JPH0128805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adding powder to molten metal.

It is well known that adding a coolant externally during the solidification process of molten steel promotes equiaxed crystallization, which improves the internal quality of steel ingots and slabs. It is effective to use

Therefore, when cooling and solidifying molten steel using the continuous casting method, a granular coolant is used and added to the molten steel. It is clear that the most stable and reliable method is to drop the granular coolant into the center of the pipe and let it roll up.

As one such method, Japanese Patent Application Laid-Open No. 54-94437
As shown in Fig. 1a, a hollow hole 5 is provided in the stopper 1 directly above the tundish nozzle 4, and the steel grains are ejected from this hole and the molten steel flow is sucked at the upper end of the nozzle 4. This is intended to completely incorporate and mix the steel grains 8 in the molten steel flow. However, in order to create a suction effect by the molten steel flow with this method, it is necessary to make the distance between the tip of the stopper 1 and the upper end of the tundish nozzle 4, that is, the stopper opening, very narrow. 2, the amount of outflow is small. Therefore, if it is necessary to flow out the molten steel 2 in excess of this flow rate, the stopper opening degree is increased so that no suction action is produced, and there is a drawback that the steel grains 8 are not ejected.

Additionally, JP-A No. 53-130234 basically has a stopper hollow hole 5, similar to the above-mentioned JP-A No. 54-94437.
Although more steel grains 8 are added to the molten steel 2,
By pneumatically transporting the steel grains 8 with a carrier gas such as Ar, the deficiency in the suction effect of the molten steel flow is compensated for. The amount of gas required to make up for this shortage is considerable, and this gas gets caught up in the molten steel flow and forms bubbles, which not only impairs the internal quality of the slab, but also induces surface vibration in the mold, causing operational problems. There is a risk of causing

The present invention has been made in order to solve the problems of the prior art, and aims to provide a method for adding powder and granules that does not deteriorate the internal quality of the slab or cause any problems in operation. purpose.

The method of adding powder or granules into molten metal according to the present invention is a method of adding powder or granules into molten metal from a hollow part provided in a stopper located above a tundish nozzle. It is characterized by using a stopper with an extended tip so that it can be set at a depth lower than 0.7l _R (where l _R is the length of the curved surface at the upper end of the nozzle).

The present invention will be specifically explained below. In Fig. 1a, a tongue of length l (= l _S + l _R ) consists of a straight part of length l _S with a constant inner diameter and a curved part of length l _R whose inner diameter increases upward. The molten steel flow velocity v in the straight section when the molten steel 2 flows out from the delivery nozzle 4 into the steel bath can be calculated using the following equation (1).

However, g: Gravitational acceleration ζ: Loss coefficient λ: Friction coefficient d: Straight part nozzle inner diameter H: Steel bath depth in the tundish. _D : Immersion depth in the steel bath inside the mold (not shown) at the nozzle tip. The pressure P _Z at the height Z from the mold surface (atmospheric pressure) is given by Berthaj's theorem as follows:
It is obtained from equation (2).

V _Z ² ／2g＋P _Z ／γ＋Z＝v ₀ ² ／2g＋P ₀ ／γ＋λ・v ₀ ² ／2
g・Z/d ₀ ...(2) However, γ: Specific weight of molten steel P ₀ , v ₀ , d ₀ : Pressure at the molten metal surface, flow velocity, and nozzle inner diameter P _Z , V _Z : Pressure and flow velocity at height Z Note that the molten steel flow velocity v _Z is constant regardless of the height Z in the straight part, but since the inner diameter differs in the curved part, it changes according to the following equation (3). Note that the cross section of the curved part is 1/
It will be 4 yen.

v _Z・1/4πd ² =K...(3) However, K: Constant Substitute the following numerical values into the above formulas (1) to (3).

That is, by substituting H=600mm, l=1000mm l _D =100mm, l _R =70mm l _S =930mm, d=60mm γ=7.2g/cm ³ , ζ=0.01 λ=0.02, g=980cm/ ^sec2 The results of calculating the nozzle internal pressure distribution are shown in FIG. 1b. As seen in this figure, in the straight part, the pressure decreases upward from the lower end of the nozzle 4, and when it enters the curved part, the pressure decreases by 30° from the lower end of the curved part.
%, and the pressure rises rapidly above that point. In order for the steel particles 8 added to the stopper hollow part 5 to be drawn into the molten steel by the suction effect of the molten steel flow, that is, by the pressure difference, the stopper hollow part 5 is at atmospheric pressure, so the pressure at the tip of the stopper 1 must be lower than atmospheric pressure. need to be lower.
According to calculations, the position where the internal pressure of the nozzle 4 becomes equal to atmospheric pressure is a point 0.7l _R from the top of the nozzle, and this is almost the same even if the nozzle length, curved surface shape, and immersion depth of the nozzle tip in the steel bath are different. Regardless, it is uniquely determined by equations (1) to (3). Therefore, if the tip opening of the stopper 1 is located at a position deeper than 0.7l _R from the upper end of the nozzle, the steel grains 8 will be attracted to the molten steel flow in the nozzle 4 and become involved.

On the other hand, increasing the pressure in the hollow part 5 of the stopper 1 using a gas such as Ar increases the pressure difference between this pressure and the pressure at the opening at the tip of the stopper 1.
This is considered to be effective in increasing the amount of steel grains added. The above-mentioned Japanese Patent Application Laid-open No. 53-130234 is based on this idea.

