JP7781582B2 - Heat Treatment Equipment - Google Patents

Description

The present invention relates to a heat treatment device.

Induction heating coils are known for performing heat treatments such as hardening on metal shafts or other workpieces (see, for example, Patent Document 1). The high-frequency heating coil described in Patent Document 1 is intended to provide satisfactory heating for workpieces of different thicknesses without the need to replace the coil. This high-frequency heating coil has a first heating coil connected to a high-frequency power source and a second heating coil through which an induced current from the first heating coil flows.

The first and second heating coils are configured to be movable relative to each other in a direction perpendicular to the axial centerline of the rotatably supported workpiece. When induction heating workpieces of different thicknesses, the first and second heating coils are moved relative to each other. This changes the distance between the two heating coils, allowing the workpiece to be inserted between the two heating coils.

Japanese Patent Application Publication No. 8-73927

However, the configuration described in Patent Document 1 requires equipment to move the first and second heating coils relative to each other. Because a large current flows through the heating coils, generating heat, a cooling water passage is provided inside. Therefore, in order to move the two heating coils relative to each other, the relative movement of the cooling water passage must also be taken into consideration, resulting in a large-scale facility. Furthermore, with the configuration described in Patent Document 1, the first and second heating coils must be moved relative to each other and the relative distance between these coils must be set each time the diameter of the workpiece is changed. In carburizing processes and the like, in order to heat the workpiece evenly, particularly its surface, the relative distance between the heating coil and the workpiece must be set, and the process of setting the relative positions of the two heating coils is time-consuming.

In view of the above problems, one object of the present invention is to provide a heat treatment device that does not require changing the relative positions of the components that make up the coil even when the thickness of the workpiece is changed.

(1) In order to solve the above problem, a heat treatment apparatus according to one aspect of the present invention includes a coil for induction heating an axial workpiece and a power source for supplying current to the coil, wherein the coil includes two heating conductors extending along the axial direction of the workpiece and a connecting conductor connecting ends of the two heating conductors, the two heating conductors being connected to the power source, the distance between the two heating conductors being set to a value smaller than the maximum outer dimension of the workpiece in an axial cross section so that separate workpieces of different thicknesses can be induction heated evenly without changing the relative positions of the two heating conductors depending on the outer dimensions of the workpiece, the distance between the connecting conductor and the workpiece being set to a value larger than the distance between the two heating conductors and the workpiece so that heating due to eddy currents caused by magnetic flux from the connecting conductor is suppressed at both axial ends of the workpiece, and the two heating conductors are opposed to the workpiece, and induction heating is performed while the two heating conductors and the workpiece are rotated relative to each other.

According to the present invention, separate workpieces of different thicknesses can be uniformly induction heated without changing the relative positions of the two heating conductors depending on the external dimensions of the workpieces, and further, heating due to eddy currents caused by magnetic flux from the connecting conductors at both axial ends of the workpieces can be suppressed.

FIG. 1 is a schematic plan view of a heat treatment apparatus according to the present invention, showing a state in which an object to be treated is placed at an induction heating position. FIG. 2 is an enlarged perspective view of a part of the induction heating coil of the heat treatment apparatus. FIG. 3 is a perspective view showing an induction heating coil and an object to be treated at an induction heating position. Fig. 4(A) is a cross-sectional view taken along line IVA-IVA in Fig. 3, with the back side of the cross section partially omitted. Fig. 4(B) is a cross-sectional view taken along line IVB-IVB in Fig. 3, with the back side of the cross section partially omitted. FIG. 5 is a conceptual plan view for explaining induction heating positions according to the outer dimensions of the workpiece. FIG. 6 shows a modified example of the connecting conductor. FIG. 7 is a diagram showing a modified example in which a third portion is provided in the induction heating coil. Fig. 8(A) is a schematic perspective view showing a modified example in which the workpiece is frustum-shaped and two heating conductors are arranged in a shape that conforms to the shape of the workpiece. Fig. 8(B) is a cross-sectional view taken along line VIIIB-VIIIB in Fig. 8(A), with the back side of the cross section not shown. FIG. 9 shows a modified example in which multiple pairs of two heating conductors are provided. FIG. 10 is a diagram showing a modified example in which the induction heating coil is rotated.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 is a schematic plan view of the heat treatment apparatus 1 of the present invention, showing the workpiece 100 placed at the induction heating position P1. In Figure 1, dashed arrows indicate electrical connections. Figure 2 is an enlarged perspective view of a portion of the induction heating coil 20 of the heat treatment apparatus 1. Figure 3 is a perspective view showing the induction heating coil 20 and the workpiece 100 at the induction heating position P1. Figure 4(A) is a cross-sectional view taken along line IVA-IVA in Figure 3, with the back side of the cross section partially omitted. Figure 4(B) is a cross-sectional view taken along line IVB-IVB in Figure 3, with the back side of the cross section partially omitted.

In the following, as shown in each figure, the left-right direction X, the front-back direction Y, and the up-down direction Z are defined based on the state in which the induction heating coil 20 of the heat treatment device 1 is viewed from the front. Furthermore, unless otherwise specified, the description will be based on the state in which the workpiece 100 is placed at the induction heating position P1. In this embodiment, the axial direction S of the workpiece 100 is parallel to the up-down direction Z. Note that the workpiece 100 may be induction heated by the heat treatment device 1 with the axial direction S of the workpiece 100 facing horizontally or in a direction inclined relative to the horizontal plane.

Referring to Figures 1 to 4(B), the heat treatment device 1 is configured to perform heat treatment on the workpiece 100 by induction heating. This heat treatment is a heating treatment. Examples of heat treatment include heat treatment for quenching, carburizing heat treatment, and soaking treatment. The heat treatment device 1 is a batch processing device that induction heats the workpiece 100 one by one. The heat treatment device 1 may induction heat the workpiece 100 in an air atmosphere, or may induction heat the workpiece 100 in an inert gas atmosphere such as nitrogen gas.

In this embodiment, the workpiece 100 is a metal part, for example, a metal shaft used as a material for a torque transmission shaft. Note that the workpiece 100 is not limited to a typical long metal shaft, but also includes a metal ring or other form with a short axial direction. In this embodiment, the workpiece 100 is a hollow shaft. In this embodiment, the workpiece 100 has a cross-sectional shape perpendicular to the axial direction S at any position in the axial direction S of the workpiece 100, which is a circle with a predetermined thickness. In this embodiment, the workpiece 100 is described as a hollow shaft, but this does not have to be the case. The workpiece 100 may also be a solid shaft.

