JPH11267812A - Continuous casting method for molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the applying position of electromagnetic force constant and produce a cast piece with superior surface quality by adjusting the feeding speed of molten metal so that the frequency signal, obtained by measuring resonance frequency at a particular phase of high frequency current and correcting an energized coil position, may be a predetermined value. SOLUTION: An energized coil position signal from a coil position detector 11 and a resonance frequency signal from a high frequency power supply 14 are input to a molten metal level detector 13, and input to a hold processing circuit after fine signal fluctuation components attributable to the energized coil vibration are removed by a noise cancel circuit. In the hold processing circuit, checking is done with an output modulation signal and the frequency signal obtained is converted into molten metal level signal on the basis of the calibration curve to indicate the correlation between the molten metal level already known and the frequency, and is input from the molten metal level detector 13 to a sliding gate controller 15 to adjust the opening of the sliding gate controller 15 to adjust the opening of a sliding gate 16, resulting in controlling the flow rate of a molten metal 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting method for molten metal, and more particularly, to a continuous casting method capable of high-speed casting by adjusting a molten metal level in a mold (hereinafter referred to as a molten metal level). It relates to a casting method.

[0002]

2. Description of the Related Art In general, in a continuous casting method, a lubricant (hereinafter, referred to as powder) charged to a molten metal surface is promoted to flow between a mold and a solidified shell to prevent seizure between the mold and the solidified shell. , A micro-vibration called oscillation is applied to the mold.

Further, in order to improve the surface quality of the slab and stabilize the casting, an electromagnetic force is applied in the vicinity of the initial solidification shell of the molten metal in the mold in recent years to promote powder inflow and enhance the lubrication effect. A method (hereinafter referred to as an electromagnetic field casting method) has been proposed.

[0004] For example, in Japanese Patent Application Laid-Open No. Hei 4-138842, a plurality of slits are provided at the top of a mold, and a high-frequency current is passed through an energizing coil that circulates around the mold, so that electromagnetic force acts on molten metal in the mold. There is disclosed a method for causing this to occur. According to this method, a slab with few surface defects can be stably manufactured by controlling the interface shape of the solidified shell near the inner wall of the mold to a shape that allows powder to flow easily.

Japanese Patent Application Laid-Open No. 8-206799 discloses that
A method of continuously casting while oscillating an energizing coil arranged on the outer periphery of a mold along a casting direction and modulating an effective value of a flowing high-frequency current into a rectangular wave (hereinafter referred to as an output modulation method) is known. It is stated that the inflow of powder is promoted, and a slab having good surface quality can be produced at high speed and in a stable manner.

As described above, in recent years, in the continuous casting method of metal, an electromagnetic force is applied to the vicinity of the initial solidified shell at the time of casting in order to improve the surface quality of the slab and to achieve a higher casting speed. Things started to happen.

[0007] Usually, in the continuous casting method of molten metal as described above, a method of supplying molten metal into a mold using an immersion nozzle is adopted. In this case, the molten metal surface level in the mold is reduced. It is important to keep it constant. By stabilizing the supply rate of the molten metal to the mold and performing casting while maintaining a constant level of the molten metal, powder is entangled in the molten metal in the mold and the molten metal on the slab surface Wrinkles can be prevented. As a result, the quality of the surface of the slab and the quality immediately below the surface can be improved and the quality can be made uniform.

For this reason, many measures have been taken to improve the level control of the molten metal level. Conventionally, ultrasonic level, microwave, RI radioisotope, etc. have been used as the surface level detection means.However, due to the measurement accuracy, ease of use, etc., those using the electromagnetic effect called an eddy current sensor have been used. Widely used.

However, the eddy current sensor is disclosed in Japanese Patent Laid-Open No.
In the case of applying an electromagnetic force due to a high-frequency current to a molten metal in a mold as in Japanese Patent No. 138843 and Japanese Patent Application Laid-Open No. Hei 8-206799, this eddy current sensor measures the electromotive force of its detection coil, There is a problem that it cannot be used.

Japanese Patent Application Laid-Open No. Hei 1-266952 discloses a measuring instrument for measuring the inductance of a coil embedded in a mold and a coil connected to the coil, and a detecting device for detecting a level of a molten metal in the mold based on the measuring instrument. And a continuous casting apparatus comprising the apparatus.

However, in this method, since the coil is buried in the mold, when a high-frequency current having a frequency of about several kHz is applied, the detection accuracy decreases due to a large attenuation of the magnetic field due to the skin effect in the metal mold. I do. Therefore, it is difficult to accurately detect the molten metal level in the mold.

