JP4345491B2 - Induction heating device - Google Patents

Description

  The present invention relates to an induction heating device used in general homes, offices, restaurants, factories, and the like, and more specifically, as a material to be heated, a low permeability and high electrical conductivity material such as aluminum or copper. The present invention relates to an induction heating apparatus that can heat aluminum, copper, and the like, particularly with an induction heating cooker that heats a heated object, an induction heating water heater, an induction heating iron, or another induction heating apparatus.

  Conventionally, as an induction heating apparatus of this type, for example, an induction heating cooker has a plurality of switching elements, generates a resonance current with a short period in the heating coil during the ON period of one switching element, and a smoothing capacitor. There is known a technique for heating an aluminum pan or the like with less noise by supplying electric power to the heating coil without causing a squealing sound due to a pulsating flow of input voltage (see, for example, Patent Document 1).

  In addition, equivalent series resistance in the input impedance of the heating coil (equivalent series resistance in the input impedance of the heating coil measured below using the frequency near the heating coil at the same position as the heated object and the electric conductor in the heated state) By simply providing an electric conductor having the function of increasing the equivalent series resistance of the heating coil) between the heating coil and an object to be heated made of a material having low magnetic permeability and high electrical conductivity such as aluminum. A technique is known in which the current flowing through the coil is reduced to reduce the buoyancy acting on the object to be heated, and even when the input power is large, the object to be heated is less displaced and lifted by buoyancy (see, for example, Patent Document 2). .

  Hereinafter, as a conventional induction heating apparatus, an induction heating apparatus (induction heating cooker) in Patent Document 2 will be described with reference to the drawings.

FIG. 5 is a perspective view showing the configuration of the heating coil 21 and its surroundings, and FIG. 6 shows a heating coil 21 housed in an induction heating device main body (not shown), a top plate 28 fixed to the upper portion of the main body, is a sectional view showing an object to be heated 29 is location mounting the top plate 28.

5 and 6, 21 is a heating coil, an inverter generates a magnetic field by about 70kHz high frequency current supplied from the (not shown), induce the heated object 29 which is location mounting on the top plate 28 Heat.

  The electric conductor 27 is formed of an aluminum plate made of a material having a thickness of about 1 mm, and is provided between the insulating plate 31 and the top plate 28.

  Since the magnetic field emitted from the upper part of the heating coil 21 is linked to the electric conductor 27, an induced current is induced in the electric conductor 27. The electric conductor 27 has a thickness of about 1 mm and a thickness greater than the penetration depth of the high-frequency current induced by the heating coil 21 current (hereinafter simply referred to as the penetration depth of the induced current). Most of these do not pass through the electric conductor 27, and detour to the outer peripheral side or the inner peripheral side before reaching the object 29 to be heated.

  When there is no electric conductor 27, the inside of the object 29 to be heated is made of aluminum, copper, or an electric conductivity equal to or higher than that of the high frequency magnetic field generated from the heating coil 21 and made of a low magnetic permeability material. An induced current is induced to generate a magnetic field in the repulsive direction. As a result, buoyancy is generated in the heated object 29 due to the interaction between the magnetic field induced from the induced current in the heated object 29 and the magnetic field generated from the heating coil 21.

  However, in this conventional technique, the electric conductor 27 is provided between the heating coil 21 and the object 29 to be heated, and the thickness thereof is larger than the penetration depth of the induced current. The magnetic field generated from the heating coil 21 is linked to the electric conductor 27 and the object to be heated 29 and generates an induced current in both. Thus, the electric conductor is generated so that the superposed magnetic field of the magnetic field generated by the induced current induced in the electric conductor 27 and the magnetic field generated by the current induced in the object to be heated 29 prevents a change in the magnetic field generated by the heating coil 21. An induced current flows through 27 and the object 29 to be heated.

  That is, the current distribution induced in the object to be heated 29 changes when an induced current is generated in the electric conductor 27 when the electric conductor 27 has a sufficient thickness. With this change in current distribution, the equivalent series resistance of the heating coil 21 is increased, the current flowing through the heating coil 21 when obtaining the same output can be reduced, the buoyancy acting on the object 29 to be heated is reduced, and By sharing a part of the buoyancy that the electric conductor 27 should act on the object 29 to be heated, the buoyancy acting on the object 29 can be reduced.

