JPH04238661A - Molten metal level detection method - Google Patents

Abstract

PURPOSE:To measure molten metal level in a vessel having narrow width in high accuracy, wide range and good environmental resistance by measuring output value exceeding the preset threshold value in the treated output value in each receiving coil. CONSTITUTION:Transmitting coils 4a, 4b...4n and the receiving coils 7a, 7b...7n are arranged in the vertical direction in plural pieces facing each other as inserting the outside of molds 2, 3, in which the molten metal 1 exists therebetween, from right and left or front and behind. AC power sources 5a, 5b...5n having different frequencies, are impressed to each transmitting coil 4a, 4b...4n and resulting respective AC magnetic fluxes are passed through the molten metal 1 and the molds 2, 3. By selecting a molten metal level detector outputting higher voltage among each outputted voltage value of the molten metal detectors than the preset value in the molten metal level detectors, respectively, the molten metal level is measured.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the molten surface position (molten steel level) of molten metal.

0002

2. Description of the Related Art The following methods are available for detecting the position of the molten surface of molten metal.

1) Method using 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 Focusing on the difference in brightness at the contact position between the top surface of the molten metal and the container, etc., this boundary line is measured by triangulation using an array sensor or a television camera, etc. do.

3) Ultrasonic method: The distance to the molten metal surface is measured 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) Method using radiation Radiation is passed through the molten metal in an oblique direction, and the surface position of the molten metal is detected from the amount of attenuation of this radiation.

5) Immersion electrode method The level of molten metal is detected 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 the molten metal is indirectly detected from changes in temperature distribution.

7) Electromagnetic induction method The method disclosed in Japanese Patent Application Laid-Open No. 48-93539 provides a coil that is long in the depth direction on the outer wall of the mold, and
With a configuration connected to one side of the dance bridge circuit, changes in the molten steel level in the mold are captured as changes in the mold wall temperature, and the resulting changes in the resistivity of the mold wall cause vortices generated in the mold. This method uses changes in current to detect the molten steel level.

0010

[Problems to be Solved by the Invention] Each of the conventional methods for detecting molten metal has the following problems. ,
1) Method of using floats There is no float material that is not corroded by high-temperature molten metal, and slag, metal, etc. may adhere to the floats, causing changes in the specific gravity of the floats, making it necessary to repair each time. .

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

3) Method 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), making measurement impossible.

4) Method using radiation There are safety issues and it cannot be used in places where there is no space to install the radiation source and detector.

5) Immersed electrode method: 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, since a refractory brick is used as the container, heat conduction is poor, resulting in not only a delay in measurement time but also poor detection accuracy. Furthermore, it is not easy to embed the thermocouple in the wall of the container or to replace it when the thermocouple is broken. 7) Electromagnetic induction method (Japanese Unexamined Patent Publication 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. This not only makes measurement errors more likely to occur, but also makes it even more difficult to capture this temperature change as an impedance change because the mold is cooled, so measurement errors are unavoidable.

[0016]

[Means for Solving the Problems] According to the present invention, transmitting and receiving coils are arranged to face each other 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. and a plurality of sets of molten metal level detectors are installed in the vertical direction to allow the resulting alternating magnetic flux to pass through the molten metal and the container, and to observe the alternating voltage induced in the receiving coil by the transmitted magnetic flux; The output voltage value of each molten metal level detector is
The molten metal level is measured by selecting a molten metal level detector that outputs a voltage higher than a value (threshold) set in advance for each molten metal level detector.

In a preferred embodiment of the present invention, when a plurality of sets of molten metal level detectors are provided in the vertical direction, each molten metal level detector is arranged so that a portion of the detection range of adjacent molten metal level detectors overlaps. are placed vertically in sequence to measure the molten metal level.

[0018]

[Operation] Hereinafter, the present invention will be explained based on the block diagrams shown in FIGS. 1 and 2.

In FIG. 2, an AC power supply 5 applies an alternating voltage to a transmitting coil 4 having an electric coil wound on a ferrite core, thereby generating an alternating magnetic flux. A part of the alternating magnetic flux is distributed directly above and below the transmitting coil 4, and a part enters the inside of 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 (depending on the level position of the molten steel at that time, it is either in the molten steel 1 or in the air 6). or at an intermediate position as shown in FIG. 2), and reaches the mold 3. A part of the magnetic flux that has reached the mold 3 enters the mold 3 and passes upward and downward through the mold 3. A small portion of the magnetic flux then reaches the receiving coil 7 and generates an induced voltage signal. This signal level 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 induced in the receiving coil 7 is several thousand times smaller than the voltage of the AC power supply 5). Therefore, in actual measurement sites, it is susceptible to harmful noise components unrelated to the molten steel level measurement signal. Therefore, the inventors succeeded in putting it into practical use by removing this harmful noise component by the means described below. That is, the output of the receiving coil 7 is first passed through a bandpass filter 8 that passes only the same frequency as that of the AC power source 5.
removes harmful noise components. However, after passing through the bandpass filter 8, only the signal synchronized with the AC power supply 5 is exchanged into a DC voltage signal using a known synchronous rectifier 9. Signal not synchronized with AC power supply 5 (unnecessary signal)
is output from the synchronous rectifier 9 as an alternating current voltage, so this alternating voltage is removed by a low-pass filter 10 that passes only the direct current voltage and very low frequencies, and only the effective signal can be extracted as the direct current signal component. can.

