Detection system for detecting the metal level in a melting furnace

Abstract

A system for detecting the level of molten steel for an EAF furnace, preferably having three AC electrodes, comprises three electromagnetic coils capable of detecting an electromagnetic field generated by the passage of current in a circuit formed between two of the electrodes and a pool of molten metal contained in the melting furnace. Preferably, the three coils are arranged only on one side of the outer surface of the arc melting furnace, along a circumferential arc facing the two electrodes forming the electromagnetic field, and on a side diametrically opposite to the third electrode.

Description

Background of the Invention

[0002] The present invention belongs to the field of metal melting, in particular to the field of steel melting by means of an electric arc furnace with alternating current electrodes.

[0003] Alternatively, the system can be applied to a ladle furnace, a vacuum arc degassing furnace. Prior art

[0004] Among other systems, an electric arc furnace for melting steel, also referred to as EAF for short, is provided with electrodes and in which the metal scrap is generally inserted with intermittent feeding, for example by means of a basket, or with continuous feeding by means of a conveyor belt. This is a well-known technology, which is very common in the iron and steel technology industry. It is important to know the level of the molten bath in such a furnace accurately and continuously at all moments of the production cycle in order to optimally manage the process, the addition of additives and the melting process. Furthermore, among other things, knowing such parameters allows the lances, in particular the supersonic oxygen lances (often present in melting furnaces) and the sampling lances to be arranged automatically or non-automatically in a vertical position, at the correct distance relative to the level of the molten bath, and also allows a clearer distinction between the areas occupied by steel and the areas occupied alternatively by slag during the sampling step.

[0005] One difficulty encountered and desired to be overcome in this type of furnace relates to the need to know whether the charged scrap accumulated in the melting shell has been sufficiently melted by the burners and the arc in order to proceed with the successive steps of managing the auxiliaries of the furnace, namely the injection of oxygen and post combustion. Furthermore, by knowing the level of the bath, it is possible to estimate in real time the efficiency with which the charged scrap is melted and turned into liquid steel during the melting process. Furthermore, this measurement can also be used to indirectly monitor the consumption of the refractory material constituting the furnace.

[0006] When looking for a solution to the problem of sensing molten metal, an important physical aspect to consider is the shielding effect of the molten pool with respect to the magnetic field generated by the three-phase electrodes through which the current flows, which is required to carry out the melting and refining steps. In the past, this problem made it extremely difficult to find a solution that achieved accurate and efficient measurements.

[0007] Devices for detecting the level of steel in a container (and possibly in an electric arc furnace) are known. For example, EP0115258 discloses a device for detecting the level of steel in a smelting shell which is almost empty and contains little steel. EP0419104 discloses a device for detecting the level of steel in a mold for continuous casting. In both applications, they are solutions based on the concept of arranging one or more transmitting coils with alternating current and one or more receiving coils inside the container, the level of steel of which needs to be measured. Since steel is a conductive material that has the function of shielding the electrical signal emitted by the transmitting coil, when the height of the liquid level changes, the signal received by the receiving coil will also change. Therefore, the liquid level signal can be estimated because the received signal will be higher when the liquid steel does not shield the coil.

[0008] However, this system of detecting the level of molten steel is ineffective in electric arc furnaces (which operate on alternating current) because the magnetic field generated by the current flowing through the electrodes and the arc closes the circuit in the liquid bath and also induces an induced electromotive force in the receiving coil. Such a signal generates interference in these molten bath level-measuring systems, thereby introducing errors in the measurement.

[0009] Such solutions therefore do not adequately meet the demands for simplicity, precision and reliability expected in the steel industry.

[0010] Therefore, a sensor for the level of the molten steel pool was produced to meet this need, which facilitates a cost-effective melting process and is reliable and accurate in various types of melting furnaces. SUMMARY OF THE INVENTION

[0012] These foregoing objects, in addition to other objects that will become clearer from the following description, are achieved by a system for detecting the level of a molten pool or non-molten scrap for a smelting furnace, the system determining the vertical direction when the furnace is arranged with its opening in the highest position, the system having two or more electrodes, including several electromagnetic receiving coils, which are configured to detect only an electromagnetic field generated by a current circulation in a circuit, the circuit consisting of at least two electrodes of the two or more electrodes, at least one electric arc and a molten pool contained in the smelting furnace, wherein the electromagnetic receiving coils are arranged at different heights in the vertical direction between the bottom of the furnace and a higher plane of the maximum liquid level that the molten pool can reach in the furnace during operation.

