Alternating current heating method and alternating current heating device

Abstract

An AC heating method according to one embodiment includes: preparing a conductive workpiece; connecting the first terminal and the second terminal to a power source capable of supplying alternating current to the workpiece; placing the first conductor in a non-grounded state and at a position where a proximity effect is generated when an alternating current passes through the workpiece; and heating at least a portion of the workpiece by passing an alternating current through the first terminal and the second terminal.

Description

Technical Field

[0001] The present invention relates to an alternating current heating method and apparatus for heating a workpiece by applying an alternating current to the workpiece. Background Art

[0002] A method for heating a conductive workpiece by applying an alternating current to the workpiece is known.

[0003] As a specific example, Patent Document 1 discloses a high-frequency resistance heating apparatus, in which a conductor having a shape substantially the same as the heating surface shape of a workpiece (object to be heated) is disposed in parallel, and the workpiece is connected to the conductor so that currents flow in opposite directions. This heating apparatus uses the phenomenon that when currents flow in opposite directions through the workpiece and the conductor, the currents in both approach each other, and uniformly heats the cross section of the workpiece.

[0004] In addition, Patent Document 2 discloses a direct current heating method, which controls the magnetic flux around a plated steel sheet when heating the plated steel sheet with an alternating current to prevent the molten plating from being deflected due to the Lorentz force.

[0005] References

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Publication, Special Publication No. 47-35107

[0008] Patent Document 2: Japanese Patent Publication No. 5669610. Summary of the Invention

[0009] In alternating current heating, it is necessary to control the heating temperature distribution of the workpiece. In order to control the heating temperature distribution, it is necessary to control the current density distribution when a current is applied to the workpiece. However, there are various problems in achieving such control using the prior art.

[0010] For example, in the high-frequency resistance heating apparatus disclosed in Patent Document 1, since a conductor is placed around the workpiece, the resistance when a current is applied increases. This increases the power consumption of current heating. In addition, since the workpiece and the conductor must be connected by a line, the movement of the workpiece and the conductor may be restricted. Further, when using a magnetic inductor (such as the direct current heating method disclosed in Patent Document 2), although the magnetic flux can be controlled, it is difficult to precisely control the current density distribution and the heating temperature distribution.

[0011] The present invention is proposed based on the above circumstances, and its object is to provide an improved alternating current heating method and alternating current heating apparatus capable of controlling the current density distribution and the heating temperature distribution of a workpiece.

[0012] In the present invention, an alternating current heating method according to an embodiment includes: preparing a conductive workpiece; connecting a first terminal and a second terminal to a power source capable of supplying alternating current to the workpiece; arranging a first conductor in a non-grounded state at a position where a proximity effect is generated when the alternating current passes through the workpiece; and heating at least a part of the workpiece by passing the alternating current through the first terminal and the second terminal.

[0013] The alternating current heating method may further include arranging a ferromagnetic body near the workpiece. In this case, the workpiece, the first conductor, and the ferromagnetic body may be arranged such that the workpiece is located between the first conductor and the ferromagnetic body.

[0014] The alternating current heating method may further include arranging a second conductor, which is connected to the second terminal and the power source and is electrically insulated from the first conductor. In this case, when at least a part of the workpiece is heated, the alternating current sequentially flows through a circuit including the first terminal, the workpiece, the second terminal, and the second conductor.

[0015] In the present invention, according to an embodiment, an alternating current heating device includes: a power source capable of providing alternating current; a first terminal and a second terminal connected to the power source and mountable to the conductive workpiece; and a first conductor in a non-grounded state and arranged at a position where a proximity effect is generated when the alternating current passes through the workpiece, and heating at least a part of the workpiece by passing the alternating current through the workpiece via the first terminal and the second terminal.

[0016] For example, the first conductor is cylindrical and includes a first part and a second part divided in the circumferential direction. In this case, the first part may have a first flange portion provided at the circumferential end, the second part may have a second flange portion provided at the circumferential end, and the first part and the second part may be electrically connected by the contact of the first flange portion and the second flange portion.

[0017] Another example is that the first part may have a first tapered surface provided at the circumferential end and inclined with respect to the radial direction of the first conductor, the second part may have a second tapered surface provided at the circumferential end and inclined with respect to the radial direction, and the first part and the second part may be electrically connected by bringing the first tapered surface into contact with the second tapered surface.

[0018] Another example is that the first part and the second part may be connected by a conductive material having elasticity or flexibility.

[0019] Another example is that one of the first part and the second part may be provided with a groove at the circumferential end, and the other of the first part and the second part may be provided with a protrusion that can be inserted into the groove.

[0020] Another example is that the first part and the second part may be connected by a conductive liquid.

[0021] The first conductor is preferably made of a metal material with excellent electrical conductivity, such as copper, copper alloy, aluminum, or aluminum alloy.

[0022] The alternating current heating device may further include a ferromagnetic body that can be placed near the workpiece. The alternating current heating device may further include a second conductor that is connected to the second terminal and the power source and is electrically insulated from the first conductor.

