AC current heating method and AC current heating device

Abstract

An AC-energization heating method according to an embodiment includes: preparing a conductive workpiece; attaching a first terminal and a second terminal connected to a power source capable of supplying alternating current to the workpiece; arranging a first conductor that is in an electrically floating state at a position where a proximity effect occurs when the alternating current is applied to the workpiece; and heating at least a portion of the workpiece by allowing the alternating current to flow to the workpiece through the first terminal and the second terminal.

Description

[Technical Field]

[0001] The present invention relates to an AC current heating method and an AC current heating device for heating a workpiece by passing an AC current through the workpiece. [Background technology]

[0002] BACKGROUND ART A method is known in which a conductive workpiece is heated by passing an alternating current through the workpiece.

[0003] To cite a specific example, Patent Document 1 discloses a high-frequency resistance heating device in which a conductor having approximately the same shape as the heating surface of a workpiece (heated object) is arranged parallel to the heating surface, and the workpiece and conductor are connected so that currents flow in opposite directions. This heating device utilizes the phenomenon in which currents in the workpiece and conductor approach each other when currents flow in opposite directions, thereby uniformly heating the cross section of the workpiece.

[0004] Furthermore, Patent Document 2 discloses a direct resistance heating method in which, when heating a plated steel sheet with an alternating current, the magnetic flux around the plated steel sheet is controlled by a magnetic flux conductor in order to prevent the molten coating from being biased due to the Lorentz force. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 47-35107 [Patent Document 2] Patent No. 5669610 Summary of the Invention [Problem to be solved by the invention]

[0006] In AC current heating, there is a demand for controlling the heating temperature distribution of a workpiece. To control the heating temperature distribution, it is necessary to control the current density distribution when current is passed through the workpiece. However, there are various problems with achieving such control using conventional technology.

[0007] For example, in the high-frequency resistance heating device disclosed in Patent Document 1, the conductors placed around the workpiece increase resistance when current is applied. This increases the power consumption of resistance heating. Furthermore, the workpiece and conductor must be connected by wiring, which can limit the movement of the workpiece and conductor. Furthermore, when using a magnetic flux conductor, as in the direct resistance heating method disclosed in Patent Document 2, it is possible to control the magnetic flux, but it is difficult to accurately control the current density distribution and heating temperature distribution.

[0008] The present invention has been made in light of the above circumstances, and one of its objects is to provide an improved AC resistance heating method and AC resistance heating device that are capable of controlling the current density distribution and heating temperature distribution of a workpiece. [Means for solving the problem]

[0009] An alternating current heating method according to one embodiment includes preparing a conductive workpiece, attaching a first terminal and a second terminal connected to a power source capable of supplying alternating current to the workpiece, arranging a first conductor in an electrically floating state in a position that generates a proximity effect when the alternating current is passed through the workpiece, and heating at least a portion of the workpiece by passing the alternating current through the workpiece via the first terminal and the second terminal.

[0010] The AC heating method may further include placing a ferromagnetic body near the workpiece. In this case, the workpiece, the first conductor, and the ferromagnetic body may be arranged so that the workpiece is located between the first conductor and the ferromagnetic body.

[0011] The AC heating method may further include arranging a second conductor connected to the second terminal and the power source in a state where the second conductor is electrically insulated from the first conductor. In this case, when at least a portion of the workpiece is heated, the AC current flows through a circuit including, in order, the first terminal, the workpiece, the second terminal, and the second conductor.

[0012] An AC current heating device according to one embodiment includes a power source capable of supplying AC current, first and second terminals connected to the power source and attachable to a conductive workpiece, and a first conductor that is in an electrically floating state and positioned at a position that generates a proximity effect when the AC current is passed through the workpiece, and heats at least a portion of the workpiece by passing the AC current through the first and second terminals.

[0013] For example, the first conductor may be tubular and include a first portion and a second portion divided in a circumferential direction, wherein the first portion has a first flange portion provided at an end in the circumferential direction, the second portion has a second flange portion provided at an end in the circumferential direction, and the first portion and the second portion are electrically connected by contacting the first flange portion and the second flange portion.

[0014] As another example, the first portion may have a first tapered surface provided at an end in the circumferential direction and inclined relative to the radial direction of the first conductor, and the second portion may have a second tapered surface provided at an end in the circumferential direction and inclined relative to the radial direction, and the first portion and the second portion may be electrically connected by contacting the first tapered surface and the second tapered surface.

[0015] As yet another example, the first portion and the second portion may be connected by a resilient or flexible conductive material.

[0016] As yet another example, one of the first part and the second part may have a recess provided at an end in the circumferential direction, and the other of the first part and the second part may have a protrusion that can be inserted into the recess.

[0017] As yet another example, the first portion and the second portion may be connected via a conductive liquid.

[0018] The first conductor is preferably made of a metal material with excellent conductivity, such as copper, a copper alloy, aluminum, or an aluminum alloy.

