JPS6245464A - Method for removing inclusion in molten steel - Google Patents

Abstract

PURPOSE:To easily and surely remove inclusions in a molten steel by rotating a rotor, setting the peripheral speed at the top end of vanes at a specific peripheral speed and blowing an inert gas from blowing parts provided in the valleys of the vanes. CONSTITUTION:A rotor body 4 is attached to a rotating body 6 supported by a bearing 5. The rotor having >=3 sheets of the vanes is used and is rotated at >=1m/sec<=5m/sec peripheral speed at the top ends of the vanes. The inert gas is admitted through the inlet 8 and is blown through a central shaft 9 in the shaft part and the inert gas blowing parts 10 in the valley parts of the vanes into the molten steel 11. Cooling air is passed from an inlet 12 and flows through a middle pipe 13 to the inside 14 of the vane part and is released to the outside through an outside pipe 15. The inert gas is thereby fined and uniformly dispersed in the molten steel, by which the inclusions in the molten steel are surely removed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for removing inclusions in molten steel.

(Prior Art) Molten steel before casting contains many inclusions, and unless these inclusions are removed, the quality of the product will deteriorate. Therefore,
It is necessary to efficiently remove inclusions.

Conventionally, as shown in Japanese Patent Publication No. 54-41989, a method has been used in which inert gas is supplied into molten steel from a stationary wall through a porous brick or the like.

However, this method is not always effective due to reasons such as insufficient coalescence and coarsening of inclusions due to diffusion of molten steel, and difficulty in stably supplying fine bubbles into molten steel. It's not satisfying.

On the other hand, in the aluminum industry, a bubble dispersion device as shown in Japanese Patent Application Laid-Open No. 58-14935 is used. However, this method has the disadvantage that since gas is blown from the bottom of the rotor, bubbles coalesce and become coarse at the bottom of the rotor. Furthermore, when this method is applied to molten steel, it cannot be easily applied because the rotor is subject to significant melting damage due to conditions such as temperature and viscosity.

(Problems to be Solved by the Invention) The present invention is capable of stabilizing the supply of fine bubbles in molten steel, uniformly dispersing the bubbles, and preventing melting damage of the rotor as much as possible, which are the disadvantages of conventional rotors as described above. The object of the present invention is to provide a method for removing inclusions in steel that facilitates earthquake resistance of high-cleanliness steel.

(Means for solving the problem) The present invention rotates a submerged rotor having three or more blades at a circumferential speed of 1 m/sec to 5 m/sec at the tips of the blades, and This method of removing inclusions in molten steel is characterized in that the inert gas is pulverized and uniformly dispersed in the molten steel by blowing inert gas through a blowing section provided in the molten steel.

(Structure and operation of the invention) The rotor used in the present invention has three or more blades. FIG. 2 shows the relationship between the circumferential speed of the tip of the rotor blade, the bubble diameter, and the bubble dispersion angle when the number of rotor blades is changed. As can be seen from FIG. 2, the number of blades has a significant influence on the bubble diameter and bubble dispersibility; if the number is less than 3, the bubble diameter will be large and the bubble dispersibility will be poor. If there are three or more sheets, the bubble diameter will be small and the bubble dispersibility will be improved. Preferably, the number is 6 or more.

Next, the rotational speed of the rotor is set to a circumferential speed of the blade tip of 1 m/sec or more and 5 m/sec or less and 7 seconds or less. FIG. 3 shows the relationship between the circumferential speed of the rotor blade tip and the bubble diameter when the amount of inert gas blown is varied. As can be seen from FIG. 3, the bubble diameter becomes smaller when the circumferential speed of the blade tip is 1 m/sec or more, regardless of the gas flow rate. Moreover, if the speed exceeds 5 m/sec, the refractory material will be severely eroded and a large vortex will be generated on the surface of the hot water, which tends to reduce the high cleanliness effect.

