JPH03275261A - Method for controlling molten metal supplying quantity into mold and molten metal supplying nozzle thereof - Google Patents

Abstract

PURPOSE:To prevent invasion of inclusion in steel downward by forming a pressurizing chamber in a mold with a nozzle and the mold, supplying inert gas and controlling gas pressure so as to almost equal to the total head of molten steel. CONSTITUTION:At lower part of the nozzle 6, a large diameter part 6B and a small diameter part 6C are formed and the pressurizing chamber 7 is formed at between these and molten steel 3' in the mold. An O ring 8 is set at between the large diameter part 6B and the mold 2. The inert gas 12 is supplied through a supplying passage 9. the molten steel surface level in the tundish 1 is measured with a molten metal surface meter 13 and molten steel pressure P1 is obtd. with a computing element 15. The molten steel surface pressure P2 in the mold is measured with a pressure gage 14 and a pressurizing machine 11 is controlled so as to be P1 P2. Discharge pressure from the nozzle 6 becomes the min., and by reducing pouring velocity of the molten steel 3 even in the high velocity casting, the molten steel can be cast and the invasion of inclusion in the steel downward can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the amount of hot water supplied to a mold in continuous casting and a hot water nozzle for the same.

[Traditional technique]

As shown in Fig. 3, in continuous casting, molten steel 3 is poured from a tundish 1 into a mold 2, firstly cooled by the mold 2, then secondarily cooled while being guided and supported by a roller apron, etc., and then cooled according to the casting speed. This is a method to continuously produce slabs by pulling the slabs at a drawing speed that is as high as It is common to use SN.

The amount of hot water supplied is controlled by a sliding nozzle SN or the like while observing the scene level in the mold or by detecting the hot water level, so that the hot water level remains constant. Further, powder 4 is supplied above the molten metal surface in the mold to prevent oxidation of the molten steel, capture inclusions, and lubricate between the mold wall and the slab.

[Problems to be solved by this invention]

However, in recent years, with the trend toward high-speed casting to improve productivity, the amount of hot water supplied from the side hole n of the submerged nozzle N has increased, and the discharge flow has to penetrate deeper into the mold, as shown in Figure 4. become a trend. At this time, inclusions in the mesh also penetrate deeply, resulting in a problem that the quality of the slab deteriorates.

As a countermeasure to these problems, methods have been used such as using EMBR (electromagnetic braking device using a static magnetic field) or increasing the inner diameter of the submerged nozzle to slow down the injection speed of molten steel, but these methods also have limitations.

On the other hand, Japanese Patent Publication No. 2-7744 discloses that a shield chamber surrounds the tundish and the mold, and an inert gas is supplied into the shield chamber to maintain the gas pressure inside the chamber at a level that is in balance with the molten steel head. We carry out the extraction of
A pressure casting method is disclosed in which molten steel is isolated from air and gas pressure is used to improve contact between the molten steel and the mold wall surface to reduce surface defects in the slab. The shield chamber includes:
Since the mold is oscillated up and down during casting, the inner cylinder attached to the tundish and the outer cylinder attached to the mold are connected via a heros, which expands and contracts in accordance with the vibrations of the mold, and the internal volume of the shield chamber remains constant. A structure that is preserved is used.

However, such a structure has the following problems.

(i) It is practically impossible to maintain a constant internal volume of the shield chamber, and it is necessary to control opening and closing with a valve according to changes in volume, making it difficult to balance the internal gas pressure with the molten steel head.

(ii) The internal volume of the shield chamber is large, the response is poor, and a large amount of inert gas is required.

(iii) It is necessary to consider the heat resistance of the members of the shield chamber.

(iv) Since the injection speed of molten steel is not considered and only a normal immersion nozzle can be used,
It is difficult to prevent inclusions from entering during high-speed casting.

