JPH1110291A - Method for preheating tundish - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a preheating method for a tundish applied with coating material containing the moisture on the surface in the tundish with a plurality of gas burners without explosion of the coating material and separation, in a continuous casting of molten steel. SOLUTION: At the time of preheating the tundish, the combustion is executed at the air fuel ratio so that adiabatic-theoretical combustion temp. of the burner becomes <=1330 deg.C. Thereafter, after the back surface temp. of the coating material becomes >100 deg.C, the preheating for accumulating the heat in the refractory is executed. By this preheating method for the tundish, the stripping- off of the coating material is fully prevented and the casting operation is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for preheating a tundish.

[0002]

2. Description of the Related Art In continuous casting of molten steel, at the start of casting, molten steel is poured from a ladle into an empty tundish in which the surface of a refractory has been preheated, and after the amount of molten steel in the tundish exceeds a predetermined amount, It is customary to start pouring from the tundish into the mold. At this time, the temperature of the molten steel in the tundish, particularly the temperature in the vicinity of the injection portion into the mold, is reduced, and the nozzle for injecting the molten steel from the tundish into the mold is clogged, thereby causing a large trouble in operation and quality.

In recent years, from the viewpoint of reducing the cost of refractories of a tundish, a coating material mainly composed of MgO has been applied to the inner surface of the tundish. However, a drying step is required. A problem occurred in that the coating material exploded during preheating, and the only way to achieve both the enhancement of heat storage in the refractory and the drying of the coating material was to increase the preheating time, which hindered productivity.

To solve such a problem, Japanese Patent Laid-Open Publication No.
In 52-116731, an electric resistor is buried in the vicinity of the injection part, heated locally by electric resistance heating, separates coating material drying and refractory heat storage, and attempts to prevent the temperature of molten steel from dropping. In this method, strong local heating can be achieved, but the cost is increased because the electric resistor is expensive.

In Japanese Patent Application Laid-Open No. Hei 7-204807, an initial heat input is 34,000 kcal / m ² / hr or less, and heating is performed for 30 minutes or less.
A tundish preheating method has been proposed in which preheating is performed with a refractory heat input of l / m ² / hr or more, and preheating is terminated when the refractory surface temperature reaches 1100 ° C. or more. The problem with this method is that, depending on the thickness of the coating material, the drying of the water inside the coating material is insufficient in the initial 30 minutes, and the coating material explodes during the subsequent strong preheating. In addition, when preheating with a low heat capacity is performed in order to avoid explosion, the preheating time becomes redundant, thereby reducing productivity.

[0006]

SUMMARY OF THE INVENTION
In the present invention, a plurality of gas burners, when preheating a tundish refractory in which a coating material containing water is applied to the inner surface of the tundish, without increasing the cost,
We propose a method for preheating tundish that does not cause blasting of the coating material.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to advantageously solve the above-mentioned object, and the gist of the present invention is that a plurality of gas burners contain water on the inner surface of a tundish. When preheating the refractory tundish with the coating material applied, the burner is burned at an air-fuel ratio so that the adiabatic theoretical burning temperature of the burner is 1330 ° C or less, and then the back surface temperature of the coating material exceeds 100 ° C. The present invention relates to a method for preheating a tundish, which comprises performing preheating for storing heat in a refractory from the ground.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of a detailed investigation of the drying and temperature of the inner surface coating material of a tundish, the present inventors found that when the coating material surface temperature reached 1000 ° C. or more, the temperature of the back surface of the coating material increased. It was found that when the temperature was below 100 ° C (water was not completely evaporated), the coating material exploded. FIG. 5 shows the range of the coating material explosion. This is because when the surface temperature of the coating material is 1000 ° C or more, the temperature gradient in the thickness direction of the coating material becomes too large, and the moisture inside the coating material is rapidly heated and evaporated, so that the vapor pressure exceeds the coating material strength. It is considered to explode or peel off.

In the preheating burner combustion method for satisfying this condition, it is important to preheat the flue gas itself without raising the temperature to 1000 ° C. or more. Therefore, the adiabatic theoretical combustion temperature was determined as an index indicating the temperature of the combustion exhaust gas, and the temperature of the combustion exhaust gas was also examined in consideration of the decrease in the temperature of the combustion exhaust gas due to the heat input to the coating material. As a result, it was found that the heat transfer efficiency from the burner to the coating material was about 25%, and the remaining 75% was used as exhaust gas sensible heat.
Accordingly, as shown in FIG. 6, in order to reduce the exhaust gas temperature to 1000 ° C. or less, if the air-fuel ratio with respect to the fuel used is set so that the adiabatic theoretical combustion temperature is 1330 ° C. or less, the coating material peeling will not occur. Does not occur. In the COG of the fuel used in this study, if the air-fuel ratio is 10 or more, the coating material does not peel off. Even if the fuel is not COG, the required air-fuel ratio is determined by the adiabatic theoretical combustion temperature theoretically determined for the fuel. This preheating combustion for drying the coating material must be performed until the temperature on the back surface of the coating material exceeds 100 ° C. Since the further drying process is useless, the time required for drying is clarified. It is possible to suppress the redundancy of the preheating time. The preheating time is set in advance by burying a thermocouple on the back of the coating material and measuring the temperature on the back of the coating material during the drying process.
As a result of examining the time when the temperature exceeds the value, it was found that the back surface temperature of the coating material can be increased to more than 100 ° C. in 2 hours. Thus, in the actual preheating operation, the coating material drying step is performed for 2 hours, and it is not necessary to bury the thermocouple on the back surface of the coating material every time. After the drying time, it is not necessary to consider the explosion due to the moisture of the coating material, so the preheating that increases the refractory surface temperature with as high a heat load (high fuel flow rate, low air-fuel ratio) as possible and stores the refractory in the tundish carry out.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a plan view showing an example of the shape of a tundish to be preheated and the arrangement of burners, where 1 indicates a tundish. 2 indicates a COG pipe, and 3 indicates a burner. FIG. 2 shows an example of the refractory lining structure of the tundish 1. The material is SiO2 quality clay brick perm bricks 5a, the material is SiO ₂ quality clay brick perm bricks 5b, the wear bricks 6 material is medium alumina bricks _{(Al 2 O 3: 40~50%} ,
The remaining SiO ₂ ) and the coating material 7 are mainly made of MgO. The back surface temperature of the coating material specified in the present invention is, as shown in the example of FIG.
The temperature of the coating material back surface portion 8, which is a position between the wear brick 6, and the coating material surface temperature, means the temperature of the coating material surface portion 9 corresponding to the inner surface of the tundish.