[0019] The AC heating device may further include a ferromagnetic body that can be placed near the workpiece. The AC heating device may also include a second conductor that is connected to the second terminal and the power source and is electrically insulated from the first conductor. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an improved AC current heating method and AC current heating device that are capable of controlling the current density distribution and heating temperature distribution of a workpiece. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an AC current heating device according to a first embodiment. [Figure 2] FIG. 2 is a schematic side view of a coil spring, a conductor, and a ferromagnetic body, which are examples of the workpiece. [Figure 3] FIG. 3 is a schematic side view showing another configuration that can be applied to a coil spring, a conductor, and a ferromagnetic material. [Figure 4] FIG. 4 is a schematic diagram for explaining the proximity effect. [Figure 5] FIG. 5 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring when no conductor is arranged. [Figure 6]FIG. 6 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring when a conductor is arranged. [Figure 7] FIG. 7 is a schematic perspective view showing the current density distribution (heating temperature distribution) of a coil spring when no conductor or ferromagnetic material is disposed. [Figure 8] FIG. 8 is a schematic perspective view showing the current density distribution (heating temperature distribution) of a coil spring when a ferromagnetic material is disposed therein. [Figure 9] FIG. 9 shows (a) a front view and (b) a side view of an example of a heating device equipped with a divided conductor. [Figure 10] FIG. 10 shows (a) a front view and (b) a side view of another example of a heating device having a divided conductor. [Figure 11] FIG. 11 shows (a) a front view and (b) a side view of yet another example of a heating device having a divided conductor. [Figure 12] FIG. 12 shows (a) a front view and (b) a side view of yet another example of a heating device having a divided conductor. [Figure 13] FIG. 13 is a diagram showing another example of a configuration that can be applied to the connection portion of the divided conductor. [Figure 14] FIG. 14 is a diagram showing yet another example of a configuration that can be applied to the connection portion of divided conductors. [Figure 15] FIG. 15 is a diagram showing yet another example of a configuration that can be applied to the connection portion of divided conductors. [Figure 16] FIG. 16 is a schematic cross-sectional view showing modified shapes that can be applied to the conductor. [Figure 17] FIG. 17 is a schematic cross-sectional view showing another modified shape that can be applied to the conductor. [Figure 18] FIG. 18 is a schematic cross-sectional view showing yet another modified shape that can be applied to the conductor. [Figure 19] FIG. 19 is a schematic cross-sectional view showing yet another modified shape that can be applied to the conductor. [Figure 20]FIG. 20 is a diagram showing a schematic configuration of a heating device according to the second embodiment. [Figure 21] FIG. 21 is a flowchart showing an example of a method for manufacturing a coil spring. [Figure 22] FIG. 22 is a flowchart showing another example of the method for manufacturing a coil spring. [Figure 23] FIG. 23 is a flowchart showing yet another example of the method for manufacturing a coil spring. DETAILED DESCRIPTION OF THE INVENTION

[0022] Several embodiments will be described with reference to the drawings. In each embodiment, a coil spring may be exemplified as the workpiece (heated object) to be heat-treated. However, the AC current heating device and the AC current heating method using the same disclosed in each embodiment can be applied to any heat-treated product.

[0023] For example, examples of workpieces other than coil springs include leaf springs, stabilizers for vehicles, various bent products, rolled materials, and composite materials. That is, the material of the workpiece may be a metal other than spring steel. Furthermore, the material of the workpiece is not limited to wire such as the wire that forms the coil spring, but may also be plate material or a deformed material such as a pipe material.

[0024] The type of heat treatment for the workpiece is not particularly limited, but examples include quenching, tempering, annealing, and softening of the workpiece surface.

[0025] [First embodiment] 1 is a diagram showing a schematic configuration of an AC current heating device 1 (hereinafter referred to as heating device 1) according to a 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.

[0026] 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. The control device 4 includes a power supply 41 that supplies AC current. The first terminal 3A and the second terminal 3B are connected to the power supply 41 via wiring. The frequency of the AC current supplied by the power supply 41 is not particularly limited, but a high frequency of 1 kHz or higher can be used, for example.

[0027] 1, each of the first terminal 3A and the second terminal 3B is divided into a lower portion 31 and an upper portion 32. The first terminal 3A and the second terminal 3B can be attached to a workpiece by sandwiching a part of the workpiece between the lower portion 31 and the upper portion 32. However, the structure for attaching the first terminal 3A and the second terminal 3B to the workpiece is not limited to this example.

[0028] Heating treatment by an AC current heating method (hereinafter referred to as the heating method) according to this embodiment is carried out using a heating apparatus 1. When carrying out heating treatment using the heating apparatus 1 according to this embodiment, a coil spring W, which is an example of a workpiece, is first prepared. The coil spring W is formed by spirally winding a wire such as spring steel using a coiling machine, and is electrically conductive.

