JP2017084565A - High frequency heating apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, in a conventional high frequency heating apparatus, a power factor cannot be prevented from being reduced by frequency switching.SOLUTION: A high frequency heating apparatus comprises: a power supply part 10 capable of changing a frequency of output power; a heating coil 31 for heating an object to be heated in accordance with the output power; temperature measuring means 32 for measuring a temperature of the object to be heated; a control part 14 which outputs a frequency switching signal instructing switching of the frequency of the output power to the power supply part 10 in response to a state where a surface temperature of the object to be heated measured by the temperature measuring means reaches a preset switching temperature; and a power factor enhancement part 11 for enhancing a power factor of the output power by matching a resonant frequency with the frequency of the output power. The power factor enhancement part 11 includes variable capacitors 21-23 which are inserted between the heating coil 31 and the power supply part 10, and changes the resonant frequency by varying capacitance values of the variable capacitors 21-23 in response to the frequency switching signal.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a high frequency heating device, for example, a high frequency heating device that heats a billet by applying high frequency power to a heating coil.

  Forging, which is one of the metal processing methods, includes a step of heating a material (hereinafter referred to as billet). In heating the billet, the billet is put into the heating coil, and the billet in the heating coil is heated by applying high-frequency power to the heating coil. An apparatus used for heating the billet is a high-frequency heating apparatus. An example of this high-frequency heating device is disclosed in Patent Document 1.

  The high-frequency heating device described in Patent Document 1 includes a rectifier that converts electric power from an AC power source into direct current, an inverter that converts direct-current power from the rectifier into high-frequency power, and an object to be heated that is supplied with high-frequency power from the inverter. A high-frequency heating device including a heating coil for heating is disclosed. And the high frequency heating apparatus of patent document 1 detects the rate of change of the said voltage value periodically based on the voltage detector which detects the voltage value applied to a heating coil, and the voltage detection signal obtained from a voltage detector. An inverter controller that increases or decreases the frequency of the inverter output according to the detection result, and the rate of change of the output frequency of the inverter is always a predetermined value with respect to the change of the resonance frequency of the heating coil due to the temperature change of the heated object The frequency in the voltage peak region is as follows.

Japanese Patent Laid-Open No. 62-190684

  However, in the high-frequency heating device of Patent Document 1, the capacitance value of the capacitor provided between the output terminal of the inverter and the heating coil and improving the power factor improvement is a fixed value. Therefore, in the high frequency heating device of Patent Document 1, there is one frequency that can improve the power factor, and there is a problem that the power factor decreases when the frequency of the output power output from the inverter changes.

  This invention is made | formed in view of the said situation, and it aims at implement | achieving a high power factor also when applying the output power of a different frequency to a heating coil.

  One aspect of the high-frequency heating device according to the present invention is a power supply unit that can change the frequency of output power, a heating coil that heats the object to be heated according to the output power, and the temperature of the object to be heated. In response to the temperature measuring means and the surface temperature of the heated object measured by the temperature measuring means reaching a preset switching temperature, the power supply unit is instructed to switch the frequency of the output power. A control unit that outputs a frequency switching signal; and a power factor improvement unit that improves a power factor of the output power by matching a resonance frequency to a frequency of the output power, and the power factor improvement unit includes the power factor improvement unit, The resonance frequency is changed by changing a capacitance value of the variable capacitor in accordance with the frequency switching signal, having a variable capacitor inserted between the heating coil and the power supply unit.

  According to one aspect of the present invention, the power factor improving unit changes the capacitance value of the variable capacitor so that the power factor becomes the highest in accordance with the switching of the frequency of the output power output from the power supply unit. The power factor can be increased for any frequency before and after switching of the frequency of the output power.

  In another aspect of the high-frequency heating device according to the present invention, the variable capacitor includes a plurality of capacitors connected in parallel to each other and a switch element connected in series with at least one of the plurality of capacitors. The open / close state of the switch element is controlled according to the frequency switching signal.

