Accumulated amount detection device in electric resistance type melting furnace and operation method of electric resistance type melting furnace

Abstract

To provide an accumulated amount detection device capable of accurately detecting an accumulated state of scrap in an electric resistance type melting furnace, and timely supplying the scrap into the electric resistance type melting furnace on a basis of a detected result.SOLUTION: A detection device of scrap 110 in an electric resistance type melting furnace 100 is provided with a transmission antenna 10 and a reception antenna 20 using microwave signals or millimeter wave signals which are arranged on respective side walls 101 of the electric resistance type melting furnace 100 opposite to each other, to determine that the scrap 110 is not accumulated when a measured distance between the transmission antenna 10 and the reception antenna 20 is equal to an installed distance between the transmission antenna 10 and the reception antenna 20 and a reception power becomes larger than a predetermined threshold level of the reception power.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a detection device for detecting the amount of scrap, such as metal, accumulated in an electric resistance melting furnace (hereinafter also referred to as an "electric furnace"), and a method for operating an electric resistance melting furnace for supplying scrap to the electric furnace based on the detection results of the detection device. [Background technology]

[0002] In an electric arc furnace, scrap such as iron, copper, stainless steel, aluminum, and alloys is fed into the furnace and piled up. A carbon electrode is inserted into the scrap and a high current is passed through it, generating an arc between the carbon electrode and the scrap. The scrap is melted by the heat of the arc, and the molten metal is recovered from the bottom of the furnace. Once a certain amount of the fed scrap has melted in the electric arc furnace, new scrap is fed in, and this process is repeated. For this reason, it is necessary to detect the amount of piled up scrap (surface height).

[0003] For example, Patent Document 1 discloses a device for detecting the surface of scrap, which transmits and receives microwave signals via a microwave distance meter installed near the top of an electric furnace, and measures the distance to the surface of the scrap from the time difference between the transmission and reception of the microwaves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-166222 Summary of the Invention [Problem to be solved by the invention]

[0005] 10 is a schematic diagram for explaining a problem that occurs when a detection wave is transmitted from above to the surface of the scrap, and as shown in FIG. 10, because each scrap lump has an irregular shape, the surface 110a of the scrap 110 accumulated inside the electric furnace 100 also has an irregular, uneven surface. Therefore, in a method including Patent Document 1 in which an antenna 135 of a rangefinder 130 is installed near the top of the electric furnace 100, a detection wave M such as a microwave is transmitted from above to the surface 110a of the accumulated scrap 110, and a reflected wave Mr reflected by the surface 110a of the scrap 110 is received, the transmitted detection wave M is reflected in various directions by the surface 110a of the scrap 110, and the reflected wave Mr does not return to the antenna 135, making it impossible to accurately detect the surface 110a of the scrap 110, i.e., the amount of accumulated scrap 110.

[0006] The present invention has been made in view of the above circumstances, and has as its object to accurately detect the state of scrap accumulation in an electric resistance melting furnace, and to provide an operating method using such a detector and supplying scrap to an electric furnace based on the detection results. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following (1) device for detecting the amount of deposition in an electric resistance melting furnace.

[0008] (1) A detection device for detecting the amount of scrap accumulated in an electric resistance melting furnace, A transmitting antenna and a receiving antenna of a distance meter using a microwave signal or a millimeter wave signal are arranged opposite to each other on a side wall of the electric resistance melting furnace, The device for detecting the amount of accumulated scrap in an electric resistance melting furnace is characterized by measuring the distance between the transmitting antenna and the receiving antenna, and determining that no scrap has accumulated when the measured distance is the same as the installation distance between the transmitting antenna and the receiving antenna and the received power exceeds a predetermined threshold value of received power.

[0009] Further, preferred embodiments of the present invention relating to the device for detecting the amount of deposition in an electric resistance melting furnace relate to the following (2) to (7).

