JPH05318049A - Dummy bar head and sealing method therefor - Google Patents

Abstract

PURPOSE:To perfectly prevent the leakage of molten metal from gap between a dummy bar head and a mold at the initial stage of casting by pouring monolithic sealing material into the gap between the dummy bar head and the mold side wall contacting with molten metal which is not yet solidified. CONSTITUTION:A supplying passage 36 for monolithic sealing material 48 is arranged in the dummy bar head 34. The supplying passage 36 is connected with a monolithic sealing material supplying system composed of a flexible hose 40, pump 42 for supplying the sealing material and sealing material storing tank 44. At the same time of starting reduction of the pressure in a reducing pressure vessel, pouring of the monolithic sealing material 48 is started. By utilizing the pouring pressure and the reduced pressure in the mold 18, the monolithic sealing material 48 is perfectly poured into the gap between the dummy bar head 34 and the mold 18. Even in the reduced pressure, the development of leakage of the molten metal is prevented and the seal between the dummy bar head 34 and the mold 18 is automatically executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dummy bar head and a sealing method for the same, in which molten metal does not leak during continuous casting of steel having good cleanliness.

[0002]

2. Description of the Related Art As is well known, in continuous casting of steel, molten steel from a ladle is once received in a tundish and then continuously cast (hereinafter referred to as "mold").
Is continuously injected into. As described above, a tundish for continuous casting of steel is generally a container for supplying molten steel from a ladle to a mold, and performs a distribution function from one tundish to a plurality of molds, The purpose is to float and separate inclusions to clean the steel.

In particular, in recent years, casting has been aimed at speeding up with the aim of improving productivity, and since it is almost impossible to expect inclusions to float in the mold, it is possible to separate inclusions in advance in the tundish. It is becoming an important technical issue. Moreover, the molten steel in the early stage of casting has a low temperature and is also contaminated by tundish refractories, and generally has poor cleanability. From the viewpoint of improving the productivity of, it is required to secure the cleanliness of molten steel from the start of casting. Conventionally, the slab length is about 5 m from the start of casting.
The ones have been discarded as crop loss.

As a method of improving such cleanliness, a method of providing a vacuum degassing apparatus in the tundish (see Japanese Patent Laid-Open Nos. 60-68142 and 56-168941) has been proposed. There is. Further, even in JP-A-56-168941, molten steel is sucked into the vacuum tank from the ladle through the suction pipe, and then is injected into the mold from the discharge pipe also provided in the vacuum tank. A method of perfusing only once is disclosed. Further, Japanese Patent Laid-Open No. 58-103943 discloses a technique of connecting a tundish and a mold to perform casting without exposing molten steel to air and without forming a molten metal surface in the mold. ..

[0005]

By the way, the inventors of the present invention preceded the invention described below, which is a combination of such a technique of connecting a tundish and a mold and a technique of providing a vacuum processing device in the tundish. (Patent application 4-11
No. 7662).

[(1) In a continuous casting method, which comprises degassing molten steel received in a tundish through a depressurization tank and then continuously casting the molten steel in a mold, The molten steel casting part is provided in the upper part, respectively, and degassing is performed by circulating the molten steel between the tundish and the decompression tank in the molten steel circulation part prior to the start of casting, and then at the start of casting. , Continuous casting of clean steel characterized by continuously injecting molten steel from the molten steel casting part to a mold connected to the molten steel casting part by further raising the vacuum degree of the depressurizing tank and raising the molten metal surface in the depressurization tank Method.

