JPH09122854A - Preheating method of tundish for continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To preheat the tundish so that erosion due to overheating is not caused to a refractory in the tundish prior to casting of molten steel and nozzle clogging is not caused to a nozzle hole at the beginning of casting. SOLUTION: In a heat pattern in which a refractory 3 lined to the inner face of shell 2 is heated prior to casting, after the refractory is heated with the max load that is the max gas flow rate of fuel gas to be supplied to a preheating burner which is arranged to a cover 5 facing downward, heat holding is maintained with a fuel gas quantity of >=50% of the max load, further, the refractory is heated with a fuel gas quantity of >=70% of the max load at least 30min prior to casting start and then casting is started.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is for continuous casting in which a tundish having a role of a molten steel buffer, which is located between a ladle and a mold of a continuous casting facility, is heated by a preheating burner before casting. It relates to a method of preheating a tundish.

[0002]

2. Description of the Related Art A tundish used in continuous casting is an intermediate container located between a ladle and a mold, which serves as a buffer when supplying molten steel from a large-capacity ladle to the mold. Also, in the case of a continuous casting machine of several strands, in addition to the role of distributing molten steel to multiple molds while adjusting the opening of the sliding nozzle from multiple upper nozzles provided at the bottom of the tundish, Has the role of floating separation of non-metallic inclusions.

A tundish having such a role is
It has a structure in which the inner surface of the iron skin is lined with a refractory, and if the tundish refractory is damaged by continuous casting with multiple charges, after repairing the damaged refractory, dry and preheat it with the combustion gas of the burner and use it. There is. Further, as a cost reduction measure, the tundish is hot-used many times without deteriorating the quality of continuously cast slabs. If the tundish is hot reused as it is, the inclusions of the slab increase due to the residual steel and slag and the quality deteriorates. For this reason, tundish, which is generally hot-reused, discharges the steel and slag remaining in the tundish after the end of casting, and uses the waiting time to heat up with combustion gas from the burner and reuse it. (See, for example, Japanese Patent Laid-Open Nos. 4-22567 and 4-238656).

In this way, the tundish is preheated before the start of continuous casting in order to minimize the temperature drop of the molten steel injected into the tundish from the ladle and to keep the tundish above the tundish. This is to prevent a hole including the nozzle hole and the sliding nozzle hole (hereinafter referred to as a nozzle hole) from being blocked by solidification of molten steel. By the way, in the case of a tundish with a capacity of 20 to 40 tons, the refractory surface temperature in the tundish is 1000 to 11 depending on the volume of the tundish.
It is generally set to 00 ° C.

Further, the heat pattern is such that the burner load is increased to 100% and maintained for 0.5 to 1 hour from the start of heating by the combustion flame (flame) of the preheating burner, and thereafter,
It is customary to reduce the burner load to 50% and keep the heat to wait for casting. This heat pattern is changed depending on the repair condition of the refractory in the tundish, that is, the proportion of the new refractory, etc., but before the casting, any heat pattern has the heat retention mode.

In any case, what the heat pattern should be is that the refractory surface in the tundish has risen to a predetermined temperature within a predetermined time. At that time, it is important to heat not only the refractory surface in the tundish but also the inside of the nozzle hole connecting the tundish and the immersion nozzle to a predetermined temperature.

[0007]

When the heat pattern having the heat retention mode by the above-described prior art burner is used, the refractory surface temperature in the tundish reaches a predetermined temperature, but the temperature of the nozzle hole does not rise. At worst,
There is a problem that the nozzle is clogged and normal casting is hindered. In addition, if the burner load is maintained at 100% without performing the heat retention mode to raise the temperature of the nozzle holes, there is a problem that the refractory in the tundish is overheated and the refractory melts. .

The present invention solves the above-mentioned problems of the prior art, and ensures that the refractory material in the tundish is not overheated and that the nozzle holes are heated without fail so as not to cause nozzle clogging. It is an object of the present invention to provide a method for preheating a tundish for continuous casting capable of achieving the above.

