JP2022044338A - Heat treatment device and heat treatment method - Google Patents

Abstract

To provide a heat treatment device and a heat treatment method that can more uniformly heat a peripheral surface of a workpiece.SOLUTION: A heat treatment device 1 heats a peripheral surface of a workpiece W. The heat treatment device 1 includes a first coil part 6 and a second coil part 7, a first lead part 16, and a second lead part 17. The first coil part 6 and the second coil part 7 are curved in a ring shape and disposed separated from each other in an axial direction. The first lead part 16 is connected with a leading end of the first coil part 6 and supplies current to the first coil part 6. The second lead part 17 is connected with a leading end of the second coil part 7 and supplies current to the second coil part 7. The first lead part 16 is disposed at a position rotated by a predetermined angle in a circumferential direction of the first coil part 6 with respect to the second lead part 17.SELECTED DRAWING: Figure 3

Description

The present invention relates to a heat treatment apparatus and a heat treatment method, and more particularly to a heat treatment apparatus and a heat treatment method using induction heating by a coil.

A method of inducing and heating the peripheral surface of a long workpiece using a ring-shaped coil is known. For example, Patent Document 1 discloses that the peripheral surface of a work is induced and heated by relatively moving the work and the coil in the axial direction of the work.

Japanese Unexamined Patent Publication No. 5-148531

When the work is induced and heated using such a coil, currents in opposite directions flow through the pair of lead wires drawn from the coil and facing each other. As a result, the magnetic field around the lead wire is canceled and the magnetic flux density in the ring is reduced. Here, when a plurality of ring-shaped coils are used separated in the axial direction, there is a problem that the decrease in magnetic flux density is more remarkable and it becomes difficult to uniformly heat the peripheral surface of the work. The same applies not only to the peripheral surface of a long work but also to induction heating of the peripheral surface of a work having another shape.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a heat treatment apparatus and a heat treatment method capable of heating the peripheral surface of a work more uniformly.

The heat treatment apparatus according to one aspect of the present invention heats the peripheral surface of the work. The heat treatment apparatus is connected to the first and second coil portions, which are curved in a ring shape and are disposed axially apart from each other, and the tip of the first coil portion, and a current is applied to the first coil portion. The first lead portion is provided with a first lead portion that is connected to the tip of the second coil portion and supplies a current to the second coil portion, and the first lead portion is the second lead portion. Rather, it is arranged at a position rotated by a predetermined angle in the circumferential direction of the first coil portion.
As a result, it is possible to suppress a decrease in the magnetic flux density in the ring of the coil portion and uniformly heat the peripheral surface of the work.

The angle is preferably 90 ° or more and 180 ° or less, and more preferably 120 ° or more and 180 ° or less. As a result, the action of canceling the magnetic field around the lead portion can be more effectively dispersed, and the peripheral surface of the work can be heated more uniformly.

The heat treatment apparatus may further include a relative moving portion that relatively moves the first and second coil portions and the work in the axial direction. This makes it possible to easily heat a long work.

Further, the heat treatment apparatus may further include a relative rotating portion that rotates the first and second coil portions and the work relatively around the axes of the first and second coil portions. As a result, the peripheral surface of the work can be heated more uniformly.

The heat treatment method according to one aspect of the present invention is a heat treatment method for heating the peripheral surface of the work. The heat treatment method includes a coil portion disposing step in which the first and second coil portions curved in a ring shape are disposed so as to be axially separated from each other, and a first coil portion connected to the tip of the first coil portion. A lead portion arranging step of arranging the lead portion at a position rotated by a predetermined angle in the circumferential direction of the first coil portion from the second lead portion connected to the tip of the second coil portion. The present invention comprises a current supply step of supplying a current to the first coil portion via the first lead portion and supplying a current to the second coil portion via the second lead portion.
As a result, it is possible to suppress a decrease in the magnetic flux density in the ring of the coil portion and uniformly heat the peripheral surface of the work.

The angle is preferably 90 ° or more and 180 ° or less, and more preferably 120 ° or more and 180 ° or less. As a result, the action of canceling the magnetic field around the lead portion can be more effectively dispersed, and the peripheral surface of the work can be heated more uniformly.

The heat treatment method may further include a relative movement step of relatively moving the first and second coil portions and the work in the axial direction. This makes it possible to easily heat a long work.

Further, the heat treatment method may further include a relative rotation step of relatively rotating the first and second coil portions and the work in the circumferential direction. As a result, the peripheral surface of the work can be heated more uniformly.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a heat treatment apparatus and a heat treatment method capable of heating the peripheral surface of a work more uniformly.

It is a schematic diagram of the circuit structure of the heat treatment apparatus which concerns on this embodiment. It is a front view of the heat treatment apparatus which concerns on this embodiment. It is a schematic perspective view for demonstrating the coil part and the lead part which concerns on this Embodiment. It is a top view of the main part of the heat treatment apparatus which concerns on this embodiment. It is a flowchart which shows the procedure of the heat treatment method by the heat treatment apparatus which concerns on this Embodiment. It is a figure which shows the relationship between the peripheral surface temperature and the heating time of the work heated by the heat treatment apparatus which concerns on this embodiment.

Hereinafter, the present invention will be described through embodiments, but the invention according to the claims is not limited to the following embodiments. Moreover, not all of the configurations described in the embodiments are indispensable as means for solving the problem. For the sake of clarity, the following description and drawings have been omitted and simplified as appropriate. In each drawing, the same elements are designated by the same reference numerals.

FIG. 1 is a schematic diagram of the circuit configuration of the heat treatment apparatus 1 according to the present embodiment. The heat treatment device 1 is a device that heats the peripheral surface of the work W by dielectric heating.

The work W is a member to be heated. The work W in this figure has a long cylindrical shape. However, the work W is not limited to this, and the work W may have an arbitrary length. Further, the work W may have a spherical shape, a hexahedron shape, or another polyhedral shape. In this embodiment, the work W is a steel material and includes, for example, S48C, S53C, SCM435 and the like. However, the material of the work W is not limited to this.

As shown in this figure, the heat treatment apparatus 1 includes an AC power supply 2, a high frequency oscillator 3, a transformer 4, a coil unit 5, and a lead unit 15.

The AC power supply 2 is a power supply for supplying electric power to the coil portion 5 of the heat treatment apparatus 1. The AC power supply 2 may be a commercial AC power supply.

The high frequency oscillator 3 is an oscillator that is connected to the AC power supply 2 and converts the AC current of the AC power supply 2 into a high frequency current.

The transformer 4 is a current transformer connected to the high frequency oscillator 3 and transforms a high frequency current output from the high frequency oscillator 3. The transformer 4 is connected to the lead portion 15 and supplies the current transformer high frequency current to the coil portion 5 via the lead portion 15.

The coil portion 5 is a conductor through which a current-transformed high-frequency current flows. The coil portion 5 may be a good conductor such as a copper alloy. The coil portion 5 is curved in a ring shape, and the work W is inserted into the hollow portion inside the ring. The coil unit 5 generates an eddy current by applying an alternating magnetic field generated by a high-frequency current flowing through itself to the work W, thereby heating the peripheral surface of the work W.

The coil portion 5 has a first coil portion 6 and a second coil portion 7. The first coil portion 6 and the second coil portion 7 are arranged so that their axial directions are substantially parallel to the axis A direction of the work W and separated from each other in the axis A direction. Both ends of the first coil portion 6 and the second coil portion 7 are opened, respectively, and the first coil portion 6 and the second coil portion 7 are electrically connected to each other at one ends. In the present embodiment, the first coil portion 6 and the second coil portion 7 have substantially the same shape, but may have different shapes. In the following, when the first coil portion 6 and the second coil portion 7 are collectively referred to as the coil portion 5, and when any of the first coil portion 6 and the second coil portion 7 is referred to without distinction, it is simply referred to as a coil. I may call it.

The lead portion 15 is a conducting wire terminal drawn from the coil portion 5 and relaying the connection between the coil portion 5 and the transformer 4 and the connection between the coils. The lead portion 15 has a first lead portion 16 and a second lead portion 17.

The first lead portion 16 is connected to the tip of the first coil portion 6 and supplies a high frequency current to the first coil portion 6. The first lead portion 16 includes a primary side first lead portion 16a and a secondary side first lead portion 16b, which are a pair of lead wires facing each other along the radial direction of the first coil portion 6. One end of the primary side first lead portion 16a is connected to the positive electrode side of the transformer 4, and the other end is connected to one end of the first coil portion 6. One end of the secondary side first lead portion 16b is connected to the other end of the first coil portion 6, and the other end is connected to one end of the primary side second lead portion 17a of the second lead portion 17.

The second lead portion 17 is connected to the tip of the second coil portion 7 and supplies a high frequency current to the second coil portion 7. The second lead portion 17 includes a primary side second lead portion 17a and a secondary side second lead portion 17b, which are a pair of lead wires facing each other along the radial direction of the second coil portion 7. One end of the primary side second lead portion 17a is connected to the secondary side first lead portion 16b, and the other end is connected to one end of the second coil portion 7. One end of the secondary side second lead portion 17b is connected to the other end of the second coil portion 7, and the other end is connected to the negative electrode side of the transformer 4.

In the present embodiment, the first lead portion 16 and the second lead portion 17 have substantially the same shape, but may have different shapes. Hereinafter, when the first lead unit 16 and the second lead unit 17 are collectively referred to, they may be referred to as a lead unit 15. Further, when the primary side and the secondary side are referred to in the first lead unit 16 or the second lead unit 17 without distinction, they may be simply referred to as leads.

In this way, the heat treatment apparatus 1 applies a high-frequency current to the coil portion 5 to induce and heat the outer periphery of the work W inserted in the hollow portion inside the ring of the coil portion 5.

FIG. 2 is a front view of the heat treatment apparatus 1 according to the present embodiment. The X-axis direction in this figure is the left-right direction of the paper surface, the Y-axis direction is the depth direction of the paper surface, and the Z-axis direction is the vertical direction of the paper surface. In this figure, the work W is shown together with the heat treatment apparatus 1. The axis A, which is the axis in the longitudinal direction of the work W, is a direction substantially parallel to the Z-axis direction.

As shown in this figure, the heat treatment apparatus 1 includes a coil portion 5, center pins 20, 21, cylinder 22, support arm 23, ball screw 24, vertical movement motor 25, and rotation motor 26. In this figure, the AC power supply 2, the high frequency oscillator 3, the transformer 4, and the lead unit 15 are omitted.

The center pins 20 and 21 are members that grip the work W while substantially aligning the axis A of the work W with the axes of the first coil portion 6 and the second coil portion 7. The center pins 20 and 21 are arranged apart from each other in the Z-axis direction. The tips of the center pins 20 and 21 are protruding and engage with recesses provided on each end surface of the work W in the Z-axis direction.

The center pin 20 is connected to the cylinder 22, and the center pin 21 is connected to the second support arm 23b of the support arm 23. The center pin 21 can be rotated by a rotation motor 26, and by rotating itself, the work W is rotated around the axis A.
As the member for gripping the work W, a chuck may be used instead of the center pins 20 and 21.

The cylinder 22 is a member that fixes the center pin 20 to the first support arm 23a of the support arm 23.

The support arm 23 includes a first support arm 23a and a second support arm 23b arranged apart from each other in the Z-axis direction. The first support arm 23a and the second support arm 23b move in the Z-axis direction while maintaining a predetermined interval, thereby moving the work W in the Z-axis direction with respect to the coil portion 5.

The ball screw 24 is arranged so as to be parallel to the Z axis, and is fixedly connected to the first support arm 23a and the second support arm 23b via a nut member.

The vertical movement motor 25 is a drive motor for moving the work W in the Z-axis direction. Further, the rotation motor 26 is a drive motor for rotating the work W around the shaft A.

The center pins 20, 21, the support arm 23, the ball screw 24, and the vertical movement motor 25 move the first coil portion 6, the second coil portion 7, and the work W relative to each other in the Z-axis direction. Also called. As a result, the long work W can be easily heated without expanding the scale of the coil portion 5 in the Z-axis direction such as the number of coils. Although the moving main body in the present embodiment is the work W, the first coil portion 6 and the second coil portion 7 may be used.

Further, since the rotation motor 26 and the center pin 21 rotate the first coil portion 6 and the second coil portion 7 and the work W relatively around the axis A while holding them at concentric positions, they are also relative rotation portions. Called. As a result, the peripheral surface of the work W can be heated uniformly. Although the main body of rotation in this embodiment is the work W, it may be the first coil portion 6 and the second coil portion 7.

The heat treatment apparatus 1 may have a cooling jacket that cools the work W by injecting a quenching liquid onto the heated work W.

