JPH0819458B2 - Immersion tube for vacuum degassing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to an improvement in a dip tube of a vacuum degassing apparatus.

<Prior Art> A so-called vacuum degassing device such as an RH degassing device or a DH degassing device that sucks molten steel into the vacuum tank by immersing the dipping pipe in the molten steel and depressurizes the vacuum tank to degas The importance is increasing with the recent trend toward higher grade and higher purity steel. In such a vacuum degassing apparatus, the processing capacity is improved by improving the degassing capacity by improving the degree of vacuum and improving the operating rate by increasing the life of the refractory.

Hereinafter, a conventional immersion pipe will be described with reference to the drawings. FIG. 2 is a front sectional view of an RH type vacuum degassing apparatus equipped with two dip tubes, which is an example of the molten steel degassing apparatus.

In the RH type vacuum degassing device, the two dipping pipes 1 provided at the lower end of the vacuum tank 8 are immersed in the ladle molten steel, the vacuum tank 8 is decompressed by the vacuum exhaust device 6, and the molten steel is sucked up into the vacuum tank 8. Then, argon gas is sucked into the inner surface of one of the dip tubes 1 to raise the molten steel in the ladle into the vacuum tank 8 to degas the gas component in the molten steel, and then descend from the other dip tube 1 to the ladle. The degassing is carried out by a series of molten steel recirculation of returning. In FIG. 2, 5 is the iron shell of the vacuum chamber 8 and 7 is the iron shell 5.
It shows the refractory lined inside.

The immersion pipe 1 is generally a cylindrical cored bar 2 with refractories 3 and 4 on both the inner and outer sides. The main role of the cored bar 2 is to protect the inner and outer refractories 3 around the cored bar 2. 4 is fixed to stabilize the structure, and outside air is prevented from being sucked into the vacuum chamber 8 through the inside and outside refractories 3 and 4.

<Problems to be Solved by the Invention> In order to fulfill the above-mentioned role, the cylindrical core metal 2 is generally made of metal such as steel, but is immersed in molten steel 10 as shown in FIG. For this reason, the temperature of the cored bar 2 reaches 1000 ° C or more as it is heated from both inside and outside surfaces and subjected to degassing treatment, and cracks occur in the refractory due to the decrease in strength and the difference in the coefficient of thermal expansion with the surrounding refractories 3 and 4. Cause the generation of. Note that 11 indicates the slag on the molten steel 10.

Therefore, the life of the refractories 3 and 4 is short and the dipping pipe 1 is frequently replaced, so that the operating rate is reduced, and further, the outside air is sucked in from the cracks 12 formed in the refractories 3 and 4 through the passages shown by the arrows 9. The refractory 7 in the vacuum chamber 8 can easily reach the inside of the chamber. When sucking the outside air, the main problems are the decrease of the vacuum degree in the tank and the dissolution of nitrogen, which occupies about 80% of the atmosphere, into the molten steel.

In order to solve the above problems of the core metal, for example, JP-A-58-96813, JP-A-59-1617 and JP-A-61-253.
No. 31, gazette proposes a means for cooling by introducing a refrigerant into a hollow cylindrical cored bar, but the temperature of the refractory material is also low only by cooling the cylindrical cored bar, which facilitates aeration and makes it easier to vacuum. It is not possible to prevent the degree of vacuum from being lowered due to the suction of the outside air into the tank, so that the molten steel is absorbed, and as a result, effective denitrification cannot be performed.

As described above, nitrogen is easily dissolved in molten steel, but it is difficult to degas even under reduced pressure, and it is an important problem because the solubility is high especially in steel types having a high chromium content.
No. 295315 proposes a method in which the outer periphery of the dip tube is sealed with Ar gas to prevent nitrification of molten steel during degassing and to efficiently denitrify. However, in the method of preventing absorption of nitrogen by sealing Ar gas, not only the degree of vacuum cannot be improved, but also Ar gas is used as the sealing gas, resulting in an increase in processing cost.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the conventional problems described above, to reduce cracks generated in a refractory of an immersion pipe, to prevent external air from being sucked into a vacuum chamber, and also to improve the life of the immersion pipe. It is a thing.

