JPH03122526A - Detection of level of molten metal - Google Patents

Abstract

PURPOSE:To remove a delay in a time of detection, to increase responsiveness and to make measurement highly precise by a method wherein a change in the impedance of a receiving coil caused by an amplitude of an eddy current generated in a molten metal itself is measured as a change in a phase. CONSTITUTION:When a molten metal 1 is filled up in molds 2, 3 and a part of a magnetic flux transmitted through the mold 2 passes through the metal 1, an eddy current is generated in the metal 1 and the impedance of a receiving coil 7 changes. Then a phase shift occurs, compared with a case when only air 6 is present, the metal 1 being absent, in the molds 2, 3, and the value of this phase shift is outputted as a voltage value by a phase difference detector 9. In the case when a melt level is positioned near transmitting and receiving coils, the output voltage value of the detector 9 changes in a reverse order and continuously. By measuring this phase shift, accordingly, the position of the level of the molten metal in the vicinity of the transmitting and receiving coils 4 and 7 can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the position of a molten surface (level) of molten metal.

[Conventional technology]

As a method for detecting the position of the molten surface of molten metal, there are the following methods.

1) Those that use a float A float is floated on the molten metal surface and the position of the float is detected using a rod or chain.

2) Optical (photoelectric conversion) method A method that focuses on the difference in brightness at the point of contact between the top surface of the molten metal and a container, etc., and measures this boundary line by triangulation using an array sensor or television camera, etc. .

3) Using ultrasonic waves A method that measures the distance to the molten metal surface by irradiating the surface of the molten metal with ultrasonic waves and measuring the time it takes for the reflected sound waves to return.

4) Items that use radiation Radiation is passed through the molten metal in an oblique direction.

This method detects the surface position of molten metal based on the amount of attenuation of this radiation.

5) An immersion electrode type that detects the level of molten metal by creating an ON-OFF state of an electric circuit using an electrode and molten metal.

6) Thermocouple method Several sets of thermocouples are embedded in the outer wall of the molten metal container, and the level of molten metal is indirectly detected from changes in temperature distribution.

7) Electromagnetic induction method The method of JP-A No. 48-93539 has a configuration in which a coil long in the depth direction is provided on the outer wall of the mold, and the coil is connected to one side of an impedance bridge circuit, so that the height of the molten steel level in the mold is The change in is captured as the mold wall temperature change,
The molten steel level is detected by utilizing the change in eddy current generated within the mold due to the change in resistivity of the mold wall caused by this.

[Problem that the invention seeks to solve]

Each of the conventional methods for detecting a molten metal surface has the following problems. Namely, 1) those using floats, there is no float material that is not corroded by high temperature molten metal, and slabs, metal, etc. adhere to the floats; The specific gravity of the float may change, requiring correction each time.

2) Optical (photoelectric exchange) method If smoke, dust, etc. are present, or if slag (which generally has low brightness and appears black) floats on the molten total refractive surface, not only will the measurement be repeated, but this smoke If the molten metal is at a high temperature, haze caused by the heat causes refraction of light, resulting in measurement errors.

3) Using ultrasonic waves If the molten metal is at a high temperature, the heat causes complex sound refraction due to air fluctuations (changes in air density), which makes measurement difficult.

4) Items that use radiation There are safety issues and they cannot be used in places where there is no space to install the radiation source and detector.

5) Immersed electrode type The electrode is severely worn out by the high-temperature molten metal, making long-term use impossible.

6) Thermocouple method In the case of high-temperature molten metal, firebrick is used as the container, which has poor heat conduction, which not only causes a delay in measurement time but also has poor detection accuracy. Furthermore, it is not easy to embed the thermocouple in the container wall or to replace it when the thermocouple breaks.

7) Electromagnetic induction method (JP-A No. 48-93539) Since the temperature change at the metal boundary is indirectly measured as the temperature change at the mold wall, the temperature distribution of the mold wall at the metal boundary becomes slow, resulting in measurement errors. Not only does this become more likely to occur, but it also becomes more difficult to capture this temperature change as an impedance change because the mold is cooled, and measurement errors are unavoidable.

[Means to solve the problem]

In order to solve the above problem, in the present invention, transmitting and receiving coils are arranged so as to sandwich the outside of a container containing molten metal from the left and right or front and back, and an alternating voltage is applied to the transmitting coil. The level of the molten metal is observed by transmitting the alternating magnetic flux generated by the molten metal through the molten metal and the container, and observing the phase difference between the alternating current signal induced in the receiving coil by the transmitted magnetic flux and the alternating voltage.

[Example and operation]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below based on a schematic diagram of an embodiment of the present invention shown in FIG.

