JPH105958A - Detection coil device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve slag detection sensitivity by interposing a conductive body to suppress propagation of the magnetic field, generated by a transmitting coil, to a receiving coil. SOLUTION: An electromagnetic shield ring 6 shields the magnetic flux from a transmitting coil 4 toward a receiving coil 5 so as to pass the ring 6 outside a nozzle 3. A signal generator 21 generates an AC signal of a prescribed frequency, an power amplifier 22 impresses the AC voltage in the form of amplified AC signal to a transmitting coil 4. The voltage to induce a receiving coil 5 is amplified by a receiver 23 and then it is given to a slag flowout detector 24. The slag flowout detector 24 compares a level/phase of the received signal to both the standard value corresponding to a shape/material of nozzle 3 and a steel kind/flow rate of molten metal and the reference value decided based on the sensitivity adjusting value set by an operator, switching from molten metal to slag is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coil device for detecting a turbulence of a fluid in a pipe, and more particularly to detecting a foreign substance mixed into a standard fluid or switching from a standard fluid to a foreign substance in a pipe. One of the most typical coil devices is a coil device for detecting slag flowing into a nozzle for injecting a molten metal into a mold.

[0002]

2. Description of the Related Art In continuous casting, for example, molten steel is supplied from a ladle to a tundish through a pouring nozzle.
The molten steel of the tundish is supplied to the mold through a pouring nozzle. Slag may be mixed into the ladle when molten steel is poured into the ladle, and the slag entering the ladle floats on the molten steel. This slag enters the pouring nozzle at the end of pouring from the ladle to the tundish (feeding molten steel) and then enters the tundish.

In order to prevent the slag from flowing into the tundish through the pouring nozzle, the molten steel flow path is circulated near the upper end of the pouring nozzle or near the molten steel outlet of the tie dish. When the detection coil device including the transmission coil and the reception coil is installed and the inside of the flow path changes from molten steel to slag, the mutual inductance between the two coils changes. Therefore, the electric quantity (induced voltage, current phase) of the reception coil due to this change , Oscillation frequency), and a technique for terminating or stopping the injection of molten steel thereat has been proposed.

For example, Japanese Patent Application Laid-Open No. Sho 62-500646 discloses that a transmitting coil, a reference coil (primary coil) and a receiving coil are provided in a perforated brick or lining around an outlet pipe of a molten metal or an outflow pipe. Coil (secondary coil)
A slag detecting device is disclosed in which a slag is wound, a primary coil is excited by an AC signal, and the presence of slag is automatically detected from the voltage (and phase) generated in the receiving coil. If the coils are arranged annularly around the outflow pipe, a difference occurs in the voltage (and phase) induced in the receiving coil due to the difference in the conductivity of the substance flowing in the outflow pipe. Since the conductivity of the molten steel is significantly higher than the conductivity of the slag, when the slag is mixed in the molten steel flowing in the outflow pipe, the local conductivity of that portion is low. Therefore, the voltage (and phase) induced in the receiving coil
The slag flowing in the outflow pipe can be detected by measuring. In order to improve the resolution, the primary coil is excited by using signal sources of a plurality of frequencies (three types of signal sources).

Japanese Patent Application Laid-Open No. 64-27768 discloses that
Japanese Patent Application Laid-Open No. Sho 62-500646 discloses a slag detection device,
An improvement in the sensing coil is shown. A transmission coil, a reception coil and a reference coil (used for the purpose of measuring accuracy) which are wound around the molten metal outflow pipe in an annular shape are housed in a protective outer cylinder made of a magnetic material, and then housed in a non-magnetic cassette. The detection coil device is arranged near the metal bottom plate of the metallurgical vessel. The purpose of this is to replace the perforated brick or lining around the coil without affecting the coil, and to replace the perforated brick or lining or the coil cassette independently. Can be done. For this reason, the cassette is arranged at a position in contact with the metal bottom plate. If the coil is arranged near the metal bottom plate, the influence of the decrease in signal amplitude and the temperature drift increases, so that consideration is given to this. The relative positions of the coils in this device are basically the same as those in the device of Japanese Patent Application Laid-Open No. 62-500646.

