Heating coil for high frequency heating device

Abstract

To provide a heating coil that is capable of efficiently performing a quenching treatment on a workpiece in a short time, effectively restraining occurrence of a situation in which a part of the workpiece is overheated due to its shape, preventing a decrease in the mechanical strength of the workpiece, and easily controlling the depth of a hardened layer to be formed by quenching the workpiece.SOLUTION: A heating coil 1 has grounding portions 2a, 2b to be brought into contact with electrodes, support portions 3a, 3b arranged to be perpendicular to the grounding portions 2a, 2b, respectively, and a series of circumferential heating portion 4 provided to connect the tips of the support portions 3a, 3b. The heating coil 1 is also provided with an attachment 21 having a shield body 26 that is interposed between the heating portion 4 and the workpiece W and functions as a heat shield for reducing the degree of quenching of the workpiece W by the heating portion 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heating coil used in a high-frequency heating device for heating a workpiece by utilizing electromagnetic induction caused by a high-frequency current. [Background technology]

[0002] In order to increase the hardness of the surface of a metal workpiece, the surface of the workpiece is heated to a temperature equal to or higher than the transformation point (austenite transformation point) of the metal and then rapidly cooled (so-called quenching). A method of performing such quenching is widely adopted in which a metal member (heating coil) through which a high-frequency current flows is brought close to the surface of the workpiece using a high-frequency heating device to heat the workpiece. As a heating coil used for such quenching, as shown in Patent Document 1, a ring-shaped coil part made of a metal pipe to be fitted around the workpiece is connected to a conductive plate (copper plate) for supplying high-frequency power. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-115428 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-mentioned conventional heating coil for high-frequency heating devices, current always flows in one direction inside the annular coil, so if a large amount of current flows inside the coil, the workpiece is overheated, the crystal grains of the quenched structure of the workpiece become coarse, and the toughness decreases, resulting in a decrease in mechanical strength. On the other hand, if only a small amount of current flows inside the coil, the hardened layer depth of the workpiece becomes shallow, resulting in insufficient quenching. Therefore, with the conventional heating coil for high-frequency heating devices, it is difficult to control the depth of the hardened layer caused by quenching the workpiece.

[0005] The object of the present invention is to provide a practical heating coil which solves the above-mentioned problems of heating coils for conventional high-frequency heating devices, can perform quenching treatment on a workpiece efficiently in a short time, can effectively prevent the occurrence of a situation in which a portion of the workpiece is overheated due to its shape, can prevent a decrease in the mechanical strength of the workpiece, and can easily control the depth of the hardened layer caused by quenching the workpiece. [Means for solving the problem]

[0006] Among the present inventions, the invention described in claim 1 is a heating coil used in a high-frequency heating device for heating a workpiece by utilizing electromagnetic induction by high-frequency current, characterized in that it comprises a coil body having a pair of plate-shaped grounding portions for contacting an electrode through which a high-frequency current is passed, a pair of plate-shaped supporting portions arranged perpendicular to each of the grounding portions, and a series of circumferential heating portions arranged to connect the tips of the supporting portions, and an attachment having a heat shield interposed between the heating portions and the workpiece to reduce the degree of hardening of the workpiece by the heating portions.

[0007] The invention described in claim 2 is the invention described in claim 1, characterized in that the attachment is capable of changing the amount of the heat shield interposed between the heating part and the workpiece.

[0008] The invention described in claim 3 is the invention described in claim 2, characterized in that the heat shield is rotatably arranged relative to the center of the heating part, and the amount of intervention between the heating part and the workpiece can be changed by changing the rotational phase of the heat shield. Effect of the Invention

[0009] The heating coil for the high-frequency heating device described in claim 1 (hereinafter simply referred to as the heating coil) has a heat shield provided on the attachment that is interposed between the workpiece and the heating portion of the coil body, thereby reducing the magnetic flux generated by the high-frequency current and preventing the workpiece from being locally overheated (i.e., the effect of suppressing temperature rise in areas that are prone to overheating can be adjusted), making it possible to easily control the depth of the hardened layer caused by quenching the workpiece.

[0010] The heating coil described in claim 2 can adjust the amount of magnetic flux generated by high-frequency current by changing the amount of heat shield of the attachment placed between the heating part of the coil body and the workpiece, so that the depth of the hardened layer caused by quenching the workpiece can be controlled (finely adjusted) with great precision.