[0013] Generally, one or more receiving coils arranged inside a furnace or vessel are designed to utilize the magnetic field generated by the alternating current, which follows the circuit formed by the electrodes and the arc to produce a measurement of the level of the molten steel.

[0014] An important advantage of the claimed invention is the simplification of the architecture of the measurement system, since the transmitting coil is eliminated, since the magnetic field generated by the current circulating in the arc and the electrodes of the furnace and closed in the liquid pool is utilized, acting as the "source" of the signal received by the receiving coil.

[0015] The invention is also applicable to any type of process in which electrodes are used with alternating current to perform an operation on molten steel.

[0016] In particular, the invention can also be used, with advantage, to derive the level of molten steel in a ladle furnace where it undergoes a refining operation, for example in a process of the vacuum arc degassing type.

[0017] A first embodiment of the system of the invention comprises all electromagnetic receiving coils configured to be arranged on only one side of the smelting furnace with respect to a vertical cross-sectional plane on any diameter of the smelting furnace.

[0018] In a variant, each electromagnetic receiving coil is configured to be arranged only along a respective circumferential arc of the perimeter or circumference of the smelting furnace, said circumferential arc facing the first and second electrodes forming the circuit and opposite the half of the circumference of said circumference facing the third electrode. Thus, the coil is arranged on the side diametrically opposite to the third electrode.

[0019] In other words, the electromagnetic receiving coil is arranged along only one cylindrical side surface portion of the circumference of the smelting furnace, which cylindrical side surface portion faces the first electrode and the second electrode and is arranged on a side diametrically opposite to the third electrode.

[0020] Preferably, the number of the electromagnetic receiving coils is at least three, and they are configured to be arranged in alignment along the vertical direction.

[0021] A second embodiment comprises more than three electromagnetic receiving coils. At least two of these electromagnetic receiving coils are arranged at different points along the periphery of the furnace, in the same plane above the maximum level of the molten metal pool, while the remaining electromagnetic receiving coils are placed at different heights below the maximum level in the vertical direction.

[0022] A variant of the invention provides that the electromagnetic receiving coil is configured to be arranged close to an outer surface of the furnace, in particular on an outer wall of the furnace, for example in a housing produced on said outer wall, thus outside a refractory layer provided inside the furnace.

[0023] Preferably, in various embodiments, the electromagnetic receiving coil is substantially rectangular, for example with rounded corners, and is configured with the smaller sides of the rectangle arranged in a vertical direction. The dependent claims describe particular embodiments of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The objects and advantages of the system for measuring the level of a steel bath of the present invention will become clear from the following detailed description of embodiments of the invention and from the accompanying drawings, which are given by way of non-limiting example only, in which:

[0026] Figure 1 shows a cross section on a vertical plane of an electric arc furnace with a diagram of the operation of the system of the invention;

[0027] Figure 2 is a cross-sectional side view of an electric arc furnace to which a system according to the invention is applied, shown in a transparent manner;

[0028] Figure 3 a graph showing the trend of a signal detected with the system according to the invention as a function of the level of molten metal in a furnace;

[0029] Figure 4 a graph showing the trend of a signal detected with the system according to the invention as a function of the level of molten metal in the furnace in a second mode represented;

[0030] Figure 5 shows a schematic axonometric view of a receiving coil of a system according to the invention;

[0031] Figure 6 Some graphs showing qualitative trends of the magnetic field detected by various receiving coils of the system according to the invention for an electric arc furnace, the system being installed on the furnace with a determined level of molten steel;

[0032] Figure 7 A graph showing the qualitative trend of the magnetic field detected by the receiving coils of the system according to the invention for a furnace, the system being installed on the furnace, with a determined level of molten steel and the presence of non-molten scrap;

[0033] Figure 8 A possible arrangement of receiving coils of the system according to the invention in an electric arc furnace is shown, seen in section on a horizontal plane;

[0034] Fig. 9 Shown are different possible arrangements of receiving coils of the system according to the invention in an electric arc furnace, seen in section on a horizontal plane;

[0035] Fig.10Two possible alternative arrangements A and B of receiving coils of the system according to the invention in an electric arc furnace, seen in cross section on a horizontal plane, are shown.