[0029] Furthermore, the first terminal 3A and the second terminal 3B are attached to the coil spring W, and the coil spring W is disposed inside the conductor 2. Note that the order in which the step of attaching the first terminal 3A and the second terminal 3B to the coil spring W and the step of disposing the coil spring W inside the conductor 2 are performed is not particularly limited.

[0030] 1, the vicinity of terminals E1 and E2 of the coil spring W (at least a part of the end turn portion) protrudes from both ends of the conductor 2. This example is not limiting, and the entire coil spring W may be surrounded by the conductor 2.

[0031] The first terminal 3A and the second terminal 3B are attached, for example, near the terminals E1 and E2 of the coil spring W. In the example of Fig. 1, the vicinity of the terminal E1 of the coil spring W is sandwiched between the lower part 31 and the upper part 32 of the first terminal 3A. The vicinity of the terminal E2 of the coil spring W is sandwiched between the lower part 31 and the upper part 32 of the second terminal 3B.

[0032] When the first terminal 3A and the second terminal 3B are attached to the coil spring W, a circuit is formed in which these elements are connected in series with the power source 41. The control device 4 starts to pass current through the coil spring W in response to an operator operating a switch or receiving a control signal from outside. In FIG. 1, the solid arrow indicates an example of the direction of current flow. This direction switches periodically depending on the frequency of the power source 41.

[0033] This current flow heats at least a portion of the coil spring W. At this time, a proximity effect, which will be described later, occurs between the conductor 2 and the coil spring W. The conductor 2 is disposed in a position where this proximity effect occurs.

[0034] The frequency, amplitude, and energization time of the alternating current can be determined appropriately depending on the characteristics of the coil spring W (e.g., wire diameter, cross-sectional shape, coil diameter, coil length, pitch, number of turns, material), the part to be heated, the target heating temperature, etc. When the time to stop heating arrives, the control device 4 stops the current supply from the power source 41.

[0035] Thereafter, the coil spring W is cooled. This cooling may be natural cooling, or, if rapid cooling is required, may be performed by spraying a fluid such as water or air onto the coil spring W. In the example of FIG. 1, the heating device 1 includes a cooling mechanism 5 for spraying such a fluid.

[0036] For example, the cooling mechanism 5 includes a large number of nozzles 51 arranged on the inner surface of the conductor 2, a fluid supply source 52 provided in the control device 4, and piping 53 connecting each nozzle 51 to the fluid supply source 52. The fluid supply source 52 supplies fluid to each nozzle 51 via the piping 53 under the control of the control device 4, for example. At this time, the fluid is sprayed from each nozzle 51 toward the coil spring W. Note that the nozzles 51 do not necessarily have to be provided on the conductor 2, and may be provided on a member different from the conductor 2.

[0037] The heating device 1 may further include a ferromagnetic body 6 that can be arranged near the coil spring W. The ferromagnetic body 6 can be made of, for example, ferrite, but is not limited to this example. In the example of FIG. 1, the ferromagnetic body 6 is inserted inside the coil spring W.

[0038] 2 is a schematic side view of the coil spring W, conductor 2, and ferromagnetic body 6 assembled as shown in FIG. 2. Note that FIG. 2 also shows a cross-sectional structure of a portion of the conductor 2. In the following description, as shown in FIG. 2, 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.

[0039] The conductor 2 is, for example, cylindrical and centered on the axis AX. In the example of FIG. 2, the conductor 2 has a single-layer structure made of a conductive metal material. The conductor 2 is in an electrically floating state and is insulated from other conductive elements such as the coil spring W. The conductor 2 is supported, for example, by an insulating member (not shown).

[0040] 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 surface of the coil spring W via the gap G1. In the example of FIG. 2, the size of the gap G1 is constant at any position in the circumferential direction Dθ, but this is not limited to this example.

[0041] The ferromagnetic body 6 is, for example, cylindrical and centered on the axis AX. The ferromagnetic body 6 may have other shapes, such as a cylindrical shape, centered on the axis AX. The ferromagnetic body 6 is also electrically floating and is insulated from other conductive elements such as the conductor 2 and the coil spring W. The ferromagnetic body 6 is supported, for example, by an insulating member (not shown).

[0042] A gap G2 is formed between the ferromagnetic body 6 and the coil spring W. That is, the outer surface of the ferromagnetic body 6 faces the inner diameter side surface of the coil spring W via the gap G2. In the example of FIG. 2, the size of the gap G2 is constant at any position in the circumferential direction Dθ, but this is not limiting.

[0043] 3 is a schematic side view showing another configuration that can be applied to the coil spring W, the conductor 2, and the ferromagnetic body 6. This figure also shows a cross-sectional structure of a portion of the conductor 2. In the example of FIG. 3, the conductor 2 includes an insulating portion 21 and a conductive portion 22.