Japanese Patent Application Laid-Open No. Hei 7-230060 discloses a method of adjusting the supply amount of molten metal so that the resonance frequency of a high-frequency current flowing through a current-carrying coil around a mold has a predetermined value. ing. The measurement principle is that when the level of the molten metal in the mold changes, the self-inductance including the mold and the molten metal changes, and as a result, the inductance of the circuit changes. It is based on the principle of electromagnetism that the frequency changes.

By the way, in continuous casting in recent years, when an electromagnetic force is applied to a molten metal in a mold in order to further increase productivity, the effective value of a high-frequency current is reduced as described in Japanese Patent Application Laid-Open No. 8-206799. It may be modulated.
At this time, the inductance and resonance frequency of the circuit change according to the modulated effective value. As a result, there is a problem in that the level signal cannot be accurately measured because the level signal changes in the same cycle as the modulation period of the high frequency power supply and is not stable.

Further, when coil vibration is accompanied to promote powder inflow as in the invention of Japanese Patent Application Laid-Open No. Hei 8-206799, the relative position between the molten metal surface level and the current-carrying coil changes, so that the inductance increases. And the resonance frequency changes. Therefore, there is a problem that a disturbance signal appears superimposed on the molten metal level signal in the same cycle as the coil oscillation period, and cannot be a stable molten metal level detection signal.

[0015]

At present, the electromagnetic field casting method, which uses a method of modulating the output of a coil vibration and a high-frequency current, for securing a good cast slab surface and achieving high speed casting by promoting powder inflow, is currently effective. There is no method for detecting the level of the molten metal, and the operation must be performed while observing the liquid level visually.

[0016] Therefore, there is a problem that not only stable continuous casting is difficult, but also the effect of the electromagnetic force cannot be sufficiently obtained due to fluctuations in the molten metal level.

Further, there is a problem that unstable fluctuations in the level of the molten metal level adversely affect the quality of the slab, such as the occurrence of powder entrainment.

The present invention relates to a method of continuously casting metal in which an electromagnetic force is applied by a high-frequency current in the vicinity of an initially solidified shell, wherein the energizing coil is vibrated in the casting direction and the effective value of the applied high-frequency current is modulated. Even so, in order to produce a slab having good surface quality at high speed and stably, an object of the present invention is to provide a method of accurately detecting a level of a molten metal in a mold and controlling the level to a constant level. .

[0019]

The gist of the present invention resides in a continuous casting method of molten metal shown in the following (1).

(1) A metal mold having an internal water-cooling structure having a plurality of slits penetrating through the mold wall, having an energizing coil on the outer periphery, a vibrating device for vibrating the energizing coil in a casting direction, and adjusting a flow rate. In a method for continuously casting molten metal using an apparatus having a means for supplying molten metal to the water-cooled mold through a molten metal supply port having a mechanism, the energized coil is vibrated in a casting direction and the energized coil is periodically cycled. A high-frequency current whose effective value has been modulated is passed through, a resonance signal at a specific phase of the effective value-modulated high-frequency current is measured, and a frequency signal obtained by correcting the position of the energizing coil is obtained in advance. A continuous casting method for molten metal, wherein a molten metal supply speed is adjusted by a molten metal supply port having the flow rate adjusting mechanism so as to have a predetermined value.

The molten metal to which the method of the present invention is applied is steel such as ordinary steel, alloy steel, and stainless steel, aluminum and its alloys, and copper and its alloys. The method of the present invention can be applied to other metals that can be continuously cast.

FIG. 1 shows an example of an apparatus to which the method of the present invention is applied. The upper part of the water-cooled mold 2 has a plurality of slits 1 penetrating the mold wall. The molten metal 5 is a tundish 1
From 8, it is supplied into the mold through a sliding gate 16 and a dipping nozzle 4.

The energizing coil 3 disposed on the outer periphery of the mold is subjected to vibration in the casting direction by the coil vibrator 20. The position of the energized coil when vibrating is determined by the coil position detector 1
1 and is input to the level detector 13 and the output modulator 19.

A high-frequency current whose effective value has been modulated is passed from the high-frequency power supply 14 via the output modulation device 19 to the current-carrying coil, and the frequency signal is transmitted to the level detector 1.
3 is input.

The level signal is supplied to the level detector 13.
Is input to the sliding gate control device 15 to control the opening and closing of the sliding gate 16 so that the level of the molten metal in the mold becomes the target level.

