Firing Furnace

Abstract

[Problem] To provide an incinerator capable of shortening time necessary for incineration. [Solution] This incinerator is for incinerating an article to be incinerated, and comprises: a coil; and an inductive heating element through which inductive current flows by means of a magnetic field generated by the coil to generate heat by means of the inductive current, and which is disposed on the inner diameter side of the coil. The inductive heating element includes a hollow part for placing the article to be incinerated. The coil is composed of a conducting wire wound about an axis. The incinerator further comprises two circulation channel members arranged between the coil and the inductive heating element. One of the circulation channel members is disposed on the inner diameter side of the other circulation channel member, and the two circulation channel members form a gas circulation channel parallel to the axis.

Description

Technical Field

[0001] The present invention relates to a firing furnace. More specifically, the present invention relates to a firing furnace capable of shortening the time required for firing.

Background Art

[0002] A person may lose teeth due to caries, periodontal disease, or trauma. In such cases, dentures, bridges, or dental implants are attached to the missing part of the tooth. A dental implant is an artificial tooth root implanted in a person's oral cavity. Dental implants have the advantage of reducing the burden on other teeth and extending the life of other teeth. For this reason, dental implants are becoming the most effective treatment for tooth loss in recent years. Generally, a dental implant is produced by building up a dental ceramic material made of ceramic powder on a metal frame produced by casting or milling, and drying and firing the built-up dental ceramic material. In recent years, dental implants are also produced by milling a semi-sintered zirconia disk into the shape of a tooth, firing it at about 1500°C, and bonding it to a metal frame after full sintering.

[0003] Techniques related to a firing furnace for firing a dental ceramic material made of ceramic powder containing zirconia are disclosed, for example, in Patent Document 1 below. Patent Document 1 below discloses a sintering furnace including a coil and a heat dissipation device arranged inside the coil and induction-heated.

[0004] Also, Patent Document 2 below discloses a technique known as a rapid sintering method capable of shortening the time required for sintering. Patent Document 2 below discloses a firing furnace having a structure in which a susceptor (induction heating element) containing a material to be sintered is surrounded by a coil. This coil is made of a water-cooled copper pipe and is connected to a high-frequency power supply unit. When an electric current flows through the coil, the susceptor is heated. The heated susceptor acts as a heat dissipation device and transfers heat to the material to be sintered.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] There are two heating methods for firing furnaces: the resistance heating method and the induction heating method. The resistance heating method is a method of heating the object to be fired by the heat generated by the resistor through which an electric current flows. The induction heating method is a method of flowing an induced current through an induction heating element by a magnetic field generated by a coil, and heating the object to be fired by the heated induction heating element. The firing furnace using the induction heating method has the advantage that the temperature inside the firing furnace can be increased at high speed and the time required for firing is short compared with the firing furnace using the resistance heating method.

[0007] However, the firing furnace using the induction heating method still had the problem that the time required for firing was long. That is, in the firing furnace as in Patent Document 1, in order to shorten the time required for firing, it is only necessary to increase the amount of current in the coil and increase the frequency of the current in the coil. However, if the amount of current in the coil is increased excessively, there is a risk that the coil will be overheated beyond its heat-resistant temperature due to the heat generated by the current flowing through the coil itself and the heat transmitted from the heated susceptor (induction heating element).

[0008] Therefore, by configuring the coil with a water-cooled copper pipe as in the firing furnace of Patent Document 2, the coil can be cooled by the water flowing through the copper pipe, and overheating of the coil can be prevented. As a result, the time required for firing can be shortened.

[0009] However, when the coil is composed of a water-cooled copper tube as in Patent Document 2, although the heat generated by the coil itself in addition to the susceptor contributes to the heating of the object to be fired, the coil is water-cooled. For this reason, there is a problem of poor energy efficiency. In addition, since a water circulation device is required, there is a problem that the cost increases.

[0010] Note that the above problems can also occur in a firing furnace for firing an object to be fired other than a dental implant.

[0011] The present invention is for solving the above problems, and an object thereof is to provide a firing furnace capable of shortening the time required for firing while achieving energy saving and cost reduction.