  According to another aspect of the present invention, since the capacitance value of the variable capacitor is switched by opening and closing the switch element, the capacitance value of the variable capacitor can be switched with a simple configuration.

  Moreover, in another aspect of the high-frequency heating device according to the present invention, the control unit outputs the output power to the power supply unit in response to the surface temperature of the heated body reaching a preset switching temperature. The frequency switching signal instructing to switch the frequency so that the frequency of the frequency is increased, and the power factor improving unit sets the capacitance value so that the capacitance value of the variable capacitor is decreased according to the frequency switching signal. Switch.

  According to another aspect of the present invention, by reducing the temperature difference between the outer peripheral portion and the peripheral portion of the heated body, temperature unevenness of the heated body can be eliminated and the heating time can be shortened.

  In another aspect of the motor temperature estimating apparatus according to the present invention, the temperature measuring means covers the radiation thermometer and the radiation thermometer, and is provided from the temperature measuring portion of the radiation thermometer toward the heating coil. A case having a cylinder, and an inert gas is allowed to flow out from the case into the heating coil.

  According to another aspect of the present invention, dirt such as oxide scale generated around the heated object adheres to the radiation thermometer by purging with an inert gas while detecting to a higher temperature with the radiation thermometer. This can prevent a decrease in accuracy of the detected temperature.

  According to another aspect of the present invention, a transformer provided between the power factor improving unit and the heating coil is further provided, and the variable capacitor is provided between the primary coil of the transformer and the power supply unit. Provided.

  According to another aspect of the present invention, a voltage optimum for the heating coil can be applied to the heating coil regardless of the voltage of the output power output from the power supply unit.

  According to the high-frequency heating device of the present invention, it is possible to prevent a reduction in power factor due to frequency switching of output power.

1 is a block diagram of a high-frequency heating device according to a first embodiment. FIG. 3 is a cross-sectional view illustrating the structure of a material heating unit according to the first embodiment. 3 is a heating graph for explaining a relationship between frequency switching and material temperature in the high-frequency heating device according to the first exemplary embodiment; It is a heating graph explaining the relationship between the frequency switching in the high frequency heating apparatus concerning a comparative example, and material temperature. It is a heating graph which compares the change of member temperature with the high frequency heating apparatus concerning a comparative example, and the high frequency heating apparatus concerning Embodiment 1. FIG. It is a figure explaining the length of the heating coil in the high frequency heating apparatus concerning Embodiment 1. FIG. It is a figure explaining the heating process at the time of using the high frequency heating apparatus concerning a comparative example. It is a figure explaining the heating process at the time of using the high frequency heating apparatus concerning Embodiment 1. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. For clarity of explanation, the following description and drawings are omitted and simplified as appropriate. In the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

  First, the block diagram of the high frequency heating apparatus 1 concerning Embodiment 1 is shown in FIG. As shown in FIG. 1, the high-frequency heating device 1 according to the first embodiment includes a power supply unit 10, a power factor improvement unit 11, a transformer 12, a material heating unit 13, and a control unit (for example, a heating control unit 14).

  The power supply unit 10 outputs output power applied to the heating coil 31 in the material heating unit 13. Moreover, the power supply unit 10 changes the frequency of the output power based on an instruction from the heating control unit 14. The power factor improvement part 11 is provided between the power supply part 10 and the heating coil 31, and makes a power factor the highest when the frequency of output electric power becomes a specific frequency. The power factor improving unit 11 improves the power factor of the output power by matching the resonance frequency with the frequency of the output power. In the example shown in FIG. 1, a transformer 12 is provided between the power factor improving unit 11 and the heating coil 31. In the example illustrated in FIG. 1, the power factor improvement unit 11 is provided between the primary coil of the transformer 12 and the power supply unit 10. Thus, by providing the transformer 12 between the power factor improvement unit 11 and the heating coil 31, an optimum voltage can be applied to the heating coil regardless of the voltage of the output power of the power supply unit 10. .

