JP5656532B2 - Induction melting furnace - Google Patents

Description

  The present invention relates to an induction melting furnace that melts a material to be melted stored in a furnace by supplying electric power to a heating coil provided on the outer periphery of the furnace wall through power supply means.

  Conventionally, as this type of induction melting furnace, as shown in Patent Documents 1 and 2 below, a power converter in which a forward converter and an inverse converter form a parallel resonance circuit (current circuit), and power conversion There is known a control device that controls the output power factor to a desired value by detecting the output power factor of the unit and controlling the frequency of the power conversion unit from the detected power factor.

  Furthermore, as shown in Patent Document 3 below, in the vacuum levitation melting apparatus, after the melting material accommodated in the copper crucible in the vacuum vessel is completely dissolved, the operating frequency of the induction coil is lowered to a preset frequency. Thus, there is known a vacuum levitation melting apparatus that performs a degassing process for removing impurities by increasing the stirring power to the molten metal (Patent Document 1, paragraph [0030]).

JP-A-60-84789 JP 60-180478 A JP 2000-74568 A

  However, in the conventional induction melting furnace control device, the power conversion unit is operated at the load resonance frequency due to this characteristic in the parallel resonance type circuit (current type circuit), so it is difficult to arbitrarily change the oscillation frequency. It is.

  Therefore, if a small amount of graphite, silicon, manganese, etc., which are component adjustment materials, is added to the molten metal during the melting operation, the molten metal agitates by the load resonance frequency before the component adjustment material melts into the molten metal. There is a problem that a part of the component adjusting agent remains unmelted and the molten metal components become non-uniform.

  On the other hand, as shown in the cited document 3, it is conceivable to increase the stirring power of the molten metal by lowering the oscillation frequency (in the cited document 3, the specific configuration for lowering the oscillation frequency is unknown). In the parallel resonant circuit, it is difficult to change the oscillation frequency as described above.

  In view of the above circumstances, an object of the present invention is to provide an induction melting furnace capable of suppressing an excessive temperature rise of a molten metal during a melting operation and sufficiently dissolving a component adjusting material.

In order to achieve the above object, the induction melting furnace of the first invention comprises:
An induction melting furnace that melts a material to be melted housed in the furnace by supplying power to the heating coil provided on the outer periphery of the furnace wall through power supply means,
A power converter in which a forward converter and an inverse converter in which the first and second switching elements operate alternately constitute a series resonant circuit;
A power factor detector for detecting an output power factor of the power converter;
A control signal generator for generating control signals for the first and second switching elements,
The control signal generator is a control signal for the first and second switching elements.
In the first stage of melting the material to be melted, a control signal having a frequency at which the output power factor detected through the power factor detector is 1 is generated,
In the second stage of adding the component adjusting material to the dissolved material to be dissolved, as a control signal having a frequency suitable for dissolving the component adjusting material into the material to be dissolved , the liquid level of the material to be dissolved by stirring is adjusted . Generate a control signal with a frequency at which the change is a predetermined magnitude,
In a third stage after the component adjusting material is dissolved in the material to be melted, a control signal having a frequency at which the output power factor detected through the power factor detecting unit is 1 is generated.

  According to the induction melting furnace of the first aspect of the invention, the control signal generator can set the control signals for the first and second switching elements of the inverse converter to an arbitrary frequency regardless of the load resonance frequency.

  Therefore, in the first stage in which the material to be melted is melted by the control signal generator, the control signals for the first and second switching elements are set so that the output power factor detected through the power factor detector is 1. The material to be dissolved can be dissolved at a high power factor.

  In addition, in the second stage of adding the component adjusting material to the melted material to be dissolved, the component adjusting material is converted into the molten metal by generating a control signal having a frequency suitable for causing the component adjusting material to be dissolved in the material to be melted. It is possible to prevent the molten metal from being overheated before melting.

  Further, in the third stage after the component adjusting material is melted into the material to be melted, the component adjusting material is generated by generating a control signal having a frequency at which the output power factor detected through the power factor detecting unit is 1. It is possible to suppress the wear of the furnace wall due to the continuation of the state even after melting, and to dissolve the material to be melted at a high power factor.

  Thus, according to the induction melting furnace of the first invention, the component adjusting material can be sufficiently dissolved in the molten metal during the melting operation.

