JP2005290410A - Apparatus and method for induction hardening shaft with high frequency - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for induction hardening a shaft with a high frequency, with which the strength can be secured by accurately and surely performing the hardening of the edge part in a hole part, especially needing the hardening and also, the cost needed to the hardening can be reduced and the accuracy in the axial direction of the shaft can be secured, and to provide a method for induction hardening a shaft with a high frequency. <P>SOLUTION: In the high frequency hardening apparatus for shaft 16 for performing high frequency hardening to the peripheral parts of hole parts composing a bar-like carbon steel material having a hollow cylindrical part 11a at the center in the axial direction and also, under the state of holding the shaft 16 bored the hole parts 12, 13 on the same outer peripheral surface of the above hollow cylindrical part 11a, this apparatus is provided with coil bodies 17, 18 disposed so as to be faced to the peripheral parts 14, 15 of the hole parts 12, 13, and the high frequency hardening apparatus for the shaft provided with a positioning means 19 for performing the positioning of the hollow cylindrical part 11a to the coil bodies 17, 18 by inserting into the hole parts 12, 13 is provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a shaft induction hardening device and a shaft induction hardening method, for example, an induction hardening device that performs hardening in order to increase the strength of a peripheral portion of a lock hole formed in a steering shaft, and a shaft high frequency hardening method. It relates to a quenching method.

For example, since the peripheral edge of the lock hole requires strength such as wear resistance, the peripheral edge of the lock hole is usually subjected to quenching.
Recently, in order to maintain the strength of the periphery of the lock hole with higher accuracy while maintaining high accuracy in the axial direction of the steering shaft, various prior arts regarding quenching of the periphery of the lock hole Has been proposed.

  For example, in Prior Art 1 (see Patent Document 1), a lock shaft structure of a steering shaft is proposed in which an induction-hardened portion is continuously formed on a circumferential surface having a lock hole (the lock hole). Yes.

  According to the above prior art 1, by bending the entire circumferential surface of the steering shaft having the lock hole portion, the bending rigidity of the steering shaft can be obtained rather than quenching only the peripheral portion of the lock hole portion. It is disclosed that the strength of the can be further increased.

However, if a quenching process is performed on the entire circumferential surface in which the lock hole is formed, the quenching time and the power consumption increase accordingly.
Furthermore, when torsional stress or bending stress is generated on the steering shaft, the peripheral edge of the lock hole is structurally stressed. Therefore, the peripheral edge of the lock hole is quenched. It can be said that the necessity of quenching the entire circumferential surface is low by reliably performing the treatment.

  In addition, when the entire circumferential surface is quenched, there is a disadvantage that distortion due to residual stress remains on a part of the circumferential surface, which affects the axial accuracy of the steering shaft.

  On the other hand, in prior art 2 (see Patent Document 2), it is proposed that quenching is performed around the lock hole formed in the steering shaft and at a symmetrical position with respect to the axis of the steering shaft.

  And in paragraph [0011] of the above prior art 2 (see Patent Document 2), there is a problem with the lock hole structure of the prior art 1 that distortion occurs when the entire circumferential surface is subjected to quenching. Also pointed out.

  With respect to this problem, the prior art 2 discloses that the axial accuracy can be maintained by quenching at symmetrical positions with respect to the axis of the steering shaft to alleviate the difference in flexural deformation.

  Furthermore, it is disclosed that the quenching time can be shortened by the amount that the entire outer periphery at the site where the lock hole portion is drilled is not subjected to quenching.

However, in the prior art 2, it cannot be said that the accuracy and certainty of quenching for the steering shaft are insufficient.
This is because it is assumed that not only the symmetrical position around the lock hole portion but also the symmetrical position of the lock hole portion is induction-hardened and hardened with respect to the axis of the steering shaft.

  That is, since the induction hardening of the portion corresponding to the symmetric position in the steering shaft is naturally performed, the portion corresponding to the symmetric position is more preferable than the peripheral portion of the lock hole portion. There is also a risk of bending deformation.

Also, in practice, when performing the quenching process, a process of fixing the steering shaft to a predetermined part or installing a high frequency coil is required. Of course, when performing these processes manually, the device Even when the process itself is performed automatically, there is a problem that a relative positional deviation between the steering shaft and the high-frequency coil inevitably occurs due to problems such as man-made problems and apparatus assembly accuracy.
In the prior art 2, such a problem is not considered at all.