[0023] According to the present invention, an improved alternating current heating method and an alternating current heating device can be provided, which can control the current density distribution and heating temperature distribution of the workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of the alternating current heating device for the first embodiment.

[0025] Figure 2 It is a schematic side view of a helical spring, a conductor, and a ferromagnetic body as examples of the workpiece.

[0026] Figure 3 It is a schematic side view of another structure applicable to the helical spring, the conductor, and the ferromagnetic body.

[0027] Figure 4 It is a schematic diagram for explaining the proximity effect.

[0028] Figure 5 It is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring when no conductor is placed.

[0029] Figure 6 It is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring when a conductor is placed.

[0030] Figure 7 It is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring when no conductor and ferromagnetic material are placed.

[0031] Figure 8 It is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring when a ferromagnetic material is placed.

[0032] Figure 9 It is a (a) front view and (b) side view showing an example of a heating device having a divided conductor.

[0033] Figure 10 It is a (a) front view and (b) side view showing another example of a heating device having a divided conductor.

[0034] Figure 11 It is a (a) front view and (b) side view showing yet another example of a heating device having a divided conductor.

[0035] Figure 12 Figures (a) and (b) are respectively a front view and a side view, showing yet another example of a heating device having a segmented conductor.

[0036] Figure 13 It is a schematic diagram of another structural example applicable to a segmented conductor connection part.

[0037] Figure 14 It is a schematic diagram of yet another further structural example applicable to a segmented conductor connection part.

[0038] Figure 15 It is a schematic diagram of yet another further structural example applicable to a segmented conductor connection part.

[0039] Figure 16 It is a schematic cross-sectional view of a modified example of the shape of a conductor.

[0040] Figure 17 It is a schematic cross-sectional view of a modified example of the shape of a conductor.

[0041] Figure 18 It is a schematic cross-sectional view of a further modified example of the shape of a conductor.

[0042] Figure 19 It is a schematic cross-sectional view of a further modified example of the shape of a conductor.

[0043] Figure 20 It is a schematic structural diagram showing a heating device according to the second embodiment.

[0044] Figure 21 It is a flowchart showing an example of a method for manufacturing a helical spring.

[0045] Figure 22 It is a flowchart showing another example of a method for manufacturing a helical spring.

[0046] Figure 23 It is a flowchart showing yet another further example of a method for manufacturing a helical spring. Detailed Description of the Invention

[0047] Multiple embodiments will be described below with reference to the accompanying drawings. In each embodiment, a helical spring can be used as an example of a workpiece (heating object) to be heat-treated. However, the alternating current heating device and the alternating current heating method disclosed in each embodiment can be applied to general heat-treated products.

[0048] For example, workpiece examples other than coil springs include leaf springs, vehicle stabilizers, various bent products, rolled materials, and composite materials. In other words, the material of the workpiece can be a metal other than spring steel. In addition, the material of the workpiece is not limited to wire materials such as the wire rods constituting coil springs, and can also be special-shaped materials such as plates or pipes.

[0049] The type of heat treatment of the workpiece is not particularly limited, such as quenching, tempering, annealing, and softening treatment of the workpiece surface.

[0050] [First Embodiment]

[0051] Figure 1 FIG. 10 is a schematic structural diagram of the alternating current heating device 1 (hereinafter referred to as the heating device 1) for the first embodiment. The heating device 1 includes a conductor 2 (first conductor), a first terminal 3A, a second terminal 3B, and a control device 4.

[0052] The conductor 2 is, for example, cylindrical and made of a metal material with excellent conductivity, such as copper, copper alloy, aluminum, aluminum alloy, or a composite material containing one or more of these materials. The control device 4 includes a power supply 41 for supplying alternating current. The first terminal 3A and the second terminal 3B are connected to the power supply 41 through lines. The frequency of the alternating current supplied by the power supply 41 is not particularly limited, but in one embodiment, a high frequency of 1 kHz or higher can be used.

[0053] In Figure 1 the example of Figure 1 as shown in FIG. 11, the first terminal 3A and the second terminal 3B are each divided into a lower part 31 and an upper part 32. By clamping a part of the workpiece between the lower part 31 and the upper part 32, the first terminal 3A and the second terminal 3B can be mounted on the workpiece. However, the structure for mounting the first terminal 3A and the second terminal 3B on the workpiece is not limited to this example.

[0054] The heating process of the alternating current heating method (hereinafter referred to as the heating method) of the present embodiment is performed using the heating device 1. When performing the heating process using the heating device 1 of the present embodiment, first, a coil spring W is prepared as the workpiece. The coil spring W is formed by winding a wire rod such as spring steel into a spiral shape using a winding machine and has conductivity.

[0055] In addition, the first terminal 3A and the second terminal 3B are fixed to the coil spring W, and the coil spring W is placed inside the conductor 2. It should be noted that the order of fixing the first terminal 3A and the second terminal 3B to the coil spring W and placing the coil spring W inside the conductor 2 is not particularly limited.