Now, when the molten metal 1 fills the molds 2 and 3, when part of the magnetic flux that has passed through the mold 2 passes through the molten metal 1, this magnetic flux causes the molten metal to Eddy currents are generated within the receiving coil 1 and are consumed as Joule heat within the receiving coil 7, so that the magnetic flux reaching the receiving coil 7 becomes too small.

However, when there is no molten metal 1 in the molds 2 and 3 and there is only air 6, the above-mentioned eddy current does not occur in the molten steel, so the attenuation of the magnetic flux here is Therefore, the magnetic flux reaching the receiving coil 7 is larger than when it is filled with molten metal 1.

When there is a molten steel level near the sending and receiving coils as shown in FIG. 3, the voltage induced in the receiving coil 7 changes sequentially and continuously depending on the molten steel level. Therefore, by measuring this induced voltage, the level of 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. Of course, as mentioned above, in the actual measurement site, harmful signals unrelated to this molten steel level signal are included, so the low-pass filter 1 of FIG.
Needless to say, the measurement is performed with an output value of 0.

By the way, when the molten steel level is far away from the sending and receiving coil positions, the detection range in the above method is
Even if you know whether it is above or below the receiving coil position,
It is impossible to know where it is located.

The inventors solved this problem by the following method. That is, as shown in FIG. 1, the same transmitting coils 4a, 4b as in the above method are placed between the outsides of the molds 2, 3 in which the molten metal 1 is placed, from the left and right or front and back.
・A plurality of receiving coils 7a, 7b...7n are arranged vertically so as to face each other, and each transmitting coil 4a, 4b...4n is connected to an AC power source 5a, which has a different frequency.
5b, . The alternating voltages induced in the receiving coils 5a, 5b...5n are filtered through bandpass filters 8a...8n, synchronous rectifiers 9a...9n, low
The same processing as described above is performed through the pass filters 10a...10n.

[0025] Then, low-pass filters 10a to 10n
The binarizers 11a to 11n are turned on when each output value is higher than the threshold value of the receiving coil induced voltage value of the receiving coil induced voltage vs. molten steel level characteristic shown in FIG. 4, and are turned off when it is lower.
are connected, and among the outputs (a pair of outputs) of adjacent detectors among the outputs of the binarizers 11a to 11n, there is an ON state and an OFF state among the signal pairs in which there is an ON state and an OFF state. A low-pass filter (10a to 10
The selection circuit 12 selects and observes the output of one of n).

One specific electrical circuit configuration for performing this selection is shown in FIG. This will be explained with reference to FIG. Now, if the molten steel level is very low, there is a space 6 at the position of all the detectors, so the low-pass filters 10a to 10n
The output voltage values (indicated by a, b, c, . . . in FIG. 6) are all higher than the threshold value. In this case, the binarizers 11a, 1
All outputs of 1b, 11c, ... are on (high level H)
Therefore, the AND gates 12a, 12b, 12c・
Open all X inputs of .... However, the binarizer 11b
, 11c, . . . outputs from inverters 13a, 13b, 13
It is also input to inverters 13a, 13b, 13
The outputs of c, . . . turn off (low level L), and the Y inputs of AND gates 12a, 12b, 12c, .
Therefore, the AND gates 12a, 12b
, 12c, ... are off (low level L),
Analog gate switch 14a, which closes when the output of AND gates 12a, 12b, 12c, . . . is on (H);
Since the switches 14b, 14c, . . . do not close, these switches 14a, 14b, 14c, . (no output).

However, if the molten steel level rises and, for example, the output value of the low-pass filter 10c becomes lower than the threshold value, the output of the binarizer 11c turns off (L), and therefore the output of the inverter 13b turns off. The output turns on (H) and the Y input of AND gate 12b opens (H), and the output of binarizer 11b remains on (H), so the output of AND gate 12b turns on. (H), so the analog gate switch 14b is closed and the low-pass filter 10
Only the output of b is passed. That is, the molten steel level detection signal of the low-pass filter 10b is selected and output.

In this way, when the adjacent signal pairs of the binarizers 11a, 11b, 11c, etc. are turned on (H) and off (L) as the molten steel level rises, , a binarizer (11b) outputting the on (H) signal.
The output of the low-pass filter (10b) to which is connected is automatically extracted by the selection circuit 11 and output as a molten steel level detection signal.

According to this, the optimum detector for measuring the molten steel level is automatically selected from among the molten steel level outputs of the plurality of molten steel level detectors, and its detection signal is output, so that the molten steel is continuously detected. Levels can be measured over a wide range.

