JPH067906A - Method for preventing clogging of molten steel flowing passage - Google Patents

Abstract

PURPOSE:To prevent the sticking of non-metallic inclusion in a molten steel to a passage wall by applying magnetic field crossing the flowing passage from a magnetic field generator and varying the magnetic field to vary molten steel flowing speed at the time of flowing the molten steel in the flowing passage made of refractories. CONSTITUTION:By applying the variable magnetic field crossing the molten steel in a nozzle with an electromagnetic coil 4, the dynamic magnetic field is vertically imparted to the molten steel in the nozzle and the speed in the advancing direction of the molten steel can be varied. Consequently, since the flowing speed of the molten steel in the nozzle is varied (vibrated), the sticking and growth of the inclusions in the nozzle are prevented. In the case of using the frequency of the commercial power source 6 as a power source as it is, either single-phase or three-phase can be used. Further, either the frequency control by using a frequency converter or the change of wave-form of an exciting current can be executed. Thus, the sticking of inclusions to the inner part of the nozzle can effectively be prevented and this prevention can greatly be contributed to the stable casting in the continuous casting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents clogging of a molten steel flow passage which prevents non-metallic inclusions in the molten steel from adhering to a refractory flow passage such as a nozzle and causing uneven flow or clogging. It is about law.

[0002]

2. Description of the Related Art For example, in continuous casting of steel, as shown in FIG.
As shown in Fig. 2, a refractory nozzle 2 is used between the tundish 1 and the mold 3, and the nozzle 2 prevents air oxidation of molten steel and controls the flow of the injection flow in the mold to be preferable. Further, it plays a role of preventing the so-called mold powder added on the surface of the molten steel in the mold from being entrained in the injection flow.

However, Al in the molten steel flowing down the nozzle
₂ O ₃ (alumina) -based inclusions adhere to the inner wall of the refractory material that constitutes the nozzle, and this adhesion layer gradually grows throughout the injection, narrowing the flow path of the molten steel flow and causing the molten steel to flow unevenly. It becomes difficult to maintain the flow rate at a predetermined rate, and sometimes injection becomes impossible. As a conventional method for eliminating nozzle clogging, a method of rotating molten steel in the nozzle by electromagnetic force to remove the molten steel is disclosed in JP-A-62-64470. However, in this method, a force to pull the molten steel downward due to the vortex due to the rotating flow works, the molten steel passing speed in the nozzle increases, and the discharge flow velocity increases, so that turbulent flow of the molten steel in the mold occurs, Upflow and downflow on the mold wall surface (short side) become large. This increase in upflow is one of the causes of slab defects due to the inclusion of powder. Also,
The increase in the downward flow reduces the levitation of the argon bubbles blown into the nozzle, and also becomes one of the causes of slab defects.

[0004]

SUMMARY OF THE INVENTION Therefore, the present invention proposes a method for preventing clogging of molten steel flow passages, which can prevent non-metallic inclusions from adhering and growing without generating a rotating flow (vortex) in the nozzle. The purpose is.

[0005]

According to the present invention, when flowing molten steel in a flow path made of refractory material, the molten steel in the flow path is crossed by a magnetic field generating device arranged around the flow path made of refractory material. Applying a magnetic field, and by changing the magnetic field, a method for preventing clogging of a molten steel flow path, characterized in that non-metallic inclusions in the molten steel are prevented from adhering to the flow path wall by varying the molten steel speed, It can be advantageously used for an immersion nozzle for connecting a tundish for continuous casting of steel and a mold.

[0006]

In the present invention, for example, a varying magnetic field that crosses the molten steel in the nozzle is applied, so that a dynamic magnetic field is applied vertically to the molten steel in the nozzle, and the velocity in the traveling direction of the molten steel can be changed.
As a result, the flow velocity of the molten steel in the nozzle changes (vibrates), so that inclusions are prevented from adhering and growing in the nozzle. Further, unlike the above-mentioned conventional method, a rotating flow (vortex) is not generated.

Further, in the present invention, since the molten steel changes its flow velocity by the action of braking by electromagnetic force, the flow velocity does not become faster than that when no electromagnetic field is applied. The principle of the method of the present invention is shown in FIGS. 2 (a), (b) and (c). (A)
FIG. 3B is a diagram showing a waveform of an exciting current, FIG. 7B is a state of molten steel flow during one period of the exciting current, and FIG.

