JP7640252B2 - Induction Heating Equipment - Google Patents

Description

The present invention relates to induction heating technology.

In the aluminum melting and holding process of aluminum casting, the aluminum ingot is preheated, for example, to about 150°C before being placed in a melting furnace in order to remove moisture, etc. This preheating of the aluminum ingot is typically performed using hot air generated by burning fossil fuels (for example, see Patent Document 1 below).

JP 2018-69333 A

However, the above-mentioned method of preheating aluminum ingots with hot air (hereinafter referred to as the hot air method) leaves room for improvement. For example, the hot air method has low efficiency (for example, 10 to 20%), so there is a need to improve efficiency. In addition, from the viewpoint of reducing _CO2 emissions, it is desirable to electrify the heating method. One method of electrification is the induction heating method, but aluminum has low electrical resistance and requires a large current for heating. In order to pass such a large current through the heating coil, an inverter for induction heating customized to the required heating conditions is required, but such an inverter is relatively expensive and cost reduction is required. Alternatively, the hot air method requires a preheating space, so the equipment becomes large, so there is a need to make the equipment compact.

These issues are not limited to preheating aluminum ingots to around 150°C, but are also common when preheating to just before melting (for example, around 500°C). Furthermore, these issues are not limited to aluminum casting, but are also common to various aluminum heat treatments (for example, the process of heating aluminum billets in forging) and the heat treatment of various non-magnetic metals (for example, copper).

The present invention has been made to solve at least some of the above problems, and can be realized, for example, in the following form:

According to a first aspect of the present invention, an induction heating device is provided. This induction heating device has an output frequency of 10 kHz or more and 100 kHz or less, and a rated output of 3 kW or more and 30 kW or less, and is equipped with an IH inverter with a first resonant capacitor built in, a transformer, a second resonant capacitor, and a heating coil. The transformer has a primary coil and a secondary coil with fewer turns than the primary coil. The IH inverter is connected to the primary coil, and the second resonant capacitor and the heating coil are connected to the secondary coil.

According to this induction heating device, an IH inverter having an output frequency of 10 kHz or more and 100 kHz or less and a rated output of 3 kW or more and 30 kW or less and a first resonant capacitor is used. Such an IH inverter is distributed as a general-purpose product designed for commercial IH cooking heaters (for example, for food service centers). Therefore, it is not necessary to use an inverter customized to the heating conditions in the heating coil, so that costs can be reduced. In addition, in a general-purpose IH inverter, the upper limit value of the current is relatively small, but since a transformer is interposed between the IH inverter and the heating coil, the current flowing through the heating coil can be amplified. Moreover, since a second resonant capacitor is interposed between the transformer and the heating coil, a resonant circuit can be formed on the secondary side of the transformer. In other words, the entire circuit including the IH inverter with the first resonant capacitor built in and the heating coil becomes a resonant circuit, and the transformer acts as a large inductance, and there is no occurrence of an event in which the number of turns of the heating coil must be reduced. Therefore, the number of turns of the heating coil can be secured to be large. By ensuring sufficient current and number of turns of the heating coil in this way, even if a general-purpose IH inverter is used, the heating capacity required to heat non-magnetic metals (especially aluminum) can be ensured and efficiency can be improved. Note that in this application, "aluminum" is used to mean both pure aluminum and aluminum alloys.

According to the second aspect of the present invention, in the first aspect, the heating coil is a solenoid coil. The induction heating device further includes a transport means for transporting the object to be heated so that it passes through the inside of the solenoid coil. According to this aspect, the object to be heated can be heated while being transported, so that the installation space of the equipment can be reduced. Furthermore, as long as the size of the object to be heated can pass through the inside of the solenoid coil, it can be heated regardless of the shape of the object to be heated. Furthermore, the temperature of each cross section perpendicular to the transport direction of the object to be heated can be made uniform.