[0011] The heating coil described in claim 3 makes it possible to change the amount of heat shield interposed between the heating part and the workpiece by changing the rotational phase of the heat shield of the attachment, so that the depth of the hardened layer caused by quenching the workpiece can be very easily controlled by simply changing the rotational phase of the heat shield of the attachment. [Brief description of the drawings]

[0012] [Figure 1] FIG. [Diagram 2] FIG. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] FIG. [Figure 6] 4A and 4B are explanatory diagrams showing a vertical cross section of a heating coil (a is a cross section taken along line AA in FIG. 3, and b is an enlarged view of a portion α in a). [Figure 7] FIG. [Figure 8] 1A and 1B are explanatory views showing the attachment with the connecting member removed (FIG. 1A is a plan view, and FIG. 1B is a front view). [Figure 9] FIG. 4 is an explanatory diagram (a cross-sectional view taken along line AA in FIG. 3) showing a state in which a heating coil is in use. [Figure 10] 13 is an explanatory diagram (plan view) showing how to change (adjust) the position of the heat shield of the attachment. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a heating coil according to the present invention will be described in detail with reference to the drawings. <Heating coil structure> 1 to 6 show a heating coil. The heating coil 1 includes a coil body 11 made of a metal base 5 integrally formed from a copper alloy (high copper alloy), an insulating plate 16 formed into a sheet from a synthetic resin (fluororesin) having insulating and heat-resistant properties, and an attachment 21 having a shield body 26 that is interposed between the heating portion 4 of the metal base 5 of the coil body 11 and the workpiece (work) and functions as a heat shield to reduce the degree of hardening of the workpiece by the heating portion 4.

[0014] <Metal substrate structure> The metal base 5 of the coil body 11 is formed by a modeling method using a three-dimensional printer, and has grounding parts 2a, 2b for contacting the electrodes of a high-frequency power supply, a series of circumferential heating parts 4 for heating the workpiece by induction heating, and supporting parts 3a, 3b for supporting the heating parts 4 at positions away from the grounding parts 2a, 2b. The metal base 5 has dimensions of length (front-back) × width (width) × height = 300 mm × 150 mm × 100 mm (lengths of the maximum parts of length, width, and height).

[0015] The heating unit 4 is for heating the workpiece inserted therein, and is ring-shaped (annular) with its base end separated into left and right. An upper heating area 13a is formed on the left side of the base end of the heating unit 4, which is arc-shaped at an angle of about 45°. The upper heating area 13a is connected to a lower heating area 15, which is arc-shaped at an angle of about 120°, via a first vertical body 17 extending vertically. On the other hand, an upper heating area 13b is formed on the right side of the base end of the heating unit 4, which is arc-shaped at an angle of about 30°. The upper heating area 13b is connected to a middle heating area 14, which is arc-shaped at an angle of about 30°, via a third vertical body 19 extending vertically. The middle heating area 14 is connected to the lower heating area 15 via a second vertical body 18 extending vertically. The upper heating regions 13a, b, the middle heating region 14, and the lower heating region 15 are arranged so that their longitudinal direction (the direction forming the circular arc) is horizontal. The lower surface of the lower heating region 15 is formed with a tapered surface 20 that is inclined so that the diameter becomes smaller from the top to the bottom (see FIG. 6). The length from the center of the heating unit 4 to the outer periphery of the lower heating region 15, which is the outermost part, is about 75 mm.

[0016] Furthermore, inside the heating part 4 (i.e., inside the left and right upper heating regions 13a, 13b, middle heating region 14, lower heating region 15, first vertical body 17, second vertical body 18, and third vertical body 19), a cooling medium flow path 6 for cooling the heating part 4 itself by flowing a cooling medium (water, etc.) downward is provided in a hollow shape. The left and right separated parts of the base end of the heating part 4 are connected to the tips (tips at the bottom ends) of the left and right support parts 3a, 3b, respectively.

[0017] Each of the support parts 3a, 3b is formed as a pair of flat rectangular parallelepipeds (plates) on the left and right, and is arranged adjacent to each other on the left and right with a predetermined distance (about 2 mm) between them, with one plate surface facing each other. The front upper part of each of the support parts 3a, 3b is chamfered in an arc shape. A cooling medium flow path (not shown) is formed inside (at the lower end edge) of each of the support parts 3a, 3b so as to communicate with the cooling medium flow path 6 inside the heating part 4.