In this embodiment, the workpiece 100 has a cross-sectional shape perpendicular to the axial direction S that varies depending on the position in the axial direction S. In this embodiment, the workpiece 100 includes a first axial portion 101 and a second axial portion 102 having an outer dimension (outer diameter) larger than that of the first axial portion 101. In this embodiment, there are two types of outer dimensions D100 of each part of the workpiece 100 in the axial direction S: outer dimension D101 of the first axial portion 101 and outer dimension D102 of the second axial portion 102. Outer dimension D102 is the maximum value of the outer dimension D100 of the workpiece 100. In this embodiment, the first axial portion 101 and the second axial portion 102 are arranged coaxially, but they may not be arranged coaxially and one may be eccentric with respect to the other.

The heat treatment device 1 has an induction heating coil 20, a power supply 3 that supplies current to the induction heating coil 20, a support mechanism 4 that supports and transports the workpiece 100, and a control unit 5.

The power supply 3 is a power supply circuit connected to a commercial power source, and converts the commercial power into power of a predetermined voltage, current, and frequency, and outputs it to the induction heating coil 20. Note that the power supply 3 is not limited to a high-frequency power supply, as long as it can cause the induction heating coil 20 to apply a magnetic flux to the workpiece 100, thereby inductively heating the workpiece 100.

The induction heating coil 20 is provided to inductively heat the workpiece 100. In this embodiment, the induction heating coil 20 is made of a material, such as copper, that generates an alternating magnetic flux when a high-frequency current is passed through it. The induction heating coil 20 may be formed by fastening multiple components together by brazing or the like, or it may be an integrally molded product formed by a lost-wax method or a metal additive manufacturing method. The heating conductors 21 and 22 and the connecting conductors 25 and 26 of the induction heating coil 20, which will be described later, may be made of the same material or different materials.

In this embodiment, the induction heating coil 20 inductively heats the workpiece 100, which is positioned vertically. For this reason, the induction heating coil 20 is formed in an elongated shape along the axial direction S of the workpiece 100 (along the vertical direction Z). The induction heating coil 20 is formed in a hollow shape, and a cooling water passage is formed inside the induction heating coil 20. Cooling water is circulated between the induction heating coil 20 and a heat exchanger, not shown, using a cooling water pump (not shown), to cool the induction heating coil 20.

The induction heating coil 20 is formed by molding a hollow, elongated material into the shape of the induction heating coil 20. In this embodiment, the cross-sectional shape of the induction heating coil 20 in a cross section perpendicular to the longitudinal direction of the induction heating coil 20 is a quadrangular ring shape (a square ring shape).

The cross-sectional shape of the induction heating coil 20 may be a circular ring, an elliptical ring, or a polygonal ring shape other than a square, and the specific shape is not limited. The induction heating coil 20 inductively heats the workpiece 100 when power is applied from the power source 3. In this embodiment, the induction heating coil 20 heats the workpiece 100 over the entire area of the workpiece 100 in the axial direction S. The induction heating coil 20 may also be a solid coil, resulting in a compact interior.

The induction heating coil 20 has two heating conductors, a first heating conductor 21 and a second heating conductor 22, extending along the axial direction S of the workpiece 100, a first connecting conductor 25 and a second connecting conductor 26 that connect these heating conductors 21 and 22, and a first terminal 27 and a second terminal 28 that connect to the power source 3.

The first heating conductor 21 and the second heating conductor 22 are provided to apply an alternating magnetic flux to the workpiece 100 to generate eddy currents in the workpiece 100. In this embodiment, the first heating conductor 21 and the second heating conductor 22 are formed in an elongated shape in the vertical direction Z and are arranged facing each other in the horizontal direction X. In this embodiment, the heating conductors 21 and 22 are formed in a symmetrical shape except for the connection portions with the terminals 27 and 28. In this embodiment, the heating conductors 21 and 22, the connecting conductors 25 and 26, and the terminals 27 and 28 of the induction heating coil 20 are integrally molded products, and their relative positions are constant.

The length of the heating conductors 21, 22 in the vertical direction Z (axial direction S) is longer than the overall length of the workpiece 100. This allows the workpiece 100 to be positioned so that the magnetic flux from the heating conductors 21, 22 acts on the entire area of the workpiece 100 in the axial direction S, thereby inductively heating the workpiece 100. In this embodiment, one side surface 21e, 22e of each heating conductor 21, 22 (a plane facing the workpiece 100, a vertical plane) faces the central axis B1 of the workpiece 100.

The heating conductors 21 and 22 are formed to a shape that matches the outer shape of the workpiece 100. Specifically, the heating conductors 21 and 22 have first portions 21a and 22a and second portions 21b and 22b.

In this embodiment, the second portions 21b and 22b are arranged below the first portions 21a and 22a.

The first portions 21a, 22a are portions that are arranged opposite the first shaft portion 101. The first portions 21a, 22a and the first shaft portion 101 face each other in a direction (horizontal direction) perpendicular to the axial direction S. In the axial direction S, it is preferable that the length of each of the first portions 21a, 22a is longer than the length of the first shaft portion 101. With this preferable configuration, the entire first shaft portion 101 can be arranged within the area in which the first portions 21a, 22a are arranged in the axial direction S. Therefore, magnetic flux from the first portions 21a, 22a can be applied evenly across the entire first shaft portion 101, generating eddy currents evenly in the first shaft portion 101 and enabling induction heating. Furthermore, the first shaft portion 101 can be positioned below the upper ends 21f, 22f of the first portions 21a, 22a, and the distance between the first connecting conductor 25 and the first shaft portion 101 can be increased, making it more difficult for magnetic flux from the first connecting conductor 25 to reach the upper end of the first shaft portion 101. This makes it possible to suppress excess heating due to eddy currents generated in the first shaft portion 101 due to magnetic flux from the first connecting conductor 25.

