JPH0318979B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for heating a tundish immersion nozzle in continuous molten steel casting equipment.

As shown in Fig. 1, the continuous casting equipment includes a ladle 10,
It is equipped with a tundish 12, a mold 14 of a continuous casting machine, a tundish immersion nozzle 16, etc., and a ladle 1.
A tundish 12 receives molten steel 18 from 0, and the molten steel is poured into a mold 14 through an immersion nozzle 16 to form a slab 20. The molten steel in the tundish 12 needs to be heated for the following reasons, and for this purpose the plasma torch 22, its power source 24, and anode electrode 26 are provided.

Taking the length of continuously cast slab 22 as the horizontal axis,
The relationship between the length of the slab and the casting temperature is shown in FIG. 3, with the casting temperature taken as the vertical axis. That is, periodic fluctuations are observed in the casting temperature. This is ladle 1
This is caused by periodic charging of the tundish 12 by 0, and when this charging is performed, the temperature of the molten steel rises, and as time passes, casting progresses and the molten steel decreases.During this period, the molten steel temperature decreases, and then When charging is performed again, the temperature of the molten steel rises, and this process is repeated thereafter. Even if the molten steel temperature and hence the casting temperature are lowered, they must of course not fall below the solidification temperature. Therefore, unless the tundish interior is heated so that the previous molten steel temperature is higher than the solidification temperature, the ladle molten steel temperature and therefore the converter tapping temperature must be increased. This results in increased costs, etc. By heating the tundish, it is possible to prevent the temperature of the molten steel from decreasing, thereby eliminating the need to increase the temperature of the steel being discharged from the converter.

Further, the temperature of the molten steel in the tundish must not be below the solidification temperature, or it is desirable that it be as close to the solidification temperature as possible. This is because when the molten steel temperature is high, the slab first solidifies from the outer periphery, and the solidification gradually spreads to the center, causing center segregation and deteriorating the quality of the slab. On the other hand, if the molten steel temperature is close to the solidification temperature, solidification will of course start from the outside, but it will also solidify relatively quickly in the center, leaving no room for center segregation and making it difficult to obtain high quality slabs. Can be done. Heating within the tundish is effective in keeping molten steel close to the solidification temperature. There is also a demand for mixing appropriate substances into molten steel for refining, and heating molten steel in a tundish is effective for this purpose as well.

The plasma torch 22 heats the molten steel in the tundish for the above-mentioned purpose. As shown in the figure, the plasma torch 22 blows a plasma arc 22a toward the steel in the tundish, and the current path connects the torch 22, the plasma arc 22a, and the molten steel 18. , anode 26, and power source 24, which merely heat the molten steel in the tundish. However, the plasma torch requires a large current of, for example, 5000 A, and the power source 24 requires a large capacity one. On the other hand, heating is also required for the submerged nozzle 16. This is because the molten steel may cool while passing through the immersion nozzle and adhere to the inner wall of the nozzle, clogging the nozzle. To avoid this, it is necessary to raise the molten steel temperature, so the temperature at which the steel is tapped from the converter is increased. Alternatively, it is necessary to perform sufficient tundish heating, and since the molten steel temperature is high, there are problems such as the aforementioned center segregation. Furthermore, if molten steel is cooled while passing through an immersion nozzle, even if the molten steel does not solidify, non-metallic inclusions such as alumina may precipitate or adhere to the molten steel, which can also cause nozzle blockage. invite

Heating the submerged nozzle is preferred to avoid such problems. However, if a nozzle heating power source is used, this also requires a considerably large-capacity power source, resulting in an increase in cost and is economically problematic. Therefore, the present invention attempts to extremely easily heat the nozzle by using the plasma arc power source 24. The present invention is a heating method for a immersed nozzle of a tundish in continuous casting equipment in which molten steel is heated by a plasma torch, in which an anode for the plasma torch, which is a cathode, is attached to the immersed nozzle, and the plasma torch, plasma arc, and tundish are heated from a plasma talk power source. The method is characterized in that a current path is formed through the molten steel in the immersed nozzle, the immersed nozzle, and the anode to the power source, and the immersed nozzle is electrically heated. Next, this will be explained with reference to examples.

FIG. 2 shows an embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. As can be seen from a comparison with FIG. 1, in FIG. 2 the anode 26 is attached to the submerged nozzle 16. In the present invention, since the submerged nozzle 16 is electrically conductive, the anode 26 only needs to be attached to the outer periphery of the submerged nozzle 16. In this way, the current path of the plasma torch 22 is the torch 22, the plasma arc 22a, the molten steel 18 in the tundish 12 and the nozzle 16, and the nozzle 1.
6. The anode 26 and the power source 24 are used, and the nozzle is heated by direct energization, which prevents the molten steel from cooling, solidifying, and precipitation of inclusions, and making it possible to set the molten steel temperature to a low temperature on the verge of solidification. Become. As a result, high-temperature tapping of the converter and high-temperature heating in the tundish are no longer necessary. It is said that the difficulty of manufacturing a plasma torch increases in proportion to the fourth power of the current, so the effect of reducing tundish heating is significant.

Since the purpose of the tundish and nozzle heating is to correct the casting temperature fluctuations as shown in Figure 3 and control the temperature to a constant level slightly above the solidification temperature, it is considered to perform feedback control by detecting the molten steel temperature. However, since the pattern is constant, open-loop heating control that follows a predetermined curve may be used. As an example, the apparatus shown in FIG. 2 was used, the immersion nozzle was made of alumina graphite refractory, and the plasma arc current was 3000A. Power consumption in the immersion nozzle, therefore heating power is 3000A x 20V = 60KW
It was hot. After four consecutive castings, the cross section of the immersion nozzle was observed, and the amount of nonmetallic inclusions attached to the inner wall was reduced to 1/3 compared to the case without heating.

As explained above, according to the present invention, nozzle heating can be performed simply by changing the anode position.
The casting temperature can be kept low to the extent that solidification and inclusion segregation do not occur, and this is extremely effective as it avoids problems such as damage to converter refractories, difficulty in plasma torch design, and center segregation due to high temperatures. be.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional method, FIG. 2 is an explanatory diagram showing an embodiment of the present invention, and FIG. 3 is a graph showing fluctuations in casting temperature. In the drawing, 22 is a plasma torch, 18 is molten steel, 1
2 is a tundish, 16 is an immersion nozzle, 24 is a plasma arc power supply, 22a is a plasma arc,
26 is an anode.

Claims (1)

[Claims] 1. In a heating method for a immersion nozzle of a tundish in a continuous casting facility in which molten steel is heated with a plasma torch, the anode for the plasma torch, which is a cathode, is attached to the immersion nozzle, and the plasma torch, plasma arc, tundish and immersion are heated by a plasma arc power source. A method for heating a tundish immersion nozzle, comprising forming a current path through molten steel in the nozzle, an immersion nozzle, and an anode to the power source.