[0056] In Figure 1In the example, the terminals E1 and E2 of the helical spring W (at least a part of the end turn portion) protrude from both ends of the conductor 2. However, it is not limited to this case only, and the entire helical spring W can also be surrounded by the conductor 2.

[0057] For example, the first terminal 3A and the second terminal 3B are fixed near the terminals E1 and E2 of the helical spring W. In Figure 1 the example, the vicinity of the terminal E1 of the helical spring W is clamped between the lower part 31 and the upper part 32 of the first terminal 3A. In addition, the vicinity of the terminal E2 of the helical spring W is clamped between the lower part 31 and the upper part 32 of the second terminal 3B.

[0058] When the first terminal 3A and the second terminal 3B are connected to the helical spring W, these elements are connected in series with the power supply 41 to form a circuit. The control device 4 starts to energize the helical spring W in response to the operator operating the switch or receiving a control signal from the outside. Figure 1 In, an example of the current flow direction is indicated by a solid arrow. This direction is switched periodically according to the frequency of the power supply 41.

[0059] This current causes at least a part of the helical spring W to heat up. At this time, a proximity effect (to be described later) occurs between the conductor 2 and the helical spring W. The conductor 2 is located at the position where this proximity effect occurs.

[0060] The frequency, amplitude, and energization time of the alternating current can be appropriately determined according to the characteristics of the helical spring W (for example, wire diameter, cross-sectional shape, coil diameter, coil length, pitch, number of turns, material), the part to be heated, and the target heating temperature. When it reaches the time to stop heating, the control device 4 stops the current supply of the power supply 41.

[0061] Then, the helical spring W is cooled. This cooling can be natural cooling, or, if rapid cooling is required, it can be achieved by spraying a fluid such as water or air onto the helical spring W. In Figure 1 the example, the heating device 1 is provided with a cooling mechanism 5 for spraying such a fluid.

[0062] For example, the cooling mechanism 5 includes a plurality of nozzles 51 provided on the inner surface of the conductor 2, a fluid supply source 52 provided in the control device 4, and pipes 53 connecting each nozzle 51 and the fluid supply source 52. The fluid supply source 52 supplies fluid to each nozzle 51 through the pipes 53 under the control of the control device 4, for example. At this time, the fluid is sprayed from each nozzle 51 onto the helical spring W. It should be noted that the nozzles 51 do not necessarily have to be provided on the conductor 2, and can also be provided on a component different from the conductor 2.

[0063] The heating device 1 can also include a ferromagnetic body 6 provided near the helical spring W. The ferromagnetic body 6 can be made of, for example, ferrite, but is not limited to this example. InFigure 1 In the example, the ferromagnet 6 is inserted into the interior of the coil spring W.

[0064] picture Figure 2 Yes Figure 1 Schematic side view of the assembled coil spring W, conductor 2 and ferromagnet 6. It should be noted that Figure 2 The structure of a partial cross section of the conductor 2 is also shown. In the following description, Figure 2 As shown, an axial direction DX along the axis AX of the coil spring W, a radial direction DR passing through the axis AX and perpendicular to the axis AX, and a circumferential direction Dθ centered on the axis AX are defined.

[0065] The conductor 2 is, for example, cylindrical, with the axis AX as its center. Figure 2 In the example of FIG. 1 , the conductor 2 has a single-layer structure of a conductive metal material. The conductor 2 is in a non-grounded state and is insulated from other conductive elements such as the coil spring W. The conductor 2 is supported by, for example, an insulating member not shown.

[0066] A gap G1 is formed between the conductor 2 and the coil spring W. That is, the inner surface of the conductor 2 faces the outer diameter side surface of the coil spring W via the gap G1. Figure 2 In the example of FIG. 1 , the size of the gap G1 is constant at any position in the circumferential direction Dθ, but the example is not limited thereto.

[0067] The ferromagnetic body 6 is, for example, cylindrical and centered on the axis AX. The ferromagnetic body 6 may also be in other shapes, such as cylindrical and centered on the axis AX. The ferromagnetic body 6 is also in a non-grounded state and is insulated from other conductive elements such as the conductor 2 and the coil spring W. The ferromagnetic body 6 is supported by, for example, an insulating member (not shown).

[0068] A gap G2 is formed between the ferromagnet 6 and the coil spring W. That is, the outer surface of the ferromagnet 6 is opposite to the inner diameter side surface of the coil spring W through the gap G2. Figure 2 In the example of , the size of the gap G2 is constant at any position in the circumferential direction Dθ, but the present invention is not limited to this example.

[0069] Figure 3 is a schematic side view showing another structure that can be applied to the coil spring W, the conductor 2 and the ferromagnetic body 6. The figure also shows the structure of a partial cross section of the conductor 2. Figure 3 In the example shown in FIG. 2 , the conductor 2 includes an insulating portion 21 and a conductive portion 22 .

[0070] The insulating portion 21 is formed into a cylindrical shape by an insulating material such as plastic. The conductive portion 22 is made of a conductive material (e.g., copper, copper alloy, aluminum, aluminum alloy, or a composite material containing one or more of these materials) and covers the inner surface of the insulating portion 21. The conductive portion 22 faces the outer diameter side of the coil spring W through the gap G1.