FIG. 3 is a schematic perspective view for explaining the coil portion 5 and the lead portion 15 according to the present embodiment. In the present embodiment, the first lead portion 16 is arranged at a position rotated by a predetermined angle θ in the circumferential direction of the first coil portion 6 with respect to the second lead portion 17. Specifically, the angle θ is a straight line connecting the connection portion of the primary side first lead portion 16a to the first coil portion 6 and the center of curvature of the first coil portion 6, and the second lead portion 17a on the primary side. The straight line connecting the connection portion to the coil portion 7 and the center of curvature of the second coil portion 7 is an angle formed on the XY plane. By providing the angle θ, the action of canceling the magnetic field due to the current I flowing through the leads facing each other can be dispersed. As a result, the decrease in the magnetic flux density in the ring is suppressed, so that the heat treatment apparatus 1 can uniformly heat the peripheral surface of the work.

Here, the angle θ may be 90 ° or more and 180 ° or less. The angle θ is preferably 120 ° or more and 180 ° or less, and more preferably 180 ° ± 5 °. In this case, the action of canceling the magnetic field can be more effectively dispersed, and the heat treatment apparatus 1 can heat the peripheral surface of the work more uniformly.

Further, the angle θ may be determined based on at least one of the distance r between the leads facing each other, the intensity I of the current flowing through the coil portion 5, the ring radius R, and the distance d in the Z-axis direction between the coils. good. The distance r between the leads is the distance between the primary side first lead portion 16a and the secondary side first lead portion 16b, and the distance between the primary side second lead portion 17a and the secondary side second lead portion 17b. Is shown. The distances between the primary side first lead portion 16a and the secondary side first lead portion 16b, and between the primary side second lead portion 17a and the secondary side second lead portion 17b are the same but different. You may. The ring radius R may be the radius of curvature of the coil portion 5.

Further, the angle θ may be determined based on at least one of the relative movement speed between the coil portion 5 and the work W and the relative rotation speed between the coil portion 5 and the work W. As a result, the peripheral surface of the work can be heated uniformly, and the cycle time can be shortened.

Here, the details of these wirings are shown in FIG. 4, considering the arrangement of the first lead portion 16 and the second lead portion 17. FIG. 4 is a top view of a main part of the heat treatment apparatus 1 according to the present embodiment. In this figure, the first coil portion 6 and the second coil portion 7 are shown so that the ring radii R are different from each other, but the actual ring radii R may be substantially the same or different from each other. May be good. In the present embodiment, the ring radii R of the first coil portion 6 and the second coil portion 7 are substantially the same.

The negative electrode side terminal 110 is connected to the negative electrode side of the transformer 4 and is formed so as to be curved along the outer periphery so as to surround the outer periphery of the first coil portion 6 and the second coil portion 7. The secondary side second lead portion 17b is connected to the negative electrode side terminal 110.

The positive electrode side terminal 100 is connected to the positive electrode side of the transformer 4 and is formed so as to be curved along the outer periphery so as to surround the outer periphery of the negative electrode side terminal 110. The primary side first lead portion 16a is connected to the positive electrode side terminal 100.

The intermediate terminal 120 is formed to be curved between the negative electrode side terminal 110 and the positive electrode side terminal 100. The secondary side first lead portion 16b and the primary side second lead portion 17a are connected to the intermediate terminal 120.

The current I supplied from the positive electrode side terminal 100 is supplied to the primary side first lead portion 16a and flows to the first coil portion 6 and the secondary side first lead portion 16b. Then, the current I is supplied to the primary side second lead portion 17a via the intermediate terminal 120, and flows to the negative electrode side terminal 110 via the second coil portion 7 and the secondary side second lead portion 17b.

With such a configuration, the first lead portion 16 and the second lead portion 17 can be easily arranged based on the set angle θ.

FIG. 5 is a flowchart showing the procedure of the heat treatment method by the heat treatment apparatus 1 according to the present embodiment.

First, the angle θ is determined (step S01; angle determination step). Next, the first coil portion 6 and the second coil portion 7 are arranged so as to be separated from each other in the axial direction (step S02; coil portion arrangement step). At this time, the directions of the first coil portion 6 and the second coil portion 7 are adjusted based on the angle θ. Next, the first lead portion 16 is disposed at a position rotated by an angle θ in the circumferential direction of the coil portion 5 from the second lead portion 17 (step S03; lead portion arranging step). The first coil portion 6, the first lead portion 16, and the second coil portion 7 and the second lead portion 17 may be connected in advance. In this case, steps S02 and 03 are performed in parallel. Next, the work W is inserted into the hollow portion in the ring of the first coil portion 6 and the second coil portion 7 so as to be substantially coaxial with each other, and is fixed by the center pins 20 and 21 (step S04; work insertion step). Next, the vertical movement motor 25 and the rotation motor 26 are turned on, and the coil portion 5 and the work W are moved and rotated relative to each other (step S05; relative movement / relative rotation step). Next, the AC power supply 2 and the high-frequency oscillator 3 are turned on, a current is supplied to the first coil section 6 via the first lead section 16, and a current is supplied to the second coil section 7 via the second lead section 17. (Step S06; current supply step).

FIG. 6 is a diagram showing the relationship between the peripheral surface temperature of the work W heated by the heat treatment apparatus 1 according to the present embodiment and the heating time. The horizontal axis of this figure shows the heating time, that is, the time t (s) at which the current was supplied in step S06 of FIG. 5, and the vertical axis shows the temperature T (° C.) of an arbitrary region S on the peripheral surface of the work W. show. The broken line shows the graph when θ = 0 (°), and the solid line shows the graph when θ = θ ₁ (> 0 °).

At θ = 0, the temperature of the region S, which was initially T ₀ , rapidly rises to T ₁ due to the induction heating by the coil portion 5. Since the coil portion 5 is rotating, when the region S faces the portion where the magnetic flux density of the coil portion 5 is lowered due to the lead portion 15, the temperature of the region S is lowered by ΔT ₀ . The depressed portion of the broken line in this figure indicates that the temperature is lowered because the region S faces the magnetic flux density lowering portion of the coil portion 5. In order to compensate for this temperature drop and make the quality of the work W after heating uniform, it is necessary to rotate the coil portion 5 by a predetermined required rotation speed N while the coil portion 5 passes through the region S. For example, when θ = 0, the required rotation speed N is 3 (rotation).

However, when θ = θ ₁ , the temperature drop ΔT ₁ in the region S due to facing the magnetic flux density drop portion is smaller than ΔT ₀ . This is because when θ = θ ₁ , the first lead portion 16 and the second lead portion 17 are separated in the circumferential direction, so that the portion where the magnetic flux density decreases is dispersed, and as a result, the decrease in the magnetic flux density is suppressed. .. Therefore, in this case, the required rotation speed N can be set small, and for example, the required rotation speed N can be set to 1 (rotation).

Here, the required rotation speed N affects the cycle time. For example, it is assumed that the length of the work W in the Z-axis direction is 600 (mm), and the relative moving speed between the work W and the coil portion 5 is currently 15 (mm / s). In this case, the cycle time is 600 (mm) / 15 (mm / s) = 40 (s).

Here, it is assumed that the sum of the thickness of the coil portion 5 in the Z-axis direction, that is, the thickness of the first coil portion 6 and the second coil portion 7 and the distance d between them is 15 (mm). At this time, the time required for the coil portion 5 to pass by the thickness of the coil portion 5 is 15 (mm) / 15 (mm / s) = 1 (s).

When θ = 0, the required rotation speed N is 3 (rotation), so the minimum relative rotation speed between the work W and the coil portion 5 is 3 (rotation) / 1 (s) = 3 (rotation / s). Is. At this time, in order to shorten the cycle time, it is conceivable to increase the relative rotation speed, but since the required rotation speed N is the rate-determining factor in the increase in the relative movement speed, it is necessary to increase the relative rotation speed at the same time. .. However, in order to increase the relative rotation speed, it becomes necessary to use a high-performance rotation motor 26, which increases the cost. In particular, when the work W is a heavy object of 10 kg or more such as an automobile part, a serious cost increase is expected, so that it is practically difficult to shorten the cycle time.

