high rotational speeds can be achieved. We found that it has the same inclusion removal effect as
The present invention has been completed.

[0009] The object of the present invention has been achieved by applying a horizontal rotational flow to the molten metal in the region where the micro-bubbles are generated, in order to promote contact between the micro-bubbles and the molten metal and to exhibit a sufficient flotation separation effect. be. That is, the present invention provides an apparatus for removing non-metallic inclusions in molten metal, which includes a rotating tank that receives molten metal and horizontally rotates it, in which non-metallic inclusions are removed from the inner surface of the side wall of the rotating tank up to 1/4 of the radius from the inner surface of the side wall toward the center. Ventilation for blowing gas to promote the floating of non-metallic inclusions in the molten metal rotating horizontally in the rotating tank, on the bottom and/or side walls from the bottom to 1/4 of the melt level height. A floating tank for floating non-metallic inclusions in the molten metal through a partition wall provided with a flow port is connected to the rotating tank. This is a non-metallic inclusion removal device.

0010

[Effect] When an inert gas is blown into horizontally rotating molten metal, the gas bubbles at the position near the container wall where the velocity is greatest are subjected to intense shearing force by the horizontally rotating flow and become fine. It was revealed. Moreover, it was found that the fine gas bubbles move in a spiral pattern in the molten metal due to the balance between buoyancy and centripetal force based on the rotational flow, increasing the time they stay in the molten metal. Naturally, the contact efficiency between the microbubbles and the molten metal increases significantly, and the probability of collision between the microbubbles and nonmetallic inclusions in the molten metal also increases. In addition, the air-permeable refractory block should be placed at a radius of 1/4 from the inner surface of the side wall of the rotating tank.
The reason for limiting the range to 1/4 of the height of the molten metal surface from the bottom of the side wall is because, as mentioned above, the speed of the horizontally rotating molten metal is the highest, and the injected gas bubbles are finely divided by the shear force. This is to make it more effective. This is because the finer the gas bubbles, the smaller their buoyancy, the longer the contact time with the molten metal, the higher the efficiency of collision with inclusions, and the more effective the removal of inclusions.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings. As shown in FIG. 1, in the apparatus of the present invention, a rotating tank 1 that receives molten metal from an inlet 3 and a flotation tank 2 that discharges molten metal from an outlet 7 are connected via a partition wall 9 having a flow port 8. A magnetism generating device 4 for generating a horizontally rotating magnetic field is attached to the outside of the rotating tank 1. Also, rotating tank 1
A ventilated refractory block 5 was embedded in the bottom surface from the inner surface of the side wall to 1/4 of the radius toward the center and on the side surface from the bottom of the side wall to 1/4 of the height of the static hot water level. In the following experiment, argon gas was not blown simultaneously from the breathable refractory blocks 5 embedded in the bottom and side surfaces, but instead was blown in individually.

Here, mechanical structural steel material S2 is used as the molten metal.
0C (C/0.20, Si/0.20, Mn/0.60
, Al/0.020, P/0.010, S/0.0
10) 100 tons of molten steel is received from a ladle (not shown) into the rotating tank 1 via the inlet 3. The molten steel in the rotating tank 1 is horizontally rotated by the magnetism generated by the magnetic field generator 4, and argon gas is blown into it from the breathable refractory block 5.

Since the molten steel is blown into the wall of the rotating tank 1 at a position where the rotational speed is highest, the argon gas bubbles are made fine by the intense shearing force caused by the horizontal rotational flow of the molten steel. The bubbles thus miniaturized rise to the surface while moving spirally in the molten steel due to the balance between their buoyancy and the centripetal force caused by the horizontal rotational flow of the molten steel, resulting in a longer residence time in the molten steel. Therefore, the contact efficiency between the microbubbles and the molten steel increases, and the probability of collision with nonmetallic inclusions also increases, resulting in an improvement in the removal rate of nonmetallic inclusions.

The molten steel from which non-metallic inclusions have been removed in the rotating tank 1 is led to the flotation tank 2 through the flow port 8 provided in the partition wall 9, where the non-metallic inclusions still remaining in the molten steel are removed. After being further cleaned by floating the molten steel, the molten steel is poured into a mold (not shown) through the outlet 7. Samples of molten steel to be poured into a mold (not shown) were collected from the sample collection hole 6 and outlet 7 provided in the lid 10 of the flotation tank 2, and the total oxygen of the molten steel was analyzed and nonmetallic inclusions were extracted. Ta.

Table 1 shows the results of total oxygen analysis and extraction of nonmetallic inclusions under different experimental conditions.

[0016]

[Table 1]

As shown in Table 1, according to the example of the present invention, the achieved oxygen value was reduced by about 55 to 75% compared to the comparative example (without rotation and with Ar), and the nonmetallic inclusion index was 2/10 to 4/10. It was confirmed that the floating separation rate of nonmetallic inclusions was significantly improved under the conditions of the present invention. It was confirmed that the present invention is very effective in producing such clean steel. In the present invention, the same operation and effect can be obtained even if a rotary blade is used instead of the rotating magnetic field generator as in the above embodiment, and the blade is immersed in molten steel in a rotating tank and rotated horizontally. Furthermore, although the explanation has been made regarding the case where argon gas is blown into the ventilation block from either the bottom surface or the side wall, it is of course possible to blow argon gas into both at the same time.

[0018]

[Effects of the Invention] As described above, the present invention has an air-permeable refractory block installed at the bottom or side wall of a rotating tank that provides horizontal rotation. By extending the contact time, the collision efficiency with non-metallic inclusions is greatly increased, the non-metallic inclusions in the molten metal are removed stably and reliably, and continuous casting of high-clean steel is reliably achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an apparatus according to an embodiment of the invention.

[Explanation of symbols]

1 Rotating tank 2 Flotation tank 3 Inlet 4 Magnetic field generator 5. Breathable refractory block 6 Sample collection hole 7 Outlet 8 Distribution port 9 Partition wall 10 Lid

Claims (1)

[Claims] 1. An apparatus for removing nonmetallic inclusions in molten metal, which comprises a rotating tank that receives molten metal and horizontally rotates the same, in which non-metallic inclusions are removed from the inner surface of the side wall of the rotating tank up to 1/4 of the radius toward the center. Ventilation for blowing gas to promote the floating of non-metallic inclusions in the molten metal rotating horizontally in the rotating tank, on the bottom and/or side walls from the bottom to 1/4 of the melt level height. A floating tank for floating non-metallic inclusions in the molten metal through a partition wall provided with a flow port is connected to the rotating tank. Non-metallic inclusion removal equipment.