Means for Solving the Problems

[0012] A firing furnace according to one aspect of the present invention is a firing furnace for firing an object to be fired, comprising a coil and an induction heating element that is disposed on the inner diameter side of the coil, through which an induced current flows due to a magnetic field generated by the coil and that generates heat due to the induced current. The induction heating element includes a hollow portion for disposing the object to be fired. The coil is composed of a conductor wire wound around an axis, and further includes each of an inner diameter side flow path member and an outer diameter side flow path member disposed between the coil and the induction heating element. The inner diameter side flow path member is disposed on the inner diameter side of the outer diameter side flow path member, and the inner diameter side flow path member and the outer diameter side flow path member constitute a flow path for a gas parallel to the axis.

[0013] Preferably, in the above firing furnace, the conductor wire is composed of a Litz wire including a plurality of strands insulated from each other and twisted together.

[0014] Preferably, in the above firing furnace, a first fan for promoting the flow of gas in the flow path is further provided.

[0015] Preferably, in the above firing furnace, a heat insulator including a groove extending in the outer diameter direction from the flow path is further included.

[0016] In the above-mentioned firing furnace, preferably, the induction heating element has a cylindrical shape with its axis as the central axis, and the heat insulator includes a lower hole connected to the hollow portion, and is a lifting portion that moves up and down between a lower position where the lower hole is opened and an upper position where the lower hole is blocked, and further includes a lifting portion including an upper surface for arranging the object to be fired.

[0017] In the above-mentioned firing furnace, preferably, it further includes a ceiling portion covering the opening at the upper part of the induction heating element, a first measurement portion hanging down from the ceiling portion into the hollow portion to measure the temperature of the hollow portion, and a control portion for controlling the current flowing through the coil based on the temperature measured by the first measurement portion.

[0018] In the above-mentioned firing furnace, preferably, it further includes a second measurement portion for measuring the temperature of the coil, and a second control portion for performing forced cooling control when the temperature measured by the second measurement portion exceeds the first temperature, and the forced cooling control includes at least one of stopping the current flowing through the coil and blowing air to the coil.

[0019] In the above-mentioned firing furnace, preferably, it further includes a second fan for blowing air to the coil.

[0020] In the above-mentioned firing furnace, preferably, the induction heating element contains molybdenum disilicide.

Effect of the Invention

[0021] According to the present invention, it is possible to provide a firing furnace that can shorten the time required for firing while achieving energy saving and cost reduction.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, the direction away from the axis AX (an example of an axis), which is the central axis of the coil 1, may be referred to as the outer diameter direction, and the direction approaching the axis AX may be referred to as the inner diameter direction.

[0024] [Configuration of the Firing Furnace]

[0025] FIG. 1 is a cross-sectional view showing the configuration of the firing furnace 100 in an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the litz wire 1a. FIG. 3 is an enlarged view of the main part of FIG. 1. FIG. 4 is a plan view showing the configuration of the lower heat insulator 3 when viewed from above.

[0026] Referring to FIGS. 1 to 4, the firing furnace 100 (an example of a firing furnace) in the present embodiment is a firing furnace that fires an object to be fired by an induction heating method. The object to be fired is, for example, a dental ceramic material made of ceramic powder containing zirconia or the like. The object to be fired may be any one. The firing furnace 100 includes a coil 1 (an example of a coil 1), an induction heating element 2 (an example of an induction heating element), a lower heat insulator 3 (an example of a heat insulator), a lifting part 4 (an example of a lifting part), a driving part 5, a ceiling part 6 (an example of a ceiling part), a flow path member 7 (an example of an inner diameter side flow path member), a flow path member 8 (an example of an outer diameter side flow path member), a measurement part 9 (an example of a first measurement part), a control part 10 (an example of a first and second control part), an upper heat insulator 11, a housing 12, an overhanging part 13, a fan 14 (an example of a first fan), and a fan 15 (an example of a second fan).

[0027] Coil 1 is made of Litz wire 1a (an example of Litz wire) wound around axis AX. Referring particularly to FIG. 2, Litz wire 1a includes a plurality of individual wires 1b (an example of individual wires). Each of the plurality of individual wires 1b is insulated from each other by an insulating coating 1c. Each of the plurality of individual wires 1b is twisted together. An alternating current is passed through coil 1, whereby coil 1 generates a periodically varying magnetic field. Note that coil 1 may be made of any conductor other than Litz wire such as a copper wire.