[0044] The insulating portion 21 is formed into a cylindrical shape from an insulating material such as plastic. The conductive portion 22 is formed from a conductive material such as copper, a copper alloy, aluminum, an aluminum alloy, or a composite material containing one or more of these, and covers the inner surface of the insulating portion 21. The conductive portion 22 faces the outer diameter side surface of the coil spring W via a gap G1.

[0045] The conductive portion 22 is, for example, a thin film formed or coated on the inner surface of the insulating portion 21. The conductive portion 22 may be a tape-like member attached to the inner surface of the insulating portion 21 via an adhesive layer. Alternatively, the conductive portion 22 may be a cylindrical member formed separately from the insulating portion 21 and fitted inside the insulating portion 21.

[0046] In one example, the conductive portion 22 covers the entire inner surface of the insulating portion 21. In another example, the conductive portion 22 may cover only a portion of the inner surface of the insulating portion 21.

[0047] Next, the role of the conductor 2 will be described. When a current flows through a workpiece such as a coil spring W, if an electrically floating conductor is placed nearby, a so-called proximity effect occurs. In this embodiment, this proximity effect is utilized to control the current density distribution (heating temperature distribution) of the coil spring W.

[0048] FIG. 4 is a schematic diagram for explaining the proximity effect, showing a rod-shaped workpiece Ws and a conductor 2s placed in its vicinity. A current I from a power source flows into the workpiece Ws. A When the magnetic field H flows, a magnetic field H IA occurs (Ampere's law).

[0049] In the conductor 2s, this magnetic field H IA The eddy current I caused by E1 occurs (Lenz's law). Furthermore, eddy current I E1 The magnetic field H caused by IE is generated around the conductor 2s. This magnetic field H IE acts on the workpiece Ws, an eddy current I E2 occurs.

[0050] current I A , eddy current I E1 and eddy current I E2 The direction of the current is as shown by the arrow in the figure. That is, in the workpiece Ws, the current I flows near the side far from the conductor 2s. A flow direction and eddy current I E2 On the other hand, near the side of the conductor 2s, the current I A flow direction and eddy current I E2 This causes the current density of the workpiece Ws to be higher near the side surface closer to the conductor 2s.

[0051] By utilizing this proximity effect, it is possible to control the current density distribution and heat density distribution of the workpiece Ws. For example, if a conductor 2s is placed so as to face a portion of the outer surface of the workpiece Ws as shown in Figure 4, it is possible to obtain a current density distribution and heat density distribution that change depending on the circumferential position on the surface and inside of the workpiece Ws. These distributions can be adjusted appropriately, for example, by changing the distance between the conductor 2s and the workpiece Ws.

[0052] Furthermore, when the conductor 2s is positioned so as to face only a portion of the workpiece Ws in the longitudinal direction, a current density distribution and a heat density distribution that change depending on the longitudinal position on the surface and inside of the workpiece Ws can be obtained.

[0053] Next, the electrical heating and proximity effect when the workpiece is a coil spring W will be explained using Fig. 5 and Fig. 6. Fig. 5 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring W when the conductor 2 is not arranged. Fig. 6 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring W when the conductor 2 is arranged. These figures show only a portion of the coil spring W and the conductor 2. Furthermore, dot patterns are added to the coil spring W in areas where the current density is high (areas where the heating temperature is high).

[0054] When an AC current flows through a workpiece such as a coil spring W, the current density on the surface increases due to the skin effect. Furthermore, in a workpiece having a non-linear bend such as a coil spring W, the current path passing through the inner surface of the bend is short, so the current density tends to increase near the inner surface of the bend.

[0055] 5, the current density near the inner diameter surface S1 of the coil spring W (the portion of the surface of the coil spring W facing the axis AX) is higher than that near the outer diameter surface S2, and therefore the area near the inner diameter surface S1 is preferentially heated.

[0056] In contrast, when the conductor 2 is disposed around the coil spring W, the current that was concentrated near the inner diameter surface S1 is drawn toward the outer diameter side due to the proximity effect described above. This makes it possible to make the current density distribution and heating temperature distribution uniform in the circumferential direction of the wire of the coil spring W, as shown in FIG. 6, for example. As another example, the gap G1 between the conductor 2 and the coil spring W may be adjusted so that the current density near the outer diameter surface S2 is higher than the current density near the inner diameter surface S1. In addition, the current density distribution and heating temperature distribution achieved by the heating device 1 can be adjusted appropriately depending on the characteristics required of the workpiece.

[0057] The current density distribution and heating temperature distribution can also be controlled by the ferromagnetic body 6. FIG. 7 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring W when the conductor 2 and the ferromagnetic body 6 are not arranged. FIG. 8 is a schematic perspective view showing the current density distribution (heating temperature distribution) of the coil spring W when the ferromagnetic body 6 is arranged. These figures show only a portion of the coil spring W and the conductor 2. As in FIGS. 5 and 6, dot patterns are added to the coil spring W at locations where the current density is high (locations where the heating temperature is high).