This invention was made to solve the above-mentioned problems, and its purpose is to make it possible to significantly reduce the injection speed of molten steel even in high-speed casting, and to
To provide a method for controlling the amount of hot water supplied to a mold, which does not cause a change in the internal volume of a gas pressure chamber even when the mold is oscillated, can easily control pressure, and can perform control with good responsiveness, and a hot water supply nozzle thereof.

[Means for Solving the Problems] As shown in FIG. 1, the present invention forms a pressurizing chamber 7 in the mold 2 by a nozzle 6 inserted into the mold 2 and the mold 2, and this pressurizing chamber An inert gas 12 is supplied into the mold 7 and the molten steel 3 is controlled while controlling the gas pressure so that the gas pressure is approximately equal to the total water head of the molten steel 3 injected into the mold 2.
is cast into a mold 2.

The hot water supply nozzle 6 that implements this method has a large diameter portion 6B formed at the tip of the nozzle inserted into the mold 2, which can be inserted airtightly into the mold cavity.
A tank bottom is used such that a pressurizing chamber 7 is formed between B and the small diameter portion 6C at the bottom thereof and the melt m3' in the mold 2.

[Function] The temperature control pressure (total water head) P injected into the mold 2 becomes almost equal to the mold surface pressure P2, and the hot water supply nozzle 6
A predetermined amount of hot water is poured while the discharge pressure is kept to a minimum. As a result, hot water is quietly supplied into the mold 2, and inclusions in the steel are completely prevented from entering below.

Even when the mold 2 is oscillated in the vertical direction, the level of the hot water inside the mold is constant, so the volume of the pressurizing chamber 7 is kept constant, and the pressure can be easily controlled. Furthermore, since the internal volume of the pressurizing chamber 7 can be reduced, responsiveness is improved and the amount of inert gas used can be reduced.

Furthermore, since the conventional stopper, sliding nozzle, etc. can be eliminated, the nozzle hole 6A of the hot water supply nozzle 6 can be made large in diameter, and the necessary amount of hot water can be secured without increasing the flow velocity in the nozzle. It can also handle high-speed casting.

〔Example〕

The present invention will be described below based on an illustrated embodiment. As shown in FIG. 1 and FIG.
A nozzle without a hot water supply amount adjustment device such as a sliding nozzle is used, and the internal nozzle hole 6A is a straight nozzle.

Furthermore, a large diameter part 6B and a small diameter part 6C are formed in order from the top at the lower end of this nozzle 6, and the large diameter part 6B and the small diameter part 6
C, so that an annular pressurizing chamber 7 is formed between the mold internal temperature m3' and the mold internal temperature m3'. The large diameter part 6B has a size and shape slightly smaller than the mold cavity, and an O ring 8 is arranged between it and the mold 2, so that airtightness is maintained even when the mold 2 is oscillated in the vertical direction with respect to the nozzle 6. so that

In such a pressurizing chamber 7, a supply path 9 provided in the mold 2,
A pressurizer 11 is connected via a supply pipe 10, and this pressurizer 1
1, an inert gas 12 such as Ar is supplied into the pressurizing chamber 7, and the pressure inside the pressurizing chamber can be adjusted. Note that the supply path 9 may be provided in the large diameter portion 6B of the nozzle 6.

The control system of the pressurizing machine 11 includes a hot water level gauge 13 provided in the tundish 1, a pressure gauge 14 attached to the supply pipe IO, and a computing unit 15.
The pressure P1 of molten steel injected into the mold from the surface level is determined, and the surface pressure P2 in the mold is adjusted based on this P+.

Further, the powder 4 is supplied to the supply pipe 1 from the powder pressurizer 16.
7, it is supplied into the pressurizing chamber 7 while being pressurized so that the pressure inside the pressurizing chamber does not fluctuate.

Although not shown, the powder thickness is measured by a thermocouple embedded in the mold.

In the above configuration, control is performed as follows.

(i) When starting casting, pour molten steel until the lower end surface of the hot water supply nozzle 6 is covered with molten steel in the mold, and once the sealed pressurizing chamber 7 is formed, the dummy bar is pulled out and the inside of the pressurizing chamber is filled. Perform pressure control.

