Mobile quenching method and mobile quenching apparatus

Abstract

Provided is a mobile hardening method characterized in that a shaft body (10) is heated by a plurality of high-frequency coils (111), a cooling unit (120) is caused to follow the high-frequency coils (111) from behind in the relative moving direction of the high-frequency coils (111) along the axial direction of the shaft body (10), the part heated by the high-frequency coils (111) is cooled by the cooling unit (120), and mobile hardening is carried out while moving the high-frequency coils (111) toward the direction perpendicular to the axial direction of the shaft body (10) so that the distances from the surface of the shaft body (10) to the respective high-frequency coils (111) are constant, wherein the speed in the axial direction of the high-frequency coils (111) at the time when the high-frequency coils (111) pass through a step part (13) is slower than the speed in the axial direction of the high-frequency coils (111) at the time when the high-frequency coils (111) pass through a small diameter part (12) or a large diameter part (11).

Description

[Technical Field]

[0001] The present invention relates to a mobile quenching method and a mobile quenching apparatus. [Background technology]

[0002] Steel parts that require a long lifespan are often subjected to various surface treatments. In particular, high-frequency induction hardening is widely used to improve the surface hardness, wear resistance, and fatigue resistance of the part surface. For this reason, various high-frequency induction hardening devices have been proposed. For example, when high-frequency induction hardening is performed on long components such as steel shafts, so-called traverse hardening is used. Traverse hardening is a method of hardening while moving a high-frequency induction heating coil (also called a high-frequency coil) and a cooling means relative to the shaft along the axial direction of the shaft.

[0003] In mobile quenching, the shaft is locally heated by a high-frequency coil until at least the surface layer becomes the austenite phase. Then, a cooling means that follows the high-frequency coil sprays a cooling medium such as a coolant onto the heated surface of the shaft, rapidly cooling it in a short time, thereby creating a structure with a desired hardness, such as the martensite phase, on the surface of the shaft.

[0004] The outer diameter of an axial body may not be constant in the direction along its axis (also called the axial direction). That is, an axial body may have a small-diameter section with a relatively small outer diameter and a large-diameter section with a relatively large outer diameter in the axial direction. Furthermore, these small-diameter and large-diameter sections are connected by a stepped section in which the outer diameter gradually changes in the axial direction. For example, in the technology disclosed in Patent Document 1 or Patent Document 2, the change in the outer diameter of the axial body is accommodated by moving a divided coil back and forth in the radial direction of the axial body which is the object to be heated.

[0005] However, while such variable-diameter coil systems have the advantage of simple equipment configuration, it is crucial to appropriately control the coil's movement speed. The reason is as follows: In order to heat uniformly in the axial direction at the stepped portion of an axial body, it is desirable to keep the movement speed along the surface as constant as possible when attempting to move the coil along the radial direction of the axial cross-section. If the axial movement speed of the coil is kept constant instead of the movement speed along the surface, heating will concentrate at the corners of the step, and heating to the recesses of the step will be reduced. If this inconvenience is suppressed while keeping the axial movement speed of the coil constant, a large current will be required to heat the recesses of the step, and due to limitations on the upper limit of the current, such as the cooling capacity of the coil, it becomes impossible to provide sufficient heating. In other words, according to the present inventors, in conventional structures using segmented coils as disclosed in Patent Document 1 or Patent Document 2, a problem has been found in that sufficient heating to obtain the desired structure is not performed at the stepped portion connecting the small-diameter and large-diameter portions and in its vicinity, as described above. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2008-150640 [Patent Document 2] Japanese Patent Publication No. 36-10457 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention has been made in view of the above circumstances, and aims to provide a mobile quenching method and a mobile quenching apparatus that can perform desired quenching on stepped portions and their vicinity in a shaft-shaped body whose outer diameter is not constant in the axial direction. [Means for solving the problem]

[0008] (1) A moving quenching method according to one aspect of the present invention is a moving quenching method for quenching an axial body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion, using a moving quenching apparatus equipped with a plurality of high-frequency coils and a cooling unit, The shaft-shaped body inserted inside the plurality of high-frequency coils is rotated relative to the plurality of high-frequency coils, and the plurality of high-frequency coils are moved relative to the shaft-shaped body in the axial direction, while the shaft-shaped body is heated by the high-frequency coils. The cooling unit follows the high-frequency coil from behind in the relative direction of movement of the high-frequency coil along the axial direction of the shaft-shaped body, and the portion heated by the high-frequency coil is cooled by the cooling unit. The distance from the surface of the axial body to each of the high-frequency coils remains constant. radius While moving the high-frequency coil in that direction, perform the moving hardening process. The high-frequency coil is characterized in that the axial speed of the high-frequency coil when it passes through the stepped portion is smaller than the axial speed of the high-frequency coil when it passes through the small-diameter portion or the large-diameter portion. (2) In the moving quenching method described in (1), the axial speed of the high-frequency coil when the high-frequency coil passes the small diameter portion or the large diameter portion is V0, the axial speed of the high-frequency coil when the high-frequency coil passes the stepped portion is Vs, and the multiple high-frequency coils radius When the velocity in the direction is Vc, the following equation 1 may also hold. V0 2 ≤Vs 2 +Vc 2 ...Formula 1 (3) In the moving quenching method described in (1) or (2), the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes the stepped portion may be made smaller than the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes the small-diameter portion or the large-diameter portion. (4) In the mobile quenching method described in any one of items (1) to (3), the cooling unit sprays a cooling medium, The amount of cooling medium injected or the ejection pressure when the high-frequency coil passes through the stepped portion may be smaller than the amount of cooling medium injected or the ejection pressure when the high-frequency coil passes through the small-diameter portion or the large-diameter portion.