  The material heating unit 13 includes a heating coil 31 and temperature measuring means (for example, a temperature sensor 32). The heating coil 31 heats the object to be heated according to the output power of the power supply unit 10 transmitted via the transformer 12. As will be described in detail later, an object to be heated is inserted into the heating coil 31. The temperature sensor 32 measures the temperature of the heated object inserted into the heating coil 31. The heating control unit 14 instructs the power supply unit 10 to switch the frequency of the output power in response to the temperature of the heated object measured by the temperature sensor 32 reaching a preset switching temperature. Is output.

  Here, the detailed structure of the power factor improvement part 11 is demonstrated. The power factor improving unit 11 has a variable capacitor inserted between the heating coil 31 and the power supply unit 10, and changes the resonance frequency by changing the capacitance value of the variable capacitor according to the frequency switching signal. . Specifically, the power factor improvement unit 11 is inserted between the heating coil 31 and the power supply unit 10 and sets the capacitance value so that the capacitance value decreases according to the frequency switching signal output from the heating control unit 14. It has a variable capacity that can be varied. In the example illustrated in FIG. 1, the power factor improvement unit 11 includes unit capacitors 21 to 23 and switch elements SW1 to SW3. The unit capacities 21 to 23 are capacitors connected in parallel to each other. The unit capacitors 21 to 23 each have a plurality of capacitors connected in parallel, but the capacitors connected in parallel within one unit capacitor have a combined capacity obtained by synthesizing the capacitance values of the capacitors connected in parallel. It can be regarded as one capacitor. For example, the unit capacitor 21 includes capacitors C11 to C14 connected in parallel to each other, but can be regarded as one capacitor having a total capacity of the capacitance values of the capacitors C11 to C14.

  The switch element SW1 is provided so as to be connected in series with the unit capacitor 21. The switch element SW2 is provided so as to be connected in series with the unit capacitor 22. The switch element SW3 is provided so as to be connected in series with the capacitors C33 and C34 among the capacitors C31 to C34 of the unit capacitance 23. Capacitors C31 and C32 are inserted between the power supply unit 10 and the primary coil of the transformer 12 without a switch element. The switch elements SW1 to SW3 are in an open state (for example, an ON state) when the heating control unit 14 instructs the power supply unit 10 to increase the frequency, and the heating control unit 14 supplies the frequency to the power supply unit 10. Is in a closed state (e.g., an off state) in a state instructing to lower.

  The power factor improving unit 11 functions as a single capacitor having a capacitance value that is a sum of capacitance values of the capacitors C31 and C32 when the switch elements SW1 to SW3 are in the off state. On the other hand, when the switch elements SW1 to SW3 are in the ON state, the power factor improvement unit 11 functions as a single capacitor having a capacitance value that is a sum of capacitance values of the capacitors C11 to C14, C21 to C24, and C31 to C34. . That is, the power factor improvement unit 11 functions as a capacitor having a small capacitance value when the surface temperature of the heated object is lower than the preset switching temperature and the frequency of the output power of the power supply unit 10 is high. On the other hand, the power factor improvement unit 11 functions as a capacitor having a large capacitance value when the surface temperature of the object to be heated is higher than a preset switching temperature and the frequency of the output power of the power supply unit 10 is low.

The unit capacitors 21 to 23 of the power factor improving unit 11 and the primary coil of the transformer 12 constitute a resonance circuit. For this reason, in the high-frequency heating device 1, the resonance frequency of the resonance circuit is lowered when the frequency of the output power of the power supply unit 10 is low by switching the capacitance value realized by the power factor improvement unit 11. It can also be considered to have a function of increasing when the frequency of the output power is high. The resonance frequency f can be expressed by equation (1), where L is the inductance of the primary coil of the transformer 12 and C is the capacitance value realized by the power factor improvement unit 11.