Since the exciting current changes as shown in (a),
The state of the molten steel flow is as shown in (b). Focusing on the electromagnetic force, it becomes as shown in (c), and it can be seen that the electromagnetic force works in the direction opposite to the molten steel advancing direction at a cycle of twice the exciting current. The outline of the method of the present invention is shown in FIGS. 1, 3, and 4. (1) When the commercial power supply frequency is used as it is A three-phase AC power supply (commercial) is made into a single phase by using a balancer circuit or the like, and a circuit as shown in FIG. 1B is assembled. As a result, an electromagnetic force acts on the molten steel at a frequency twice the frequency of the commercial power source in the traveling direction, causing a speed change (vibration). Figure 1
1B is a view taken along the arrow AA ′ of FIG.

Further, as shown in FIGS. 3 (a) and 3 (b), a method of utilizing all three-phase power sources and exerting an electromagnetic force over a wide range is effective when the nozzle is long. Note that FIG. 3B is a view taken along the arrow AA ′ of FIG. (2) When frequency control is performed by a frequency conversion device As shown in FIG. 4, frequency conversion may be performed using a frequency conversion device or the like to apply electromagnetic force at a required frequency.

(3) When changing the waveform of the exciting current An irregular electromagnetic force can be applied to the molten steel by exciting the electromagnetic coil with a current other than a sine wave (for example, a rectangular wave). Of the above methods, an appropriate method for the target equipment is selected, and the flow velocity in the molten steel advancing direction is changed (vibrated) to prevent the inclusion of inclusions in the nozzle.

According to the present invention, by applying a dynamic magnetic field to molten steel in this way, an electromagnetic force is generated at a frequency twice as high as the exciting current in the direction opposite to the traveling direction of molten steel, which changes the velocity of molten steel in the nozzle (vibration). ), And adhesion of inclusions can be prevented.

[0012]

EXAMPLE An apparatus shown in FIG. 4 was attached to an immersion nozzle connecting a tundish of a continuous casting machine and a mold, and an experiment was conducted with a coil applied current of 500A. When the generated magnetic flux density was measured, 1000 Gauss was generated at the center of the nozzle at a frequency of 50H ₂ coil current of 500A without molten steel.
Considering the magnitude of the molten steel injection rate, a sufficient magnetic flux density was obtained to change the flow rate.

A continuous casting experiment was conducted under the above conditions, and after the casting was completed, the nozzle was recovered and the inner wall was examined. As a result, almost no inclusions were observed when a dynamic magnetic field was applied. In addition, when the magnetic field was not applied to the ascending flow and the descending flow of the molten steel in the mold, it was almost the same, and no special slab defect due to the magnetic field application occurred.

[0014]

As described above, according to the present invention, it is possible to effectively prevent the inclusion of inclusions from the inner wall of the nozzle without generating a special slab defect due to the application of a magnetic field. It has become possible to contribute greatly to stable casting. In the above description, application to a nozzle of continuous casting has been described as an example, but the present invention is not limited to this, and for example, all that requires equipment for flowing molten steel into a refractory flow path. Applicable and exerts an excellent effect of preventing inclusions from adhering to the walls of refractory materials.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a usage example of a commercial frequency and a single-phase power source.

FIG. 2 is an explanatory diagram showing a waveform of an exciting current, a molten steel flow state, and an electromagnetic force state.

FIG. 3 is an explanatory diagram showing a usage example of a commercial frequency and a three-phase power source.

FIG. 4 is an explanatory diagram showing an example of frequency conversion and use of a single-phase power supply.

FIG. 5 is an explanatory diagram of a conventional method showing occurrence of nozzle clogging and drift.

[Explanation of symbols]

 1 Tundish 2 Immersion nozzle 3 Mold 4 Electromagnetic coil 5 Frequency converter 6 Commercial power supply

Claims (2)

[Claims] 1. When flowing molten steel in a flow path made of refractory material, a magnetic field is applied by a magnetic field generator arranged around the flow path made of refractory material to cross the molten steel in the flow path. A method for preventing clogging of a molten steel flow path, which is characterized by varying the molten steel speed to prevent non-metallic inclusions in the molten steel from adhering to the flow path wall. 2. The method for preventing clogging of a molten steel flow passage according to claim 1, wherein the molten steel flow passage is an immersion nozzle connecting a tundish for continuous casting of steel and a mold.