JPH0941029A - Vacuum degassing equipment composed of vacuum degassing apparatus and ladle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a degassing equipment having the optimum shape so as to prolong the service life of an immersion tube refractory and sufficiently display the performance as the degassing apparatus by holding a positional relationship between an immersion tube and a ladle to the optimum. SOLUTION: In the vacuum degassing equipment composed of a vacuum degassing apparatus and the ladle, the center of the immersion tube is eccentrically set to a porous plug position and the center of the ladle, and the plural ladles having the same eccentric ratio of a porous plug position to the immersion tube center are combined with the vacuum degassing apparatus so as to be changable in the relative position between the immersion tube and the ladle by each treating process. Further, the immersion tube is rotated so as to be changable in the relative position between the immersion tube and the ladle by each treating process. The eccentric immersion tube center is made to the eccentricity having 0.05-0.02 times of the diameter of the immersion tube to the ladle center. The diameter at the height part which the molten steel head does not reach is smaller than e.g. 0.60-0.90 time the diameter of the immersion part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum degassing equipment, and more particularly to a vacuum degassing equipment including a vacuum degassing device having a straight barrel type immersion pipe and a ladle.

[0002]

2. Description of the Related Art A technique for refining molten steel using a degassing apparatus having a straight barrel type dipping tube for injecting a large amount of reflux gas from a porous plug at the bottom of a ladle is disclosed in JP-A-7-41832 and JP-A-3-146540. It is disclosed in the publication. FIG. 3 is a conceptual diagram of a vacuum degassing equipment in which a vacuum degassing apparatus having a straight-body type immersion pipe and a ladle are combined. In FIG. 3, the vacuum degassing apparatus 1 is provided on the molten steel 3 of the ladle 2. It has a straight barrel type dipping tube 4 to be dipped. The porous plug 5 at the bottom of the ladle 2 is located eccentrically with respect to the center of the dip tube 4, and argon gas is blown from the porous plug 5 to one side of the dip tube 4 to form a plume 6 of a gas-liquid mixed phase. Molten steel 3
Circulates in the ladle 2 and the dipping tube 4 by becoming an ascending flow and rising on one side in the dipping tube 4 together with the gas and descending from the other side.

With this vacuum degassing equipment, (1) the blowing depth is deep and the molten steel recirculation speed is high, so that the uniform mixing time in the steel bath is shortened. (2) Expanded volume (plume) of gas is increased, bubble active area under the vacuum surface can be sufficiently secured, decarburization time in extremely low carbon region is shortened, and decarburization limit is improved. There is.

Further, in the above-mentioned publication, the cross-sectional area (diameter) shape of the immersion pipe and the position where the bottom blowing gas is blown in, especially the relative position with respect to the immersion pipe, are explained, but the relative position between the immersion pipe and the ladle, etc. No clear optimum point is shown, and the positions of the center of the ladle and the center of the dipping pipe are usually the same.

[0005]

However, when assuming a refractory structure on an actual machine scale for the immersion pipe, a large diameter immersion pipe is required, and its durability becomes a problem.
In particular, in order to improve the decarburization efficiency, a large amount of gas is blown into the dipping pipe from the porous plug at the bottom of the pot to increase the circulation amount of molten steel in the pot and dipping pipe to shorten the uniform mixing time. Since the reflux gas is blown from the porous plug located at a position eccentric to the center of the dip tube, the part of the tip and inner circumference of the dip tube where the plume formed by the bottom blowing gas collides is the plume. The direct attack of the steel causes local melting damage. For this reason, the refractory cost is increased instead of improving the metallurgical effect, and because it requires a great deal of time for replacement of the immersion pipe, refractory repair, etc.,
There are problems such as poor productivity.

Further, although the disclosed method improves the degassing characteristics in the immersion pipe, sufficient knowledge has not been obtained regarding the uniform mixing of molten steel in the immersion pipe and in the ladle, and the degassing apparatus Is not fully exerting his ability as.

Further, regarding the shape of the immersion pipe, the whole of the immersion pipe is mainly of a straight body type, and the refractory unit consumption is lowered.
No knowledge about the optimum shape taking into consideration the suppression of metal adhesion is disclosed. Therefore, when the immersion part has a large diameter in order to secure a bubble active surface under the vacuum surface, the whole immersion pipe has a large diameter when the immersion pipe is a perfect straight body, and therefore the refractory material is also on the upper side. As the basic unit increases, the amount of heat radiation increases, which promotes the amount of bare metal deposited, which is not preferable.

Therefore, the present invention maintains the relative positional relationship between the dipping pipe and the ladle at an optimum value to prolong the life of the dipping pipe refractory, and at the same time, the dipping is performed in an optimum shape so that the capability as a degassing device is fully exhibited. A vacuum degassing facility having a tube is provided.

[0009]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention has a fixed position where a rising flow of molten steel generated by a plume generated by bottom blowing gas collides with the tip end portion and the inner circumference of the immersion pipe. It is intended to disperse the melting loss of the refractory and make it uniform so as not to be biased.

