Metal dissolving equipment

Abstract

To provide a metal melting device, when a metallic material is melted by an arc discharge from an electrode, capable of estimating the position of the tip of the electrode at high precision from a time in which the melting of the metallic material is not so progressed so as to control the height position of the electrode based on the estimated result.SOLUTION: A metal melting device 1 comprises: an electrode lifting device 30; an electrode length measurement device 40; a lifting control unit 52 lowering the electrode by the electrode lifting device 40 with the progress of the melting of a metallic material M; an electrode evaluation unit 53 estimating the height position of the tip 15a of an electrode 15 during the melting of the metallic material M based on the length of the electrode 15 measured by the electrode length measurement device 40 before the start of the melting of the metallic material M and the consumption of the electrode 15 corresponding to the electric energy charged to the electrode 15; and a voltage control unit 51 controlling the voltage to be fed to the electrode 15. The voltage control unit 51 controls the voltage to be fed to the electrode 15 based on the height position of the tip 15a of the electrode 15 estimated by the electrode estimation unit 53 during the melting of the metallic material M.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a metal melting apparatus, and more particularly to a metal melting apparatus that melts a metal material by arc discharge while controlling the height of an electrode. [Background technology]

[0002] In an arc furnace in which metal scraps and other metal materials are melted by arc discharge from electrodes, an electrode lifting device is often provided to adjust the height of the electrodes relative to the metal material. The electrode lifting device can be used to adjust the height of the electrode tip relative to the metal material, thereby controlling the conditions for melting the metal material. The conditions for efficiently melting the metal material depend on the state of the metal material in the furnace, the positional relationship between the metal material and the electrodes, and the like, so the state of the metal material in the furnace, the height of the electrodes, or parameters reflecting them can be used to control the conditions for melting, such as the power input to the electrodes.

[0003] For example, in Patent Document 1, the heat flux on the inner peripheral surface of the furnace wall is calculated based on the temperatures measured at a plurality of positions on the inside and outer surfaces of the furnace wall of an electric furnace, and the start of melting through of scrap (metallic material) is judged based on the calculation result. In Patent Document 2, the operating conditions are adjusted based on the position of the electrode and an in-furnace profile created by connecting the positions of temperatures predetermined as the melting temperature of the lump of material (metallic material) that is produced by adhering to the inner wall of the furnace body. In Patent Document 2, the position of the electrode is estimated based on the electrode length measured by a lifting amount measuring device, which is the amount of relative displacement of the electrode from a reference position determined on the edge of the furnace body, and the amount of displacement of the electrode from the reference position. When controlling the conditions for melting by the height position of the electrode tip, it is important to actually measure the length of the electrode. For example, Patent Document 3 discloses an electrode length measuring device that actually measures the length of the electrode outside the furnace body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-226864 A [Patent Document 2] JP 2008-116066 A [Patent Document 3] JP 2016-148465 A Summary of the Invention [Problem to be solved by the invention]

[0005] When melting a metal material by arc discharge from an electrode, it is effective to control the power input to the electrode based on the positional relationship between the metal material and the electrode so that the input power is used to heat the metal material with high efficiency, in order to reduce energy loss. In this case, accurate evaluation of the positional relationship between the metal material and the electrode is important for reducing energy loss due to control of the input power. In particular, in the early stage of melting when there is a large amount of metal material around the electrode, it is effective in reducing energy loss to actively input power to rapidly melt the metal material.

[0006] However, in the case of estimating the state of the furnace from the temperature distribution on the furnace wall, such as the determination of burn-through disclosed in Patent Document 1 and the creation of the furnace profile disclosed in Patent Document 2, when the volume occupied by the metal material in the furnace is large in the early stage of melting, the amount of heat transferred to the furnace wall is small, making it difficult to estimate the state of the metal material in the furnace with high accuracy. In Patent Document 2, the position of the electrode is used to adjust the operating conditions together with the furnace profile, but the position of the electrode is estimated based on the electrode length measured by the lifting amount measuring device. The lifting amount measuring device only measures the amount of lifting of the electrode by the electrode lifting device, and even if the tip of the electrode is worn out while the metal material is being melted, the wear is not reflected in the estimated electrode length. The electrode length measuring device disclosed in Patent Document 3 can actually measure the length of the electrode with high accuracy, but since the measurement is performed outside the furnace body, it cannot accurately measure the length of the electrode by taking into account the wear of the tip of the electrode during the melting of the metal material.

