JP2002143991A - Method of heating molten steel in tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise impressed electric power and to improve plasma heating ability by easily raising the impressed electric power in heating the molten steel in a tundish by a twin torch plasma heater. SOLUTION: When the molten steel 5 in the tundish 1 is heated by the twin torch plasma heater, a wall 10 for insulation or a weir is arranged between electrodes 3 and 4 in a heating chamber 2 to raise the generated voltage, by which the plasma heating ability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating molten steel in a tundish by a twin torch type plasma heating apparatus.

[0002]

2. Description of the Related Art In recent years, in continuous casting of steel, the heating of molten steel in a tundish has been carried out for the purpose of reducing costs and improving the quality of slabs by reducing the tapping temperature of a steelmaking furnace, making the molten steel temperature in a tundish uniform. In practice, plasma arc heating is the most commonly used method of heating molten steel. In recent years, the number of twin torch type plasma heating apparatuses has been increased because a tundish side electrode is not required and a voltage is about twice as high as that of a single torch type, so that a high output can be obtained with a low current.

[0003] Twin torch type plasma arc heating is performed as shown in FIG. The molten steel 5 received in the tundish 1 from the ladle is introduced into the heating chamber 2, where it is heated to a required temperature and then cast through the casting device 9. The heating of the molten steel 5 in the heating chamber 2 is performed by generating a plasma arc 7 between the molten steel 5 that is in communication with the cathode-side plasma torch 3 and the molten steel 5 that is in communication with the anode-side plasma torch 4. . At this time, argon (Ar) is supplied as a plasma gas to the cathode-side plasma torch 3 and the anode-side plasma torch 4, and the heating chamber 2 is usually heated with an argon gas as the sealing gas 14. The chamber 2 has an argon atmosphere.

[0004] When performing plasma heating, the amount of heating of the molten steel 5 is determined by the applied power, so that by changing the applied power, the temperature of the molten steel during casting is controlled so as to be within a predetermined range. Specifically, the scheduled temperature of the molten steel 5 and the molten steel thermometer 1
1 is compared with the indicated value, and the applied power is changed according to the magnitude of the difference. There are two methods of adjusting the applied power, current adjustment and voltage adjustment. The current adjustment is performed by changing the current setting of the power supply device 6, and the voltage adjustment is performed by controlling the position of the torch elevating device 12 (the plasma length). Change). The plasma length is detected by a plasma arc length detector 13.

[0005] In the heating of molten steel by the plasma arc, it is important to maintain the stable generation of the plasma arc 7, and the above-described current adjustment and voltage adjustment are important operating factors in the operation of the molten steel heating. .

However, the range of current adjustment is limited by the size of the plasma torch and the size of the heating chamber. For example, in a torch using a tungsten tip with an external shape of 25 mm, the maximum current is limited to about 7000 A. It is actually operating.

In the voltage adjustment, an operation of changing the arc length is performed. However, if the arc length is too short in order to lower the voltage, there is a problem that splash of molten steel adheres to the torch. Conversely, if the arc length is set too long to increase the voltage, the arc will be disturbed and unstable, and the arc will break, so the arc length is actually around 350 mm. For this reason, as another method of increasing the voltage, a method has been developed in which the atmosphere gas in the heating chamber 2 is switched to a mixed gas of a gas different in conductivity from argon and argon, and is disclosed in, for example, Japanese Patent No. 2969931. As described above, there is a method in which the atmosphere gas in the heating chamber is set to argon at the start of heating, and after a plasma arc is generated, the atmosphere gas is switched to a mixed gas of a gas different in conductivity from argon and argon. In the above method, it is preferable to change the argon ratio in the mixed gas during plasma heating based on the temperature of the molten steel in the tundish, and it is further preferable that nitrogen is used as a gas having a conductivity different from argon. ing.

[0008]

However, there is a limit to the voltage that can be raised only by controlling the atmospheric gas, and when nitrogen gas is used, a problem of nitrogen pickup into molten steel also occurs. An object of the present invention is to provide a method for heating molten steel in a tundish in which the applied power can be further improved by increasing the applied voltage by a simple method.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a method for heating molten steel in a tundish, wherein when a molten steel in a tundish is heated by a twin torch type plasma heating apparatus, an insulating wall or weir is provided between electrodes in the heating chamber. This is a method for heating molten steel in a tundish, characterized by improving the plasma heating capability by increasing the generated voltage by disposing.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Atmospheric gas mainly composed of argon in a heating chamber, although having low conductivity, is not a perfect insulator. Therefore, in the twin torch type plasma heating apparatus, there is a current flowing through a short path in the atmosphere gas in addition to a main current flowing through the molten steel between the two torches. Therefore, the generated voltage is increased by disposing an insulating wall or weir between the electrodes in the heating chamber so as to block the short-path current. Thus, the voltage is further increased under the condition that the current and the torch gap are kept constant, thereby improving the plasma heating ability.

[0011]

FIG. 1 shows an embodiment of the present invention. In this embodiment, an insulating wall 10 is provided between the electrodes of the heating chamber 2.

The control of the applied power by this configuration is performed as follows. When the target temperature of the molten steel is set, the arithmetic and control unit 16 first controls the thyristor of the power supply device 6 according to the difference from the measured value of the molten steel thermometer 11 to increase or decrease the current. Subsequently or simultaneously, the torch elevating device 12 is controlled to change the voltage. In this way, current and voltage control are performed as needed, and the molten steel temperature is maintained near the set temperature.

Next, the test results of the present invention will be described. In this test, it is possible to increase the applied voltage and increase the applied power by installing the insulating wall 10 between the electrodes in the heating chamber 2 as shown in FIG. Table 1 shows the results. In the example of the present invention, the applied voltage can be increased by 7.9% by increasing the applied voltage by 7.9%. The same effect can be obtained by forming the insulating wall 10 provided between the electrodes in the heating chamber 2 as a weir having a structure immersed in molten steel.

[0014]

[Table 1]

[0015]

According to the present invention, the applied power can be increased by further increasing the voltage under the condition that the current and the torch gap are kept constant, and the plasma heating ability can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a conventional heating method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tundish 2 Heating chamber 3 Cathode side plasma torch 4 Anode side plasma torch 5 Molten steel 6 Power supply device 7 Plasma arc 8 Long nozzle 9 Casting device 10 Insulating wall 11 Molten steel thermometer 12 Torch elevating device 13 Plasma arc length detector 14 Heating chamber sealing gas 15 Atmospheric gas adjustment device 16 Operation controller 17 Flow meter

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Keisuke Fujisaki 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (72) Inventor Kosaku Tamura 20-1 Shintomi Futtsu City Nippon Steel Corporation Technology Development Division F-term (reference) 3K084 AA09 AA12 BD03 BD05 4E014 AA01

Claims (1)

[Claims] In the method for heating molten steel in a tundish, when a molten steel in a tundish is heated by a twin torch type plasma heating device, an increased voltage is generated by disposing an insulating wall or a weir between electrodes in a heating chamber. A method for heating molten steel in a tundish, characterized by improving the plasma heating ability by causing the steel to be heated.