(i molten steel pressure P, and molten steel surface pressure P2 (PI > P2
) P2 is controlled by the pressurizer 10 in response to the decreasing P+ so that the pressure difference becomes n().

The molten steel 3゛ in the mold 2 is descending at the drawing speed ■,
Molten steel is supplied from the nozzle 6 at an amount corresponding to AV (A: cross-sectional area of the mold cavity), but since there is no pressure difference, the discharge speed from the nozzle 6 becomes extremely slow.

Furthermore, when the nozzle flow velocity is V and the nozzle hole cross-sectional area is a, av=AV, and by increasing the cross-sectional area of the nozzle hole 6A, the nozzle flow velocity V can be kept low.

As a result, even in high-speed casting, in combination with the fact that the discharge pressure from the nozzle 6 is extremely low, the injection speed from the nozzle 6 can be extremely slow, and the necessary flow rate can be secured without increasing the flow velocity in the nozzle.

〔Effect of the invention〕

As mentioned above, the present invention forms a pressurized chamber in the mold by a hot water supply nozzle inserted into the mold, supplies an inert gas into this pressurized chamber, and this gas pressure is applied to the molten steel injected into the mold. Since the gas pressure is controlled so that it is approximately equal to the total water head, the following effects are achieved.

(i) The discharge pressure from the nozzle becomes extremely low, and even in high-speed casting, the injection speed of molten steel can be significantly reduced. This completely prevents inclusions in the steel from penetrating downward, making it possible to significantly improve the quality of the slab.

(11) Since a pressurized chamber is formed between the hot water supply nozzle and the mold surface which remains constant during casting, the volume of the pressurized chamber remains constant even when the mold is oscillated in the vertical direction, allowing pressure control. can be done easily.

(iii) Since the internal volume of the pressurizing chamber can be reduced, responsiveness can be improved and the amount of inert gas used can be reduced.

(iv) Since it is possible to eliminate the conventional sliding nozzle, etc., the nozzle hole of the hot water supply nozzle can be made larger, and the discharge pressure from the nozzle is extremely small, which makes it possible to reduce the depth of inclusion penetration, which is necessary. It is possible to easily secure a sufficient amount of hot water supply and support high-speed casting.

(v) Since the pressurizing chamber can be formed by the hot water supply nozzle, there is no need to consider heat-resistant members.

[Brief explanation of drawings]

1 and 2 are a partially enlarged view and an overall view showing an embodiment of a device for implementing the method of controlling the amount of hot water supplied to a mold according to the present invention, and FIG. 3 is a conventional casting method. FIG. 4 is a schematic diagram showing the flow of molten steel from the immersion nozzle. 1...Tandateishu, 2...Mold 1...? Yonggang, 4...Powder...
...Slab, 6...Hot water nozzle A...Nozzle hole, 6B...Large diameter section C...Small diameter section, 7...・Pressure chamber...○Ring, 9...
... Supply path 0 ... Supply pipe, 11 ...
- Pressurizer 2... Inert gas, 13...
Water level gauge 4...Pressure gauge, 15...Calculator 6...Powder pressurizer, 17...Supply pipe 2 Fig. 3 N Fig.

Claims (2)

[Claims] (1) With the nozzle and mold inserted into the mold,
A pressurized chamber is formed in the mold, an inert gas is supplied into the pressurized chamber, and the molten steel is pumped while controlling the gas pressure so that the gas pressure is approximately equal to the total water head of the molten steel injected into the mold. A method for controlling the amount of hot water supplied to a mold, characterized by casting hot water into the mold. (2) A large diameter part is formed at the tip of the nozzle that can be inserted into the mold cavity in an airtight manner, and the large diameter part and the small diameter part at the lower part of the nozzle allow the molten steel in the mold to be absorbed. A hot water supply nozzle for a mold, characterized in that a pressurized chamber is formed between the nozzle and the pressurized chamber.