[0028] The induction heating element 2 is disposed on the inner diameter side of coil 1. The induction heating element 2 has a cylindrical shape with axis AX as its central axis. An induction current flows through the induction heating element 2 due to the magnetic field generated by coil 1. The induction heating element 2 generates heat due to this induction current and heats the object to be fired. The induction heating element 2 includes a lower end surface 21, an outer peripheral surface 22, and an inner peripheral surface 23. The induction heating element 2 is made of a material containing ceramics or the like, and preferably made of a material containing molybdenum disilicide. This is because molybdenum disilicide has good heating efficiency due to the induction current and high heat resistance. The induction heating element 2 includes a hollow portion SP1 (an example of a hollow portion) for disposing the object to be fired. The hollow portion SP1 is defined by the inner peripheral surface 23 of the induction heating element 2.

[0029] The lower heat insulator 3 is provided below the induction heating element 2. The lower heat insulator 3 includes a main body portion 31, a flange portion 32, a lower hole 33 (an example of a lower hole), and a recess 34. The main body portion 31 has a cylindrical shape with axis AX as its central axis. The main body portion 31 includes an inner peripheral surface 311 and an outer peripheral surface 312. The inner peripheral surface 23 of the induction heating element 2 and the inner peripheral surface 311 of the lower heat insulator 3 constitute a continuous curved surface.

[0030] The flange portion 32 extends in the outer diameter direction from the lower end portion of the main body portion 31. Particularly referring to FIGS. 3 and 4, the flange portion 32 has a substantially square shape when viewed from above. The flange portion 32 includes an upper surface 321, a circular groove 322, a linear groove 323 (an example of a groove), a lower surface 324, and an outer peripheral surface 325. The upper surface 321 of the flange portion 32 is flat, and the circular groove 322 and the linear groove 323 are each formed in the upper surface 321. The upper surface 321 is divided into four substantially rectangular portions by the circular groove 322 and the linear groove 323 respectively. The circular groove 322 surrounds the outer periphery of the main body portion 31. There are four linear grooves 323 here. Each of the four linear grooves 323 is provided so as to have an equal central angle when centered on the axis AX. Each of the four linear grooves 323 extends in the outer diameter direction from the circular groove 322. In other words, each of the four linear grooves 323 extends in the outer diameter direction from the flow passage SP2 described later. The outer diameter side end portions of each of the four linear grooves 323 reach the outer peripheral end portion of the flange portion 32 (of the upper surface 321).

[0031] The lower hole 33 is formed near the axis AX of the main body portion 31. The lower hole 33 is connected to the hollow portion SP1 of the induction heating element 2. The lower hole 33 is defined by the inner peripheral surface 311 of the lower heat insulator 3.

[0032] The recess 34 is provided on the inner diameter side at the upper end of the main body portion 31. The recess 34 is a recess that is recessed downward along the axis AX direction. The lower end surface 21 of the induction heating element 2 is in contact with the upper surface 341 of the recess 34. The outer peripheral surface 22 near the lower end portion of the induction heating element 2 is in contact with a portion 311a that extends upward from the recess 34 on the inner peripheral surface 311 of the main body portion 31.

[0033] The elevating portion 4 is fitted into the lower hole 33. The elevating portion 4 has a cylindrical shape and has a size and shape corresponding to the lower hole 33. The elevating portion 4 covers the lower opening of the induction heating element 2. The elevating portion 4 includes a stage 41 for arranging the object to be fired (an example of the upper surface for arranging the object to be fired).

[0034] The drive unit 5 is attached to the lower part of the lifting unit 4. The drive unit 5 moves the lifting unit 4 up and down between a lower position where the lifting unit 4 opens the lower hole 33 (in other words, a lower position where the lifting unit 4 exists below the lower hole 33) and an upper position where the lifting unit 4 closes the lower hole 33 (in other words, an upper position where the lifting unit 4 fits with the lower hole 33).