[0071] The conductive part 22 is, for example, a thin film formed or coated on the inner surface of the insulating part 21. The conductive part 22 may be a strip-shaped member pasted on the inner surface of the insulating part 21 through an adhesive layer. The conductive part 22 may also be a cylindrical member formed separately from the insulating part 21 and installed inside the insulating part 21.

[0072] In one example, the conductive part 22 covers the entire inner surface of the insulating part 21. In another example, the conductive part 22 may cover a part of the inner surface of the insulating part 21.

[0073] Next, the function of the conductor 2 will be explained. When an electric current flows through a workpiece (such as a helical spring W), if a conductor in a non-grounded state is placed nearby, the so-called proximity effect will occur. In this embodiment, the proximity effect is used to control the current density distribution (heating temperature distribution) of the helical spring W.

[0074] Figure 4 FIG. is a schematic diagram for explaining the proximity effect, showing a rod-shaped workpiece Ws and a conductor 2s arranged nearby. When an electric current IA from a power source flows through the workpiece Ws, a magnetic field HIA (Ampere's law) will be generated around the workpiece Ws.

[0075] In the conductor 2s, an eddy current IE1 (Lenz's law) will be induced by this magnetic field HIA. In addition, a magnetic field HIE caused by the eddy current IE1 will be generated around the conductor 2s. When this magnetic field HIE acts on the workpiece Ws, an eddy current IE2 will be generated in the workpiece Ws.

[0076] The directions of the electric current IA, the eddy current IE1, and the eddy current IE2 are as shown by the arrows in the figure. That is, in the workpiece Ws, near the side surface far from the conductor 2s, the directions of the electric current IA and the eddy current IE2 are opposite. On the other hand, near the side surface close to the conductor 2s, the flowing direction of the electric current IA is the same as the flowing direction of the eddy current IE2. Therefore, the current density of the workpiece Ws will be higher near the side surface close to the conductor 2s.

[0077] Using this proximity effect, the current density distribution and the heat density distribution of the workpiece Ws can be controlled. For example, as Figure 4 shown, when the conductor 2s is arranged to face a part of the outer surface of the workpiece Ws, a current density distribution and a heat density distribution that vary with the circumferential position can be obtained on the surface and inside of the workpiece Ws. These distributions can be appropriately adjusted, for example, by the distance between the conductor 2s and the workpiece Ws.

[0078] In addition, when the conductor 2s is arranged to face only a part of the longitudinal direction of the workpiece Ws, a current density distribution and a heat density distribution that vary with the longitudinal position can be obtained on the surface and inside of the workpiece Ws.

[0079] Next, reference will be made to Figure 5 and Figure 6 to describe the energization heating and proximity effect when the workpiece is the helical spring W. Figure 5 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the helical spring W when the conductor 2 is not arranged. Figure 6 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the helical spring W when the conductor 2 is arranged. These figures only show a part of the helical spring W and the conductor 2. In addition, a dot pattern is applied to the part with a higher current density (higher heating temperature) of the helical spring W.

[0080] When an alternating current flows through a workpiece such as the helical spring W, the skin effect increases the surface current density. In addition, for a workpiece with a non-linear bend like the helical spring W, since the path of the current through the inner surface of the bend is shorter, the current density tends to increase near the inner surface of the bend.

[0081] Specifically, in the example of Figure 5 the current density near the inner surface S1 (the part of the surface of the helical spring W facing the axis AX) of the helical spring W is higher than the current density near the outer surface S2. Therefore, the area near the inner surface S1 is preferentially heated.

[0082] Conversely, when the conductor 2 is arranged around the helical spring W, due to the above proximity effect, the current originally biased near the inner surface S1 will be pulled outward. This enables the current density distribution and heating temperature distribution in the circumferential direction of the wire of the helical spring W to be uniformized, for example as shown in Figure 6 Another example is that by adjusting the gap G1 between the conductor 2 and the helical spring W, the current density near the outer diameter surface S2 can be made higher than the current density near the inner diameter surface S1. In addition, the current density distribution and heating temperature distribution of the heating device 1 can be appropriately adjusted according to the required characteristics of the workpiece.

[0083] The current density distribution and heating temperature distribution can also be controlled by the ferromagnetic body 6. Figure 7 is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring W when the conductor 2 and the ferromagnetic body 6 are not arranged. Figure 8 is a schematic perspective view of the current density distribution (heating temperature distribution) of the helical spring W when the ferromagnetic body 6 is arranged. Only a part of the helical spring W and the conductor 2 are shown in the figure. In addition, similar to Figure 5 and Figure 6 a dot pattern is applied to the part with a higher current density (higher heating temperature) of the helical spring W.

[0084] As described above, when the conductor 2 and the ferromagnetic body 6 are not arranged, as shown in Figure 7As shown, the current density near the inner diameter side S1 is higher than that near the outer diameter side S2. The function of the ferromagnetic body 6 is to affect the magnetic flux generated when current passes through and to diffuse the non-uniform current density as shown Figure 7 to the outer diameter side of the helical spring 2.