[0009] (5) A mobile quenching apparatus according to one aspect of the present invention is a mobile quenching apparatus for quenching an axial body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion in the axial direction, The aforementioned mobile quenching apparatus is In the aforementioned axial direction, the system comprises a plurality of high-frequency coils and a cooling unit. The system includes a control unit capable of controlling the movement of the plurality of high-frequency coils and the cooling unit, Each of the aforementioned high-frequency coils has a high-frequency induction section for heating the axial body and a conductive section connected to the high-frequency induction section, and is movable relative to the axial body in the axial direction, In the radial direction of the axial body with respect to the axial body Relatively movable, The cooling unit has an injection unit capable of spraying a cooling medium and is movable relative to the shaft in the axial direction. The control unit, The distance from the surface of the axial body to each of the high-frequency coils is kept constant. radial direction The movement of the high-frequency coil can be controlled in the above, The high-frequency coil is characterized in that its axial speed when passing through the stepped portion is controllable to be smaller than its axial speed when passing through the small-diameter portion or the large-diameter portion. (6)(5) In the mobile hardening apparatus, the control unit sets V0 the axial speed of the high-frequency coil when the high-frequency coil passes the small diameter portion or the large diameter portion, Vs the axial speed of the high-frequency coil when the high-frequency coil passes the stepped portion, and the plurality of high-frequency coils radiusWhen the speed in the direction is Vc, the high-frequency coil may be controllable so that the following formula (1) holds. V0 2 ≤ Vs 2 + Vc 2 ···Formula (1) (7) In the moving quenching device according to (5) or (6), when the high-frequency coil passes through the stepped portion, the control unit controls the distance between the high-frequency coil and the cooling unit in the axial direction to be smaller than the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes through the small-diameter portion or the large-diameter portion. It may be controllable. (8) In the moving quenching device according to any one of (5) to (7), when the high-frequency coil passes through the stepped portion, the control unit controls the injection amount or ejection pressure of the cooling medium to be smaller than the injection amount or ejection pressure of the cooling medium when the high-frequency coil passes through the small-diameter portion or the large-diameter portion. It may be controllable.

Advantages of the Invention

[0010] According to the moving quenching method and the moving quenching device of the present invention, it is possible to perform desired quenching on the stepped portion and its vicinity in the shaft-shaped body whose outer diameter is not constant in the axial direction.

Brief Description of the Drawings

[0011] [Figure 1] It is a side view schematically showing a part of the moving quenching device of an embodiment of the present invention, with the moving quenching device broken away. [Figure 2] It is a cross-sectional view schematically showing a partial cross-section of the shaft-shaped body and two high-frequency coils in a plan view in the direction along the axis of the shaft-shaped body, and shows a state where the high-frequency coil has moved in accordance with the outer diameter of the small-diameter portion. [Figure 3] It is a cross-sectional view schematically showing a partial cross-section of the shaft-shaped body and two high-frequency coils in a plan view in the direction along the axis of the shaft-shaped body, and shows a state where the high-frequency coil has moved in accordance with the outer diameter of the large-diameter portion. [Figure 4]This is a schematic cross-sectional view showing a partial cross-section of the shaft and three high-frequency coils when viewed from above along the axis of the shaft, illustrating the state in which the high-frequency coils have moved to match the outer diameter of the small diameter section. [Figure 5] This is a schematic cross-sectional view showing a partial cross-section of the shaft and three high-frequency coils when viewed in a plan view along the axis of the shaft, illustrating the state in which the high-frequency coils have moved to match the outer diameter of the large-diameter section. [Figure 6] This is a schematic perspective view illustrating the positional relationship between the heating section and the cooling section with respect to the axial body in an embodiment of the present invention. [Figure 7] This is a schematic cross-sectional view of the shaft and the high-frequency coil, taken from a plane passing through the axis of the shaft. [Figure 8] This is a schematic cross-sectional view showing a partial cross-section of an axial body and a single high-frequency coil when viewed in a plan view along the axis of the axial body, illustrating the state in which the high-frequency coil has moved to match the outer diameter of the small-diameter section. [Figure 9] This is a schematic cross-sectional view showing a partial cross-section of an axial body and a single high-frequency coil, viewed from above along the axis of the axial body, illustrating the state in which the high-frequency coil has moved to match the outer diameter of the large-diameter section. [Figure 10] This is a block diagram illustrating a mobile quenching apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention, namely a mobile quenching method and a mobile quenching apparatus, will be described with reference to Figures 1 to 10. It is obvious that the present invention is not limited to the following embodiments. Furthermore, it is obvious that within the scope of the present invention, the elements of the following embodiments can be combined.

[0013] As shown in Figure 1, the traverse hardening apparatus 100 of this embodiment is a device for performing traverse hardening on a shaft-shaped body 10 using high-frequency current. Traverse hardening is a method of hardening an object while moving a heating section equipped with a high-frequency induction heating coil (also called a high-frequency coil) and a cooling section equipped with a cooling ring that follows the heating section relative to the object to be heated. The object to be heated is, for example, a shaft-shaped body.

[0014] (Axial body) The shaft-like body 10 comprises a large-diameter portion 11 (large-diameter portion 11A and large-diameter portion 11B) and a small-diameter portion 12 provided between the large-diameter portion 11A and the large-diameter portion 11B in the direction along axis C. The large-diameter portion 11A, the large-diameter portion 11B, and the small-diameter portion 12 are each formed in a cylindrical shape. The central axes of the large-diameter portion 11A, the large-diameter portion 11B, and the small-diameter portion 12 are arranged to coincide with a common axis, axis C. In this embodiment, axis C is the central axis of the shaft-like body 10. Hereinafter, the portion located on one side D1 in the direction along axis C relative to the small-diameter portion 12 will also be referred to as the first large-diameter portion 11A. The portion located on the other side D2 in the direction along axis C relative to the small-diameter portion 12 will also be referred to as the second large-diameter portion 11B.

[0015] The first large-diameter portion 11A, the small-diameter portion 12, and the second large-diameter portion 11B are each formed in a cylindrical shape and share an axis C as a common central axis. When viewing a cross-section perpendicular to the axis C of the large-diameter portions 11A and 11B, the outer diameter of the small-diameter portion 12 is smaller than the outer diameters of the large-diameter portions 11A and 11B, respectively. In this embodiment, the outer diameters of the large-diameter portion 11A and 11B are the same, but the outer diameters of the large-diameter portion 11A and 11B may be different.

[0016] Between the large-diameter portion 11A or large-diameter portion 11B and the small-diameter portion 12, there is a stepped portion 13 (stepped portion 13A and stepped portion 13B) for connecting them. The stepped portions 13A and 13B are inclined at a predetermined angle with respect to the axis C of the shaft-like body 10. The inclination angle is, for example, in the range of 15° to 90°. The outer diameter of the stepped portion 13 is not particularly limited in the plane containing the axis C of the shaft-like body 10, but it may be a shape that smoothly connects the large-diameter portion 11 and the small-diameter portion 12, as illustrated in Figure 1. In the mobile quenching apparatus 100 of this embodiment, the shaft-like body 10 is arranged so that its axis C is parallel to the vertical direction of the mobile quenching apparatus 100.

