JP2821279B2 - Inert gas supply device for tundish - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for supplying an inert gas for preventing reoxidation of molten steel in a tundish in a continuous casting facility. More specifically, the present invention relates to an apparatus for supplying an inert gas for preventing oxidation so as to cover molten steel in a tundish.

[0002]

2. Description of the Related Art In a tundish in which molten steel reduced to a predetermined oxygen content in a refining process in a continuous casting facility is once pooled, care must be taken to prevent the molten steel from being reoxidized. For this reason, it has been widely practiced to supply an inert gas into a tundish and replace it with air before pouring the molten steel, and thereafter cover the flowed molten steel with the inert gas. This inert gas envelope must be formed stably on the molten steel in the tundish so that it is not easily broken, and if it is disturbed when adding molten steel, it will be restored as soon as possible, removing the molten steel from the air. It is preferable to shield. In general, in order to discharge and replace the oxidizing gas, that is, air, in the tundish by injecting an inert gas, two processes are considered in contrast to the piston flow type and the completely mixed flow type.

[0003] a) Fluid A in a piston flow type tundish volume changes fluid B to a flow rate Q
_{When i} is sequentially replaced by supplying the piston as if moving the cylinder, the replacement time τ ₀ is τ ₀ = V / Q _i . This gives the shortest replacement time in theory.

B) Completely mixed flow type The replacement process which gives the longest replacement time in theory is the completely mixed flow type. In the case of the completely mixed flow type, fluid B is filled with Q _i per unit time in a container of volume V filled with fluid A.
And completely mixes with the fluid A at the same time as the inflow, and flows out at a rate of Q ₀ per hour. At this time, the following equation 1 holds for the fluid B accumulated in the container. However, the volume of the fluid in the container is fixed, and the amount of the fluid B existing in the container at time t is M
(T).

[0005]

[Number 1] and _{Q i = Q 0 (= Q} ) C i · Q i · dt-C 0 · Q 0 · dt = dM here to equation (1) to organize by substituting the following conditions, C _i = 1. 0 C ₀ = {M (t) + Q _i · dt} / V The following differential equation 2 is obtained.

[0006]

DM / (1−M) = dt · Q / V This is integrated to obtain the concentration C (t) in the container at time t from the initial condition M = 0 at t = 0.

[0007]

C (t) = M (t) / V = 1−exp (−Q / V · t) That is, in the completely mixed flow type, the fluid A is replaced with the fluid B according to an exponential function. .

[0008]

However, in practice, the replacement process often shows complicated behavior because the piston flow type and the completely mixed fluid are mixed irregularly. For example, if a piston flow type is to be realized in a tundish with a constant supply amount of the inert gas, the jet velocity of the inert gas becomes a very low value. On the other hand, since the inside wall of the tundish is heated to 1200 ° C. or more before molten steel is injected, convection accompanied by a strong upward flow is generated inside the tundish. Even if a low-speed inert gas is supplied in this state, the inert gas is disturbed by the convection, and it is almost impossible to blow in the piston flow type to reach the bottom of the tundish.

On the other hand, if the supply speed of the inert gas is increased to relatively reduce the disturbance due to the convection, the air flow is vigorously sucked and mixed in the inert gas jet, so that the completely mixed flow having the worst displacement efficiency is performed. You will be closer to the mold.

[0010] For these reasons, conventionally,
In the process of replacing the inert gas in the tundish, it was not possible to form a flow form that does not contain non-inert gas inside the fluid while maintaining a stable flow direction that is not affected by disturbance such as convection .

[0011] The present invention provides a method for preparing a tank free of inert gas.
The air in the dish and the inert gas can be quickly replaced,
An object of the present invention is to provide an inert gas for a tundish that can be stably maintained.

[0012]

In order to achieve the above object, an inert gas supply device according to the present invention further comprises an inert gas supply device for ejecting an inert gas to a tundish at a high speed from around an inert gas nozzle. An inert gas having a lower velocity than the inert gas is blown out.

[0013]

Therefore, the inert gas ejected at a high speed reaches the bottom of the tundish without being affected by disturbance such as convection and removes air outside the tundish. At this time, there is a problem that the gas in the tundish around the high-speed inert gas flow is entrained, but the inert gas flowing at a low speed flows around the inert gas injected at a high speed. Is formed, the inert gas flows in the air. Therefore, air outside the inert gas flowing at a low speed is not taken into the high-speed flow of the inert gas.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the present invention will be described below in detail with reference to the embodiments shown in the drawings.

