JPS61150758A - Method for heating molten metal in tundish for continuous casting - Google Patents

Abstract

PURPOSE:To heat efficiently and uniformly a molten metal to an adequate temp. with an extremely simple and long-life heater by inserting electrodes each consisting of a mixture composed of a high melting metallic oxide and graphite or carborundum to the side wall of a tundish and conducting directly electricity to the molten metal. CONSTITUTION:The electrodes 12 which are constituted by mixing the high melting metallic oxide such as Al2O3, MgO, CaO or SiO2 and 10-30wt% graphite or carborundum and elute extremely little C to the molten metal are inserted to the side wall of the tundish in the state of insulating the electrodes from the side wall. The electricity is directly conducted to the molten metal 14 by such electrodes 12, by which the molten metal is heated to the adequate temp. The molten metal 14 is uniformly heated to the adequate temp. by the extremely simple and long-life heater. The life of the device is further extended if a cap 12A of the same material as the material of the electrodes 12 is fitted to the top end of each electrode in the side wall and only the cap 12A is exchanged when worn.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for heating molten metal in a tundish for continuous casting, and particularly relates to a heating method that has excellent heating efficiency and is easy to operate and maintain. Widely available.

[Conventional technology]

In continuous casting of molten metal (hereinafter referred to as continuous casting),
For example, in the case of continuous steel casting, molten steel produced in a converter is stored in a ladle and transferred to a continuous casting tundish, where it is injected into the mold through a submerged nozzle that reaches the mold from the bottom of the tundish. be done.

As described above, the temperature of molten steel inevitably decreases as it is transferred from the ladle to the tundish and then to the mold. However, since the casting temperature is extremely important in continuous casting,
A tundish equipped with a molten steel heating device is used to heat the molten steel in the tundish if there is a risk that the molten steel in the tundish may drop below the planned pouring temperature.

Figures 3 and 4 are conventional techniques for heating the molten metal contained in the tundish.

A method as shown in Fig. 5 (5) @ has been considered.

(a) A method in which an electrode 4 is inserted from above the tundish 2 and arc heating is performed using electric power E, as shown in FIG.

Middle) A method of resistance heating by disposing a heating resistor 8 between the tundish 2 and its top cover 6 as shown in FIG.

(c) As shown in FIG. 5 (5) (g), a method in which a groove-type induction furnace 10 is arranged on the side or bottom of the tundish 2 and low-frequency induction heating is performed.

All of the above methods are already established techniques for heating molten metal, but each method has the following drawbacks when used in a continuous casting tundish.

Method (a) is technically difficult for continuous casting equipment due to the ladle and the ladle, and since the upper surface of the molten metal is heated, the temperature distribution within the tundish becomes uneven and only the upper layer becomes high temperature.

Naka)'s method uses indirect radiant heating, which has low energy efficiency, and since it heats only the top surface, the temperature distribution inside the tundish is uneven, and only the top layer becomes high temperature.

The method of ``g→'' is superior to other methods in that it has excellent heating efficiency and can heat with a uniform temperature distribution due to the stirring effect within the tundish 2, and is also used in actual continuous casting tundishes. However, due to its unique shape, it is difficult to inspect and repair the inside of the trench furnace, and it is cumbersome to attach and remove the trench furnace when repairing the tundish.

[Problem that the invention seeks to solve]

It is an object of the present invention to provide an effective heating method that solves the problems of the above-mentioned conventional heating methods, has excellent heating efficiency, and is easy to operate and maintain.

[Means and operations for solving the problems] The gist of the present invention is as follows.

That is, in a method of heating molten metal housed in a tundish for continuous casting, an electrode made of a mixture of a high melting point metal oxide and graphite or carborundum is inserted through the side wall of the tundish and immersed in the molten metal. This is a method for heating molten metal in a continuous casting tundish, which is characterized by directly applying electricity.

When heating molten metal using graphite, which is used in arc furnaces, etc. as an electrode material, graphite, which is normally used as an electrode material, has a high solubility in the molten metal, so it cannot be used for heating the molten metal in a continuous casting tundish. do not have. However, according to the experiments of the present inventors, for example, λl, 0. , MgO,Cl
In the case of a mixture in which 10 to 50% by weight of graphite or carborundum (5iC) is added to a high melting point metal oxide such as l0.8 tow, the elution rate of C into the molten metal is extremely low unless the graphite or SIC is oxidized. I discovered that.

Moreover, these mixtures have excellent thermal conductivity and spalling resistance, and it is clear from the following calculation example that they can be energized. However, the heating current in this case is determined by the physical properties of the electrode material made of a mixture of high melting point metal oxide and graphite or 8+C. for example,
Graphite content 4 with cross-sectional area 100 cm” and length 30 cIR
If the specific resistance of the electrode material made of a mixture of 0 and 0 is ρ, then ρ is 1. If ρ = 2X10Qcm including the contact resistance of the connection part, then the total resistance R = 2X10-'' (Ωcrn)
X 30crs ÷ 100i = 6X10 Ω Therefore, in the case of DC with terminal voltage 1000V, current 1 = 10
"v15X10-38=1.6X101Amp, that is, it is possible to pass a current of 1.6X10'Amp through the molten metal.