[0010] (2) The device for detecting the amount of deposition in an electric resistance melting furnace described in (1) is characterized in that the transmitting antenna and the receiving antenna are installed separately using one controller to transmit and receive signals. (3) The device for detecting the amount of deposition in an electric resistance melting furnace according to (1) or (2), characterized in that a plurality of pairs of the transmitting antenna and the receiving antenna are arranged opposite each other on the side wall. (4) The device for detecting the amount of deposition in an electric resistance melting furnace according to (1) or (2), characterized in that the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips. (5) The device for detecting the amount of deposition in an electric resistance melting furnace described in (4), characterized in that the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips, and the waveguide has an inlet for burner gas. (6) The device for detecting the amount of deposition in an electric resistance melting furnace according to (3), characterized in that the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips. (7) The device for detecting the amount of deposition in an electric resistance melting furnace described in (6), characterized in that the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips, and the waveguide has an inlet for burner gas.

[0011] In order to solve the above problems, the present invention provides the following (8) method for operating an electric resistance melting furnace.

[0012] (8) Using the detection device according to any one of (1) to (7), measuring the distance between the transmitting antenna and the receiving antenna; When the measurement distance is equal to the installation distance between the transmitting antenna and the receiving antenna, and the received power exceeds the predetermined threshold value of the received power, a detecting means for detecting the amount of scrap piled up to the position where the transmitting antenna and the receiving antenna face each other, and then providing new scrap;

[0013] In the following description, the "detection device for detecting the amount of deposition in an electric resistance melting furnace" will also be simply referred to as the "detection device." [Effects of the Invention]

[0014] The detection device of the present invention extracts the direct incident signal by determining the reception distance and reception power of the direct incident signal transmitted from the transmitting antenna and directly incident on the receiving antenna, and comparing the reception distance and reception power with the reception distance and reception power of the wave signal reflected by the surface of the piled scrap and the multi-reflected wave signal multiply reflected by the furnace wall.The amount of piled scrap can then be accurately detected by comparing the reception power of the direct incident signal with a threshold value.

[0015] Furthermore, in the method of operating an electric resistance melting furnace of the present invention, new scrap can be supplied appropriately based on the detection results of the above-mentioned detector, thereby enabling good operation. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view schematically showing the overall configuration of the detection device of the present invention along the axis of an electric furnace. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA of the electric furnace shown in FIG. 1, showing the arrangement of the transmitting antenna and the receiving antenna. [Figure 3] FIG. 3 is a diagram showing the circuit configuration of the controller. [Figure 4] Figure 4 shows the received power of the direct incident signal L1, the scrap reflected signal L2, and the multiple reflected signal L3 when the distance of the received signal is not taken into account. Figure 4(A) shows the case where there is no scrap between the receiving antenna and the transmitting antenna, and Figure 4(B) shows the case where there is scrap between the receiving antenna and the transmitting antenna. [Figure 5]Figure 5 shows the distance and received power of the direct incident signal L1, the scrap reflected signal L2, and the multiple reflected signal L3 in the present invention, where (A) shows the case where there is no scrap between the receiving antenna and the transmitting antenna, and (B) shows the case where there is scrap between the receiving antenna and the transmitting antenna. [Figure 6] FIG. 6 is a cross-sectional view according to FIG. 2 showing a state in which a plurality of pairs of transmitting and receiving antennas are arranged facing each other at the same height. [Figure 7] FIG. 7 is a cross-sectional view showing a state in which a plurality of pairs of transmitting and receiving antennas are arranged facing each other at different heights, according to FIG. [Figure 8] FIG. 8 shows an antenna with a burner, in which (A) is a cross-sectional view and (B) is a view taken along the arrow BB in (A). [Figure 9] FIG. 9 is an enlarged view showing the oxygen inlet pipe of the burner antenna. [Figure 10] FIG. 10 is a schematic diagram for explaining the problem that occurs when a detection wave is transmitted from above to the surface of the scrap. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will now be described in detail with reference to the drawings.

[0018] [Detection device] FIG. 1 is a cross-sectional view schematically illustrating the overall configuration of the detection device of the present invention, taken along the axis of an electric furnace. FIG. 2 is a cross-sectional view of the electric furnace shown in FIG. 1 taken along line AA, showing the arrangement of the transmitting antenna and the receiving antenna. As shown in FIG. 1, in an electric furnace 100, a carbon electrode 120 is inserted into scrap 110 of metal such as iron or alloy that has been supplied and accumulated in the furnace. A high current is passed through the carbon electrode 120 to generate an arc between the carbon electrode 120 and the scrap 110, and the scrap 110 is melted by the heat of the arc. Molten metal 111 is then recovered from the bottom of the furnace.