The level detector 13 converts the resonance frequency of the high-frequency current flowing through the current-carrying coil into a level signal based on a calibration curve that indicates the correlation between the level and the frequency, which is known in advance.

At this time, in the electromagnetic field casting method using both the coil vibration and the output modulation method of the high-frequency current, a disturbance signal is generated at the resonance frequency due to the influence of the coil vibration and the output modulation method. It does not become a hot water level signal.

According to the method of the present invention, in the level detector, correction of a disturbance signal to a frequency corresponding to a change in the position of a vibrating energizing coil and correction of a disturbance signal to a frequency accompanying the execution of an output modulation method. , An accurate level signal can be obtained, and the sliding gate control based on the level signal can maintain the level of the level at the target level.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, a mold 2 is provided with a mold vibration device (not shown). The mold vibrator is
Any device can be used as long as it can provide vibration of a normal sine wave or other waveforms, such as a structure using a motor and an eccentric cam or a hydraulic drive structure. Usually, mold vibration is applied. However, in the case of an electromagnetic field casting method in which powder inflow is promoted by electromagnetic force, a mold vibration device is not necessarily required.

Powder or granular powder is supplied to the upper surface of the molten metal 5 in the mold, and the powder melted by the heat of the molten metal 5 flows into the gap between the mold 2 and the solidified shell 7 to lubricate and prevent seizure. Has the effect of

The energizing coil 3 is made of water-cooled copper and is supported by a coil vibrating device 20. Further, vibration having an amplitude of several mm to several tens mm is added in the casting direction. The vibration of the energizing coil is detected by a coil position detector 11, and this position signal is input to an output modulator 19 and a level detector 13.

By inputting the position signal of the current-carrying coil to the output modulator 19, output modulation for modulating the effective value of the high-frequency current supplied to the current-carrying coil into a rectangular wave in synchronization with the vibration of the current-carrying coil is performed. Thereby, the interface shape of the solidified shell near the inner wall of the mold is periodically changed to promote powder inflow.

FIG. 2A is a diagram showing a position signal of the energizing coil when the energizing coil is vibrated. FIG.
(B) is a diagram showing a modulated signal output from the output modulation device. The modulation signal has a rectangular signal waveform indicating the phase of vibration of the energizing coil. Here, the signal of the time when the energizing coil is falling from the top dead center to the bottom dead center of the vibration is defined as phase A, and conversely, the signal of the time when the energizing coil is rising from the bottom dead center to the top dead center of the vibration is The signal is in phase B.

FIG. 2C is a diagram showing an effective value of a high-frequency current whose output signal is modulated by the power supply 14 when a modulation signal output from the output modulation device is input to the power supply 14. The high-frequency current output-modulated as described above is passed from the power supply 14 to the energizing coil, and a resonance frequency signal represented by a current or a voltage is input to the level detector 13. FIG. 2D is a diagram illustrating the resonance frequency signal input to the molten metal level detector 13 at this time.

When the high-frequency current of the current-carrying coil is high output (corresponding to the time of the above-described phase A; hereinafter, the same state is meant) and when it is low output (corresponding to the time of the above-described phase B; hereinafter, the same). This means that the resonance frequency signal level changes in proportion to the output modulation.

Further, since the fluctuation component caused by the vibration of the current-carrying coil is superimposed, the frequency signal is generated even during the time between the steps of phase A and phase B as shown in FIG.
A behavior in which the resonance frequency signal gradually changes with time is shown. The resonance frequency signal is once input to the level detector, but the level cannot be accurately detected with the level determined from the resonance frequency signal.

A method for detecting the level of the molten metal by using the method of the present invention will be specifically described.

The energized coil position signal is supplied to the coil position detector 1
1 and the resonance frequency signal from the high-frequency power supply 14 are input to the molten metal level detector 13. From the resonance frequency signal input into the level detector 13, a small signal fluctuation component caused by vibration of the energized coil is removed by a noise canceling circuit.

FIG. 2E shows a frequency signal obtained by removing a signal fluctuation component due to the vibration of the energizing coil. The signal fluctuation component caused by the vibration of the energizing coil is minute and is known in advance. For the resonance frequency signal,
By adding / subtracting a signal fluctuation component due to the energized coil vibration in accordance with the energized coil vibration cycle, the influence of the energized coil vibration on the frequency can be eliminated.

