JPS5877754A - Continuous casting method and immersion nozzle - Google Patents

Abstract

PURPOSE:To agitate the molten metal in a water-cooled mold effectively without using any electromagnetic agitator in the mold in the stage of discharging the molten metal through an immersion nozzle into the mold by directing discharge flow toward specific directions thereby generating swirling flow in horizontal directions. CONSTITUTION:The flow of the molten metal 3 flowing down in the body 11 of an immersion nozzle 1 and discharged in a small arrow direction tangentially from a discharge pipe 12 abuts on the walls 21, 22 of a mold 2 and circulates, thereby generating the swirling flow in a large arrow direction as a whole. The nozzle 1 used for this purpose consists of the body 11 which is, for example, a bottomed cylindrical body, and plural short discharge pipes 12 located below the same, and the directions of the pipes 12 are tangential with respect to the section of the body and are horizontal or slightly downward below the same.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a continuous casting method for molten metal.
The invention also relates to a submerged nozzle for use in carrying out the method.

In continuous casting of alloys such as steel, the solidifying molten metal is stirred to reduce bubbles and inclusions under the skin, and to minimize segregation in the slab and crystal growth in the direction of cooling. This is necessary, and various efforts are being made to achieve this goal.

Usually, electromagnetic stirring is used, and for the most powerful stirring, an electromagnetic stirring device EMS (electromagnetic stirring device) is used.
ro Magnetic 5tirrer) inside the mold (M-EMS) and under the mold (S-EM
S) and the final stage (F-EMS) just before total solidification.

However, M-EMS requires a large amount of equipment cost, and it is questionable whether it can provide a sufficient stirring effect.

An object of the present invention is to provide a means for effectively stirring molten metal within a mold without using M-EMS.

Another object of the present invention is to provide a stirring means that can be used in combination with M-EMS to further enhance the stirring effect and obtain slabs of excellent quality.

As a measure to realize this intention, the present inventors created a natural swirling flow by utilizing the force of the molten metal discharged into the bank where the molten metal is supplied into the mold through the immersion nozzle 5 in continuous casting. I came up with the idea of using it for stirring.

Therefore, we first conducted an experiment using a water model using a mold and immersion nozzle similar to the actual device.

The conditions were: glue in the mold 48x37tYn, nozzle immersion depth 20crn, withdrawal speed 0.5 m/min, (
90,'8 t/min), and apart from the thermal conditions, the mechanical conditions (Reynolds number and Froude number) are the same as in reality. Established through this experiment,
The present invention was completed by confirming the effective discharge method and the shape of the immersion nozzle that achieves it by applying it to an actual device.

With this background, the continuous casting method of the present invention is a continuous casting method in which molten metal is supplied and discharged into a water-cooled mold through a submerged nozzle, and the discharge flow is directed to a plurality of symmetrical positions with respect to the center of discharge. It is characterized by generating a horizontal swirling flow in the molten metal in the mold in a tangential direction and in an oblique direction that is neither parallel nor perpendicular to the surface of the mold.

FIG. 1 shows this principle, in which the flow of the molten metal 3 that flows down inside the nozzle 10 body 11 and is discharged from the discharge pipe 12 in the tangential direction as shown by the small arrows flows through the walls 21 and 22 of the mold 2. The liquid hits and circulates, creating an overall swirling flow as shown by the large arrow.

In the illustrated example, there are four discharge streams, and this number is effective whether the mold is square or circular, but is optimal for a rectangular mold. If there are two or three discharge streams,
Although it is effective for circular molds, the swirling flow may be weak in square molds. On the other hand, it has been experienced that five or more discharge streams disperse the force of the discharge, and the swirling ability is rather reduced.

In addition, "symmetrical" with respect to the center of discharge does not necessarily mean that all four points are in rotationally symmetrical positions with respect to the center, in the above example, it is sufficient that two points facing each other are symmetrical with respect to each other. It will be understood.

The direction in which the molten metal discharge flow collides with the mold wall is
At or near right angles, the flow splits into left and right,
Do not turn. It goes without saying that even if the angle is parallel, there is no effect, and in general, the optimum angle is 45°, which is between the angles of right angle and parallel, and the further away from that angle, the less effective it becomes. However, it has been found that a similar effect can usually be obtained within the range of (45±10)0.