[0036] The same numerals and the same letters referenced in the drawings denote the same elements or components.

[0037] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0038] With reference to the accompanying drawings, a system or apparatus for detecting the level of molten metal during operation, installed in an electric arc furnace 2 containing a tank 3 of molten steel, is described below and is indicated as a whole by the reference numeral 1. The detection system 1 comprises Figure 1 One or two receiving coils 1 ′, 1 ″ as shown in the figure, or three receiving coils 1 ′, 1 ″, 1 ″′ as shown in the other figures. Furthermore, a system for detecting the level of a molten metal can be realized with more than three receiving coils.

[0039] In all configurations, the receiving coils are fixed to the outer wall of the furnace 2. According to embodiments of the invention, the arrangement of the receiving coils on the outer wall is different. The coils of the detection system can be arranged along the perimeter or circumference of the furnace, approximately along lines representing meridians and therefore at different heights, or along ideal parallel lines, such as Figure 8 and Fig. 9 In particular, this arrangement makes it possible to detect non-melted scrap at several points on the inner periphery of the furnace. The receiving coils can also be arranged according to a combination of an arrangement along one or more vertical lines and an arrangement along one or more horizontal lines.

[0040] In this specification, horizontal orientation and vertical orientation are defined relative to the position of the furnace 2, wherein the filling opening faces upwards. For example, when the furnace is arranged with the opening in the highest position of the furnace, the smelting furnace 2 defines (ie determines) a vertical direction.

[0041] Another possible arrangement of the receiving coils is an arrangement in which all three receiving coils 1', 1", 1"' are arranged along a single vertical meridian of the furnace in order to completely detect the liquid level of the entire height of the part of the furnace 2 occupied by the molten metal 3, such as Figure 2 As shown in .

[0042] Another possible arrangement, alternative to the previous one, is one in which several receiving coils are arranged vertically along several meridians of the surface of the electric arc furnace.

[0043] Therefore, from the above explanation, it is clear to a person skilled in the art that, although for simplicity, the embodiment described herein is mainly an embodiment in which the detection system comprises three coils 1', 1", 1"', which are arranged vertically, i.e. arranged along the same vertical direction, depending on the needs of the detection, more than three coils may be used to constitute the detection system of the present invention, since there is no restriction on the number of receiving coils except in financial and dimensional aspects. It is clear that the greater the number of receiving coils, the more accurate the measurement of the liquid level of the molten steel can be.

[0044] A more general basic diagram of the detection system of the present invention is Figure 1 , where three-phase electrodes 4, 5, 6 are part of a circuit, where current flows through electrode 6 in a first direction, and alternating current flows through the other two electrodes 4, 5 in a second direction opposite to the first direction, and the steel pool 3 completes the circuit. The trend of this circuit is Figure 6 , Figure 7 11. If the electric arc furnace also has only two electrodes or more than three electrodes (for example four electrodes), the circuit will be formed in a similar way. As is known, the three-phase alternating current flowing through the circuit 11 generates an electromagnetic field. Such an electromagnetic field can be detected by the receiving coils 1', 1", 1"' of the detection system 1, which is fixed to the inside of the refractory wall of the furnace 2.

[0045] The operating principle of the system for detecting the level of a molten pool according to the present invention will now be described. When the receiving coils arranged, for example, on the outer wall of the furnace are above the level of the steel pool, Figure 2 In the system shown in FIG. 1 , the magnetic flux generated by the alternating current of the electrode produces a voltage signal over time, which can be detected by a voltmeter or ammeter conveniently connected to the end of the receiving coil. If the voltage signal of any receiving coil is a signal with a detectable strength, then the liquid level of the molten steel is below the plane in which the coil is arranged. On the contrary, if the voltage signal of the same coil is particularly low, then the liquid level of the molten steel is above the receiving coil because the molten steel pool has a strong shielding ability against the magnetic flux. This arrangement is schematically represented in FIG. Figure 6 , wherein, in the case where the liquid level of the molten steel is shown, the voltage curve "a" corresponds to the receiving coil 1', the voltage curve "b" corresponds to the receiving coil 1", and the voltage curve "c" corresponds to the receiving coil 1'". Naturally, these are schematic, purely illustrative voltage curves, which illustrate the operating principle of the system of the invention.