[0007] The problem that the present invention aims to solve is to provide a metal melting device that, when melting a metal material by arc discharge from an electrode, can accurately estimate the position of the tip of the electrode from a period when melting of the metal material has not progressed much, and can control the height position of the electrode based on the estimation result. [Means for solving the problem]

[0008] In order to solve the above problems, the metal melting apparatus of the present invention includes a furnace body that contains a metallic material, an electrode that is inserted into the furnace body and generates an arc between the electrode and the metallic material to melt the metallic material, an electrode lifting device that holds the electrode with a gripping part and adjusts the height position of the electrode relative to the furnace body, an electrode length measuring device that measures the length of the electrode, a lifting control unit that lowers the electrode using the electrode lifting device as the melting of the metallic material progresses, an electrode evaluation unit that estimates the height position of the tip of the electrode during melting of the metallic material based on the length of the electrode actually measured by the electrode length measuring device before starting melting of the metallic material and the amount of wear of the electrode according to the amount of power input to the electrode, and a voltage control unit that controls the voltage supplied to the electrode, and the voltage control unit controls the voltage supplied to the electrode based on the height position of the tip of the electrode estimated by the electrode evaluation unit during melting of the metallic material.

[0009] Here, the voltage control unit may be configured to increase the voltage supplied to the electrode from a low level value to a high level value when the height position of the tip of the electrode estimated by the electrode evaluation unit becomes lower than a reference position.

[0010] In this case, the bottom of the furnace body is used as a reference, the height of the furnace body is L, the height position of the gripping part is L1, and the height distance from the gripping part to the tip of the electrode is L2, and the reference position is preferably defined as the height position of the electrode where (L1-L2) / L is 0.5 or more and 0.7 or less.

[0011] The high level value may be set to be equal to or greater than 85% and equal to or less than 95% of the maximum secondary voltage of a transformer that supplies power to the electrodes. Effect of the Invention

[0012] In the metal melting apparatus according to the above invention, the electrode evaluation unit estimates the height position of the electrode tip by taking into consideration both the length of the electrode actually measured by the electrode length measuring device before starting to melt the metal material and the amount of wear of the electrode according to the amount of power input to the electrode. Thus, taking into consideration the wear of the electrode due to the melting of the metal material, the height position of the electrode tip at each point during the melting of the metal material can be accurately estimated, from a time when the melting of the metal material has not progressed much to a time when the melting has progressed considerably. Then, the voltage control unit controls the voltage supplied to the electrode based on the height position of the electrode tip estimated in this way, so that it is possible to control the input power according to a purpose, such as improving energy efficiency, with high accuracy.

[0013] Here, if the voltage control unit is configured to increase the voltage supplied to the electrode from a low level to a high level when the height position of the electrode tip estimated by the electrode evaluation unit becomes lower than the reference position, the energy efficiency of the entire metal material melting process can be improved by increasing the voltage supplied to the electrode when the melting of the metal material has progressed to a certain extent and the height position of the electrode tip has become lower.

[0014] In this case, if the bottom of the furnace body is taken as the reference, the height of the furnace body is L, the height position of the gripping part is L1, and the height distance from the gripping part to the tip of the electrode is L2, and the reference position is determined as the height position of the electrode where (L1-L2) / L is 0.5 to 0.7, it is possible to increase the power input to the electrode at a relatively early stage of melting the metal material while avoiding the generation of sparks on equipment components such as the furnace wall, and the energy efficiency of the entire process of melting the metal material can be effectively improved.