[0085] Therefore, by arranging the ferromagnetic body 6 as shown Figure 8 , the current density distribution and the heating temperature distribution can be controlled in the same way as when the conductor 2 is arranged. In the example of Figure 8 , the current density distribution and the heating temperature distribution are uniform in the circumferential direction of the wire of the helical spring W, but are not limited thereto.

[0086] In the example of Figures 1 to 3 , the conductor 2 is a seamless cylindrical member. However, it is not limited thereto, and the conductor 2 may also be divided into multiple parts. Figure 9 FIG. (a) is a front view and FIG. (b) is a side view of an example of the heating device 1 equipped with the divided conductor 2. In the example of this figure, the conductor 2 has a first part 2A and a second part 2B divided in the circumferential direction Dθ.

[0087] With this configuration, the conductor 2 can be easily arranged around the helical spring W. For example, even after connecting the first terminal 3A and the second terminal 3B to the helical spring W, the installation of the conductor 2 will not be hindered by these terminals 3A, 3B or the lines connecting these terminals 3A, 3B and the power supply 41.

[0088] On the other hand, if the first part 2A and the second part 2B are separated as shown Figure 9 , when the helical spring W is energized, the eddy current IE1 generated in the conductor 2 will turn back at the ends of the first part 2A and the second part 2B. This makes the proximity effect on the helical spring W non-uniform, resulting in non-uniformity in the current density distribution. It should be noted that even if the ends of the first part 2A and the second part 2B are in contact with each other, the current density distribution of the helical spring W may be disturbed near the boundary between the first part 2A and the second part 2B.

[0089] Figure 10 FIG. (a) is a front view and FIG. (b) is a side view showing another example of the heating device 1 having the divided conductor 2. In the example of this figure, the conductor 2 is also divided into a first part 2A and a second part 2B. In addition, the first part 2A has a first flange portion 23A, and the second part 2B has a second flange portion 23B.

[0090] The first flange portion 23A projects radially DR from both ends of the first part 2A in the circumferential direction Dθ. The second flange portion 23B projects radially DR from both ends of the second part 2B in the circumferential direction Dθ. These flange portions 23A, 23B extend parallel to the axial direction DX.

[0091] The flange portions 23A and 23B can be connected by a plurality of connecting members 24. The connecting members 24 are used to press the flange portions 23A and 23B together, for example, and can be a combination of a bolt and a nut, or a clip-like member that clamps the flange portions 23A and 23B.

[0092] By pressing the flange portions 23A and 23B together, the first portion 2A and the second portion 2B can conduct electricity well, and the influence of the boundary therebetween on the eddy current IE1 can be reduced. Therefore, the eddy current IE1 flows through the conductor 2 almost seamlessly without turning back at the boundary. This makes the proximity effect on the helical spring W uniform and a suitable current density distribution can be obtained.

[0093] Figure 11 FIG. (a) is a front view and FIG. (b) is a side view showing another example of the heating device 1 having the divided conductor 2. In the example shown in this figure, the conductor 2 is also divided into a first portion 2A and a second portion 2B. In addition, the first portion 2A has a first tapered surface 25A, and the second portion 2B has a second tapered surface 25B.

[0094] The first tapered surface 25A is provided at both circumferential Dθ ends of the first portion 2A and is inclined with respect to the radial DR. The second tapered surface 25B is provided at both circumferential Dθ ends of the second portion 2B and is inclined with respect to the radial DR.

[0095] The tapered surfaces 25A and 25B of the first portion 2A and the second portion 2B are in surface contact with each other. Connecting members can also be provided to press the first portion 2A and the second portion 2B together so that the tapered surfaces 25A and 25B are pressed against each other.

[0096] In Figure 11 the example, the tapered surfaces 25A and 25B are provided, thereby increasing the contact area at both ends of the first portion 2A and the second portion 2B. This ensures good electrical conductivity between the first portion 2A and the second portion 2B, thus achieving the same effect as in Figure 10 the example.

[0097] Figure 12 FIG. (a) is a front view and FIG. (b) is a side view showing another example of the heating device 1 including the divided conductor 2. In the example shown in this figure, the conductor 2 is also divided into a first portion 2A and a second portion 2B. In addition, the first portion 2A and the second portion 2B are connected by a plurality of conductive materials 26.

[0098] The conductive material 26 is, for example, in a sheet shape, one end of which is connected to one end of the first portion 2A in the circumferential Dθ direction, and the other end of which is connected to one end of the second portion 2B in the circumferential Dθ direction. The conductive material 26 has flexibility, and when the ends of the first portion 2A and the second portion 2B approach each other, the conductive material 26 can bend, for example, asFigure 12 (as shown in (b)). In Figure 12 , the ends of the first part 2A and the second part 2B are separated from each other, but when powered on, the first part 2A and the second part 2B are pressed together so that the ends come into contact with each other. The conductive material 26 is not limited to a flexible sheet material. Another example is that the conductive material 26 can be an elastic leaf spring or the like.