  FIG. 7 shows the relationship between power consumption and buoyancy when the object to be heated 29 is an aluminum pan. When there is an aluminum electrical conductor 27 (shown by B) and when there is no electrical conductor 27 (shown by A). FIG. 8 shows an example of the measurement result of the relationship between the power consumption and the heating coil current when the electric conductor 27 is present (indicated by B) and when the electric conductor 27 is absent (indicated by A). However, the resonance frequency of the inverter is about 70 kHz.

  According to these measurement results, by inserting the electric conductor 27, the equivalent series resistance of the heating coil 21 is increased, the buoyancy acting on the object to be heated 29 is reduced, and the current of the heating coil 21 is also reduced.

FIG. 9 shows the tendency regarding the thickness and buoyancy of the electric conductor 27. By making the thickness of the electrical conductor 27 equal to or greater than the penetration depth, it is possible to obtain a buoyancy reduction effect.
Japanese Patent Laid-Open No. 2003-257609 JP 2003-264054 A

  However, in the conventional technique, induction heating of the electric conductor 27 is performed simultaneously with induction heating of the object 29 to be heated. Furthermore, since the thickness of the electric conductor 27 is larger than the penetration depth of the induced current, the high-frequency magnetic field generated from the heating coil 21 hardly penetrates and passes through the electric conductor 27, that is, sufficient to not penetrate and pass. A large induced current is induced in the electrical conductor 27. Therefore, the subject that the loss by the heat_generation | fever of the electrical conductor 27 became large especially occurred.

  Further, regarding the tendency regarding the thickness and buoyancy of the electric conductor 27 shown in FIG. 9, a technology for induction heating of aluminum, copper, or a low magnetic permeability material having an electric conductivity substantially equal to or higher than these is newly developed, and sufficient knowledge has been obtained. In addition, the measurement points were discrete in the experiments at that time, and sufficient knowledge was not presented about the behavior of buoyancy between the measurement points.

  The present invention solves the above-mentioned conventional problems, can heat a heated object formed of a material having low magnetic permeability and high electrical conductivity, reduces buoyancy acting on the heated object, and It aims at providing the induction heating apparatus with few losses.

In order to solve the above-described conventional problems, an induction heating apparatus of the present invention is a heating coil comprising a heating coil that is supplied with a high-frequency current of about 70 kHz to induction-heat an object to be heated, and a material having low magnetic permeability and high electrical conductivity. buoyant reducing function of reducing the buoyancy acting on the object to be heated when the magnetic field from the heating coil is generated between the objects, provided with aluminum or copper electrical conductors, the thickness of the electrical conductors 10 ˜30 μm .

  Such an electrical conductor increases the equivalent series resistance of the heating coil as compared to when there is no electrical conductor. Therefore, it has a buoyancy reduction function for reducing the buoyancy acting on the object to be heated by the magnetic field generated by the heating coil by reducing the current flowing through the heating coil when obtaining the same output.

  Accordingly, it is possible to prevent the object to be lifted or shifted when the object to be heated made of aluminum, copper, or an electric conductivity equivalent to or higher than these is heated and made of a low magnetic permeability material.

  Further, since the thickness of the electric conductor is sufficiently small, the high frequency magnetic field generated from the heating coil penetrates and passes through the electric conductor. Energy that does not allow the high-frequency magnetic field generated from the heating coil to pass through, that is, induction current, is not generated inside the electric conductor, reducing loss due to heat generation of the electric conductor, facilitating cooling near the heating coil, and heating The power transmitted to the object can be increased.

The induction heating apparatus of the present invention can heat an object to be heated formed of a material having low magnetic permeability and high electrical conductivity, reduces buoyancy acting on the object to be heated, and has little loss. Can be provided. In addition, the effect of reducing buoyancy is greater than when the thickness of the electrical conductor is sufficiently large, and in addition, loss due to heat generation of the electrical conductor can be reduced.

The first invention includes a main body and an aluminum or copper or top plate provided on an upper portion of the body for placing the object to be heated made of a low permeability material having these substantially equal or higher electrical conductivity constituting an outer shell And a heating coil that is provided below the top plate and that is supplied with a high-frequency current of about 70 kHz to induction-heat the object to be heated, and is provided between the heating coil and the object to be heated , the heating coil wherein when the magnetic field is generated from the buoyant reducing function of reducing the buoyancy acting on the object to be heated, and a aluminum or copper electrical conductors, induction heating and the thickness of the electrical conductors and the 10~30μm It is a device.