[0015] In addition, when the high level value is set to be 85% or more and 95% or less of the maximum secondary voltage of the transformer supplying power to the electrode, it is possible to effectively increase the power input to the electrode while avoiding application of an excessive load to the power supply device, thereby contributing to improving the energy efficiency in melting metal materials. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing a configuration of a metal melting apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 13 is a schematic diagram for explaining parameters relating to the electrode height. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a metal melting apparatus according to one embodiment of the present invention will be described with reference to the drawings.

[0018] [Metal melting equipment configuration] First, a brief description will be given of the configuration of a metal melting apparatus 1 according to one embodiment of the present invention. Fig. 1 shows an outline of the metal melting apparatus 1. The metal melting apparatus 1 has an arc furnace 10 equipped with a furnace body 11 and an electrode 15, an electrode lifting device 30, an electrode length measuring device 40, and a control device 50. The control device 50 has a voltage control unit 51, a lifting control unit 52, and an electrode evaluation unit 53.

[0019] In the arc furnace 10, a metal material M such as metal scrap is accommodated in the furnace body 11. Then, the electrode 15 is inserted into the furnace body 11 through the lid 12, and an arc discharge is performed between the electrode 15 and the metal material M, thereby heating and melting the metal material M. The electrode 15 is held by a holding part 31 of the electrode lifting device 30, and the height position can be changed by the electrode lifting device 30. In the illustrated embodiment, only one electrode 15 is provided, but a plurality of electrodes 15, such as three electrodes 15, may be provided. Even when a plurality of electrodes 15 are provided, the control of the height position of the electrode 15, the estimation of the height position of the tip 15a of the electrode 15, and the control of the voltage supplied to the electrode 15, which will be described later, are performed independently for each electrode 15.

[0020] A power supply circuit 20 for supplying power to the arc furnace 10 is provided with a furnace transformer 21 equipped with a tap changer, and a primary circuit 22 of the furnace transformer 21 is connected to a commercial power supply. A secondary circuit 23 of the furnace transformer 21 leads to the electrode 15 and supplies power to the electrode 15. Three-phase AC is supplied to the electrode 15 from the secondary circuit 23. The furnace transformer 21 can change the voltage supplied to the electrode 15 by changing the output pattern under the control of a voltage control section 51 of the control device 50. In other words, the power input to the electrode 15 can be changed. An instrument current transformer and an instrument voltage transformer are provided in the secondary circuit 23 (collectively and simply shown as a secondary measuring instrument 25 in the figure), and the current and voltage of the secondary circuit 23 can be measured. The current and voltage of the secondary side circuit 23 measured by the secondary side measuring instrument 25 are input to the control device 50 and used as information for controlling the elevation and lowering of the electrode 15, which will be described later, as well as for estimating the amount of wear of the electrode 15 in order to estimate the tip position of the electrode 15.

[0021] The electrode lifting device 30 has a gripping part 31 and a driving part 32, and the driving shaft 33 of the driving part 32 and the gripping part 31 are connected via a support member 34. The gripping part 31 is a clamp-shaped member that clamps and grips the electrode 15. The driving part 32 is composed of an electric motor or a hydraulic cylinder, etc., and can drive the movement of the driving shaft 33 in the vertical direction. The driving of the vertical movement by the driving part 32 drives the lifting movement of the electrode 15 gripped by the gripping part 31, and the height position of the electrode 15 with respect to the furnace body 11 can be changed. The driving part 32 is connected to a control device 50, and the lifting and lowering of the electrode 15 by the driving part 32 is controlled by a lifting control part 52 of the control device 50. The driving part 32 is provided with a position detection part 35 composed of a linear encoder, and can detect the vertical position of the gripping part 31 based on the distance that the driving shaft 33 moves in the vertical direction. The electrode lifting device 30 can also rotate about its axis while holding the electrode 15 .