  In the example shown in FIG. 1, the example in which the capacitance value is varied by increasing or decreasing the number of capacitors in parallel has been described. However, it is also possible to connect a plurality of capacitors in series and increase or decrease the number of capacitors in series by a switch element. The capacitance value can be varied. When connecting a plurality of capacitors in series, a switch element is connected in parallel to the capacitor to be increased or decreased. Then, when it is desired to increase the capacitance value of the power factor improvement unit 11, the switch element is turned off, and when it is desired to decrease the capacitance value of the power factor improvement unit 11, the switch element is turned on.

  Then, the structure of the material heating part 13 is demonstrated in detail. FIG. 2 is a cross-sectional view illustrating the structure of the material heating unit 13 according to the first embodiment. The cross-sectional view shown in FIG. 2 schematically shows the configuration of the material heating unit 13.

  As shown in FIG. 2, in the power factor improving unit 11, a material to be heated (hereinafter referred to as a billet) is introduced into the heating coil 31. The loading and unloading of this material is performed by a plunger. An upper lid 33 is provided on the upper part of the heating coil 31, and the lower part is closed with a plunger.

  In the example shown in FIG. 2, four temperature sensors 32 a to 32 d are provided as the temperature sensor 32. Each temperature sensor has a radiation thermometer (41a-41d of FIG. 2) and a case. The case includes a cylinder that covers the radiation thermometer and is provided from the temperature measurement unit of the radiation thermometer toward the inside of the heating coil. And in the high frequency heating apparatus 1, the inert gas purge which flows out inert gas (for example, nitrogen, argon, etc.) toward the inside of the heating coil 31 from the inside of a case is performed. 2, the temperature sensor 32a measures the temperature near the center of the upper end face of the billet, the temperature sensor 32b measures the temperature of the surface of the center of the billet in FIG. 2, and the temperature sensors 32c and 32d Measure the temperature at the surface of the billet end.

  Here, in the high frequency heating apparatus 1 according to the first embodiment, the surface temperature of the billet is measured by a radiation thermometer. In the heating process in forging, the billet is heated to about 1200 ° C. Therefore, when a thermocouple is used for temperature measurement, there is a demerit that the thermocouple is severely deteriorated and the thermocouple needs to be replaced frequently. On the other hand, when a radiation thermometer is used for temperature measurement, the radiation thermometer does not deteriorate because the heat of the billet is not directly applied to the radiation thermometer. Further, in the heating process, dirt such as oxide scale is generated around the billet, and if this dirt adheres to the radiation thermometer, the temperature measurement accuracy of the radiation thermometer may be deteriorated. However, in the high-frequency heating device 1 according to the first embodiment, an inert gas purge is performed on the path from the temperature measurement unit of the radiation thermometer toward the billet. As a result, the generation of dirt such as oxide scale is reduced, and the generated dirt such as oxide scale is prevented from adhering to the radiation thermometer.

  In the example shown in FIG. 2, the surface temperature of the billet is measured using a plurality of temperature sensors. Thus, when using a plurality of temperature sensors for billet temperature measurement, the heating control unit 14 determines whether or not to switch the frequency of the output power using the lowest temperature among the temperatures measured by the temperature sensor. It is preferable to judge.

この（２）式より、電流浸透深さδは、出力電力の周波数が低いほど深くなることがわかる。実施の形態１にかかる高周波加熱装置１では、ビレットの表面温度が予め設定した切り替え温度に達するまでは出力電力の周波数を低くしてビレットの中心部の加熱を促進し、ビレットの表面温度が切り替え温度に達した後は出力電力の周波数を高くすることでビレットの中心部よりも端部の加熱を促進する。 Then, frequency control of the high frequency heating apparatus 1 concerning Embodiment 1 is demonstrated. First, the billet current penetration depth δ will be described. The current penetration depth δ indicates how deep the current penetrates from the surface of the billet. The current penetration depth δ [mm] is (2) when the frequency [Hz] of the output power applied to the heating coil is f, the specific resistance [μΩ · cm] of the billet is ρ, and the permeability of the billet is μs. It can be expressed by a formula.