[0035] The ceiling part 6 is provided above the induction heating element 2. The ceiling part 6 covers the opening above the induction heating element 2. The ceiling part 6 includes a lower surface 61, an outer peripheral surface 62, and an upper surface 63. The induction heating element 2 is fixed to the lower surface 61 of the ceiling part 6. The induction heating element 2 protrudes downward from the lower surface 61 of the ceiling part 6. The hollow portion SP1 is sealed by the stage 41 of the lifting unit 4 and the lower surface 61 of the ceiling part 6.

[0036] Each of the flow path members 7 and 8 is disposed between the coil 1 and the induction heating element 2. The flow path member 7 is disposed on the inner diameter side of the flow path member 8. The flow path members 7 and 8 constitute a gas flow path SP2 parallel to the axis AX. The gas flowing through the flow path SP2 is, here, air supplied from the outside of the housing 12 by the fan 14. The gas flowing through the flow path SP2 may be any gas.

[0037] The flow path member 7 is fixed on the flange portion 32 and is disposed on the outer peripheral side of the induction heating element 2. The flow path member 7 has a cylindrical shape with the axis AX as the central axis. The flow path member 7 includes a lower end portion 71, an inner peripheral surface 72, and an outer peripheral surface 73. The lower end portion 71 of the flow path member 7 is disposed in the circular groove 322 of the flange portion 32. The inner peripheral surface 72 of the flow path member 7 is fixed to each of the outer peripheral surface 62 of the ceiling part 6 and the outer peripheral surface 312 of the main body part 31. Also, the inner peripheral surface 72 of the flow path member 7 is disposed on the outer peripheral side of the induction heating element 2 with a space therebetween. The flow path member 7 is preferably made of a material with high heat insulation and heat resistance such as ceramic.

[0038] The flow path member 8 is fixed to the upper heat insulator 11 and is disposed on the outer peripheral side of the flow path member 7. The flow path member 8 has a cylindrical shape with the axis AX as the central axis. The flow path member 8 includes a lower end surface 81, an outer peripheral surface 82, an inner peripheral surface 83, and an upper end surface 84. A part of the lower end surface 81 of the flow path member 8 is in contact with the upper surface 321 of the flange portion 32, and another part of the lower end surface 81 of the flow path member 8 straddles the upper portion of the linear groove 323. The coil 1 is wound around the outer peripheral surface 82 of the flow path member 8. The space defined by the outer peripheral surface 73 of the flow path member 7 and the inner peripheral surface 83 of the flow path member 8 is the flow path SP2. One end (starting point) of the flow path SP2 is the upper end surface 84 of the flow path member 8, and the other end (ending point) of the flow path SP2 is the lower end surface 81 of the flow path member 8. The other end of the flow path SP2 is connected to the linear groove 323. The flow path member 8 is preferably made of a material with high heat insulation and heat resistance such as ceramic.

[0039] The measurement unit 9 is fixed to the ceiling portion 6 and hangs down from the ceiling portion 6 into the hollow portion SP1. The measurement unit 9 measures the temperature of the hollow portion SP1 and transmits information (such as a voltage value) indicating the measured temperature to the control unit 10. Considering the temperature unevenness in the hollow portion SP1, a plurality of measurement units 9 may be provided.

[0040] The control unit 10 controls the entire firing furnace 100. The control unit 10 controls the current flowing through the coil 1 based on the temperature measured by the measurement unit 9. The control unit 10 controls the air volume of each of the fans 14 and 15 based on the temperature measured by the measurement unit 9 or the current flowing through the coil 1. Further, the control unit 10 controls the lifting operation of the lifting unit 4. The control unit 10 is composed of, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 10 includes an operation unit 101 and a display unit 102. The operation unit 101 receives various operations such as setting the firing temperature and firing time. The display unit 102 displays various information.

[0041] The upper heat insulator 11 is provided on the upper part of the flow path member 8. The upper heat insulator 11 has a substantially square shape when viewed from above. The upper heat insulator 11 includes a lower surface 111, an inner peripheral surface 112, an outer peripheral surface 113, and an upper surface 114. The lower surface 111 of the upper heat insulator 11 is in contact with the upper end surface 84 of the flow path member 8. The flow path member 8 extends downward from the lower surface 111 of the upper heat insulator 11. The inner peripheral surface 83 of the flow path member 8 and the inner peripheral surface 112 of the upper heat insulator 11 constitute a continuous curved surface.