According to the third embodiment of the present invention, the heating coil in the first embodiment is a planar coil. The induction heating device further includes a transport means for transporting the object to be heated so that it passes near the planar coil. According to this embodiment, the object to be heated can be heated while being transported, so that the installation space of the equipment can be reduced. In addition, since the object to be heated can be heated simply by bringing it close to the planar coil (in other words, since there is no need to pass the object to be heated through the inside of the solenoid coil as in the second embodiment), no space is required to put the object to be heated in and out of the solenoid coil. Therefore, further space saving is possible. In addition, even if the size of the object to be heated changes, the object can be heated as long as the shape of the surface of the object facing the planar coil does not change substantially, and this has excellent versatility.

According to a fourth aspect of the present invention, in the third aspect, the planar coil includes a first planar coil and a second planar coil connected in series to each other. The first planar coil and the second planar coil are arranged so as to be aligned in a direction perpendicular to the transport direction of the object to be heated. According to this aspect, if the object to be heated is transported so that the longitudinal direction of the object is perpendicular to the transport direction of the object to be heated, it is possible to further save space while increasing the number of turns of the planar coil as a whole.

According to the fifth aspect of the present invention, in the fourth aspect, the length of the first planar coil and the second planar coil in the transport direction is 200 mm or more. With this aspect, the number of turns of the planar coil as a whole can be further increased. Furthermore, if the object to be heated is, for example, an aluminum ingot having a short-side length of 100 mm or less, the two ingots can be heated simultaneously.

According to the sixth aspect of the present invention, in the fourth or fifth aspect, the planar coil includes a third planar coil and a fourth planar coil. The first planar coil, the second planar coil, the third planar coil, and the fourth planar coil are connected in series with each other. The third planar coil and the fourth planar coil are arranged so as to be aligned in a direction perpendicular to the conveying direction. The first planar coil, the second planar coil, the third planar coil, and the fourth planar coil are arranged so that the first planar coil and the second planar coil and the third planar coil and the fourth planar coil face each other with the area in which the heated object is conveyed sandwiched therebetween. According to this aspect, if the heated object is conveyed so that the longitudinal direction of the heated object is perpendicular to the conveying direction of the heated object, the heated object can be heated more uniformly while earning the number of turns of the planar coil as a whole. In addition, since the required number of turns of the heating coil can be distributed to the first to fourth planar coils, the number of turns per one planar coil can be reduced. In other words, the length of each of the first to fourth planar coils in the transport direction of the objects to be heated can be reduced. Therefore, the objects to be heated can be heated one by one.

According to the seventh aspect of the present invention, a method for heating a non-magnetic metal object is provided. This method includes the steps of preparing an induction heating device according to any one of the first to sixth aspects, and heating the object by the induction heating device. This method provides the same effects as the first to sixth aspects. This method is particularly suitable for heating aluminum and copper, which have low electrical resistance.

1 is a schematic diagram showing a circuit configuration of an induction heating device according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing an example of the configuration of an aluminum ingot transport means. FIG. 2 is a schematic diagram showing an example of a configuration of an aluminum ingot transport means and an arrangement of heating coils. FIG. 2 is a schematic diagram showing an example of a configuration of an aluminum ingot transport means and an arrangement of heating coils.

Figure 1 is a schematic diagram showing the circuit configuration of an induction heating device 10 (hereinafter simply referred to as heating device 10) according to one embodiment of the present invention. In the following, the heating device 10 is described as being used to preheat an aluminum ingot as an object to be heated in aluminum casting. As shown in the figure, the heating device 10 is equipped with an IH inverter 30. The IH inverter 30 is a general-purpose IH inverter designed for commercial IH cooking heaters (e.g., for food service centers), and has an output frequency of 10 kHz or more and 100 kHz or less, and a rated output of 3 kW or more and 30 kW or less. Typically, a general-purpose IH inverter with a rated output of 3 kW, 5 kW, 10 kW, 15 kW, 20 kW, or 30 kW can be selected depending on the heating conditions.

Since the configuration of a general-purpose IH inverter is well known, the IH inverter 30 will be briefly described. In this embodiment, the IH inverter 30 employs a full-bridge configuration consisting of four IGBTs. However, a half-bridge configuration may also be employed. The IH inverter 30 is connected to an AC power source 20. First resonant capacitors 31 and 32 are connected to the IGBTs as viewed from the AC power source 20 side.