From this equation (2), it can be seen that the current penetration depth δ increases as the frequency of the output power decreases. In the high-frequency heating device 1 according to the first embodiment, until the billet surface temperature reaches a preset switching temperature, the frequency of the output power is lowered to promote heating of the center of the billet, and the billet surface temperature is switched. After reaching the temperature, the frequency of the output power is increased to promote the heating of the end portion rather than the center portion of the billet.

  FIG. 3 shows a heating graph for explaining the relationship between frequency switching and material temperature in the high-frequency heating device according to the first embodiment. The heating graph shown in FIG. 3 is obtained by measuring the temperature change of each part of the billet by installing thermocouples at the upper part, the central part, the lower part and the upper part of the central part, the central part, and the lower part of the surface of the billet. In the heating graph shown in FIG. 3, the horizontal axis represents the heating time, and the vertical axis represents the billet temperature.

  As shown in FIG. 3, in the high-frequency heating device 1 according to the first embodiment, the frequency of the output power of the power supply unit 10 is increased from 800 Hz in response to the surface temperature of the billet reaching the switching temperature (for example, 750 ° C.). Switch to 1200 Hz. In the high-frequency heating device 1 according to the first embodiment, the temperature (surface temperature) of the outer peripheral portion of the billet is not greatly deviated from the target 1200 ° C., and the temperature difference between each part is small. Is done. Also, heating proceeds in a state where the temperature difference between the parts is small even at the center of the billet.

  Here, in order to explain the temperature change of the billet by the high-frequency heating device 1 according to the first embodiment, a comparative example in which heating is performed with the frequency of the output power of the power supply unit 10 fixed at 1200 Hz will be described. FIG. 4 shows a heating graph for explaining the relationship between frequency switching and material temperature in the high-frequency heating apparatus according to the comparative example.

  As shown in FIG. 4, in the high-frequency heating device according to the comparative example, the temperature difference at the outer peripheral portion of the billet is larger than when heating is performed by the high-frequency heating device 1 according to the first embodiment. In particular, in the upper part of the outer periphery of the billet, the temperature is higher by about 100 ° C. than other parts. A temperature exceeding 1300 ° C. is an overheated state for forging and is judged to be defective.

  Such temperature unevenness occurs because the balance between heat input in the billet and heat radiation by radiant heat differs depending on the part. Specifically, since the frequency of the output power is high, the heat input at the outer peripheral portion is more easily promoted than the heat input at the central portion. On the other hand, in terms of heat dissipation, the lower part of the billet is susceptible to heat removal from the plunger that is not affected by induction heating by the heating coil, while the upper part of the billet is less affected by heat removal from the plunger. Is easy to promote.

  On the other hand, in the high-frequency heating device 1 according to the first embodiment, the inside of the billet is first promoted at the frequency of the low-frequency output power, and the billet outer periphery is changed in response to the billet surface temperature reaching the switching temperature. The frequency is switched to the frequency of the output power that facilitates heating of the part. Thereby, in the high frequency heating apparatus 1 concerning Embodiment 1, the balance of a heat input and heat radiation can be improved compared with a comparative example.

  Here, the heating time is compared between the high-frequency heating device according to the comparative example and the high-frequency heating device 1 according to the first embodiment. FIG. 5 shows a heating graph for comparing changes in member temperature between the high-frequency heating device according to the comparative example and the high-frequency heating device according to the first embodiment. FIG. 5 is a graph in which the heating graph of the central portion of the outer peripheral portion and the central portion of FIG. 3 and the heating graph of the central portion of the outer peripheral portion and the central portion of FIG.