Specifically, as is apparent from FIG. 6A schematically showing a state in which a relative positional deviation has occurred between the steering shaft 31 and the high frequency coils 32 and 33, a hollow cylinder The part 34 usually has a positional deviation (Δα) in the circumferential direction with respect to the high-frequency coils 32 and 33.
For this reason, since the values of the induced electromotive force received from the high-frequency coil 32 are different at both edges 36a and 36b of the lock hole 35 in the circumferential direction of the hollow cylindrical portion 34, the degree of quenching is also different.

However, when torsional stress or bending stress is applied to the steering shaft 31, as described above, concentrated stress is applied to both edge portions 36a, 36b of the lock hole portion 35.
In addition, since the lock key slides on the peripheral edge 36 of the lock hole 35, the peripheral edge 36 of the lock hole 35 needs to have wear resistance.

  From the above, the peripheral edge 36 of the lock hole 35 should be hardened by the occurrence of the positional deviation (Δα) although it is necessary to perform an accurate and reliable hardening process. There is a problem that the number of parts decreases or the part is hardened in a part away from the lock hole part 35, or the temperature of the peripheral part 36 of the lock hole part 35 rises too much to reach a so-called overheat temperature. Have.

  Further, for example, when the value of the high-frequency current flowing through each of the high-frequency coils 32 and 33 is different due to problems in current management such as a high-frequency current generator and a high-frequency coil, the locks facing the high-frequency coils 32 and 33 correspondingly There arises a situation in which the quenching conditions of the holes are different from each other.

  Note that the steering shaft 40 originally needs to be attached to the high-frequency coils 32 and 33 so as to have the same interval. However, due to problems such as attachment accuracy, the pair of steering shafts 40 as shown in FIG. It is also conceivable that the distances (d1, d2) between the high-frequency coils 32 and 33 and the steering shaft 31 are slightly different.

  For this reason, naturally, since the temperature rise at the time of quenching is also different, the hollow cylindrical portion 34 is distorted, and the steering shaft 31 is slightly bent.

Utility Model Registration Publication No. 2573196 JP 2003-175801 A

  Therefore, in the present invention, the edge of the hole portion that particularly needs to be hardened is accurately and reliably hardened to ensure strength and reduce the cost required for hardening, and the shaft shaft. It is an object of the present invention to provide an induction hardening apparatus for a shaft and an induction hardening method for a shaft that can ensure direction accuracy.

  The induction hardening apparatus for shafts according to the present invention is made of rod-like carbon steel having a hollow cylindrical portion in the middle in the axial direction, and two or more so as to evenly distribute the outer peripheral surface to the same outer peripheral surface of the hollow cylindrical portion. The coil body is disposed opposite to the peripheral portion of each hole so as to perform induction hardening on the peripheral portion of the hole while holding the shaft in which the hole is formed. To do.

  Further, the induction hardening apparatus for a shaft of the present invention is made of a rod-like carbon steel having a hollow cylindrical portion in the axial center, and holds a shaft having a hole formed in the same outer peripheral surface of the hollow cylindrical portion. In a state, in order to perform induction hardening on the peripheral portion of the hole, an induction hardening apparatus for a shaft provided with a coil body disposed opposite to the peripheral portion of the hole, the insert being inserted into the hole, A positioning means for positioning the hollow cylindrical portion with respect to the coil body is provided.

  The positioning means is physically applied to the positioning of the hollow cylindrical portion with respect to the coil body, for example, by being fitted to the edge of the hole portion or abutting against the inner wall surface of the hollow cylindrical portion. The

  Furthermore, in the induction hardening apparatus for the shaft, the shaft is a shaft in which the two or more hole portions are evenly distributed on the outer peripheral surface of the hollow cylindrical portion, and holding bodies that hold the shaft are adjacent to each other. The hole portion is configured to be rotatable so as to stop at every angle formed with respect to the central axis of the hollow cylindrical portion.

  In addition, the induction hardening method for a shaft of the present invention comprises a rod-shaped carbon steel having a hollow cylindrical portion in the middle in the axial direction, and a shaft having a hole formed in the outer peripheral surface of the hollow cylindrical portion. An induction quenching method for performing an induction quenching process for performing an induction quenching process in which an induction quenching is performed on a peripheral edge of the hole by using a coil body disposed opposite to the peripheral edge of the hole. The positioning jig is inserted into the hole portion, and the positioning step of the hollow cylindrical portion with respect to the coil body is performed.

