JPH09241720A - Ladle refining apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ladle refining apparatus which can stably obtain high cleanliness of an alloy and can sufficiently respond to the demand of quality in the recent year. SOLUTION: Gas 4 is blown into the inner part from a plug 2 arranged at the bottom part of a ladle 1 and molten metal 3 in the inner part is stirred so as to catch impurity in the molten metal 3 into slag 5 existing on the surface of the molten metal 3. Flow rate of the gas 4 is 20-40Nl/min, and at the time of using R for the radius at the bottom part of the ladle 1, the plug is arranged so as to be apart from the outer peripheral edge part of the bottom part by >=1/4R, and in the case of arranging >=2 sets of the plugs, the plug is apart from the other plugs by >=1/2R.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ladle refining device for removing impurities by stirring molten metal in a ladle, and more particularly to a ladle refining device capable of obtaining high cleanliness. .

[0002]

2. Description of the Related Art Generally, a ladle refining apparatus is used for secondary refining after decarburizing stainless steel in an AOD furnace, for example, and an inert gas such as Ar gas is introduced from a blow port provided at the bottom of the ladle. The gas is blown into the molten metal, and the molten metal is agitated by the rising flow of the inert gas. Then, the principle of the ladle refining device is to stir the molten metal to cause the non-metallic inclusions contained in the molten metal to float while being aggregated, and to capture the non-metallic inclusions in the slag existing on the surface of the molten metal. By the way, as an alloy refined using the above-described ladle refining apparatus, Fe-Ni for IC lead frames is used.
There are alloys, but in recent years, ICs having a large number of pins have been developed, and accordingly, high cleanliness is required for alloy materials.

[0003]

In order to effectively remove non-metallic inclusions (hereinafter abbreviated as inclusions) in the molten metal,
It is necessary to stir the molten metal to some extent to frequently bring the inclusions into contact with each other, and to increase the frequency with which the inclusions aggregated with each other come into contact with the slag. For that purpose, it is necessary to stir the molten metal to some extent, but if the molten metal is stirred too strongly, it is known that the slag is caught in the molten metal and returned to increase inclusions (“melt refining reaction”). Physical Chemistry and Process: Iron and Steel Institute of Japan P292).

Also, Joo.S and Guthrie have reported a study on the number and arrangement of gas inlets in a ladle refining device (Steel making Conf. Proc Vol. 72 P.51).
7), this study was to make the molten steel composition and molten steel temperature uniform, and was not aimed at removing inclusions. For this reason, the technique described in the research report cannot be said to be useful for highly cleaning molten steel. Therefore, the present invention can stably obtain high cleanliness,
It is an object of the present invention to provide a ladle refining device that can sufficiently meet the recent demands for quality.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have studied in detail the flow rate of gas that can effectively remove inclusions without involving slag. As a result, if the flow rate of the gas to be blown is less than 20 NL / min, inclusions cannot be effectively removed due to insufficient stirring of the molten metal, while if it exceeds 40 NL / min, the stirring is too strong. It was found that the slag was caught in the molten metal.
It was also found that such a phenomenon occurs similarly even when the capacity of the ladle is different.

The ladle refining device according to claim 1 is based on such knowledge, and gas is blown into the inside of a ladle provided at the bottom of the ladle by stirring the molten metal inside. In the ladle refining device in which the slag existing on the surface of the molten metal is made to capture impurities in the molten metal, the flow rate of the gas blown from one blowing port is set to 20 to 40 NL / min. It should be noted that the number of blow ports of this ladle refining device may be one or two or more, but when the blow ports are two or more, the distance between the blow ports is set as described in claim 2. Is desirable.