[0017] The shaft-like body 10 is formed of a conductive material such as carbon steel or low-alloy steel containing 95% or more by weight of iron (Fe), which is, for example, a ferrite phase or pearlite phase. The shaft-like body may be an axle for a railway vehicle, etc. The number of large-diameter sections 11 and stepped sections 13 on the shaft-like body 10 is not limited to the example in Figure 1. The number of small-diameter sections 12, large-diameter sections 11, and stepped sections 13 may be 1, 2, or 3, or 4 or more, respectively. For example, the shaft-like body targeted by the mobile quenching method and mobile quenching apparatus of this embodiment may be a shaft-like body having one large-diameter section and one small-diameter section.

[0018] (Mobile quenching device) The mobile hardening apparatus 100 comprises a heating section 110, a cooling section 120, a support section 130, a heating section moving device 140, a cooling section moving device 150, and a control unit 160. As shown in Figure 1, the heating section 110 comprises a plurality of high-frequency coils 111 (high-frequency coils 111A and 111B). The heating section 110 is connected to the heating section moving device 140, which is a means of moving the heating section. The cooling section 120 comprises a cooling ring 121. The cooling section 120 is connected to the cooling section moving device 150, which is a means of moving the heating section. The support section 130 comprises an upper center 131 and a lower center 132. The upper center 131 supports the first large diameter section 11A of the shaft-shaped body 10 from above the first large diameter section 11A. The lower center 132 supports the second large diameter section 11B of the shaft-shaped body 10 from below the second large diameter section 11B. The upper center 131 and the lower center 132 support the shaft-shaped body 10 such that one side D1 in the direction of axis C is upward and the other side D2 is downward. The shaft-shaped body 10 is rotatable in the circumferential direction of the shaft-shaped body 10 around axis C while supported by the upper center 131 and the lower center 132. The shaft-shaped body 10 can be rotated around its axis during mobile hardening by a drive device (not shown) via the upper center 131 and the lower center 132. Rotating the shaft-shaped body 10 around its axis means rotating the shaft-shaped body 10 in any direction in the circumferential direction of the shaft-shaped body 10 around axis C. The line connecting the center of the upper center 131 and the center of the lower center 132 is the vertical direction (also referred to as the vertical direction) of the mobile hardening apparatus 100.

[0019] The heating unit moving device 140 supports the heating unit 110 and comprises a support member 141 and a motor (not shown). The heating unit moving device 140 is attached to a rack member 180. The rack member 180 extends in the vertical direction. A pinion gear 141a is provided on the support member 141, and the pinion gear 141a meshes with the gear portion 180a of the rack member 180. When the motor is driven, the pinion gear 141a rotates, and the heating unit moving device 140 moves upward or downward relative to the rack member 180.

[0020] The cooling unit moving device 150 supports the cooling unit 120 and comprises a support member 151 and a motor (not shown). The cooling unit moving device 150 is attached to a rack member 180. A pinion gear 151a is provided on the support member 151, and the pinion gear 151a meshes with the gear portion 180a of the rack member 180. When the motor is driven, the pinion gear 151a rotates, and the cooling unit moving device 150 moves upward or downward relative to the rack member 180.

[0021] The heating section moving device 140 and the cooling section moving device 150 are each independently controlled by the control unit 160. As the heating section moving device 140, which supports the heating section 110, and the cooling section moving device 150, which supports the cooling section 120, move vertically, mobile quenching is performed in the axial direction of the shaft-shaped body 10. In other words, the vertical direction of the mobile quenching device 100 can be said to be the direction in which mobile quenching is performed.

[0022] Figure 1 shows an example in which a rack and pinion gear are used as the vertical movement mechanism for the heating section 110 and the cooling section 120. However, the movement mechanism of the present invention is not limited to this, and any mechanism that allows the heating section 110 and the cooling section 120 to move relative to the shaft-shaped body 10 in the vertical direction is acceptable. Also, Figure 1 shows an example in which the heating section 110 and the cooling section 120 move relative to a fixed shaft-shaped body 10. However, the mobile quenching method and mobile quenching apparatus of the present invention are not limited to this configuration. The heating section 110 and the cooling section 120 may be fixed, and the shaft-shaped body 10 may be moved relative to the heating section 110 and the cooling section 120. Furthermore, Figure 1 assumes an example in which the axial direction of the shaft-shaped body 10 is oriented vertically. However, the mobile quenching method and mobile quenching apparatus of the present invention are not limited to this configuration. The axial direction of the shaft-shaped body 10 may be oriented horizontally, or the axial direction of the shaft-shaped body 10 may be tilted with respect to the vertical direction.

[0023] (heating part) The heating unit 110 of this embodiment is equipped with a plurality of high-frequency coils. Figure 2 shows a schematic plan view of the high-frequency coils 111A and 111B of the heating unit 110 and the shaft-shaped body 10, viewed from the direction AA in Figure 1 (parallel to the axial direction) along the axis C. In Figure 2, the shaft-shaped body 10 is shown broken in the middle of the small-diameter portion 12. As shown in Figure 2, the high-frequency coils 111A and 111B of the heating unit 110 have high-frequency induction portions 112A and 112B, which are formed in a C shape so as to surround the shaft-shaped body 10 when viewed in plan from the direction along the axis C of the shaft-shaped body 10. The high-frequency induction portion 112A is connected to conductive portions 113a and 113b at its end. Similarly, the high-frequency induction portion 112B is connected to conductive portions 113c and 113d at its end.

[0024] The high-frequency coils 111A and 111B are arranged side by side, spaced apart from each other in the circumferential direction (also referred to as the circumferential direction) centered on the axis C of the shaft-shaped body 10. This circumferential direction is parallel to the direction in which the high-frequency induction portion 112A of the high-frequency coil 111A and the high-frequency induction portion 112B of the high-frequency coil 111B extend. That is, the plane (also referred to as the transverse plane) in which the high-frequency induction portions 112A and 112B extend is perpendicular to the vertical direction of the mobile hardening apparatus 100. Furthermore, the transverse plane is perpendicular to the axial direction of the shaft-shaped body 10.

[0025] In the horizontal plane described above, the shapes of the high-frequency induction portion 112A of the high-frequency coil 111A and the high-frequency induction portion 112B of the high-frequency coil 111B may be arc-shaped as shown in Figure 2. Having arc shapes for the high-frequency induction portions 112A and 112B has the advantage that the high-frequency coil 111 and the axial body 10 are uniformly and generally close in the circumferential direction.

[0026] When the shapes of the high-frequency induction sections 112A and 112B are arc-shaped, it is preferable that the diameter of the inscribed circle on the transverse plane that is in contact with the inner surfaces (the surfaces on the axial body 10 side) of the high-frequency induction sections 112A and 112B facing the axis C is larger than the outer diameter of the small-diameter section 12 and smaller than the outer diameter of the large-diameter section 11 of the axial body 10.