In addition, according to the induction melting furnace of the first invention, since the stirring force in the molten metal cannot be directly measured, an arbitrary frequency can be obtained based on the change in the liquid level of the material to be melted by stirring. The control signals of the first and second switching elements that can be made to be the stirring frequency suitable for the dissolution of the component adjusting material. As a result, it is possible to prevent the molten metal from being overheated before the component adjusting material melts into the molten metal, and to prevent a part of the component adjusting agent from being unmelted. Can be dissolved.

The whole block diagram which shows the structure of an induction melting furnace. Explanatory drawing which shows the structure of a control part. Explanatory drawing which shows the processing content by a control part. The flowchart which shows the melting method in an induction melting furnace.

  With reference to FIG. 1, the induction melting furnace of this embodiment is demonstrated.

  The induction melting furnace melts the material to be melted X housed in the melting furnace. Specifically, the power source 1, the high-voltage power receiving panel 2, the converter transformer 3, and the power converter 4. A high-frequency matching device 5, an induction heating device 6, a liquid level measuring device 7, and a controller 100.

  The power conversion device 4 and the high frequency matching device 5 correspond to the power conversion unit of the present invention.

  The power source 1 is an AC power source and is connected to the high voltage power receiving panel 2.

  The high-voltage power receiving panel 2 is a device that energizes / stops the power to the induction heating device 6 and shuts off the power when a failure occurs, and includes a power fuse 2a and a circuit breaker 2b. The power fuse 2a is a means for interrupting current in the event of a short circuit accident, and the circuit breaker 2b performs an opening / closing operation accompanying energization and stop of the power source.

  The transformer for converter 3 is connected to the high voltage power receiving panel 2 and adjusts so that the input voltage to the power converter 4 becomes a predetermined value.

  The power conversion device 4 is a device for generating an arbitrary high-frequency current from a commercial power supply of 50 Hz or 60 Hz, connected to the transformer 3 for the conversion device, and is a control circuit 10 and an AC / DC converter. Converters 41a and 41b and inverse converters 42a and 42b, which are DC / AC converters, are controlled by an output control signal from the control circuit 10.

  Specifically, the power conversion device 4 includes diode-type forward converters 41a and 41b on the input side, IGBT-type reverse converters 42a and 42b on the output side, and each of the forward converters 41a and 41b is smoothed in series. Reactors 43a and 43b are connected, and smoothing capacitors 44a and 44b are connected in parallel to forward converters 41a and 41b.

  Further, the power conversion device 4 detects a DC voltage on the output side of the forward converters 41a and 41b and outputs a DC voltage signal (a); and a DC current signal ( b), and output values of the DC voltage detector 45 and the DC current detector 46 are output to the control circuit 10.

  Details of the control content of the power conversion device 4 by the control circuit 10 will be described later.

  The high-frequency matching device 5 is provided between the power conversion device 4 and the induction heating device 6 and improves the load power factor because the induction heating device 6 has a low power factor.

  Specifically, the high-frequency matching device 5 detects and outputs the resonance capacitors 51a and 51b, the current detector 52 that detects the output current of the high-frequency matching device 5 and outputs the output current signal (d), and the output voltage. The voltage detector 53 is configured to output a voltage signal (e).

  Resonance capacitors 51a and 51b are provided with adjustment capacitors 51ac and 51bc, respectively, in parallel. The adjustment capacitors 51ac and 51bc are provided with contactors 51ad and 51bd, respectively, and the adjustment capacitors 51ac and 51bc are connected in parallel to the resonance capacitors 51a and 51b by the contactors 51ad and 51bd. Adjustment capacitors 51ac and 51bc can prevent the reactive power of the load resonance circuit from increasing even when an oscillation frequency sufficiently lower than the resonance frequency of the load resonance circuit is output from power converter 4.

  The induction heating device 6 generates an eddy current in the material X to be melted accommodated in the melting furnace body by energizing the heating coil 61 with a high-frequency current supplied from the power conversion device 4 and the high-frequency matching device 5. The melted material X is heated and melted by Joule heat generated by eddy current.