[0058] As described above, when the conductor 2 and the ferromagnetic body 6 are not provided, the current density near the inner diameter surface S1 is higher than that near the outer diameter surface S2, as shown in Fig. 7. The ferromagnetic body 6 has a function of influencing the magnetic flux generated when current is passed through, and spreading the uneven current density shown in Fig. 7 toward the outer diameter side of the coil spring 2.

[0059] Therefore, by arranging the ferromagnetic material 6 as shown in Fig. 8, it is possible to control the current density distribution and the heating temperature distribution in the same way as when arranging the conductor 2. In the example of Fig. 8, the current density distribution and the heating temperature distribution are made uniform in the circumferential direction of the wire of the coil spring W, but this is not limiting.

[0060] 1 to 3 illustrate an example in which the conductor 2 is a seamless cylindrical member. However, this is not limiting, and the conductor 2 may be divided into multiple parts. FIG. 9 shows (a) a front view and (b) a side view of an example of a heating device 1 including a divided conductor 2. In the example shown in this figure, the conductor 2 has a first part 2A and a second part 2B divided in the circumferential direction Dθ.

[0061] This configuration facilitates the task of arranging the conductor 2 around the coil spring W. For example, even after the first terminal 3A and the second terminal 3B are attached to the coil spring W, the conductor 2 can be installed without being obstructed by these terminals 3A, 3B or the wiring connecting these terminals 3A, 3B to the power source 41.

[0062] On the other hand, if the first portion 2A and the second portion 2B are spaced apart as shown in FIG. 9, an eddy current I generated in the conductor 2 when current is applied to the coil spring W will flow. E1 is folded back at the ends of the first portion 2A and the second portion 2B. This causes the proximity effect on the coil spring W to be non-uniform, resulting in undesirable irregularities in the current density distribution. Note that even when the ends of the first portion 2A and the second portion 2B are in contact with each other, the current density distribution of the coil spring W may be disrupted near the boundary between the first portion 2A and the second portion 2B.

[0063] 10 shows (a) a front view and (b) a side view of another example of a heating device 1 including a divided conductor 2. In this example, the conductor 2 is also divided into a first portion 2A and a second portion 2B. Furthermore, the first portion 2A has a first flange portion 23A, and the second portion 2B has a second flange portion 23B.

[0064] The first flange portion 23A protrudes in the radial direction DR from both ends of the first portion 2A in the circumferential direction Dθ. The second flange portion 23B protrudes in the radial direction DR from both ends of the second portion 2B in the circumferential direction Dθ. These flange portions 23A, 23B extend parallel to the axial direction DX.

[0065] The flange portions 23A, 23B may be connected by a plurality of connecting members 24. The connecting members 24, for example, press the flange portions 23A, 23B together, and may be a combination of bolts and nuts, or a clip-like member that clamps the flange portions 23A, 23B.

[0066] By pressing the flange portions 23A and 23B together, the first portion 2A and the second portion 2B are electrically connected to each other, and the boundary between them is free from eddy current I E1 Therefore, the influence of the eddy current I E1 The current does not turn back at the boundary and flows almost seamlessly through the conductor 2. This makes the proximity effect on the coil spring W uniform, and a suitable current density distribution can be obtained.

[0067] 11 shows (a) a front view and (b) a side view of yet another example of a heating device 1 including a divided conductor 2. In this example, the conductor 2 is also divided into a first portion 2A and a second portion 2B. Furthermore, the first portion 2A has a first tapered surface 25A, and the second portion 2B has a second tapered surface 25B.

[0068] The first tapered surfaces 25A are provided at both ends of the first portion 2A in the circumferential direction Dθ and are inclined with respect to the radial direction DR. The second tapered surfaces 25B are provided at both ends of the second portion 2B in the circumferential direction Dθ and are inclined with respect to the radial direction DR.

[0069] The first portion 2A and the second portion 2B are arranged so that the tapered surfaces 25A and 25B are in surface contact with each other. A connecting member may be further provided to press the first portion 2A and the second portion 2B together so that the tapered surfaces 25A and 25B are in pressure contact with each other.

[0070] 11, 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, thereby providing good electrical conduction between the first portion 2A and the second portion 2B, thereby achieving the same effect as the example of FIG.

[0071] 12 is a front view (a) and a side view (b) showing yet another example of a heating device 1 including a divided conductor 2. In this example, the conductor 2 is also divided into a first portion 2A and a second portion 2B. Furthermore, the first portion 2A and the second portion 2B are connected by a plurality of conductive members 26.