The second portions 21b and 22b are positioned opposite the second shaft portion 102. The second portions 21b and 22b face the second shaft portion 102 in a direction (horizontal direction) perpendicular to the axial direction S. In the axial direction S, it is preferable that the length of each of the second portions 21b and 22b is longer than the length of the second shaft portion 102. With this preferred configuration, the entire second shaft portion 102 can be positioned within the region in which the second portions 21b and 22b are positioned in the axial direction S. Therefore, the magnetic flux from the second portions 21b and 22b can be applied evenly across the entire area of the second shaft portion 102, generating eddy currents evenly in the second shaft portion 102 and enabling induction heating. Furthermore, the second shaft portion 102 can be positioned above the lower ends 21g, 22g of the second portions 21b, 22b, and the distance between the second connecting conductor 26 and the second shaft portion 102 can be increased, making it more difficult for magnetic flux from the second connecting conductor 26 to reach the lower end of the second shaft portion 102. This makes it possible to suppress excess heating due to eddy currents generated in the second shaft portion 102 as a result of magnetic flux from the second connecting conductor 26.

The two heating conductors 21, 22 are arranged at positions corresponding to the outer dimension D100 in the axial cross section of the workpiece 100. By linking the positions of the two heating conductors 21, 22 to the outer dimension D100 at each position in the axial direction S of the workpiece 100, the distance D10 between the workpiece 100 and the two heating conductors 21, 22 is set to be equal . The distance D3 is the distance between the two heating conductors 21, 22.

In this embodiment, as viewed from the axial direction S, the second portions 21b, 22b are arranged in regions on the side away from the workpiece 100 relative to the corresponding first portions 21a, 22a. In this embodiment, the second portions 21b, 22b are arranged offset by a predetermined offset amount OF (shown in FIG. 4A ) from the corresponding first portions 21a, 22a along a direction perpendicular to the corresponding one side surface 21e, 22e of the heating conductors 21, 22. As a result, the distance from the central axis B1 of the workpiece 100 to each of the second portions 21b, 22b is longer than the distance from the central axis B1 of the workpiece 100 to each of the first portions 21a, 22a. Meanwhile, in this embodiment, the offset amount OF is approximately the difference between the radius of the second shaft portion 102 and the radius of the first shaft portion 101. As a result, the distance D10 (shortest distance D11) between each first portion 21a, 22a of the heating conductors 21, 22 and the first axis portion 101 of the workpiece 100 and the distance D10 (shortest distance D12) between each second portion 21b, 22b of the heating conductors 21, 22 and the second axis portion 102 of the workpiece 100 are set to be equal .

In this embodiment, the first portions 21a and 22a are arranged opposite the first shaft portion 101, and the second portions 21b and 22b are arranged opposite the second shaft portion 102, but this is not necessarily the case. For example, the lower end of the first shaft portion 101 on the second shaft portion 102 side and the second portions 21b and 22b may be arranged to face each other horizontally, or the upper end of the second shaft portion 102 on the first workpiece 100 side and the first portions 21a and 22a may be arranged to face each other horizontally.

When the workpiece 100 is induction heated, a portion of the workpiece 100 is positioned between the first heating conductor 21 and the second heating conductor 22 in the circumferential direction C. The distance D3 between the two heating conductors 21, 22 is set to a value smaller than the maximum value D102 of the outer dimension D100 of the workpiece 100 in an axial cross section. In this embodiment, at locations where the first heating conductor 21 and the second heating conductor 22 are positioned to sandwich a portion of the workpiece 100, the distance D3 between the two heating conductors 21, 22 at each position in the axial direction S is set to a value smaller than the outer dimension D100 of the workpiece 100 at that position.

Referring to Figures 4(A) and 4(B), in this embodiment, at the location where the first shaft portion 101 is disposed, the distance D3 (D31) between the two heating conductors 21, 22 is set to be less than the outer dimension D101 of the first shaft portion 101 (D31 < D101). Similarly, in this embodiment, at the location where the second shaft portion 102 is disposed, the distance D3 (D32) between the two heating conductors 21, 22 is set to be less than the outer dimension D102 of the second shaft portion 102 (D32 < D102).

At least a portion of the workpiece 100 at induction heating position P1 is sandwiched between the heating conductors 21 and 22 at a location (rear portion 105) that is located rearward from the central axis B1 of the workpiece 100 in the workpiece carry-in direction A1, which will be described later. A distance D4 from the central axis B1 to the rear portion 105 (the distance between the central axis B1 and the heating conductors 21 and 22 in the front-to-rear direction Y) is specified. At each portion in the axial direction S, the upper limit of distance D4 is less than the radius of the workpiece 100 at that portion. Meanwhile, at each portion in the axial direction S, a location (front portion 106) that is closer to the rear portion 105 in the workpiece carry-out direction A2, which will be described later, is not sandwiched between the heating conductors 21 and 22. In this embodiment, the central axis B1 of the workpiece 100 is located at a location that is located rearward from the area sandwiched between the heating conductors 21 and 22 in the workpiece carry-out direction A2.

With the above-described configuration, induction heating is performed by placing the workpiece 100 on the outside of the inner circumference of the induction heating coil 20, which is formed in a ring shape by the heating conductors 21, 22 and the connecting conductors 25, 26.

Referring again to Figures 1 to 4(B), in this embodiment, the opening angle θ (shown in Figure 1) is set to approximately 90 degrees. The opening angle θ is the minor angle between two lines extending from the central axis B1 toward the center of one side surface 21e, 22e of the heating conductors 21, 22, as viewed, for example, from the axial direction S. It is set in terms of design based on factors such as the size of the workpiece 100, the relative positional relationship between the workpiece 100 and the induction heating coil 20, which affects heat treatment quality, and the ease of attaching and detaching the workpiece 100. The opening angle θ is set, for example, between 30 and 150 degrees. Setting the opening angle θ within this range ensures that the two heating conductors 21, 22 are appropriately spaced apart in the circumferential direction C. This ensures that the magnetic flux from the heating conductors 21, 22 reaches a sufficiently large area of the workpiece 100 in the circumferential direction C, generating eddy currents over a wide area of the workpiece 100, enabling induction heating. Furthermore, the heating conductors 21 and 22 can be arranged so that the distance D3 between them is not greater than the maximum value D102 of the outer dimension D100 of the workpiece 100. Note that the opening angle θ is not limited to the above-mentioned angle range.

The upper ends 21f and 22f of the heating conductors 21 and 22 are located above the workpiece 100. Similarly, the lower ends 21g and 22g of the heating conductors 21 and 22 are located below the workpiece 100.

The upper ends 21f and 22f of the heating conductors 21 and 22 are connected to each other by a first connecting conductor 25. Similarly, the lower ends 21g and 22g of the heating conductors 21 and 22 are connected to each other by a second connecting conductor 26. The heating conductors 21 and 22 are connected to each other by the connecting conductors 25 and 26, thereby forming a series coil.