[0099] By providing such a conductive material 26, even if the ends of the first part 2A and the second part 2B are separated from each other (for example, as shown in Figure 12 (b)), the first part 2A and the second part 2B can be reliably electrically connected. This can provide the same effect as the examples of Figure 10 and Figure 11 .

[0100] Each conductive material 26 can be provided at a position where the boundary surface between the first part 2A and the second part 2B faces the outer diameter surface of the helical spring W, as shown in Figure 12 (a). This makes the path of the eddy current IE1 generated along the helical spring W less likely to be disturbed.

[0101] Figures 13 to 15 Other configuration examples applicable to the connection between the first part 2A and the second part 2B are shown. In these examples, a groove 200A is provided at the end of the first part 2A, and a protrusion 200B is provided at the end of the second part 2B.

[0102] The groove 200A and the protrusion 200B have a shape that mates with each other. Specifically, in the example of Figure 13 (a), both the groove 200A and the protrusion 200B have a V-shaped cross-sectional shape. In the example of Figure 14 (a), both the groove 200A and the protrusion 200B have a rectangular cross-sectional shape.

[0103] As shown in Figure 13 (b) and Figure 14 (b), when connecting the first member 2A and the second member 2B, the convex portion 200B is inserted into the concave portion 200A. This suppresses misalignment between the first member 2A and the second member 2B, and increases the contact area between the first member 2A and the second member 2B compared to the case where the ends of the first member 2A and the second member 2B are flat, thereby firmly connecting the first member 2A and the second member 2B.

[0104] Figure 15 The shapes of the concave portion 200A and the convex portion 200B in the example of Figure 13 are the same as those in the Figure 15(b) In the example, a conductive liquid 201 is provided between the joint surfaces of the first component 2A and the second component 2B. For example, conductive paste, conductive grease, or conductive adhesive can be used as the conductive liquid 201. This conductive liquid 201 can be coated onto the groove 200A before connection, or onto the protrusion 200B, or onto both the groove 200A and the protrusion 200B simultaneously.

[0105] Please note that in Figures 13 to 15 , a structure is shown where a groove is provided on the first part 2A located at the bottom and a protrusion is provided on the second part 2B located at the top. This example is not limited to this, and a protrusion can also be provided on the first part 2A and a groove can be provided on the second part 2B. Additionally, in Figure 10 , 11 , 12, and 14, in the structures shown, Figure 15 the conductive liquid 201 shown can be provided at the end of the first part 2A or the second part 2B.

[0106] Figures 9 to 15 An example is shown where the conductor 2 is divided into two parts in the circumferential direction Dθ. However, it is not limited to this, and the conductor 2 can also be divided into three parts or more parts in the circumferential direction Dθ. Additionally, the conductor 2 can also be divided into multiple parts in the axial direction DX. In these cases, the same structure as shown in Figures 10 to 15 can be applied to the connection of the divided parts.

[0107] Figure 1 and Figure 2 , the cylindrical conductor 2 is taken as an example for illustration. However, depending on the workpiece, the conductor 2 can have various shapes. Figures 16 to 19 is a schematic cross-sectional view showing various shapes that can be applied to the conductor 2. In these figures, the cross-section of a part of the workpiece Wt and the cross-section of the conductor 2 near that part are shown respectively. For example, if the workpiece Wt is a helical spring W, the cross-section of the workpiece Wt in each figure corresponds to the cross-section of the wire of the helical spring W.

[0108] In Figures 16 to 19 , in the example, the conductor 2 surrounds the workpiece Wt from three sides. Specifically, in Figure 16 , in the example, the conductor 2 has a pair of flat portions 27a, 27b and a curved portion 27c connecting the flat portions 27a, 27b. The cross-sectional shape of the curved portion 27c is an arc and it bends smoothly along the outer peripheral surface of the workpiece Wt.

[0109] In Figure 17 , in the example, the conductor 2 has a pair of parallel flat portions 28a, 28b and a flat portion 28c connecting the flat portions 28a, 28b. The flat portion 28c is perpendicular to the flat portions 28a, 28b.

[0110] InFigure 19 In the example of, the conductor 2 has a pair of parallel flat portions 28a and 28b and a flat portion 28c connecting the flat portions 28a and 28b. As Figure 18 shown, the conductor 2 has a pair of parallel flat portions 29a and 29b and a bent portion 29c connecting the flat portions 29a and 29b. The cross-sectional shape of the bent portion 29c is a smooth curved arc along the outer peripheral surface of the workpiece Wt.

[0111] In Figure 19 the example of, the conductor 2 covers the entire circumference of the workpiece Wt. The cross-sectional shape of the conductor 2 is, for example, a perfect circle, but it can also be other shapes such as an ellipse.

[0112] For example, when the workpiece Wt is a helical spring W, the conductor 2 can have Figures 16 to 18 the structure in which any of the shapes shown are arranged continuously in the axial direction DX. The conductor 2 can also be formed by appropriately combining Figures 16 to 19 the shapes shown. The conductor 2 can also adopt various other shapes.