The gas blown from the porous plug at the bottom of the pot normally has a divergence angle of 12 ° on one side, that is, 24 ° as a whole, forms a plume and rises with molten steel flow. The portion of the immersion pipe that is melted and damaged is the region where this upward flow directly collides, so the position of the blowing gas is changed for each ladle so that the collision position does not coincide with the same position of the immersion pipe.

For that purpose, it is effective to change the gas injection position for each processing charge, but normally, the relative positional relationship between the dipping tube and the ladle is based on the optimization of the mixing in the ladle described above. The optimum position should be set the same for each processing charge, and the porous plug position should be eccentric with respect to the immersion tube, but this eccentricity ratio should also be set to the optimum ratio.

Therefore, in order to change the position at which the plume formed by the rise of the bottom blowing gas collides, it is preferable to use a pot having a porous plug at each position with the same eccentricity ratio with respect to the immersion pipe. .

Therefore, the present invention provides a molten steel vacuum degassing equipment comprising a vacuum degassing device having a dip tube and a ladle, wherein the center of the dip tube is eccentric with respect to the position of the porous plug at the bottom of the ladle and the center of the ladle. In order to change the relative position of the dip tube and the ladle for each processing unit, a vacuum degassing device having a plurality of ladle and dip tube in which the bolus plug position has the same eccentricity ratio with respect to the center of the dip tube is provided. Combined to form a vacuum degassing facility.

Usually, since a plurality of pots of about 10 units are used alternately, the positions of the porous plugs are set at about 4 positions, and the pots with one porous plug installed at each position are alternately replaced at regular intervals. By changing the position of the porous plug for each treatment charge used, the position of the plume that collides with the dip tube is changed, and the melting loss of the refractory is made uniform. In addition, with respect to one ladle, a porous plug may be installed at each plug position and gas may be blown alternately.

Further, in order to change the position of the plume that collides with the dip tube, the dip tube may be rotatable in order to change the relative position of the dip tube and the ladle and the porous position in processing units. By rotating the dip tube body, the collision position of the upward flow can be changed even for the porous plugs at the same position on the bottom of the pan. Regarding the rotation of the immersion pipe, the rotation stop position is set to about 4 positions, and the melt damage position of the immersion pipe can be dispersed by rotating the immersion pipe for each processing charge.

Next, in order to promote the mixing in the dip tube and in the ladle to improve the degassing ability and to shorten the uniform mixing time in the ladle, the relative positional relationship between the dip tube and the ladle is examined with a water model or the like. However, it was found that the relative positional relationship between the ladle and the dip tube had a great influence on the mixing in the ladle, and a detailed investigation was conducted. As a result, the optimum relative positional relationship between the ladle and the dip tube was obtained by decentering the center of the dip tube with respect to the center of the ladle by 0.05 to 0.20 times the diameter of the dip tube.
Further, the eccentric direction is most suitable on the porous plug installation direction side.

Further, by making the dip tube eccentric, it is possible to secure a space between the ladle edge and the outer circumference of the dip tube, which has the advantage of facilitating temperature measurement sampling work in the pan.

Further, as a result of studying the shape of the main body of the dip tube, in the case of the straight body type dip tube, it is desirable that the diameter of the vacuum chamber is large in order to secure the bubble activated surface by the bottom blowing gas in the dip tube as much as possible. . However, in the case where the diameter is the same up to the upper portion of the pipe, such as a normal dip pipe, a large diameter is not required in the upper portion where the molten steel head does not reach, and it is sufficient to have the minimum diameter necessary for decompression. Therefore, as a result of studying this optimum diameter, the diameter in the region where the stationary molten metal surface does not reach under reduced pressure is smaller than the immersion portion of the immersion pipe, and the optimum value is 0.6 to 0.9 times the diameter of the immersion portion. It turned out to be. By narrowing down to 0.9 times or less, the required volume of decompression is reduced and at the same time the amount of refractory construction is reduced, and the reduction of the brick surface area reduces the amount of bare metal adhesion due to heat dissipation, reducing refractory costs by about 20%. . However, when it is narrowed down to less than 0.6, metal adhesion occurs on the inclined portion, which causes a problem in operation.

[0019]

According to the present invention, by changing the position of the porous plug with respect to the immersion pipe for each treatment charge, the position where the upward flow of the molten steel generated by the plume collides with the tip part of the immersion pipe and the inner circumference is biased to a certain position. Because it will not be
The melting loss of the refractory can be made uniform.

Further, by setting the ladle and the immersion pipe in the optimum relative positional relationship, the upward flow of the molten steel due to the plume generated by the bottom blowing gas is reversed in the immersion pipe to form the downward flow, and the downward flow of the molten steel. The stirring effect in the pan due to the flow is effectively used.

That is, by adjusting the downward flow of molten steel in the dip tube to the center of the ladle as much as possible, uniform mixing in the tank and in the ladle is promoted, which is the flow velocity of the downward molten steel flow. Is sufficiently fast for upflow.