In this embodiment, the connecting conductors 25, 26 extend in a direction perpendicular to the axial direction S and are arranged horizontally. The distance (shortest distance) between the workpiece 100 and the first connecting conductor 25 is defined as the first distance D5 (D51). In this embodiment, the first distance D51 is the distance from the first axis portion 101 to the first connecting conductor 25. Similarly, the distance (shortest distance) between the workpiece 100 and the second connecting conductor 26 is defined as the first distance D5 (D52). In this embodiment, the first distance D52 is the distance from the second axis portion 102 to the second connecting conductor 26.

The distance (shortest distance) from the workpiece 100 to the heating conductors 21 and 22 is defined as the second distance D6. In this embodiment, the second distance D6 is the minimum value of the distance between the first portion 21a or 22a of either of the heating conductors 21 or 22 and the first axis portion 101, or the distance between the second portion 21b or 22b of either of the heating conductors 21 or 22 and the second axis portion 102. In this embodiment, the second distance D6 = distance D11 = distance D12. In this embodiment, the first distance D5 is greater than the second distance D6 (D51 > D6, D52 > D6). That is, the distances D51 and D52 between the connecting conductors 25 and 26 and the workpiece 100 are set to values greater than the distance D6 between the two heating conductors 21 and 22 and the workpiece 100. This makes it difficult for the magnetic flux from the connecting conductors 25, 26 to reach both axial ends of the workpiece 100, suppressing heating due to eddy currents caused by the magnetic flux at both axial ends of the workpiece 100.

In this embodiment, the connecting conductors 25, 26 are both formed symmetrically, but may also be formed asymmetrically. When viewed from the axial direction S, each connecting conductor 25, 26 is formed in a shape that resembles a partially cut-out rectangular frame. In this embodiment, within a horizontal region perpendicular to the axial direction S, each connecting conductor 25, 26 initially extends from the first heating conductor 21 away from the workpiece 100 generally along the radial direction of the workpiece 100, then changes direction by 90 degrees to extend toward the second heating conductor 22, then changes direction by 90 degrees at the center position between the heating conductors 21, 22 in the left-right direction X to extend toward the front-back direction Y, and then extends toward the workpiece 100 along the radial direction of the workpiece 100 to connect to the second heating conductor 22.

The first terminal 27 and the second terminal 28 are provided to supply high-frequency power from the power source 3 to the heating conductors 21 and 22. The heating conductors 21 and 22 are connected to the power source 3 via the terminals 27 and 28. In this embodiment, the terminals 27 and 28 are connected to the second heating conductor 22. Specifically, one end of the terminals 27 and 28 is connected to the middle of the second heating conductor 22 in the axial direction S. The other end of the terminals 27 and 28 is connected to an electrode of the power source 3 directly or via another conductive member (not shown), such as a connector.

While the terminals 27 and 28 are connected to the second heating conductor 22 in this embodiment, this is not necessarily the case. One end of the terminals 27 and 28 may be connected to either the heating conductors 21 and 22 or the connecting conductors 25 and 26. Furthermore, while the serially arranged conductors 21, 22, 25, and 26 are connected to the power source 3 via the terminals 27 and 28 in this embodiment, this is not necessarily the case. For example, the heating conductors 21 and 22 may be physically independent, preventing direct current from flowing between them. Specifically, a conductive member such as a cable may be connected to each of the upper and lower ends of the first heating conductor 21, connecting the power source 3 to the first heating conductor 21 via these conductive members, and a conductive member such as a cable may be connected to each of the upper and lower ends of the second heating conductor 22, connecting the power source 3 to the second heating conductor 22 via these conductive members. Furthermore, the power supply circuit to which the first heating conductor 21 is connected and the power supply circuit to which the second heating conductor 22 is connected may be separate power supply circuits that are independent of each other.

Next, we will explain the support mechanism 4.

The support mechanism 4 is configured to support the workpiece 100 and to allow the workpiece 100 to move relative to the induction heating coil 20. The support mechanism 4 transports the workpiece 100 between an induction heating position P1, which is the position during induction heating, and a retracted position P2 (shown in FIG. 1) where the workpiece 100 is retracted from the induction heating coil 20. The retracted position P2 is, for example, a position where the workpiece 100 is taken in and out of the heat treatment device 1, or a position where the workpiece 100 is transferred to and from another transport mechanism (not shown) within the heat treatment device 1.

The support mechanism 4 has a support table 41 on which the workpiece 100 is placed, and a transport mechanism 42 that transports the support table 41.

The support base 41 has a rotation motor 43 and a holder 44 that is rotated by the rotation motor 43.

When the workpiece 100 is induction heated, the rotary motor 43 rotates the workpiece 100 together with the holder 44 around an axis extending in the axial direction S (e.g., the central axis B1 of the workpiece 100). The rotary motor 43 has a housing 43a and an output shaft 43b protruding from the housing 43a. The holder 44 is attached to the output shaft 43b.

The holder 44 has a shaft 45, a mounting portion 46 attached to the lower part of the shaft 45, and a cap 47 attached to the upper part of the shaft 45.

The shaft 45 is connected to the output shaft 43b so as to be rotatable together with it, and is supported by the output shaft 43b. The shaft 45 may also be connected to the output shaft 43b via a speed reduction mechanism (not shown). In this embodiment, the shaft 45 extends in the vertical direction Z. The shaft 45 and the output shaft 43b may be attached removably, or may be molded integrally.

The mounting portion 46 is formed, for example, from an annular plate and is held by the shaft 45. It is preferable that the mounting portion 46 be detachable from the shaft 45. In this case, a mounting portion 46 of a size corresponding to the size of the workpiece 100 is attached to the shaft 45.

The mounting portion 46 may have any shape that allows the workpiece 100 to be placed thereon. The mounting structure to the shaft 45 is not limited, and the mounting portion 46 may be molded integrally with the shaft 45. Alternatively, the mounting portion 46 may have an internally threaded hole and the shaft 45 may have an external thread formed on its outer periphery, thereby threadably connecting the mounting portion 46 and the shaft 45. In this case, by adjusting the height position of the mounting portion 46 relative to the shaft 45, the height position of the workpiece 100 relative to the shaft 45 can be adjusted, and as a result, the height position of the workpiece 100 relative to the induction heating coil 20 can be adjusted. When the workpiece 100 is placed on the mounting portion 46, the shaft 45 penetrates the workpiece 100 in the axial direction S.