In FIG. 1, an alternating current power source 5 is applied to a transmitting coil 4 wound on a ferrite core, thereby generating an alternating magnetic flux. Part of the alternating magnetic flux is distributed directly above and below the coil 4, and another part enters the mold 2 made of a steel plate and passes above and below the mold 2. Furthermore, although the magnetic flux density is small, some of the magnetic flux passes through the mold 2 and enters the molten steel 1 or the air 6 (this depends on the level position of the molten steel at that time, either in the molten steel 1, in the air 6, or in the first mold 2). (in one of the intermediate positions as shown in the figure) and mold 3.
6 A part of the magnetic flux that reached mold 3 reaches mold 3
It enters the mold 3 and passes upward and downward. Then, the magnetic flux in the negative part reaches the receiving coil 7 and generates an induced voltage signal. This signal value is extremely small because the magnetic flux that reaches the receiving coil 7 is minute (according to actual measurement results by the inventors, the voltage value induced in the receiving coil 7 is (approximately 1/100 of the voltage value of the power supply 5), therefore, in an actual measurement site, it is easily affected by harmful noise components unrelated to the molten steel level measurement signal. Therefore, harmful noise components are removed from the output of the receiving coil 7 by a bandpass filter 8 that passes only the frequencies near the same as those of the AC power supply 5. The signal that has passed through the bandpass filter 8 is input to a known phase difference detector 9, which converts the phase difference with the signal derived from the AC power source 5 into a voltage signal.

Now, when the mold 2.3 is filled with molten gold ff1l, when part of the magnetic flux that has passed through the mold 2 passes through the molten metal l, this magnetic flux generates an eddy current in the molten metal l. However, since this is consumed as Joule heat inside this, the impedance consisting of L (inductance) and R (resistance) of the receiving coil 7 changes isometrically, and therefore, the molten metal 1 is inside the molds 2 and 3. A phase shift occurs compared to the case where there is no air 6 only (According to actual measurement results by the inventors, when the frequency of the alternating voltage output from the AC power supply 5 is 600 Hz, the phase shift is 70 to 90 d.
eg), this phase shift value is output as a voltage value by the phase difference detector 9.

Then, this phase shift value, that is, the output voltage value of the phase difference detector 9 is transmitted and received as shown in the actual measurement data shown in FIG. Continuously changing. Therefore, by measuring this phase shift, the level position of the molten metal near the transmitting and receiving coils 4 and 7 can be detected from the receiving coil induced voltage versus molten steel level characteristics shown in FIG.

By the way, the bandwidth (bandwidth) of bandpass filter 8
If it is made narrower, the effect of removing nozzle signals that are harmful to measurement will be greater, but if it is made too narrow, if the frequency of the AC power source 5 changes due to drift, etc., the frequency will be greatly reduced from the center passing frequency of this bandpass filter 8. The phase changes,
This is larger than the phase change caused by the change in the molten metal level as intended by the present invention, so in order to avoid this influence, the band width should be widened or the center frequency of this bandpass filter 8 should be slightly shifted from the frequency of the AC power supply 5. It is a good idea to keep it.

Although the present embodiment deals with molten steel, the present invention is not limited to molten steel, and the present invention can be implemented with other liquid metals or liquids that can conduct electric current, such as saline solution. I can do it.

Further, in the case of this embodiment, the material on the outside of the molten steel is a steel plate, but the material is not limited to this, and other materials such as refractory bricks may be used.

〔Effect of the invention〕

As described above, according to the method of the present invention, since the sensor is not inserted into the molten metal, the sensor is not worn out by high-temperature molten metal, so maintenance is unnecessary and highly reliable semi-permanent use is possible. shall be.

Furthermore, because it is magnetic, it is completely unaffected by the presence of smoke, dust, steam, etc., or by fluctuations in the air due to high temperatures.

Furthermore, since the method of the present invention is a method of measuring the impedance change of the receiving coil due to the magnitude of eddy current generated in the molten metal itself as a phase change, for example, Since this is not an indirect measurement method that involves an object with a thermal time constant between the measurement targets, such as the couple method, there is no detection time delay, and the response is therefore very good.

In addition, this method measures five phase shifts.

It has the feature of being able to measure with high precision even if the power supply voltage value fluctuates without being affected by it.

In addition, since it does not use harmful substances such as radiation,
There are no safety issues at all.

It has many features such as.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment according to the method of the present invention. FIG. 2 is a graph showing the results of measuring the characteristics of the induced voltage of the receiving coil versus the molten steel level according to the embodiment of the present invention. l: Molten steel 4: Transmitting coil 6: In air 8: Band pass filter 9 = Phase difference detector 2.3: Mold 5: AC power supply 7: Receiving coil voice 1 figure

Claims (1)

[Claims] A transmitting coil and a receiving coil are placed facing each other so as to sandwich the outside of a container or the like in which molten metal is contained from the left and right or front and back, and an alternating voltage is applied to the transmitting coil, and the alternating magnetic flux generated by this is applied to the molten metal. and a method for detecting a level of molten metal, which comprises transmitting the magnetic flux through a container and observing the phase difference between the phase of an alternating current signal induced in a receiving coil by the transmitted magnetic flux and the alternating voltage.