  The liquid level measuring device 7 is a device that measures the liquid level height of the material to be melted X melted in the melting furnace, and outputs the measured liquid level height to the controller 100. As a method for measuring the liquid level by the liquid level measuring device 7, for example, various known liquid level displacement measuring methods can be adopted in addition to the optical measuring method described in Japanese Patent Application Laid-Open No. 2004-151088.

  In the present embodiment, the liquid level measuring device 7 measures the rising height of the liquid level by irradiating the measurement laser toward the liquid level of the material X to be melted from the upper side of the melting furnace body. .

  The controller 100 controls the overall operation of the induction melting furnace including the operation / stop of the control induction melting furnace. A method for melting the material X to be melted in the induction melting furnace by the controller 100 will be described later.

  Next, the control circuit 10 which has been described later will be described with reference to FIGS.

  The control circuit 10 mainly performs control such as output adjustment, and also generates a control signal for controlling the power factor detection unit for detecting the output power factor and the IGBT inverse converters 42a and 42b as a control device for the induction melting furnace. A function as a part is provided.

  As shown in FIG. 2, the control circuit 10 includes a power factor detection circuit 11 and a PLL control circuit 12.

  The power factor detection circuit 11 includes an output current signal (d) of the high-frequency matching device 5 that is an output value of the current detector 52, and an output voltage signal (e) of the high-frequency matching device 5 that is an output value of the voltage detector 53. From this, the output power factor of the alternating current / voltage output from the high-frequency matching device 5 is calculated.

  The PLL control circuit 12 includes a voltage-controlled oscillation circuit 13 and adjusts a value corresponding to the output power factor detected by the power factor detection circuit 11 with respect to a frequency reference generated by a reference frequency generation unit (not shown). A frequency (control frequency) is generated. Then, a triangular wave having this control frequency as the oscillation frequency is generated by the voltage controlled oscillation circuit 13, and the triangular wave is subtracted from the output reference and divided, whereby each control signal (indicated by the IGBT inverse converters 42a and 42b) ( Gate signal). FIG. 3 schematically shows how this control signal (gate signal) is generated.

  A switch 14 is provided between the power factor detection circuit 11 and the PLL control circuit 12. This is because if the frequency reference signal and the power factor detection signal set from the outside are enabled at the same time, it can be a contradictory frequency change, so if you want to intentionally change the oscillation frequency, turn off the switch, Only the frequency reference signal is valid.

A method of melting the material to be melted by the induction melting furnace configured as described above will be described with reference to FIG.

  First, the controller 100 starts the operation of the power converter 4 when the user starts to introduce the material X to be melted into the induction furnace main body (FIG. 4 / STEP 11).

  In the first stage of melting the material to be melted X, the control circuit 10 controls the control signals (gates) of the IGBT inverse converters 42a and 42b so that the output power factor becomes 1 through the power factor detector 11. Signal). Thereby, the material to be dissolved can be dissolved at a high power factor.

  Next, the controller 100 checks whether or not the introduction of the material X to be melted into the induction furnace main body has been completed (FIG. 4 / STEP 12), and if the introduction has not been completed (FIG. 4 / STEP 12). NO), repeat this check until charging is complete.

  On the other hand, when the charging is completed (YES in FIG. 4 / STEP 12), the controller 100 checks whether or not it is a component adjustment stage in which the component adjustment material is added to the molten metal in which the material X is dissolved. (FIG. 4 / STEP 13).

  If it is not the component adjustment stage (NO in FIG. 4 / STEP 13), this check is repeated until the component adjustment stage is reached. On the other hand, in the component adjustment stage (FIG. 4 / YES in STEP 13), the controller 100 executes the following processing via the control circuit 10.

  That is, in the second stage of adding the component adjusting material to the melted material X, the control circuit 10 turns off the switch 14 and lowers the frequency reference to lower the oscillation frequency (STEP 21 in FIG. 4).

  At this time, the stirring force F acting on the melted material X is expressed by the following formula (1).

・・・・・（１）

(1)

  Here, the stirring force F increases by decreasing the oscillation frequency f of the above equation (1). Therefore, the component adjusting material can be dissolved in the material X to be dissolved in a short time by reducing the oscillation frequency and generating a stirring force F suitable for being dissolved in the material X in which the component adjusting material is dissolved. It is possible to prevent the molten metal from being overheated before the component adjusting material melts into the molten metal.