The cap 47 is formed, for example, from an annular plate, and is passed through by the shaft 45. The cap 47 presses the upper end of the workpiece 100 toward the mounting portion 46.

The cap 47 may have any shape that allows it to be placed on the upper end of the workpiece 100, and there are no limitations on the structure by which it is attached to the shaft 45. For example, the hole in the cap 47 may be an internally threaded hole and external threads may be formed on the outer periphery of the shaft 45, thereby threading the cap 47 and shaft 45 together. In this case, the workpiece 100 can be temporarily fixed to the shaft 45 by pressing the workpiece 100 in the vertical direction Z with the cap 47 and the mounting portion 46.

The holder 44 and workpiece 100 can be removed together from the rotary motor 43 by attaching and detaching the shaft 45 to and from the output shaft 43b of the rotary motor 43. The support table 41 (rotary motor 43 and holder 44) having the above configuration is transported between the induction heating position P1 and the retracted position P2 by the transport mechanism 42.

The transport mechanism 42 is, for example, an actuator including an electric motor, and is configured to rotate the support table 41 around the central axis B1 of the workpiece 100. The transport mechanism 42 may be configured to move the support table 41 at least in a direction perpendicular to the axial direction S (horizontal direction) relative to the heating conductors 21, 22 of the induction heating coil 20.

The transport mechanism 42 is, for example, a linear actuator that moves the support table 41 linearly between the induction heating position P1 and the retracted position P2. In this embodiment, the transport mechanism 42 supports the housing 43a of the electric motor 43 and moves this housing 43a between the induction heating position P1 and the retracted position P2. The transport mechanism 42 may also be a rotary actuator that moves (oscillates) the support table 41 back and forth between the induction heating position P1 and the retracted position P2 around a rotation axis parallel to the central axis B1.

The control unit 5 is formed using a PLC (Programmable Logic Controller) or the like. The control unit 5 is electrically connected to the power supply 3, the rotary motor 43, and the transport mechanism 42. The control unit 5 controls, for example, the output value (current, voltage, and frequency) of the power supply 3 and the on/off of the power supply from the power supply 3 to the induction heating coil 20. Regarding the control of the power supply 3, the control unit 5 may only control the on/off of the power supply from the power supply 3 to the induction heating coil 20. The control unit 5 controls the on/off of the drive of the rotary motor 43. The control unit 5 controls the position of the workpiece 100 by controlling the operation of the transport mechanism 42.

The control unit 5 stores position information for the induction heating position P1 corresponding to the outer dimension D100 of the workpiece 100. For example, the position of the induction heating position P1 corresponding to the outer dimension D100 of the workpiece 100 is set by an operator operating an operation unit (not shown) provided in the heat treatment device 1.

Figure 5 is a conceptual plan view illustrating the induction heating position P1 according to the outer dimension D100 of the workpiece 100. Figure 5 shows the outer edge shape of a relatively small-diameter workpiece 100 (1001) and the outer edge shape of a relatively large-diameter workpiece 100 (1002).

Referring to FIG. 5, when a workpiece 1001 with a relatively small diameter is to be induction heated, the control unit 5 sets the induction heating position P1 (P11) relatively farther back from the induction heating coil 20. As a result, the distance D10 between the workpiece 1001 and the first portions 21a, 22a of the heating conductors 21, 22 is set to a predetermined value. On the other hand, when a workpiece 1002 with a relatively large diameter is to be induction heated, the control unit 5 sets the induction heating position P1 (P12) relatively farther forward from the induction heating coil 20. As a result, the distance D10 between the workpiece 1002 and the first portions 21a, 22a of the heating conductors 21, 22 is set to the same value as the predetermined value.

In this way, the transport mechanism 42 of the support mechanism 4 changes the induction heating position P1 relative to the induction heating coil 20 depending on the external dimensions D100 of the workpiece 100.

Regardless of the outer dimension D100 of the workpiece 100, it is preferable that the distance D10 between the workpiece 100 and the heating conductors 21, 22 at the induction heating position P1, for example the distance D11 between the first shaft portion 101 and the first portions 21a, 22a of the heating conductors 21, 22, be a constant (fixed value). With this preferred configuration, the distance (gap) between the heating conductors 21, 22 and the workpiece 100 can be constant regardless of the outer dimension D100 of the workpiece 100. Therefore, regardless of the specific value of the outer dimension D100 of the workpiece 100, the magnetic flux density of the magnetic flux acting from the heating conductors 21, 22 to the workpiece 100 can be made more uniform, resulting in less variation in the amount of heat applied to each workpiece 100. This allows for more uniform quality of the workpieces 100.

Regarding the outer dimension D100 of the workpiece 100, the distance D10 between the workpiece 100 and the heating conductors 21, 22 at the induction heating position P1 may be a constant (fixed value), for example, the distance D12 between the second shaft portion 102 and the second portions 21b, 22b of the heating conductors 21, 22. In this case, too, the quality of the workpieces 100 can be made more uniform for the same reasons as in the configuration in which the distance D11 is a constant (fixed value) described above. In this way, regardless of the outer dimension D100 of the workpiece 100, it is preferable to set the induction heating position P1 so that the variation in the distance D10 between each part of the workpiece 100 and the heating conductors 21, 22 is minimized.

The above is a general description of the configuration of heat treatment apparatus 1. Next, an example of the heat treatment operation in heat treatment apparatus 1 will be described.

1 to 4(B), the heat treatment operation of the workpiece 100 in the heat treatment apparatus 1 begins with the holder 44, to which the workpiece 100 is attached, placed on the rotary motor 43 at the retracted position P2. From this state, the control unit 5 drives the transport mechanism 42 to transport the workpiece 100 and support base 41 from the retracted position P2 to the induction heating position P1. Next, the control unit 5 turns on the power supply from the power source 3 while rotating the output shaft 43b of the rotary motor 43. This supplies high-frequency power to the induction heating coil 20. As a result, the two heating conductors 21, 22 are positioned opposite the workpiece 100, and induction heating is performed while the two heating conductors 21, 22 and the workpiece 100 are rotated relative to each other around the central axis B1. At this time, the workpiece 100 receives magnetic flux from the heating conductors 21, 22 at the point sandwiched between them, generating eddy currents, resulting in induction heating. As the workpiece 100 is rotated by the rotary motor 43, the area sandwiched between the heating conductors 21 and 22 moves sequentially in the circumferential direction C. As a result, the workpiece 100 is induction heated over the entire area of the workpiece 100 in the circumferential direction C.

When a predetermined time has elapsed since the start of induction heating, the control unit 5 turns off the power supply from the power source 3 and stops the rotation of the output shaft 43b of the rotary motor 43. The control unit 5 then drives the transport mechanism 42 to transport the workpiece 100 and support table 41 from the induction heating position P1 to the retracted position P2, completing the heating process of the workpiece 100.

As described above, in this embodiment, the distance D3 between the two heating conductors 21 and 22 is set to a value smaller than the maximum value D102 of the outer dimension D100 of the workpiece 100 in the axial cross section, and induction heating is performed while the two heating conductors 21 and 22 and the workpiece 100 are rotated relative to each other. With this configuration, the two heating conductors 21 and 22 inductively heat the workpiece 100 while rotating relative to the workpiece 100, sandwiching the workpiece 100 at a location other than the thickest portion. This allows each portion of the workpiece 100 in the circumferential direction C to be sequentially positioned closest to the two heating conductors 21 and 22. That is, the workpiece 100 can be induction heated with the distance D10, which is the gap between the workpiece 100 and the two heating conductors 21 and 22, set uniformly at each portion of the workpiece 100 in the axial direction S. Therefore, induction heating can be achieved by applying magnetic flux uniformly to each portion of the workpiece 100 in the circumferential direction C. During this induction heating, the two heating conductors 21, 22 can instantaneously apply magnetic flux to a narrow portion of the workpiece 100 in the circumferential direction C of the workpiece 100 to uniformly heat the entire circumferential area of the workpiece 100, which is rotating relative to the two heating conductors 21, 22. Therefore, it is sufficient for the two heating conductors 21, 22 to be able to induction heat the narrow portion of the workpiece 100, regardless of the external dimensions of the workpiece 100. Then, by appropriately setting the relative positions of the two heating conductors 21, 22 and the workpiece 100 according to the external dimension D100 of the workpiece 100, it is possible to minimize changes in the relative distance (gap) between the two heating conductors 21, 22 and the workpiece 100 and to inductively heat the narrow portion of the workpiece 100 with a similar magnetic flux density, regardless of the external dimensions of the workpiece 100. That is, regardless of the value of the outer dimension D100 of the workpiece 100, changes in the heating conditions caused by the two heating conductors 21, 22 can be minimized. Moreover, since the relative distance between the two heating conductors 21, 22 and the workpiece 100 can be set according to the outer dimension D100 of the workpiece 100, it is not necessary to change the relative positions of the two heating conductors 21, 22 according to the outer dimension D100 of the workpiece 100. As described above, the heat treatment apparatus 1 can uniformly inductively heat separate workpieces 100 of different diameters. Furthermore, the heat treatment apparatus 1 does not require changing the relative positions of the components 21, 22 constituting the induction heating coil 20 even when the diameter of the workpiece 100 is changed.

In addition, according to this embodiment, the distances D51 and D52 between the connecting conductors 25 and 26 and the workpiece 100 are set to values greater than the distance D6 between the two heating conductors 21 and 22 and the workpiece 100 (D51 > D6, D52 > D6). With this configuration, the relatively large distance between the connecting conductors 25 and 26 and the workpiece 100 makes it difficult for the magnetic flux from the connecting conductors 25 and 26 to reach the workpiece 100. This prevents overheating of the workpiece 100, particularly near the connecting conductors 25 and 26, due to induction heating caused by the magnetic flux from the connecting conductors 25 and 26. In this embodiment, even though the ends of the workpiece 100 are located near the connecting conductors 25 and 26, overheating of the upper and lower ends of the workpiece 100 can be prevented. On the other hand, because the distance between the two heating conductors 21, 22 and the workpiece 100 is relatively small, the magnetic flux from the two heating conductors 21, 22 can be reliably applied to the workpiece 100, thereby reliably inductively heating the workpiece 100.

Furthermore, in this embodiment, the two heating conductors 21, 22 are positioned to correspond to the outer dimension D100 in the axial cross section of the workpiece 100. By adjusting the positions of the two heating conductors 21, 22 to correspond to the outer dimension D100 in the axial direction S of the workpiece 100, the distance D10 between the two heating conductors 21, 22 and the workpiece 100 is set to be uniform . This ensures a distance at which the workpiece 100 faces the two heating conductors 21, 22. This configuration makes it possible to more uniformize the relative distance (gap) between the two heating conductors 21, 22 and the workpiece 100 in a cross section perpendicular to the axial direction S at each position in the axial direction S of the workpiece 100. This makes it possible to more uniformize the density of the magnetic flux acting on the workpiece 100 from the two heating conductors 21, 22 at each position in the axial direction S, thereby more uniformizing the amount of heat generated by induction heating. Therefore, the entire workpiece 100 can be induction-heated more uniformly.

The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the claims. Below, differences from the above-described embodiment will be mainly explained, and similar components to those in the above-described embodiment will be assigned the same reference numerals in the figures, and detailed explanations will be omitted.

(1) In the above embodiment, the shape of each of the connecting conductors 25, 26 as viewed in the axial direction S is described as a shape equivalent to a portion of a rectangular frame, but this need not be the case. The shape of each of the connecting conductors 25, 26 as viewed in the axial direction S may be, for example, a shape equivalent to a portion of a polygonal frame such as a triangular frame or a pentagonal frame, or may be a horseshoe shape, a shape equivalent to a portion of a circular arc frame, or a shape equivalent to a portion of an elliptical frame. Furthermore, as long as the connecting conductors 25, 26 do not interfere with the workpiece 100 and the first distance D5 (D51, D52) is equal to or greater than the second distance D6, the shape and size of the connecting conductors 25, 26 are not limited to the above-described sizes.

(2) In the above embodiment, the connecting conductors 25, 26 are arranged horizontally along a horizontal direction perpendicular to the axial direction S, but this is not necessarily the case. For example, the connecting conductors 25, 26 may be inclined relative to the horizontal direction so that they move further away from the workpiece 100 as they move away from the heating conductors 21, 22. Furthermore, the distance between each connecting conductor 25, 26 and the workpiece 100 may be sufficiently large so that the density of the magnetic flux from the connecting conductors 25, 26 is sufficiently small at the workpiece 100, and the amount of heating of the workpiece 100 by the connecting conductors 25, 26 is sufficiently small. In this case, the connecting conductors 25, 26 may be inclined relative to the horizontal direction so that they move closer to the workpiece 100 as they move away from the heating conductors 21, 22.