[0006]

However, it is presumed that the slag detection sensitivity is low in the apparatus disclosed in JP-A-62-500646 or in the apparatus disclosed in JP-A-64-27768. In the method in which the magnetic flux generated by the transmission coil is detected by the reception coil via a route (hereinafter, referred to as a detection route) in which a conductor (molten metal) exists, as described above, the detection route is used. If the change in the received signal caused by the change in the electrical conductivity is a signal component (S), and the magnetic flux generated by the transmitting coil is the noise component (N) that is directly received by the receiving coil outside the detection route, Sensitivity is S /
It is expressed by N ratio (signal component level / noise component level). In the above conventional device, the detection coil device has a configuration in which the transmission coil and the reception coil are coaxially adjacent to each other,
Excitation flux generated by the transmission coil is directly coupled to the reception coil, and a secondary voltage is often induced. That is, the S / N ratio is low because there are many noise components.

The present invention has been made in view of the above, and has as its object to provide a detection coil device having a high S / N ratio.

[0008]

According to a first aspect of the present invention, there is provided a detecting coil device including a transmitting coil (4) surrounding a tube (3) and a receiving coil (5) surrounding the tube (3). In (3-7), the magnetic field generated by the transmitting coil (4) is transmitted to the receiving coil (5) between the transmitting coil (4) and the receiving coil (5) outside the tube (3). Characterized in that a conductor (6) for suppressing the occurrence of an electric current is interposed.

According to this, the alternating magnetic flux (φ2) generated by the transmitting coil (4) and directed to the receiving coil (5) outside the detection route hits the conductor (6). As a result, an alternating magnetic flux (φ
An eddy current flows in a direction orthogonal to (2), and the eddy current generates a magnetic flux (φ2 ′) in a direction that prevents a change (alternating) of the alternating magnetic flux (φ2). Since the conductor (6) is made of a material having high conductivity, the eddy current loss is small, and therefore, the size of the AC magnetic flux (φ2) and the newly generated AC magnetic flux (φ2 ′) are substantially the same. Become. As described above, since magnetic fluxes having the same magnitude and opposite directions are generated, the two magnetic fluxes cancel each other to form an electromagnetic shield.

Therefore, outside the detection route, the transmitting coil (4)
The propagation of the alternating magnetic flux (φ2) generated in the receiving coil (5) is small. That is, the above-mentioned noise level N is low.

On the other hand, the alternating magnetic flux (φ1) of the detection route is linked with the receiving coil (5), whereby a voltage (signal level S) corresponding to the level of the alternating magnetic flux (φ1) is applied to the receiving coil (5). Occur. Since the alternating magnetic flux (φ1) of the detection route is not shielded by the conductor (6), the voltage (signal level S) becomes the same level as in the conventional example. Therefore, the S / N ratio improves as the noise level N decreases.

As in the prior art, when the conductivity of the detection route changes, for example, when the molten metal is switched to slag, the molten metal is substantially a conductor and the AC of the detection route is changed. Although the magnetic flux (φ1) was greatly attenuated, the slag was virtually an insulator and eddy currents did not easily flow.
The attenuation of (φ1) is reduced, and the induced voltage corresponding to the alternating magnetic flux (φ1) of the receiving coil (5) increases. Further, the current phase of the receiving coil (5) changes. By monitoring at least one of these changes with an electric circuit, it is possible to detect the arrival of slag to the detection coil section. S / N as described above
Since the ratio is high, the detection accuracy of the slag arrival is improved.

According to a second aspect of the present invention, there is provided a transmitting coil (4) surrounding a tubular body (3) and a receiving coil surrounding a tubular body (3).
In the detection coil device (3 to 7) including (5), the tubular body (3)
Outside and between the transmitting coil (4) and the receiving coil (5),
It is characterized in that a ferromagnetic material is interposed to suppress the magnetic field generated by the transmitting coil (4) from spreading to the receiving coil (5).

In the second embodiment, a ferromagnetic material is used in place of the shielding conductor (6). The ferromagnetic material also generates a magnetic flux between the transmitting coil (4) and the receiving coil (5). It shuts off. As a result, the above-described functions and effects of the first embodiment are obtained with a similar tendency. However, the ferromagnetic material also has the effect of reducing the AC magnetic flux (φ1) of the detection loop or shunting (shunting) it to the receiving coil (5). Sensitivity is reduced. Therefore, the first
Embodiments are preferred.