[0027] Alternatively, one or both of the high-frequency induction sections 112A and 112B may constitute part of an ellipse in the above-mentioned horizontal plane, or they may be composed of multiple straight lines. Furthermore, the high-frequency coils 111A and 111B may have a shape such that a part of the high-frequency coil 111A and a part of the high-frequency coil 111B overlap when viewed in the axial direction of the axial body 10. For example, the conductive sections 113a and 113b in Figure 2 may be located closer to the high-frequency induction section 112B than the conductive sections 113d and 113c, respectively. In this case, the high-frequency coils 111A and 111B are positioned at different locations in the axial direction.

[0028] Each of the conductive parts 113a, 113b, 113c, and 113d extends from each end of the high-frequency induction part 112A or high-frequency induction part 112B in a direction away from the axial body 10. It is more preferable that each of the conductive parts 113a, 113b, 113c, and 113d extends in a direction perpendicular to the axis C of the axial body 10 at the position where the high-frequency coil 111A and the high-frequency coil 111B are closest to each other.

[0029] Each of the high-frequency coils 111A and 111B is movable in a direction away from or closer to the axial body 10. Figure 2 shows the state in which the high-frequency coils 111A and 111B are closest to the small-diameter portion 12 of the axial body 10. It is preferable to heat the small-diameter portion 12 in this state.

[0030] On the other hand, Figure 3 shows a state in which the high-frequency coils 111A and 111B move in a direction away from the shaft-like body 10 (direction P in Figure 3) to match the outer diameter of the large-diameter portion 11B, and surround the large-diameter portion 11B of the shaft-like body 10. It is preferable to heat the large-diameter portion 11 in this state. In the state shown in Figure 3, the high-frequency coils 111A and 111B move in the direction of the axis C of the shaft-like body 10, and the high-frequency coils 111A and 111B are located at the position of the large-diameter portion 11 in the axial direction.

[0031] The conductive parts 113a and 113b of the high-frequency coil 111A are connected to a power source (not shown). When a high-frequency current is supplied from the power source to the high-frequency induction part 112A, an induced current is generated in the shaft-shaped body 10, and Joule heat is generated in the shaft-shaped body 10 due to its electrical resistance. The same applies to the high-frequency coil 111B. For example, current flows in the high-frequency coils 111A and 111B in the direction of arrow i shown in Figure 2. In multiple high-frequency coils 111, the current flows in the same direction in the circumferential direction.

[0032] Each of the high-frequency coils 111A and 111B may be connected to the heating unit 110 via a coil moving unit (not shown). The coil moving unit includes a drive motor and a stage, and is configured to move each of the high-frequency coils 111A and 111B in a direction perpendicular to the axis C of the axial body 10, i.e., on a horizontal plane. The movement of the high-frequency coils 111A and 111B on the horizontal plane is controlled by the control unit 160. The power supply may be fixed to the heating unit 110, or it may be moved together with the high-frequency coils 111 by the coil moving unit.

[0033] The number of high-frequency coils 111 in the mobile hardening apparatus 100 is preferably two, from the viewpoint of maximizing the continuous circumferential length of the proximity between the high-frequency coils 111 and the shaft-shaped body 10. Furthermore, from the viewpoint of ensuring that the gap between the high-frequency coils 111 and the shaft-shaped body 10 does not widen too much, even when the distance between the high-frequency coils 111 is narrowed or widened to follow changes in the diameter of the shaft-shaped body 10, while still increasing the length of the proximity, three coils, as shown in Figures 4 and 5, are preferable. When using three high-frequency coils 211 (high-frequency coils 211A, 211B, and 211C) as shown in Figures 4 and 5, the same configuration as when using the two high-frequency coils 111 and heating unit 110 described above can be adopted. The multiple high-frequency coils 111 are arranged spaced apart from each other in the horizontal plane. It is preferable that each of the multiple high-frequency coils 111 is movable in a direction perpendicular to the axis C of the shaft-shaped body 10 being subjected to mobile hardening.

[0034] The cross-sections of each part of the high-frequency coil 111 in the direction of extension may be rectangular, as shown in Figure 1, or they may be elliptical or circular. Furthermore, the inside of the high-frequency coil 111 may be hollow, allowing a coolant to flow through it. The high-frequency coil 111 is preferably made of a material such as copper, because it is non-magnetic, less prone to eddy current loss, has low electrical resistance, and is less prone to Joule loss. Furthermore, to prevent short circuits even if the high-frequency coils 111 come into contact with each other or with the shaft-like body 10, the surface of the high-frequency coil 111 may be covered with a heat-resistant and highly insulating material such as bakelite or silicon.

[0035] The high-frequency coil 111 may be connected to the heating section 110 via support members (not shown) at each of the conductive sections 113a, 113b, 113c, and 113d.

[0036] (cooling section) The cooling section 120 is positioned behind the heating section 110 in the relative direction of movement. The relative direction of movement refers to the direction in which the heating section 110 moves axially relative to the shaft body 10 during moving quenching. In this embodiment, since moving quenching is performed while the heating section 110 moves in the direction of D1 in Figure 1, the cooling section 120 is positioned below the heating section 110, as shown in Figure 1. Figure 6 illustrates the positional relationship between the heating section 110 and the cooling section 120 with respect to the shaft body 10 in this embodiment.

[0037] In this embodiment, the cooling section 120 is formed in an annular shape. The cooling section 120 has an internal space through which the axial body 10 can be inserted. On the inner circumferential surface 121a of the cooling section 120, which faces the internal space of the cooling ring 121, a plurality of injection nozzles 122, which are injection sections, are formed spaced apart from each other in the circumferential direction. A cooling medium can be injected from each injection nozzle 122 toward the internal space. The shape of the cooling section 120 is not limited to an annular shape as shown in Figure 6, and may be circular, elliptical, rectangular, or the like in a horizontal plane perpendicular to the vertical direction.

[0038] A pump (not shown) is connected to the cooling unit 120. The pump supplies a cooling medium cl to the cooling unit 120. The cooling medium cl supplied to the cooling ring 121 of the cooling unit 120 is sprayed towards the shaft body 10 through a plurality of injection nozzles 122, cooling the shaft body 10. The cooling medium cl is, for example, water, oil, or an aqueous solution similar to oil. The amount of cooling medium cl sprayed can be adjusted, for example, by controlling the pump with a control unit 160.

[0039] Figure 7 shows a schematic cross-sectional view of the shaft 10 and the high-frequency coil 111 in a plane passing through the axis of the shaft 10. The X-axis in Figure 7 is perpendicular to the axis C of the shaft 10 and is perpendicular to the Z-axis and Y-axis. The Y-axis is perpendicular to the plane of the paper in Figure 7 and is perpendicular to the X-axis and Z-axis. The Z-axis is parallel to axis C (the vertical direction of the mobile hardening device 100), and the positive direction of the Z-axis coincides with the direction of D1.