[0113] In the heating device 1 and the heating method of the present embodiment described above, the current density distribution and the heating temperature distribution in the workpiece are controlled by the proximity effect generated between the conductor 2 in the non-grounded state and the workpiece. This makes it possible to control the distribution of characteristics such as hardness, stress, and structure of each part of the workpiece. When a ferromagnetic material 6 is used in addition to the conductor 2, the control accuracy of the current density distribution, the heating temperature distribution, and the resulting characteristic distribution will be further improved.

[0114] More specifically, by adjusting control factors such as the distance between the conductor 2 and the workpiece, the shape and material of the conductor 2, the orientation position of the conductor 2 on the workpiece surface, the distance between the ferromagnetic body 6 and the workpiece, the shape and material of the ferromagnetic body 6, the orientation position of the ferromagnetic body 6 on the workpiece surface, the time of energizing the workpiece (heating time), and the frequency of the power supply 41, the distribution of characteristics in the depth direction from the workpiece surface, the circumferential direction of the workpiece, the length direction of the workpiece, etc. can be controlled. In addition to the above effects, the present embodiment can also obtain various other preferred effects.

[0115] [Second Embodiment]

[0116] The second embodiment will be described below. Elements identical to those in the first embodiment are denoted by the same reference numerals, and repeated descriptions are omitted. Figure 20 is a schematic structural diagram of the heating device 1 of the second embodiment. Similar to the first embodiment, the heating device 1 includes a conductor 2 (first conductor), a first terminal 3A, a second terminal 3B, and a control device 4. The heating device 1 may further include a cooling mechanism 5 and a ferromagnetic body 6, as Figure 1As shown. In addition, the heating device 1 further includes a conductor 7 (second conductor) and a third terminal 3C. The shape of the conductor 7 enables it to surround the conductor 2 and the helical spring W. For example, the conductor 7 is in the shape of a cylinder with both ends open, but other shapes can also be adopted.

[0117] The conductor 7 is made of a metal material with excellent electrical conductivity, such as copper, copper alloy, aluminum, aluminum alloy, or a composite material containing one or more of the above materials. The conductor 7 is electrically insulated from the conductor 2. The conductor 2 and 7 can be simply arranged separately from each other, or an insulating layer can be provided between them.

[0118] The second terminal 3B is connected to the conductor 7 through a wire. The conductor 7 is connected to the third terminal 3C through a wire. In addition, the third terminal 3C is connected to the power source 41 through a wire. When the first terminal 3A and the second terminal 3B are connected to the helical spring W, a circuit will be formed in which the power source 41, the first terminal 3A, the helical spring W, the second terminal 3B, the conductor 7, and the third terminal 3C are connected in this order. Figure 20 In the figure, the solid arrow indicates an example of the current flow in the circuit. The direction of the current is periodically switched according to the frequency of the power source 41. Even in the structure of the heating device 1 according to the present embodiment, like in the first embodiment, the current density distribution and the heating temperature distribution of the helical spring W can be controlled through the conductor 2 and the ferromagnetic body 6. All the various structures disclosed in the first embodiment can be applied to the heating device 1 according to the second embodiment. The conductor 7 can be divided into multiple parts like Figures 9 to 15 the conductor 2 shown. In this case, it is more convenient to install the conductor 7 around the helical spring W and the conductor 2. The arrangement of the conductor 2, the conductor 7, the helical spring W, and the ferromagnetic body 6 is not limited to Figure 20 the arrangement shown. For example, the conductor 7 can be provided inside the helical spring W. In this case, the conductor 2 can be provided between the helical spring W and the conductor 7, and the ferromagnetic body 6 can be provided outside the helical spring W.

[0119] [Application Example of Helical Spring Manufacturing Method]

[0120] Here, a helical spring manufacturing method that employs the heating method of the heating device 1 disclosed in the first and second embodiments will be described.

[0121] Figure 21 is a flowchart showing an example of the helical spring manufacturing method. This example corresponds to so-called hot forming. First, a wire such as spring steel is heated (step P11). Then, the wire heated to a high temperature in step P11 is wound into a helix by a winding machine (step P12). In steps P11 and P12, the wire is quenched. If necessary, surface quenching is performed after step P12 to reduce the hardness near the surface inside the wire (step P13). Then, the wire is tempered (step P14).

[0122] After step P13, a surface softening treatment can be carried out to soften the surface of the wire (step P15). The surface softening treatment can be carried out for the entire helical spring or for a part of the helical spring in the longitudinal direction (such as the end turn part).

[0123] Figure 22 FIG. is a flowchart showing another example of a method for manufacturing a helical spring. In this example, first, a wire is wound into a helical shape using a wire winding machine (step P21). After step P21, the wire is quenched (step P22). After that, if necessary, a surface hardening similar to step P13 is carried out on the wire (step P23). In addition, a tempering treatment similar to step P14 is carried out on the wire (step P24). After step P23, a surface softening treatment similar to step P15 can be carried out (step P25).