[0019] In the present invention, the transmitting antenna 10 and the receiving antenna 20 of the range finder are placed opposite each other on the side wall 101 of the electric furnace 100. In this case, as shown by the dashed line 15 in FIG. 2, the transmitting antenna 10 and the receiving antenna 20 are placed opposite each other at a position where the carbon electrode 120 is not on the opposing line between the transmitting antenna 10 and the receiving antenna 20.

[0020] 3 is a diagram showing the circuit configuration of the controller. As shown in FIG. 3, the transmitting antenna 10 and the receiving antenna 20 are connected to the controller 40 by coaxial cables 30A and 30B. In the controller 40, a microwave or millimeter wave (hereinafter collectively referred to as a "detection wave") is frequency-modulated from a signal generator 41 and output as a detection wave signal. The detection wave signal is then split into two by a splitter 42, one of which is sent to an amplifier 43 and the other to a mixer 44. The detection wave signal amplified by the amplifier 43 propagates through the coaxial cable 30A and is transmitted from the transmitting antenna 10 toward the furnace interior. The detection wave signal received by the receiving antenna 20 propagates through the coaxial cable 30B, is amplified by an amplifier 45, and is then sent to the mixer 44.

[0021] The mixer 44 synthesizes and multiplies the detection wave signal output from the signal generator 41 with the detection wave signal received by the receiving antenna 20 to generate an IF signal. The IF signal is sampled by an AD converter 46 and output to a signal processing circuit 47. The signal processing circuit 47 then performs distance calculations and finds the distance from the time difference between the transmitted signal and the received signal.

[0022] Generally, when the transmitting antenna 10 and the receiving antenna 20 are arranged opposite each other, two controllers are required, one for the transmitting side and one for the receiving side. However, by using a configuration with a distributor 42 and a mixer 44 as described above, there is an advantage that only one controller 40 is required.

[0023] 1 again, as shown by the dashed lines in the figure, the detection wave signal transmitted from the transmitting antenna 10 includes not only a signal that directly enters the receiving antenna 20 (M1 in the figure: hereinafter referred to as the "direct incident signal M1"), but also a signal reflected by the surface 110a of the scrap 110 (M2 in the figure: hereinafter referred to as the "scrap reflected signal M2") and a signal that is reflected multiple times by the furnace wall (M3 in the figure: hereinafter referred to as the "multiple reflected signal M3"), all of which are received at once by the receiving antenna 20. Therefore, as shown in Figures 4(A) and 4(B), the received power is the sum of the received power L1 of the directly incident signal M1, the received power L2 of the scrap reflected signal M2, and the received power L3 of the multiple reflected signal M3.

[0024] 4A and 4B show the received powers of the direct incident signal M1, the scrap reflected signal M2, and the multiple reflected signal M3 when the distance of the received signal is not taken into consideration, and FIG. 4A shows the received powers L1 to L3 of the signals M1 to M3 when there is no scrap 110 between the transmitting antenna 10 and the receiving antenna 20. As shown in the figure, the received power L1 of the direct incident signal M1 exceeds a preset threshold value L0.

[0025] 4(B) shows the case where there is a scrap 110 between the transmitting antenna 10 and the receiving antenna 20, and the received power L1 of the directly incident signal M1 is below the threshold L0. However, even if the detection wave propagating directly between the transmitting antenna 10 and the receiving antenna 20 is blocked by the scrap 110, if the received power L2 of the scrap reflected signal M2 or the received power L3 of the multiple reflected signal M3 is large, or if the sum of the received power L2 of the scrap reflected signal M2 and the received power L3 of the multiple reflected signal M3 is large, the total received power of the signals M1 to M3 exceeds the threshold L0, and it is erroneously determined that there is no scrap 110 between the transmitting antenna 10 and the receiving antenna 20.