[0040] Here, if the coil is controlled to maintain a constant speed along the surface of the stepped portion, and the cooling ring is made to follow the coil, the speed of the cooling ring will decrease significantly when the curved portion of the stepped portion moves. This results in the problem that the cooling will not be uniform in the axial direction of the heated object. In the mobile hardening apparatus 100 of this embodiment, the distance from the surface of the shaft-shaped body 10 to the high-frequency coils 111A and 111B is controlled to be constant. The distance from the surface of the shaft-shaped body 10 to the high-frequency coils 111A and 111B is defined as the shortest distance between the surface of the shaft-shaped body 10 and the surface of the high-frequency coils 111. The eddy currents generated in the shaft-shaped body 10, which is the heated object, by the current flowing through the high-frequency coils 111 change greatly depending on the distance between the high-frequency coils 111 and the heated object. By keeping this distance constant to prevent this change, the magnitude of the eddy currents becomes constant, and the heating is also kept constant. The imaginary line m in Figure 7 is a line drawn in a plane passing through the axis of the shaft-like body 10, such that the distance from the surface of the shaft-like body 10 in a direction perpendicular to the surface of the shaft-like body 10 remains constant. The nearest contact point of the high-frequency coil 111 with respect to the shaft-like body 10 moves along this imaginary line m.

[0041] Here, let Vz be the Z-coordinate component of the relative movement velocity of the high-frequency coil 111 with respect to the axial body 10, and let Vx be the X-coordinate component of the relative movement velocity of the high-frequency coil 111 with respect to the axial body 10. Vz corresponds to the relative movement velocity of the high-frequency coil 111 with respect to the axial body 10 in the axial direction. Vx corresponds to the relative movement velocity of the high-frequency coil 111 with respect to the axial body 10 in a direction perpendicular to the axis C of the axial body 10.

[0042] When defined in this way, in the mobile quenching apparatus of this embodiment, when the high-frequency coil 111 passes through the large-diameter section 11 or the small-diameter section 12, the high-frequency coil 111 moves in the axial direction and does not move in the direction perpendicular to the axis C, so Vx becomes 0. Therefore, the moving speed V0 of the high-frequency coil 111 along the imaginary line m when the high-frequency coil 111 passes through the large-diameter section 11 or the small-diameter section 12 is equal to the velocity V0z of the Z coordinate component.

[0043] On the one hand, when the high-frequency coil 111 passes through the step portion 13, the high-frequency coil 111 moves in the axial direction and also moves in a direction orthogonal to the axis C. Therefore, the moving speed V1 of the high-frequency coil 111 along the virtual line m when the high-frequency coil 111 passes through the step portion 13 satisfies the relationship of the following formula A. V1 2 =V1x 2 +V1z 2 ···Formula A Here, V1x is the speed of the X coordinate component when the high-frequency coil 111 passes through the step portion 13, and V1z is the speed of the Z coordinate component when the high-frequency coil 111 passes through the step portion 13.

[0044] In the moving quenching device 100 of the present embodiment, it is desirable that the moving speed of the high-frequency coil 111 along the virtual line m when the high-frequency coil 111 passes through the large-diameter portion 11, the small-diameter portion 12, and the step portion 13 is as constant as possible. In other words, this means that the high-frequency coil 111 moves so as to satisfy the relationship V0 = V1. Here, from the relationships V0 = V0z, V0 ≤ V1 and Formula A, the following formula B is derived. V0z 2 ≤V1x 2 +V1z 2 ···Formula B

[0045] As for the control of the moving quenching device 100, it is desirable to satisfy the relationship V0 = V1. However, for example, due to various restrictions such as the response performance of an actuator such as a motor for moving the moving device and the response performance when changing the flow rate of the cooling medium Cl jetted by the cooling unit 120, there may be cases where V0 = V1 cannot be achieved. Even under such limitations, it is desirable to approach V0 = V1 as much as possible. Eddy currents generated in the shaft-shaped body 10, which is the heated object, by the current flowing through the high-frequency coil 111 cause the surface of the heated object to generate heat. However, by keeping the moving distance per unit time constant as described above, the heat generation energy per unit time per unit length of the surface of the shaft-shaped body 1 becomes constant.

[0046] As is clear from equation B, the axial speed V1z of the high-frequency coil 111 when it passes through the stepped portion 13 is smaller than the axial speed V0z of the high-frequency coil 111 when it passes through the large-diameter portion 11 or the small-diameter portion 12. With this configuration, the mobile hardening apparatus 100 of this embodiment makes it possible to perform desired hardening on the stepped portion and its vicinity in a shaft-shaped body whose outer diameter is not constant in the axial direction.

[0047] In other words, in the mobile hardening apparatus 100 of this embodiment, when the axial speed of the high-frequency coil 111 when the high-frequency coil 111 passes through the stepped portion 13 is Vs, and the speed of the high-frequency coil 111 in a direction perpendicular to the axial direction is Vc, it is more preferable that the moving speed of the high-frequency coil 111 be controlled such that the following equation 1 holds true. V0 2 ≤Vs 2 +Vc 2 ...Formula 1 Vs is the same as V1z above, and Vc is the same as V1x above.

[0048] The distance from the surface of the shaft-like body 10 to the high-frequency coils 111A and 111B is the average distance from the surface of the shaft-like body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 in the direction perpendicular to the surface of the shaft-like body 10 in the horizontal plane, as shown in Figure 8. For example, in the example in Figure 8, the distance d from the surface of the shaft-like body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 in the small-diameter portion 12 is constant in the circumferential direction. On the other hand, in the example in Figure 9, for example, the distance from the surface of the shaft-like body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 in the large-diameter portion 11 is not constant in the circumferential direction. In this case, the arithmetic mean of the shortest and longest distances from the surface of the shaft-like body 10 to the high-frequency induction portion 112 of the high-frequency coil 111 is adopted. In Figure 8 or Figure 9, only one high-frequency coil 111A is shown for illustrative purposes. Furthermore, it is preferable that the multiple high-frequency coils 111 move at the same speed relative to each other in the lateral plane.

[0049] Generally, if cooling after heating for quenching is delayed, some parts of the quenched area may undergo pearlite transformation, resulting in insufficient quenching. Even if cooling after heating is performed quickly, the grain size of the crystals in the quenched area may change or the volume fraction of retained austenite may change depending on the time between heating and cooling, altering the hardness and mechanical properties of the quenched material. However, the mobile quenching apparatus 100 of this embodiment can suppress such changes in the hardness and mechanical properties of the quenched material by having the following configuration.