[0072] The conductive material 26 is, for example, sheet-shaped, with one end connected to an end of the first portion 2A in the circumferential direction Dθ and the other end connected to an end of the second portion 2B in the circumferential direction Dθ. The conductive material 26 has flexibility that allows it to bend when the ends of the first portion 2A and the second portion 2B are brought close to each other, as shown in FIG. 12(b), for example. Note that FIG. 12 shows a state in which the ends of the first portion 2A and the second portion 2B are spaced apart, but when electricity is applied, the first portion 2A and the second portion 2B are pressed together so that these ends contact each other. Note that the conductive material 26 is not limited to a flexible sheet-shaped material. As another example, the conductive material 26 may be an elastic leaf spring or the like.

[0073] By providing such conductive material 26, it is possible to reliably establish electrical continuity between first portion 2A and second portion 2B even when the ends of first portion 2A and second portion 2B are spaced apart, as shown in Fig. 12(b), for example, thereby achieving the same effects as those achieved by the examples of Figs. 10 and 11.

[0074] As shown in Fig. 12(a), each conductive material 26 may be disposed at a position where the boundary between the first portion 2A and the second portion 2B faces the outer diameter side surface of the coil spring W. This prevents the eddy current I generated along the coil spring W from flowing. E1 This makes the path less likely to be disrupted.

[0075] 13 to 15 are diagrams showing other examples of configurations that can be applied to the connection portion between the first portion 2 A and the second portion 2 B. In these examples, a recess 200A is provided at the end of the first portion 2 A, and a protrusion 200B is provided at the end of the second portion 2 B.

[0076] The recessed portion 200A and the protruding portion 200B have shapes that fit together. Specifically, the recessed portion 200A and the protruding portion 200B in the example of Fig. 13(a) both have V-shaped cross sections. Furthermore, the recessed portion 200A and the protruding portion 200B in the example of Fig. 14(a) both have rectangular cross sections.

[0077] 13(b) and 14(b), when connecting the first portion 2A and the second portion 2B, the protrusion 200B is inserted into the recess 200A. This prevents the first portion 2A and the second portion 2B from shifting, and increases the contact area between the first portion 2A and the second portion 2B compared to when their ends are flat, resulting in good electrical continuity between the first portion 2A and the second portion 2B.

[0078] The shapes of the recessed portion 200A and the protruding portion 200B in the example of FIG. 15(a) are the same as those in the example of FIG. 13. However, in the example of FIG. 15(b), a conductive liquid 201 is disposed between the connection surfaces of the first portion 2A and the second portion 2B. For example, the conductive liquid 201 may be a conductive paste, a conductive grease, or a conductive adhesive. Such conductive liquid 201 may be applied to the recessed portion 200A before connection, to the protruding portion 200B, or to both the recessed portion 200A and the protruding portion 200B.

[0079] 13 to 15 show an example of a configuration in which a recess is provided in the first portion 2A located at the bottom and a protrusion is provided in the second portion 2B located at the top. However, this example is not limiting, and a protrusion may be provided in the first portion 2A and a recess may be provided in the second portion 2B. Furthermore, a conductive liquid 201 shown in FIG. 15 may be disposed on the end of the first portion 2A or the second portion 2B in the configurations shown in FIGS. 10, 11, 12, and 14.

[0080] 9 to 15 show an example in which the conductor 2 is divided into two parts in the circumferential direction Dθ. However, the conductor 2 may be divided into three or more parts in the circumferential direction Dθ. Also, the conductor 2 may be divided into multiple parts in the axial direction DX. In these cases, the same structures as those shown in FIGS. 10 to 15 may be applied to connect the multiple divided parts.

[0081] 1 and 2, a conductor 2 having a regular cylindrical shape is shown as an example. However, various shapes can be applied to the conductor 2 depending on the workpiece. FIGS. 16 to 19 are schematic cross-sectional views showing modified shapes that can be applied to the conductor 2. These figures show a cross-section of a portion of the workpiece Wt and a cross-section of the conductor 2 in the vicinity thereof. For example, if the workpiece Wt is a coil spring W, the cross-section of the workpiece Wt in each figure corresponds to the cross-section of the wire of the coil spring W.

[0082] 16 to 19, the conductor 2 surrounds the workpiece Wt on three sides. Specifically, in the example of Fig. 16, the conductor 2 has a pair of flat portions 27a, 27b and a bent portion 27c connecting these flat portions 27a, 27b. The cross-sectional shape of the bent portion 27c is a smoothly curved arc that follows the outer peripheral surface of the workpiece Wt.

[0083] 17, the conductor 2 has a pair of flat portions 28a and 28b that are parallel to each other, and a flat portion 28c that connects these flat portions 28a and 28b. The flat portion 28c is perpendicular to the flat portions 28a and 28b.

[0084] 18, the conductor 2 has a pair of parallel flat portions 29a, 29b and a bent portion 29c connecting the flat portions 29a, 29b. The cross-sectional shape of the bent portion 29c is a smoothly curved arc that follows the outer peripheral surface of the workpiece Wt.