According to a third aspect of the present invention, there is provided a detection coil device including a transmitting coil (4) having a center radius of R surrounding a tube (3) and a receiving coil (5) rotating around the tube (3). (3-7) In order to suppress the magnetic field generated by the transmitting coil (4) from spreading to the receiving coil (5) in the outer space of the tube (3), the center of the transmitting coil (4) D between the sensor and the center of the receiving coil (5)
Is set to D ≧ R / 2.

In the third embodiment, the distance D between the transmitting coil (4) and the receiving coil (5) is increased instead of using the shielding conductor (6). As a result, the above-described functions and effects of the first embodiment are obtained with a similar tendency. However, even if the thickness of the shielding conductor (6) is relatively small, the shielding effect is high, whereas in the case of a void, the gap (D)
Has a low magnetic flux attenuation effect. Therefore, the distance D has to be made larger than the case where the shielding conductor (6) is used, and D is larger than R / 2.

However, as the distance D becomes longer, the detection route length (distance in the tube through which the AC magnetic flux φ1 passes) becomes longer, and the attenuation of the AC magnetic flux (φ1) of the detection route becomes larger by that amount. (S) is reduced. Therefore, the first embodiment is more preferable, and also in the first embodiment, it is preferable that the shielding conductor (6) be as thin as possible with high conductivity (eg, copper or aluminum).

Further, in any of the first, second and third embodiments, the ampere-turn (AT) of the transmitting coil (4) is made larger than before so that the AC flux of the detection route is increased.
It is preferable to increase the level of (φ1) and increase the number of turns of the receiving coil (5). As a result, the signal level S increases, which further contributes to the improvement of the S / N ratio. This is particularly preferred in the second and third aspects. Conventionally, the number of ampere turns of the transmitting coil is about 5 AT, and the number of turns n1 of the transmitting coil and the number of turns n2 of the receiving coil are n1> n2. However, in the preferred embodiment of the present invention, the number of ampere turns of the transmitting coil is not limited. n1 / I1 ≧ 7AT, n1 ≦ n2 and S /
The N ratio was increased.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

【Example】

First Embodiment FIG. 1 shows a longitudinal section of a first embodiment of the present invention (an example of the above-described first embodiment). The detection coil devices (3 to 7) shown in FIG. 1 are of a mode of detecting slag entering into a pouring nozzle 3 for supplying molten metal from a ladle to a tundish in a continuous casting facility. A non-magnetic material (a temperature higher than the Curie point) molten metal 2 flows through a nozzle 3 made of a refractory material. An annular hollow casing surrounding the nozzle 3
Thing 7 is arranged. The casing 7 is made of stainless steel, which is non-magnetic and has relatively low conductivity.
In the internal space, a transmitting coil (exciting coil), a copper flange-shaped electromagnetic shielding ring 6, and a receiving coil 5 are housed in this order from the top.

An electromagnetic shielding ring 6 between the transmission coil 4 and the reception coil 5 blocks a magnetic flux (φ2) from the transmission coil 4 toward the reception coil 5 so as to pass through the ring 6 outside the nozzle 3. That is, the two coils 4 and 5 are in a loosely coupled state in the casing 7. Signal generator 21
Generates an AC signal of a predetermined frequency, and the power amplifier applies an AC voltage obtained by amplifying the AC signal to the transmission coil 4. The voltage induced in the receiving coil 5 is amplified by the receiver 23. The receiver 23 converts the amplified signal into a signal
Phase detection is performed on the basis of the phase-shifted signal of the AC signal generated by the detection circuit, and an AC magnetic flux φ1 of a detection loop (φ1 loop in FIG. 2) is detected.
A corresponding received signal (S) is generated and given to the slag outflow detector 24. The slag outflow detector 24 compares the level and phase of the received signal (S) with a standard value corresponding to the shape and material of the nozzle 3, the type of molten metal and the flow velocity,
Switching from molten metal to slag is detected by comparing with a reference value determined according to a sensitivity adjustment value set by an operator, and this is reported.

