JPH0629452B2 - Molten steel heating equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molten steel heating apparatus for immersing an electrode in molten steel and performing arc heating in the molten steel.

(Prior Art) Conventionally, when immersing an electrode having an inner and outer cylinder in molten steel and performing arc heating in the molten steel, for example, JP-A-53-839.
An electrode made of graphite was used as shown in Japanese Unexamined Patent Publication No. 32 (1989). Further, as shown in Japanese Patent Publication No. 60-43887, the arc generating gas was made to flow at a constant flow rate in the immersion pipe.

(Problems to be solved by the invention) However, the graphite electrode is corroded by molten steel and changes in the composition of the molten steel because it melts into the molten steel. Therefore, heating after refining, for example, heating molten steel in a continuous casting tundish, etc. There was a problem that it could not be applied. Further, in the conventional method, when the discharge distance is increased to increase the output, the discharge between the center electrode and the molten steel is easily transferred to the discharge (side arc) between the center electrode and the outer cylinder electrode, which significantly reduces the heating efficiency. In addition, there is a problem that the outer cylinder electrode wears faster. further,
A plasma arc is desirable from the viewpoint of increasing the output, but in the conventional method, the cross-sectional area of the dip tube (outer cylinder electrode) is too large and the flow velocity of the gas for arc generation is low, reducing the diameter of the arc column peculiar to plasma There was a problem in that a heat pinch for increasing the temperature was hardly generated, and the amount of high heat generated by the increase in the current density was limited to the arc discharge.

Note that the thermal pinch effect is "basics of plasma engineering" (October 1985, published by Sangyo Tosho Co., Ltd.), page 131, pages 11-20.
As described in the line, for example, the temperature obtained by an atmospheric pressure DC arc is around 10,000 K, but the gas flow rate near the wall surface is increased and the discharge column is narrowed down (this is called thermal pinch) to increase the power density. By increasing the electric input per unit volume of the arc portion, a high temperature of 20000K or more can be obtained.

(Means for Solving Problems) The present invention provides (i) a heating device comprising an outer cylinder electrode and a center electrode for immersing the electrode in the melt steel and performing arc heating in the melt steel, wherein the outer cylinder electrode and the center electrode A heating device for molten steel, characterized in that: consists of conductive ceramics; (ii) In the heating device for molten steel according to (i) above, an insulating, heat-resistant, and corrosion-resistant ceramic sprayed coating is formed on the inner peripheral surface of the outer cylinder electrode. In the apparatus for heating molten steel according to (iii), in the apparatus for heating molten steel according to (i) above, in the outer cylindrical electrode, on the inner peripheral surface of the outer cylindrical electrode near the center electrode tip, It is a molten steel heating device provided with a squeezing member for working gas.

(Function) Since the conventional graphite electrode is replaced with conductive ceramics, the ceramic material originally has heat resistance and corrosion resistance to molten steel, which prevents the electrode material from melting into the molten steel. By forming the insulating layer on the inner peripheral surface of the outer cylinder electrode by thermal spraying, the inner peripheral surface of the outer cylinder electrode becomes insulative, and the arc spot is prevented from moving to the inner peripheral surface of the outer cylinder electrode. Cooling the surface of the arc column by passing the working gas through the squeezing member and concentrating it near the wall surface of the arc column, reducing the diameter of the arc column to generate a thermal pinch effect, increasing the current density, and increasing the volume per unit volume. To increase the input electric power, raise the temperature of the arc column, and increase the heat input to the molten steel.

(Example) Hereinafter, description will be given based on the example of FIG.

The center electrode 1 is made of zirconium boride, which is a conductive ceramic, and has a screw on the top.
The arc length can be changed by screwing the nut 12 into this screw and turning the nut 12. The center electrode 1 and the nut 12 are attached to the outer cylinder electrode 2 via the insulator 5 and the center electrode support metal 6. The outer cylinder electrode 2 is also made of zirconium boride, which is a conductive ceramic. The zirconium boride is
A compound of boron B and zirconium Zr, to which carbon is added in order to improve the thermal shock resistance, and it has excellent electrical conductivity. (Specific resistance 1
0 ^-5 Ωm) The center electrode supporting metal member 6 is provided with an inlet for the working gas 11, and the working gas 11 is supplied from the gas source into the outer cylinder electrode 2 via the flow rate control valve 8. Outer cylinder electrode 2
Inside, the squeezing member 3 for squeezing the flow of the working gas 11 is provided on the inner peripheral surface of the outer cylinder electrode near the tip of the center electrode.
Is attached. The squeezing member is preferably an electrically insulating and heat-resistant substance, for example, foamed concrete, castable material (asbestos, etc.), foamed silica, or the like is used. The squeezing member has a doughnut-shaped cross section and is formed such that the inner diameter gradually decreases from the upper side to the lower side, and the minimum inner diameter is about 20 to 30 mm larger than the outer diameter of the center electrode. To do so. As a method of attaching the squeezing member to the inner peripheral surface of the outer cylinder electrode, for example, a plurality of through holes are formed in the squeezing member, and the inner peripheral surface of the outer cylinder electrode is held by the bolt so as to be held. Further, the ceramic film 4, for example, silica SiO ₂ or zirconia ZrO ₂ is sprayed on the inner peripheral surface of the outer cylinder electrode 2 within a range of a length approximately corresponding to the arc length from the lower end.