[0050] In the mobile quenching apparatus 100 of this embodiment, it is more preferable to control the axial distance between the high-frequency coil 111 and the cooling unit 120 when the high-frequency coil 111 passes through the stepped section 13 to be smaller than the axial distance between the high-frequency coil 111 and the cooling unit 120 when the high-frequency coil 111 passes through the large-diameter section 11 or the small-diameter section 12. With this configuration, the time from heating to the start of cooling becomes closer to constant, and changes in grain size and volume fraction of retained austenite can be suppressed, so that the hardness and mechanical properties of the material become constant. In addition, there is the advantage that the movement speed of the cooling unit 120 becomes closer to constant, and the cooling capacity also becomes closer to constant. Specifically in this operation, it is desirable to control the axial position of the cooling unit 120 so that the end of the cooling unit 120 (the front end in the direction of movement) passes through the axial position that the end of the high-frequency coil 111 (the rear end in the direction of movement) has passed through after a certain period of time. Due to this operation, the axial distance between the high-frequency coil 111 and the cooling unit 120 becomes smaller when the axial movement speed of the high-frequency coil 111 is slow compared to when the axial movement speed of the high-frequency coil 111 is fast.

[0051] The distance between the high-frequency coil 111 and the cooling section 120 in the axial direction is the distance from the lower end of the high-frequency coil 111 to the upper end of the cooling section 120 in the vertical direction of the mobile hardening apparatus 100, as illustrated by distance L in Figure 1. In other words, the lower end of the high-frequency coil 111 is the end at the rear in the direction of movement, and the upper end of the cooling section 120 is the end at the front in the direction of movement.

[0052] In the mobile quenching apparatus 100 of this embodiment, it is more preferable that the amount of cooling medium Cl injected when the high-frequency coil 111 passes through the stepped portion 13 is controlled to be less than the amount of cooling medium Cl injected when the high-frequency coil 111 passes through the large-diameter portion 11 or the small-diameter portion 12. Regarding the cooling method, it is desirable to control the cooling capacity by adjusting the injection rate or injection pressure of the cooling medium Cl so that the cooling rate on the CCT curve is kept within a range where no change in hardness occurs. More specifically, if the axial movement speed of the high-frequency coil 111 is fast, the injection rate of the cooling medium Cl should be increased or the injection pressure of the cooling medium Cl should be increased, and if the axial movement speed of the heating coil is slow, the injection rate of the cooling medium Cl should be decreased or the injection pressure of the cooling medium Cl should be decreased. The relationship between the heat transfer coefficient h and the injection water volume (water density) W has been shown, for example, that h is proportional to W raised to the power of n (where n is a constant determined by the water cooling conditions) (Mitsuka: Cooling Technology for High-Temperature Steel Materials, Iron and Steel / Vol. 79 No. 6, pp. N405-N416 (1993)). Here, if the movement speed of the cooling section 120 is fast, the cooling capacity per unit time decreases inversely proportional to the speed, so W should be increased by the rate of increase in speed so that the heat transfer coefficient h increases. n The amount of water sprayed W is determined. In this way, the cooling capacity can be kept constant regardless of the movement speed of the cooling unit 120, and the cooling rate of the heated object can be kept within a desirable range.

[0053] Figure 10 shows a block diagram of the mobile hardening apparatus 100 of this embodiment. In this embodiment, the control unit 160 was described as controlling the axial movement of the heating unit mobile device 140 and the cooling unit mobile device 150, the lateral movement of the high-frequency coil 111, or the amount of cooling medium Cl injected by the pump provided in the cooling unit 120. However, the mobile hardening apparatus 100 may be equipped with multiple control units, and each control unit may be configured to control the movement of these units or the amount of cooling medium injected. For example, it may be equipped with a coil position control unit that can independently change the axial movement speed Vz of the shaft body 10 of the high-frequency coil 111 and Vx in the direction perpendicular to the axis C. It may also be equipped with a control unit that can control the axial movement speed of the cooling unit 120 by the cooling unit mobile device 150, independently of the movement speed of the heating unit 110 by the heating unit mobile device 140.

[0054] Next, a method for performing mobile quenching on the shaft-shaped body 10 using the mobile quenching apparatus 100 of this embodiment will be described.

[0055] First, as shown in Figure 1, the heating unit 110 and the cooling unit 120 are positioned on the lower end side of the shaft-shaped body 10. Next, a high-frequency current is passed through the high-frequency coil 111. The pump is also driven to eject the cooling medium cl from the multiple injection nozzles 122 of the cooling unit 120. Next, the shaft-shaped body 10 is rotated by the support unit 130. Then, the motor is driven to move the heating unit moving device 140 and the cooling unit moving device 150 upward relative to the rack member 180. As a result, the heating unit 110 and the cooling unit 120 are sequentially fitted onto the shaft-shaped body 10 and moved upward.

[0056] In the heating section 110, the high-frequency current supplied to the high-frequency coil 111 induces an induced current on the surface of the axial body 10, and Joule heat is generated due to the electrical resistance of the axial body 10, heating the surface layer of the axial body 10 to the region where the austenite phase is formed.

[0057] Next, the cooling unit 120 rises to the area heated by the heating unit 110, and the cooling medium cl is sprayed onto the heated area of ​​the shaft 10. As a result, at least the surface layer of the shaft 10 is rapidly cooled, and a martensite structure is formed. As the heating unit 110 and the cooling unit 120 rise from the lower end to the upper end of the shaft 10, heating by the heating unit 110 and cooling by the cooling unit 120 are performed sequentially, and the surface of the shaft 10 is high-frequency hardened.

[0058] In the moving hardening method of this embodiment, the high-frequency coils 111 are moved in a direction perpendicular to the axial direction of the shaft body 10 so that the distance from the surface of the shaft body 10 to each high-frequency coil 111 is constant. The axial speed of the high-frequency coil 111 when it passes through the stepped portion 13 is smaller than the axial speed of the high-frequency coil 111 when it passes through the small-diameter portion 12 or the large-diameter portion 11. This makes it possible to perform the desired hardening on the stepped portion 13 and its vicinity in the shaft body 10, where the outer diameter is not constant in the axial direction.