(2) In a continuous casting apparatus comprising a tundish, a pressure reducing tank and a mold, the pressure reducing tank is equipped with at least one suction pipe and at least two discharge pipes, and one of these discharge pipes is used. The lower end of the discharge pipe of the book is connected to the mold, and the partition height in the decompression tank between the discharge pipe connected to the mold and another discharge pipe or suction pipe is different from that of the other discharge pipe and the suction pipe. The continuous casting apparatus for clean steel, characterized in that the height is higher than the partition height in the decompression tank during the period. 2 and 3 are respectively explanatory views showing the configuration of the method and apparatus for continuously casting clean steel according to this proposal. In FIG. 2 or 3, the tundish 14 is provided with a decompression tank 16 having suction pipes 20, 21 and discharge pipes 22 which are immersion pipes, while
The discharge pipe 24, which is one downcomer pipe, is used as a kind of connecting pipe and connected to the mold 18, and continuous casting is performed without using a conventional immersion nozzle. Here, the operation sequence for starting continuous casting by the continuous casting method and apparatus shown in FIG. 2 or 3 will be described.

First, tundish molten steel 12 from ladle 10.
Hot water is supplied to 14, and the molten steel in the initial stage is supplied to the portion of the tundish 14 where the decompression tank 16 is installed via the weir 25. By the way, the molten steel in the initial stage has a low temperature and is also contaminated by the tundish refractory, and generally has poor cleanliness, and the cast piece obtained by casting the cast steel is cropped as an unsteady portion. Therefore, according to the apparatus according to this proposal, with respect to the molten steel containing a relatively large amount of inclusions at the initial stage of casting, the vacuum degree of the decompression tank 16 is adjusted by the exhaust device 30, and the molten metal surface in the decompression tank is shown in the figure. Set to the position indicated by the dotted line. At such a level of molten metal, the molten steel does not reach the discharge pipe 24, and the suction pipes 20, 21 and the discharge pipe 22 serve as an ascending pipe and a descending pipe of the RH treatment tank, respectively. By circulating the 12 together with the decompression tank 16, degassing and removal of inclusions are performed for cleaning.

Of course, the suction pipes 20, 21 corresponding to the rising pipes
From here, Ar gas is blown in through the porous plug 26 to generate an upward flow of molten steel. In FIG. 2, A → B → C
→ D → E molten steel reflux is continuously formed. Also, FIG.
Then, since the suction pipe 21 is further provided, F → G → H →
A molten steel reflux D → E is formed.

Then, when the cleaning of the initial molten steel is completed,
By raising the degree of vacuum further and raising the level of the molten metal in the decompression tank 16 to the position shown by the alternate long and short dash line in the figure, hot water is supplied into the mold 18 from the discharge pipe 24 directly connected to the mold 18 via the route I → J. By doing so, continuous casting is started and the slab 32 is cast.

However, in the above continuous casting method and apparatus, when the downcomer 24 and the mold 18 are depressurized at the start of casting, the contact portion of the dummy bar head 34 with the mold 18 (the dummy bar head Apply on the side wall)
The dry amorphous seal is sucked upward in the mold 18 and peeled off, and when the unsolidified molten steel enters the mold 18 on the dummy bar head 34, the dummy bar head 34 and the mold
Leakage from the gap between the side wall of 18 and breakout
(Blood leak) It was found that the risk of causing an accident increases.

Here, an object of the present invention is, for example, when performing continuous casting in an apparatus in which a tundish and a mold are connected to each other and a vacuum processing apparatus is provided in the tundish, a dummy bar head and a mold at the initial stage of casting are used. It is to provide a means capable of completely preventing hot water leakage from the gap between and.

[0013]

SUMMARY OF THE INVENTION Here, the gist of the present invention is a dummy bar head which is pulled downward in a continuous casting mold, wherein an irregular sealing material for a gap between the mold and a side wall of the mold. It is a dummy bar head characterized in that it is preferably provided internally with a supply path. From another aspect, in the continuous casting of steel, the present invention is characterized by injecting an amorphous sealing material into a gap between a dummy bar head and a side wall of a mold which come into contact with a cast unsolidified molten steel. This is the method of sealing the head.

According to a preferred embodiment of the present invention, for example, when continuous casting is performed using the continuous casting method and apparatus shown in FIGS. 2 and 3, the vacuum degassing process in the decompression tank is made continuous. At the same time, casting is performed by performing sufficient degassing treatment before starting casting, and at this time by injecting an irregularly shaped sealing material into the gap between the dummy bar head and the side wall of the mold, the gap between the mold and the dummy bar head Prevent hot water leakage.