FIG. 2 schematically shows a state of electromagnetic coupling between the transmission coil 4, the reception coil 5 and the electromagnetic shielding ring 6 shown in FIG. The transmitting coil 4 has an AC magnetic flux φ1 surrounding it.
(Magnetic flux of the detection route) and φ2 (magnetic flux deviating from the detection route). The magnetic flux .phi.2 deviating from the detection route hits the electromagnetic shielding ring 6 made of a conductive material, and an eddy current flows through the electromagnetic shielding ring 6. Magnetic flux φ generated by the eddy current
2 ′ is substantially the same size and opposite direction as the magnetic flux φ2, and the two magnetic fluxes cancel each other, so that the magnetic flux φ2 does not substantially reach the receiving coil 4. That is, it is cut off by the electromagnetic shielding ring 6.

The detection route φ1 goes around the reception coil 5 so as to pass through the molten metal 2 in the nozzle 3 and pass outside the reception coil 5, the ring 6 and the transmission coil 4. That is, it is coupled to the receiving coil 5 and induces a secondary voltage in the receiving coil 5. However, since the molten metal 2 is a conductor, when the inside of the nozzle 3 is filled with the molten metal 2, the detection route φ1 is greatly attenuated by the molten metal 2, so that the reception signal output by the receiver 23 is output. (S)
Level is low. When slag enters the detection route,
Since the slug is substantially an insulator, there is little magnetic flux attenuation, and the level of the reception signal (S) output from the receiver 23 rises. Also, the phase of the received signal (S) changes.

Here, the voltage e2 induced in the receiving coil 5
Is e2∝dB / dt∝ωB, and B = B1 + BE (1) BE = BYK + BSG (2) Where B is the magnetic flux density coupled to the receiving coil. B1
Is the magnetic flux density directly coupled from the transmitting coil 4 to the receiving coil 5. BE is the magnetic flux density coupled to the receiving coil 5 via the nozzle. BYK is the magnetic flux density according to the magnetic permeability when only molten metal is present in the nozzle. BSG is the magnetic flux density according to the magnetic permeability when a slab exists in the nozzle. It is.

Since the slag detection sensitivity SNS is SNS = (BYK−BSG) / (B1 + BYK) (3), if B1 (magnetic flux density directly coupled from the transmitting coil 4 to the receiving coil 5) Is large, the denominator of the equation (3) becomes large, and the slag detection sensitivity SNS decreases. Conversely, if B1 is small, the slag detection sensitivity SNS increases.

As described above, in the first embodiment, B1 is small because the electromagnetic shielding ring 6 is interposed between the transmission coil 4 and the reception coil 5 and the two are loosely coupled, and the slag detection sensitivity is small. SNS is high. Electromagnetic shielding ring 6 is 2 × 10
^It was manufactured from a copper plate having a conductivity of ⁶ S / m or more.

Table 1 shows the space between the transmitting coil 4 and the receiving coil 5 shown in FIG. 1 (the exclusive space of the electromagnetic shielding ring 6).
Is a comparison when air, stainless steel (SUS) and copper are used. The excitation signal is a sine wave having a frequency of 500 Hz.

[0029]

[Table 1]

In Table 1, the change Δk in the peak value (= maximum value / effective value) is Δk = [(peak value of the secondary voltage when the inside of the nozzle is slag) − (molten metal in the nozzle (Peak value of the secondary voltage when the nozzle is air)] ÷ (peak value of the secondary voltage when the inside of the nozzle is air) (4), and the phase difference Δp is: Phase of secondary voltage at the time)-(phase of secondary voltage at the time of molten metal inside the nozzle) (5).

As shown in Table 1, no matter which material is used for the space between the transmitting coil 4 and the receiving coil 5 (electromagnetic shielding ring 6), the substance (molten metal or slag) flowing in the nozzle. Of the peak value on the receiving coil side or the phase difference Δp on the receiving coil side according to the difference between the two can be detected. However, when stainless steel (SUS) or copper is used as the material, The change Δk of the high value and the phase difference Δp are large. From the results, a copper plate having a conductivity of 2 × 10 ⁶ S / m or more was used for the electromagnetic shielding ring 6 in this example. However, when stainless steel (SUS) or copper is used as the material, the secondary voltage induced in the receiving coil becomes a very small value. This is because the transmission coil 4 and the reception coil 5 are loosely coupled, and the electromagnetic shielding ring 6 is provided between the transmission coil 4 and the reception coil 5, so that BE (BE = B
This is because (YK + BSG) becomes smaller.

