JPH0455772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing clogging of a submerged nozzle of a continuous casting machine in a steel mill.

During continuous casting in steel plants, it is difficult to control the injection flow rate by directly injecting molten steel produced in a converter from the ladle into a continuous casting machine. ).

FIG. 3 is a schematic cross-sectional view showing the structure of a conventional mold section in a continuous casting machine, in which 1 is a tundish into which molten steel in a ladle (not shown) is injected; The molten steel flows continuously into the immersion nozzle 2 attached to the bottom 1a of the immersion nozzle 2. It is designed to flow into a mold 3 located below the tundish 1. The molten steel flowing into the mold 3 passes through a spray zone and guide rolls (not shown) provided directly below the mold 3, is cooled and molded to form slabs, and is continuously extracted by pinch rolls. It is becoming possible to obtain

However, when slabs are continuously cast in this way, non-metallic materials mainly containing aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), etc., contained in the molten steel are removed. When the inclusions 4 pass through the immersion nozzle 2, they are deposited on the inner surface of the immersion nozzle 2, causing clogging, and the amount of molten steel passing through the immersion nozzle 2 gradually decreases, resulting in a significant decrease in the operating efficiency. Therefore, conventionally, in order to prevent the nonmetallic inclusions 4 from adhering and depositing on the inner surface of the immersion nozzle 2, the amount of nonmetallic inclusions in the molten steel has been suppressed. In addition, in preparation for non-metallic inclusions 4 adhering to the inner surface of the immersion nozzle 2, a gas blowing tube 5 is provided, the lower end of which is inserted into the upper part of the immersion nozzle 2. If nonmetallic inclusions 4 are deposited, the molten steel in the tundish 1 is temporarily emptied, and high-pressure gas such as oxygen or argon is blown into the immersion nozzle 2 from the gas blowing pipe 5. The nonmetallic inclusions 4 are removed by melting or scattering. However, in the case of such high-pressure gas spraying, a large amount of non-metallic inclusions 4 that have melted into the mold are temporarily contained in the slab, and the quality of the slab is partially deteriorated. There are problems such as deterioration of the production efficiency, and there are problems that cause a decrease in operation efficiency and a decrease in quality.

Conventionally, as a countermeasure against this problem, ultrasonic vibrations were applied to the immersion nozzle to remove non-metallic inclusions and prevent their adhesion. There was a problem of damage or breakage.

The present invention has been made in view of the above circumstances, and includes a vibration system between the piezoelectric vibrator and the bottom of the tundish in the immersion nozzle, a vibration system between the piezoelectric vibrator and the molten steel surface in the mold, and the thickness of the immersion nozzle. By applying vibrations within the range of 2 to 7 MHz to the immersion nozzle at the matched resonance frequencies of the vibration systems in each direction, non-metallic inclusions can be prevented from adhering to the inner surface of the immersion nozzle. It is an object of the present invention to provide a method for preventing clogging of a submerged nozzle, which can prevent clogging of a submerged nozzle, prevent a decrease in the operating rate of a continuous casting machine, and improve the quality of slabs.

EMBODIMENT OF THE INVENTION Hereinafter, the method for preventing clogging of a submerged nozzle according to the present invention will be explained in detail with reference to drawings showing examples. FIG. 1 is a schematic cross-sectional view showing the structure near the immersion nozzle to which the present invention is applied in a continuous casting machine,
Components that correspond to those shown in the figures are given the same reference numerals. As shown in FIG. 1, a cylindrical immersion nozzle 2 is integrally attached to the bottom 1a of the tundish 1, with its upper end communicating with the inside of the tundish 1. A plurality of molten steel outlets 2a are opened on the lower peripheral surface of the immersion nozzle 2, and these molten steel outlets 2a are located in a mold 3 located below the tundish 1. Therefore, when molten steel is injected into the tundish 1, the molten steel continuously flows into the immersion nozzle 2 and is charged into the mold 3 through the molten steel outlet 2a.
The molten steel charged into the mold 3 is cooled by a spray zone (not shown) provided directly below the mold 3, and is molded into a predetermined shape by guide rolls to form a slab.
This slab is continuously extracted by pinch rolls.

A piezoelectric vibrator 6 is attached to the outer surface of the portion of the immersion nozzle 2 located above the mold 3. The tip of this piezoelectric vibrator 6 is a recess 2b formed on the outer surface of the immersion nozzle 2 by an appropriate length.
It is embedded in the body and fixed integrally with a heat-resistant adhesive containing ceramic or the like. One end of a lead wire 7 for charging is connected to the rear end of the piezoelectric vibrator 6 by soldering or welding, and the other end of the lead wire 7 has a frequency of 2 to 7 MHz.
It is connected to the output terminal 8a of the high frequency generator 8 in the range of . The reason why the frequency is set to 2 to 7 MHz is because if the frequency is less than 2 MHz, the frequency is too small and the removal effect of non-metallic inclusions is small, and if it exceeds 7 MHz, the vibration becomes large and there is a risk of damage to the nozzle. As this high frequency generator 8, an oscillating part of an ultrasonic generator can be used. When this high-frequency generator 8 is driven, the piezoelectric vibrator 6 is charged with electricity through the lead wire 7 and vibrates ultrasonically, so that the immersion nozzle 2 can be continuously vibrated ultrasonically.

In this ultrasonic vibration of the immersion nozzle 2, the fixed part of the immersion nozzle 2 to the tundish 1 and the molten steel surface in the mold 3 are the fixed ends of the vibration operation, and its natural frequency ω is determined by i as a coefficient, c as a wave velocity, and l. When is the length of the vibrating part (distance from the vibrator 6 to the upper or lower fixed end), ω=iπc/l. This ultrasonic vibration prevents nonmetallic inclusions such as aluminum oxide (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ) in the molten steel from adhering to the inner surface of the immersion nozzle 2 even when the molten steel passes through the immersion nozzle 2 . is hindered. Therefore, it is possible to prevent nonmetallic inclusions from adhering to the immersion nozzle 2,
Improved slab quality and operational efficiency can be achieved.