In the present invention, an electrical conductor is provided between the heating coil and the object to be heated, and the thickness thereof is made thinner than the penetration depth of the high-frequency current induced by the heating coil current of about 70 kHz . Therefore, the high frequency magnetic field generated from the heating coil reaches the object to be heated while penetrating and passing through the electric conductor. That is, the total heating area viewed from the heating coil is the area covered by the electrical conductor as viewed from the heating coil, and the area covered by the electrical conductor as viewed from the heating coil. The area to be heated is added. The electric conductor has an action of strengthening the magnetic coupling between the heating coil and the object to be heated. By increasing the total heating area seen from this heating coil, the equivalent series resistance of the heating coil increases, the current flowing through the heating coil when obtaining the same output can be reduced, and the buoyancy acting on the object to be heated is reduced. To do.

The electric conductor is 10 to 30 μm and is sufficiently thin, and a high-frequency magnetic field generated from the heating coil penetrates and passes through the electric conductor. In other words, a large induced current that does not allow the magnetic field from the heating coil to pass through does not occur inside the electric conductor. Compared to the case where the thickness of the conventional electric conductor is sufficiently large, the thickness as in the present application is reduced. In an electrical conductor having a configuration that is thinner than the penetration depth of the high-frequency current induced by the heating coil current, it is possible to reduce loss due to heat generation of the electrical conductor. In addition, the effect of reducing buoyancy can be increased as compared with the case where the thickness of the conventional electric conductor is sufficiently large.

According to a second aspect of the invention, in the first aspect of the invention, the electric conductor is an induction heating device configured to be joined to the top plate. Accordingly, the heat generated by the electrical conductor, becomes more easily transmitted to the object to be heated location mounting the top plate and the top thereof to suppress the electrical conductor temperature, it is possible to increase the heating efficiency of the object to be heated.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited by this embodiment.

(Embodiment 1)
FIG. 1 shows an induction heating apparatus according to Embodiment 1 of the present invention, and is a schematic cross-sectional view of a main part of an induction heating cooker.

  In FIG. 1, a top plate 2 made of heat-resistant ceramics, which is an insulator, is provided on an upper portion of a main body 1 constituting an outer shell. Below the top plate 2, there is provided a heating coil 3 that is formed by winding a stranded wire bundled with strands in a multilayered manner on a flat plate. The rod-shaped ferrite 4 is arranged substantially in parallel with the surface of the heating coil 3, and in particular, both ends thereof are bent upward and vertically toward the top plate 2.

  Between the top plate 2 and the heating coil 3, a conductive coating film 5 made of a carbon material is disposed between insulating plates 6 and 7 made of mica. This conductive coating 5 is connected to the terminal 8 and further to a commercial power source potential via a capacitor 9 or to a potential obtained by rectifying a commercial power source input by an inverter (not shown) for supplying a high frequency current to the heating coil 3 or to the ground. Connected.

  The thermistor 10 serving as temperature detecting means is in contact with the surface of the top plate 2 on the heating coil 3 side.

  The electric conductor 11 is formed of an aluminum coating having a thickness of about 15 μm, and is provided between the insulating plate 6 and the top plate 2. In particular, the electric conductor 11 is bonded to the surface of the top plate 2 on the heating coil 3 side by transfer. ing.

  FIG. 2 is a shape diagram of the electric conductor 11 as viewed from the heating coil 3 side. The electric conductor 11 has a substantially donut shape whose outer diameter and inner diameter are substantially the same as those of the heating coil 3, and a slit 12 having a width of 10 mm is provided from the outer periphery to the inner periphery. I am doing. An opening 13 is provided at the center, and the outer periphery thereof is set smaller than the outer end of the ferrite 4. In the inner periphery of the electric conductor 11, about 40 slits 14 having a depth of about 25 mm and a width of about 1 mm are provided radially from the center.

Heated object 15 made of a low permeability material with aluminum or copper or their substantially equivalent or electrical conductivity, so as to face the heating coil 3 across the top plate 2, is location mounting on the top plate 2 .

  In the above configuration, the operation of the present embodiment will be described.

