JPH07204807A - Method for preheating tundish - Google Patents

Abstract

PURPOSE:To prevent the clogging of a nozzle without increasing a cost and to reduce the consumption of preheating gas by preventing the clogging of the nozzle at the initial stage of continuous casting process with a specific preheating method of a tundish. CONSTITUTION:At the time of preheating the tundish refractory with plural gas burners, heat input rate to the refractory is made to <=34000kcal/m<2> for 30min after starting the preheating and successively, the preheating is executed at >=90000kcal/m<2>, and when the surface temp. of the refractory can be secured at >=1100 deg.C, the preheating is completed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for preheating a tundish.

[0002]

2. Description of the Related Art In continuous casting of slabs, molten steel is injected from a ladle into an empty tundish preheated to a surface temperature of refractory of about 900 ° C. at the start of casting so that the amount of molten steel in the tundish exceeds a predetermined amount. After that, it is customary to start the injection from the tundish into the mold.

At this time, the temperature of the molten steel in the tundish, especially the temperature in the vicinity of the injection portion into the mold, is lowered, and the nozzle for injecting the molten steel from the tundish into the mold is clogged, which causes a serious trouble in operation. .

In order to prevent such nozzle clogging, Japanese Patent Laid-Open Nos. 1-138046 and 3-128156
Japanese Patent Publication has been proposed.

The former is a method of bubbling near the mold injection part of the tundish and stirring the molten steel to secure the temperature of the molten steel in this part. In this method, a refractory for bubbling is required, which increases the cost. Cause

In the latter case, a hollow weir is arranged in the tundish, and the molten steel flow is squeezed by this weir to increase the molten steel flow rate, so that the molten steel having an increased flow rate can be supplied to the vicinity of the mold injection portion, and the molten steel temperature can be increased. Although it is intended to prevent lowering and to prevent nozzle clogging, it is necessary to construct a weir in the tundish, which causes an increase in cost.

[0007]

In view of the above, the present invention provides a method capable of reducing the preheating gas without increasing the cost by devising a method for preheating the nozzle clogging at the initial stage of casting, by preheating the tundish. .

[0008]

The present invention has been made to advantageously solve the above-mentioned object, and its gist is to preheat tundish refractories with a plurality of gas burners. , Refractory heat input 3 after starting preheating
The tank is characterized by preheating with refractory heat input of 90,000 kcal / m ² , hr or more for 3 minutes and 34,000 kcal / m ² or less for 0 minutes, and ending preheating when the refractory surface temperature of 1100 ° C or more can be secured. Regarding preheating method of dish.

[0009]

The present inventors have investigated in detail the relationship between the nozzle clogging and the temperature of the refractory inside the tundish when pouring molten steel into the mold from the tundish in the early stage of casting.
It has been found that when the refractory surface temperature is 1100 ° C. or higher, the molten steel is supplied from the ladle to eliminate the occurrence of nozzle clogging.

Moreover, it has been found that the surface temperature may be 1100 ° C. or higher regardless of the heat retention of the entire refractory.

On the other hand, for the preheating of the tundish refractory, it is common practice to use COG at integrated steelworks to heat the interior of the refractory to a high temperature, reduce the temperature distribution, and increase the heat capacity before use. Is to prevent peeling phenomenon 34
² at a refractory heat input of 000 kcal / m ² or less
Preheated for 3 hours and heated inside, then 67500 kcal
/ M ² , heat for about 4 hr with refractory heat input of about hr,
The internal temperature was raised and a surface temperature of about 900 ° C. was secured before use.

Here, the inventors of the present application have conducted various experiments in connection with the exfoliation of the refractory to determine whether such a conventional heating pattern is absolutely necessary.
It was found that the heat input of the refractory material of 00 kcal / m ² , hr or less was sufficient for heating for 30 minutes or less.

Thereafter, in order to preheat the surface temperature to 1100 ° C. or more, the refractory heat input amount is 135,000 kcal / m ² , hr
Although it has been found that peeling due to heat shock does not occur even with the above, even if a large amount of heat is supplied, it is not effectively used to raise the temperature of the refractory material, resulting in waste.

