KR20020004634A - Apparatus and method for measuring the molten metal level in electromagnetic continuous casting - Google Patents

Abstract

The present invention relates to an apparatus and a method for detecting a free surface level of a molten metal in an electromagnetic continuous casting using an alternating electromagnetic field. After measuring an overlapping magnetic field of an applied magnetic field by an induction coil and an induced magnetic field due to eddy currents generated in a hot water surface, The present invention relates to an apparatus and a method for detecting a water level of a molten metal by removing a variation of an applied magnetic field caused by a variation of an induced current.

Therefore, according to the present invention, it is possible to improve the surface quality of the casting product by accurately measuring the level of the water by distinguishing whether the detection value variation of the detection coil is due to the change of the applied magnetic field or the level of the water surface. Can be obtained.

Description

Apparatus and method for surface level detection in electromagnetic continuous casting {APPARATUS AND METHOD FOR MEASURING THE MOLTEN METAL LEVEL IN ELECTROMAGNETIC CONTINUOUS CASTING}

The present invention relates to an apparatus and a method for detecting a level of molten metal in an electromagnetic continuous casting, and more particularly, to an apparatus and a method for measuring the level of a molten surface in an electromagnetic continuous casting machine using an alternating electromagnetic field.

In general, electromagnetic continuous casting technology applies an alternating electromagnetic field to a position where a solidified shell is formed in a casting mold and exits the casting mold by using Joule heat and electromagnetic force generated by the electromagnetic field. Unlike the conventional continuous casting process, as a process of smoothing the surface of the cast steel, a strong alternating electromagnetic field is applied to the molten free surface (hereinafter, referred to as the molten surface) area of the casting mold. This electromagnetic field is applied by an induction coil through which an alternating current flows outside the casting mold, which is installed where the hot water surface is located.

On the other hand, the continuous casting process must accurately adjust the position of the hot water for the solidification of the molten metal and safe casting operation. In general, continuous casting of steel adjusts the position of the bath surface within an error range of ± 5mm.

Methods of measuring the water surface position used in the existing steel continuous casting process include a method using radiation that does not penetrate the molten metal, a method using an eddy current sensor (US Patent US4567435,1987), a method using a capacitive sensor (US Patent, US4555941,1985). ). However, these methods cannot be used due to heating or spatial constraints of the measuring device in the electromagnetic continuous casting in which a strong alternating magnetic field exists in the surface area. The method by the eddy current sensor has to place the sensor inside the mold, the strong magnetic field strength in the hot water area, such as electromagnetic continuous casting loses its function as a sensor because the sensor is magnetically saturated. The method of capacitive measurement requires no conductor that affects the potential nearer than the distance between the electrode and the surface, which leads to not only spatial constraints but also a significant effect on the dielectric constant of powder in the surface of molten steel casting. The error range is quite large because the output varies depending on the thickness of the powder. In addition, the conductors must be installed relatively close to the hot water surface, and the strong electromagnetic field of the electromagnetic continuous casting makes the conductors inductively heated so that they cannot serve as sensors. Devices that use radiation also cannot play its role due to induction heating by electromagnetic fields.

As a method of measuring the position of the tap surface which can be used in electromagnetic continuous casting, a method using a frequency change of an induction coil that applies an electromagnetic field from the outside (US Patent, US4446562, 1984), or a method using a change of inductance of an induction coil (Japanese Patent, 6-122056). In principle, when the position of the hot water surface changes, the electrical load of the electromagnetic continuous casting equipment consisting of induction coil, casting mold, molten metal, etc. changes, so that voltage, current, inductance and frequency applied from the power supply to the induction coil are changed. Change. The above methods measure the position of the tap surface by using this phenomenon, which is excellent when the tap surface is in the induction coil region, but when the tap surface leaves the induction coil region, the degree decreases rapidly, so the detection band is reduced in the induction coil region. It is limited to.