  The heating coil 3 is supplied with a high-frequency current of about 70 kHz. The heating coil 3 generates a magnetic field when a high-frequency current is supplied, but there is a ferrite 4 that is a high permeability material below the heating coil 3, and the magnetic field concentrates on the ferrite 4, so that the magnetic field is heated 15. Can be prevented from swelling to the opposite side. The same effect can be obtained by configuring the ferrite 4 by combining a plurality of ferrite cores.

  On the other hand, since the magnetic field emitted upward of the heating coil 3 is linked to the electric conductor 11, an induced current is induced inside the electric conductor 11. At this time, the frequency of the induced current is about 70 kHz, and the penetration depth δ of the induced current when the electric conductor 11 is made of aluminum is about 300 μm. In the present embodiment, since the electric conductor 11 is about 15 μm, which is sufficiently thinner than the penetration depth of the induced current, the magnetic field from the heating coil 3 cannot be shielded, and the magnetic field penetrates and passes through the electric conductor 11. Then, it is guided toward the object to be heated 15. Since both end portions of the ferrite 4 are bent vertically upward, the ferrite 4 has an action of efficiently inducing a magnetic field toward the heated object 15 above.

  The magnetic field emitted upward of the heating coil 3 becomes a combined magnetic field of the magnetic field that has permeated and passed through the electric conductor 11 and the magnetic field that has passed through the slits 12 and 14 and the opening 13 of the electric conductor 11 and reaches the object 15 to be heated. To do. The induced current induced in the object to be heated 15 is generated by this combined magnetic field. For this reason, the presence of the electric conductor 11 changes the induced current distribution as compared to the case without the electric conductor 11.

  The total heating area to be induction-heated as viewed from the heating coil 3 is the area of the electric conductor 11 and the heated object 15 above the slits 12 and 14 and the opening 13 that is not covered by the electric conductor 11 as viewed from the heating coil 3. In addition, the area to be heated 15 of the portion covered with the electric conductor 11 when viewed from the heating coil 3 is added to the area. The electric conductor 11 has an action of strengthening the magnetic coupling between the heating coil 3 and the object to be heated 15. By increasing the total heating area as viewed from the heating coil 3, the equivalent series resistance of the heating coil 3 is increased, so that the current flowing through the heating coil 3 when obtaining the same output can be reduced. Buoyancy is reduced.

  FIG. 3 shows the relationship between the thickness of the electrical conductor 11 and the equivalent series resistance of the heating coil 3 measured with the aluminum pan as the object to be heated 15 in the same position arrangement as in the heated state (shown in FIG. 3A). And an example of a measurement result is shown about the case where there is no to-be-heated material 15 (it shows by FIG.3 (b)). However, the high frequency current frequency of the heating coil 3 is about 70 kHz.

  As shown in FIG. 3 (b), when there is no object to be heated 15, the equivalent series resistance increases monotonically from 0 (no state) to 10 μm, and monotonically decreases when the thickness of the electric conductor 11 is 10 μm or more. is doing. In the region where the penetration depth δ of the induced current in aluminum exceeds about 300 μm, the equivalent series resistance has a substantially constant value.

  This is presumably because the electric conductor 11 is the object to be heated instead of the article 15 to be heated. When the electrical conductivity of the aluminum electrical conductor 11 is σ, the thickness is t, and the penetration depth of the induced current in the electrical conductor 11 is δ, when the thickness of the electrical conductor 11 is smaller than δ, the electrical conductor 11 skin The high-frequency resistance Rs (hereinafter simply referred to as the skin resistance) viewed from the induced current flowing through is defined by Rs = 1 / (t · σ). That is, the skin resistance is inversely proportional to the thickness t. When the thickness of the electric conductor 11 is larger than δ, it is defined by Rs = 1 / (δ · σ), and the skin resistance is a constant value.

  When the thickness of the electric conductor 11 is 0 (no state) to 10 μm, the thickness of the electric conductor 11 is sufficiently small, and the skin resistance is theoretically very large. That is, it becomes a state close to an insulator, and the magnetic field generated from the heating coil 3 easily passes therethrough, so that the state is almost the same as when there is no electric conductor 11. The equivalent series resistance of the heating coil 3 is substantially the same as the high-frequency resistance of the heating coil 3 without the object to be heated 15 and the electric conductor 11 and the combined resistance such as the high-frequency resistance of the nearby ferrite 4 and is a small value. However, it increases monotonically as the thickness of the electrical conductor 11 increases. In the region where the thickness of the electric conductor 11 is 10 μm or more and 300 μm or less, the equivalent series resistance of the heating coil 3 also decreases monotonously in a substantially inversely proportional relationship with the thickness of the electric conductor 11 due to the influence of the skin resistance reduction of the electric conductor 11. In the region where the thickness of the electric conductor 11 is 300 μm or more, the skin resistance of the electric conductor 11 is constant, so that the equivalent series resistance of the heating coil 3 is also substantially constant.