[0042] The housing 12 houses each of the coil 1, the induction heating element 2, the lower heat insulator 3, the elevating part 4, the ceiling part 6, the flow path members 7 and 8, the measuring part 9, and the upper heat insulator 11 inside thereof. The housing 12 has a substantially rectangular parallelepiped shape. The housing 12 is made of a material such as aluminum that has good heat dissipation and little heat generation due to dielectric. The housing 12 includes a bottom surface 121, an inner peripheral surface 122, a ceiling surface 123, a plurality of through holes 124 to 127, an upper surface 128, and an outer peripheral surface 129.

[0043] The bottom surface 121 of the housing 12 is in contact with the lower surface 324 of the flange part 32. A through hole 124 for receiving the elevating part 4 is formed in the bottom surface 121 of the housing 12.

[0044] The inner peripheral surface 122 of the housing 12 is in contact with each of the outer peripheral surface 325 of the flange part 32 and the outer peripheral surface 113 of the upper heat insulator 11. The inner peripheral surface 122 of the housing 12 faces the outer peripheral surfaces 82 of the coil 1 and the flow path member 8 with a space SP3 therebetween. A plurality of through holes 125 are formed at positions on the inner peripheral surface 122 of the housing 12 that face the coil 1. Also, a plurality of through holes 126 are formed at positions on the inner peripheral surface 122 of the housing 12 that correspond to the outer peripheral side ends of the linear grooves 323.

[0045] The ceiling surface 123 of the housing 12 is in contact with the upper surface 114 of the upper heat insulator 11. The ceiling surface 123 of the housing 12 faces the upper surface 63 of the ceiling part 6 with the space SP4 therebetween. A part of the measuring unit 9 is provided in the space SP4. A plurality of through holes 127 are formed in the upper part of the flow path SP2 on the ceiling surface 123 of the housing 12.

[0046] The overhanging part 13 is arranged at the upper part of the housing 12. The overhanging part 13 constitutes a space SP5 with the upper surface 128 of the housing 12. The space SP5 exists above the space SP4 with the housing 12 therebetween. A part of the measuring unit 9 is provided in the space SP5. The overhanging part 13 includes an upper surface 131 and a through hole 132. The through hole 132 is formed in the central part of the upper surface 131.

[0047] The fan 14 is fixed to the upper surface 131 of the overhanging part 13 so as to cover the through hole 132. The fan 14 promotes the flow of the gas in the flow path SP2. Here, the fan 14 causes the air taken in from the outside of the housing 12 to flow through the flow path SP2.

[0048] Note that the fan 14 may be fixed to the outer peripheral surface 129 of the housing 12 so as to cover the through hole 126. Also, the fan 14 may be configured to discharge the air taken in from the flow path SP2 to the outside of the housing 12.

[0049] The fan 15 is fixed to the outer peripheral surface 129 of the housing 12 so as to cover one of the plurality of through holes 125. The fan 15 blows air to the coil 1. The fan 15 blows gas (here, the air taken in from the outside of the housing 12) to the coil 1, for example, from the outer diameter direction of the coil 1.

[0050] [Operation of the firing furnace]

[0051] FIG. 5 and FIG. 6 are cross-sectional views for explaining the operation of the firing furnace 100.

[0052] Referring to FIG. 5, when the control unit 10 receives a predetermined operation at the operation unit 101, as indicated by the arrow AR1, the lifting unit 4 is lowered along the axis AX. The lifting unit 4 is lowered to a position where the lower hole 33 is opened (in other words, a position that was below the lower hole 33). As a result, the stage 41 of the lifting unit 4 is exposed outside the housing 12.

[0053] Next, an object to be fired BS is placed on the stage 41 of the lifting unit 4 by the user of the firing furnace 100. Here, several stacked dental ceramic materials are shown as the object to be fired BS. Note that the object to be fired BS may be placed at any position in the hollow portion SP2.

