Induction heating method and induction heating device

Abstract

To provide an induction heating method and an induction heating device that can save space and reduce costs.SOLUTION: A workpiece W is transported by gravity to a magnetic field B formed by a heating coil 12.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to an induction heating method and an induction heating device for induction heating a metal workpiece using a heating coil. [Background technology]

[0002] The rotating parts of rotating machines such as machine tools and industrial machines are supported by rolling bearings against parts that do not rotate during use, such as housings. In particular, when a large load is applied to the rotating parts, roller bearings using rollers as rolling elements and tapered roller bearings using tapered rollers are used.

[0003] Rolling elements such as rollers and tapered rollers are manufactured by heat treatment to impart mechanical strength, and then by finishing processes such as grinding.

[0004] 2. Description of the Related Art As a heating method for subjecting a metal workpiece to heat treatment, a method of induction heating the workpiece using a heating coil is known.

[0005] JP 2017-227314 A discloses a heat treatment facility that induces heating of a rod-shaped workpiece while transporting it along its axial direction at a predetermined speed to perform a quenching process. The conveying device constituting the heat treatment facility described in JP 2017-227314 A rotates the first shaft member and the second shaft member in the same direction by an electric motor in a state where the rod-shaped workpiece is placed between the cylindrical outer circumferential surface of the first shaft member and the groove bottom surface of the spiral groove of the second shaft member, thereby rotating the workpiece around its central axis and transporting it in the axial direction. In the induction heating device described in JP 2017-227314 A, while the conveying device rotates the workpiece around its central axis and transports it in the axial direction, the first heating coil heats the workpiece during transport to a predetermined temperature below the quenching temperature, and the second heating coil maintains the workpiece during transport at the quenching temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-227314 A Summary of the Invention [Problem to be solved by the invention]

[0007] The conveying device described in JP 2017-227314 A conveys the workpiece with its axis oriented horizontally, which poses a problem of a large installation area for the induction heating device.

[0008] Furthermore, in the heat treatment equipment described in JP 2017-227314 A, the workpiece being transported is maintained at the quenching temperature for a predetermined period of time by the transport device, which tends to make the problem of the large installation area of ​​the induction heating device more noticeable.

[0009] In addition, the conveying device described in JP 2017-227314 A has a large number of components and requires expensive parts such as a second shaft member having a spiral groove on its outer circumferential surface, resulting in high costs.

[0010] An object of the present disclosure is to provide an induction heating method and an induction heating device that can save space and reduce costs. [Means for solving the problem]

[0011] An induction heating method according to one aspect of the present disclosure is a method for induction heating a metal workpiece using a heating coil, comprising: A supplying process of transporting the workpiece to a magnetic field formed by the heating coil by utilizing the effect of gravity; an induction heating step of induction heating the workpiece to a target temperature in the magnetic field; Equipped with.

[0012] In the induction heating method according to one aspect of the present disclosure, the workpiece can be transported by being guided along a transport path provided inside a cylindrical guide member.

[0013] In the induction heating method according to one aspect of the present disclosure, the inclination angle of the conveying direction of the workpiece relative to a horizontal plane can be set to be equal to or greater than 10 degrees and equal to or less than 90 degrees.

[0014] In the induction heating method according to one aspect of the present disclosure, the workpiece can be induction heated to the target temperature by utilizing the effect of gravity while passing through the magnetic field.

[0015] Alternatively, the induction heating method of one aspect of the present disclosure can utilize the magnetic levitation effect caused by the magnetic field to temporarily hold the workpiece in the magnetic field.

[0016] In the induction heating method of one aspect of the present disclosure, after the induction heating step, the workpiece can be dropped into a cooling liquid.

[0017] The induction heating method of one aspect of the present disclosure may include a preheating step of induction heating the workpiece by a preheating coil to a preheat temperature lower than the target temperature, prior to the induction heating step.

[0018] An induction heating device according to one aspect of the present disclosure is a device for induction heating a metal workpiece, A heating coil that generates a magnetic field; A cylindrical guide member having a conveying path for guiding the workpiece therein and extending in an inclined direction with respect to a horizontal plane; Equipped with.