  As shown in FIG. 5, in the heating process using the high-frequency heating device 1 according to the first embodiment, the heating rate at the center is faster and the heating rate at the outer periphery is slower than in the comparative example. However, in the heating process using the high-frequency heating device 1 according to the first embodiment, the difference in heating rate between the central portion and the outer peripheral portion is smaller than that in the comparative example. Therefore, in the heating process using the high-frequency heating device 1 according to the first embodiment, the time until the billet heating is completed is shorter than that in the comparative example.

  More specifically, in the high-frequency heating device 1 according to the first embodiment, the temperature gradient inside the billet is increased by setting the frequency of the output power that drives the heating coil 31 low during the period when the billet temperature is low. . On the other hand, in the high-frequency heating device 1 according to the comparative example, the temperature inside the billet is raised based on the heat transfer from the billet surface. In addition, in the high-frequency heating device 1 according to the first embodiment, the billet is heated with low-frequency output power at the beginning of heating. However, when the frequency of the output power is low, the end of the billet is hardly heated. Therefore, in the high-frequency heating device 1 according to the first embodiment, after the temperature of the Curie temperature at which iron is magnetic (for example, 750 ° C.) is set as the switching temperature, the billet surface temperature reaches this switching temperature. The heating coil 31 is provided with output power having a frequency that does not cause the billet surface to overheat (for example, about 1200 Hz). In the high-frequency heating device 1 according to the first embodiment, the inside of the billet is heated to a specified temperature while the surface temperature is made uniform by advancing heating with high-frequency output power. For this reason, in the heating process using the high-frequency heating device 1 according to the first embodiment, the time until the billet heating is completed is shorter than in the comparative example.

  From the above description, in the high-frequency heating device 1 according to the first embodiment, the capacity value of the power factor improvement unit 11 is switched in accordance with the switching of the frequency of the output power, thereby preventing the power factor from being lowered due to the switching of the frequency of the output power. can do.

  Further, in the high-frequency heating device 1 according to the first embodiment, switching is performed so that the frequency of the output power is increased in response to the billet temperature reaching the switching temperature. Thereby, in the high frequency heating apparatus 1 concerning Embodiment 1, heating time can be shortened, eliminating the temperature nonuniformity of a billet.

  Further, in the high-frequency heating device 1 according to the first embodiment, the power factor improving unit 11 has a variable capacity, and the variable capacity is connected in series to a plurality of capacitors having a predetermined capacity value. A switch element is used. And the capacitance value of a variable capacitor is increased / decreased by controlling the opening / closing state of a switch element. By setting it as such a structure, in the high frequency heating apparatus 1 concerning Embodiment 1, the capacitance value of a variable capacity | capacitance can be switched with a simple structure.

  Moreover, in the high frequency heating apparatus 1 concerning Embodiment 1, the radiation thermometer stored in the case is used for the temperature measurement of a billet. And in the high frequency heating apparatus 1 concerning Embodiment 1, an inert gas purge is performed toward the billet from the inside of a case by flowing an inert gas in the cylinder provided in the case. Thereby, it can prevent that the temperature measurement part of a radiation thermometer becomes dirty with the oxide scale etc. which generate | occur | produced around the billet. Further, by performing an inert gas purge in the heating coil, it is possible to prevent the generation of oxide scale around the billet.

  In the high-frequency heating device 1 according to the first embodiment, the transformer 12 is provided between the power factor improving unit 11 and the heating coil 31. Thereby, in the high frequency heating device 1 according to the first embodiment, an optimum voltage can be applied to the heating coil 31 regardless of the voltage of the output power output from the power supply unit 10.

  Moreover, when the high frequency heating apparatus 1 concerning Embodiment 1 is used, the coil length of the heating coil 31 can be shortened. This effect will be specifically described with reference to FIG. FIG. 6 is a diagram for explaining the length of the heating coil in the high-frequency heating device according to the first embodiment.