Next, the frequency signal output from the noise cancellation circuit is input to the hold processing circuit. The fluctuation width of the frequency signal due to the output modulation is relatively large with respect to the signal width detected as the level signal, and the rise and fall of the signal height are sharp and sharp. When a signal width is added to or subtracted from a noise signal, a noise signal is easily generated.

Therefore, the hold processing circuit collates with the output modulation signal, outputs the input frequency signal as it is during the time of phase A, and outputs the input signal as it is during the time of phase B. 2 (e) the value of the position of the code F)
Is designed to hold. Although the measurement phase is set to the phase A here, the time of the phase B may be output as the measurement time, and the time between the phases A may hold the final signal value of the phase B.

FIG. 2F shows a frequency signal finally obtained by correcting the fluctuation of the frequency due to the vibration of the current-carrying coil and the output modulation. The signal of the obtained frequency is converted into a level signal based on a calibration curve that indicates the correlation between the level and the frequency, which is known in advance, and is input from the level detector 13 to the sliding gate control device 15. Is done.

The sliding control device 15 adjusts the opening of the sliding gate 16 based on the molten metal level signal in the same manner as the molten metal level detection by the conventional eddy current sensor. The flow rate of the molten metal 5 is controlled so as to have a predetermined value.

In FIG. 1, a sliding gate is used as a mechanism for adjusting the flow rate of the molten metal, but the method is not particularly limited. For example, as shown in FIG. 5, the opening degree of the molten metal supply port of the type of the stopper 21 and the immersion nozzle 4 may be adjusted based on the molten metal level detection signal.

For these flow control, existing process control mechanisms such as a so-called PI (two-operation controller) and PID (three-operation controller) are sufficient.

By applying the above-described method of the present invention, even in electromagnetic field casting in which the energizing coil 3 vibrates and a high-frequency current flowing through the energizing coil is output modulated, the level of the molten metal can be detected with high accuracy. Since the flow rate of the molten metal 5 can be controlled based on this, the level of the molten metal can be maintained at a predetermined position. In addition, the electromagnetic force acts on the solidified shell at an appropriate position, the powder inflow is stably promoted, and it is possible to continuously cast slabs having good surface quality stably at high speed. is there.

[0047]

EXAMPLE A continuous casting test of molten steel was performed using a continuous casting apparatus having the structure shown in FIG. Table 1 shows the chemical composition of a medium carbon steel with a tested carbon content of 0.45% by weight. Table 2
Figure 3 shows the continuous casting conditions during the test.

[0048]

[Table 1]

[0049]

[Table 2]

The slab has a round cross section of 266 mm in diameter.
The casting speed was high speed casting of 2 m / min. In the upper part of the mold wall, a slit 30 having a width of 0.25 mm and a length of 250 mm
The book is provided in the casting direction. The molten steel surface is at a position about 100 mm below the upper end of the mold. Therefore,
Even if the molten steel surface slightly fluctuates up and down, it hits the position of the slit. The energizing coil is wound around the mold three times, and the coil height is 40 mm in the casting direction.

With respect to the vibration of the energizing coil, a vibration having a vibration frequency of 120 cpm and an amplitude of ± 8 mm was added. A current of 4500 A was passed through the energizing coil at a high frequency of 20 kHz.

In the output modulation, the output is 100% in the phase A at the time of high output, the output is 15% in the phase B at the time of low output, and the duty ratio (high signal level time ratio in one cycle) is 50%.
The frequency was set to the modulation mode of 2 Hz which is the same as that of the current-carrying coil.

Table 3 shows the chemical composition of the powder used. This powder is commonly used.

[0054]

[Table 3]

(Embodiment 1) In Embodiment 1, the oscillation of the energizing coil and the output modulation are synchronized so that the energizing coil has a phase A in the falling period from the top dead center to the bottom dead center of the oscillation. Further, the detection of the resonance frequency was performed only during the time between the phases A, and the final signal value of the phase A was held at the phase B as described above.

FIG. 3 (a) shows the change over time of the molten metal level when continuous casting is performed under the above conditions. The level of the molten metal is stably controlled within ± 5 mm from the target level.

When the thickness of the powder film was measured from the powder collected directly below the mold, the thickness was 1.21 mm on average, and it was confirmed that sufficient powder inflow was performed. In addition, no slab surface defects considered to be caused by insufficient powder inflow such as surface cracks and seizure of the slab were found.

(Comparative Example 1) A test was conducted using the same apparatus and casting conditions as in Example 1 described above. However, the fluctuation component of the frequency signal caused by the vibration of the energizing coil was not removed, and only the process of holding the final signal value of the phase A was performed during the time between the phases B.