[0019] In the induction heating device according to one aspect of the present disclosure, the inclination angle of the guide member with respect to the horizontal plane can be set to be equal to or greater than 10 degrees and equal to or less than 90 degrees.

[0020] The induction heating device according to one aspect of the present disclosure may include a cooling tank that is disposed below the lower opening of the guide member and that stores a cooling liquid.

[0021] The induction heating device according to one aspect of the present disclosure may include a preheating coil arranged around the guide member and above the heating coil. Effect of the Invention

[0022] According to the induction heating method and induction heating device of one aspect of the present disclosure, it is possible to save space and reduce costs. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a partially cutaway perspective view showing an example of a radial cylindrical roller bearing equipped with cylindrical rollers that can be manufactured by induction heating using the induction heating method and induction heating device according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a cross-sectional view that illustrates a schematic diagram of an induction heating device according to a first embodiment of the present disclosure. [Diagram 3] FIG. 3 is a cross-sectional view illustrating a schematic diagram of an induction heating device according to a second embodiment of the present disclosure. [Figure 4] FIG. 4 is a cross-sectional view illustrating a schematic diagram of an induction heating device according to a third embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] An induction heating method according to an embodiment of the present disclosure is a method for induction heating a metal workpiece having a circular cross-sectional shape using a heating coil, comprising the steps of: A supply process of transporting the workpiece to a magnetic field formed by the heating coil by utilizing the effect of gravity; an induction heating step of induction heating the workpiece to a target temperature in the magnetic field; Equipped with.

[0025] An induction heating device according to an embodiment of the present disclosure is a device for induction heating a metal workpiece having a circular cross-sectional shape, A heating coil that generates a magnetic field; A cylindrical guide member having a conveying path for guiding the workpiece therein and extending in an inclined direction with respect to a horizontal plane; Equipped with.

[0026] [Example 1] As a first example of an embodiment of the present disclosure, an example of induction heating and heat treatment of a workpiece W, which is the material for cylindrical rollers 4 of a radial cylindrical roller bearing 1, using an induction heating method and induction heating device of one embodiment of the present disclosure will be described with reference to Figures 1 and 2.

[0027] However, the induction heating method and induction heating device of an embodiment of the present disclosure are not limited to the workpiece W that is the material for the cylindrical rollers 4 of the radial cylindrical roller bearing 1, and can be applied to various workpieces as long as they have a circular cross-sectional shape. For example, the induction heating method and induction heating device of an embodiment of the present disclosure can be applied to heat treatment of workpieces that are the material for cylindrical rollers of a thrust cylindrical roller bearing, needle rollers, i.e., needles, of a radial needle roller bearing or a thrust needle roller bearing, rod rollers of a radial rod roller bearing or a thrust rod roller bearing, tapered rollers of a radial tapered roller bearing or a thrust tapered roller bearing, spherical rollers of a radial self-aligning roller bearing or a thrust self-aligning roller bearing, or a support shaft around which a ring-shaped rotating member such as a planetary gear is arranged so as to be relatively rotatable.

[0028] The radial cylindrical roller bearing 1 comprises an inner ring 2, an outer ring 3, and a plurality of cylindrical rollers 4.

[0029] The inner ring 2 has a cylindrical inner ring raceway 5 around its entire circumference, on the outer peripheral surface of the axial middle portion, whose outer diameter does not change in the axial direction, and also has an outward flange portion 6 around its entire circumference, protruding radially outward, at its end on one axial side (the right side in Figure 1).

[0030] The outer ring 3 has a cylindrical outer ring raceway 7 around its entire circumference, on its inner surface in the axial middle portion, and its inner diameter does not change in the axial direction. Also, at both axial ends, it has inward flange portions 8 around its entire circumference, protruding radially inward.

[0031] A plurality of cylindrical rollers 4 are arranged between an inner ring raceway 5 and an outer ring raceway 7 so as to be able to roll freely while being held in pockets 10 provided in a plurality of locations of a cage 9 at equal intervals in the circumferential direction.