Next, the preheating condition of the tundish according to the present invention will be described with reference to FIGS. 3 (a), 3 (b) and 3 (c) together with the conventional method which is the preheating condition described in JP-A-7-204807. Will be explained. In the conventional preheating, as shown in FIG.
Perform low heat load preheating for the drying process in the initial 30 minutes,
After that, high heat load preheating for refractory heat storage is performed, and as shown in FIG. 3 (b), preheating is performed at an air-fuel ratio = 7. Further, as shown in FIG. 3 (c), the adiabatic theoretical combustion temperature is constant at 1820 ° C. because the air-fuel ratio is constant. In the preheating method of the present invention, in addition to the low heat load, combustion at a high air-fuel ratio (air-fuel ratio = 11) is performed for 2 hours when the coating rear surface temperature exceeds 100 ° C. (Fuel ratio = 7) to achieve refractory heat storage. Figure 4 shows the behavior of the backside temperature of the coating material. In the conventional preheating pattern, the backside temperature of the coating material did not reach 100 ° C during the preheating with the initial low heat load, and the coating material exploded due to the subsequent preheating with a high load. doing. On the other hand, in the preheating method of the present invention, the coating backside temperature exceeds 100 ° C in two hours due to the low air-fuel ratio low heat load preheating of 2 hours, and no explosion occurs even if the high heat load preheating is performed. No preheating operation has been realized.

<Example> Tundish preheating was carried out by a tundish preheating apparatus having the structure shown in FIG. This tundish is for three strands and has a tundish inner surface area of 22m2. The tundish refractory lining is shown in FIG. There are three preheating burners, the fuel for preheating is COG, and the combustion heat is 4500 kcal / Nm ³
It is. For comparison with the conventional method, the preheating condition is shown in FIG.
The test was performed for 5 hours at the COG flow rate and air-fuel ratio shown in (a) and (b). In addition, as the combustion of the burner alone, COG is supplied at a flow rate obtained by dividing the COG flow rate by the number of burners 3, and the air flow rate corresponding thereto is obtained by multiplying the COG flow supplied to the burner alone by the air-fuel ratio. Burning.

Each of the conventional method and the method of the present invention was carried out 100 times, and the state of the coating material explosion and peeling in the tundish was visually inspected. The results are shown in FIG. 7 which shows the explosion rate of the coating material of the present invention and the conventional method. In the conventional method,
While the coating material explosion occurred seven times, in the method of the present invention, no coating material explosion occurred.

[0014]

As described above, according to the present invention, even when the coating material is applied to the inner surface of the tundish,
Drying and heat storage of the coating material of the tundish are possible without explosion and peeling of the coating material.

[Brief description of the drawings]

FIG. 1 is a plan view of a tundish and a diagram showing a preheating burner arrangement in an embodiment of the present invention.

FIG. 2 is a view showing a refractory lining structure of a tundish.

FIG. 3 (a) is a diagram showing a COG flow pattern of the present invention and a conventional tundish preheating method. (b) is a figure which shows the air-fuel ratio pattern of this invention and the conventional tundish preheating method. (c) is a diagram showing the theoretical adiabatic combustion temperature of the present invention and the conventional tundish preheating method.

FIG. 4 is a diagram showing a coating back surface temperature behavior in the present invention and a conventional tundish preheating method.

FIG. 5 is a diagram illustrating a coating material explosion range during preheating of a tundish.

FIG. 6: Adiabatic theoretical combustion temperature and exhaust gas sensible heat with respect to air-fuel ratio
It is a figure which shows the exhaust gas temperature at the time of 75%.

FIG. 7 is a diagram showing the rate of occurrence of a coating material explosion during preheating of a tundish according to the present invention and a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tundish 2 COG piping 3 Burner 4 Steel 5a Perm brick 5b Perm brick 6 Wear brick 7 Coating material 8 Coating material back surface 9 Coating material surface

Claims (1)

[Claims] When preheating a tundish refractory in which a coating material containing water is applied to the inner surface of a tundish with a plurality of gas burners, the adiabatic theoretical combustion temperature of the burner is set to 1330 ° C. or less. A preheating method for a tundish, comprising performing combustion at an air-fuel ratio, and then performing preheating for storing heat in the refractory after the back surface temperature of the coating material exceeds 100 ° C.