[0018] On the other hand, each grounding portion 2a, 2b is formed in a pair of flat rectangular parallelepipeds (plates) on the left and right, and is arranged so that the inner side faces each other and are adjacent to each other on the left and right at a predetermined distance (about 2 mm). The inner edge of each grounding portion 2a, 2b is connected to the base end edge of the left and right support portions 3a, 3b, and the plate surface of each grounding portion 2a, 2b is perpendicular to the plate surface of each support portion 3a, 3b. In addition, cylindrical exhaust pipes 7a and injection pipes 7b are provided near the center (approximately the center in the height direction) of the back surface of each grounding portion 2a, 2b, and the exhaust pipes 7a and injection pipes 7b are connected to a cooling medium flow path (not shown) formed vertically inside each grounding portion 2a, 2b. Furthermore, the cooling medium flow path inside each grounding portion 2a, 2b is connected (communicates) with the cooling medium flow path (not shown) inside each support portion 3a, 3b at the lower end of each grounding portion 2a, 2b.

[0019] Furthermore, a sheet-like insulating plate 16 having a predetermined thickness (about 2.0 mm) is sandwiched between the left and right grounding parts 2a, 2b of the metal base 5, between the left and right supporting parts 3a, 3b, and between the left and right base end parts of the heating part 4, and in this state, the left and right supporting parts 3a, 3b and the insulating plate 16 are screwed together by screw members (bolts and nuts) 10, 10 inserted through screw holes (not shown). Note that the screw members 10, 10 screw together the supporting parts 3a, 3b and the insulating plate 16 via bushes (not shown) made of synthetic resin (glass epoxy resin) having insulating and heat-resistant properties, so that the supporting parts 3a, 3b are not electrically connected to each other via the screw members 10, 10.

[0020] <Method of manufacturing metal substrate> The above-mentioned metal base 5 can be integrally formed by a modeling method based on three-dimensional data using a three-dimensional printer (hereinafter referred to as a three-dimensional additive manufacturing method). When formed by such a three-dimensional additive manufacturing method, it is possible to continue using it for a long period of time without damage even under high output conditions, and it is possible to reproducibly manufacture the same characteristics at the time of manufacture, and it is preferable to obtain a metal base 5 that is lightweight and has good handleability. As such a three-dimensional additive manufacturing method, a modeling method (partial deposition lamination method of conductive material powder layer) in which powder made of a conductive material is laid, melted (melted by irradiation of a laser such as a semiconductor laser, a carbon dioxide gas laser, an excimer laser, a YAG laser, or a fiber laser), solidified, and laminated based on three-dimensional data, or a modeling method (melt extrusion lamination method of conductive material) in which a molten conductive material is laminated based on three-dimensional data, etc. can be adopted. In addition, when the partial deposition lamination method of conductive material powder layer is used as the three-dimensional additive manufacturing method, it is preferable because it is possible to easily manufacture a metal base 5 having a complex shape and structure.

[0021] In addition, as the conductive material used as the raw material for the three-dimensional additive manufacturing method, copper, brass, silver, etc. can be suitably used. Among these conductive materials, copper is preferable because it can reduce the cost of materials, etc., and can manufacture the metal base cheaply and easily using a three-dimensional printer. In addition, the conductivity of the metal base is very good, and the heat generation efficiency by electromagnetic induction is high. In addition, when copper is used as the conductive material, it is possible to use pure copper, but it is preferable to use an alloy (high copper alloy) in which copper contains iron, tin, nickel, titanium, beryllium, zirconium, chromium, silicon, etc. in a smaller proportion than copper, because it is possible to increase the absorption of the laser and promote the temperature rise. Furthermore, among these copper alloys, it is more preferable to use a copper-chromium alloy in which copper contains chromium, because it is possible to effectively increase the strength of the metal base while maintaining high manufacturing efficiency by the three-dimensional printer, and it is particularly preferable to use an alloy in which copper contains chromium and zirconium in a predetermined proportion.

[0022] <Attachment structure> FIG. 7 shows the attachment 21, which is composed of a support member 22 to which a shield member 24 (shield body 26) is fixed so that its position can be adjusted, and a pair of left and right connecting members 23a, 23b for attaching the support member 22 to the coil body 11.