  On the other hand, when the object to be heated 15 is present as shown in FIG. 3A, the equivalent series resistance increases monotonously and has a peak when the thickness of the electric conductor 11 is 0 to 15 μm. The equivalent series resistance monotonously decreases and becomes the minimum until the thickness of the electric conductor 11 becomes 200 μm. The equivalent series resistance again monotonously increases until the thickness of the electric conductor 11 is 1200 μm.

  The peak of the equivalent series resistance of the heating coil 3 when the thickness of the electric conductor 11 is 15 μm is the same as in FIG. 3B when there is no object to be heated 15, and the thickness of the electric conductor 11 is sufficiently small and the skin resistance of the electric conductor 11 is large. This is considered to be caused by a balance between a region that is regarded as an insulator and a region where the thickness increases to some extent and the electric resistance skin resistance decreases.

  From another viewpoint, as described above, it can be said that the effect of increasing the apparent total induction heating area due to the magnetic field penetrating and passing through the electric conductor 11 is maximum when the electric conductor 11 has a thickness of 15 μm.

  Further, in the region where the thickness of the electric conductor 11 is 15 μm or more, the thickness of the electric conductor 11 increases, and thus the skin resistance of the electric conductor 11 decreases monotonously. Furthermore, since the induced current easily flows inside the electric conductor 11, the magnetic field generated from the heating coil 3 is shielded to some extent, and the total heating area viewed from the heating coil 3 is reduced. That is, the equivalent series resistance of the heating coil 3 is reduced.

  On the other hand, since the electric conductor 11 that is in a state in which an induced current easily flows with a small skin resistance is arranged at a position close to the heating coil 3, the magnetic coupling between the heating coil 3 and the electric conductor 11 is strong, An effect of increasing the equivalent series resistance of the coil 3 also occurs. The sufficiently thick electric conductor 11 shields the magnetic field generated from the heating coil 3, but a part of the magnetic field bypasses the electric conductor 11 and induction heats the side opposite to the heating coil 3 of the electric conductor 11. Even when the skin depth of 11 exceeds about 300 μm, the equivalent series resistance of the heating coil 3 increases. Therefore, it is estimated that the equivalent series resistance of the heating coil 3 has a minimum point when the thickness of the electric conductor 11 is 200 μm. However, if the thickness of the electric conductor 11 is equal to or greater than a certain value, the equivalent series resistance of the heating coil 3 becomes a substantially constant value.

  As a result of detailed studies, the inventors have found a point where the equivalent series resistance of the heating coil 3 is maximized when the thickness of the electric conductor 11 is about 15 μm. Therefore, the current flowing through the heating coil 3 when obtaining the same output can be reduced, and the buoyancy acting on the object to be heated 15 is reduced. According to experiments by the inventors, if the equivalent series resistance of the heating coil 3 is the same regardless of whether the electrical conductor 11 is thinner or thicker than the penetration depth of the induced current, the same heating coil 3 current reduction effect and buoyancy reduction are achieved. It was confirmed that an effect was obtained. Moreover, since the equivalent series resistance of the heating coil 3 is almost uniquely determined with respect to the target buoyancy as the induction heating device, the thickness of the electric conductor 11 is changed to obtain a predetermined heating coil 3 equivalent series resistance. Is possible. Accordingly, when buoyancy acting on the object to be heated 15 is accepted to some extent, in the heating configuration of the present embodiment, induction that provides a predetermined buoyancy by setting the thickness of the electric conductor 11 to be smaller or larger than 15 μm. A heating device is obtained.

  In particular, from the experimental data shown in FIG. 3 (a), when the thickness of the electric conductor is thick, the maximum point of 3.6Ω is shown at 1000 μm, and from the figure, the thickness at the electric conductor is less than the penetration depth. When the thickness is set to 10 to 30 μm, an equivalent series resistance value higher than 3.6Ω can be obtained, and the effect of reducing buoyancy is great compared to the case where the thickness of the conventional electric conductor is sufficiently large. It is possible to reduce loss due to heat generation.