[0022] The electrode length measuring device 40 is a device that measures the distance from the position of the gripping part 31 of the electrode lifting device 30 to the tip 15a of the electrode 15 gripped by the gripping part 31 of the electrode lifting device 30. As the electrode length measuring device 40, the device disclosed in Patent Document 3 or the like can be used. Although detailed description is omitted, in the electrode length measuring device 40 of Patent Document 3, the electrode 15 gripped by the gripping part 31 is advanced from above into a container 41 filled with sand 42 and supported from below by a coil spring 43, using the descent of the electrode lifting device 30. Then, the length of the electrode 15 is calculated based on the amount of movement of the gripping part 31 until the descent of the container 41 is detected by a limit switch 44 attached below the container 41. The length of the electrode 15 is calculated by inputting the output from the limit switch 44 and the output from the position detection part 35 provided in the electrode lifting device 30 to the electrode evaluation part 53 of the control device 50. The electrode evaluation unit 53 calculates the amount of movement of the gripping portion 31 from the reference position based on the output value of the position detection unit 35, and based on that, evaluates the length of the electrode 15, i.e., the length from the point gripped by the gripping portion 31 to the tip 15a.

[0023] The control device 50 is configured as a calculation and control device such as a computer, and has a voltage control unit 51, a lift control unit 52, and an electrode evaluation unit 53 as part of its functions. Among these, the lift control unit 52 can drive the lifting and lowering of the electrode 15 by issuing a command signal to the drive unit 32 of the electrode lifting and lowering device 30. The lifting and lowering of the electrode 15 is performed not only when opening and closing the lid 12, or when the electrode 15 is pulled up from the furnace body 11 to perform an operation outside the furnace, such as measurement by the electrode length measuring device 40, but also to control the conditions for melting while the metal material M is melted in the furnace body 11. As for the control of the height position of the electrode 15 while the metal material M is melted, the electrode 15 is controlled to be lowered by the electrode lifting and lowering device 30 as the melting of the metal material M progresses. In other words, the height position of the electrode 15 is lowered as the melting of the metal material M progresses, the proportion of the metal material M that has changed from a solid state to a molten state increases, and the overall volume occupied by the metal material M decreases. The height position of the electrode 15 can be controlled by impedance control. That is, the current value (V) and the current value (I) in the secondary circuit 23 are input from the secondary measuring instrument 25 to the elevation control unit 52, and the impedance between the electrode 15 and the metal material M calculated as V / I is used as an index, and the height position of the electrode 15 is controlled so as to maintain the impedance at a predetermined value.

[0024] As described above, when the electrode evaluation unit 53 is not melting the metal material M and is measuring the length of the electrode 15 by the electrode length measuring device 40 outside the furnace, the electrode evaluation unit 53 receives signal inputs from the electrode length measuring device 40 and the electrode lifting device 30 and plays a role in evaluating the length of the electrode 15. Furthermore, while the electrode 15 is placed in the furnace body 11 and the metal material M is being melted, the electrode evaluation unit 53 can estimate the height position of the tip 15a of the electrode 15 (the heightwise distance from the furnace bottom 11a to the tip 15a of the electrode 15) based on the length of the electrode 15 and the height position of the gripper 31 input from the electrode lifting device 30. The value of the length of the electrode 15 used to estimate the height position of the tip 15a is estimated based on the length of the electrode 15 actually measured by the electrode length measuring device 40 before starting to melt the metal material M and the amount of wear of the electrode 15 accompanying the melting of the metal material M by arc discharge. Specifically, the electrode evaluation unit 53 receives an input of a current value and a voltage value from the secondary side measuring device 25, calculates the amount of power input to the electrode 15 up to that point in time, and estimates the amount of wear of the electrode 15 based on that amount of power. Then, the amount of wear is subtracted from the length of the electrode 15 actually measured by the electrode length measuring device 40 before starting to melt the metal material M, to estimate the length of the electrode 15 at each point in time while the metal material M is being melted. The amount of wear of the electrode 15 can be estimated using information obtained by evaluating the relationship between the calculated amount of power and the amount of wear of the electrode 15 through a prior test.

[0025] 2, with respect to the furnace bottom 11a of the furnace body 11, the height position of the gripping part 31 is L1, and the height distance from the gripping part 31 to the tip 15a of the electrode 15 is L2. The height position L1 of the gripping part 31 is input from the electrode lifting device 30 to the electrode evaluation part 53. As described above, the distance L2 is a value estimated by the electrode evaluation part 53 by subtracting the amount of wear of the electrode 15 during melting from the electrode length actually measured before the start of melting of the metal material M. In this case, the height position of the tip 15a of the electrode 15 at each time point during the melting of the metal material M can be estimated as L1-L2.

[0026] During melting of the metal material M, the voltage control unit 51 controls the furnace transformer 21 based on the height position of the tip 15a of the electrode 15 estimated by the electrode evaluation unit 53 as described above, and controls the voltage supplied from the secondary side circuit 23 to the electrode 15. The control of the voltage by the voltage control unit 51 will be described in detail below.

[0027] [Voltage control based on the height position of the electrode tip] As described above, in the metal melting apparatus 1 according to this embodiment, the voltage control unit 51 controls the voltage supplied to the electrode 15 based on the height position of the tip 15a of the electrode 15 estimated by the electrode evaluation unit 53 during melting of the metal material M. As the melting of the metal material M progresses, the electrode 15 is lowered, so the height position of the tip 15a of the electrode 15 is a good indicator of the degree of progress of the melting of the metal material M. Based on this indicator, the voltage supplied to the electrode 15 can be controlled to an appropriate level depending on the degree of progress of the melting of the metal material M.

[0028] For example, the voltage supplied to the electrode 15 may be changed depending on the degree of progress of the melting of the metal material M so as to increase the energy efficiency, that is, the ratio of the amount of power used for heating the metal material M to the amount of power supplied to the electrode 15. In a stage where the melting of the metal material M has only progressed slightly after the arc discharge between the electrode 15 and the metal material M has started, it is preferable in terms of energy efficiency to keep the voltage supplied to the electrode 15 low, while increasing the voltage when the melting of the metal material M has progressed to a certain extent. In a stage where the melting of the metal material M has only progressed slightly and most of the surface of the electrode 15 faces the equipment members in the furnace, such as the furnace wall, in addition to the arc being generated between the tip 15a of the electrode 15 and the metal material M, a spark is generated between the tip 15a and the metal material M, and energy is likely to be consumed for purposes other than the melting of the metal material M, so it is preferable not to excessively increase the voltage supplied to the electrode 15. On the other hand, when the melting of the metal material M has begun to progress to a certain extent and the electrode 15 is lowered, the amount of metal material M surrounding the electrode 15 increases and unnecessary sparks are less likely to occur, so that the voltage supplied to the electrode 15 can be increased to input a large amount of heat to the metal material M, thereby efficiently melting the metal material M. In this way, the energy efficiency can be improved and energy loss can be reduced in total for the entire process of melting the metal material M.

[0029] As the electrode 15 descends, the voltage supplied to the electrode 15 may be increased continuously or may be changed discontinuously in stages. In terms of ease of control, a form in which the voltage is changed in stages is preferable. In this case, it is preferable to change the voltage between two levels, but the voltage may be changed in a larger number of stages.

[0030] In the metal melting apparatus 1 according to the present embodiment, the height position of the electrode 15 is controlled by impedance control so as the melting of the metal material M progresses, and the height position of the tip 15a of the electrode 15 is used as an index showing the degree of progress of the melting of the metal material M. Unlike the temperature distribution of the furnace wall as disclosed in Patent Document 1, the height position of the tip 15a of the electrode 15 is a parameter that accurately and sensitively reflects the degree of progress of the melting of the metal material M from an early stage in which the melting of the metal material M has not progressed much. Therefore, by controlling the voltage supplied to the electrode 15 based on the height position of the tip 15a of the electrode 15, it is possible to accurately control the voltage according to the purpose, such as improving energy efficiency, according to the degree of progress of the melting of the metal material M, even in a stage in which the melting of the metal material M has not progressed much. As described above, when the melting of the metal material M has only progressed slightly, even if a large amount of electric power is supplied to the electrode 15, energy loss is likely to occur due to the generation of sparks. However, once the melting begins to progress steadily, by actively inputting a large amount of electric power from a relatively early stage of the melting process, heat can be efficiently applied to the unmelted metal material M, and electric power can be used highly efficiently for heating and melting the metal material M in the total of the entire melting process.

[0031] Furthermore, in the metal melting apparatus 1 according to the present embodiment, the height position of the tip 15a of the electrode 15, which is estimated by the electrode evaluation unit 53 and used as an index for controlling the voltage supplied to the electrode 15, is based on the electrode length at each time point during melting of the metal material M, which is estimated by subtracting the amount of wear of the electrode 15 caused by the arc discharge during melting of the metal material M from the electrode length actually measured by the electrode length measuring device 40 outside the furnace before starting melting of the metal material M, so that the estimation of the tip position of the electrode 15 can be performed with high accuracy. By actually measuring the electrode length with the electrode length measuring device 40, the electrode length before the start of melting can be accurately grasped. Furthermore, as the melting of the metal material M progresses, the electrode 15 is worn and gradually shortened, but by considering the amount of wear of the electrode 15 estimated based on the input power amount measured by the secondary side measuring device 25, it is possible to estimate the electrode length during the melting of the metal material M in real time. Then, from the early stage when the dissolution of the metal material M has not progressed much and the amount of wear of the electrode 15 is small, to the final stage of the dissolution when the dissolution of the metal material M has progressed significantly and the amount of wear of the electrode 15 has increased, the height position of the tip 15a of the electrode 15 at each point in time can be accurately estimated and used to control the voltage supplied to the electrode 15. As a result, the objective of improving energy efficiency can be effectively achieved by controlling the voltage according to the degree of progress of the dissolution of the metal material M.

[0032] As described above, in order to improve the total energy efficiency throughout the entire process of melting the metal material M, it is effective to control the voltage supplied to the electrode 15 to be increased at a stage where the melting of the metal material M has progressed to a certain extent. There is no particular limitation on how the voltage supplied to the electrode 15 is changed with respect to the height position of the tip 15a of the electrode 15, but for example, a preferred embodiment is to increase the voltage supplied to the electrode 15 from a low level value to a high level value when the height position of the tip 15a of the electrode 15 estimated by the electrode evaluation unit 53 becomes lower than a reference position.

[0033] In this case, the reference position of the tip 15a of the electrode 15 at which the voltage supplied to the electrode 15 is switched from a low level value to a high level value can be determined, for example, as follows. As described above, the height position of the electrode 15 while the metal material M is being melted is estimated as L1-L2. In this case, the height of the furnace body 11 is set as L with respect to the hearth 11a, and the relative height L' is set as L'=(L1-L2) / L. The reference position at which the voltage supplied to the electrode 15 is switched may be determined in a range where the relative height L' is 0.5 or more and 0.7 or less. The larger the value of the relative height L', the higher the tip 15a of the electrode 15 is located. L'=0 corresponds to the position of the hearth 11a, and L'=1 corresponds to the position of the upper edge of the furnace body 11. By setting the relative position L' at the reference position to 0.5 or more, the voltage is switched to the high level value at a relatively early stage in the entire process of melting the metal material M, when the position of the electrode 15 has not yet dropped significantly. Then, at the stage where there is an abundance of unmelted metal material M in the furnace, heat is actively input to the unmelted metal material M, and energy efficiency can be improved. On the other hand, by setting the relative position L' at the reference position to 0.7 or less, it is possible to suppress a situation where the voltage is switched to a high level value and energy is consumed to generate sparks at the stage where sparks are likely to occur between the electrode 15, which is not surrounded by the metal material M, and equipment members such as the furnace wall because the position of the electrode 15 has not yet been lowered sufficiently. Note that, usually, when the metal material M to be melted, such as metal scrap, is placed in the furnace body 11, the position of the upper surface of the metal material M is set to about 0.9 to 1.0 in terms of relative height L'.

[0034] The high level value, which is a value adopted after the height position of the tip 15a of the electrode 15 becomes lower than the reference position, is preferably set to 85% to 95% of the secondary maximum voltage of the furnace transformer 21. Here, the secondary maximum voltage indicates the maximum voltage that the furnace transformer 21 can output to the secondary circuit 23. By setting the high level value to 85% or more of the secondary maximum voltage, a large amount of power is input when the height position of the tip 15a of the electrode 15 becomes lower than the reference position, and the energy efficiency in melting the metal material M can be effectively improved. Preferably, the high level value is set to 90% or more of the secondary maximum voltage. On the other hand, by limiting the high level value to 95% or less of the secondary maximum voltage, it becomes easier to avoid application of an excessive load to the power supply equipment such as the furnace transformer 21.

[0035] In the metal melting apparatus 1 according to the present embodiment, the height position of the tip 15a of the electrode 15, which takes into account the wear of the electrode 15 due to the arc discharge, is used to determine the degree of progress of melting of the metal material M with high accuracy, without relying on other parameters that reflect the state inside the furnace, and the input power can be controlled. However, as an index for controlling the input power, other parameters that reflect the melting state of the metal material M in the furnace can also be used in combination with information on the height position of the tip 15a of the electrode 15. As such parameters, parameters that reflect the state inside the furnace, such as the temperature distribution on the furnace wall as disclosed in Patent Documents 1 and 2, the frequency distribution of the sound generated from the furnace body 11, and the intensity of the high-frequency component in the primary side circuit 22, which are described in detail in JP 2020-016345 A by the applicant, can be used. When the height position of the tip 15a of the electrode 15 estimated by the electrode evaluation unit 53 and the progress of dissolution of the metal material M estimated by combining these parameters exceed a predetermined threshold value, the voltage supplied to the electrode 15 can be switched from a low level value to a high level value. EXAMPLES

[0036] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[0037] [Test Method] Iron scrap was melted using a metal melting apparatus having the configuration shown in Figure 1 and described above. Three electrodes were used. In melting, the reference position of the electrode tip when the voltage supplied to the electrodes was switched from a low level to a high level was changed in increments of 0.1 from 0.2 to 1.0 in terms of relative height L' (= (L1-L2) / L), and melting was performed multiple times. Here, the relative height L' to 0.2 corresponds to the position at which the electrodes can be lowered to the maximum extent possible in terms of the equipment configuration of the metal melting apparatus.

[0038] During melting, the occurrence of sparks between the equipment components and the electrode was visually observed, and the power loss index was estimated. The power loss index indicates the proportion of the amount of power (calculated from the amount of heat removed from the furnace wall) that was not used to melt the metal material out of the amount of power input to the electrode, and here the power loss index is displayed with the value when the reference position of the electrode tip is L' = 0.2 as the standard of 100%.

[0039] [Test Results] The relationship between the reference position of the electrode tip when switching the voltage supplied to the electrode, the spark generation state, and the power loss index is summarized in Table 1 below. When the reference position of the electrode tip was set to L' = 0.8 or more, the dissolution test could not be continued due to the generation of sparks, and the power loss index could not be estimated.

[0040] [Table 1]

[0041] According to Table 1, when the reference position of the electrode tip where the voltage supplied to the electrode is switched is in the range of 0.5 to 0.7 in terms of relative height L', the occurrence of sparks between the electrode and the equipment member does not occur or is suppressed to a minor level. In addition, the power loss index is stably suppressed to a low level. In contrast, when the reference position is less than L'=0.5, the power loss index is larger than the above range, and the lower the reference position (the smaller the relative height L'), the larger the power loss index. On the other hand, when the reference position is greater than L'=0.7, sparks occur between the electrode and the equipment member, making it impossible to continue melting. From this, it can be said that by setting the reference position of the electrode tip where the voltage supplied to the electrode is switched to a high level value to 0.5 to 0.7 in terms of relative height L', it is possible to suppress the occurrence of unnecessary sparks and to improve energy efficiency by actively inputting power from a relatively early stage of the melting of metal materials.

[0042] In Table 1, the change in the power loss index when the reference position is changed is small, but the power loss index is a highly stable value and the change is sufficiently significant. In addition, since a large amount of metal material is melted in the operation of a general metal melting device, if the power loss index can be reduced even slightly, the required power amount can be significantly reduced as an integrated value over a specified period such as one month or one year.

[0043] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0044] 1 Metal melting equipment 10. Arc Furnace 11 Furnace body 11a hearth bottom 15 electrodes 15a Electrode tip 20 Power circuit 21 Furnace transformer 25 Secondary side measuring instrument 30 Electrode lifting device 31 Gripping part 32 Drive unit 34 Support member 35 Position detection unit 40 Electrode length measuring device 41 Container 50 Control device 51 Voltage control section 52 Lifting control section 53 Electrode Evaluation Unit M Metal material

Claims

1. A furnace body that contains a metal material; an electrode that is inserted into the furnace body and generates an arc between the electrode and the metal material to melt the metal material; an electrode lifting device that holds the electrode with a gripping portion and adjusts the height position of the electrode relative to the furnace body; an electrode length measuring device for measuring the length of the electrode; a lifting control unit that lowers the electrode by the electrode lifting device as the melting of the metallic material progresses; an electrode evaluation unit that estimates a height position of a tip end of the electrode during melting of the metallic material based on a length of the electrode actually measured by the electrode length measuring device before starting melting of the metallic material and an amount of wear of the electrode corresponding to an amount of power input to the electrode; A voltage control unit that controls a voltage supplied to the electrode, The voltage control unit controls a voltage supplied to the electrode based on a height position of the tip of the electrode estimated by the electrode evaluation unit during melting of the metallic material, and when the height position of the tip of the electrode estimated by the electrode evaluation unit becomes lower than a reference position, the voltage control unit increases the voltage supplied to the electrode from a low level value to a high level value, With the bottom of the furnace body as a reference, the height of the furnace body is L, and the height position of the gripping part is L1; The distance in the height direction from the gripping portion to the tip of the electrode is L2, The reference position is defined as a height position of the electrode where (L1-L2) / L is 0.5 or more and 0.7 or less.

2. 2. The metal melting apparatus according to claim 1, wherein the high level value is set to be 85% or more and 95% or less of a maximum secondary voltage of a transformer that supplies power to the electrodes.

3. A furnace body that contains a metal material; an electrode that is inserted into the furnace body and generates an arc between the electrode and the metal material to melt the metal material; an electrode lifting device that holds the electrode with a gripping portion and adjusts the height position of the electrode with respect to the furnace body; an electrode length measuring device for measuring the length of the electrode; a lifting control unit that lowers the electrode by the electrode lifting device as the melting of the metallic material progresses; an electrode evaluation unit that estimates a height position of a tip end of the electrode during melting of the metallic material based on a length of the electrode actually measured by the electrode length measuring device before starting melting of the metallic material and an amount of wear of the electrode corresponding to an amount of power input to the electrode; A voltage control unit that controls a voltage supplied to the electrode, The voltage control unit controls a voltage supplied to the electrode based on a height position of the tip of the electrode estimated by the electrode evaluation unit during melting of the metallic material, and when the height position of the tip of the electrode estimated by the electrode evaluation unit becomes lower than a reference position, the voltage control unit increases the voltage supplied to the electrode from a low level value to a high level value, A metal melting apparatus, wherein the high level value is set to be 85% or more and 95% or less of the maximum secondary voltage of a transformer that supplies power to the electrodes.

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