In addition, in order to more effectively prevent non-metallic inclusions from adhering to the immersion nozzle 2, it is desirable to appropriately change the frequency in response to variations in the thickness of the immersion nozzle 2 and the molten steel surface within the mold 3. .

This relationship will be explained with reference to FIG.

For example, a piezoelectric vibrator 6 attached to the immersion nozzle 2
The upper side _of the vibrator ₆ is
Assuming that the resonance frequencies f of the lower vibration system and the vibration system in the thickness direction of the nozzle 2 are made to match, f=i ₁ c/4l ₁ = i ₂ c/4l ₂ = i ₃ c/2t.

However, c = 5.57 × 10 ⁵ cm/sec For example, if l ₁ = 20 cm and t = 2 cm, then f = (i ₁ − _{i 2} − Zi ₃ ) c/4 (l ₁ − l ₂ − t) ≒ i × 1.39 ×10 ⁵ / (18−l ₂ ).

Therefore, it is most effective to obtain l ₂ from the measurement data of the level of the molten steel in the mold, and to excite the vibrator 6 at the resonance frequency f determined by the above equation according to its fluctuation.

In addition, if the non-metallic inclusion is to be re-separated from the immersion nozzle 2 while the diameter is sufficiently small, the vibration frequency f is set so that it becomes the resonant frequency of the wavelength corresponding to the diameter (d) of the non-metallic inclusion. Should. For this purpose, it is necessary to set the vibration frequency f to a sufficiently high value. For example, if l ₂ =8 cm, f=c/2d, and d=100μ, a vibration frequency of approximately f=0.7×10 ⁷ Hz7MHz is required.

On the other hand, the output of the high frequency generator 8 requires 300 to 1500 W since the reflectance between the piezoelectric vibrator 6 and the immersion nozzle 2 is about 30%.

Experiments have confirmed that below 300W, vibration damping is less effective in preventing the adhesion of non-metallic inclusions, and above 1500W, cavities form in the molten steel in the immersion nozzle 2, making it impossible to achieve the objective. This is because it was done. It was also confirmed that the amplitude of ultrasonic vibration was sufficiently small in the output range of 300 to 1500 W, and no problems such as breakage of the ceramic immersion nozzle occurred.

The specific effects of the present invention are as follows. In other words, when an ultrasonic signal with an ultrasonic frequency of 7 MHz and an output of 500 W is applied to a piezoelectric vibrator to cause the immersion nozzle to vibrate ultrasonically, Si-Al killed steel adheres to the inner surface of the immersion nozzle after 320 tons of continuous casting. The amount of nonmetallic inclusions was
The amount of adhesion was 200g, which was a good result, drastically reducing the amount of adhesion when no ultrasonic vibration was applied, which was 500g. The material of the immersion nozzle in this example is alumina graphite, and the inner diameter of the immersion nozzle is
The diameter was 90 mm, and the continuous casting time was 160 minutes.

As described in detail above, the method for preventing clogging of a submerged nozzle according to the present invention involves fixing a piezoelectric vibrator to the submerged nozzle for charging molten steel into the mold of a continuous casting machine, and applying an electric current to the piezoelectric vibrator to increase the vibration frequency. 2~7MHz
The resonance frequency is within the range of the vibration system from the piezoelectric vibrator to the bottom of the tundish, the vibration system between the piezoelectric vibrator and the molten steel surface in the mold, and the vibration system in the thickness direction of the immersion nozzle. , or in addition, by applying vibration to the immersed nozzle at a resonant frequency of a wavelength corresponding to the diameter of the non-metallic inclusion, the adhesion of the non-metallic inclusion to the inner surface of the immersed nozzle 2 is prevented. Highly efficient continuous casting is possible without reducing operation efficiency. Also, non-metallic inclusions 4 can be removed from the immersion nozzle 2 by ultrasonic vibration alone.
The present invention has excellent effects, such as preventing the adhesion of the steel, so there is no effect on the components of the slab, and quality can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the vicinity of the immersed nozzle for applying the method for preventing clogging of the immersed nozzle according to the present invention, and FIG. 2 shows the mounting position of the piezoelectric vibrator, the tundish, the molten steel surface in the mold, and the vibration frequency. FIG. 3, an explanatory diagram for examining the relationship, is a schematic cross-sectional view of the vicinity of a conventional immersion nozzle in which nonmetallic inclusions attached to the immersion nozzle are removed. 1...Tandate dish, 2...Immersion nozzle, 3
...Mold, 4...Nonmetal inclusion, 6...Piezoelectric vibrator, 8...High frequency generator.

Claims (1)

[Scope of Claims] 1. A piezoelectric vibrator is fixed to a suitable position of an immersion nozzle for charging molten steel into a mold of a continuous casting machine, and by applying electricity to the piezoelectric vibrator, the vibration frequency is in the range of 2 to 7 MHz, The vibration system from the piezoelectric vibrator to the bottom of the tundish, the vibration system from the piezoelectric vibrator to the molten steel surface in the mold, and the vibration system in the thickness direction of the immersion nozzle vibrate against the immersion nozzle at the same resonance frequency. A method for preventing clogging of an immersion nozzle, characterized by providing the following. 2. The method for preventing nozzle clogging of a submerged nozzle according to claim 1, wherein the piezoelectric vibrator applies vibration to the submerged nozzle at a resonant frequency of a wavelength corresponding to the diameter of the nonmetallic inclusion.