  Further, since the electric conductor 11 is thin, the high frequency magnetic field generated from the heating coil 3 penetrates and passes through the electric conductor 11. That is, a large energy that generates a repulsive magnetic field that does not allow the magnetic field from the heating coil 3 to pass through, that is, a large induced current is not generated inside the electric conductor 11, compared to a case where the thickness of the electric conductor 11 is large. Thus, loss due to heat generation of the electric conductor 11 can be reduced, and cooling in the vicinity of the heating coil 3 can be facilitated. Further, it is possible to increase the electric power transmitted to the object to be heated 15 and improve the heating efficiency.

  The electrical conductor 11 is provided with slits 12 and 14. The slit 12 that divides the electric conductor 11 into two parts is induced by a magnetic field generated from the heating coil 3, and suppresses an induced current inside the electric conductor 11 that flows in the circumferential direction of the heating coil 3. FIG. 4 is a diagram showing the induced current flowing inside the electric conductor 11, and shows the case where there is no slit 12 (shown in FIG. 4A) and the case where there is a slit 12 (shown in FIG. 4B). It is. For simplification, unlike the electric conductor 11 in the present embodiment, it is shown in a shape without the slit 14. As shown in FIG. 4A, when there is no slit 12, the magnetic field generated from the heating coil 3 generates a concentric induction current in a large loop inside the electric conductor 11. This induced current is distributed so as to flow largely in an intermediate portion between the inner peripheral portion and the outer peripheral portion of the heating coil 3, and generates a large amount of heat. However, as shown in FIG. 4B, by providing the slit 12, the induced current that becomes a loop is suppressed, and thus it is possible to suppress the heat generation of the electric conductor 11.

  Further, as shown in FIG. 2, by providing the slit 14 in the inner peripheral portion of the electric conductor 11, it is possible to set a long current path for the induced current in the inner peripheral portion of the electric conductor 11. The peripheral resistance increases. Since the induced current flows in a direction in which it easily flows, the amount of induced current in the inner periphery of the electric conductor 11 is reduced and heat generation is also suppressed. That is, the slit 14 is an induction current limiting unit that limits the induced current generated in the electric conductor 11, and is a heat generation limiting unit that limits heat generation by the induced current.

The electric conductor 11 is joined to the surface of the top plate 2 on the heating coil 3 side by transfer. Therefore, to the heating of the electrical conductors 11 is easy to give the top plate 2 by heat conduction, the same applies with respect to the heated object 15 which is location placing the top plate 2 upper. Thus, the increase in loss due to the heat generated in the electric conductor 11 is transmitted to the object to be heated 15 as a result, and the temperature of the electric conductor 11 can be suppressed and the heating efficiency of the object to be heated 15 can be increased.

The conductive coating 5 is provided close to the upper portion of the heating coil 3 and is connected to the commercial power source potential or the rectified potential of the commercial power source input to the inverter that supplies high-frequency current to the heating coil 3 or the ground via the capacitor 9. Therefore, the leak current leaking from the heating coil 3 to the user can be reduced. In addition, since the conductive coating 5 has a small film thickness and low electrical conductivity, the amount of induction current is extremely small, and there is almost no action to change the distribution of the magnetic field generated from the heating coil 3 . Such an effect of increasing the equivalent series resistance, an effect of reducing the heating coil 3 current, and an effect of reducing the buoyancy are hardly obtained.

  As described above, according to the present embodiment, the thickness of the electric conductor 11 is made thinner than the penetration depth of the high-frequency current induced by the heating coil 3 current. Therefore, the high frequency magnetic field generated from the heating coil 3 reaches the object to be heated 15 while penetrating and passing through the electric conductor 11. That is, the total heating area as viewed from the heating coil 3 is the area of the electric conductor 11 and the area of the object to be heated 15 that is not covered with the electric conductor 11 when viewed from the heating coil 3. The area to be heated 15 of the portion covered with 11 is added. The electric conductor 11 has an action of strengthening the magnetic coupling between the heating coil 3 and the object to be heated 15. By increasing the total heating area as viewed from the heating coil 3, the equivalent series resistance of the heating coil 3 is increased, so that the current flowing through the heating coil 3 when obtaining the same output can be reduced. Buoyancy is reduced.