FIG. 1 shows the structure of the nozzle 1 of the inert gas supply device of the present invention. The nozzle 1 includes an inner nozzle 2 for injecting an inert gas 4 at a high speed, and an outer nozzle 3 for injecting an inert gas 5 at a low speed so as to surround the nozzle 2. The inert gas 4 is ejected from the inner nozzle 2 at a high speed, and the inert gas 5 is ejected from the inner nozzle 2 at a lower speed than the inner inert gas 4 so as to surround the inert gas. In addition, a stable flow direction is maintained without being affected by disturbance such as convection generated in the tundish, and a flow of an inert gas containing no non-inert gas is formed. In order to form such a flow form, it is necessary to have a high-speed jet jet injected from a single-hole or multi-hole injection port and a structure capable of supplying an inert gas from the surroundings at a flow rate of 1/10 to 1/20 of the high-speed jet. is required. For example, in the case of the present embodiment, the small-diameter inner nozzle 2 is disposed at the center of the large-diameter outer nozzle 3, and the inner diameter of the outer nozzle 3 is much smaller than the large-diameter nozzle 7 of the outer nozzle 3. Nozzle 2. Therefore, when the inert gas is supplied to each of the nozzles 2 and 3 from one inert gas supply source, the high-speed inert gas 4 is output from the inner nozzle 2 and the low-speed inert gas 5 is output from the outer nozzle 3. Are respectively injected. Of course, different types of inert gas may be supplied to the nozzles 2 and 3 from different inert gas supply sources under the same conditions.

As the inert gas, an argon gas, a nitrogen gas or the like is generally used. However, the present invention is not particularly limited to this, and a gas inert to the molten steel is used if necessary. For example, in the case of the present embodiment, the same gas is used for high-speed diversion and low-speed diversion. In some cases, expensive argon gas is used as high-speed diversion inert gas and inexpensive nitrogen is used as surrounding low-speed diversion inert gas. It is also possible to increase the economic efficiency by using gas.

FIG. 3 shows an embodiment of the inert gas supply device of the present invention. As is clear from the figure, one or more, for example, two nozzles 1 for injecting the inert gas are installed near the opening 7 above the tundish 6, and the inert gas 4 is injected along the wall of the tundish 6. 5 is provided so as to flow, collide at the center of the tundish 6 while licking the bottom thereof, change the direction of the flow upward, and flow out of the tundish 6. The air in the tundish 6 is discharged by the flow of the inert gases 4 and 5 and replaced with the inert gases 4 and 5, and the oxygen concentration in the tundish 6 is rapidly reduced.

FIG. 2 shows the result of removing the air in the tundish 6 using this apparatus. In this experiment, the capacity of the tundish 6 was 2 m ³ , the used inert gas was nitrogen gas, the supply amount of the inert gas was 30 Nm ³ / hr, and the temperature of the tundish was 800 ° C. As a result, in the case where the inert gas is supplied by the method of the present invention as compared with the case where the inert gas is simply ejected from the nozzle at a speed of 15.4 m / s, it takes about half of the time for the oxygen concentration to be reduced by half. Was achieved in about 1 minute, and the time required for complete replacement with the inert gas was achieved in about 2/3 of the comparative example, that is, about 4 minutes.

[0019]

As is clear from the above description, the inert gas supply device for a tundish of the present invention further comprises an inert gas nozzle for ejecting an inert gas at a high speed toward the tundish from around the inert gas nozzle. , So as to eject an inert gas at a lower speed than the inert gas, so that air in the tundish is eliminated by a high-speed inert gas that is not affected by convection and the like in the tundish , The high velocity inert gas flow is shut off from the air in the tundish by the surrounding low velocity inert gas to prevent suction mixing. That is, according to the present invention, while maintaining a stable flow direction that is not affected by disturbance such as convection generated in a tundish heated to a high temperature, an inert gas that does not contain a non-inert gas inside the fluid is maintained. A gas flow form is formed, and the non-inert gas in the tundish is efficiently discharged to the outside in a short time by the flow, and the inside of the tundish is replaced with the inert gas without remaining air to remove the molten steel. Reoxidation can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an inert gas supply device for a tundish of the present invention.

FIG. 2 is a diagram showing a comparison of the change over time of the oxygen concentration in a tundish from the start of purging when the apparatus according to the present invention is used and when it is not.

FIG. 3 is a schematic diagram showing an example in which a plurality of inert gas supply devices according to the present invention are preferably installed.

[Explanation of symbols]

 Reference Signs List 1 nozzle 2 inner nozzle 3 outer nozzle 4 high-speed inert gas 5 low-speed inert gas 6 tundish

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Tatsuo Fukuzumi 1-9-31 Shinonome, Koto-ku, Tokyo Mitsubishi Steel Corporation Tokyo Works (72) Inventor Hideo Ueno 1-9-31, Shinonome, Shinonome, Koto-ku, Tokyo Mitsubishi Steel In Tokyo Manufacturing Co., Ltd. (72) Inventor Ryo Hara 1-9-31 Shinonome, Koto-ku, Tokyo Mitsubishi Steel Corporation In Tokyo Manufacturing Co., Ltd. (56) References JP-A-2-104454 (JP, A) JP-A-2- 37949 (JP, A) JP-A-63-188460 (JP, A) JP-A-59-27760 (JP, A) JP-A-2-11651 (JP, U) JP-A-57-116362 (JP, U) (58) Field surveyed (Int.Cl. ⁶ , DB name) B22D 11/10

Claims (2)

(57) [Claims] 1. An inert gas nozzle for jetting an inert gas at a high speed toward a tundish, and an inert gas having a lower speed than the inert gas is jetted around the inert gas nozzle. Gas supply device for tundish. 2. The inert gas for a tundish according to claim 1, wherein the inert gas surrounding the central inert gas has a flow velocity of 1/10 to 1/20 of that of the central inert gas. Gas supply device.