[0023] The support member 22 is made of ceramics and formed into a flat cylindrical shape having a certain width (i.e., a certain inner diameter (196 mmφ) and outer diameter (225 mmφ)) and an integral height (approximately 15 mm). Then, horizontally elongated insertion holes 31, 31 having a certain vertical width are provided on the left and right sides so as to penetrate between the inner wall and the outer wall. In addition, an angle display section 34 indicating the rotation angle (rotation phase) of the shield member 24 (shield body 26) relative to the center is formed on the left surface of the support member 22, and eight scales are provided at angular intervals of 5°. Furthermore, screw holes 33, 33 for mounting the connection members 23a, 23b are drilled on the left and right sides of the base end side (the attachment side of the connection members 23a, 23b) of the support member 22.

[0024] On the other hand, the shield member 24 is made of ceramics and has a shape in which a ring-shaped (strip-shaped) shield body 26 with a constant width and a central angle of 90° protrudes inward from the lower end of a flat cylindrical abutment body 25. The abutment body 25 has an outer diameter (about 195 mmφ) that is slightly smaller than the inner diameter (196 mmφ) of the support member 22, and has a thickness of about 5.0 mm. Therefore, when the attachment 21 is attached to the coil body 11, the inner wall of the abutment body 25 faces the outer circumferential surface of the lower heating region 15 of the heating unit 4 at a distance of about 15 mm (see FIG. 3, etc.).

[0025] Two cylindrical (rod-shaped) male screw members 27, 27 are provided on the left and right outer sides of the abutment body 25 at a predetermined angle (about 25°) between them, so as to protrude in a radial direction from the center of the abutment body 25 and be detachable (detachable by screwing). The male screw members 27, 27 on the left and right base ends of the abutment body 25 are arranged symmetrically with respect to the center of the abutment body 25. On the other hand, the shield body 26 is formed in a plate-like annular (strip-like) shape with a constant thickness, and a tapered portion 32 is provided at the tip portion, the diameter of which gradually increases from the top to the bottom. The shield body 26 is provided integrally with the lower end of the inner wall of the abutment body 25 so that the surface (upper surface) is horizontal.

[0026] Meanwhile, the left and right connecting members 23a, 23b are formed by fixing metal connecting bodies 30a, 30b, which are bent into an L-shape, to the upper surface of a metal rectangular prism-shaped vertical body 29 by using a screw member. A screw hole (not shown) for screwing the support member 22 is drilled in the lower end surface of the vertical body 29, and a screw hole (not shown) for screwing the connecting bodies 30a, 30b to the coil body 11 (metal base 5) is drilled in the base end side of each of the connecting bodies 30a, 30b.

[0027] The attachment 21 is formed by fitting the annular abutment body 25 of the shield member 24 into the annular support member 22, screwing two male screw members 27, 27 into the left and right outer sides of the abutment body 25 using the horizontally long insertion holes 31, 31 of the support member 22, and screwing nuts 28 into the tip sides of the male screw members 27, 27... (see FIG. 6), thereby integrating the support member 22 and the shield member 24. The attachment 21 is integrally assembled to the support member 22 thus integrated with the shield member 24 by screwing a pair of connecting members 23a, 23b into the support member 22 thus integrated with the shield member 24 using the left and right screw holes 33, 33 on the base end side so that the inner surfaces of the connecting bodies 30a, 30b face each other closely.

[0028] The above-mentioned attachment 21 is screwed to the left and right support parts 3a, 3b of the above-mentioned coil body 11 (metal base 5) by utilizing screw holes (not shown) on the base end sides of the connecting bodies 30a, 30b of the left and right connecting members 23a, 23b, and the support member 22 and the shield member 24 (the abutting body 25 and the shield body 26) are arranged concentrically outside the heating part 4 of the metal base 5. Then, as shown in Fig. 6, the tip part (tapered part 32) of the shield body 26 of the shield member 24 is closely opposed to the lower side of the tapered surface 20 (the lower side of a part of the tapered surface 20) of the lower heating region 15 of the heating part 4 of the metal base 5.