[0054] Next, when the control unit 10 receives a predetermined operation at the operation unit 101, as indicated by the arrow AR2, the lifting unit 4 is raised along the axis AX. The lifting unit 4 is raised to a position where the lower hole 33 is closed (in other words, a position that is fitted with the lower hole 33). As a result, the hollow portion SP1 is sealed with the object to be fired BS housed therein.

[0055] Referring to FIG. 6, next, when the control unit 10 receives a predetermined operation at the operation unit 101, an alternating current is passed through the coil 1 by applying an alternating voltage to the coil 1. Due to the fluctuation of the magnetic field generated by the coil 1, an induced current flows through the induction heating element 2. The induction heating element 2 is heated by this induced current, and the inside of the hollow portion SP1 is heated by the heated induction heating element 2, and the object to be fired BS is heated. The control unit 10 controls the frequency, voltage, etc. of the alternating voltage applied to the coil 1 so that the inside of the hollow portion SP1 reaches the required firing temperature for the required firing time based on the temperature acquired from the measurement unit 9.

[0056] The coil 1 is cooled by the gas flowing through the flow path SP2. Since the gas in the flow path SP2 is heated by the induction heating element 2, natural convection of the gas occurs in the flow path SP2. Therefore, the fan 14 may be omitted.

[0057] Also, the control unit 10 rotates each of the fans 14 and 15 at necessary timings from the start of firing to the cooling after the end of firing. The control unit 10 may control the air volume (rotation speed) of each of the fans 14 and 15 based on the set firing time, the elapsed time since the start of firing, the temperature acquired from the measurement unit 9, or the like.

[0058] As shown by the solid arrow WD1, the fan 14 circulates the air taken in from the outside of the housing 12 through the flow path SP2 and discharges it to the outside of the housing 12. That is, the air taken in from the outside of the housing 12 passes through the through hole 132, the space SP5, the through hole 127, and the space SP4 in this order and enters the flow path SP2. This air advances downward in the flow path SP2 and hits the bottom surface of the circular groove 322. Thereafter, the air changes its traveling direction to the horizontal direction and advances in the linear groove 323, and is discharged to the outside of the housing 12 through the through hole 126. The blowing direction by the fan 14 may be the direction opposite to the arrow WD1.

[0059] As shown by the dotted arrow WD2, the fan 15 blows the air taken in from the outside of the housing 12 to the portion of the coil 1 facing the fan 15 and discharges it to the outside of the housing 12. That is, the air taken in from the outside of the housing 12 passes through the through hole 125 provided with the fan 15 and the space SP3 and hits the portion of the coil 1 facing the fan 15. The air hitting the coil 1 advances along the outer peripheral surface of the coil 1 in the space SP3 and is discharged to the outside of the housing 12 through a through hole 125 different from the through hole 125 provided with the fan 15. The blowing direction by the fan 15 may be the direction opposite to the arrow WD2.

[0060] Note that the firing furnace 100 may further include a measurement unit 16 (an example of a second measurement unit) that measures the temperature of the coil 1. The control unit 10 may further control at least one of the current flowing through the coil 1 and the fan for cooling the firing furnace 100 based on the temperature measured by the measurement unit 16. Here, the fan for cooling the firing furnace 100 means at least one of the fans 14 and 15.

[0061] When the measurement value of the measurement unit 16 exceeds the first temperature, the control unit 10 may detect an abnormality and perform forced cooling control. The forced cooling control may include at least one of stopping the current flowing through the coil 1 and blowing air to the coil 1 (here, blowing air by at least one of the fans 14 and 15). When the measurement value exceeding the first temperature subsequently falls below the second temperature (assuming that the second temperature is a temperature equal to or lower than the first temperature), the control unit 10 may end the forced cooling control and return to the normal control for firing as described above.

[0062] In this way, by measuring the temperature of the coil 1 and performing forced cooling control based on the measurement value, it is possible to monitor damage to the coil 1 due to overload and maintain an appropriate firing cycle.