Further, as a result of a detailed study on the slag winding, the present inventors have obtained a remarkable finding that the slag winding is greatly influenced by the arrangement of the blow-in port. That is, as shown in FIG. 1, when the gas 4 is blown into the molten metal 3 from the blow-in port 2 of the ladle 1, the molten metal 3 in that portion rises together with the gas 4, rises close to the surface, and then sinks downward. When the molten metal 3 sinks, the slag 5 is also dragged downward, and the phenomenon in which the dragged slag 5 separates from the others and sinks is the above-mentioned entrainment. Then, as a result of examining the position of the blow-in port based on the finding that the slag 5 is likely to be rolled up near the wall of the ladle 1, the inventors have found that when the radius of the bottom of the ladle is R, It has been found that slag entrainment can be effectively prevented by setting the distance L1 from the side wall surface of the ladle located on the surface of the molten metal to the blow-in port to 1 / 4R or more.

Further, as shown in FIG. 2, when the molten metal 3 raised by the gas 4 blown from the two blowing ports 2 sinks, the slag 5 is the molten metal 3 in the middle thereof.
Are dragged downward by the two flows of. Therefore, as a result of examining the distance between the two air inlets, the present inventors found that if the distance L2 between the air inlets is set to 1 / 2R or more,
It has also been found that slag inclusion can be effectively prevented.

The ladle refining device according to claim 2 is obtained by the above-mentioned experimental result, and gas is blown into the inside from a blow-in port provided at the bottom of the ladle, and the molten metal inside is agitated. In a ladle refining device in which impurities in the molten metal are captured by the slag existing on the surface of the ladle, when the radius of the bottom part of the ladle is R, blowing from the side wall surface of the ladle located on the molten metal surface Place the ports at a distance of 1 / 4R or more, and if the number of blow ports is 2 or more, set the blow ports to 1/2.
The feature is that they are arranged at least R apart.

When there are two or more blow ports, the blow ports should be placed at a distance of 1 / 4R or more from the side wall of the ladle located on the surface of the molten metal, or the blow ports should be placed at a distance of 1 / 2R or more. It is also possible to employ either one of them. Further, even in such a ladle refining device, it is more effective if the flow rate of the gas blown from the blowing port is set to 20 to 40 NL / min. Furthermore, in order to prevent the slag from being caught more effectively, it is desirable to arrange the blow-out port at a distance of 1 / 3R or more from the side wall surface of the ladle located on the surface of the molten metal. It is desirable to dispose at least 3 R apart.

As a result of further research conducted by the present inventors, the weight of the molten metal in the ladle is preferably 20 tons or less, and the weight of the molten metal is 20 tons or less when the number of the injection port is one. In some cases, it was also found that the number of blowing ports is preferably one. The reason for this is that if there is only one inlet and the weight of the molten metal exceeds 20 tons, the agitation becomes insufficient, and if there are two or more inlets when the molten metal has a weight of 20 tons or less, the agitation is too strong and the slag is involved. Is. However, in a ladle having a molten metal weight of 20 tons or more, it is better to increase the number of blowing ports as the molten metal weight increases. This is because it is possible to increase the stirring area by increasing the blowing port, and to stir the entire area of the molten metal to promote the aggregation, flotation and inclusion of inclusions in the molten metal in the slag.

The ladle refining apparatus according to claim 3 is obtained as a result of the inventors of the present invention examining the stirring state of the molten metal by changing the size of the ladle. When the weight tonnage of the molten metal that can be poured into the ladle is W and the number of blow ports is N, the following formula

## EQU2 ## It is characterized in that (N-1) .times.20 <W.ltoreq.N.times.20.

[0013]

Next, an embodiment of the present invention will be described. A. Cold model experiment First, we made cylindrical water tanks with a size of 1/4 of 60 ton ladle and 18 ton ladle, respectively, and inject water into them, and float N-pentane on the surface of the water to make molten metal. / A water model of slag was created.

First, a plug (blowing port) provided at the bottom of the water tank
A gas (air) was blown into the inside of the container to observe the behavior of N-pentane. At that time, the position where the N-pentane was dragged when the water that rose together with the gas descended was observed while changing the position of the plug little by little. From this, it was estimated at which position the slag would be caught when operating in an actual ladle. As a result, in any water model,
It was found that the N-pentane was dragged at a certain distance from the plug in the radial direction.