[0026] Therefore, the propagation time from transmission to reception of each signal M1-M3 is measured to distinguish between the direct incident signal M1, the scrap reflected signal M2, and the multiple reflected signal M3. That is, the longer the propagation time, the farther the received signal power appears. Therefore, as shown in FIG. 5, the received power L1 of the direct incident signal M1 appears at the closest reception distance D1, the received power L2 of the scrap reflected signal M2 appears at the next closest reception distance D2, and the received power L3 of the multiple reflected signal M3 appears at the farthest reception distance D3. The reception distance D1 is determined by the installation positions of the transmitting antenna 10 and the receiving antenna 20. Note that FIG. 5 is a diagram showing the respective distances and received powers of the direct incident signal M1, the scrap reflected signal M2, and the multiple reflected signal M3 in the present invention.

[0027] In addition, the received power of each signal M1 to M3 varies depending on the receiving distance. Figure 5(A) shows the case where there is no scrap between the receiving antenna and the transmitting antenna, but the received power L1 to L3 of all signals M1 to M3 exceeds the threshold L0.

[0028] In contrast, Figure 5(B) shows the case where there is a scrap 110 between the transmitting antenna 10 and the receiving antenna 20. However, because transmission and reception of the direct incident signal M1 is blocked, the received power L1 is greatly attenuated and falls well below the threshold L0, and the received power L2 of the scrap reflected signal M2 is also slightly smaller. Furthermore, the received power L3 of the multiple reflected signal M3, which is hardly affected by the blockage of transmission and reception, is about the same as when there is no scrap 110 between the transmitting antenna 10 and the receiving antenna 20 in Figure 5(A).

[0029] Therefore, as a method for determining whether scrap 110 is present between the transmitting antenna 10 and the receiving antenna 20, the received power L1 of the direct incident signal M1 at the receiving distance D1 is calculated, and if the received power L1 exceeds the threshold value L0, it is determined that there is no scrap, and if it is below the threshold value L0, it is determined that there is scrap. This enables accurate determination without being affected by multiple reflections of the detection wave or reflections on the scrap surface.

[0030] The scrap 110 is deposited unevenly, and its surface has various irregularities. Fig. 6 is a cross-sectional view, according to Fig. 2, showing a state in which multiple pairs of transmitting antennas and receiving antennas are arranged facing each other at the same height. As shown in Fig. 6, multiple pairs (four pairs in the figure) of transmitting antennas 10A-10D and receiving antennas 20A-20D may be installed facing each other at the same height so that the carbon electrode 120 is not on the line of opposition between the transmitting antenna 10 and the receiving antenna 20. This increases the number of detection points, making it possible to eliminate detection errors due to the surface shape or deposition state of the scrap 110.

[0031] However, when multiple pairs of transmitting and receiving antennas are installed, there is a possibility that transmitted waves from the wrong pair may be received, resulting in false detection. Therefore, false detection can be prevented by staggering the transmission timing of the transmitting antennas 10A to 10D. Furthermore, when transmitting at the same time, it is advisable to change the frequency of the detection wave signal for each of the transmitting antennas 10A to 10D.

[0032] 7 is a cross-sectional view showing, in accordance with FIG. 1, a state in which multiple pairs of transmitting antennas and receiving antennas are arranged facing each other at different heights. As shown in FIG. 7, multiple pairs (two pairs in the figure) of transmitting antennas 10E-10F and receiving antennas 20E-20F may be installed facing each other at different heights in multiple stages. This allows the pile level of scrap 110 to be detected in multiple stages.

[0033] Although not shown, in FIGS. 6 and 7, each set of transmitting antennas 10A to 10F and receiving antennas 20A to 20F is connected to the controller by a coaxial cable as shown in FIG.

[0034] Incidentally, while the scrap 110 is being melted, a large amount of splashes are scattered inside the electric furnace 100, and the splashes adhere to and accumulate on the transmitting antenna 10 and the receiving antenna 20. This may interfere with the transmission and reception of the detection wave, making it difficult to stably detect the amount of accumulated scrap 110 over a long period of time.