[0030]

[Example] In the twin-belt continuous casting method, as shown in Fig. 1, a coil is wound 770 times on a ferrite core at a distance of 20 mm from the belt so as to sandwich the outside of a belt mold made of steel sheet in which molten steel is contained. Four sets of transmitting coils and receiving coils were placed facing each other at intervals of 110 mm in the vertical direction, and overlapped with each other by 30 mm within each level detection range. At this time, each transmitting coil is given 400~1000H to avoid mutual interference.
Alternating voltages with different frequencies were applied to each of z. As a result, each 0 induced in the receiving coil
．． An alternating voltage signal of 5 to 7 mV was detected by the method of the present invention, and the signal was processed to obtain a molten steel level output.

This will be explained in more detail based on FIG.

Now, when the molten steel level is at L1, from FIG. 6, the output voltage level a of the level detector a is Va (V), which is lower than the threshold value, so the corresponding binary conversion in FIG. The output of the circuit 11c becomes off (L), and the AND gate of FIG.
Close the port 12c. Furthermore, since the output voltage levels b and c of the level detectors b and c in FIG. 6 are Vb and Vc (V), respectively, which are higher than the threshold values, the corresponding binarizer 11 in FIG.
The outputs of the gates b and 11a are turned on (H), and the input gates X of the AND gates 12b and 12c in FIG. 5 are opened (H). The input gate Y of the AND gate 12a is the binarizer 1
Since 1b is on (H), the inverter 13 connected to it
Since the output of a is off (L), the AND game is executed with that output.
The gate 12a is closed (L). However, the binarizer 1 in FIG.
Since the output of 1c is off (L), the output of the inverter 13b connected to it is on (H), so that only the AND gate 12b is turned on (H), and only the analog gate switch 14b is closed. In the end, only the output voltage level b of the level detector b in FIG. 6 is output.

In this way, the binarizers 11a, 11b, 11c, . . . in FIG.
・Of the outputs of pairs, where adjacent pairs are on and off,
Only the output of the low-pass filter connected to the binarizer outputting the on signal is automatically selected.

In this example, molten steel was used as the molten metal, but it is not necessarily limited to molten steel, and other liquid metals or liquids that can conduct electric current, such as salt water, may be used. If so, the method of the present invention can be similarly applied. Further, in the case of this embodiment, the material (mold) outside the molten steel was a steel plate, but it is not limited to this, and other materials such as refractory bricks may be used.

[0035]

Effects of the Invention As described above, according to the method of the present invention, since the sensor is not inserted into molten metal, the sensor is not worn out by high-temperature molten metal, thus requiring no maintenance and achieving high reliability. allows semi-permanent use. Furthermore, since it is magnetic, it is completely unaffected by the presence of smoke, dust, steam, etc., or even by fluctuations in the air due to high temperatures. Furthermore, since the method of the present invention directly measures the magnitude of eddy currents generated within the molten metal itself, there is no detection time delay, and the response is therefore very good. In addition, since the method does not use harmful substances such as radiation, there are no safety issues.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an apparatus that implements the method of the present invention in one embodiment.

FIG. 2 is a block diagram showing only one set of the plurality of detector sets shown in FIG. 1;

3 is a graph showing the output voltage of the detector shown in FIG. 2. FIG.

4 is a graph showing output voltages of multiple sets of detectors shown in FIG. 1. FIG.

5 is a block diagram showing the configuration of the selection circuit 11 shown in FIG. 1. FIG.

6 is a graph showing the output voltage of the detector applied to the selection circuit 11 shown in FIG. 5. FIG.

[Explanation of symbols]

1: Molten steel
2, 3: Mold 4, 4b to 4n: Transmission coil
5, 5a, 5b to 5n: AC power supply 6: Air
7, 7a, 7b to 7n: Receiving coil 8: Band pass filter - 9, 9a, 9b
~9n: Synchronous rectifier 10, 10a, 10b ~ 10n: Low-pass filter 11
a, 11b to 11n: Binarizer 12: Selection circuit
12a-12c: AND gate 13a-13c: Inverter

Claims (2)

[Claims] [Claim 1] The outside of a container, etc. containing molten metal,
A transmitting coil and a receiving coil are arranged to face each other so as to be sandwiched from the left and right or front and back, and an alternating voltage is applied to the transmitting coil, and the resulting alternating magnetic flux is transmitted through the molten metal and the container, and the transmitted magnetic flux is used for reception. Multiple sets of molten metal level detectors that observe the alternating voltage induced in the coil are installed in the vertical direction, and the output voltage value of each molten metal level detector is a value set in advance for each molten metal level detector. A molten metal level detection method characterized by measuring a molten metal level by selecting a molten metal level detector outputting a higher voltage. 2. When a plurality of sets of molten metal level detectors are provided in the vertical direction, each molten metal level detector is sequentially arranged in the vertical direction so that a part of the detection range of adjacent molten metal level detectors overlaps. 2. The molten metal level detection method according to claim 1, wherein the molten metal level is measured by: