JP7600738B2 - Metal Melting Equipment - Google Patents

Description

The present invention relates to a metal melting device, and more specifically, to a metal melting device that melts metal materials by arc discharge while controlling the height of the electrodes.

In an arc furnace, which melts metal scrap and other metallic materials by arc discharge from electrodes, an electrode lifting device is often installed to adjust the height position of the electrode relative to the metallic material. The electrode lifting device can be used to adjust the height position of the electrode tip relative to the metallic material, thereby controlling the conditions for melting the metallic material. The conditions for efficiently melting metallic materials depend on the state of the metallic material in the furnace and the positional relationship between the metallic material and the electrodes, and so the state of the metallic material in the furnace, the height position of the electrodes, or parameters that reflect these, can be used to control the conditions for melting, such as the power input to the electrodes.

For example, in Patent Document 1, the heat flux on the inner circumferential surface of the furnace wall is calculated based on the temperatures measured at multiple positions inside and outside the furnace wall of an electric furnace, and the start of the melting of scrap (metallic material) is judged based on the calculation results. In Patent Document 2, the operating conditions are adjusted based on the position of the electrode and the furnace profile created by connecting the positions of temperatures predetermined as the melting temperature of the lumps generated when the melted material (metallic material) adheres 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 by 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.

JP 2017-226864 A JP 2008-116066 A JP 2016-148465 A

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, from the viewpoint of reducing energy loss. In this case, accurate evaluation of the positional relationship between the metal material and the electrode is important for reducing energy loss through control of the input power. In particular, in the early stages of melting when there is an abundance of metal material around the electrode, aggressive input of power to rapidly melt the metal material is effective in reducing energy loss.

However, in the case of estimating the state of the furnace from the temperature distribution on the furnace wall, such as the burn-through judgment 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 stages 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 addition, in Patent Document 2, the electrode position is used to adjust the operating conditions along with the furnace profile, but the electrode position 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 wears out while the metal material continues to melt, 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.

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

In order to solve the above problems, the metal melting apparatus of the present invention includes 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 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 metal material progresses, an electrode evaluation unit that estimates the height position of the tip of the electrode during the melting of the metal material based on the length of the electrode actually measured by the electrode length measuring device before starting the melting of the metal 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 the melting of the metal material.

Here, the voltage control unit may 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.

In this case, the furnace bottom 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 determined as the height position of the electrode where (L1-L2)/L is 0.5 or more and 0.7 or less.

The high level value may be set to 85% or more and 95% or less of the maximum secondary voltage of the transformer that supplies power to the electrode.

In the metal melting device according to the above invention, the electrode evaluation unit estimates the height position of the electrode tip by taking into account 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. Therefore, taking into account the wear of the electrode due to the melting of the metal material, it is possible to accurately estimate the height position of the electrode tip at each point during the melting of the metal material, from when the melting of the metal material has not progressed much to when it 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 the purpose, such as improving energy efficiency, with high accuracy.

Here, if the voltage control unit is 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 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.

In this case, if the furnace bottom is used 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 or more and 0.7 or less, 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 is effectively improved.

In addition, if the high level value is set to 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 the application of excessive load to the power supply device, thereby contributing to improving the energy efficiency in melting metal materials.

1 is a diagram showing a configuration of a metal melting apparatus according to an embodiment of the present invention. FIG. 11 is a schematic diagram for explaining parameters relating to the electrode height.

Below, a metal melting device according to one embodiment of the present invention will be described with reference to the drawings.

[Configuration of metal melting apparatus]
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 includes an arc furnace 10 including 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 includes a voltage control unit 51, a lifting control unit 52, and an electrode evaluation unit 53.

In the arc furnace 10, metal material M such as scrap metal is stored 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 to heat and melt the metal material M. The electrode 15 is held by the 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 multiple electrodes 15, such as three, may be provided. Even when multiple 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.

The power supply circuit 20 that supplies power to the arc furnace 10 is provided with a furnace transformer 21 equipped with a tap changer, and the primary circuit 22 of the furnace transformer 21 is connected to a commercial power source. The 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 the voltage control unit 51 of the control device 50. In other words, the power input to the electrode 15 can be changed. The secondary circuit 23 is provided with an instrument current transformer and an instrument voltage transformer (collectively and simply shown as a secondary measuring instrument 25 in the figure), making it possible to measure the current and voltage of the secondary circuit 23. The current and voltage of the secondary circuit 23 measured by the secondary measuring instrument 25 are input to the control device 50 and used as information for controlling the elevation of the electrode 15, which will be described later, and also for estimating the amount of wear of the electrode 15 in order to estimate the tip position of the electrode 15.

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 relative to the furnace body 11 can be changed. The driving part 32 is connected to the control device 50, and the lifting and lowering of the electrode 15 by the driving part 32 is controlled by the 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 the vertical position of the gripping part 31 can be detected based on the distance moved in the vertical direction by the driving shaft 33. The electrode lifting device 30 can also rotate around its axis while holding the electrode 15.

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. The electrode length measuring device 40 can be a device disclosed in Patent Document 3 or the like. 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 inserted 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 the 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 unit 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, that is, the length from the point gripped by the gripping unit 31 to the tip 15a.

The control device 50 is configured as a calculation/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. Of 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 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 operations outside the furnace, such as measuring the length using 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 lifting device 30 controls the electrode 15 to lower 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. In other words, the current value (V) and current value (I) in the secondary circuit 23 are input from the secondary measuring device 25 to the lift 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.

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 outside the furnace using the electrode length measuring device 40, 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 evaluation unit 53 is placing the electrode 15 in the furnace body 11 and melting the metal material M, the electrode evaluation unit 53 can estimate the height position of the tip 15a of the electrode 15 (the height-wise 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 due to the melting of the metal material M by arc discharge. Specifically, the electrode evaluation unit 53 receives current and voltage values from the secondary measuring device 25, calculates the amount of power input to the electrode 15 up to that point, and estimates the amount of wear of the electrode 15 based on that amount of power. Then, the electrode evaluation unit 53 estimates the length of the electrode 15 at each point while the metal material M is being melted by subtracting the amount of wear from the length of the electrode 15 actually measured by the electrode length measuring device 40 before starting to melt the metal material M. The amount of wear of the electrode 15 can be estimated by using information evaluated in advance by testing the relationship between the calculated amount of power and the amount of wear of the electrode 15.

As shown in FIG. 2, with the bottom 11a of the furnace body 11 as the reference, 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 unit 53. As described above, the distance L2 is a value estimated by the electrode evaluation unit 53 by subtracting the amount of wear of the electrode 15 during melting from the electrode length actually measured before the start of melting 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.

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 circuit 23 to the electrode 15. The control of voltage by the voltage control unit 51 will be described in detail below.

[Voltage control based on height position of 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 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 melting of the metal material M.

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 proportion of the amount of power used to heat the metal material M out of the amount of power supplied to the electrode 15. In the 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 the 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, sparks are 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 progressed to a certain extent and the electrode 15 is lowered, the amount of metal material M surrounding the electrode 15 increases, making it difficult for unnecessary sparks to occur, so by increasing the voltage supplied to the electrode 15 and inputting a large amount of heat into the metal material M, the melting of the metal material M can be efficiently promoted. In this way, the total energy efficiency of the entire process of melting the metal material M can be improved and energy loss can be reduced.

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

In the metal melting apparatus 1 according to the present embodiment, the height position of the electrode 15 is controlled to be lowered as the melting of the metal material M progresses by impedance control, 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 the early stage when 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 at a stage when 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 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 supplying a large amount of power from a relatively early stage of the melting process, heat can be efficiently applied to the unmelted metal material M, and power can be used highly efficiently to heat and melt the metal material M throughout the entire melting process.

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 point during the melting of the metal material M, which is estimated by subtracting the amount of wear of the electrode 15 due to the arc discharge during the melting of the metal material M from the electrode length actually measured by the electrode length measuring device 40 outside the furnace before the melting of the metal material M is started. Therefore, 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 out and gradually shortens, 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 is not progressing very much and the amount of wear of the electrode 15 is small, to the final stage when the dissolution of the metal material M has progressed significantly and the amount of wear of the electrode 15 is large, 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.

As described above, in order to increase 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 when the melting of the metal material M has progressed to a certain extent. There are no particular limitations on how the voltage supplied to the electrode 15 is changed in relation to the height position of the tip 15a of the electrode 15. 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 the reference position.

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 to L with respect to the furnace bottom 11a, and the relative height L' is set to L' = (L1-L2)/L, and 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 furnace bottom 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 a 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, improving energy efficiency. On the other hand, by setting the relative position L' at the reference position to 0.7 or less, it is possible to prevent a situation in which the voltage is switched to a high level value and energy is consumed to generate sparks at a stage where the position of the electrode 15 has not yet been lowered sufficiently and sparks are likely to occur between the electrode 15, which is not surrounded by the metal material M, and equipment components such as the furnace wall. Note that, usually, when metal scrap or other metal material M to be melted is placed in the furnace body 11, the position of the upper surface of the metal material M is set to a relative height L' of about 0.9 to 1.0.

The high level value, which is the 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 keeping the high level value to 95% or less of the secondary maximum voltage, it becomes easier to avoid applying an excessive load to the power supply equipment such as the furnace transformer 21.

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, the voltage supplied to the electrode 15 can be switched from a low level to a high level.

The present invention will be specifically explained below with reference to examples. The present invention is not limited to these examples.

[Test Method]
Using the metal melting apparatus having the configuration shown in FIG. 1 and described above, iron scrap was melted. The number of electrodes was three. In melting, the reference position of the tip of the electrode when the voltage supplied to the electrode was switched from a low level value to a high level value 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 electrode can be lowered to the maximum extent possible in terms of the equipment configuration of the metal melting apparatus.

During the melting process, 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. Here, the power loss index is displayed with the value when the reference position of the tip of the electrode is set to L' = 0.2 as the reference of 100%.

[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.

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 the metal material.

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 during the operation of a typical metal melting device, if the power loss index can be reduced even slightly, the required amount of power can be significantly reduced when calculated over a specified period such as one month or one year.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the gist of the present invention.

Reference Signs List 1 Metal melting device 10 Arc furnace 11 Furnace body 11a Furnace bottom 15 Electrode 15a Electrode tip 20 Power supply circuit 21 Furnace transformer 25 Secondary side measuring instrument 30 Electrode lifting device 31 Grip unit 32 Drive unit 34 Support member 35 Position detection unit 40 Electrode length measuring device 41 Container 50 Control device 51 Voltage control unit 52 Lifting control unit 53 Electrode evaluation unit M Metal material

Claims (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,
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. 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. 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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