Next, the flow rates of the gas blown in the 60-ton and 18-ton water models were changed, and the flow velocity of water at the position where N-pentane was dragged was measured. The water flow rate was measured with a 3 mm propeller velocimeter. FIG. 3 is a diagram showing the flow velocity of water with respect to the flow rate of gas blown in. In the figure, “◯” indicates an 18-ton model, and “Δ” indicates a 60-ton model. In addition, when N-pentane sank and was caught when the water descended, those reference numerals were shaded.

As can be seen from the results shown in FIG. 3, the flow velocity of water with respect to the flow rate of the injected gas is 18 in the 60-ton model.
The same is true for the Ton model, and moreover, when the flow rate of the blown gas exceeds 2 NL / min, entrainment of N-pentane occurs. From the above results, in the actual operation of the ladle, the slag entrainment occurs at the same position regardless of the ladle capacity, and the slag entrainment occurs when the gas flow rate exceeds a predetermined value. You can infer that.

B. Experiment by actual machine When the present inventors converted various conditions of the above water model into various conditions in operation in a ladle, and converted,
The gas flow limit value of 2 NL / min corresponds to 40 NL / min. That is, whether it is a 60-ton ladle or an 18-ton ladle, 1
If the flow rate of gas blown from one plug exceeds 40 NL / min, slag entrainment will occur. Therefore, we changed the gas flow rate in an actual ladle and observed the transition of the number of inclusions in the molten metal. In addition, the number of plugs and the arrangement thereof were set variously to carry out the operation, and the transition of the number of inclusions under each condition was observed. A ladle having a cylindrical shape was used, and in this operation, a molten metal of Ni42wt% -Fe alloy was used.

Table 1 shows the respective operating conditions. Here, in the experiments of Nos. C to h, the plug was placed at a position separated from the center of the bottom of the ladle by 2 / 3R (where R is the radius of the bottom of the ladle). Further, in the No.i experiment, as shown in FIG. 4 (A), one plug 2 was arranged at the center of the bottom of the ladle 1 and two plugs were arranged linearly on both sides thereof. The position of the outer plug 2 in this case is 2 / from the center of the bottom.
It is 3R.

Table 2 shows the relationship between the stirring time (gas blowing time) and the number of inclusions under each operating condition, and the results of Table 2 are shown in FIG. 5 as a diagram. In this case, for example, AO
After injecting the molten metal subjected to primary refining in the D furnace into a ladle and allowing it to calm down, let the number of linear inclusions that start stirring by blowing gas be 1 and express the number of inclusions after each stirring time as an index. did. In addition, the total stirring time from the start to the end of stirring was set as a constant time, and the stirring time in the middle was divided by the total stirring time to be represented by an index.

[0020]

[Table 1]

[0021]

[Table 2]

As can be seen from Table 2 and FIG.
In and b, since no gas was blown in, the inclusion index hardly changed even after the stirring time. In addition,
In No. b, the inclusion index decreased slightly, but this is considered to be due to the convection of the molten metal. In addition, No.
In c, e, and h, the gas flow rate was 70 NL / min, which resulted in strong agitation, slag entrainment occurred, and the final inclusion index exceeded 1. The same phenomenon occurs in N0.g where the gas flow rate is 30 NL / min and the 18-ton ladle has two plugs. In particular, in Nos. G and h, the plugs were closer to 1 / 10R, which resulted in stronger stirring, and as a result, the inclusion index changed significantly with the passage of stirring time, and the final inclusion index was It greatly exceeded 1.

On the other hand, in No. d, the gas injection rate was 30 NL / min, and since there was one plug for the 18-ton ladle, the inclusion index was favorable from the start of stirring. Has fallen to. Also, in No.i, the gas flow rate was 30 NL / min, and the plug was 60
Since three tonnage ladles are provided corresponding to the ton ladle, the inclusion index has been steadily decreasing since the start of stirring. The final number of inclusions in these experiments was sufficient to meet the recent demand for high cleanliness.