  Furthermore, in the induction hardening method for a shaft according to the present invention, the shaft is a shaft in which two or more of the hole portions are evenly distributed on the outer peripheral surface of the hollow cylindrical portion, and a holding body that rotatably holds the shaft. However, it is characterized in that the induction hardening process is performed while stopping at every angle formed between the hole portions adjacent to each other with respect to the central axis of the hollow cylindrical portion.

  According to the first aspect of the invention, the shape, area, etc. can be obtained by subjecting only two or more peripheral portions of the hole portion formed on the same outer peripheral surface of the hollow cylindrical portion to induction hardening. Can be induction-hardened on an object under the same conditions. Therefore, the amount of bending deformation of the portion subjected to induction hardening can be made uniform.

  In addition, since the shaft is intended for the hole that is bored in a state of being uniformly distributed with respect to the outer peripheral surface, the hollow cylinder can be obtained by subjecting the peripheral edge of the hole to induction hardening. Induction hardening is performed from the part which divides | segments the outer peripheral surface of a part equally with respect to the circumferential direction.

  As described above, since the shaft can be prevented from bending, the accuracy in the axial direction of the shaft can be kept high.

According to the invention which concerns on Claim 2 or Claim 4, the hollow cylindrical part of the shaft with respect to a coil body can be positioned with a positioning means.
Accordingly, the induction hardening of the peripheral portion of the hole portion that requires strength because the concentrated load is most easily applied due to the structure can be performed accurately and reliably.

  In other words, it is possible to improve the strength such as wear resistance and bending rigidity only by induction hardening only at the peripheral edge of the hole, as well as ensuring sufficient strength against torsional stress acting on the shaft. can do.

  Furthermore, since it is not necessary to perform induction hardening on the entire outer peripheral surface of the hollow cylindrical portion, the quenching time can be shortened.

  Moreover, according to the invention which concerns on Claim 3 or Claim 5, although each coil body is made to oppose each hole drilled in the said hollow cylindrical part, all hole parts are made to each coil body. Since it will be made to oppose sequentially, the peripheral part of all the hole parts can be induction-hardened on the same conditions.

  Therefore, in each coil body, even if the flowing high-frequency current value does not always match, not only is it not affected by the difference in the high-frequency current value, but also the distance between the peripheral edge of each hole and the coil body facing it. Even if a difference exists, it is not affected by the difference in the interval.

  For this reason, since the induction hardening is equally performed on the peripheral portions of all the holes, it is possible to eliminate the troublesomeness of current management such as always maintaining a constant high frequency current value between the coil bodies.

  Moreover, since induction hardening can be performed without causing deformation in the hollow cylindrical portion, the accuracy in the axial direction of the shaft can be kept high. In particular, when applied to a steering shaft, a good operational feeling can be obtained during driving.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows a steering shaft 11 extending from a steering wheel of an automobile, and the steering shaft 11 is made of hollow cylindrical carbon steel as shown in FIG.

As shown in FIGS. 1 and 2, two lock hole portions 12 and 13 into which a key lock can be inserted are formed in the hollow cylindrical portion 11 a in the middle in the axial direction of the steering shaft 11. Specifically, the two lock hole portions 12 and 13 are formed in a long hole shape that is long in the axial direction at a predetermined facing portion facing the shaft center on the outer peripheral surface of the hollow cylindrical portion 11a. Yes.
2 is a view of the hollow cylindrical portion 11a in FIG. 1 when viewed from the side.

  Of the two lock hole portions 12 and 13, one lock hole portion is set as the first lock hole portion 12, and the other lock hole portion is set as the second lock hole portion 13.

  Further, the peripheral edge portions 14 and 15 of the lock hole portions 12 and 13 in the steering shaft 11 are subjected to induction hardening (see FIG. 2), but the steering shaft 16 (see FIG. 2) that has not been quenched yet. Hereinafter, the configuration of an induction hardening apparatus that performs induction hardening on the steering shaft 16 will be described.

  The holding portion (not shown) for holding the steering shaft 16 includes an upper side holding portion and a lower side holding portion, and each of them is arranged to face each other in the vertical direction. The steering shaft 16 is attached to the holding portion with the upper portion held by the upper holding portion and the lower portion held by the lower holding portion.

  Further, the upper side holding portion holds the steering shaft 16 in a rotatable state. On the other hand, the lower side holding portion includes a motor that rotates the steering shaft 16 around the axis, and a brake is built in the motor. When the brake is released, the lower holding portion also holds the steering shaft 16 rotatably like the upper holding portion.