As an attempt to overcome this problem, attempts have been made to expand the floor detection band by installing an auxiliary coil on the induction coil, but this is also limited to the area where the two coils occupy (Iron and Steel, Vol. 84, p625 (1998). )). In the method of measuring the inductance change of the induction coil using the detecting coil of Japanese Patent Application Laid-Open No. 6-122056, the measured value of the detecting coil is influenced by the current change of the induction coil which is arbitrarily changed according to the casting conditions. It is difficult to apply to the measurement of the water surface without correcting it.

Another method using the magnetic field sensor (Domestic Patent Application No. 99-28920) has a high sensitivity of the sensor and a wide detection band, so that it can be applied to measuring the surface position in electromagnetic continuous casting. In this case, there is a possibility that the error of the measurement result is increased.

Accordingly, the present invention has been made to solve the above-described problems, the purpose of which is to effectively remove the noise generated from the power supply itself of the electromagnetic continuous casting machine and the noise introduced from the outside, and in accordance with the accurate level of water level detection in the future It is an object of the present invention to provide an apparatus and method for detecting a surface level in electromagnetic continuous casting, which is capable of providing surface level data suitable for other equipment.

1 is a block diagram of a surface level detection apparatus in the electromagnetic continuous casting according to the present invention.

2 is a block diagram showing the configuration of a level detecting means for implementing the present invention.

3 is a graph showing a change in the applied magnetic field and the induced magnetic field according to the present invention.

4 is a graph showing the surface level detection result of the induction coil current variation according to the present invention.

Explanation of symbols on the main parts of the drawings

1 ... mold, 3 ... induction coil,

4 molten metal, 6 index coils,

7 power supply, 8 level detecting means,

9 ... insulation amplifier, 10 ... band pass filter,

11 ... RMS operator, 12 ... maximum detector,

13 low pass filter, 14 differential output converter,

15 ... analog / digital converter,

16 ... Operation.

In order to achieve the above object, the apparatus for detecting the bottom surface of an electromagnetic continuous casting according to the present invention is an induction magnetic field generated by an applied magnetic field and an eddy current generated in an induction coil to detect the surface level of a molten metal contained in a mold in an electromagnetic continuous casting process. In the apparatus for detecting the level of water surface by measuring the

A power supply unit applying predetermined AC power to the induction coil;

A detection coil for detecting the applied magnetic field and the induced magnetic field;

An amplification and filtering unit which receives the signal detected by the detection coil, amplifies the signal to a predetermined level, and filters the noise to remove noise;

An arithmetic unit for detecting the level of the water level by removing an applied magnetic field component caused by a change in AC power applied to an induction coil from the magnetic field signal detected by the detection coil using the amplified and filtered signal and a power variable input from the power supply unit. Characterized in that provided with.

In addition, in the continuous surface level detection method of electromagnetic continuous casting according to the present invention, in order to detect the surface level of molten metal contained in the mold in the electromagnetic continuous casting process, the detection coil overlaps the induced magnetic field generated by the induction coil and the induced magnetic field due to the eddy current. In the method for detecting the water level by measuring through,

Amplifying and filtering an overlapping magnetic field measured through the detection coil to a predetermined level,

And removing the applied magnetic field component due to the change of the applied current applied to the induction coil from the amplified and filtered signal to determine and output the level of the water level.

Hereinafter, with reference to the accompanying drawings, the configuration and operation effects of the apparatus for detecting the water level in the electromagnetic continuous casting according to the preferred embodiment of the present invention will be described in detail.

1 is a system diagram showing a schematic configuration of an apparatus for detecting the water level in electromagnetic continuous casting for implementing the present invention. As shown in FIG. 1, the apparatus for detecting the water level in the continuous electromagnetic casting according to the present invention is installed on the outer circumferential surface of the mold 1 to generate an applied magnetic field in accordance with an alternating current applied thereto. And a power supply unit 7 for applying a predetermined alternating current to the induction coil 3, an induction magnetic field caused by eddy current generated by being applied to the molten metal 4, and an applied magnetic field generated by the induction coil 3. And a level detecting means (8) for detecting the level of hot water of the molten metal (4) from the superimposed magnetic field detected by the detecting coil (6).