[0009]

The present invention has been made based on the results of various studies on a heat pattern for preheating a tundish, particularly a heat retention mode thereof, and the gist thereof is as follows. It is as follows. The present invention, a tundish having a role of a buffer of molten steel located between the ladle and the mold of the continuous casting equipment, in the preheating method of the continuous casting tundish for heating using a preheating burner before casting, Based on the heat pattern of raising the temperature of the tundish before casting, after heating with the max load which is the maximum flow rate of the fuel gas supplied to the preheating burner, it is maintained with a fuel gas flow rate of 50% or less with respect to the max load. A method for preheating a tundish for continuous casting, characterized in that heat is maintained and the temperature is raised at a fuel gas flow rate of 70% or more of the max load at least 30 minutes before the start of casting.

[0010]

According to the present invention, heat is raised at a max load, which is the maximum flow rate of the fuel gas supplied to the preheating burner, and then heat retention is performed at a fuel gas flow rate of 50% or less of the max load. The temperature of the nozzle hole was maintained while preventing overheating of the refractory in the tundish because it was maintained and heated at least 30 minutes before the start of casting at a fuel gas flow rate of 70% or more of the max load. It is possible to prevent a decrease in temperature and to perform continuous casting at a stable molten steel temperature without causing nozzle clogging at the start of casting.

FIG. 2 shows a preheating heat pattern of the tundish. In Fig. 2, when the preheating burner is ignited to start the heat up, the burner load is increased linearly within a short time at a steep gradient, and the burner load is maintained at 100% to heat up the tundish for the required time. . And line A shows the burner load
Shows the mode in which the temperature is reduced from 100% to 50% to retain heat, and casting is started as it is. Straight line B shows that after heating the tundish with the burner load maintained at 100% for the required time,
Shows the mode in which the burner load is reduced from 100% to 70% to raise the temperature and then casting is started. Furthermore, straight line C is held at 100% burner load for the required time, and once the tundish is heated, it is once lowered to 50% burner load shown by straight line A and held, but the burner load is increased to 70% 30 minutes before the start of casting. , A mode in which casting is started after the heat is raised in a state in which the combustion flame goes out from the nozzle hole.

When the tundish was preheated in the pattern according to the mode of the straight line A, nozzle clogging frequently occurred in the nozzle holes of the tundish. In this case, the combustion frame of the preheating burner was not generated from the nozzle hole, and the temperature rise of the nozzle hole was insufficient. Further, when the tundish was preheated in the pattern according to the mode of the straight line B, the refractory in the tundish was overheated, and melting of the refractory was confirmed.

From the above experimental results, when the burner opening such that the combustion frame of the preheating burner is generated from the nozzle hole of the tundish was obtained from the actual tundish,
It was found that the burner load was 70%, and as a result, the pattern according to the mode of the straight line C, that is, the burner load was 100%.
% To 50% to keep the tundish warm and increase the burner load to 70% 30 minutes before the start of casting without overheating the refractory in the tundish and without clogging the nozzle holes. A heating pattern could be obtained.

The duration of heating with a burner load of 70% was determined to be 30 minutes by measuring the temperatures of the tundish refractory and the nozzle holes. This is because the combustion frame of the preheating burner occurs in the nozzle hole at a burner load of 70%, and overheating of the tundish can be prevented even at a burner load of 100% 30 minutes before the start of casting. For this reason, it is the basis for a heat pattern in which the fuel gas flow rate is increased to 70% or more of the burner max load at least 30 minutes before the start of casting.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a vertical section of a continuous casting tundish located between a ladle and a mold. As shown in FIG.
A tundish body 4 with a capacity of 40 tons, in which the refractory 3 is lined on the inner surface of the iron skin 2, is covered with a lid 5, and the tundish body 4 is placed from above by using preheating burners 1 installed at two positions of the lid 5 downward. It is designed to heat refractory lining. An upper nozzle 6 is provided at the bottom of the tundish body 4, and a sliding nozzle 7 is arranged below it. For the preheating burner 1 installed at the preheating position, COG is used as combustion gas, and the maximum amount of fuel gas flow per burner (max load) =
It can supply 700 Nm ³ .