[0029] <How to use the heating coil> The heating coil 1 constructed as described above has the left and right grounding portions 2a, 2b of the metal base 5 grounded to the electrodes, and the workpiece W is inserted inside the series of circumferential heating portions 4 as shown in FIG. 9. With the workpiece W rotated as necessary, an external power source (high-frequency power source) is turned on via the electrodes, whereby the workpiece W can be heated (hardened) by utilizing the electromagnetic induction phenomenon. In addition, cooling medium (water) is injected from the injection pipe 7b on the back of the right grounding portion 2b, passes through the cooling medium flow path (not shown) inside the right grounding portion 2b, the cooling medium flow path (not shown) of the right support portion 3b, and the cooling medium flow path 6 of the heating portion 4, and then passes through the cooling medium flow path (not shown) of the left support portion 3a and the cooling medium flow path (not shown) of the left grounding portion, and is then drained from the discharge pipe 7a on the back of the left grounding portion 2a.This efficiently cools the heating portion 4, the supports 3a, 3b, and the grounding portions 2a, 2b, and accurately prevents damage due to melting of the insulating plate 16.

[0030] 9, the shield body 26 of the shield member 24 of the attachment 21 is interposed between the base end side of the lower heating zone 15 of the heating part 4 of the metal base 5 and the workpiece W. This reduces the amount of magnetic flux generated in the overlapping portion with the shield body 26 of the lower heating zone 15, making it possible to effectively prevent the portion of the workpiece W adjacent to the lower heating zone 15 (the β portion in FIG. 9) from being overheated.

[0031] In the attachment 21, the phase of the contact body 25 and the shield body 26 with respect to the support member 22 (i.e., the degree of overlap with the lower heating region 15 of the heating unit 4) can be adjusted by loosening the bolts 28, 28... threaded into the male screw members 27, 27... as shown in Fig. 10. By adjusting the phase of the contact body 25 and the shield body 26 in this manner, the degree of hardening of the portion of the workpiece W adjacent to the lower heating region 15 (the β portion in Fig. 9) can be adjusted.

[0032] <Effect of heating coil> As described above, the heating coil 1 includes a coil body 11 (metal base 5) having a pair of plate-shaped grounding parts 2a, 2b for contacting the electrodes through which high-frequency current is applied, a pair of plate-shaped supporting parts 3a, 3b arranged so as to be perpendicular to the grounding parts 2a, 2b, respectively, and a series of circumferential heating parts 4 provided to connect the tips of the supporting parts 3a, 3b, and an attachment 21 having a shield body 26 interposed between the heating parts 4 and the workpiece W to function as a heat shield for reducing the degree of hardening of the workpiece W by the heating parts 4. Therefore, according to the heating coil 1, by interposing the shield body 26 provided on the attachment 21 between the workpiece W and the heating parts 4 (i.e., the lower heating region 15) of the coil body 11, it is possible to prevent the workpiece W from being locally overheated, and it is possible to easily control the depth of the hardened layer caused by hardening the workpiece W.

[0033] Furthermore, since the heating coil 1 is capable of changing the amount of the shield body 26 between the heating section 4 and the workpiece W (i.e., the degree of overlap between the lower heating area 15 of the heating section 4 and the shield body 26) by using the attachment 21, by changing the amount of the shield body 26, the depth of the hardened layer caused by hardening the workpiece W can be controlled (finely adjusted) with great precision.

[0034] Furthermore, the heating coil 1 has a shield body 26 that is rotatable relative to the center of the heating portion 4, and the amount of space between the heating portion 4 and the workpiece W can be changed by changing the rotational phase of the shield body 26. Therefore, by simply changing the rotational phase of the shield body 26, the depth of the hardened layer caused by quenching the workpiece W can be very easily controlled (finely adjusted).

[0035] Furthermore, since the heating coil 1 has the angle display portion 34 provided on the support member 22 of the attachment 21, the rotational phase of the shield body 26 relative to the support member 22 can be adjusted very accurately and very easily.

[0036] <Example of changing the heating coil> The heating coil according to the present invention is not limited to the above-described embodiment, and the materials, shapes, structures, and other configurations of the coil body (metal base, grounding portion, support portion, heating portion), insulating plate, and attachments (support member, connecting member, shield member (shield body: heat shield)) can be appropriately changed as necessary without departing from the spirit of the present invention.

[0037] For example, the heating section of the heating coil is not limited to a top-bottom multi-stage circular ring-shaped structure in plan view (i.e., a structure in which peripheral bodies are arranged horizontally above and below and connected by vertical cylindrical bodies extending in the vertical direction) as in the above embodiment, but can also be changed to a simple circular ring-shaped structure or a ring-shaped structure at least a portion of which has a shape other than an arc shape.