In the above-described configuration, the power supply unit 7 applies an alternating current of several tens to hundreds of kHz and thousands of amperes to the induction coil 3, and at this time, in the applied magnetic field and the molten metal generated by the induction coil 3. The induced magnetic field due to the generated eddy current is an alternating magnetic field of the same frequency.

On the other hand, when an alternating current is applied to the induction coil 3 by using the power supply unit 7, the magnetic field passing through the mold 1 is applied to the molten metal, and the induction magnetic field is generated by the eddy current generated in the molten metal. The detection coil 6 measures the sum of the induction magnetic field and the applied magnetic field to detect the molten metal level of the molten metal.

The detected level signal is applied to the level detecting means 8 to remove noise and to measure the level of the water level, and to stably control the level of the water level so that the solidification cell is stably formed, thereby improving the surface quality of the cast product. .

2 is a block diagram showing a detailed configuration of the level detecting means according to the present invention. As shown in Fig. 2, the signal output from the detection coil is input to the isolation amplifier 9 and amplified to a predetermined level. At this time, since the detection coil 6 is in the form of a coil, the noise flowing from the outside may be large. Therefore, a commonly used differential amplifier cannot remove common mode noise of 10V or more, and uses an isolation amplifier to protect the system and to provide stable amplification.

Since the signal amplified by the isolation amplifier 9 to a predetermined level contains noise due to the electric fluctuations of the power supply device, it is necessary to acquire only a signal in a unique frequency range necessary for level measurement. Thus, the amplified signal is noise removed through the bandpass filter 10. On the other hand, the signal passing through the bandpass filter 10 still has the signal characteristics of the alternating current in order to utilize the signal in the water level control using the RMS operator 11 or the maximum detector 12 within a predetermined time It should be converted into a direct current signal. The converted signal still contains high frequency noise, so the low pass filter 13 is used to remove the noise. Since the measurement signal of the noise level detection coil that removes noise has to be transmitted over a long distance according to a situation, the analog signal is amplified to a predetermined level using the differential output converter 14 and then converted into an analog signal through an analog / digital converter 15. Transmit to the calculator without introducing noise.

On the other hand, the measured value of the detection coil 6 converted into a digital signal through the A / D converter 15 is input to the calculation unit 16 to determine the level of the water level, the water level by the detection coil (6) The principle of the detection method will be described first.

The basic principle of the detection coil in the present invention is to use an electromagnetic induction to apply an alternating magnetic field to the molten metal by using the electromagnetic continuous casting power supply, and the sum of the induced magnetic field and the applied magnetic field generated in the molten metal by the applied alternating magnetic field. It is to measure the level of molten metal of the molten metal by measuring with a detection coil.

When a magnetic field that changes with time is applied near a conducting material, the magnetic field B of the vertical component in contact with the conductor generates an electromotive force (ε) inside the conductor, as shown in Equation (1). To form an induced current circuit that follows Ohm's law.

The direction of the induced magnetic field generated by the induced current changes with the change of the magnetic field applied from the outside in a direction in which a constant magnetic field is always maintained in the conductor. In other words, as indicated by the negative sign in Equation 1, the magnetic field is opposite to the applied magnetic field.

Since the detection coil 6 of the present invention is a search coil type magnetic sensor, the magnetic field is measured by measuring the electromotive force induced in the detection coil. In other words, the level of the surface is measured by measuring the induced magnetic field caused by the current loop generated in the surface. Therefore, the rate of change of the magnetic flux crossing the area surrounded by the detection coil is applied to the applied magnetic field due to the current of the induction coil. Induced magnetic field due to the rate of change of time and current induced in the melt The sum of the rate of change of time is detected. Therefore, the output of the detection coil can be expressed as Equation 2 below.