  Further, the electric conductor 11 is sufficiently thin, and the high frequency magnetic field generated from the heating coil 3 penetrates and passes through the electric conductor 11. That is, a large induced current that does not allow the magnetic field from the heating coil 3 to pass through is not generated inside the electric conductor 11, and compared to a case where the thickness of the electric conductor 11 is large, loss due to heat generation of the electric conductor 11. Can be reduced.

The electric conductors 11, by means such as a transfer, because it is joined to the top plate 2, the heat generated by the electrical conductor 11, more transferred to the heated object 15 which is location placing the top plate 2 and its upper Therefore, the temperature of the electric conductor 11 can be suppressed and the heating efficiency of the object to be heated 15 can be increased.

  In the present embodiment, the electric conductor 11 is transferred to the top plate 2. However, the present invention is not limited to this. For example, the electric conductor 11 and the top plate 2 may be joined by thermal spraying or vapor deposition. Further, the electric conductor 11 may be made of copper instead of aluminum, and the top plate 2 may be plated. Furthermore, a minute unevenness may be formed by surface processing of the top plate 2 to enhance the bondability between the electric conductor 11 and the top plate 2. It is only necessary to select an appropriate joining means in order to adopt a material of the electric conductor 11 that is easy to manufacture and low in cost and to have a required thickness of the electric conductor 11.

  Moreover, since the electric conductor 11 is joined to the top plate 2, it is easy to handle at the time of assembly in a factory or the like.

  The electric conductor 11 has an inner diameter and an outer diameter that are substantially the same as those of the heating coil 3. However, the larger the area of the electric conductor 11 and the closer the electric conductor 11 is to the heating coil 3, the equivalent series resistance of the heating coil 3. The increase effect of is increased. In order to obtain the necessary buoyancy reduction effect, it may be determined in consideration of conditions such as the area of the electric conductor 11, the distance between the electric conductor 11 and the heating coil 3, and heat generation of the electric conductor 11.

  Moreover, since the electrical conductor 11 is provided with the opening 13, the magnetic field generated from the vicinity of the center of the heating coil 3 and particularly directed upward by the end portion on the inner peripheral side of the ferrite 4 is concentrated and the article 15 to be heated is concentrated. To reach. Therefore, it is possible to increase the magnetic field reaching the object to be heated 15 and improve the heating efficiency.

  As described above, the induction heating device according to the present invention can heat an object to be heated formed of a material having low magnetic permeability and high electrical conductivity, reduce buoyancy acting on the object to be heated, and Since an induction heating device with low loss can be provided, not only as an induction heating cooker, but also of induction heating water heaters and induction heating irons that heat materials with high electrical conductivity and low permeability such as aluminum and copper Or other induction heating type heating devices.

Main part schematic sectional drawing of the induction heating apparatus in Embodiment 1 of this invention Shape of electrical conductor as seen from the heating coil side of the induction heating device The figure which shows the correlation of the electric conductor thickness of the same induction heating device and the equivalent series resistance of the heating coil The figure which shows the induction current which flows into the inside of the electric conductor 11 of the same induction heating apparatus Main part perspective view of a conventional induction heating device Cross section of the main part of the induction heating device The figure which shows the correlation of the equivalent series resistance and buoyancy of the heating coil of the same induction heating device The figure which shows the correlation of the equivalent series resistance of the heating coil of the same induction heating apparatus, and a heating coil electric current value The figure which shows the correlation of the buoyancy which acts on the to-be-heated material, and the thickness of the electrical conductor of the induction heating apparatus

Explanation of symbols

1 Body 2 Top plate 3 Heating coil 11 Electrical conductor 15 Object to be heated

Claims (2)

A body constituting an outer shell, and aluminum or copper or top plate provided on an upper portion of the body for placing them substantially object to be heated made of low permeability material having a same or higher electrical conductivity, of the top plate A heating coil that is provided below and that is provided with a high-frequency current of about 70 kHz to inductively heat the object to be heated, and is provided between the heating coil and the object to be heated, and when a magnetic field is generated from the heating coil And an aluminum or copper electrical conductor having a buoyancy reduction function for reducing the buoyancy acting on the object to be heated , wherein the thickness of the electrical conductor is 10 to 30 μm. The induction heating apparatus according to claim 1, wherein the electrical conductor is configured to be joined to the top plate.

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