The direction of the discharge flow in the vertical plane is horizontal or slightly (within 15° or 20°) downward.
This is preferable because downward momentum is added to the discharge flow. Needless to say, the molten metal that has hit the mold wall is carried downward as the slab is pulled out, but some of it moves upward from the position of the immersion nozzle discharge pipe.

The direction in which the swirling flow is generated is preferably to the left (counterclockwise) when viewed from above the molten metal surface. this is,
This is because vortices that occur in the Northern Hemisphere rotate counterclockwise due to the influence of the Earth's rotation, so if you choose the same direction, it will be easier to turn.

When using the method of the present invention, for example, in a mold having a typical shape and size in steel casting, a flow rate of 10 c
A swirling flow of the molten metal at a speed of about m/sec (several rpm in terms of rotation speed) is generated. This stirring power is a full-fledged M-EMS
Although it is not as good as that of M-EMS, if the requirements for steel quality are not particularly strict, it can provide slabs of reasonable quality even without M-EMS. Even if M-EMS is used together, a simple one will suffice. Alternatively, if a powerful M-EMS is installed, it is possible to maximize the effect of stirring and produce slabs that meet strict quality requirements.

As mentioned above, the present invention also includes an improved submerged nozzle for use in carrying out the continuous casting method described above.

The continuous casting method nozzle of the present invention typically has a side view shown in FIG. 2, a longitudinal section shown in FIG. Bottom cylindrical body 11
and a plurality of short discharge pipes 12.12.1 located at the bottom thereof.
2.12, the direction of the discharge pipe 12 is tangential to the cross section of the main body, and horizontal or slightly downward (
The examples in FIGS. 2 and 3 are characterized in that they are oriented downward.

Another embodiment of the submerged nozzle of the present invention is illustrated in FIGS. 4A and 4B. Although the direction of discharge is horizontal, the discharge pipe is curved to facilitate swirling flow.

The submerged nozzle of the present invention may have various other embodiments, all of which may be manufactured using known techniques.
In this case, care should be taken to select a material with excellent erosion resistance. This is to ensure that the generation of swirling flow is not impaired due to changes in the nozzle shape and that stirring power is maintained from the initial stage to the end of casting.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram seen from above a mold for explaining the principle of generating a swirling flow of molten metal in the continuous casting method of the present invention. 2 and 3 are diagrams showing the shape and structure of a typical embodiment of the immersion nozzle of the present invention, in which FIG. 2 is a side view, FIG. 3A is a longitudinal sectional view, and FIG. Figure B is the second
It is a cross-sectional view taken along the line I-I in FIG. FIG. 4 is a diagram showing the structure of another embodiment of the submerged nozzle of the present invention, and A and B are respectively shown in FIG.
FIG. 1... Immersion nozzle 11... Main body 12... Discharge pipe 2...
... Mold 3 ... Molten metal patent applicant Daido Steel Co., Ltd. Agent Patent attorney Sou Suga Fusai 2 Fig. 8 A Fang 4 Fig. A-1

Claims (6)

[Claims] (1) In continuous casting, in which molten metal is supplied and discharged into a water-cooled mold through a submerged nozzle, the discharge flow is directed tangentially at multiple positions symmetrical about the center of discharge.
A continuous casting method characterized by generating a horizontal swirling flow in the molten metal in the mold in a direction oblique to the mold surface. (2) The continuous casting method according to claim 1, wherein there are four discharge streams, and the discharge streams are discharged in a direction of (45±10)0 with respect to a rectangular mold surface. (3) The continuous dispensing method according to claim 1 or 2, wherein the direction of discharge is horizontal or slightly downward. (4) The continuous casting method according to any one of claims 1 to 3, wherein the direction of the swirling flow is counterclockwise when viewed from above. . (5) The continuous casting method according to any one of claims 1 to 4, wherein the molten metal is molten steel. (6) A cylindrical main body 11 with a bottom and a plurality of short discharge pipes 12 located at the bottom thereof.12. , 12.12 One immersion nozzle for continuous casting, characterized in that the direction of the discharge pipe 12 is tangential to the cross section of the main body, and horizontal or slightly downward.