[0059] The present invention relates to a mobile hardening apparatus for hardening an axial body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion in the axial direction, wherein the mobile hardening apparatus comprises a plurality of high-frequency coils and a cooling section in the axial direction, and a control unit capable of controlling the movement of the plurality of high-frequency coils and the cooling section, each high-frequency coil having a high-frequency induction section for heating the axial body and a conductive section connected to the high-frequency induction section, and is movable relative to the axial body in the axial direction and also movable relative to a plane perpendicular to the axial direction, the cooling section having an injection section capable of spraying a cooling medium and is movable relative to the axial body in the axial direction, and the control unit is capable of controlling the movement of the high-frequency coils in the plane such that the distance from the surface of the axial body to each high-frequency coil is constant, and is capable of controlling the axial speed of the high-frequency coil when it passes the stepped portion to be smaller than the axial speed of the high-frequency coil when it passes the small diameter portion or the large diameter portion.

[0060] In the use of the mobile hardening apparatus described above, the control unit may control the high-frequency coils such that the following equation 1 holds true, where V0 is the axial speed of the high-frequency coil when it passes through a small-diameter or large-diameter section, Vs is the axial speed of the high-frequency coil when it passes through a stepped section, and Vc is the speed of the multiple high-frequency coils in a direction perpendicular to the axial direction. V0 2 ≤Vs 2 +Vc 2 ...Formula 1 In the use of the mobile hardening apparatus described above, the control unit may be able to control the axial distance between the high-frequency coil and the cooling unit when the high-frequency coil passes through a stepped section so that it is smaller than the axial distance between the high-frequency coil and the cooling unit when the high-frequency coil passes through a small-diameter section or a large-diameter section. In the use of the mobile quenching apparatus described above, the control unit may be able to control the amount or pressure of the cooling medium injected when the high-frequency coil passes through a stepped section so that it is smaller than the amount or pressure of the cooling medium injected when the high-frequency coil passes through a small-diameter section or a large-diameter section. [Examples]

[0061] [Experimental Example 1] Numerical simulation analysis was performed to verify the heating state at the stepped section when a axial body having a small diameter section, a large diameter section, and a stepped section connecting the small and large diameter sections was subjected to mobile hardening using a mobile hardening apparatus equipped with multiple high-frequency coils. In this experimental example, the axial body was made of carbon steel, with an outer diameter of 170 mm at the small diameter section and an outer diameter of 200 mm at the large diameter section. The number of high-frequency coils was set to four.

[0062] In this experiment, the distance of the high-frequency coil from the surface of the shaft was kept constant by controlling the movement speed of the high-frequency coil in the axial direction and perpendicular to the axial direction of the shaft when passing the high-frequency coil through the large-diameter section, the stepped section, and the small-diameter section in that order. Furthermore, the movement speed of the high-frequency coil was controlled so that the axial speed of the high-frequency coil when passing through the stepped section was lower than the axial speed of the high-frequency coil when passing through the large-diameter section or the small-diameter section. Specifically, as shown in Table 1 below, the movement speed (feed speed) of the high-frequency coil was kept constant. Therefore, the axial speed of the high-frequency coil was slower when passing through the stepped section than when passing through the large-diameter section or the small-diameter section. The times from 59 seconds to 74 seconds and from 105 seconds to 121 seconds represent the time spent passing through the stepped section. The movement speed of the cooling section was set to be the same as the axial speed of the high-frequency coil.

[0063] [Table 1]

[0064] The surface temperature of the axial body at the boundary between the large-diameter section and the stepped section was 1176°C. Furthermore, the depth from the surface of the region heated to over 800°C at that location was 5 mm.

[0065] [Experimental Example 2] Numerical simulation analysis similar to that in Experimental Example 1 was performed. In this experimental example, the same axial body and high-frequency coil as in Experimental Example 1 were used. Similar to Experimental Example 1, the distance of the high-frequency coil from the surface of the axial body was kept constant by controlling the movement speed of the high-frequency coil in the axial direction of the axial body and in the direction perpendicular to the axial direction.

[0066] In this experiment, the high-frequency coil was controlled to move at a constant speed in the axial direction. Therefore, as shown in Table 2 below, the movement speed (feed speed) of the high-frequency coil varied between the large-diameter section, the small-diameter section, and the stepped section. The movement speed of the cooling section was the same as the axial speed of the high-frequency coil. The times from 36 seconds to 43.4 seconds and from 64.1 seconds to 71.95 seconds represent the time spent passing through the stepped section.

[0067] [Table 2]

[0068] The surface temperature of the axial body at the boundary between the large-diameter section and the stepped section was 1287°C. Furthermore, the depth from the surface of the region heated to over 800°C at that location was 4 mm.

[0069] From the results above, in Experimental Example 1, an appropriate heating temperature was obtained on the surface of the stepped portion of the shaft, and the hardening depth to reach the predetermined temperature was also sufficient. Furthermore, as can be seen from Tables 1 and 2, in Experimental Example 2, the current amplitude value applied to the high-frequency coil had to be increased around the stepped portion in order to achieve the above heating temperature. On the other hand, in Experimental Example 1, it can be seen that the desired hardening temperature and hardening depth were obtained while suppressing the increase in the current amplitude value.

[0070] [Experimental Example 3] In this experimental example, numerical simulation analysis was performed to verify the quenching state when a cylindrical shaft made of carbon steel with a constant outer diameter (170 mm) was subjected to mobile quenching using a mobile quenching apparatus equipped with multiple high-frequency coils. The shape of the high-frequency induction section of the high-frequency coil was aligned with the outer diameter of the shaft, and the number of high-frequency coils was set to three.

[0071] As shown below, the hardness distribution of the shaft was calculated when the cooling capacity of the cooling unit, the distance between the high-frequency coil and the cooling unit, and the movement speed of the high-frequency coil and the cooling unit were changed, and the surface hardness and quenching depth were evaluated. The evaluation method for surface hardness and quenching depth was performed by determining the temperature distribution of the shaft using magnetic field analysis and heat transfer analysis, and then calculating the hardness after cooling after inferring the phase transformation from the time-series change in the temperature distribution of each part of the shaft. Tables 3 and 4 show the ratio of surface hardness when the hardness of a martensite fraction of 90% is set to 1, and Tables 5 and 6 show the thickness from the surface (mm, quenching depth) in the range where the hardness is 70% or more of a martensite fraction. The cooling capacity of the cooling unit in the table refers to the convective heat transfer coefficient of the shaft surface. The distance between the high-frequency coil and the cooling unit was as specified in the above embodiment. In addition, the high-frequency coil and the cooling unit were assumed to move at the same speed shown in the table in the axial direction of the shaft.

