JPH07284882A - Twin roll type continuous casting apparatus - Google Patents

Abstract

PURPOSE:To prevent the stickiness of solidified metal caused by surface temp. drop of molten steel and to stably produce a cast strip without defect, such as surface crack, by restraining heat radiation of the molten carbon steel supplied into a molten steel pool part in a twin roll type continuous casting. CONSTITUTION:In a twin roll type continuous casting apparatus for casting the cast strip 4 by supplying the molten carbon steel into the molten steel pool part 3 formed with one pair of casting rolls 1a, 1b, a heat insulating cover 6 covering the upper part of the casting rolls 1a, 1b is arranged and a heating device 8 is arranged in the heat insulating cover 6. A thermometer 9 for detecting the temp. of the heat insulating cover 6 and a thermometer 12 for detecting the molten steel temp. in the molten steel pool part 3 are arranged, and a temp. control device 14 for controlling the heating device 8 is arranged so that the measured temp. with each thermometer 9, 12 corresponds to the setting temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a twin-drum type continuous casting apparatus for directly producing a strip cast from a molten carbon steel, and more particularly to an apparatus for controlling the surface temperature of the molten metal in a molten metal pool within a predetermined range. It is a thing.

[0002]

2. Description of the Related Art In the twin-drum type continuous casting method, the surface temperature of the molten metal in the molten metal pool tends to decrease because no powder is used. Particularly, since the molten metal of carbon steel has a high melting point, solidification proceeds from the surface. Bullion is generated. When this metal is caught between the casting drum and the solidified shell, surface unevenness and plate thickness unevenness occur in the slab due to non-uniform cooling of this part. It may become a hot band, breakout may occur, and the slab may be broken. Even if the metal is not caught, if the metal grows on the surface of the molten metal, it becomes difficult to control the level of the molten metal, and casting may not be continued.

As a method of preventing the temperature of the molten metal in the molten metal pool from decreasing, a reflector 15 is installed above the molten metal pool 3 as shown in FIG. No. 52148) is known. However, in order to obtain a sufficient effect of preventing the generation of metal, it is necessary to set the surface temperature of the reflection plate to about 1000 ° C. or higher, and it is necessary that the reflectance be large when heated to a high temperature of 1000 ° C. or higher. However, the reflection plate 15 is not practical because the surface of the reflection plate 15 is contaminated by gas or the like generated from the molten metal and the reflectance is reduced, and therefore it is necessary to clean the surface of the reflection plate during casting.

As another method for preventing a decrease in the surface temperature of the molten metal in the basin, a method of supplying a heat insulating material to the basin (Japanese Patent Laid-Open No. 2-41741) is known. However, with this method, it is difficult to sufficiently suppress the heat radiation from the molten metal in the hot water pool part, the molten metal is contaminated by the reaction between the heat insulating material and the molten metal, and the strictness according to the level of the heat insulating material Position control is necessary and not practical.

[0005]

SUMMARY OF THE INVENTION In the twin-drum type continuous casting, the present invention suppresses the heat radiation of the molten carbon steel supplied to the molten metal pool portion, so that the generation of the metal due to the decrease of the surface temperature of the molten metal is prevented. It is an object to prevent and stably produce a cast slab without defects such as surface cracks.

[0006]

A twin-drum type continuous casting apparatus of the present invention which solves the above-mentioned problems supplies a molten steel of carbon steel to a molten metal pool portion formed by a pair of casting drums to form a thin strip slab. In a twin-drum type continuous casting device for casting, a heat insulating cover for covering the upper part of the casting drum is provided, a heating device is provided for the heat insulating cover, and a thermometer for detecting the temperature of the heat insulating cover and the molten metal temperature of the hot water pool portion are provided. A thermometer for detecting is provided, and a temperature control device for controlling the heating device is provided so that the temperature detected by each of the thermometers matches a set temperature.

[0007]

According to Stefan-Boltzmann's law, heat transfer due to thermal radiation is generally directly proportional to the fourth power of the temperature of the thermal radiation object (molten metal) and inversely proportional to the thermal emissivity. That is, the radiant heat transfer of the molten metal increases as the temperature difference between the molten metal and the heat receiving surface increases. Therefore, in order to suppress the heat radiation of the molten metal in the molten metal pool, it is effective to increase the temperature on the heat receiving surface side from the molten metal in the molten metal pool. According to the present invention, in order to increase the temperature of the heat receiving surface side from the molten metal in the hot water pool portion, the heat insulating cover is provided above the cooling drum to increase the inner surface temperature (heat receiving surface side) of the heat insulating cover. Thereby, the temperature difference between the molten metal and the heat insulating cover is reduced to suppress the heat radiation from the molten metal, thereby preventing the surface temperature of the molten metal from decreasing.