[0032] Each of the cylindrical rollers 4 has a circular cross-sectional shape. Specifically, each of the cylindrical rollers 4 has a columnar shape whose outer diameter does not change in the axial direction, except for chamfered portions provided at both ends in the axial direction. Each of the cylindrical rollers 4 is made of hard metal such as bearing steel, such as high carbon chromium bearing steel (SUJ2-4), medium carbon steel, or carburized steel.

[0033] Each cylindrical roller 4 is manufactured by forming a workpiece W having an approximate outer shape by performing processes such as forging and cutting on a hard metal material, then performing heat treatment on the workpiece W to impart mechanical strength thereto, and further performing finishing processes such as grinding.

[0034] In this embodiment, the workpiece W is induction-heated using an induction heating device 11 as shown in FIG. 2, and thereby the workpiece W is subjected to a quenching treatment, which is a type of heat treatment.

[0035] However, the induction heating method and induction heating device according to an embodiment of the present disclosure may be applied to tempering, annealing, and / or normalizing instead of or in addition to quenching.

[0036] The induction heating device 11 includes a heating coil 12 and a guide member 13 .

[0037] When a current is applied to the heating coil 12, the heating coil 12 generates a magnetic field B. The heating coil 12 is configured into a cylindrical shape as a whole by winding a conductive wire in a spiral shape.

[0038] The heating coil 12 has an axial length L that is sufficient to heat the surface portion of the workpiece W passing through the magnetic field B, which forms a hardened layer by hardening, to a desired target temperature, specifically, about 800°C to 1000°C, which is the hardening temperature of the hard metal constituting the workpiece W. Therefore, the axial length L of the heating coil 12 is not limited to the example shown in the figure, and can also be longer than the axial length of the workpiece W.

[0039] The frequency of the AC current applied to the heating coil 12 and the output of the heating coil 12 are appropriately set according to the outer diameter, hardening depth, etc. of the workpiece W. Specifically, although not limited thereto, the frequency of the AC current can be about 5 kHz to 400 kHz, and the output can be about 0.1 kW to 100 kW.

[0040] The guide member 13 is configured in a cylindrical shape, extends in a direction inclined (non-parallel) to the horizontal plane P, and guides the workpiece W to the magnetic field B. Specifically, the guide member 13 is supported radially inside the heating coil 12 and coaxially with the heating coil 12. In other words, the heating coil 12 is supported around the guide member 13 and coaxially with the guide member 13.

[0041] The guide member 13 has a conveying passage 14 therein that penetrates in the axial direction.

[0042] The inclination angle θ of the extension direction of the guide member 13 with respect to the horizontal plane P can be 10 degrees or more and 90 degrees or less, and is preferably 20 degrees or more and 90 degrees or less. In this example, the inclination angle θ is 90 degrees. That is, the guide member 13 extends in the vertical direction (the axial direction is oriented in the vertical direction).

[0043] In the induction heating device 11 of this embodiment, the heating time of the workpiece W is adjusted by adjusting the axial length L of the heating coil 12, the inclination angle θ of the guide member 13, and the drop start height of the workpiece W from the upper end of the heating coil 12, i.e., the height H of the upper opening 16a from the upper end of the heating coil 12. 0 Specifically, the longer the axial length L of the heating coil 12, the longer the heating time of the workpiece W. The larger the inclination angle θ of the guide member 13, the faster the workpiece W falls, and the shorter the heating time of the workpiece W. In addition, the falling start height H of the workpiece W from the upper end of the heating coil 12 is adjusted. 0 The larger the value, the faster the workpiece W falls and the shorter the heating time of the workpiece W.