  6 illustrates the heating state of the billet in the first comparative example in which the coil length is the same L1 as that of the heating coil 31 according to the first embodiment and the frequency of the output power is not switched. It is. In the first comparative example, the overhang of the coil length with respect to the billet length Y is X1. The middle diagram of FIG. 6 illustrates the heating state of the billet in the second comparative example in which the coil length is L2 longer than that of the heating coil 31 according to the first embodiment and the frequency of the output power is not switched. It is. In this second comparative example, the overhang of the coil length with respect to the billet length Y was set to X2, which is longer than X1. 6 illustrates the heating state of the billet when the heating coil 31 according to the first embodiment in which the coil length is L1 is used.

  As shown in FIG. 6, in the first comparative example, the end of the billet is not sufficiently heated, so that uneven baking occurs. A second comparative example eliminates the unevenness of burning without performing frequency switching control of the output power applied to the heating coil. In the second comparative example, by increasing the overhang amount from X1 to X2, the permeation current at the end portion is increased and the uneven baking is eliminated. However, in the high-frequency heating device 1 according to the first embodiment, by controlling the frequency of the output power, the temperature difference between the center portion and the end portion of the billet is reduced, so that uneven baking occurs even with a short coil length. The billet can be heated without causing it.

  The net efficiency in the heating coil 31 is about 65%, resulting in a loss of about 35%. Of this 35% loss, a loss of about 20% is a loss due to the copper loss of the heating coil. Therefore, the loss resulting from the copper loss can be reduced by shortening the coil length of the heating coil 31. And by reducing the loss of the heating coil 31, the high-frequency heating device 1 according to the first embodiment can reduce power consumption.

  Moreover, the use of the high-frequency heating device 1 according to the first embodiment can increase the productivity of the entire forging process and the flexibility of the installation area required for the forging process. This effect will be specifically described with reference to FIGS. FIG. 7 is a diagram for explaining a heating process when the high-frequency heating device according to the comparative example is used. This comparative example is a schematic view of a heating coil portion of a continuous heating high-frequency heating device used in a mass production process of forged products. As shown in FIG. 7, in the high-frequency heating device according to the comparative example, the billet is heated by flowing the billet through a long coil, and the billet is heated to a specified temperature until the billet reaches the end of the heating coil. To do. Then, the billet heated to a specified temperature is supplied to the forging device. In addition, in the high-frequency heating device according to the comparative example shown in FIG. 7, the heating coil cannot be sealed, and therefore oxide scales adhere around the billet.

  Moreover, as shown in FIG. 7, in the process using the high-frequency heating device according to the comparative example, when a failure occurs in the process after the heating process and the process is stopped, the billet put in the heating coil is discarded as a heat cooling material. There is a need to. This is because the high-frequency heating device according to the comparative example cannot be stopped in a state where the temperature of the billet is kept constant in the heating coil. And in the process using the high frequency heating apparatus concerning a comparative example, injection | throwing-in of a billet in a heating coil is restarted according to having recovered the post process.

  That is, in the process using the high-frequency heating device according to the comparative example shown in FIG. 7, a heat-cooled material is generated when the post-process is stopped. Further, in the process using the high-frequency heating device according to the comparative example shown in FIG. 7, there is a problem that it takes time to restart the process. Furthermore, in the process using the high-frequency heating device according to the comparative example shown in FIG. 7, the length of the heating coil cannot be shortened regardless of the manufacturing capacity of the process. Equipment installation area is required. Moreover, since the size of the apparatus does not change, a certain amount of power is consumed by the high-frequency heating apparatus regardless of the amount of product produced in the process.

  FIG. 8 is a diagram for explaining a heating process when the high-frequency heating device 1 according to the first embodiment is used. As shown in FIG. 8, in the high frequency heating apparatus 1 according to the first embodiment, the length of the heating coil can only heat one billet, and each billet is heated individually. And in the process using the high frequency heating apparatus 1 concerning Embodiment 1, in the state in which the post process is operating, a billet is heated one by one and the billet after heating is transferred to the post process.