FIG. 2 compares the heat pattern C of the present invention example with the heat pattern B of the conventional example A and the comparative example. In the heat pattern C of the present invention, the preheating burner is ignited to burn the fuel gas and the burner load is taken for about 30 minutes.
After reaching 100% and heating the tundish for 20 minutes, the burner load was reduced to 50% and heat was maintained for 40 minutes. Then, 30 minutes before the start of casting, the burner load was increased to 70% and the temperature was raised for 30 minutes to start casting.

On the other hand, the conventional example (heat pattern A)
Then, after raising the burner load by 100% in the same manner, the burner load was reduced to 50% and the heat retention of the tundish was continued for 70 minutes until the start of casting. In the comparative example (heat pattern B), After similarly heating the load at 100%, the burner load was reduced to 70% and heating of the tundish was continued for 70 minutes until the start of casting.

In the example of the present invention according to the pattern C, the refractory surface could be heated to a predetermined temperature of 1000 to 1100 ° C. without melting the refractory in the tundish. In addition to preventing nozzle clogging by lowering the temperature of the upper nozzle holes and sliding nozzle holes, casting could be started without lowering the molten steel temperature. As a result, not only the burden on the equipment for heating the molten steel can be reduced, but also the temperature for continuous casting can be lowered, and the cost of raw materials for refining systems such as converters and degassing equipment can be reduced.

In comparison with this, in the conventional example of the heat pattern A, the molten steel temperature decreased due to insufficient preheating of the tundish, especially the temperature of the nozzle hole was low, and nozzle clogging frequently occurred in which the molten steel solidified at the beginning of casting. . Further, in the comparative example of the heat pattern B, the refractory in the tundish was overheated and refractory melting loss occurred. This increased the frequency of repairs due to melting of the refractory material, and increased repair costs.

[0020]

As described above, according to the present invention, in the heat pattern for raising the temperature of the tundish before casting, after raising the temperature with the max load which is the maximum flow rate of the fuel gas supplied to the preheating burner, For the max load
The heat retention is continued by the fuel gas flow rate of 50% or less, and the temperature is raised to a fuel gas flow rate of 70% or more of the max load at least 30 minutes before the start of casting. As a result, the refractory in the tundish can be preheated to a predetermined temperature without being melted and the casting can be started without the nozzle hole being clogged.

As a result, the burden on the equipment for heating the molten steel can be made relatively low, and the temperature for continuous casting can be lowered, so that the cost of raw materials for refining systems such as converters and degassing equipment can be reduced. To be done.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing a tundish for continuous casting equipped with a preheating burner according to the present invention.

FIG. 2 is a graph showing a heat pattern for preheating a continuous casting tundish in comparison with the examples of the present invention, conventional examples and comparative examples.

[Explanation of symbols]

 1 Preheat burner 2 Iron skin 3 Refractory 4 Tundish body 5 Lid 6 Upper nozzle 7 Sliding nozzle

Claims (1)

[Claims] 1. A method for preheating a tundish for continuous casting, in which a tundish having a role of a buffer for molten steel located between a ladle and a mold of a continuous casting facility is heated by a preheating burner before casting. Based on a heat pattern for heating the tundish before casting, after heating with a max load that is the maximum flow rate of the fuel gas supplied to the preheating burner, the fuel gas flow rate is 50% or less with respect to the max load. A preheating method for a continuous casting tundish, characterized in that the heat retention is continued and the temperature is raised at a fuel gas flow rate of 70% or more of the max load at least 30 minutes before the start of casting.