[0046] The same situation also occurs when the receiving coil is arranged above the liquid steel level, but is covered by non-molten metal scrap 15, because the scrap also has shielding capabilities. Figure 7It is schematically represented in FIG. 1 , wherein a voltage curve “a” corresponds to a receiving coil 1 ′ in the case where the level of liquid steel 3 is shown and scrap 15 is present above the level of the steel 3 .

[0047] Typically, at an operating frequency of 50 Hz, the electromagnetic field is reduced by 95% to a steel depth of 250 mm.

[0048] Specific reference Figure 2 , Figure 3 , Figure 4 , Figure 6 , Figure 7 , which has three receiving coils 1 ′, 1 ″, 1 ′″, each receiving coil being connected to a respective voltmeter, the detection system 1 can typically, but not exclusively, operate in three different modes.

[0049] Waste Detection Operation Modes:

[0050] The upper coil 1' is often placed above the maximum level of the molten steel and therefore said upper coil often detects a high voltage signal in the modulus. In contrast, if the upper coil 1' is shielded by non-molten metal scrap, which may occur during a smelting process where scrap is charged from the top, the upper coil 1' detects a low value signal and therefore the detection system indicates the presence of non-molten scrap above the molten pool, said scrap being placed in front of the coil, i.e. it intersects the substantially horizontal plane in which the coil is positioned.

[0051] In addition, if Figure 8 and Fig. 9 As shown, if several upper coils 1'a, 1'b, 1'c, 1'd are arranged above the maximum level of the steel pool at different points along the periphery of the furnace, the presence of non-melted scrap in the furnace can be verified at several points of the pool.

[0052] When the scrap 15 is completely melted, the signal received by the upper coil 1 ' or by several upper coils 1 'a, 1 'b, 1 'c, 1 'd has a high value.

[0053] exist Figure 8 In a variant of , two upper receiving coils 1'a, 1'b are provided, which are arranged along the periphery of the furnace 2, in particular on the outer wall of the furnace, for example in a housing obtained on the outer wall. Preferably, said upper receiving coils 1'a, 1'b are positioned on the same substantially horizontal plane. Alternatively, in Fig. 9In a variant of the invention, four upper receiving coils 1'a, 1'b, 1'c, 1'd are provided, which are arranged along the periphery of the furnace 2, in particular on the outer wall of the furnace, for example in a housing obtained on the outer wall. Preferably, said upper receiving coils 1'a, 1'b, 1'c, 1'd are positioned on the same substantially horizontal plane. Optionally, these four upper receiving coils are arranged two by two symmetrically with respect to a vertical section on the diameter of the smelting furnace 2.

[0054] The first detection mode for detecting the molten steel level:

[0055] In order to derive the steel level 3, the voltage (or current) received from the receiving coil 1', 1" or 1"' is compared with the electromagnetic model. The current through the electrodes 4, 5, 6 is known because it is a value that can be obtained by appropriate measurements. Moreover, when the scrap 15 is completely molten and there is no scrap accumulation above the pool, the trend of such a signal is Figure 3 (K1, K2, K3) is shown in the curve diagram.

[0056] The signal of the upper coil 1' can also be used as a "reference signal", and the signals received from the other coils 1", 1"' in the middle position and the lower position are divided by the reference signal, thereby obtaining a dimensionless value independent of the current flowing through the electrode, which represents the liquid level of the molten steel 3. The trend of such a signal is Figure 4 (K4, K5) are shown in the curve diagram.

[0057] The second detection mode for detecting the molten steel level:

[0058] Using three coils 1', 1", 1"' arranged in different positions in the vertical direction, the entire range of changes in the liquid level of the molten steel can be covered. The middle receiving coil 1" is more sensitive to the middle and high pool levels, while the lower receiving coil 1"' is more sensitive to the middle and low pool levels. This trend of such a signal is also Figure 3 The curve diagram is shown in FIG.

[0059] Thus, the detection system 1 detects electromagnetic fields generated during operation of an electric arc furnace in the presence of a bath of molten metal and / or scrap intended for smelting.

[0060] Special References Figure 5 , the receiving coil is schematically shown as having N turns. Preferably, but not exclusively, the shape of the coil is rectangular, the size of the larger side of the coil is L1 and the size of the smaller side of the coil is L2, and the receiving coil is usually arranged on the wall of the furnace, wherein the smaller side L2 is in the vertical direction.

[0061] Alternatively, the coil may have an oval shape or other suitable elongated shape.