Now, when the flow rate of molten steel in the nozzle 4 is Q and the flow rate of molten steel in the nozzle 4 is v, the pressure P in the nozzle 4 is expressed by the following equation (4).

P=γ/g・Q・v (4) However, the amount of gas that can be blown into the tundish nozzle from the standpoint of the internal quality of the slab and operational aspects varies depending on the operating conditions, but is generally around 100/min. This is 10
The pressure P (relative pressure) when flowing into the hollow part of mmφ is
It is about 0.006Kg/ ^cm2 . Even if there is an increase in pressure, the position of the opening at the tip of the stopper 1 that can be increased is very small as can be seen from FIG. In addition to impairing the internal quality,
This can be said to be a drawback of No. 130234. In other words,
Even when blowing a gas such as Ar, it is necessary to set the opening position of the tip of the stopper 1 to a position deeper than 0.7l _R.

Accordingly, in the present invention, the granular material is added using a stopper that can realize this. FIG. 2 is a schematic diagram showing the implementation state of the method of the present invention, and FIG. 3 is an enlarged view of the vicinity of the stopper tip. In the figure, numeral 3 denotes a continuous casting tundish, in which molten steel 2 supplied from a ladle (not shown) is stored. The flow rate of the molten steel 2 is adjusted by a stopper 11, and the molten steel 2 is charged into a mold 9 through a nozzle 4. The stopper 11 is different from the conventional one shown in Fig. 1a, and has a length at its tip.
It has a thin extension part 6 of about 150 mm, and the inner diameter of the hollow part 5 through which the steel grains 8 should flow is 10 mm. The value is selected to allow the molten steel to flow between the curved surface portion of the nozzle 4 and the extension portion 6 at a required speed. Its shape may also be determined in accordance with the shape of the curved surface portion of the nozzle 4.

The extension part 6 may be integrated with the stopper 11,
Alternatively, it may be of a split type that is screwed onto the stopper 11. Further, the stopper 11 is supported by a support device (not shown) via the steel grain supply pipe 7, and the steel grains 8 that have passed through the steel grain supply pipe 7 from a steel grain storage tank (not shown) storing the steel grains 8 are transferred to the stopper 11. sent to.

The nozzle 4 is a refractory with a total length of 1000 mm with l _R = 76 mm and l _S = 924 mm, and its lower part is in the molten steel 2 in the mold 9.
100mm immersed.

Under the operating conditions described above, a stopper 1 is installed at a depth exceeding 0.7l _R (=53mm) below the upper end of nozzle 4.
The opening degree of the stopper is limited so that the lower end of the extension part 6 at the lower part is occupied. Thereby, the object of the present invention can be achieved.

Next, examples of the method of the present invention will be described. First, by the method of the present invention described above, the nozzle 4 is
It has been confirmed that when the lower end of the extension part 6 is located at a depth of mm (>0.7l _R ), the steel grains 8 decrease by a predetermined amount per hour and are normally added to the molten steel. It was done. Therefore, raise the stopper 11 a little and remove the nozzle 4.
When the lower end of the extension part 6 is located at a depth of about 53 mm (=0.7 l _R ) below the upper end, the steel grains 8 will no longer decrease and the supply will stop. When the stopper 11 was left in the same position and the extension 6 was observed after the casting was completed, it was found that the tip was blocked by metal. This confirmed the significance of the present invention.

The length of the extension part 6 is determined by the shortest length because it is necessary to position its tip at a depth exceeding 0.7l _R from the upper end of the nozzle 4.
In terms of strength, it is preferable that the length be 500 mm or less. In the above explanation, continuous casting of steel has been taken as an example, but the present invention can also be applied to continuous casting of other metals or casting by an ingot method. Of course, in addition to the coolant such as grains and iron powder grains, a ferroalloy or a deoxidizing agent may also be used. Furthermore, the method of the present invention does not interfere with the action of blowing gas such as Ar.

As explained above, when using the method of the present invention, the powder or granules are forcibly drawn into the molten metal flow due to the pressure difference between atmospheric pressure and the internal pressure of the nozzle 4, thereby stably and reliably adding the powder or granules into the molten metal. It is possible to obtain high-quality slabs. In addition, since the molten metal flows between the narrow extension 6 of the stopper 11 and the curved surface of the nozzle 4, the present invention does not require a long time to introduce the molten metal into the mold, which does not affect the operation. has excellent effects.

[Brief explanation of drawings]

Fig. 1a is a schematic diagram showing the implementation state of the conventional method, Fig. 1b is a diagram of the pressure inside the nozzle, Fig. 2 is a schematic diagram showing the implementation state of the present invention, and Fig. 3 is a partially enlarged view thereof. . 1, 11... Stopper, 2... Molten steel, 3... Tundish, 4... Nozzle, 5... Hollow part, 6
...Extending portion, 8...Steel grains.

Claims (1)

[Claims] 1 In the method of adding powder to molten metal through a hollow part provided in a stopper located above the tundish nozzle, the tip is 0.7l _R below the upper end of the nozzle (where l _R is the curved part of the upper end of the nozzle). A method for adding powder to molten metal, characterized by using a stopper with an extended tip so that the stopper can be set at a depth exceeding the length of the metal.