For example, as shown in the modified example of FIG. 6, the connecting conductors 25, 26 may be arranged vertically. FIG. 6 is a diagram showing a modified example of the connecting conductors 25, 26. In this modified example, the connecting conductors 25, 26 extend away from the corresponding upper end portions 21f, 22f and lower end portions 21g, 22g of the heating conductors 21, 22 along the axial direction S, with the portions on the heating conductor 21 side and the portions on the heating conductor 22 side connected to each other. In this case, the connecting conductors 25, 26 may be formed in a shape corresponding to a portion of a polygonal frame when viewed from a direction perpendicular to the axial direction S, or may have a horseshoe shape, a shape corresponding to a portion of a circular arc frame, or a shape corresponding to a portion of an elliptical frame. Although the connecting conductors 25, 26 are arranged symmetrically in the axial direction S in the above-described embodiment and the modified example shown in FIG. 6, they may also be arranged asymmetrically in the axial direction S.

(3) In addition, in the above-described embodiment, the entire area of the workpiece 100 in the axial direction S is induction heated, but this does not have to be the case. For example, only a portion of the workpiece 100 in the axial direction S may be heated by the induction heating coil 20. In this case, the total length (length in the axial direction S) of the two heating conductors 21, 22 may be shorter than the configuration described in the embodiment.

(4) Furthermore, in the above-described embodiment, an example was described in which the workpiece 100 has two portions with different external dimensions (two shaft portions 101, 102). However, this does not have to be the case. For example, as shown in the modified example of FIG. 7, the workpiece 100 may include a third shaft portion 103 in addition to the first shaft portion 101 and the second shaft portion 102.

Figure 7 shows a modified example in which third portions 21c and 22c are provided in the induction heating coil 20. The outer dimension D100 (D103) of the third shaft portion 103 is larger than the outer dimension D100 (D101 and D102) of the shaft portions 101 and 102 and is the maximum outer dimension of the workpiece 100. In this case, during induction heating of the workpiece 100, each heating conductor 21 and 22 of the induction heating coil 20 includes the third portions 21c and 22c in addition to the first and second portions 21a, 22a, 21b, and 22b. The third portions 21c and 22c are arranged opposite the third shaft portion 103 in a direction perpendicular to the axial direction S. The third portions 21c and 22c are arranged in a region away from the workpiece 100 relative to the second portions 21b and 22b. The distance D3 between the two heating conductors 21 and 22 is set to a value smaller than the maximum value D103 of the outer dimension D100 of the workpiece 100 in its axial cross section.

The distance D10 (D13) between the third portions 21c, 22c of the heating conductors 21, 22 and the third axial portion 103 is preferably the same as the distance D10 (D12) between the second portions 21b, 22b of the heating conductors 21, 22 and the second axial portion 102. Similarly, the distance D13 is preferably the same as the distance D10 (D11) between the first portions 21a, 22a of the heating conductors 21, 22 and the first axial portion 101. With this configuration, the two heating conductors 21, 22 are disposed at positions corresponding to the outer dimension D100 in the axial cross section of the workpiece 100, and the positions of the two heating conductors 21, 22 are linked to the outer dimension D100 at each position in the axial direction S of the workpiece 100, thereby setting the distances D11, D12, D13 between the two heating conductors 21, 22 and the workpiece 100 uniformly . Therefore, the density of the magnetic flux acting from the heating conductors 21 and 22 can be made more uniform in each of the first to third shaft portions 101 to 103, and the amount of heating due to eddy currents generated by the magnetic flux can be made more uniform, resulting in more uniform heat treatment quality for the first to third shaft portions 101 to 103.

(5) Note that the arrangement order of the first to third portions 21a, 21b, and 21c of the first heating conductor 21 in the axial direction S and the arrangement order of the first to third portions 22a, 22b, and 22c of the second heating conductor 22, i.e., the arrangement order of the axial portions 101, 102, and 103, are shown as an example in FIG. 7, but are not particularly limited. On the other hand, it is preferable that the distance D10 (D11) between the first axial portion 101 and the first portions 21a and 22a, the distance D10 (D12) between the second axial portion 102 and the second portions 21b and 22b, and the distance D10 (D13) between the third axial portion 103 and the third portions 21c and 22c are the same.

(6) Four or more types of shaft portions with different outer dimensions may be provided in the workpiece 100. In this case, it is preferable that the shapes of the heating conductors 21, 22 are set so that the distances between the first and second heating conductors 21, 22 and the corresponding shaft portions are equal and generally coincident with each other at each position in the axial direction S.

(7) Alternatively, the workpiece 100 may be inductively heated by the induction heating coil 20, with the second shaft portion 102 disposed between two first shaft portions 101, 101 along the axial direction S. In this case, the heating conductors 21, 22 are respectively arranged along the axial direction S in the order of first portions 21a, 22a, second portions 21b, 22b, and first portions 21a, 22a. Alternatively, the workpiece 100 may be inductively heated by the induction heating coil 20, with the second shaft portion 102 disposed between two second shaft portions 102, 102 along the axial direction S. In this case, the heating conductors 21, 22 are respectively arranged along the axial direction S in the order of second portions 21b, 22b, first portions 21a, 22a, and second portions 21b, 22b.

(8) The workpiece 100 may also be a linear shaft with a single outer dimension. In this case, the heating conductors 21, 22 are arranged linearly along the axial direction S.

(9) The workpiece 100 may also be configured so that its outer dimensions change continuously along the axial direction S by being formed in a truncated cone shape. Figure 8(A) is a schematic perspective view showing a modified example in which the workpiece 100 is truncated cone-shaped and the two heating conductors 21, 22 are arranged in a shape that follows the shape of the workpiece 100. Figure 8(B) is a cross-sectional view taken along line VIIIB-VIIIB in Figure 8(A), with the back portion of the cross section not shown.