  When the steering shaft 16 is attached to the holding portion, the coil bodies 17 and 18 are respectively provided on the opposite sides of the two lock hole portions 12 and 13 with respect to the peripheral portions 14 and 15 as shown in FIG. The steering shaft 16 is disposed with a slight gap.

  The two coil bodies 17 and 18 are configured in the same form, the coil body facing the first lock hole 12 is set as the first coil body 17, and the coil facing the second lock hole 13 is set. The body is set to the second coil body 18.

Since the coil bodies 17 and 18 are configured in the same bowl shape, the first coil 17 will be taken and described below.
Specifically, the length in the length direction and the width direction of the first coil body 17 is slightly longer than the length in the length direction and the width direction of each first lock hole portion 12.

  In the length direction of the first coil body 17, two linear conductors 17 a and 17 a are configured, and the upper ends of the two conductors 17 a and 17 a are mutually in the width direction of the hollow cylindrical part 11 a. They are connected by an arcuate conductor 17b with a radius of curvature slightly larger than the radius of curvature.

On the other hand, each lower end portion of the two conductors is a conductor 17c having the same radius of curvature as the arcuate conductor, up to an intermediate portion in the width direction. , Bent in the direction opposite to the side having the lock holes 12 and 13.
Thus, the bent conducting wire 17c is connected to a high frequency current generator (not shown). The coil bodies 17 and 18 are configured in the above form, and the high frequency current supplied from the high frequency current generator flows through the coil bodies 17 and 18.

  Moreover, the positioning jig 19 (see FIG. 3) is retracted on the opposite side of the first lock hole 12 from the first coil body 17. The positioning jig 19 is configured in a substantially vertically long rectangular prism shape made of stainless steel, and is attached to a pneumatic cylinder (not shown) with the steering shaft 16 held in the vertical direction lying down in the horizontal direction. Yes.

  Specifically, the intermediate portion in the width direction of the positioning jig 19 and the intermediate portion in the width direction of the first coil body 17 coincide with each other, and the portion corresponding to the middle in the length direction of the first lock hole portion 12. Is attached.

  Further, the positioning jig 19 is formed to have a width that is longer than the interval in the width direction of the first lock hole portion 12 and shorter than the length in the width direction of the first coil body 17. Furthermore, both corners in the width direction on the end side facing the first lock hole portion 12 in the positioning jig 19 are notched into a tapered shape to form tapered portions 19a and 19b.

  As described above, the positioning jig 19 is attached to the tip of the piston rod of the pneumatic cylinder so as to be arranged as described above. When the piston rod of the pneumatic cylinder extends, the positioning jig 19 is It can be moved straight in the direction of the first lock hole 12 (see the phantom line in FIG. 3), and in the expanded / contracted state, as described above, the positioning jig 19 is steered with respect to the first coil body 17. Retraction is performed at a retreat position opposite to the shaft 16.

  In addition, although not shown, it is configured to include a cooling unit that cools the steering shaft 16 as appropriate after the quenching process, a transport unit that transports the steering shaft 16, and a control unit that controls the above-described components. .

Next, a series of steps for performing a quenching process on the steering shaft 16 by the quenching apparatus adopting the above configuration will be described.
The transport unit transports an arbitrary steering shaft 16 to the vicinity of the holding unit, and the upper portion of the steering shaft 16 is arranged so that the coil bodies 17 and 18 and the lock hole portions 12 and 13 are in a substantially opposed relationship as described above. The lower part is held by the holding part.
At this time, since the brake of the motor in the upper holding portion is released, the rotation about the axis of the steering shaft 16 is not restricted by the holding portion and is in a rotatable state.

  In this way, when the mounting of the steering shaft 16 is completed, the piston rod of the pneumatic cylinder extends, and the positioning jig 19 advances straight from the retracted position toward the first lock hole portion 12 of the steering shaft 16.

  Here, for example, as shown in FIG. 4, when the steering shaft 16 has a position deviation (Δα) in the counterclockwise direction with respect to the positioning jig 19 (see FIG. 4A), the pneumatic cylinder Immediately before reaching the maximum stroke, the right edge 14a of the peripheral edge 14 of the first lock hole 12 abuts against the right taper forming portion 19a (see FIG. 4B).

  However, since the steering shaft 16 is rotatably held by the holding portion, no load is applied to the tip of the piston rod of the cylinder even if the positioning jig 19 abuts against the steering shaft 16.