Further, by making the diameter of the height portion above the immersion pipe where the molten steel head does not reach at the time of pressure reduction smaller than that of the immersion portion of the immersion pipe, the heat radiation amount is reduced and the adhesion of the metal is reduced.

[0023]

EXAMPLE FIG. 1 is an explanatory view showing the positions of the porous plugs of each ladle on the same plane. In FIG. 1, the positions of the porous plugs 5 of each ladle 2 are the first ladle and the second ladle. The ladle, the third ladle, and the fourth ladle are the same, and the positions of the respective porous plugs 5 have the same eccentricity ratio with respect to the immersion pipe 4.

In this example, as is clear from Table 1, no influence on the degassing reaction was observed, while the refractory life was determined by the plume, where the direct erosion site at the lower end of the immersion pipe was dispersed. It has improved more than three times.

[0025]

[Table 1] Next, in a degassing facility having a 350-t straight-body type vacuum tube, the relative position of the ladle and the dipping tube and the relative position of the porous plug were variously changed, and the uniform mixing time in the ladle and the decarburization rate were measured. FIG. 2 is an explanatory view of the relative positional relationship between the dipping tube and the ladle according to the present invention, and Table 2 shows the test results.

[0026]

[Table 2] As is clear from Table 2, the eccentricity of the immersion pipe with respect to the ladle has an optimum value of 0.05 to 0.20 times the diameter of the immersion pipe, and the eccentric direction is the eccentric direction of the bolus brag with respect to the ladle. preferable.

Table 3 shows the basic unit of refractory and the amount of metal adhered on the shape of the immersion pipe.

[0028]

[Table 3] As is clear from Table 3, in the examples of the present invention, the amount of refractory applied was reduced, and the amount of bare metal adhered due to heat dissipation was reduced due to the reduction in the brick surface area. Therefore, the refractory cost was reduced by about 20%. However, in the case of narrowing it to 0.5 or less, there was a problem in operation due to the adhesion of metal to the inclined portion.

[0029]

The effects of the present invention are as follows.

(1) Dispersion of the impingement pipe collision sites makes it possible to make the melting loss of the refractory uniform, and as a result, the life of the immersion pipe refractory is improved without reducing the degassing characteristics. The refractory unit consumption is greatly improved.

(2) By setting the positions of the dipping pipe and the ladle in the optimum relative positional relationship, the stirring in the ladle is optimized,
As a result, the uniform mixing time can be shortened and the degassing efficiency in the immersion pipe is improved.

(3) By making the shape of the dip tube fine, it is possible to reduce the construction refractory material and the refractory surface area, and to reduce heat dissipation and metal adhesion.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the position of a porous plug of each ladle according to the present invention on the same plane.

FIG. 2 is an explanatory view of a relative positional relationship between a dip tube and a ladle according to the present invention.

FIG. 3 is a conceptual diagram of a vacuum degassing facility in which a vacuum degassing apparatus having a straight body type immersion pipe and a ladle are combined.

[Explanation of symbols]

1 vacuum degasser, 2 ladle, 3 molten steel, 4
Immersion tube, 5 porous plugs, 6 plumes

Claims (5)

[Claims] 1. A molten steel vacuum degassing facility comprising a vacuum degassing device having a dip tube and a ladle, wherein the dip tube center is eccentric with respect to the position of the porous plug at the ladle bottom and the ladle center. In order to change the relative position between the ladle and the ladle for each processing unit, the bolus plug position is a combination of a plurality of ladles having the same eccentricity ratio with respect to the center of the immersion pipe and a vacuum degassing device having the immersion pipe. Vacuum degassing equipment characterized by. 2. In a molten steel vacuum degassing equipment comprising a vacuum degassing device having a dip tube and a ladle, the center of the dip tube is eccentric with respect to the position of the porous plug at the bottom of the ladle and the center of the ladle. A vacuum degassing equipment characterized in that the dipping pipe is rotatable in order to change the relative positions of the pipe, the ladle and the porous position for each processing unit. 3. A molten steel vacuum degassing facility comprising a vacuum degassing device having a dip tube and a ladle, wherein the center of the dip tube is eccentric with respect to the position of the porous plug at the bottom of the ladle and the center of the ladle. The vacuum degassing equipment according to claim 1 or 2, wherein the tube center is eccentric with respect to the center of the ladle by 0.05 to 0.20 times the diameter of the immersion tube. 4. A molten steel vacuum degassing facility comprising a vacuum degassing device having a dip tube and a ladle, wherein the dip tube center is eccentric with respect to the position of the porous plug at the ladle bottom and the ladle center. Vacuum degassing equipment, characterized in that the diameter of the height portion above which the molten steel head does not reach when decompressing is made smaller than that of the immersion portion of the immersion pipe. 5. The diameter of a height portion above the immersion pipe where the molten steel head does not reach is 0.60 with respect to the diameter of the immersion portion.
The vacuum degassing equipment according to claim 4, wherein the vacuum degassing equipment is set to be 0.90 times.