[0035] Therefore, Fig. 8 is a diagram showing an antenna with a burner, and as shown in Fig. 8, it is preferable that the transmitting antenna 10 and the receiving antenna 20 are made into a burner-equipped antenna 50. Here, the transmitting antenna 10 is shown, but the receiving antenna 20 has a similar configuration. Note that (A) in the figure is a cross-sectional view, and (B) is a view taken along the arrow BB in (A).

[0036] The burner-equipped antenna 50 is equipped with a coaxial-waveguide converter 51 at the right end in the figure. The coaxial-waveguide converter 51 is used to propagate a detection wave signal sent from the controller (reference numeral 40 in FIG. 1) via a coaxial cable 30A to a waveguide 52, and the coaxial cable 30A is connected to a connection terminal 51a. The detection wave signal output from the coaxial-waveguide converter 51 propagates through the waveguide 52 and is sent to an oxygen inflow pipe 53. An oxygen inflow hole 54 is formed inside the oxygen inflow pipe 53 and runs along the axis, and an oxygen inlet 55 branching off from the oxygen inflow pipe 53 is continuous with the oxygen inflow hole 54. Therefore, oxygen supplied from the outside through the oxygen inlet 55 flows through the oxygen inflow hole 54.

[0037] Figure 9 is an enlarged view of the oxygen inlet pipe of the burner-equipped antenna. As shown in Figure 9, oxygen inlet hole 54 has a large number of oxygen inlet ports 54a formed therein, and the opening diameter of each port is smaller than radius a, calculated by the following equation, where f is the frequency of the detection wave signal and C is the speed of light, and is a dimension that facilitates the inflow of oxygen. The detection wave signal propagates through oxygen inlet pipe 53, but by setting the opening diameter of oxygen inlet port 54a in this way, the detection wave signal does not leak from oxygen inlet port 54a. a=(1.841×C) / (2πf)

[0038] The number of oxygen inlets 54a is determined by the flow rate and pressure of the oxygen to be supplied, and the amount of oxygen to be sprayed from the burner-equipped antenna 50 can be determined by setting the number of oxygen inlets 54a to an appropriate number.

[0039] At the connection between the waveguide 52 and the oxygen inlet pipe 53, the oxygen inlet hole 54 is blocked with a plug member 56 to prevent the taken-in oxygen from flowing into the coaxial-waveguide converter 51. The plug member 56 is preferably made of Teflon (registered trademark), but any material other than Teflon (registered trademark) may be used as long as it does not impede the propagation of the detection wave.

[0040] A main body 57 is connected to the oxygen inflow pipe 53. A metal pipe 58 is formed inside the main body 57 along the axis, and the end opening of the metal pipe 58 on the oxygen inflow pipe side is continuous with the oxygen inflow hole 54. Therefore, oxygen supplied from the oxygen intake port 55 of the oxygen inflow pipe 53 flows into the metal pipe 58 through the oxygen inflow hole 54.

[0041] The other end of the metal tube 58 tapers toward the tip (left side in the figure) of the main body 57, and the metal tube 58 functions as an antenna. A detection wave signal is transmitted from the tapered portion 59, and the supplied oxygen is ejected.

[0042] A flammable gas inlet 60 branches off from the main body 57 near the connection with the oxygen inlet pipe 53, and flammable gas such as LNG is supplied from the outside and sent to a gas reservoir 61. In addition, a plurality of flammable gas metal pipes 62 are arranged in the main body 57 so as to surround the metal pipe 58. One end of each flammable gas metal pipe 62 is connected to the gas reservoir 61, and an opening 62a at the other end surrounds the tapered portion 59 of the metal pipe 58.

[0043] Then, the oxygen injected from the tapered portion 59 of the metal tube 58 and the combustible gas injected from the opening 62a of the combustible gas metal tube 62 are mixed and ignited at the furnace temperature, forming a burner flame in front of the burner-equipped antenna 50. The ejection of this burner flame prevents splashes from adhering. Even if splashes do adhere, they are instantly melted by the heat of the burner flame, so they do not accumulate.

[0044] There are no particular limitations on the temperature, strength, spread, etc. of the burner flame as long as splashes do not adhere or accumulate on the front surface of the burner-equipped antenna 50 .