  Next, the controller 100 checks whether or not the height of the liquid level measured by the liquid level measuring device 7 is higher than a predetermined height (target value) (before the oscillation frequency is lowered). (FIG. 4 / STEP22).

  Here, the predetermined height (target value) is a stirring force suitable for dissolving the component adjusting material into the material X to be melted based on the physical properties of the material X to be dissolved and the component adjusting material to be added and their masses. This is a value set as the height of the liquid surface in the case of occurrence of

  As a result, since the stirring force in the molten metal cannot be directly measured, the stirring force F suitable for dissolving the component adjusting material can be applied by using the change in the liquid level of the material to be melted by stirring as a reference. It can be generated in the molten metal X.

  When the liquid level measured by the liquid level measuring device 7 is not equal to or higher than a predetermined height (target value) (NO in FIG. 4 / STEP 22), the controller 100 controls the control circuit 10. The oscillation frequency is further lowered via

  On the other hand, when the height of the liquid level measured by the liquid level measuring device 7 is equal to or higher than the predetermined height (target value) (YES in FIG. 4 / STEP 22), the inside of the melt of the material X to be melted Ingredient adjustment material is put into (FIG. 4 / STEP23).

  Here, the component adjusting material is, for example, graphite, silicon, manganese or the like, and these are added in a predetermined amount (a small amount) so that the material X to be dissolved after adding the component adjusting material becomes a desired chemical component.

  Next, the controller 100 checks whether or not the introduction of the component adjusting material has been completed (FIG. 4 / STEP 24). If the introduction has not been completed (NO in FIG. 4 / STEP 24), this check is performed until the introduction is completed. repeat.

  On the other hand, when the introduction of the component adjusting material is completed (YES in FIG. 4 / STEP 24), as the third stage, the switch 14 is turned on and the frequency reference is returned to before the change, and the power factor 1 of the oscillation frequency is set. The control state to be maintained is restored (FIG. 4 / STEP 31).

  Thereafter, the controller 100 ends the operation of the power converter 4 (FIG. 4 / STEP 32), and ends a series of melting operations for melting the material X to be melted.

  The above is the melting method of the material to be melted by induction melting of the present embodiment, and as described above, according to the induction melting furnace of the present embodiment, the molten metal is brought into an overheated state before the component adjusting material melts into the molten metal. It is possible to prevent the component adjusting material from being sufficiently dissolved in the molten metal during the melting operation.

  In the present embodiment, the case where the controller 100 performs the entire control process in the induction melting furnace has been described. However, the present invention is not limited to this, and a part or all of the process by the controller 100 is performed by the user. It may be executed.

DESCRIPTION OF SYMBOLS 1 ... Power supply, 2 ... High voltage receiving board, 3 ... Transformer for converters, 4 ... Power converter, 5 ... High frequency matching device, 6 ... Induction heating device, 7 ... Liquid level measuring device, 10 ... Control circuit, 11 ... Power factor detector, 12 ... PLL controller (control signal generator), 41a, 41b ... Diode forward converter, 42a, 42b ... IGBT inverse converter, 61 ... Heating coil, 100 ... Controller, X ... Melting Wood.

Claims (1)

An induction melting furnace that melts a material to be melted housed in the furnace by supplying power to the heating coil provided on the outer periphery of the furnace wall through power supply means,
A power converter in which a forward converter and an inverse converter in which the first and second switching elements operate alternately constitute a series resonant circuit;
A power factor detector for detecting an output power factor of the power converter;
A control signal generator for generating control signals for the first and second switching elements,
The control signal generator is a control signal for the first and second switching elements.
In the first stage of melting the material to be melted, a control signal having a frequency at which the output power factor detected through the power factor detector is 1 is generated,
In the second stage of adding the component adjusting material to the dissolved material to be dissolved, as a control signal having a frequency suitable for dissolving the component adjusting material into the material to be dissolved , the liquid level of the material to be dissolved by stirring is adjusted . Generate a control signal with a frequency at which the change is a predetermined magnitude,
An induction melting furnace characterized by generating a control signal having a frequency at which the output power factor detected through the power factor detector is 1 in the third stage after the component adjusting material has melted into the material to be melted .

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