Referring to Figures 8(A) and 8(B), the outer peripheral surface of the workpiece 100 in this modified example is formed in a truncated cone shape. The outer peripheral surface of the workpiece 100 is inclined at an inclination angle θ' with respect to the axial direction S. The outer dimension D100 of the workpiece 100 increases as it progresses downward, and the outer dimension D100' at the bottom end of the workpiece 100 is the maximum outer dimension of the workpiece 100 in an axial cross section. The thickness of the workpiece 100 may be constant at each part in the axial direction S, or may increase as it progresses downward; the specific value is not limited.

The two heating conductors 21, 22 extend along the axial direction S of the workpiece 100. Each heating conductor 21, 22 is inclined at an inclination angle θ' with respect to the axial direction S, and in this modified example, they are arranged symmetrically. The distance D3 between the two heating conductors 21, 22 is set to a value smaller than the maximum outer dimension D100' of the workpiece 100 in an axial cross section.

Furthermore, the two heating conductors 21, 22 are arranged at positions corresponding to the outer dimension D100 in the axial cross section of the workpiece 100, and the positions of the two heating conductors 21, 22 are linked to the outer dimension D100 at each position in the axial direction S of the workpiece 100, thereby setting an equal distance between the two heating conductors 21, 22 and the workpiece 100. More specifically, the inclination angle θ' of the outer peripheral surface of the workpiece 100 with respect to the axial direction S and the inclination angles of the heating conductors 21, 22 are both the same. With this configuration, the distance D10 between the heating conductors 21, 22 and the workpiece 100 can be made equal at each position in the axial direction S where the truncated cone-shaped workpiece 100 is arranged. Therefore, the density of the magnetic flux acting on the workpiece 100 from the heating conductors 21, 22 can be made more uniform at each part of the axial direction S, and the amount of heating of the workpiece 100 due to eddy currents generated by the action of the magnetic flux can be made more uniform at each part of the workpiece 100.

(10) In the above-described embodiment, a pair of two heating conductors 21, 22 has been described as an example. However, this is not necessarily the case. As shown in the modified example of FIG. 9, multiple pairs of two heating conductors (two pairs in FIG. 9) may be provided. FIG. 9 illustrates a modified example in which multiple pairs of two heating conductors are provided. In FIG. 9, an induction heating coil 20A is provided in addition to the induction heating coil 20. That is, the heat treatment apparatus 1 has a first pair of heating conductors 21, 22 and a second pair of heating conductors 21A, 22A. The heating conductors 21A, 22A are formed in the same shape as the heating conductors 21, 22, except that they are positioned in front of the heating conductors 21, 22 in the front-to-rear direction Y and on the outside in the left-to-right direction X. The upper ends of the heating conductors 21A, 22A are connected by a first connecting conductor 25A, and the lower ends of the heating conductors 21A, 22A are connected by a second connecting conductor (not shown). It is preferable that the positions of the first pair of heating conductors 21, 22 and the second pair of heating conductors 21A, 22A in the axial direction S are aligned. In this case, high-frequency power is supplied to each induction heating coil 20, 20A from the power source 3. The phases of the high-frequency currents in each induction heating coil 20, 20A are aligned. In this modification, the two pairs of heating conductors 21, 22; 21A, 22A allow a greater amount of magnetic flux to act on the workpiece 100 in a short period of time, generating a greater amount of eddy current in the workpiece 100 and enabling the workpiece 100 to be heated more quickly.

(11) In the above embodiment, the cross-sectional shape of the workpiece 100 in a cross section perpendicular to the axial direction S is annular, but this does not have to be the case. The cross-sectional shape of the workpiece 100 may be annular with a polygonal shape greater than a triangle .

(12) In addition, in the above-described embodiments and modifications, the induction heating coil 20, 20A is not rotated, and the workpiece 100 is rotated by the rotation motor 43. However, this is not necessarily the case. For example, the induction heating coil 20 may be rotated around the workpiece 100. FIG. 10 is a diagram showing a modification in which the induction heating coil 20 is rotated. Referring to FIG. 10, in this modification, the heat treatment device 1 has a coil rotation mechanism 50 that rotates the induction heating coil 20 around the workpiece 100. The specific configuration of the coil rotation mechanism 50 is not limited as long as it is capable of rotating the induction heating coil 20 (heating conductors 21, 22, connecting conductors 25, 26, and terminals 27, 28) around the central axis B1. In this modification, the coil rotation mechanism 50 has a rotating member 51 fixed to the first connecting conductor 25 and a coil rotation motor 52 that rotates the rotating member 51. The coil rotation motor 52 is connected to the control unit 5, and its operation is controlled by the control unit 5. A pinion gear, for example, is connected to the output shaft of the coil rotation motor 52 so that they can rotate together, and external teeth formed on the outer periphery of the rotating member 51 mesh with this pinion gear. The terminals 27, 28 are connected to the power source 3, for example, via a flexible cable that can maintain a connection with the terminals 27, 28 within the rotation range of the induction heating coil 20. This maintains the connection between the terminals 27, 28 and the power source 3 regardless of the position of the induction heating coil 20 in the circumferential direction C. Note that any configuration that allows relative rotation between the heating conductors 21, 22 and the workpiece 100 may be used; in this modified example, the rotation motor 43 that rotates the rotating workpiece 100 may be omitted.

The present invention can be widely applied as a heat treatment device.

1 Heat treatment device 3 Power source 20 Coils 21, 22 Heating conductors 25, 26 Connection conductor 100 Workpiece D3 Distance between two heating conductors D51, D52 Distance between connection conductor and workpiece D6 Distance between two heating conductors and workpiece D100 Outer dimension D100' Maximum outer dimension D102 Maximum outer dimension S Axial direction

Claims (1)

a coil for induction heating a shaft-shaped workpiece;
a power source that supplies current to the coil;
In a heat treatment apparatus comprising:
the coil includes two heating conductors extending along the axial direction of the workpiece and a connecting conductor connecting ends of the two heating conductors together ,
the two heating conductors are connected to the power source, and the distance between the two heating conductors is set to a value smaller than the maximum outer dimension of the axial cross section of the workpiece so that the workpieces having different thicknesses can be uniformly induction heated without changing the relative positions of the two heating conductors according to the outer dimensions of the workpieces;
a distance between the connecting conductor and the workpiece is set to a value greater than a distance between the two heating conductors and the workpiece so as to suppress heating due to eddy currents caused by magnetic flux from the connecting conductors at both axial ends of the workpiece,
The heat treatment apparatus is configured so that the two heating conductors face the object to be treated, and performs induction heating while rotating the two heating conductors and the object to be treated relatively.