  Therefore, since the piston rod of the pneumatic cylinder further extends until the maximum stroke is reached, the right taper forming portion 19a of the positioning jig 19 and the right edge portion 14a of the first lock hole portion 12 slide during that time. The positioning jig 19 passively rotates the steering shaft 16 clockwise.

  At substantially the same time as the piston rod reaches the maximum stroke, the taper forming portions 19a and 19b of the positioning jig 19 abut against both edges 14a and 14b in the width direction of the first lock hole portion 12 (FIG. 4). (See (c)). That is, since the tip of the positioning jig 19 is fitted into the first lock hole 12, the rotation of the steering shaft 16 stops, and the first coil body 17, the first lock hole 12, and the positioning jig 19 Each of the jigs 19 can be positioned in a state where they match in the width direction.

  As described above, when the positioning of the hollow cylindrical portion 11a with respect to the coil bodies 17 and 18 is completed, the brake is activated, and the holding portion restrains the rotation of the steering shaft 16 in the axial direction. In this state, the piston rod contracts again, and the positioning jig 19 retracts to the initially retracted position, and then the brake is released.

  When the positioning process is completed, the high-frequency current generator operates for a predetermined time, and a high-frequency induction current (for example, 100 KHz to 110 KHz) flows through the coil bodies 17 and 18. The peripheral edge portions 14 and 15 of the lock hole portions 12 and 13 induced by the high-frequency induced current rise in temperature due to Joule heat generation, and induction hardening and hardening progress.

  At this time, in the circumferential direction of the hollow cylindrical portion 11a, the lock hole portions 12 and 13 have no positional deviation (Δα) with respect to the coil bodies 17 and 18; Induction hardening can be promoted evenly with respect to both edge portions of the holes 12 and 13.

  That is, by positioning using the positioning jig 19 described above, only specific edges (for example, 14b) of the peripheral edge portions 14 and 15 of the lock hole portions 12 and 13 in the circumferential direction of the hollow cylindrical portion 11a are induction-hardened. Will not be incomplete. Further, in consideration of the situation where the induction hardening is incomplete, it is not necessary to perform the hardening for a time longer than the induction hardening, and the peripheral portions 14 and 15 are not excessively heated.

  Further, during the induction hardening process, the positioning jig 19 is retracted as described above with respect to the first coil body 17, so that it does not interfere with the first coil body 17, and The heat generation temperature of the peripheral edge 14 of the one lock hole 12 and further the cooling by the cooling unit are not affected.

In this way, a certain amount of quenching hardening is allowed to proceed to the respective edge portions 14 and 15 of the two lock hole portions 12 and 13 until a predetermined time elapses after the induction hardening process. Then, the motor is driven after the lapse of the predetermined time, and the steering shaft 16 attached to the holding portion rotates around the axis of the steering shaft 16 by 180 ° (see π in FIG. 5).
Thereby, the first lock hole 12 faces the second coil body 18, and the second lock hole 13 faces the first coil body 17.

  After the coil bodies 17 and 18 and the lock hole portions 12 and 13 are opposed to each other in this manner, the first lock hole portion 12 is subjected to a high frequency current by a high frequency current flowing in the second coil body 18 for the same predetermined time as described above. The second lock hole 13 is quenched and hardened by the high frequency current flowing through the first coil body 17.

  At the same time as the predetermined time elapses, the steering shaft 16 is again rotated by 180 ° by the holding portion, and the coil bodies 17 and 18 and the lock hole portions 12 and 13 are in the predetermined opposing relationship at the beginning of quenching. During this period, induction hardening is performed. Quenching is performed by repeating such a series of steps.

  After performing the quenching process as described above, the cooling unit or the like appropriately performs a process of lowering the temperature of the hollow cylindrical part 11a, and the induction hardening process is performed on the peripheral edge parts 14 and 15 of the lock hole parts 12 and 13. The steering shaft 11 having been subjected to is completed.

  As described above, when the quenching process is executed, the first lock hole 12 and the second lock hole 13 are equally induction-hardened and hardened from the first coil body 17 and the second coil body 18, respectively. The

For this reason, it is not influenced by the difference of the electric current value which flows into the 1st coil body 17 and the 2nd coil body 18. FIG. Furthermore, even if there is a difference in distance between the two coil bodies 17 and 18 and the lock hole portions 12 and 13 (D1 and D2 in FIG. 5), the difference in the distance ( In FIG. 5, there is no influence of D1, D2).
Therefore, the peripheral edge portion 14 of the first lock hole portion 12 and the peripheral edge portion 15 of the second lock hole portion 13 can be equally induction-hardened.