Therefore, the ampere turn (AT) of the transmitting coil 4 and the receiving coil 5 is increased to increase the magnetic flux density to cope with the level decrease. That is, when the number of turns n1 of the transmission coil 4 is 1, the current I1, and the number of turns n2 of the reception coil 5, the ampere turn (AT) is n1 × I1 ≧ 7A.
T, n1 ≦ n2, the slag detection sensitivity was increased.

When the ampere turn (AT) is increased, B1 naturally increases. However, since the increase of BYK and BSG, which are signal components, is larger than the increase of B1, slag is detected as a result. Sensitivity can be increased.

The slag content may be calculated from the phase difference Δp (deg) by using the above equation (5) for the slag outflow detector 24. Used for calculation (phase of secondary voltage when slag is inside the nozzle) and (2 when phase is molten metal inside the nozzle)
The phase of the next voltage) is obtained in advance by an experiment.

-Second Embodiment- A second embodiment (an embodiment of the second aspect described above) converts the electromagnetic shielding ring 6 to a ferromagnetic material, and is equivalent in drawing notation to FIG. In this embodiment, the electromagnetic shielding ring 6 of the first embodiment is a ferromagnetic plate having the same shape as the first embodiment, and the number of turns n1 of the transmission coil 4 and the current I
1 and the number of turns n2 of the receiving coil 5, the ampere turn (AT) is n1 × I1 ≧ 7AT, n2 = 1.2n1. Other configurations are the same as in the first embodiment.

Third Embodiment FIG. 3 shows a longitudinal section of a third embodiment (an embodiment of the third aspect described above). In this embodiment, the electromagnetic shielding ring 6 of the first embodiment is omitted, and the center distance D between the transmitting coil 4 and the receiving coil 5 is set to 1.2 R / 2. R is the center radius of the sending and receiving coils 4 and 5. Number of turns n of transmission coil 4
1, when the current I1 and the number of turns n2 of the receiving coil 5 are set, the ampere turn (AT) is n1 × I1 ≧ 7AT, n2
= 1.2n1. Other configurations are the same as in the first embodiment.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of a first embodiment of the present invention.

FIG. 2 is a schematic diagram corresponding to a longitudinal sectional view showing a state of magnetic coupling between a transmission coil 4 and a reception coil 5 of the detection coil devices (3 to 7) shown in FIG.

FIG. 3 is a longitudinal sectional view showing the configuration of a third embodiment of the present invention.

[Explanation of symbols]

1: Slag 2: Molten metal 3: Molten metal nozzle (fire resistance) 4: Transmitting coil 5: Receiving coil 6: Electromagnetic shielding ring 7: Casing

Claims (5)

[Claims] 1. A detection coil device including a transmitting coil circling a tube and a receiving coil circling the tube, wherein a detecting coil device is provided outside the tube and between the transmitting coil and the receiving coil.
A detection coil device comprising a conductor interposed to suppress a magnetic field generated by a transmission coil from spreading to a reception coil. 2. A detection coil device including a transmission coil circling a tube and a reception coil circling the tube, wherein a detection coil device is provided outside the tube and between the transmission coil and the reception coil.
A detection coil device including a ferromagnetic material that suppresses the transmission of a magnetic field generated by a transmission coil to a reception coil. 3. A detection coil device including a transmitting coil having a center radius of R and a receiving coil circling the tube, receiving a magnetic field generated by the transmitting coil in an outer space of the tube. In order to suppress the influence on the coil, the distance D between the center of the transmitting coil and the center of the receiving coil is set as D ≧
A detection coil device characterized by R / 2. 4. The detection coil device according to claim 1, wherein the tube is a nozzle for injecting a molten metal into a mold. 5. When the number of turns of the transmitting coil is n1, the effective current value of the alternating current is I1, and the number of turns of the receiving coil is n2, n1 × I1 ≧ 7AT and n1 ≦ n2. The detection coil device according to claim 2, 3, or 4.