[0063] [Effects of the Embodiment]

[0064] The coil 1 is heated by the current flowing through the conductor wire constituting the coil 1 itself and also by the conduction heat from the dielectric heating element 2. For this reason, the coil 1 is easily damaged by heat. In particular, when the coil 1 is made of the litz wire 1a, the coil 1 is easily damaged by heat. According to the present embodiment, the flow path members 7 and 8 disposed between the coil 1 and the dielectric heating element 2 constitute the flow path SP2, and the coil 1 is cooled by the gas flowing through the flow path SP2, thereby preventing overheating of the coil 1. As a result, the amount of current flowing through the coil 1 can be increased, and the time required for firing can be shortened. Further, since the coil 1 is cooled by gas, the amount of cooling of the coil can be suppressed as compared with the case where the coil is water-cooled. Thereby, the coil 1 can be efficiently heated and energy can be saved. Furthermore, since the water circulation device for cooling the coil 1 can be omitted, cost can be saved.

[0065] In addition, in order to shorten the waiting time for starting the firing of the next cycle after firing, it is necessary to cool the induction heating element 2 as quickly as possible after the firing is completed. According to the present embodiment, the induction heating element 2 can also be cooled as needed by the gas flowing through the flow path SP2.

[0066] In addition, according to the present embodiment, by adopting the coil 1 made of the litz wire 1a, the induction heating element 2 can be efficiently heated. Generally, when the frequency increases, due to the skin effect, the current only flows on the surface of the conductor, and due to the proximity effect, the electromagnetic distributions of adjacent electric fields negatively affect each other. As a result, the high-frequency loss of the wire increases. The litz wire has the effect of reducing the high-frequency loss of this wire.

[0067] FIG. 7 is a diagram showing the frequency characteristics of the AC resistance.

[0068] Referring to FIG. 7, Invention Example 1 of the present invention is a litz wire composed of 510 strands having a diameter of 0.1 mm. Invention Example 2 of the present invention is a litz wire composed of 1036 strands having a diameter of 0.07 mm. The comparative example is a single copper wire. The equivalent conductor cross-sectional areas of Invention Example 1, Invention Example 2, and the comparative example are all 4.0 mm 2 There is. As is clear from FIG. 7, at high frequencies in the range of about 10 KHz to about 1 MHz, the AC resistance of each of Invention Examples 1 and 2 is smaller than the AC resistance of the comparative example.

[0069] According to the present embodiment, by adopting the coil 1 made of the litz wire 1a, the current amount of the coil 1 can be increased and the frequency of the current of the coil 1 can be increased, so that the induction heating element 2 can be efficiently heated. As a result, the time required for firing can be shortened. As an example, according to the present embodiment, the hollow portion SP1 can be heated from room temperature to 1500° C. to 1600° C. in a time of 5 minutes or less.

[0070] In addition, by providing the fan 14, the flow of the gas in the flow path SP2 can be promoted. Thereby, the coil 1 can be efficiently cooled.

[0071] Also, by providing the linear groove 323 in the flange portion 32, the gas heated when flowing through the flow path SP2 can be quickly discharged to the outside of the housing 12.

[0072] Also, by providing the fan 15, air can be blown to the coil 1 from the outer diameter direction of the coil 1. Thereby, the coil 1 can be efficiently cooled.

[0073] Also, since the current amount of the coil is large, when a liquid such as water is used for cooling the coil, there are concerns about coil short - circuit and an increase in the size of the configuration. In this embodiment, since gas is used for cooling the coil 1, coil short - circuit is prevented, and the reliability of the firing furnace can be improved. Also, the size of the configuration can be reduced.

[0074] [Others]