[0072] [Table 3]

[0073] [Table 4]

[0074] [Table 5]

[0075] [Table 6]

[0076] As can be seen from the results in Tables 3 and 4, when the movement speed of the high-frequency coil and the cooling section slows down, the hardness due to quenching tends to decrease. On the other hand, reducing the distance between the high-frequency coil and the cooling section can suppress the decrease in hardness. From this, it can be seen that when a shaft has a stepped section, and the axial speed of the high-frequency coil when passing through the stepped section is smaller than the axial speed of the high-frequency coil when passing through a small-diameter or large-diameter section, the quenched hardness can be ensured by making the distance between the high-frequency coil and the cooling section in the axial direction of the shaft smaller when the high-frequency coil passes through the stepped section than the distance between the high-frequency coil and the cooling section in the axial direction when the high-frequency coil passes through a small-diameter or large-diameter section.

[0077] Furthermore, as can be seen from the results in Tables 3 and 4, when the movement speed of the high-frequency coil and the cooling unit slows down, the hardness due to quenching tends to decrease. However, the decrease in hardness can also be suppressed by improving the cooling capacity of the cooling unit. From this, it can be seen that quenching hardness can be ensured by making the amount or pressure of the cooling medium injected when the high-frequency coil passes through the stepped section smaller than the amount or pressure of the cooling medium injected when the high-frequency coil passes through the small-diameter section or large-diameter section.

[0078] Furthermore, as can be seen from the results in Tables 5 and 6, the burning depth can be kept constant by adjusting the cooling capacity of the cooling unit in accordance with the movement speed of the coil and the cooling unit. In Table 5, the convective heat transfer coefficient was adjusted to a burning depth of 5 mm. In Table 6, the convective heat transfer coefficient was adjusted to a burning depth of 3 mm.

[0079] The results of this experiment demonstrate that the desired hardening hardness can be ensured by appropriately controlling not only the speed of the heating coil, but also the movement speed and cooling capacity of the cooling section. This suppresses changes in grain size and volume fraction of retained austenite, thereby maintaining a consistent hardness and mechanical properties of the material. [Industrial applicability]

[0080] The mobile quenching method and mobile quenching apparatus of the present invention make it possible to perform desired quenching on stepped portions and their vicinity in shaft-shaped bodies whose outer diameter is not constant in the axial direction, and therefore their industrial value is extremely high. [Explanation of Symbols]

[0081] 100 Mobile quenching apparatus 110 Heating section 111A, 111B, 211A, 211B, 211C High-Frequency Coils 112A, 112B, 212A, 212B, 212C High-frequency induction section 113a, 113b, 113c, 113d, 213a, 213b, 213c, 213d, 213e, 213f Conductive part 120 Cooling section 130 Support part 140 Heating section moving device 150 Cooling unit moving device 160 Control Unit 10 Axial body 11A, 11B Large diameter section 12 Small diameter section 13A, 13B Stepped section

Claims

1. A mobile quenching method for quenching an axial body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion, using a mobile quenching apparatus equipped with multiple high-frequency coils and a cooling unit, wherein the axial body has a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion, The shaft-shaped body inserted inside the plurality of high-frequency coils is rotated relative to the plurality of high-frequency coils, and the plurality of high-frequency coils are moved relative to the shaft-shaped body in the axial direction, while the shaft-shaped body is heated by the high-frequency coils. The cooling unit follows the high-frequency coil from behind in the relative direction of movement of the high-frequency coil along the axial direction of the shaft-shaped body, and the portion heated by the high-frequency coil is cooled by the cooling unit. Movement quenching is performed while moving the high-frequency coils radially along the shaft so that the distance from the surface of the shaft to each of the high-frequency coils remains constant. The axial speed of the high-frequency coil when it passes through the stepped portion is smaller than the axial speed of the high-frequency coil when it passes through the small-diameter portion or the large-diameter portion. A mobile quenching method characterized by the following features.

2. When the axial velocity of the high-frequency coil as it passes through the small-diameter portion or the large-diameter portion is V0, when the axial velocity of the high-frequency coil as it passes through the stepped portion is Vs, and when the radial velocity of the plurality of high-frequency coils is Vc, then the following equation 1 holds true. The mobile quenching method according to feature 1. V0 ２ ≦Vs ２ +Vc ２ ・・・Form 1

3. The distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes through the stepped portion is made smaller than the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes through the small-diameter portion or the large-diameter portion. The mobile quenching method according to claim 1 or 2, characterized by the features described herein.

4. The cooling unit sprays a cooling medium, The amount or pressure of the cooling medium injected when the high-frequency coil passes through the stepped portion is made smaller than the amount or pressure of the cooling medium injected when the high-frequency coil passes through the small-diameter portion or the large-diameter portion. The mobile quenching method according to feature 1.

5. A mobile quenching apparatus for quenching a shaft-shaped body having a small diameter portion, a large diameter portion, and a stepped portion connecting the small diameter portion and the large diameter portion in the axial direction, The aforementioned mobile quenching apparatus is In the aforementioned axial direction, the system comprises a plurality of high-frequency coils and a cooling unit. The system includes a control unit capable of controlling the movement of the plurality of high-frequency coils and the cooling unit, Each of the aforementioned high-frequency coils has a high-frequency induction section for heating the axial body and a conductive section connected to the high-frequency induction section, and is movable relative to the axial body in the axial direction and relative to the axial body in the radial direction. The cooling unit has an injection unit capable of spraying a cooling medium and is movable relative to the shaft in the axial direction. The control unit, The movement of the high-frequency coils in the radial direction can be controlled such that the distance from the surface of the axial body to each of the high-frequency coils remains constant, The axial speed of the high-frequency coil when it passes through the stepped portion can be controlled to be smaller than the axial speed of the high-frequency coil when it passes through the small-diameter portion or the large-diameter portion. A mobile quenching apparatus characterized by the following features.

6. The control unit can control the high-frequency coil such that the following equation 1 holds true, where V0 is the axial speed of the high-frequency coil when it passes through the small-diameter portion or the large-diameter portion, Vs is the axial speed of the high-frequency coil when it passes through the stepped portion, and Vc is the radial speed of the plurality of high-frequency coils. The mobile quenching apparatus according to feature 5. V0 ２ ≦Vs ２ +Vc ２ ・・・Form 1

7. The control unit can control the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes the stepped portion to be smaller than the distance between the high-frequency coil and the cooling unit in the axial direction when the high-frequency coil passes the small-diameter portion or the large-diameter portion. The mobile quenching apparatus according to claim 5 or 6.

8. The control unit can control the amount or pressure of the cooling medium injected when the high-frequency coil passes through the stepped portion so that it is smaller than the amount or pressure of the cooling medium injected when the high-frequency coil passes through the small-diameter portion or the large-diameter portion. The mobile quenching apparatus according to feature 5.

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