The torch 16 composed of the center electrode 1, the outer cylinder electrode 2, the center electrode support metal 6 and the like is set by the torch lifting device 17 on the torch support plate 13 provided with the heat insulating material 14 on the lower surface installed on the ladle, Follow the steps below.

First, the torch 16 is immersed until the center electrode 1 contacts the molten steel 9. Then, energization is started from the power source 7 connected to the center electrode 1 and the outer cylinder electrode 2. The output voltage of the power supply at this time is almost 0V. After that, when the working gas 11 is supplied through the flow rate control valve 8, the molten steel in the outer cylinder electrode 2 is pushed down by the gas pressure, and when the center electrode 1 and the molten steel surface are separated, an arc discharge 10 is generated. After that, the torch 16 is gradually lowered and installed at a predetermined depth, and the heating operation is started.

The supplied working gas 11 is finally discharged from the bottom portion of the outer cylinder electrode 2, becomes bubbles 15 and floats in the molten steel, agitates the molten steel at that time, and promotes the floating of inclusions.

Table 1 shows the results of the investigation described above and conducted by the apparatus. Table 1 shows a conventional example A in which a graphite electrode is used as the outer cylinder electrode 2,
The operation result according to Example B of the present invention using conductive ceramics is shown, and the mass increment is obtained from the composition analysis of the molten steel before and after heating, and the component increase amount per unit time is obtained from the heating time.

During operation, in the torch of Conventional Example A, an opening considered to be caused by a side arc was generated in the outer cylinder electrode, whereas in Example B in which the inner peripheral surface of the outer cylinder electrode 2 was sprayed with silica or zirconia, the opening was not formed. Did not occur.

Further, the operating voltage was about 50 V in the torch without the squeezing member 3, whereas the operating voltage was about 60 V when the squeezing member was used, and the input power increased by 20%.

(Effects of the Invention) According to the present invention, as shown in Table 1, the increase in the content of C is reduced to 1/30 as compared with the conventional method in which graphite is used for the outer cylinder electrode, and the composition change of molten steel is small. Therefore, the outer cylinder electrode is hardly worn. Further, no side arc is observed in the outer cylinder electrode having the CERAX film sprayed on the inner peripheral surface thereof, there is no trouble of opening on the wall surface of the outer cylinder electrode, and the life thereof can be greatly extended. Further, the adoption of the squeezing member causes the thermal pinch effect of the arc column, the input electric power is increased by about 20%, and the heating efficiency of the molten steel can be significantly improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention. 1 ... center electrode, 2 ... outer cylinder electrode, 3 ... squeezing member,
4 ... Ceramic film, 5 ... Insulator, 6 ... Center electrode support metal, 7 ... Power supply, 8 ... Flow control valve, 9 ... Molten steel, 10 ... Arc discharge, 11 ... Working gas, 12 ......
Nut, 13 ... Torch support plate, 14 ... Insulation material, 15
... bubble, 16 ... torch, 17 ... torch lifting device.

Claims (3)

[Claims] 1. A heating device comprising an outer cylinder electrode and a center electrode for immersing an electrode in the melt steel and performing arc heating in the melt steel, wherein the outer cylinder electrode and the center electrode are made of conductive ceramics. Heating device. 2. The heating apparatus for molten steel according to claim 1, wherein the inner peripheral surface of the outer cylinder electrode has a ceramic sprayed coating of insulation, heat resistance and corrosion resistance. 3. The heating apparatus for molten steel according to claim 1, wherein a working gas squeezing member is provided on the inner peripheral surface of the outer cylinder electrode in the outer cylinder electrode, in the vicinity of where the tip of the center electrode is located. Molten steel heating device provided.