  On the other hand, when the post process is stopped due to a malfunction, the high frequency heating apparatus 1 according to the first embodiment keeps the billet warm in the heating coil. This is a function that is possible because the high-frequency heating device 1 according to the first embodiment can heat the billet one by one and adjust the frequency of the output power that gives the heating temperature to the heating coil. is there. In the process using the high-frequency heating device 1 according to the first embodiment, the billet is reheated according to the recovery of the post-process, and the billet heated according to the completion of the heating of the billet is completed. Is transferred to the subsequent process.

  In the process using the high-frequency heating device 1 according to the first embodiment, no waste member such as a heat-cooled material is generated even when the post-process is stopped, so that high production efficiency can be realized. Moreover, in the process using the high-frequency heating device 1 according to the first embodiment, the high-frequency heating device according to the comparative example is used by reheating the billet in the heat-retaining state even when the post-process is recovered after being stopped. The heated billet can be supplied to the subsequent process in a shorter time than the process. That is, in the process using the high-frequency heating device 1 according to the first embodiment, the operation efficiency of the process can be increased.

  Moreover, in the process using the high frequency heating apparatus 1 according to the first embodiment, it is possible to flexibly cope with a change in production capacity required for the heating process by increasing or decreasing the number of apparatuses to be installed. In the process using the high-frequency heating device 1 according to the first embodiment, when the required production capacity is small, the number of installed devices can be reduced, and the power consumption and the installation area of the device can be reduced. .

  In the above description, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the embodiments already described, and various modifications can be made without departing from the scope of the invention. It goes without saying that changes are possible.

DESCRIPTION OF SYMBOLS 1 High frequency heating apparatus 10 Power supply part 11 Power factor improvement part 12 Transformer 13 Material heating part 14 Heating control part 21 Unit capacity 22 Unit capacity 23 Unit capacity 31 Heating coil 32 Temperature sensor 33 Upper lid 41 Radiation thermometer SW1 Switch element SW2 Switch element SW3 Switch element

Claims (5)

A power supply that can change the frequency of the output power; and
According to the output power, a heating coil for heating the object to be heated;
Temperature measuring means for measuring the temperature of the heated object;
In response to the surface temperature of the object to be heated measured by the temperature measuring unit reaching a preset switching temperature, a frequency switching signal for instructing the power supply unit to switch the frequency of the output power is output. A control unit,
A power factor improvement unit that improves the power factor of the output power by matching a resonance frequency to the frequency of the output power, and
The power factor improving unit is
Having a variable capacity inserted between the heating coil and the power supply;
A high-frequency heating apparatus that changes the resonance frequency by changing a capacitance value of the variable capacitor in accordance with the frequency switching signal. The variable capacity is
A plurality of capacitors connected in parallel to each other;
A switching element connected in series with at least one of the plurality of capacitors,
The high frequency heating apparatus according to claim 1, wherein the switch element is controlled to be opened and closed in accordance with the frequency switching signal. The control unit instructs the power supply unit to switch the frequency so that the frequency of the output power is increased in response to the surface temperature of the heated body reaching a preset switching temperature. Output frequency switching signal,
The high-frequency heating device according to claim 1 or 2, wherein the power factor improvement unit switches the capacitance value so that the capacitance value of the variable capacitance is reduced according to the frequency switching signal. The temperature measuring means includes
A radiation thermometer,
A case that includes a cylinder that covers the radiation thermometer and is provided from the temperature measurement unit of the radiation thermometer toward the inside of the heating coil;
The high-frequency heating device according to any one of claims 1 to 3, wherein an inert gas flows out from the case toward the heating coil. A transformer provided between the power factor improving unit and the heating coil;
5. The high-frequency heating device according to claim 1, wherein the variable capacitor is provided between a primary coil of the transformer and the power supply unit. 6.

Images