Therefore, according to the above-mentioned preferred embodiment, since it is possible to completely prevent leakage of molten metal and perform casting, it is not necessary to use a dipping nozzle in continuous casting of molten steel, and the molten steel flows in the mold. Is eliminated, and the floating separation of inclusions is promoted. Further, not only there is no molten metal surface but also the secondary part of the molten steel can be effectively prevented because it is an extension of the decompression tank.

However, the present invention is not limited to such an embodiment, and is equally applicable to a dummy bar head generally used in the continuous casting method.

[0017]

Next, the operation of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory view of the dummy bar head 34, the mold 18, and the vicinity of the dummy bar 38 according to the present invention.

In the tundish-mold direct-coupling type continuous casting apparatus having the above-described depressurization tank, molten steel is supplied from the ladle, and depressurization is started when the suction pipe of the depressurization tank is immersed in the molten steel. However, the seal between the dummy bar head 34 provided at the tip of the dummy bar 38 and the mold 18 is such that, as in the conventional case, the amorphous seal material 48 is applied and dried in advance on the inner surface of the dummy bar head 34 to the mold 18. In this case, the seal between the dummy bar head 34 and the mold 18 is peeled off, and when molten steel enters the mold 18, molten metal leaks between the dummy bar head 34 and the mold, causing a breakout accident. There is a risk of causing it.

Therefore, in the present invention, as shown in FIG.
Using the dummy bar head 34 having the supply path 36 of the irregular sealing material 48 inside the dummy bar head 34, the supply path 36 is
For example, flexible hose 40, pump 42 for supplying sealing material
And the sealing material storage tank 44 is connected to the irregular sealing material supply system, and at the same time when decompression of the decompression tank is started, injection of the irregular sealing material 48 is started, and the injection pressure and the decompression in the mold are started. Use and the dummy bar head 34 and mold
By completely injecting the irregular shape sealing material 48 into the gap between 18 and 18, completely preventing the occurrence of hot water leak even under reduced pressure, and automatically and automatically sealing the dummy bar head 34 and the mold 18. Do it completely.

The supply passage 36 and the injection portion 37 are provided so that the irregular sealing material is filled in the entire gap between the dummy bar head 34 and the mold 18. However, the arrangement of the supply passage 36 in the dummy bar head 34 is not limited at all. Not a thing. But,
It is preferable that the injection parts 37 are dispersed at appropriate intervals so that the sealing material is uniformly injected into all the spaces. In particular,
It may be appropriately determined in consideration of the mold cross section and the same cross section of the dummy bar head. The shape may be a nozzle shape or a slit shape.

The irregular sealing material is not particularly limited, and a known irregular sealing material such as CaO-SiO ₂ type sealing material (Hi-Seal: trademark manufactured by Kogaku Kagaku Kogyo) is used. Good.

As shown in FIG. 1, the dummy bar 38
In order to prevent the catching part from being plastically deformed at the catching part and the vicinity (marked with × in the figure) of
A cooling material 46 such as iron powder or a spring is placed near the dummy bar head 34 for the purpose of rapid cooling. Next, the effects of the present invention will be described more specifically by way of examples.

[0023]

[Example] Using a one-point straightening continuous casting machine with a bending radius of 10 m,
Casting speed of 3.0m / for a slab measuring 200 mm thick and 1500 mm wide
It was continuously cast in minutes. The steel type was a low carbon aluminum killed steel whose composition is shown in Table 1. At the time of continuous casting, the No. 1 tundish was cast according to the conventional method without a pressure reducing tank, and the No. 2 tundish was cast according to the method shown in Fig. 2 with a pressure reducing tank. Were compared.