[0045] Furthermore, at the same time as the burner flame is generated, a detection wave signal is also transmitted from the metal tube 58, but the microwaves and millimeter waves that are the detection waves pass through the burner flame and do not affect the transmission.

[0046] However, the detection wave signal transmitted through the burner flame into the electric furnace 100 is scattered by splashes scattered inside the furnace and propagates to the receiving burner antenna (not shown). Therefore, to reduce the influence of scattering by splashes, the detection wave signal to be used is preferably in the 10 to 24 GHz band, which has a frequency with a wavelength sufficiently long compared to the size of the splashes.

[0047] The burner-equipped antenna 50 can be modified in various ways. Although not shown in the drawings, for example, the oxygen flow path is a metal tube 58, and the combustible gas flow path is separated into a metal tube 62 for combustible gas, but the combustible gas may be directly supplied to the metal tube 58 and mixed. Also, the burner-equipped antenna 50 may be made into a multi-tube structure, with cooling water flowing inside for water cooling.

[0048] [Operation method] In the present invention, the above-mentioned detection device is used to detect the surface 110a of the scrap 110 that has been supplied to and accumulated in the electric furnace 100, and when the received power L1 of the direct incident signal M1 exceeds the threshold value L0, it is determined that there is no scrap 110 between the transmitting antenna 10 and the receiving antenna 20 and that the amount of accumulated scrap is insufficient, and new scrap 110 is supplied, thereby enabling stable operation. [Explanation of symbols]

[0049] 10, 10A, 10B, 10C, 10D, 10E, 10F Transmitting antenna 20, 20A, 20B, 20C, 20D, 20E, 20F Receiving antenna 30A, 30B coaxial cable 40 Controller 41 Signal Generator 42 Distributor 43,45 Amplifier 44 Mixer 46 AD converters 47 Signal Processing Circuit 50 Burner antenna 51 Coaxial-waveguide converter 51a connection terminal 52 Waveguide 53 Oxygen inlet pipe 54 Oxygen inlet 54a Oxygen inlet 55 Oxygen intake 56 Plug member 57 Main body 58 Metal tube 59 Tapered section 60 Combustible gas intake 62 Metal pipes for flammable gases 62a aperture 100 Electric resistance melting furnace (electric furnace) 101 Side wall 110 Scrap 110a surface 111 Molten Metal 120 Carbon electrode

Claims

1. A detection device for detecting the amount of scrap accumulated in an electric resistance melting furnace, A transmitting antenna and a receiving antenna of a distance meter using a microwave signal or a millimeter wave signal are arranged opposite to each other on a side wall of the electric resistance melting furnace, The device for detecting the amount of accumulated scrap in an electric resistance melting furnace is characterized by measuring the distance between the transmitting antenna and the receiving antenna, and determining that no scrap has accumulated when the measured distance is the same as the installation distance between the transmitting antenna and the receiving antenna and the received power exceeds a predetermined threshold value of received power.

2. 2. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 1, wherein the transmitting antenna and the receiving antenna are installed separately using a single controller for transmitting and receiving signals.

3. 3. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 1, wherein a plurality of pairs of the transmitting antenna and the receiving antenna are arranged opposite to each other on the side wall.

4. 3. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 1, wherein the transmitting antenna and the receiving antenna are antennas with burners that spray burner flames from their tips.

5. 5. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 4, wherein the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips, and the waveguide is provided with an inlet for burner gas.

6. 4. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 3, wherein the transmitting antenna and the receiving antenna are antennas with burners that spray burner flames from their tips.

7. 7. The device for detecting the amount of deposition in an electric resistance melting furnace according to claim 6, wherein the transmitting antenna and the receiving antenna are burner-equipped antennas that spray burner flames from their tips, and the waveguide is provided with an inlet for burner gas.

8. Using the detection device according to claim 1 or 2, measuring the distance between the transmitting antenna and the receiving antenna; When the measurement distance is equal to the installation distance between the transmitting antenna and the receiving antenna, and the received power exceeds the predetermined threshold value of the received power, a detecting means for detecting the amount of scrap piled up to the position where the transmitting antenna and the receiving antenna face each other, and then providing new scrap;

Images