[0038] Furthermore, the heating coil is not limited to the one in which a single cooling medium flow-down passage (mainly for cooling the heating portion itself) is provided inside the heating portion of the metal base as in the above embodiment, but may be changed to one in which a plurality of cooling medium flow-down passages are provided inside the heating portion (for example, one in which a cooling medium flow-down passage having a cooling medium injection hole for cooling the workpiece is separately provided). In addition, when two types of cooling medium flow-down passages are provided in this way, there is an advantage that the cooling of the workpiece after heating and the cooling of the heating portion itself can be performed more efficiently. In addition, the heating coil is not limited to the one in which a single cooling medium flow-down passage is provided so that the cooling medium injected from the grounding portion on one side passes through the support portion on the same side to reach the heating portion, and then passes through the support portion on the opposite side to be discharged from the grounding portion on the opposite side as in the above embodiment, but may be one in which the cooling medium flow-down passage is divided into left and right, etc.

[0039] Furthermore, the heating coil is not limited to one in which the metal base is formed by a modeling method based on three-dimensional data using a three-dimensional printer, as in the above embodiment, but may be one in which the metal base (all or part) is formed by another modeling method (for example, a brazing method, etc.).

[0040] Furthermore, the heating coil is not limited to an attachment in which the entire attachment (i.e., the shield member, the support member, and the connecting member) are formed from ceramics as in the above embodiment, and at least a portion of the attachment may be formed from a material other than ceramics (for example, a synthetic resin having insulating and heat-resistant properties such as polyacetal (POM), polyphenylene sulfide (PPS), polyether ether ketone (PEEK), etc.).

[0041] Furthermore, the heating coil is not limited to the above embodiment in which the heat shield (shield body) rotates around the center of the heated portion of the metal base to change the amount of space between the heated portion and the workpiece (i.e., the degree of overlap with the heated portion (lower heating area)), but can also be changed to one in which the heat shield changes the amount of space between the heated portion and the workpiece (i.e., the degree of overlap with the heated portion) by sliding in a radial direction relative to the center of the heated portion of the metal base (i.e., by sliding the heat shield toward or away from the workpiece).

[0042] In addition, the heating coil of the present invention is not limited to the above embodiment in which the pair of grounding parts and the pair of supporting parts are insulated by an insulating plate made of fluororesin (PTFE, PFA, FEP, ETFE, PCTFE, ECTFE, PVDF), but can also be changed to a coil in which the pair of grounding parts and the pair of supporting parts are insulated by an insulating plate made of other synthetic resins such as POM, PPS, PEEK, etc., having insulating and heat-resistant properties, or ceramics.

[0043] In addition, the heating coil according to the present invention can be modified as appropriate in terms of the shape and size of the coil body and attachments, the type (material) and thickness of the insulating plate, the number of bolts for clamping the insulating plate, the structure for attaching the attachments to the coil body, etc., depending on the shape of the workpiece to be hardened, etc. [Industrial Applicability]

[0044] Since the heating coil according to the present invention has the excellent effects as described above, it can be suitably used as a member for heating a workpiece by utilizing electromagnetic induction. [Explanation of symbols]

[0045] 1. Heating coil 2a,2b...Grounding part 3a,3b...Support part 4. Heating section 5...Metal base 11. Coil body 15...Lower heating area 16 Insulating plate 21 Attachment 22 Support member 23a, 23b Connection members 24 Shielding material 26··Shield body (heat shield) 34...Angle display section

Claims

1. A heating coil for use in a high-frequency heating device for heating a workpiece by utilizing electromagnetic induction caused by a high-frequency current, a coil body including a pair of plate-shaped grounding portions for contacting electrodes through which high-frequency current is passed, a pair of plate-shaped supporting portions disposed so as to be perpendicular to the grounding portions, and a series of circumferential heating portions provided so as to connect the tips of the supporting portions; and an attachment having a heat shield interposed between the heating portion and the workpiece to reduce the degree of hardening of the workpiece by the heating portion.

2. 2. The heating coil according to claim 1, wherein the attachment is capable of changing an amount of the heat shield disposed between the heating portion and the workpiece.

3. 3. The heating coil as described in claim 2, characterized in that the heat shield is rotatably arranged relative to the center of the heating portion, and the amount of intervention between the heating portion and the workpiece can be changed by changing the rotational phase of the heat shield.

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