Further, in the present invention, the inert gas blowing section is provided in the valleys of the blades of the single rotor. Figure 4 shows the relationship between the circumferential speed of the rotor blade tip and the bubble diameter when the position and method of the inert gas blowing part are changed. As can be seen from FIG. 4, by providing the blowing portion in the valley of the blade, significantly smaller air bubbles can be obtained than in the case where the blowing portion is provided at the bottom or the peak of the blade.

By injecting gas from the valleys of the blades rather than the bottom of the rotor or the ridges of the blades, the centrifugal force and flow of molten steel from the rotation of the rotor are used to form small bubbles and prevent them from coalescing and becoming coarse. Furthermore, the injected air bubbles move the rotor by 1m/
By rotating for more than a second, before they come out from the valleys of the blades, they are sheared by the blades and further become fine bubbles, which spread uniformly into the molten steel on the flow of molten steel caused by the rotation of the rotor. After colliding with the inclusions and reaching a stable state of energy, that is, a state in which the inclusions are trapped in bubbles, it floats to the surface of the molten metal.

In addition, as the molten steel is spread by the molten steel flow caused by the rotation of the rotor, inclusions may coalesce and become coarse due to collisions with each other.
It also becomes easier to levitate.

An example of an apparatus for carrying out the present invention will be explained with reference to FIG.

The drive unit W2 and the casing 3 are set on the fixed base 1 as shown in the figure.

Then, the rotor body 4 is attached to a rotating body 6 supported by a bearing 5, and a rotary joint 7 is set at the upper end of the rotor body 4. Inert gas flows through the inlet 8, passes through the central axis 9 of the shaft, and is blown into the molten steel 11 through the inert gas blowing part 1o in the blade valley. Cooling air flows from the inlet 12, passes through the middle pipe 13, and enters the inside of the blade section 14.
is discharged to the outside through the outer tube 15. The shaft portion 16 and the blade portion 17 of the rotor body 4 are made of a high alumina monolithic refractory, and the slag line portion 18 is made of magnesia graphite or a zirconia-containing refractory. Furthermore, calcareous flux 20 is sprinkled on the hot water surface 19 for the purpose of preventing air oxidation and adsorbing floating non-metallic inclusions.

(Example) The results of implementing the present invention are combined with the results of the prior art in the first example.
Shown in the table. Haruka 1 to 6 in Table 1 are conventional techniques, and Haruka 7 to 18 are
and 38 to 40 are comparative examples with the present invention, and 19 to 37 are examples in which the present invention was implemented. .

The molten steel composition used was almost the same under all conditions.

(Effects of the Invention) As shown in Table 1, by using the present invention, inclusions in molten steel can be easily and reliably removed. Further, even if a large amount of gas is blown into the melt, boiling does not occur on the surface of the hot water, re-rolling of floating inclusions and floating slag, and air oxidation of the molten steel can be prevented, making it possible to obtain highly clean molten steel.

[Brief explanation of drawings]

FIG. 1(a) is a partially enlarged sectional view of an embodiment of a device for carrying out the present invention, FIG. 1(b) is a plan view of a blade, and FIG.
, ) is a diagram showing the relationship between the rotor blade tip circumferential speed, bubble diameter, and bubble dispersion angle when the number of rotor blades is changed;
b) is an explanatory diagram of the bubble dispersion angle, FIG. 3 is a diagram showing the relationship between the circumferential speed of the rotor blade tip and the bubble diameter when the amount of inert gas blown is changed, and FIG. FIG. 6 is a diagram showing the relationship between the circumferential speed of the blade tip of the rotor and the bubble diameter when the position method of the inert gas blowing part is changed. 4... Rotor body 10... Inert gas blowing part 11... Molten steel 16... Rotor shaft part 17.
・Rotor blade part

Claims (1)

[Claims] While rotating a submerged rotor with three or more blades at a circumferential speed of 1 m/s to 5 m/s at the tip of the blades, inert gas is blown from a blowing part provided in the valley of the blades. A method for removing inclusions in molten steel, which is characterized by finely distributing inert gas in molten steel and uniformly dispersing it.