  In addition, since the peripheral edge portion 14 of the first lock hole portion 12 and the peripheral edge portion 15 of the second lock hole portion 13 are bent by the same amount in the hollow cylindrical portion 11a and at the opposite positions with respect to the shaft center, steering is performed. The shaft 11 is not bent.

  In addition, by performing induction quenching, it is possible to accurately quench the part to be quenched, so that when the time necessary for quenching elapses in advance, the quenching can be surely completed and no unnecessary quenching time is required.

  The steering shaft 16 is rotated by driving the motor included in the holding portion so that the edges of all the lock hole portions 12 and 13 are evenly quenched. However, the steering shaft 16 is fixed during induction hardening. Alternatively, the coil body on the outer peripheral side of the steering shaft 16 may rotate around the steering shaft 16.

  In the correspondence between the above-described embodiment and the configuration of the present invention, the steering shaft 11 (16) of the present embodiment corresponds to the shaft of the present invention, and hereinafter the positioning jig 19 corresponds to the positioning means. However, the present invention is not limited only to the configuration of the above-described embodiment, and many embodiments can be obtained.

The side view of the steering shaft in this embodiment. The side view of the hollow cylindrical part shown in FIG. The perspective view which shows the hollow cylindrical part when the steering shaft is mounted | worn, and its vicinity. Explanatory drawing which showed the positioning process in this embodiment in the cross section. Explanatory drawing which showed the mode of the hardening process of the steering shaft in this embodiment in the cross section. Explanatory drawing which showed the trouble of the conventional hardening process in the cross section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 (16) ... Steering shaft 11a ... Hollow cylindrical part 12 ... 1st lock hole part 13 ... 2nd lock hole part 14 ... Peripheral part of 1st lock hole part 15 ... Perimeter part of 2nd lock hole part 17 ... 1st Coil body 18 ... 2nd coil body 19 ... Jig for positioning

Claims (6)

A shaft made of rod-shaped carbon steel having a hollow cylindrical portion in the middle in the axial direction, and having two or more holes formed on the same outer peripheral surface of the hollow cylindrical portion so as to distribute the outer peripheral surface evenly. An induction hardening apparatus for a shaft in which a coil body is disposed oppositely to the peripheral edge of each hole so as to perform induction hardening on the peripheral edge of the hole while holding. It is made of rod-like carbon steel with a hollow cylindrical part in the axial center, and is induction-hardened at the peripheral part of the hole while holding a shaft with a hole formed in the same outer peripheral surface of the hollow cylindrical part In order to perform the induction hardening apparatus of the shaft provided with the coil body disposed opposite to the peripheral portion of the hole,
An induction hardening apparatus for a shaft including positioning means for positioning the hollow cylindrical portion with respect to the coil body by being inserted into the hole. The shaft is a shaft in which the two or more hole portions are evenly distributed on the outer peripheral surface of the hollow cylindrical portion,
The induction hardening apparatus for a shaft according to claim 2, wherein the holding body for holding the shaft is configured to be rotatable so as to stop at every angle formed by the holes adjacent to each other with respect to the central axis of the hollow cylindrical portion. It is made of a rod-shaped carbon steel having a hollow cylindrical portion in the middle in the axial direction, and a mounting step of mounting a shaft having a hole formed on the outer peripheral surface of the hollow cylindrical portion is executed, and the peripheral portion of the hole An induction hardening method for performing an induction hardening step of induction hardening to the peripheral edge of the hole using a coil body disposed opposite to
After the mounting step, a positioning jig is inserted into the hole,
An induction hardening method for a shaft, which performs a step of positioning the hollow cylindrical portion with respect to the coil body. The shaft is a shaft in which the two or more hole portions are evenly distributed on the outer peripheral surface of the hollow cylindrical portion,
5. The shaft according to claim 4, wherein the induction hardening step is performed while the holding body that rotatably holds the shaft stops at each angle formed by the holes adjacent to each other with respect to the central axis of the hollow cylindrical portion. Induction hardening method. A shaft induction-hardened by the induction hardening apparatus for a shaft according to claim 1, claim 2, or claim 3, or a shaft induction-hardened by the induction hardening method for a shaft according to claim 4 or 5.

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