<Means for Solving the Problem> The present invention for achieving the above-mentioned object is an immersion pipe of a vacuum degassing apparatus in which the inner circumference and the outer circumference of a cylindrical cored bar are covered with a refractory material. At least one step is provided in the height direction on the outer circumference of the brim-shaped baffle plate for preventing the intake of outside air, and a technical fluid means for cooling is provided in the cylindrical cored bar and the brim-shaped baffle plate.

That is, according to the present invention, in a dipping pipe of a vacuum degassing apparatus, in which the inner circumference and the outer circumference of a cylindrical cored bar (2) are coated with a refractory, the cylindrical cored bar (2) is used for a cooling fluid passage. A steel plate (2e) is interposed between the spiral steel pipes (2d) and welded to form an integral structure, and the spiral steel pipe (2d) and the spiral steel pipe (2d) are provided on the outer periphery of the cylindrical core metal (2). Steel plate (2e ') between the steel pipes (2d') for communicating fluid passages for cooling
A submerged pipe for a vacuum degassing apparatus, characterized in that at least one step is provided in the height direction with a collar-shaped baffle plate (13) for blocking the intake of the outside air, which is welded and integrated with the interposition of.

FIG. 1 is a front sectional view showing the structure of another immersion tube according to the present invention. In FIG. 1, a cored bar 2 covered with an outer refractory material 3 and an inner refractory material 4 is formed by welding a spiral steel pipe 2d with a steel plate 2e interposed therebetween to form an integral structure. It is used as a cooling fluid passage.

A brim-shaped baffle plate 13 for blocking the intake of outside air is provided on the outer periphery of the cored bar 1 in the height direction. This baffle plate 13 projects outside the core metal 2 and has a structure in which a steel plate 2e 'is interposed between steel pipes 2d' communicating with the spiral steel tubular 2d of the core metal 2 and welded together.

A supply pipe 16a is connected to the upper end of the spiral steel pipe 2d, and a discharge pipe 16b is connected to the lower end thereof. The cooling fluid 14 is supplied to the cylindrical core metal 2 and the collar-shaped baffle plate 13 to be cooled and then discharged. It is supposed to do.

Reference numeral 15 denotes a flange that connects the dip tube 1 to the lower end of the vacuum chamber 8.

In FIG. 1, the collar-shaped baffle plate 13 is provided in one step in the height direction, but it is more effective to have two or more steps. In order to enhance the effect of preventing the outside air from being sucked into the vacuum chamber 8, the mounting position of the brim-shaped baffle plate 13 should be positioned below the surface of the molten steel 10 in the ladle and mounted on the outer periphery of the cored bar 2. preferable. When the baffle plate 13 is provided in only one step, it is particularly desired to be below the surface of the molten steel 10.

<Operation> According to the present invention, since the upper surface of the collar-shaped baffle plate 13 provided on the outer periphery of the cylindrical core metal 2 is brought into close contact with the outer refractory 3 of the dip tube 1 above it by the above-mentioned means, the outside air 9 can be prevented from being sucked, and low-nitrogen steel can be melted in a short time.

Further, since the core metal 2 and the baffle plate 13 are cooled by the cooling fluid, they can be reused.

<Example> Hereinafter, an example of the present invention is described based on a drawing. The immersion pipe 1 having a structure in which the cylindrical cored bar 2 and the collar-shaped baffle plate 13 are cooled by using the spiral steel pipe 2d shown in FIG. 1 is applied to an RH type vacuum degassing apparatus to perform vacuum degassing treatment of 280 tons of molten steel. did.