This IH inverter 30 is designed on the assumption that no impedance matching device is connected beyond the first resonant capacitors 31, 32 as viewed from the AC power source 20 side. In other words, the IH inverter 30 is commercially available with a heating coil directly connected beyond the first resonant capacitors 31, 32 as viewed from the AC power source 20 side. In this embodiment, the IH inverter 30 is incorporated into the heating device 10 with this heating coil removed.

The heating device 10 further includes a transformer 40, second resonant capacitors 51 and 52, and a heating coil 60 for heating an aluminum object to be heated. The IH inverter 30 is connected to the primary coil 41 of the transformer 40, and the second resonant capacitors 51 and 52 and the heating coil 60 are connected to the secondary coil 42 of the transformer 40. In this embodiment, the second resonant capacitors 51 and 52 are connected in series with the heating coil 60. The number of turns of the secondary coil 42 is less than the number of turns of the primary coil 41.

According to this heating device 10, the transformer 40 is interposed between the general-purpose IH inverter 30 and the heating coil 60, so that the current flowing through the heating coil 60 can be amplified. Moreover, the second resonant capacitors 51 and 52 are interposed between the transformer 40 and the heating coil 60, so that a series resonant circuit can be formed on the secondary side of the transformer 40. In other words, the entire circuit including the IH inverter 30 with the first resonant capacitors 31 and 32 built in and the heating coil 60 becomes a resonant circuit, so that the transformer 40 acts as a large inductance, and the inductance of the heating coil 60 cannot be secured large (i.e., the number of turns of the heating coil 60 must be reduced). Therefore, the number of turns of the heating coil 60 can be secured large. By sufficiently securing the current and the number of turns of the heating coil 60 in this way, the heating capacity required for heating aluminum can be secured even when a general-purpose IH inverter 30 is used. In addition, the efficiency can be improved to about 55%. Moreover, by using a general-purpose IH inverter 30, costs can be significantly reduced compared to using an inverter customized to the heating conditions of the heating coil. Normally, when designing an induction heating circuit, it is common technical knowledge to determine the specifications from the heating coil side and then the power supply specifications last, but in this embodiment, the above-mentioned effects are achieved by determining the power supply specifications first, based on the opposite idea.

The number and connection form of the second resonant capacitors interposed between the transformer 40 and the heating coil 60 are not limited to the example shown in FIG. 1, and may be changed as appropriate. For example, the number of second resonant capacitors may be one. Alternatively, the number and connection form of the second resonant capacitors interposed between the transformer 40 and the heating coil 60 are not limited to the example shown in FIG. 1, and may be changed as appropriate. For example, the number of second resonant capacitors may be one. Alternatively, a second resonant capacitor may be interposed in parallel between the transformer 40 and the heating coil 60, and a parallel resonant circuit may be formed only on the secondary side of the transformer 40.

2 is a schematic diagram showing an example of the configuration of the conveying means for the aluminum ingot 90. In this example, a plurality of conveying rollers 80 having insulating properties are used as the conveying means for the aluminum ingot 90. The conveying rollers 80 are configured to be rotated by a motor or a chain (not shown). Two coil units 70 including an IH inverter 30, a transformer 40, second resonant capacitors 51 and 52, and a heating coil 60 are arranged side by side in the conveying direction D1 of the aluminum ingot 90. The heating coil 60 is a solenoid coil. The aluminum ingot 90 is conveyed by the conveying rollers 80 so as to pass through the inside of the heating coil 60. The two coil units 70 are arranged at a distance of about 100 mm to 150 mm to avoid magnetic field interference. The length of the conveying direction D1 of the heating coil 60 is, for example, 250 mm to 300 mm, and the number of turns of the heating coil 60 can be about 30 for one coil unit 70. The number of coil units 70 installed can be set to any number greater than or equal to 1 depending on the heating conditions and transport speed.

According to the configuration of FIG. 2, the aluminum ingot 90 can be preheated while being transported, thereby saving space in the equipment. Furthermore, as long as the size of the aluminum ingot 90 is such that it can pass through the inside of the heating coil 60, it can be heated regardless of the shape of the aluminum ingot 90. Furthermore, the temperature of each cross section perpendicular to the transport direction D1 can be made uniform.