[0075] The above - described embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0076] 1 Coil (an example of a coil) 1a Litz wire of the coil (an example of a Litz wire) 1b Strand of the Litz wire (an example of a strand) 1c Insulating coating of the Litz wire 2 Induction heating element (an example of an induction heating element) 3 Lower heat insulator (an example of a heat insulator) 4 Lifting part (an example of a lifting part) 5 Driving part 6 Ceiling part (an example of a ceiling part) 7, 8 Flow path members (an example of an inner - diameter - side flow path member and an outer - diameter - side flow path member) 9, 16 Measuring parts (an example of a first and a second measuring part) 10 Control part (an example of a first and a second control part) 11 Upper heat insulator 12 Housing 13 Protruding portion 14, 15 Fans (an example of the first and second fans) 21 Lower end surface of the induction heating element 22 Outer peripheral surface of the induction heating element 23 Inner peripheral surface of the induction heating element 31 Main body part of the lower heat insulator 32 Flange part of the lower heat insulator 33 Lower hole of the lower heat insulator (an example of the lower hole) 34 Depression of the lower heat insulator 41 Stage of the lifting part (an example of the upper surface for placing the object to be fired) 61 Lower surface of the ceiling part 62 Outer peripheral surface of the ceiling part 63 Upper surface of the ceiling part 71 Lower end part of the flow path member 72, 83 Inner peripheral surface of the flow path member 73, 82 Outer peripheral surface of the flow path member 81 Lower end surface of the flow path member 84 Upper end surface of the flow path member 100 Firing furnace (an example of the firing furnace) 101 Operation part of the control unit 102 Display part of the control unit 111 Lower surface of the upper heat insulator 112 Inner peripheral surface of the upper heat insulator 113 Outer peripheral surface of the upper heat insulator 114 Upper surface of the upper heat insulator 121 Bottom surface of the housing 122 Inner peripheral surface of the housing 123 Ceiling surface of the housing 124, 125, 126, 127 Through holes of the housing 128 Upper surface of the housing 129 Outer peripheral surface of the housing 131 Upper surface of the protruding portion 132 Through hole of the protruding portion 311 Inner peripheral surface of the main body part 311a Portion extending upward from the depression 312 Outer peripheral surface of the main body part 321 Upper surface of the flange part 322 Circular groove of the flange portion 323 Straight groove of the flange portion (an example of a groove) 324 Lower surface of the flange portion 325 Outer peripheral surface of the flange portion 341 Upper surface of the depression AX axis (an example of an axis) BS Object to be fired SP1 Hollow portion (an example of a hollow portion) SP2 Flow passage SP3, SP4, SP5 Spaces

Claims

1. A firing furnace for firing an object to be fired, comprising: a coil; an induction heating element disposed on the inner diameter side of the coil, through which an induced current flows due to the magnetic field generated by the coil and which generates heat due to the induced current; the induction heating element includes a hollow portion for disposing the object to be fired; the coil is composed of a conductor wire wound around an axis; further comprising each of an inner diameter side flow path member and an outer diameter side flow path member disposed between the coil and the induction heating element; the inner diameter side flow path member is disposed on the inner diameter side of the outer diameter side flow path member; the inner diameter side flow path member and the outer diameter side flow path member constitute a flow path for a gas parallel to the axis, the firing furnace.

2. The firing furnace according to claim 1, wherein the conductor wire is composed of a litz wire including a plurality of strands insulated from and twisted with each other.

3. The firing furnace according to claim 1 or 2, further comprising a first fan for promoting the flow of gas in the flow path.

4. The firing furnace according to claim 1, further comprising a heat insulator including a groove extending in the outer diameter direction from the flow path.

5. the induction heating element has a cylindrical shape with the axis as the central axis; the heat insulator includes a lower hole connected to the hollow portion; a lifting part that moves up and down between a lower position where the lower hole is opened and an upper position where the lower hole is closed, and further comprising a lifting part including an upper surface for disposing the object to be fired, the firing furnace according to claim 4.

6. a ceiling part covering the opening at the upper part of the induction heating element; a first measuring part hanging down from the ceiling part into the hollow portion for measuring the temperature of the hollow portion; The firing furnace according to claim 5, further comprising a first control part for controlling the current flowing through the coil based on the temperature measured by the first measuring part.

7. a second measuring part for measuring the temperature of the coil; further comprising a second control part for performing forced cooling control when the temperature measured by the second measuring part exceeds a first temperature; The forced cooling control includes at least one of stopping the current flowing through the coil and blowing air to the coil, the firing furnace according to claim 1.

8. The firing furnace according to claim 1, further comprising a second fan for blowing air to the coil.

9. The firing furnace according to claim 1, wherein the induction heating element contains molybdenum disilicide.

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