FIG. 3B shows the fluctuation of the molten metal level at this time. Fluctuations in the frequency signal caused by the vibration of the current-carrying coil caused minute periodic fluctuations in the bath level of 2 Hz. Further, in this figure, a large swelling level change was observed in addition to the fine cycle level change. This undulation is caused by the sliding gate control device 1 according to the minute fluctuation of the level signal corresponding to the vibration of the energizing coil.
5 adjusts the degree of opening of the gate, so that the inflow of molten steel changes periodically, and as a result, a relatively long period of molten metal level fluctuation is caused.

Although such a level change does not make the continuous casting operation so unstable, a periodic horizontal stripe pattern corresponding to the level change is found in a part of the obtained slab. There was also some evidence of powder entrainment.

From the powder collected directly below the mold, it was found that the average thickness of the powder film was 0.93 mm, and the powder inflow function was insufficient compared to Example 1.

(Comparative Example 2) A test was conducted using the same apparatus and casting conditions as in Example 1 described above. However, only the noise canceling process of the resonance frequency fluctuation due to the vibration of the energizing coil was performed, and the test was performed without performing the process of holding the final signal value of the phase A during the time between the phases B.

FIG. 3 (c) shows the fluctuation of the molten metal level at this time. 2H having a relatively large amplitude compared to the minute level change of the molten metal level corresponding to the vibration of the energizing coil in Comparative Example 1.
Fluctuation in the surface level of z occurred. This is noise generated by fluctuation of the resonance frequency signal due to modulation of the effective value of the high-frequency current of the energizing coil. Further, as in Comparative Example 1, a large change in the level of the molten metal surface was observed.

From the results of observation of the surface condition of the mold and the immersion nozzle after the test, the level of the molten metal is ± 10 m from the target level.
m, which does not greatly affect the operation of continuous casting, but adversely affects the surface quality of the slab.

A periodic horizontal stripe pattern corresponding to the change in the level of the molten metal is observed on the surface of the slab, pinhole defects having a small diameter are generated, and powder is scattered inside. It turned out to be occurring quite frequently.

From the recovered powder, the average thickness of the powder film was 0.67 mm. Compared with Example 1, the powder level did not sufficiently flow between the mold and the solidified shell due to large fluctuations in the molten metal level. all right.

[0067]

According to the method of the present invention, the molten metal in the mold is subjected to an electromagnetic force that modulates the effective value of the high-frequency current of the energized coil, and the energized coil is vibrated. In this way, the flow of powder can be promoted in between, and the level of the molten metal level can be accurately controlled. Therefore, since the position where the electromagnetic force is applied can be kept constant, it is possible to manufacture a cast piece having excellent surface quality.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a continuous casting apparatus to which the method of the present invention is applied.

FIG. 2 is a timing chart illustrating a resonance frequency and a processed frequency signal.

FIG. 3 is a diagram showing a level signal in a test of an example of the present invention and a comparative example.

FIG. 4 is a block diagram illustrating conversion of a resonance frequency signal in the apparatus for detecting a level of a molten metal to which the method of the present invention is applied.

FIG. 5 is a diagram showing an example of a molten metal supply port device of a stopper and a dipping nozzle type.

[Explanation of symbols]

1: Slit 2: Mold 3: Electric coil 4: Dipping nozzle 5: Molten metal 6: Unmelted powder 7: Solidified shell 8: Molten powder 11: Coil position detector 13: Metal surface level detector 14: High frequency power supply 15: Sliding gate control device 16: Sliding gate 18: Tundish 19: Output modulation device 20: Coil vibration device 21: Stopper rod 22: Stopper elevating cylinder

Claims (1)

[Claims] 1. A metal mold having an internal water-cooled structure having a plurality of slits penetrating a mold wall, having an energizing coil on an outer peripheral portion, a vibrating device for vibrating the energizing coil in a casting direction, and a flow rate adjusting mechanism. In a method of continuously casting molten metal using an apparatus having a means for supplying molten metal to the water-cooled mold through a molten metal supply port having a method, while vibrating an energized coil in the casting direction, periodically energizing the energized coil A high-frequency current subjected to RMS modulation is passed, a resonance signal at a specific phase of the RMS-modulated high-frequency current is measured, and a frequency signal obtained by correcting the position of the energized coil is determined in advance. Wherein the molten metal supply speed is adjusted by a molten metal supply port having the flow rate adjusting mechanism so as to obtain a given value.