[0044] In this example, the inclination angle θ of the guide member 13 is 90 degrees. Therefore, in order to heat the surface portion of the workpiece W to the hardening temperature of about 800 degrees to 1000 degrees by the induction heating device 11 of this example, the axial length L of the heating coil 12 can be set to 3 mm or more and 1000 mm or less, and preferably 5 mm or more and 1000 mm or less. If the axial length L of the heating coil 12 is smaller than 3 mm, the surface portion of the workpiece W passing through the magnetic field B may not be heated sufficiently. If the axial length L of the heating coil 12 is larger than 1000 mm, the surface portion of the workpiece W passing through the magnetic field B may be heated excessively. In addition, the drop start height H of the workpiece W from the upper end of the heating coil 12 may be set to 1000 mm or more. 0 The drop start height H can be set to 5 mm or more and 1000 mm or less. 0 If is greater than 1000 mm, the falling speed of the workpiece W will be excessively fast, the time it passes through the magnetic field B will be short, and the surface portion of the workpiece W passing through the magnetic field B may not be heated sufficiently.

[0045] The conveying path 14 has an inner diameter slightly larger than the outer diameter of the workpiece W. Therefore, the workpiece W can move along the conveying path 14 without rattling in the extension direction of the guide member 13. In this example, since the inclination angle θ is 90 degrees, the resistance acting on the workpiece W falling along the conveying path 14 is basically air resistance only.

[0046] The axial length of guide member 13 is longer than the axial length of heating coil 12. Specifically, although not limited to this, guide member 13 protrudes from the upper surface of heating coil 12 by about 100 mm to 1000 mm. The amount of protrusion of guide member 13 from the lower surface of heating coil 12 can be, although not limited to this, about 100 mm to 500 mm.

[0047] The guide member 13 is made of a non-magnetic material with low thermal conductivity, specifically, the guide member 13 can be made of quartz glass, ceramics, or the like.

[0048] The induction heating device 11 of this embodiment further includes a cooling tank 15 .

[0049] The cooling tank 15 is disposed below the opening 16 b on the lower side of the transport path 14 of the guide member 13 .

[0050] The cooling tank 15 stores a cooling liquid 17. The cooling liquid 17 is appropriately selected depending on the cooling speed of the heated workpiece W. Specifically, the cooling liquid 17 may be a water-soluble quenching liquid, quenching oil, water, or the like.

[0051] In the induction heating device 11 of this example, the workpiece W is heated to a desired target temperature by the heating coil 12, and then quickly dropped into the cooling liquid 17 to be cooled. For this reason, the height h from the liquid level of the cooling liquid 17 to the bottom surface of the heating coil 12 is set to about 10 mm to 500 mm.

[0052] When implementing the induction heating method and induction heating device according to an embodiment of the present disclosure, if the workpiece W after heat treatment is air-cooled, the cooling tank 15 can be omitted. In this case, the workpiece W that has fallen from the lower opening 16b of the transport path 14 is left in the air by arranging it on a pallet, or is cooled using a cooling fan.

[0053] Hereinafter, a method of performing quenching, which is a type of heat treatment, on the workpiece W using the induction heating device 11 will be described.

[0054] First, electricity is applied to the heating coil 12 to generate a magnetic field B around the heating coil 12 including its radially inner portion.

[0055] Next, the workpieces W are fed (inserted) into the conveying path 14 of the guide member 13 from the upper opening 16a. The workpieces W can be fed into the conveying path 14 continuously as shown in Fig. 2, or can be fed intermittently one by one. The method of feeding the workpieces W from the upper opening 16a is not particularly limited, and can be manual by an operator or automatic by a robot.

[0056] The workpiece W introduced into the conveying path 14 moves downward along the conveying path 14 due to the action of gravity. In this example, the resistance acting on the workpiece W moving downward along the conveying path 14 is basically only air resistance.

[0057] As a result, the workpiece W is transported to the magnetic field B generated by the heating coil 12, and is then passed through the magnetic field B. When the workpiece W is positioned in the magnetic field B, eddy currents flow within the workpiece W in a direction that prevents changes in the magnetic flux, and Joule heat is generated within the workpiece W. In this example, the workpiece W is heated to a desired target temperature, specifically, to about 800°C to 1000°C, which is the hardening temperature, while passing through the magnetic field B due to the action of gravity.