[0062] The side L2 of the coil, which is intended to be arranged vertically, is small enough to increase the sensitivity of the coil and to control the size. However, the product N*L1*L2 must be high enough so that the voltage V is detectable.

[0063] In practice, the voltage across the winding is calculated using the following formula:

[0064] V(t)=N*L1*L2*dB / dt

[0065] Where B is the electromagnetic field component normal to the surface of the sensor (i.e., receiving coil), and therefore the voltage modulus is:

[0066] V=N*L1*L2*2π*f*B,

[0067] Here, f is the frequency of the current circulating in the circuit 11 .

[0068] Furthermore, if the current and voltage (magnitude and phase) of the electrodes are known, knowing the phase of the received current and voltage also provides information about the received voltage level. In fact, by varying the level of liquid steel or the presence or absence of scrap, the impedance of the coil varies in magnitude and phase.

[0069] Therefore, the voltage is proportional to the number of turns, the voltage is proportional to the area defined by the coil (which can be calculated by multiplying L1*L2), and the voltage is also proportional to the frequency f.

[0070] An electromagnetic model was created by mathematical simulation, which also allows a detection system 1 comprising only three coils to accurately detect the height of the molten pool, also in an intermediate position between two adjacent coils. A graph showing the magnetic field strength to which each of the three coils 1 ', 1", 1"' is subjected as a function of the distance from the molten pool surface and completed due to extrapolation in the cross section between adjacent coils, can be used to accurately detect the height of the molten steel pool.

[0071] The receiving coil is designed with support and winding wires capable of withstanding high temperatures and may be provided with a cooling system, preferably in air.

[0072] In order to obtain the desired received signal, a magnetic flux concentrator may also be used to generate the coil.

[0073] Preferably, but not exclusively, the wires constituting the turns of the receiving coil are made of nickel-plated copper, with mica insulation and glass fiber protection. The turns are fixed to a support structure made of a mica-based material or similar.

[0074] In AC furnaces, especially three-phase electric arc furnaces ( Fig.10 ), the best and more efficient position of the detection system for detecting the magnetic field generated by the current circulation in the circuit formed by at least two of the three electrodes 4, 5, 6, by at least one electric arc and by the molten pool 3 contained in the smelting furnace 2 is a position in which all the receiving coils 1', 1", 1"' are arranged along a substantially vertical line, along corresponding circumferential arcs in front of two of the three electrodes 4, 5, 6 on the outer surface of the furnace 2, at Fig.10 The receiving coil is arranged in such a preferred position B, i.e. in the area in front of the two electrodes 4, 5. Such an area is conventionally defined as a "cold point", since it is the area farthest from the arc, i.e. where the non-molten scrap accumulates mostly. Position B is the best possible position, since it is the position closest to the electrodes 4 and 5 and it is able to detect a magnetic field having a component orthogonal to the receiving coil. On the contrary, Fig.10 The position indicated by A in FIG. 1 may be an area that must be avoided because it is in the shadow of the third electrode 6 and if the receiving coil is placed in such a position A, a lower force signal will be detected. Figure 7 According to the law of Biot Savart, the electrode 6 generates a purely tangential electromagnetic field both at point B and at point A. For the purpose of the received signal, i.e. for the purpose of the voltage induced at the ends of the receiving coil, only the electromagnetic field is counted in a direction orthogonal to the coil, so the contribution of the electrode 6 to the detection is always zero.

[0075] Advantageously, the coil is inserted inside the carpentry of the melting furnace, but, nevertheless, on the outer surface, in an area well insulated from the heat, there is advantageously provided cooling means, preferably air, incorporated in the coil to reduce its size, or forced cooling means to ensure a suitable operating temperature of the components of the detection system. Preferably, the receiving coil is arranged inside the bricks constituting the refractory wall of the furnace, since said bricks do not shield the electromagnetic fields generated in the electric arc furnace.

[0076] Alternatively, the receiving coils can be arranged outside the refractory wall, thereby creating an opening in the smelting shell having a size at least equal to the size of the corresponding receiving coil. In this last case, the efficiency of the receiving coils is reduced, since the magnetic field tends to decrease faster inside the opening. In general, to ensure the correct operation of the receiving coils, there should be no metal surfaces in front of said coils, which could shield the magnetic field used to detect the level of the molten steel.