[0085] 19, the conductor 2 covers the entire periphery of the workpiece Wt. The cross-sectional shape of the conductor 2 is, for example, a perfect circle, but may be another shape such as an oval.

[0086] For example, when the workpiece Wt is a coil spring W, the conductor 2 may have a structure in which the shapes shown in any of Figures 16 to 18 are continuously arranged in the axial direction DX. Also, the conductor 2 may be formed by appropriately combining the shapes shown in Figures 16 to 19. In addition, various other shapes may be applied to the conductor 2.

[0087] In the heating device 1 and heating method according to the present embodiment described above, the proximity effect occurring between the electrically floating conductor 2 and the workpiece controls the current density distribution and heating temperature distribution in the workpiece. This makes it possible to control the distribution of properties such as hardness, stress, and structure in 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, heating temperature distribution, and the resulting property distributions is further improved.

[0088] 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 position where the conductor 2 faces on the workpiece surface, the distance between the ferromagnetic material 6 and the workpiece, the shape and material of the ferromagnetic material 6, the position where the ferromagnetic material 6 faces on the workpiece surface, the time during which current is passed through the workpiece (heating time), and the frequency of the power source 41, it is possible to control the distribution of characteristics in the depth direction from the surface of the workpiece, the circumferential direction of the workpiece, the length direction of the workpiece, etc. In addition to the above, various other advantageous effects can be obtained from this embodiment.

[0089] [Second embodiment] A second embodiment will be described. The same elements as those in the first embodiment are given the same reference numerals, and redundant explanations will be omitted.

[0090] 20 is a diagram showing a schematic configuration of a heating device 1 according to a second embodiment. Like the first embodiment, this 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 also include a cooling mechanism 5 and a ferromagnetic body 6, like the example in FIG.

[0091] 20 further includes a conductor 7 (second conductor) and a third terminal 3C. The conductor 7 has a shape that allows it to be arranged so as to surround the conductor 2 and the coil spring W. For example, the conductor 7 is cylindrical with both ends open, but may have other shapes.

[0092] The conductor 7 is made of a metal material with excellent conductivity, such as copper, a copper alloy, aluminum, an aluminum alloy, or a composite material containing one or more of these. The conductor 7 is electrically insulated from the conductor 2. The conductors 2 and 7 may simply be spaced apart, or an insulating layer may be disposed between them.

[0093] The second terminal 3B is connected to the conductor 7 via a wire. The conductor 7 is connected to the third terminal 3C via a wire. Furthermore, the third terminal 3C is connected to the power supply 41 via a wire.

[0094] When the first terminal 3A and the second terminal 3B are attached to the coil spring W, a circuit is formed in which the power source 41, the first terminal 3A, the coil spring W, the second terminal 3B, the conductor 7, and the third terminal 3C are connected in this order. In Figure 20, the solid arrows indicate an example of the current flowing in this circuit. The direction of this current flow switches periodically depending on the frequency of the power source 41.

[0095] As in the first embodiment, the configuration of the heating device 1 according to this embodiment also makes it possible to control the current density distribution and heating temperature distribution of the coil spring W by the conductor 2 and the ferromagnetic material 6. All of the various configurations disclosed in the first embodiment can also be applied to the heating device 1 according to the second embodiment.

[0096] The conductor 7 may be divided into multiple parts, like the conductor 2 shown in FIGS. 9 to 15. In this case, the conductor 7 can be easily installed around the coil spring W and the conductor 2. The arrangement of the conductor 2, the conductor 7, the coil spring W, and the ferromagnetic body 6 is not limited to that shown in FIG. 20. For example, the conductor 7 may be arranged inside the coil spring W. In this case, the conductor 2 may be arranged between the coil spring W and the conductor 7, and the ferromagnetic body 6 may be arranged outside the coil spring W.

[0097] [Example of application to coil spring manufacturing methods] Here, a method for manufacturing a coil spring incorporating the heating method using the heating device 1 disclosed in the first and second embodiments will be exemplified.

[0098] 21 is a flowchart showing an example of a method for manufacturing a coil spring. This example corresponds to so-called hot forming, in which a wire such as spring steel is first heated (step P11). Furthermore, the wire, which has been heated in step P11, is formed into a spiral shape using a coiling machine (step P12). In steps P11 and P12, the wire is quenched. If necessary, after step P12, surface quenching is performed to reduce the hardness of the inner part of the wire near the surface (step P13). Thereafter, the wire is tempered (step P14).

[0099] After step P13, a surface softening treatment may be performed to soften the surface of the wire (step P15). This surface softening treatment may be performed on the entire coil spring or on a portion of the coil spring in the longitudinal direction, such as the end turn portion.

[0100] 22 is a flowchart showing another example of a method for manufacturing a coil spring. In this example, first, a wire is formed into a spiral shape using a coiling machine (step P21). After step P21, the wire is quenched (step P22). Thereafter, if necessary, the wire is subjected to surface quenching similar to step P13 (step P23). Furthermore, the wire is subjected to tempering similar to step P14 (step P24). After step P23, a surface softening treatment similar to step P15 may be performed (step P25).