[0058] The workpiece W heated to the target temperature is quickly dropped from the lower opening 16 b of the transport path 14 into the cooling liquid 17 in the cooling tank 15 .

[0059] In this example, the height h from the liquid level of the cooling liquid 17 to the bottom surface of the heating coil 12 is set to about 10 mm to 500 mm, so that the workpiece W quickly falls into the cooling liquid 17 after passing the bottom surface of the heating coil 12. That is, in the induction heating method of this example, a holding time for holding the workpiece W at the target temperature is not substantially provided.

[0060] The workpiece W is cooled in the cooling liquid 17 until it reaches a predetermined temperature. As a result, the workpiece W is subjected to a quenching process.

[0061] The workpiece W that has been subjected to the hardening treatment as described above is then subjected to finishing processing such as grinding in the subsequent finishing process, and is completed as cylindrical rollers 4 that constitute the radial cylindrical roller bearing 1.

[0062] In this example, the workpiece W is transported by utilizing the effect of gravity to the magnetic field B formed by the heating coil 12. Specifically, a cylindrical guide member 13 that guides the workpiece W to the magnetic field B is provided so as to extend at an incline with respect to the horizontal plane P. For this reason, the induction heating device 11 of this example can easily achieve space saving compared to the case where the workpiece is transported with its axis oriented horizontally, such as the induction heating device described in JP 2017-227314 A.

[0063] In particular, in this example, the guide member 13 is provided so as to extend in the vertical direction. Therefore, the installation area of ​​the induction heating device 11 is sufficient to be a size determined by the outer shape of the heating coil 12, excluding the power supply equipment and the like.

[0064] Furthermore, in this embodiment, there is substantially no holding time for holding the workpiece W at the target temperature, which makes it easy to shorten the cycle time for the heat treatment of the workpiece W.

[0065] Furthermore, in the induction heating device 11 of this embodiment, the guide member 13 is provided so as to extend in the vertical direction, and the resistance acting on the workpiece W moving downward along the conveying path 14 is basically air resistance alone. This makes it possible to sufficiently increase the moving speed of the workpiece W moving along the conveying path 14. From this perspective as well, it is easy to shorten the cycle time of the heat treatment of the workpiece W.

[0066] In this example, the workpiece W is transported by utilizing the action of gravity. That is, the induction heating device 11 of this example does not require a drive source such as an electric motor to transport the workpiece. Also, in this example, the transport direction of the workpiece W is simply guided by the cylindrical guide member 13. That is, in the induction heating device 11 of this example, the structure for transporting the workpiece W can be easily configured with a small number of parts. Therefore, costs can be reduced.

[0067] [Example 2] A second embodiment of the present disclosure will be described with reference to FIG.

[0068] The induction heating device 11a of this embodiment is configured to temporarily hold the workpiece W in the magnetic field B by utilizing the magnetic levitation effect caused by the magnetic field B generated by the heating coil 12a.

[0069] More specifically, the induction heating device 11a of this example adjusts the strength of the magnetic field B generated by the heating coil 12a to apply a levitation force to the workpiece W that balances the gravity acting on the workpiece W, thereby levitating the workpiece W in the magnetic field B.

[0070] The strength of the magnetic field B is appropriately set depending on the weight of the workpiece W, its falling speed, etc.

[0071] When performing heat treatment on the workpiece W using the induction heating device 11a of this example, current is passed through the heating coil 12a to generate a magnetic field B in a portion including the radially inner side of the heating coil 12a, and the workpiece W is then inserted through the upper opening 16a of the conveying path 14.

[0072] When the workpiece W put into the transport path 14 moves into the magnetic field B, the magnetic levitation effect causes the workpiece W to float in the magnetic field B and prevent it from falling further downward. Therefore, the workpiece W is induction heated to the desired target temperature by the heating coil 12a while being held in the magnetic field B. Therefore, according to this example, the workpiece W can be reliably heated to the target temperature.

[0073] After the workpiece W has been heated to the target temperature, the power supply to the heating coil 12a is stopped, and the buoyant force acting on the workpiece W is lost. Then, due to the action of gravity, the workpiece W starts to move downward again along the conveying path 14.