If a heat insulating cover is provided to cover the upper part of the casting drum, the surface temperature of the heat insulating cover becomes sufficiently high due to heat radiation from the molten steel during normal casting without heating the heat insulating cover. The inner surface temperature of the heat insulating cover is low at the start of casting when the amount of molten metal is small and at a non-steady state such as the end of casting when the molten metal temperature becomes low. Therefore, for temperature compensation during non-steady state, a heating device is provided on the heat insulating cover to heat the heat insulating cover to 1000 ° C. or more before starting casting. After the start of casting, the molten metal temperature inside the pool is continuously detected, and the detected molten metal temperature is compared with the molten metal temperature (set temperature) to prevent the formation of metal on the molten metal surface inside the molten pool. The heating device of the heat insulating cover is controlled so that the molten metal temperature matches the set temperature.

In the twin-drum type continuous casting apparatus, as shown in FIG.
As shown in Fig. 7, a pair of casting drums 1a and 1b that rotate in opposite directions are arranged to face each other, and a pair of side dams 2a and 2b (front side 2b is not shown) are pressed against both end surfaces of the casting drums 1a and 1b. The casting pools 1a, 1b and the side weirs 2a, 2b form the molten metal pool 3 in the section. The molten metal of carbon steel supplied to the molten metal pool portion 3 is cooled at the portions contacting the casting drums 1a and 1b to become solidified shells, and the solidified shells are cast drums 1a and 1b.
And the drums are pressed against each other at the portions where they are closest to each other to form the strip slab 4. In the figure, reference numeral 5 denotes a molten metal injection nozzle.

The heat insulating cover 6 is made of a refractory 7 which can withstand a high temperature of 1000 ° C. or more. The refractory 7 has a porosity of, for example, 50 in order to reduce radiative heat transfer to the inner surface (heat receiving surface) of the cover. % Or more is used. The heat insulating cover 6 has a heating device 8 using an electric heater or an induction heating device, a thermometer 9 for detecting the inner surface temperature of the heat insulating cover 6, and a metal surface level for detecting the metal surface level of the molten metal in the water pool 3. A total of 13 are installed. The tundish 10 is provided with a thermometer 11 for detecting the temperature of the molten metal in the tundish, and the hot pool 3 is provided with a thermometer 12 for detecting the surface temperature of the molten metal in the hot pool.
It is supported and installed by. The thermometers 11 and 12 are
For example, a thermocouple or a radiation thermometer is used. Reference numeral 14 denotes a temperature control device, which is a target level of the molten metal in the pool 3 and a surface temperature of the molten metal in the pool 3 so that no metal is generated and a temperature of the molten metal in the tundish 10 and a heat retention. Each set value of the inner surface temperature of the cover is set.

Before the start of casting, the inner surface temperature of the heat insulating cover 6 measured by the thermometer 9 is the temperature control device 14.
The temperature control device 14 controls the electric power supplied to the heating device 8 so that the measured temperature matches the set temperature, and the heat insulating cover 6 is heated to 1000 ° C. or more by the heating device 8. It At the initial stage of casting, the level of the molten metal in the pool 3 is low, and the surface temperature of the molten metal in the pool 3 is low. Therefore, the molten metal temperature in the molten metal pool 3 continuously detected by the thermometer 12 and the molten metal level continuously detected by the molten metal level meter 13 are:
In the temperature control device 14, each set value is compared, and the temperature control device 14 supplies the heating device 8 with the electric power required for raising the surface temperature of the molten metal in the pool 3 to the set temperature. In the steady state of casting, the above control is continued, but the level of the molten metal in the pool 3 is high, and the surface temperature of the molten metal in the pool 3 is close to the set value. The control of the heat insulating cover 6 by the thermometer 9 hardly operates. At the final stage of casting, the molten metal level in the tundish 10 decreases before the molten metal temperature in the tundish 3 as well as the molten metal level decreases. So thermometer 1
1 and the molten metal temperature and the molten metal level in the tundish 10 which are continuously detected by the molten metal level gauge 13 are compared with each set value in the temperature control device 14, and the molten metal pool 3 from the temperature control device 14. Electric power required to raise the surface temperature of the inner molten metal to the set temperature is supplied to the heating device 8.

As described above, in the steady state of casting, the level of the molten metal in the pool 3 is high, and the surface temperature of the molten metal in the pool 3 is close to the set value. The heating device 8 may be controlled only by the temperature of the molten metal, but at the end of casting, the surface temperature of the molten metal in the pool 3 decreases, so it is necessary to catch this temperature decrease earlier and prevent a control delay. is there. For this purpose, it is desirable to detect the temperature of the molten metal in the tundish and control the heating device 8 according to the detected temperature. Also, the hot water pool 3
When the level of the molten metal decreases, the heat capacity of the molten metal decreases, so that even if the temperature of the molten metal does not decrease, metal is likely to be generated. Therefore, it is desirable to detect the molten metal level and control the heating device 8 in accordance with the detected molten metal level at the early stage or the final stage of casting when the molten metal level is low.

[0013]

Example A molten steel of SS400 was supplied to a twin-drum type continuous casting apparatus to cast a carbon steel slab having a thickness of 3 mm and a width of 1330 mm. Liquidus temperature of this carbon steel is 1530 ℃
(T _LL ), the solidus temperature is 1510 ° C (T _SL ), and the set temperature of the molten metal surface in the molten metal pool is 1540 to 1560 ° C.
And FIG. 3 shows the temperature transition of the surface of the molten metal in the molten metal pool in each Example, and Table 1 shows the casting conditions and casting results.