Therefore, the superimposed magnetic field measured by the detection coil is amplified to a predetermined level through the amplification and filtering means, and after the noise is removed, it is input to the operation unit to determine the level of the floor.

At this time, the calculation unit 16 removes the value of the applied magnetic field due to the applied current input from the electronic device from the superimposed magnetic field through the equation shown in Equation 3 below to change the position of the hot water surface which does not depend on the change of the applied magnetic field. Detect the level of the water surface accordingly.

In the above formula, a = C1 * V1 + C2, b = C3 * V2 + C4, d = C5 * V2 + C6, k = C7, V1: superposition field, and C1, C2, C3, C4, C5, C6 And C7 are constant values related to the configuration of the electromagnetic continuous casting system.

Due to the characteristic of electromagnetic continuous casting, there is a strong magnetic field due to the induction coil in the tap surface area, so the detection coil simultaneously measures the applied magnetic field caused by the induction coil and the induced magnetic field caused by the eddy current generated in the tap surface.

As described above, when the position of the hot water surface is changed, the applied magnetic field changes the electrical load of the electromagnetic continuous casting facility, so that the current applied to the induction coil from the power supply unit is also changed. Therefore, the applied magnetic field due to the induction coil current also changes. In addition, the applied magnetic field is directly affected when the current applied to the induction coil has to be changed in the electromagnetic continuous casting process. Therefore, it is necessary to remove the components of the applied magnetic field from the magnetic field measured around the surface of the water so that the accurate surface level can be measured in the electromagnetic continuous casting process.

On the other hand, the induction magnetic field includes both a component that changes according to the change of the applied magnetic field when the position of the tap surface changes, and a component that varies depending on the position of the tap surface even if the applied magnetic field is the same. Therefore, it is necessary to distinguish whether the source of the output change of the detection coil is due to the change of the applied magnetic field or the change of the level of the water level to accurately detect the water level.

Accordingly, in the present invention, the power supply variable V2 is used to correct the change value of the applied magnetic field according to the change of the induction magnetic field from the output value of the detection coil, and the V2 is supplied from a power supply for supplying power to the induction coil. It is a variable that can represent authorized magnetic field. In addition, the power supply variable has a one-to-one correspondence with the current value applied to the induction coil, regardless of the variation of the electrical load of the electromagnetic continuous casting such as a change in the position of the hot water surface, and this is called the power supply variable. In this case, the power variable may be set to a current, a voltage, and a power set to apply an AC current to the induction coil in the power supply device.

On the other hand, Figure 3 is a graph showing a comparison of the change in the applied magnetic field and the induced magnetic field according to the change of the water surface position. As shown in Fig. 3, the change in the applied magnetic field has a narrow detection band and the induced magnetic field component has a wide detection band. On the other hand, the variables a, b, d and k in Equation (3), respectively, a is the lowest floor level (for example, 300mm), b is the highest level indicating when the surface level reaches the upper end of the mold (for example 0mm) And d represents the surface level of the surface when the slope of the induced magnetic field graph is k.

As can be seen from Equation 3 above, the power supply variable V2 of the power supply device is included in a, b, and d, respectively, so that it is changed depending on the applied magnetic field and the water surface position. The influence of the magnetic field can be eliminated. That is, in the present invention, the signal input through the A / D converter is separated by the magnetic field value for the change of the induced magnetic field due to the change in the position of the tap surface in the calculator to measure the position of the tap surface. Therefore, even if the induced current applied to the induction coil arbitrarily changed in accordance with the needs of the process in the continuous casting process, it is possible to stably measure the level of the hot water.

Figure 4 is a graph showing the detection value of the applied current and the surface level of the induction coil according to an embodiment of the surface level detection apparatus according to the present invention. As shown in Fig. 4, when the adjustment current or one of the electrical signals of the power supply itself is drawn and applied to the level detecting means, even if the value of the current applied to the induction coil changes abruptly, that is, the value of the applied magnetic field. This sudden change does not affect the result of measuring the water level. On the other hand, in Figure 4, the position of the hot water gradually changes between 80 and 90 mm because the hot water position is changed in the process to prevent erosion of the nozzle injecting the molten metal.