[0074] Alternatively, the next workpiece W is inserted from the upper opening 16a of the transport path 14, and the workpiece W held in the magnetic field B is pushed downward to remove it from the magnetic field B, while the next workpiece W is held in the magnetic field B. The workpiece W that has been removed downward from the magnetic field B starts to move downward again along the transport path 14 due to the action of gravity.

[0075] Thereafter, the workpiece W falls from the lower opening 16b into the cooling liquid 17 in the cooling tank 15.

[0076] The configuration and the effects of other parts of the second example are similar to those of the first example.

[0077] [Example 3] A third embodiment of the present disclosure will be described with reference to FIG.

[0078] The induction heating device 11b of this example includes a preheating coil 18 disposed around the guide member 13 and above the heating coil 12.

[0079] When the induction heating device 11b of this embodiment is used to perform a quenching process on the workpiece W, the workpiece W is induction heated by the preheating coil 18 to a predetermined preheat temperature lower than the quenching temperature before the workpiece W is induction heated to the quenching temperature by the heating coil 12. Specifically, the workpiece W is induction heated by the preheating coil 18 to a temperature close to the Curie temperature.

[0080] Thereafter, the workpiece W is further heated by the heating coil 12 to the hardening temperature.

[0081] According to this example, the workpiece W can be heated uniformly.

[0082] The configuration and the effects of the other parts of the third example are similar to those of the first example.

[0083] The first to third examples of the embodiment of the present disclosure can be implemented in any suitable combination as long as no contradiction occurs. [Explanation of symbols]

[0084] 1 Radial cylindrical roller bearing 2. Inner Circle 3 Outer ring 4 Cylindrical rollers 5 Inner raceway 6 Outward flange 7 Outer raceway 8 Inward flange 9 Cage 10 Pocket 11, 11a, 11b induction heating device 12, 12a Heating coil 13 Guide member 14 Transport Path 15 Cooling tank 16a, 16b opening 17 Coolant 18 Preheat coil

Claims

1. A method for induction heating a metal workpiece to a target temperature using a heating coil, comprising the steps of: A supply process of transporting the workpiece to a magnetic field formed by the heating coil by utilizing the effect of gravity; an induction heating step of induction heating the workpiece to a target temperature in the magnetic field; The induction heating method comprises:

2. 2. The induction heating method according to claim 1, wherein the workpiece is guided along a conveying path provided inside a cylindrical guide member.

3. 2. The induction heating method according to claim 1, wherein an inclination angle of the workpiece conveying direction with respect to a horizontal plane is 10 degrees or more and 90 degrees or less.

4. 2. The induction heating method according to claim 1, wherein in the induction heating step, the workpiece is induction heated to the target temperature by utilizing the effect of gravity while passing through the magnetic field.

5. 2. The induction heating method according to claim 1, wherein in the induction heating step, the workpiece is temporarily held in the magnetic field by utilizing a magnetic levitation effect caused by the magnetic field.

6. The induction heating method according to claim 1 , further comprising dropping the workpiece into a cooling liquid after the induction heating step.

7. 2. The induction heating method according to claim 1, further comprising a preheating step of induction heating the workpiece by a preheating coil to a preheat temperature lower than the target temperature, prior to the induction heating step.

8. An induction heating device for induction heating a metal workpiece, comprising: A heating coil that generates a magnetic field; A cylindrical guide member having a conveying path for guiding the workpiece therein and extending in an inclined direction with respect to a horizontal plane; An induction heating device comprising:

9. 9. The induction heating device according to claim 8, wherein an inclination angle of the extension direction of the guide member with respect to the horizontal plane is equal to or greater than 10 degrees and equal to or less than 90 degrees.

10. 9. The induction heating device according to claim 8, further comprising a cooling tank arranged below the lower opening of the guide member and storing a cooling liquid.

11. The induction heating device according to claim 8 , further comprising a preheating coil disposed around the guide member and above the heating coil.

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