The mounting position of the baffle plate 13 is 100 mm from the surface of the molten steel 10 in the ladle.
One step was provided in the height direction of the cored bar 2 so as to be downward. As the cooling fluid, 200 Nm ³ / hr of nitrogen gas, which is inexpensive and less dangerous and does not oxidize the core metal 2, was used.

As an example of the melting result, Table 1 shows the case where the present invention and the conventional immersion pipe are used for the case where the aluminum killed steel is subjected to the vacuum degassing treatment. As is apparent from Table 1, according to the present invention, the suction amount of outside air is reduced, so that the degree of vacuum in the vacuum chamber 8 is improved, and the processing time is shortened by about 2 minutes as compared with the conventional dip tube. Was done.

As a result, the processing cost can be reduced by reducing the amount of steam used in the vacuum exhaust system, and the molten steel residence time can be shortened to lower the tapping temperature of the converter, improving the life of refractory materials in the converter and ladle, and degassing the vacuum. Great effects such as improved productivity by increasing the operating rate of the gas system were obtained.

Moreover, the concentration of gas components in the steel after the vacuum degassing process was also improved steadily because the degree of vacuum in the tank was improved, and the effect of quality assurance could be obtained.

In addition, as shown in Table 1, denitrification, which could hardly be expected with conventional dip tube treatment, can be performed. Therefore, low-nitrogen stainless steel that has been conventionally melted by the VOD method, which requires high treatment cost, etc. For example, RH degassing equipment that can process efficiently at low cost can be used for smelting, and significant cost reduction can be achieved. Since the amount of outside air that oxidizes the cored bar passed through the refractory was reduced, the cored bar could be reused and the dip pipe construction cost could be reduced.

Similar results were obtained when vacuum degassing the other steel types.

<Effects of the Invention> As described above, according to the present invention, the vacuum degassing treatment time can be shortened by the simple means of cooling the immersion pipe core bar and providing the baffle plate. It is possible to obtain great effects that cannot be obtained by simply cooling the core metal, such as manufacturing and reusing the core metal, and it is very useful for reducing the manufacturing cost of steel and improving productivity.

[Brief description of drawings]

FIG. 1 is a front sectional view showing the structure of an immersion pipe according to the present invention,
FIG. 2 is a front sectional view showing a conventional RH type vacuum degassing apparatus,
FIG. 3 is a front sectional view showing a conventional dipping tube. 1 ... Immersion tube, 2 ... Cylindrical core metal, 3 ... Outer refractory material, 4 ... Inner refractory material, 5 ... Degassing tank iron skin, 6 ... Vacuum exhaust device, 7 ... Degassing tank Refractory, 8 ... vacuum tank, 9 ... passage of outside air, 10 ... molten steel, 11 ... slag, 12 ... crack, 13 ... collar-shaped baffle, 14 ... cooling fluid, 15 ... Flange, 16a ... Supply pipe, 16b ... Discharge pipe.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Harushi Okuda 1-chome, Mizushima Kawasaki-dori, Kurashiki City, Okayama Prefecture (no address), Kawasaki Steel Co., Ltd. Mizushima Works (56) Reference JP-A-58-96813 (JP, Sho A) Actual development Sho 62-132156 (JP, U)

Claims (1)

[Claims] 1. A dip tube for a vacuum degassing apparatus, comprising a cylindrical cored bar (2) having an inner periphery and an outer periphery covered with a refractory material, wherein the cylindrical cored bar (2) serves as a cooling fluid passage. A steel plate (2e) is interposed between the spiral steel pipes (2d) and welded to form an integral structure, and the outer circumference of the cylindrical core metal (2) communicates with the spiral steel pipe (2d). Collar-shaped baffle plate (13) for external air intake shutoff, in which a steel plate (2e ') is interposed between steel pipes (2d') for cooling fluid passage
An immersion pipe for a vacuum degassing device, characterized in that at least one step is provided in the height direction.