On the other hand, when θ = θ ₁ , the required rotation speed N is 1 (rotation), so that the minimum relative rotation speed between the work W and the coil portion 5 is 1 (rotation) / 1 (s) = 1 ( Rotation / s) is suppressed. If so, by setting the relative rotation speed to 3 (rotation / s), it is theoretically possible to increase the relative movement speed up to 3 times, and it is possible to shorten the cycle time by about 67%. .. However, in practice, it should be noted that the rate of temperature rise is the rate-determining factor for the increase in the relative movement speed here. Here, the time required for raising the temperature to T ₁ (for example, 1000 ° C.) is currently 10 (s), but it can be shortened to 5.7 (s) at the maximum. In this case, the relative moving speed can be increased up to 15 (mm / s) × 10 (s) /5.7 (s) ≈26.3 (mm / s). As a result, the cycle time becomes 600 (mm) /26.3 (mm / s) = 22.8 (s), which is reduced by about 43% as compared with the case of θ = 0 even when the temperature rising rate is taken into consideration. be able to.

As described above, according to the heat treatment apparatus 1 of the present embodiment, the magnetic flux received by the work W while passing through the coil portion 5 can be made uniform, and the cycle time can be easily shortened while maintaining the uniform quality.

The present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit. For example, in the above embodiment, the heat treatment apparatus 1 includes two sets of coils, but the number n of coils may be 3 or more. In this case, the angle θ is θ _n ± 30 °, preferably θ _n ± 15 °, and more preferably θ _n ± 5 °. However, θ _n = 360 (°) / n. For example, when n = 3, the angle θ may be 90 ° or more and 120 ° or less, preferably 105 ° or more and 120 ° or less, and more preferably 115 ° or more and 120 ° or less. Further, the angle θ may be determined based on at least one of the values of the distance r between the pair of leads, the intensity I of the current, the ring radius R, and the distances d and n between the coils. As a result, the action of canceling the magnetic field can be more effectively dispersed, and the heat treatment apparatus 1 can heat the peripheral surface of the work more uniformly.

1 Heat treatment device 2 AC power supply 3 High frequency oscillator 4 Transformer 5 Coil part 6 1st coil part 7 2nd coil part 15 Lead part 16 1st lead part 16a Primary side 1st lead part 16b Secondary side 1st lead part 17 2nd Lead 17a Primary side 2nd lead part 17b Secondary side 2nd lead part 20 Center pin 21 Center pin 22 Cylinder 23 Support arm 23a 1st support arm 23b 2nd support arm 24 Ball screw 25 Vertical movement motor 26 Rotation motor 100 Positive electrode Side terminal 110 Negative electrode side terminal 120 Intermediate terminal W work A axis

Claims (10)

A heat treatment device that heats the peripheral surface of the work.
The first and second coil portions, which are curved in a ring shape and are arranged axially apart from each other,
A first lead portion connected to the tip of the first coil portion and supplying a current to the first coil portion, and a first lead portion.
A second lead portion connected to the tip of the second coil portion and supplying a current to the second coil portion is provided.
The first lead portion is a heat treatment apparatus arranged at a position rotated by a predetermined angle in the circumferential direction of the first coil portion from the second lead portion. The heat treatment apparatus according to claim 1, wherein the angle is 90 ° or more and 180 ° or less. The heat treatment apparatus according to claim 2, wherein the angle is 120 ° or more and 180 ° or less. The heat treatment apparatus according to any one of claims 1 to 3, further comprising a relative moving portion for relatively moving the first and second coil portions and the work in the axial direction. The invention according to any one of claims 1 to 4, further comprising a relative rotating portion for rotating the first and second coil portions and the work relative to the axis of the first and second coil portions. Heat treatment equipment. A heat treatment method that heats the peripheral surface of the work.
A coil portion arranging step of arranging the first and second coil portions curved in a ring shape so as to be axially separated from each other.
The first lead portion connected to the tip of the first coil portion is formed at a predetermined angle in the circumferential direction of the first coil portion from the second lead portion connected to the tip of the second coil portion. The lead part placement process to be placed at the rotated position and the lead part placement process
A heat treatment method comprising a current supply step of supplying a current to the first coil portion via the first lead portion and supplying a current to the second coil portion via the second lead portion. The heat treatment method according to claim 6, wherein the angle is 90 ° or more and 180 ° or less. The heat treatment method according to claim 7, wherein the angle is 120 ° or more and 180 ° or less. The heat treatment method according to any one of claims 6 to 8, further comprising a relative moving step of relatively moving the first and second coil portions and the work in the axial direction. The heat treatment method according to any one of claims 6 to 9, further comprising a relative rotation step of relatively rotating the first and second coil portions and the work in the circumferential direction.

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