Figure 3 is a schematic diagram showing an example of the configuration of the transport means for the aluminum ingot 90 and the arrangement of the heating coils. Figure 3(a) is a view from the front in the transport direction D2 of the aluminum ingot 90, and Figure 3(b) is a plan view. In this example, two insulating conveyors 180 are used as the transport means for the aluminum ingot 90. The two conveyors 180 are arranged at a distance from each other in a direction perpendicular to the transport direction D2. The aluminum ingot 90 is stretched between the two conveyors 180 so that its longitudinal direction is perpendicular to the transport direction D2.

In this example, the heating coil 60 is a planar coil, and one coil unit includes a first planar coil 61 and a second planar coil 62. The first planar coil 61 and the second planar coil 62 are connected in series without any other elements interposed therebetween, and are arranged so as to be aligned in a direction perpendicular to the conveying direction D2. The first planar coil 61 and the second planar coil 62 are arranged between the two conveyors 180 so that the aluminum ingot 90 passes near the first planar coil 61 and the second planar coil 62. A small gap is formed between the aluminum ingot 90 and the first planar coil 61 and the second planar coil 62.

According to the configuration of FIG. 3, the aluminum ingot 90 can be heated while being transported, so the equipment can be space-saving. Also, since there is no need to pass the aluminum ingot 90 through the inside of the heating coil 60 as in the example of FIG. 2, no space is required to insert and remove the aluminum ingot 90 from the heating coil 60, so space can be further saved. Even if the size of the aluminum ingot 90 changes, as long as the shape of the surface of the aluminum ingot 90 facing the heating coil 60 remains almost the same, the aluminum ingot 90 can be heated, so this is highly versatile. Furthermore, the arrangement of the first planar coil 61 and the second planar coil 62 increases the number of turns of the heating coil 60 as a whole, thereby saving space.

In this embodiment, the length L1 in the transport direction D2 of each of the first planar coil 61 and the second planar coil 62 is 200 mm or more. This allows the heating coil 60 to have a total of about 30 turns. In this case, as shown in FIG. 3(b), two aluminum ingots 90 having a short-side length L2 of 100 mm or less can be heated simultaneously.

Although only one coil unit is shown in FIG. 3, two or more coil units may be arranged side by side in the conveying direction D2 depending on the heating conditions and conveying speed.

Figure 4 is a schematic diagram showing another example of the configuration of the conveying means for the aluminum ingot 90 and the arrangement of the heating coil. The configuration shown in Figure 4 differs from the configuration shown in Figure 3 in that the heating coil 60 includes a third planar coil 63 and a fourth planar coil 64 in addition to the first planar coil 61 and the second planar coil 62. The first planar coil 61, the second planar coil 62, the third planar coil 63, and the fourth planar coil 64 are connected in series without any other elements being interposed. The third planar coil 63 and the fourth planar coil 64 are arranged to be aligned in a direction perpendicular to the conveying direction D2. The first planar coil 61 and the second planar coil 62, and the third planar coil 63 and the fourth planar coil 64 are arranged to face each other with the conveying area of the aluminum ingot 90 between them. More specifically, the first planar coil 61 and the second planar coil 62 are located below the transport area of the aluminum ingot 90, and the third planar coil 63 and the fourth planar coil 64 are located above the transport area of the aluminum ingot 90.

In this example, the length L3 in the transport direction D2 of the first planar coil 61, the second planar coil 62, the third planar coil 63, and the fourth planar coil 64 is about half the length L1 in the transport direction D2 of the first planar coil 61 and the second planar coil 62 in FIG. 3. However, since the third planar coil 63 and the fourth planar coil 64 are added, the heating coil 60 as a whole can have about the same number of turns as in the example in FIG. 3. Therefore, the same effect as in the example in FIG. 3 can be obtained.