[0124] Figure 23 FIG. is a flowchart showing another example of a method for manufacturing a helical spring. This example corresponds to so-called cold forming. First, the wire is quenched (step P31). After quenching, the wire is tempered (step P32).

[0125] After step P32, the wire is formed into a helical shape using a wire winding machine (step P33). The wire is further heated to a predetermined temperature for annealing (step P34). After step P33, a surface softening treatment similar to step P15 can be carried out (step P35).

[0126] The heating method using the heating device 1 disclosed in each embodiment can be applied to the heat treatment after the wire is formed, such as the surface hardening in steps P13 and P23, the tempering in steps P14 and P24, or the surface softening in steps P15, P25, and P35. For example, when performing the surface softening treatment in steps P15, P25, and P35 on a part of the helical spring in the longitudinal direction (such as the end turn), the first terminal 3A and the second terminal 3B can be fixed to both ends of this part.

[0127] The heating method using the heating device 1 disclosed in each embodiment can be applied to the heat treatment of the wire before it forms a helical shape, such as the quenching in step P31 and the tempering in step P32.

[0128] The above-described first and second embodiments and the application examples of the helical spring manufacturing method do not limit the scope of the present invention to the configurations disclosed in these embodiments and application examples. The present invention can be implemented by modifying the configurations disclosed in these embodiments and application examples in various ways.

[0129] The reference numerals in the accompanying drawings of the specification include:

[0130] 1. AC heating device; 2. Conductor (first conductor); 3A. First terminal; 3B. Second terminal; 4. Control device; 5. Cooling mechanism; 6. Ferromagnet; 7. Conductor (second conductor); 4I. Power supply; W. Helical spring (workpiece); DX. Axial direction; DR. Radial direction; Dθ. Circumferential direction.

Claims

1. An alternating current heating method, comprising the following steps: Prepare a conductive workpiece, Connect a first terminal and a second terminal to a power source capable of supplying alternating current to the workpiece, Arrange a first conductor in a non-grounded state at a position where proximity effect is generated when alternating current passes through the workpiece, And heat at least a part of the workpiece by passing alternating current through the first terminal and the second terminal.

2. In the alternating current heating method according to claim 1, characterized in that, It further includes placing a ferromagnetic body near the workpiece.

3. In the alternating current heating method according to claim 2, characterized in that, The workpiece, the first conductor and the ferromagnetic body are arranged such that the workpiece is located between the first conductor and the ferromagnetic body.

4. In the alternating current heating method according to any one of claims 1 to 3, it further includes, Set the second terminal and the second conductor connected to the power source to a state of being electrically insulated from the first conductor, It is characterized in that When at least a part of the workpiece is heated, an alternating current flows through a circuit sequentially including the first terminal, the workpiece, the second terminal and the second conductor.

5. An alternating current heating device, comprising, characterized in that, A power source capable of providing alternating current, A first terminal and a second terminal, connected to the power source and installable to a conductive workpiece, A first conductor in a non-grounded state and arranged at a position where proximity effect is generated when alternating current passes through the workpiece, Characterized in that by passing alternating current through the first terminal and the second terminal, at least a part of the workpiece is heated.

6. In the alternating current heating device according to claim 5, characterized in that, The first conductor is cylindrical and includes a first part and a second part divided circumferentially. The first part has a first flange portion provided at one circumferential end, the second part has a second flange portion provided at one circumferential end, and the first part and the second part are electrically connected by the contact of the first flange portion and the second flange portion.

7. In the alternating current heating device according to claim 5, characterized in that, The first conductor is cylindrical and includes a first part and a second part divided circumferentially. The first part is provided at one circumferential end and has a first tapered surface inclined with respect to the radial direction of the first conductor. The second part is provided at one circumferential end and has a second tapered surface inclined with respect to the radial direction. And the first part and the second part are electrically connected by the contact of the first tapered surface and the second tapered surface.

8. In the alternating current heating device according to claim 5, characterized in that, The first conductor is cylindrical and includes a first part and a second part separated in the circumferential direction, The first part and the second part are connected by a conductive material having elasticity or flexibility.

9. In the alternating current heating device according to claim 5, characterized in that, The first conductor is cylindrical and includes a first part and a second part separated in the circumferential direction, One of the first part and the second part is provided with a groove at one end in the circumferential direction, The other of the first part and the second part has a protrusion that can be inserted into the groove.

10. In the alternating current heating device according to claim 5, characterized in that, the first conductor is cylindrical and includes a first part and a second part separated in the circumferential direction, the first part and the second part are connected by a conductive liquid.

11. In the alternating current heating device according to any one of claims 5 to 10, characterized in that, the first conductor is copper, a copper alloy, aluminum or an aluminum alloy.

12. In the alternating current heating device according to any one of claims 5 to 10, further comprising, characterized in that, a ferromagnetic body that can be placed near the workpiece.

13. In the alternating current heating device according to any one of claims 5 to 10, further comprising, characterized in that, a second conductor connected to the second terminal and the power supply and electrically insulated from the first conductor.

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