The apparatus for detecting the water level in electromagnetic continuous casting according to the present invention is not limited to the above-described embodiment, and may be implemented in various modifications within the range permitted by the technical idea of the present invention.

As described above, in the apparatus for detecting the water level in the continuous electromagnetic casting according to the present invention, and the method, the induction coil is applied by the induction coil from the output value of the detection field for measuring the applied magnetic field due to the induction coil and the fluctuations in the position of the water surface. By removing the magnetic field component, it is possible to obtain an effect that can accurately detect the level of the water level, regardless of the variation of the applied current and the applied voltage applied to the induction coil from the power supply device.

In addition, according to the present invention, it is possible to detect the level of the water surface with high accuracy and stability, so that it can be used as a basic signal for controlling the level of water, thereby improving the surface quality of the cast product, thereby reducing the production process of steel products and saving energy. You can get the effect.

Claims (6)

In the apparatus for detecting the surface level by measuring the applied magnetic field generated in the induction coil and the induced magnetic field caused by the eddy current to detect the surface level of the molten metal contained in the mold in the electromagnetic continuous casting process, A power supply unit applying predetermined AC power to the induction coil; A detection coil for detecting the applied magnetic field and the induced magnetic field; An amplification and filtering unit which receives the signal detected by the detection coil, amplifies the signal to a predetermined level, and filters the noise to remove noise; An arithmetic unit for detecting the level of the water level by removing an applied magnetic field component caused by a change in AC power applied to an induction coil from the magnetic field signal detected by the detection coil using the amplified and filtered signal and a power variable input from the power supply unit. Floor level detection device in the electromagnetic continuous casting, characterized in that provided with. The method of claim 1, wherein the amplification and filtering unit An insulation amplifier which receives the magnetic field signal measured by the detection coil and amplifies and outputs the magnetic field signal to a predetermined level; A band pass filter for outputting the amplified signal by filtering only a signal of a predetermined band; A DC signal converter for receiving the band-passed signal and converting the signal into a DC signal; A low pass filter controlling the noise by receiving and filtering the DC signal; And an A / D converter for receiving the low-pass signal and converting the signal into a digital signal and outputting the digital signal to the operation unit. The method of claim 1, wherein the operation unit Noodle level = (Where a = C1 * V1 + C2, b = C3 * V2 + C4, d = C5 * V2 + C6, k = C7, C1, C2, C3, C4, C5, C6, C7 = constant) And a water level is detected by removing a component of an applied magnetic field generated in an induction coil from a signal output from the detection coil. The method according to claim 1 or 3, The power supply variable V2 is a variable that can represent an applied magnetic field from a power supply unit supplying power to the induction coil, and this variable is independent of the change in electrical load of the electromagnetic continuous casting such as a change in the position of the hot water, An apparatus for detecting the level of water in an electromagnetic continuous casting, characterized in that it is set to a value having a one-to-one correspondence with an applied current value. In the method for detecting the surface level of the molten metal contained in the mold in the electromagnetic continuous casting process by measuring the superposition of the applied magnetic field generated in the induction coil and the induced magnetic field due to the eddy current through the detection coil, Amplifying and filtering an overlapping magnetic field measured through the detection coil to a predetermined level, And removing the applied magnetic field component due to the change of the applied current applied to the induction coil from the amplified and filtered signal to determine and output the level of the wet surface. . The method of claim 5, wherein Noodle level = (Where a = C1 * V1 + C2, b = C3 * V2 + C4, d = C5 * V2 + C6, k = C7, C1, C2, C3, C4, C5, C6, C7 = constant) And a tang surface level is detected by removing fluctuation components of an applied magnetic field caused by a change in an applied current of an induction coil from the signal output from the detection coil.