In this example, as shown in FIG. 4(b), the aluminum ingots 90 can be efficiently heated one by one. In addition, since the same number of turns as in the example of FIG. 3 can be secured, the heating time for the aluminum ingots 90 can be halved compared to the example of FIG. 3. With this configuration, when continuously heating a predetermined number of aluminum ingots 90, the first and last aluminum ingots 90 transported can also be efficiently heated. Although only one coil unit is shown in FIG. 4, two or more coil units may be arranged side by side in the transport direction D2 depending on the heating conditions and transport speed.

Although the embodiments of the present invention have been described above, the above-mentioned embodiments of the invention are intended to facilitate understanding of the present invention and do not limit the present invention. The present invention may be modified or improved without departing from its spirit, and the present invention includes equivalents thereof. Furthermore, any combination or omission of each component described in the claims and specification is possible within the scope of solving at least part of the above-mentioned problems or achieving at least part of the effects.

For example, the transport methods shown in Figures 3 and 4 are merely examples, and the heating device 10 shown in Figure 1 can be combined with any transport method. For example, an insulating robot arm may be used. In this case, the aluminum ingot 90 may be heated while being transported vertically. The coil arrangement of the heating coil 60 shown in Figures 2 to 4 may also be changed to any form. For example, a two-layer wound coil may be used.

Alternatively, the heating device 10 can be applied to various aluminum heating processes, not limited to preheating the aluminum ingot 90. For example, the heating device 10 may be used to heat an aluminum billet in forging. In this case, for example, a two-layer solenoid coil may be used as the heating coil 60.

Furthermore, the above-mentioned heating device 10 is particularly suitable for heating aluminum and copper, which have low electrical resistance, but can be applied to heating any non-magnetic metal.

REFERENCE SIGNS LIST 10... induction heating device 20... AC power supply 31... first resonant capacitor 40... transformer 41... primary coil 42... secondary coil 51... second resonant capacitor 60... heating coil 61... first planar coil 62... second planar coil 63... third planar coil 64... fourth planar coil 70... coil unit 80... conveying roller 90... aluminum ingot 180... conveyor D1, D2... conveying direction

Claims (7)

An induction heating device, comprising:
an IH inverter having an output frequency of 10 kHz or more and 100 kHz or less and a rated output of 3 kW or more and 30 kW or less, and having a first resonant capacitor built therein;
A transformer having a primary coil and a secondary coil having fewer turns than the primary coil;
a second resonant capacitor;
A heating coil;
the IH inverter is connected to the primary coil, and the second resonant capacitor and the heating coil are connected to the secondary coil ;
The second resonant capacitor and the heating coil form a resonant circuit on the secondary side of the transformer.
Induction heating equipment. 2. The induction heating device according to claim 1,
the induction heating device includes a plurality of coil units each including the IH inverter, the transformer, the second resonant capacitor, and the heating coil;
the heating coil is a solenoid coil;
The induction heating device further includes a conveying means for conveying an object to be heated through an inside of the solenoid coil,
The induction heating device, wherein the plurality of coil units are arranged adjacent to each other in a conveying direction of the object to be heated. 2. The induction heating device according to claim 1,
The heating coil is a planar coil,
The induction heating device further includes a transport means for transporting an object to be heated so that the object passes near the planar coil. 4. The induction heating device according to claim 3,
the planar coil comprises a first planar coil and a second planar coil connected in series with each other;
The induction heating device, wherein the first planar coil and the second planar coil are arranged to be aligned in a direction perpendicular to a transport direction of the object to be heated. 5. The induction heating device according to claim 4,
The induction heating device, wherein the first planar coil and the second planar coil have a length in the transport direction of 200 mm or more. The induction heating device according to claim 4 or 5,
the planar coil comprises a third planar coil and a fourth planar coil;
the first planar coil, the second planar coil, the third planar coil, and the fourth planar coil are connected in series with each other;
the third planar coil and the fourth planar coil are arranged to be aligned in a direction perpendicular to the transport direction,
the first planar coil, the second planar coil, the third planar coil, and the fourth planar coil are arranged such that the first planar coil and the second planar coil, and the third planar coil and the fourth planar coil face each other with a region in which the object to be heated is transported therebetween. A method for heating a non-magnetic metal object, comprising the steps of:
A step of preparing an induction heating device according to any one of claims 1 to 6;
and heating the object to be heated by the induction heating device.

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