[0077] A typical melting cycle in an electric arc furnace, in which the method of detecting the level of molten metal implemented using the system of the present invention is particularly useful, will now be described as a non-limiting example.

[0078] During the smelting process, several baskets filled with scrap are loaded into the furnace in sequence. When the last basket of scrap has been loaded, the next step is refining, in which the scrap is smelted and the pool is flat. At this time, the level of the molten metal can be measured by a second mode of detecting the level of the molten pool, which uses the ratio between the signal received in each of the coils 1 ", 1"' in the middle position and the lower position and the signal received from the upper coil 1 ".

[0079] If non-molten scrap is present above the level of the molten pool, a first level detection mode is used, whereby the voltage received from the coil is compared to an electromagnetic model and the current flowing through the electrode is known.

[0080] Furthermore, after each basket of scrap is loaded, it may happen that not all the scrap is melted and is still partially solid, and it is necessary to detect the level of the pool. Thanks to the system of the invention, the height of the melt pool and the height of the scrap layer can also be measured in such a case.

[0081] Furthermore, another typical steel melting process is the continuous loading process, where the scrap is not charged from the top, but enters through a special side door of the electric arc furnace. Similarly, in this case it is also advantageous that the detection system can be used to measure the level of the molten steel and detect non-molten scrap.

Claims

1. An arc melting furnace (2) using alternating current, comprising a detection system for detecting the liquid level of a molten pool (3) or non-molten scrap (15), the arc melting furnace defining a vertical direction Z and comprising two or more electrodes (4, 5, 6), the detection system comprising a plurality of electromagnetic receiving coils (1', 1'', 1'''), the electromagnetic receiving coils (1', 1'', 1''') being configured to detect only one electromagnetic field generated by current circulation in a circuit (11), the circuit (11) consisting of at least two of the two or more electrodes (4, 5, 6), at least one electric arc and the molten pool (3) contained in the arc melting furnace (2), wherein: The plurality of electromagnetic receiving coils (1', 1'', 1''') are arranged at different heights above the bottom of the arc melting furnace along the vertical direction Z, wherein the upper coil (1') of the plurality of electromagnetic receiving coils (1', 1'', 1''') is always placed above a higher plane of the maximum liquid level of molten steel that can be reached in the arc melting furnace during a melting operation of the molten pool, Characterized in that the plurality of electromagnetic receiving coils (1', 1'', 1''') are provided with cooling devices integrated in the coils; And the electromagnetic receiving coil is arranged inside the bricks constituting the refractory wall of the arc melting furnace.

2. The arc melting furnace according to claim 1, wherein: All the electromagnetic receiving coils (1', 1", 1''') are configured to be arranged only on one side of the arc melting furnace (2) relative to a vertical cross-sectional plane on any diameter of the arc melting furnace (2).

3. The arc melting furnace according to claim 2, wherein: Each electromagnetic receiving coil (1', 1'', 1''') is configured to be arranged only in one corresponding circumferential arc of the circumference of the arc melting furnace (2), the circumferential arc facing the first electrode and the second electrode and opposite to the half-circle of the circumference facing the third electrode.

4. The arc melting furnace according to claim 1, wherein: The number of the electromagnetic receiving coils (1', 1", 1'') is at least three, and they are configured to be arranged in alignment along the vertical direction.

5. The arc melting furnace according to claim 1, wherein: More than three electromagnetic receiving coils (1', 1'', 1''') are provided, and at least two (1'a, 1'b, 1'c, 1'd) of the electromagnetic receiving coils (1') are arranged at different points along the periphery of the arc melting furnace (2) and on the same plane above the maximum liquid level, while the remaining electromagnetic receiving coils (1'', 1''') are placed at different heights along the vertical direction and at liquid levels below the maximum liquid level.

6. The arc melting furnace according to one of claims 1 to 3 and 5, wherein: The electromagnetic receiving coil (1', 1", 1''') is configured to be arranged close to an outer surface of the arc melting furnace.

7. The arc melting furnace according to one of claims 1 to 3 and 5, wherein: The electromagnetic receiving coil (1', 1", 1'') is substantially rectangular in plane and is configured with the smaller sides of the rectangle arranged in the vertical direction.

8. The arc melting furnace according to claim 1, wherein: At least three electromagnetic receiving coils (1', 1'', 1''') are provided, and the electromagnetic receiving coils are arranged at different distances from the bottom of the arc melting furnace (2) along the vertical direction.

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