[0101] 23 is a flowchart showing yet another example of a method for manufacturing a coil spring. This example corresponds to so-called cold forming, in which the wire is first quenched (step P31). After quenching, the wire is tempered (step P32).

[0102] After step P32, the wire is formed into a spiral shape using a coiling machine (step P33). Furthermore, the wire is annealed by heating it to a predetermined temperature (step P34). After step P33, a surface softening treatment similar to step P15 may be performed (step P35).

[0103] The heating method using the heating device 1 disclosed in each embodiment can be applied to heat treatments after the wire is formed into a spiral shape, 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 the surface softening in steps P15, P25, and P35 is performed on a portion of the coil spring in the longitudinal direction, such as the end turn portion, the first terminal 3A and the second terminal 3B may be attached to both ends of that portion.

[0104] The heating method using the heating device 1 disclosed in each embodiment may be applied to heat treatment of the wire before it is formed into a spiral shape, such as quenching in step P31 or tempering in step P32.

[0105] The scope of the present invention is not limited to the configurations disclosed in the first and second embodiments and the application examples to the manufacturing method of a coil spring. The present invention can be implemented by modifying the configurations disclosed in the embodiments and application examples in various ways. [Explanation of symbols]

[0106] 1...AC heating device, 2...conductor (first conductor), 3A...first terminal, 3B...second terminal, 4...control device, 5...cooling mechanism, 6...ferromagnetic material, 7...conductor (second conductor), 41...power source, W...coil spring (workpiece), DX...axial direction, DR...radial direction, Dθ...circumferential direction.

Claims

1. Prepare a conductive workpiece. a first terminal and a second terminal connected to a power source capable of supplying alternating current are attached to the workpiece; a first conductor in an electrically floating state is disposed at a position where a proximity effect occurs when the AC current is passed through the workpiece; At least a portion of the workpiece is heated by passing the AC current through the first terminal and the second terminal. An alternating current heating method comprising:

2. Further comprising disposing a ferromagnetic body in the vicinity of the workpiece. The AC heating method according to claim 1 .

3. The workpiece, the first conductor, and the ferromagnetic material are arranged so that the workpiece is located between the first conductor and the ferromagnetic material. The AC heating method according to claim 2.

4. further comprising disposing a second conductor connected to the second terminal and the power source in an electrically insulated state from the first conductor; When at least a portion of the workpiece is heated, the AC current flows through a circuit including the first terminal, the workpiece, the second terminal, and the second conductor in this order. The AC heating method according to any one of claims 1 to 3.

5. a power source capable of supplying alternating current; a first terminal and a second terminal connected to the power source and attachable to a conductive workpiece; a first conductor that is in an electrically floating state and is disposed at a position where a proximity effect occurs when the AC current is passed through the workpiece; Equipped with At least a portion of the workpiece is heated by passing the AC current through the first terminal and the second terminal. AC heating device.

6. the first conductor is cylindrical and includes a first portion and a second portion that are circumferentially divided; the first portion has a first flange portion provided at an end portion in the circumferential direction, the second portion has a second flange portion provided at an end portion in the circumferential direction, When the first flange portion and the second flange portion are brought into contact with each other, the first portion and the second portion are electrically connected. The AC heating device according to claim 5.

7. the first conductor is cylindrical and includes a first portion and a second portion that are circumferentially divided; the first portion is provided at an end in the circumferential direction and has a first tapered surface inclined with respect to a radial direction of the first conductor; the second portion has a second tapered surface provided at an end in the circumferential direction and inclined with respect to the radial direction, The first portion and the second portion are electrically connected by bringing the first tapered surface and the second tapered surface into contact with each other. The AC heating device according to claim 5.

8. the first conductor is cylindrical and includes a first portion and a second portion that are circumferentially divided; the first portion and the second portion are connected by a conductive material having elasticity or flexibility; The AC heating device according to claim 5.

9. the first conductor is cylindrical and includes a first portion and a second portion that are circumferentially divided; one of the first portion and the second portion has a recess provided at an end portion in the circumferential direction, the other of the first portion and the second portion has a protrusion that can be inserted into the recess. The AC heating device according to claim 5.

10. the first conductor is cylindrical and includes a first portion and a second portion that are circumferentially divided; the first portion and the second portion are connected via a conductive liquid; The AC heating device according to claim 5.

11. the first conductor is copper, a copper alloy, aluminum, or an aluminum alloy; The AC heating device according to any one of claims 5 to 10.

12. Further comprising a ferromagnetic body that can be arranged in the vicinity of the workpiece. The AC heating device according to any one of claims 5 to 10.

13. a second conductor connected to the second terminal and the power source and electrically insulated from the first conductor; The AC heating device according to any one of claims 5 to 10.

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