However, in this case, assuming that electricity is applied to molten steel with the same cross-sectional area and length of 506n, the specific resistance of molten steel at 1500°C is approximately 150 μΩ, so total resistance R = 15
0X10-'ΩzX 50crn÷10〇-=75
X 10 Ω Therefore, Joule heat generated = 75 Xl0-'ΩX(1,
6 cutting 05 noodles) 2#1900KW That is, it is possible to generate about 1900KW of Joule heat.

It was confirmed that the experimental results obtained by the present inventors also substantially coincided with the above calculation.

As described above, an electrode material made of a mixture of a high melting point metal oxide and 10 to 50% by weight of graphite or 8+C can conduct electricity, and the elution rate of C is extremely low. Since it was found that processing was possible, we focused on using this as an electrode for heating molten metal in a continuous casting tundish, and as a result of research, we have completed the present invention.

Embodiments of the present invention will be described with reference to FIGS. 1 and 2.

As shown in FIG. 1, the two electrodes 12 are inserted through the two side walls of the tundish 2 and immersed in the molten steel 14 housed inside.The electrode materials include A I2O3,
1 for high melting point metal oxides such as MgO, C-0, 8102, etc.
It is a mixture to which 0 to 50% by weight of graphite or SIC is added. If the blending ratio of graphite or SIC is less than 10%, machinability and electrical conductivity will be poor, and if it exceeds 50%, the solubility of C will become somewhat high, so a blending ratio of 10 to 50% is preferable.

Power is supplied to the electrode 12 from a power supply unit 16 via a water-cooled cable 18 and a power supply band 20 that grips the electrode 12 . The water supply to the water cooling cable 18 and the power supply band 20 is circulated by a water supply unit 22.

Next, the portion through which the two side walls of the tundish of the electrode 12 made of a mixture of high melting point metal oxide and graphite or SIC used in the present invention is constructed as shown in FIG.

That is, the outer shell 24 of the tundish 2 is insulated by insulating refractory tuyere bricks 26 and mica 28 provided around the electrode 12, and the gap between the shell 24 and the shell 24 is filled with refractory mortar 30. There is. In addition, the inner part of the electrode 12 that is immersed in the molten steel 14 is covered with a cap 12A made of the same material so that it does not need to be replaced every time, and when it wears out, only the cap 12A can be replaced and is exposed to the atmosphere. The outer portion is coated with an antioxidant 32 such as a glass film forming material, and is forcedly air cooled from the outside.

The electrode 12 according to the present invention thus constructed is immersed in the molten steel 14 inside the tundish 2 through insulation through the steel skin 24, the refractory material 34, and the inner lining 36, so that resistance heating due to current conduction occurs. Molten steel 14 is heated.

The heated molten steel 14 becomes an upward flow and reaches the tandish 2.
Since the convection stirring action takes place inside the tandish 2
The molten steel 14 inside was uniformly heated, and no non-uniformity in temperature was observed as in the conventional case.

〔Effect of the invention〕

As is clear from the above embodiment, the method for heating molten metal in a continuous casting tundish according to the present invention involves inserting a set of electrodes made of a mixture of a high melting point metal oxide and graphite or carborundum through the side wall of the tundish. By immersing it in the molten metal contained inside and directly applying electricity, we were able to achieve the following effects.

@) The heating device is extremely simple, has a long service life and is economical.

(b) According to the present invention, there is no need for an output stabilization function or a flicker suppression function such as in conventional arc heating, and there is no need for a pinching suppression function such as in groove-type induction heating, and the heating controllability is excellent. There is.

(c) The molten metal in the tundish is heated by Joule heat due to the resistance between the electrodes, so as long as the molten metal is in contact with the electrodes, it can be heated regardless of the initial, middle, or final stages of continuous casting. , and has high heating efficiency.

2) The high temperature molten metal heated at the bottom of the tundish has a stirring action that causes it to rise due to natural convection, so the temperature distribution of the molten metal contained therein is uniform.

(e) Since the configuration of the heating device is simple as in (a),
Maintenance and inspection are easy, and heating output can be increased by lowering the resistance of the electrode material or the contact resistance between the electrode material and the current-carrying cable.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an apparatus for carrying out the method of heating molten metal in a continuous casting tundish according to the present invention, FIG. 2 is a partially enlarged view showing the penetration part of the tundish side wall of an electrode according to the present invention, FIGS. 3 and 4 . Figures 5 (G) and @ all show the conventional methods of heating molten metal in the continuous casting tundish, Figure 3 is the top arc heating method, Figure 4 is the top resistance heating method, and Figure 5 ( ), @
2A and 2B are schematic cross-sectional views showing the groove-type induction heating method. 2...Continuous casting tundish, 2A...Side wall 1
2... Electrode 24... Iron skin 26
...Refractory tuyere brick, 28...Mica 3
0...Fireproof mortar agent Patent attorney Takeo Nakaji Figure 1

Claims (1)

[Claims] (1) In a method of heating molten metal housed in a tundish for continuous casting, an electrode made of a mixture of a high melting point metal oxide and graphite or carborundum is inserted through the side wall of the tundish to the molten metal. A method for heating molten metal in a tundish for continuous casting, characterized by dipping the metal and directly applying electricity.