Further, in No. 2 tundish, 50 trials of the present invention example in which a dummy bar head is provided with a supply path for an irregular shaped sealing material and a comparative example in which it is not provided are cast, and troubles at the beginning of casting ( We mainly compared the occurrence rate of hot water leakage.

In FIG. 4, the amount of large inclusions in the unsteady casting portion (slab top portion: 0 to 5 m) within 5 minutes after the start of casting is continuously cast using No. 1 tundish and No. 2 tundish. The result of microscopic examination of the cast slab is shown in a graph. The number of inclusions with a size of 100 μm or more is coded in 1 to 10 steps. No. 2 tundish using the method with a vacuum tank is No. 1
The inclusion level was about 1/5 that of the tundish, indicating that the floating separation of inclusions was sufficiently performed.

FIG. 5 is a graph showing the results of the same examination of the steady portion (slab length: 100 to 150 m) at the beginning of casting 60 minutes after the start of casting. Inclusion levels were reduced to almost 1/6 or less by providing a decompression tank.

As described above, when the decompression tank is not provided, the unsteady part is much worse than the stationary part and causes a crop loss. However, by providing the decompression tank, cleanliness comparable to that of the stationary part can be obtained. , Yield loss decreased. Further, by providing the decompression tank, continuous casting of clean steel could be performed over the entire region including the unsteady part at the initial stage of casting.

Furthermore, by performing static injection using a decompression tank without using a dipping nozzle, a stationary part (slab length: 100
Fig. 6 shows the results of the significant reduction in pinholes even at ~ 150 m). In FIG. 6, the number of pinholes generated was evaluated and coded on a scale of 0 to 10.

In the No. 2 tundish, an example of the present invention in which a dummy bar head was provided with a supply path for an irregular shaped sealing material and a comparative example not provided were cast for 50 trials each,
Fig. 7 shows the occurrence rate of troubles (mainly molten metal leakage) at the beginning of casting. With the present invention, the trouble occurrence rate is 1/10
Reduced to

The amorphous sealing material used in the examples of the present invention was SiO ₂ : 42% by weight, Al ₂ O ₃ : 21% by weight, CaO: 3% by weight, MgO: 2% by weight, methyl alcohol: 30%. % By weight.

[0031]

[Table 1]

[0032]

According to the present invention, during continuous casting of steel having good cleanliness, the seal between the mold and the dummy bar head can be completely sealed, and accidents such as leakage of molten metal do not occur. Therefore, by performing continuous casting using the dummy bar head according to the present invention, it is possible to stably perform continuous casting and produce clean steel.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a dummy bar head according to the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a continuous casting apparatus for clean steel proposed by Japanese Patent Application No. 4-117662.

FIG. 3 is an explanatory view showing another configuration of the continuous casting apparatus for clean steel proposed by Japanese Patent Application No. 4-117662.

FIG. 4 is a graph showing the inclusion level in the unsteady part.

FIG. 5 is a graph showing inclusion levels in a stationary part.

FIG. 6 is a graph showing a pinhole generation level in a stationary part.

FIG. 7 is a graph showing the trouble occurrence rate at the initial stage of casting for the example of the present invention and the comparative example.

[Explanation of symbols]

10: Ladle 12: Molten Steel
14: Tundish 16: Decompression tank 18: Mold
20: Suction tube 21: Suction tube 22: Discharge tube
25: Weir 26: Ar gas supply pipe 30: Exhaust device
32: Slab 34: Dummy bar head 36: Seal material supply path
38: Dummy bar 40: Flexible hose 42: Pump for supplying sealing material
44: Storage tank 46: Cold material 48: Amorphous seal material

Claims (2)

[Claims] 1. A dummy bar head pulled downward in a continuous casting mold, comprising a supply path of an irregular sealing material to a gap between the continuous casting mold and a side wall of the continuous casting mold. 2. A seal for a dummy bar head, characterized in that in a continuous casting of steel, an irregular sealing material is injected into a gap between a dummy bar head that comes into contact with a cast unsolidified molten steel and a side wall of a continuous casting mold. Method.