By the way, in No. f, since the gas flow rate is within the range of the present invention, the inclusion index does not occur and the inclusion index decreases with the passage of stirring time, and the final inclusion index is No. It became smaller than d. However, the number of inclusions finally reached within a predetermined stirring time cannot be said to sufficiently satisfy the requirement. That is, in No. f, since the number of inclusions before the start of stirring was considerably large, the number of inclusions did not decrease to a desired value. This is because the number of plugs was one for the 60-ton ladle, and the stirring was weak. It is generally known that the larger the lot, the larger the amount of inclusions tends to be. Therefore, in the operation with a 60-ton ladle, it is necessary to reduce the inclusions to the extent that can be seen in No. i. On the other hand, in No. d, the amount of inclusions is relatively small at the start of stirring because it is an 18-ton ladle. Therefore, even if the final inclusion index is higher than No. f, sufficient cleanliness can be obtained.

From the above experimental results, the gas flow rate is 70N.
At L / min, it was found that the inclusion index increased rather than decreased and did not function as a ladle refining device. When the gas flow rate is 30 NL / min, No.
It has been found that sufficient cleanliness can be obtained if there is no other factor that causes strong stirring such as g. Therefore, the above experimental results clarified the justification for setting 40 NL / min, which is slightly higher than 30 NL / min, as the upper limit value of the gas flow rate.

The arrangement of the plugs is shown in FIG.
It is not limited to the one shown in (A). For example, the arrangement shown in FIGS. 4B and 4C can be adopted. However, when pouring molten metal into the ladle 1 from the AOD furnace or the like, if the molten metal is directly poured into the plug 2, the plug 2 may be damaged. Therefore, in order to secure a large area where the plug 2 does not exist at the bottom of the ladle 1, in FIG.
(A) and (B) are preferred.

By the way, the above-mentioned experiment using an actual machine was carried out using a cylindrical ladle, but the numerical limitation of the ladle refining apparatus of the present invention is applicable to ladle of any shape. For example, the same action and effect can be obtained even with a ladle having a tapered shape that tapers downward. In this case, from the side wall located on the surface of the slag of the ladle to the bottom 1/4
The plugs may be arranged at a distance of R (preferably 1 / 3R) or more.

[0028]

As described above, in the ladle refining apparatus of the present invention, the molten metal is appropriately stirred while the inclusion of the slag is prevented without vigorous stirring, and the inclusions are effectively removed. be able to. Therefore, the high cleanliness of the alloy can be stably obtained, and the recent demand for quality can be sufficiently satisfied.

[Brief description of drawings]

FIG. 1 is a side sectional view for explaining an arrangement of plugs in the present invention.

FIG. 2 is a side sectional view for explaining the arrangement of plugs in the present invention.

FIG. 3 is a diagram showing a relationship between a gas flow rate and a flow velocity at a winding position.

FIG. 4 is a plan view showing an example of arrangement of plugs according to the present invention.

FIG. 5 is a diagram showing a temporal transition of inclusions in molten steel.

[Explanation of symbols]

 1 Ladle 2 Plug (inlet) 3 Molten metal 4 Gas 5 Slag

Claims (3)

[Claims] 1. Ladle refining in which gas is blown into the inside of the ladle at the bottom of the ladle and the molten metal inside is agitated to capture impurities in the molten metal in the slag existing on the surface of the molten metal. The ladle refining apparatus is characterized in that the flow rate of gas blown from one blowing port is set to 20 to 40 normal liters / minute. 2. Ladle refining in which gas is blown into the inside of a ladle provided at the bottom of the ladle and the molten metal inside is agitated to capture impurities in the molten metal by the slag existing on the surface of the molten metal. In the apparatus, when 1 or 2 or more of the above-mentioned inlets are provided, and the radius of the bottom of the ladle is R, the inlet is 1 / 4R from the side wall surface of the above-mentioned ladle located on the surface of the molten metal. The ladle refining device is characterized in that it is arranged at a distance above the above, and when the number of blow openings is two or more, the blow openings are placed at a distance of 1 / 2R or more. 3. When the weight tonnage of the molten metal that can be poured into the ladle is W and the number of the blowing ports is N, the following formula is obtained: (N-1) × 20 <W ≦ N × 20 is satisfied, The ladle refining device according to claim 1 or 2 characterized by things.