In order to raise the temperature effectively without waste, it is convenient that the refractory heat input amount is 90,000 kcal / m ² , hr or more, and the upper limit is 135,000 kcal / m ² , hr.

Although the upper limit of the preheating end temperature is not particularly limited,
For the purpose of preventing nozzle clogging in the initial stage of casting in the present invention, heating may be performed to the molten steel temperature.

Needless to say, the fuel used for preheating is not limited to COG and may be LPG.

[0017]

EXAMPLE FIG. 1 is a plan view showing the shape of a tundish to be preheated and the arrangement of burners, and 1 is a tundish of two vessels type (H type) tundish with a capacity of 60 t,
The refractory surface area is 40 m ² . 2 is a COG pipe, 3 is a burner, and a total of 8 are arranged.

The lining refractory structure of the tundish 1 is shown in FIG.
Shown in.

The material of the perm brick 5a is SiO ₂ clay clay brick, the material of the perm brick 5b is SiO ₂ clay brick, and the material of the wear brick 6 is medium alumina brick (Al ₂
O _3: 40~50%, the material of the remaining SiO _2), the coating material 7 is using MgO principal.

The tundish is preheated after the partial repair of the coating material 7 from the refractory surface temperature of 60 ° C. to the heating pattern shown in FIG. 3 according to the new method until the surface temperature of 1100 ° C. is secured, and the conventional method is 900 ° C. Each pattern was preheated until secured.

FIG. 4 shows the temperature distribution inside the refractory in each pattern. In the conventional pattern, the temperature inside the refractory increases, but the temperature in the vicinity of the refractory surface rises only up to about 900.degree.

On the other hand, in the new pattern, the internal temperature of the refractory is lower than that of the conventional pattern, but the temperature in the vicinity of the refractory surface can rise to 1100 ° C. or higher, and the refractory is peeled off. There wasn't.

FIG. 5 shows the amount of temperature drop of molten steel in the tundish at the initial stage of casting, that is, at the timing of occurrence of nozzle clogging trouble, in each preheating pattern.

The new pattern can increase the molten steel temperature in the vicinity of the mold injection portion in the tundish by 5 ° C. as compared with the conventional method.

FIG. 6 shows the frequency of occurrence of initial clogging. What happened 5 times a year in the conventional pattern, but 0 in the new pattern
It has become possible to set the times / year.

FIG. 7 shows the amount of gas used in the conventional pattern and the new pattern. Compared with the conventional pattern, the new pattern can significantly reduce the amount of gas used.

[0027]

As described above, only the temperature of the refractory surface is
By performing the preheating to secure at 1100 ° C or higher, it is possible to prevent the occurrence of nozzle clogging in the initial stage of casting.

This method does not require the use of a special refractory material or a weir so that there is no increase in costs associated therewith, and since the amount of gas used can be reduced, the total cost can be kept lower than the conventional method.

In addition, the number of tundish stocks can be reduced by shortening the preheating time.

[Brief description of drawings]

FIG. 1 is a plan view of tundish used in Examples of the present invention and Comparative Examples and an explanatory view showing a preheating burner arrangement.

FIG. 2 is a diagram showing a refractory structure with a lining of the tundish of FIG.

FIG. 3 is an explanatory view showing a heating pattern in an example of the present invention and a comparative example.

FIG. 4 is a diagram showing temperature distribution inside and on the surface of the refractory material at the end of preheating in Examples and Comparative Examples.

FIG. 5 is a diagram showing operational results in Examples and Comparative Examples.

FIG. 6 is a diagram showing operation results in Examples and Comparative Examples.

FIG. 7 is a diagram showing operational results in Examples and Comparative Examples.

[Explanation of symbols]

 1 Tundish 2 COG piping 3 Burner 4 Iron skin 5a Perma brick 5b Perma brick 6 Wear brick 7 Coating material

Claims (1)

[Claims] 1. When preheating a tundish refractory with a plurality of gas burners, the refractory heat input is kept at 34,000 kcal / m ² · hr or less for 30 minutes after the start of preheating, and subsequently 90,000 kcal / m ² · hr or more. The preheating method for a tundish, which comprises preheating with the heat input amount of the refractory and ending the preheating when the refractory surface temperature of 1100 ° C. or more can be secured.