[0014]

[Table 1]

Example 1 is a comparative example in the case of casting without installing a heat insulating cover. In this case, the metal was generated on the surface of the molten metal at the molten metal pool due to the heat radiation from the surface of the molten metal in the early stage of casting. This metal did not redissolve even in the steady state. At the end of casting, the level of the molten metal decreased, the volume of the molten metal in the pool decreased, and the temperature of the supplied molten metal also decreased. As a result, surface cracks occurred in the slab due to the inclusion of the metal in the slab.

Example 2 is a comparative example in which a heat insulating cover was installed but was cast without heating. In this case, the temperature of the heat insulating cover before the start of casting is room temperature, and the amount of heat released from the surface of the molten metal is large before the temperature of the heat insulating cover rises.
Metal was formed on the surface of the molten metal at the beginning of casting. In the steady state, the initially formed metal gradually remelted, but it was not perfect, and at the end of casting, the level of the molten metal decreased, and the temperature of the supplied molten metal also decreased, so that the metal again formed.
As a result, surface cracks occurred in the cast piece.

Example 3 is an example of the present invention in which the inner surface temperature of the heat insulating cover was heated to 1000 ° C. before the start of casting by using the apparatus shown in FIG. 1 and the molten metal surface temperature in the pool was controlled while casting. is there. Since the heat insulating cover was sufficiently heated in advance, no metal was generated from the start of casting to the end of casting. As a result, a slab having a good surface quality could be stably manufactured.

Example 4 uses the apparatus shown in FIG. 1 to heat the inner surface temperature of the heat insulating cover to 1100 ° C. before starting casting.
It is an example of the present invention cast while controlling the surface temperature of the molten metal in the pool. Also in this example, since the heat insulating cover was sufficiently heated in advance, no metal was generated from the start of casting to the end of casting. As a result, a slab having a good surface quality could be stably manufactured.

Example 5 is a comparative example in which the inner surface temperature of the heat insulating cover was heated to 1000 ° C. before the start of casting by using the apparatus shown in FIG. 1 and the temperature was not controlled during casting. No metal was generated from the start of casting to the steady state, but at the end of casting, the volume of the molten metal in the pool decreased and the temperature of the molten metal supplied to the pool also decreased, so the surface of the molten metal in the pool The temperature dropped and metal was formed. As a result, surface cracks occurred in the cast piece.

As is clear from the above examples, in the present invention, the heating temperature of the heat insulating cover before the start of casting is preferably 1000 to 1100 ° C., and while controlling the surface temperature of the molten metal in the pool. It is a casting. This control is performed by heating the heat retaining cover with an electric heater or an induction heating device as described above, and does not limit the heating means in particular, the point is that the temperature detected by each thermometer of the molten metal and the heat retaining cover is Any heating means that can be controlled to match the set temperature and that matches the mechanical or thermal characteristics of the cover may be used. Further, the shape and arrangement of the heat insulating cover are not particularly limited, but preferably the inner surface has a curvature, is a shape advantageous for radiative heat transfer, and covers the entire molten metal surface, and further The heating device inside the cover may be any array that can uniformly heat the inner surface of the cover.

[0021]

According to the present invention, since the surface temperature of the molten carbon steel supplied to the molten metal pool is controlled so as to always be higher than the liquidus temperature, no metal is formed on the surface of the molten metal. . Therefore, it is possible to prevent surface cracks and uneven plate thickness of the slab due to non-uniform cooling of the solidified shell caused by the metal being caught between the casting drum and the solidified shell, and further prevent slab rupture due to hot bands. It is possible to stably produce a slab having a good surface quality.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a twin-drum type continuous casting apparatus for carrying out the present invention.

FIG. 2 is a side sectional view showing a conventional twin-drum type continuous casting apparatus.

FIG. 3 is a diagram showing a transition of a molten metal surface temperature in a molten metal pool portion in an example.

[Explanation of symbols]

 1a, 1b ... Casting drum 2a, 2b ... Side weir 3 ... Hot water pool portion 4 ... Thin strip slab 5 ... Injection nozzle 6 ... Insulating cover 7 ... Insulating cover refractory 8 ... Heating device 9 ... Insulating cover thermometer 10 ... Tundish 11 ... Tundish thermometer 12 ... Hot water pool thermometer 13 ... Level gauge 14 ... Temperature control device 15 ... Reflector

Claims (1)

[Claims] 1. A twin-drum type continuous casting apparatus for casting a thin strip slab by supplying a molten metal of carbon steel to a basin formed by a pair of casting drums, wherein a heat insulating cover for covering the upper part of the casting drum is provided. A heating device is provided on the heat retaining cover, and a thermometer for detecting the temperature of the heat retaining cover and a thermometer for detecting the molten metal temperature of the hot water pool are provided, and the temperature detected by each of the thermometers matches the set temperature. Thus, a twin-drum type continuous casting apparatus is provided with a temperature control device for controlling the heating device.