JP5489325B2 - High frequency induction heating method and high frequency induction heating apparatus - Google Patents

Description

  The present invention relates to a high-frequency induction heating method and a high-frequency induction heating apparatus for induction heating a work that is axial and has a non-uniform outer shape or cross-sectional shape.

In many cases, tempering is performed after quenching a workpiece made of a steel material. Tempering is mainly intended for adjusting the hardness, removing internal stress and imparting toughness. Tempering is a heat treatment in which the workpiece is heated to a temperature lower than the quenching temperature and then cooled. That is, as is well known, when the temperature of a steel material is raised, the structure of the steel is transformed into austenite. When this is rapidly cooled, it transforms into hard martensite and quenching is performed.
However, martensite produced by quenching is hard and brittle and contains internal stress. Accordingly, the temperature of the workpiece is raised again, and thereafter the workpiece is cooled, thereby adjusting the hardness, removing internal stress, and imparting toughness.

  When quenching using high-frequency induction heating, the workpiece is heated to the quenching temperature (temperature above the A1 transformation point) by the induction heating coil for quenching, and this is quenched and quenched. Finish and then temper with another induction heating coil. That is, separately from quenching, an induction heating coil dedicated to tempering is used, and after quenching by quenching, the workpiece is heated again with the induction heating coil dedicated to tempering.

  When quenching by high-frequency induction heating in this way, it is usual that tempering is performed by an induction heating coil dedicated to tempering. For example, Patent Document 1 discloses an invention related to a heating coil dedicated to tempering.

  On the other hand, although rare, there is an example in which the same induction heating coil is used for quenching and tempering. That is, Patent Document 2 discloses a surface quenching / tempering method using the same induction heating coil. The invention described in Patent Document 2 is intended to perform tempering not only on the quenched portion but also on the periphery of the quenched portion in order to relieve the residual stress at the time of quenching. That is, tempering is performed over a wider area than the quenched area. Therefore, after quenching, the same induction heating coil is heated again near the quenching part, and then the induction heating coil is shifted and the temperature other than the quenching part is heated by the same induction heating coil. .

  That is, the induction heating coil employed in the invention described in Patent Document 2 is a circular one-turn coil as shown in FIG. 14 (FIG. 2 of Patent Document), and has a very short total axial length. In the invention described in Patent Document 2, when quenching, the induction heating coil is brought close to the boundary portion between the desired portion F (FIG. 13) and the thin portion of the workpiece, and the desired quenching portion F is heated. (FIG. 14b). Then, the portion is rapidly cooled to finish the quenching operation (FIG. 14c).

Subsequently, a tempering operation is performed. In the invention described in Patent Document 2, the tempering operation is performed using the same induction heating coil as that used in the quenching. That is, the induction heating coil is again brought close to the desired quenching point F of the workpiece, and the desired quenching point F is heated (FIG. 14d). Then, the induction heating coil is shifted and moved to a position deviated from the desired quenching point F (FIG. 14e). At this time, the temperature of the portion that has been previously raised for tempering begins to drop, and the cooling for tempering begins.
On the other hand, at the part where the induction heating coil is newly moved, the temperature is newly increased by the induction heating coil. In addition, the part is also cooled after being heated to a certain temperature.

JP 2008-150661 A JP-A-63-238212

  As described above, generally, the induction heating coil for quenching the workpiece and the induction heating coil for tempering are separately provided.

However, recently, there has been a demand for sharing a quenching heating coil and a tempering heating coil in order to reduce the size and simplify the apparatus.
Here, when the shape of the workpiece is a simple cylindrical shape or the like, there is no particular problem even if tempering is performed using a heating coil for quenching.
For example, in the measure disclosed in Patent Document 1, the part to be quenched is the F region in FIG. 13 and the surface has a simple cylindrical shape.
Therefore, the temperature rise curve at the time of quenching is the same as the temperature rise curve at the time of tempering, and the region F in FIG. 13 can be raised to the target tempering temperature.

  However, when quenching and tempering workpieces with unusually different external shapes and extremely different wall thicknesses, an attempt was made to use both a heating coil for quenching and a heating coil for tempering. Unexpected variation in hardness occurred.

  For example, like the workpiece 100 shown in FIGS. 1 and 2, a part 101 has a part 101 having a large diameter, and the other part has a shape and a cross section depending on the position in the axial direction as in the case of a work having a small diameter. When induction hardening and tempering are performed on a workpiece having a different shape and a part A that is difficult to heat up and a part B that is easy to heat up, the hardness varies between the part B that is easy to heat up and the part A that is difficult to heat up. occured.

When the present inventors investigated to solve this problem, it was found that when the workpiece was tempered, the surface temperature of the workpiece varied, and the surface hardness varied due to this temperature variation.
That is, at the time of quenching, there was no significant difference in the temperature difference between the part A where it is difficult to raise the temperature and the part B where it is easy to raise the temperature. There was a considerable temperature difference in the temperature of difficult site A.
More specifically, the temperature of the part A that is difficult to raise is significantly higher than the temperature of the part B that is easy to raise.
That is, at the time of tempering, the temperature of the part A, which has a large cross-sectional area and the like and is difficult to raise, tends to be lower, and the temperature of the part B that should be easily raised tends to be lower.
According to the actual measurement by the present inventors, the temperature difference between the two is about 200 degrees Celsius, which is a temperature difference that cannot be ignored.

In other words, tempering includes tempering called high-temperature tempering and tempering called low-temperature tempering. The temperature is raised. In this way, the target temperature for raising the temperature is different depending on the purpose, and the temperature range at which tempering can be ideally performed is as narrow as about 50 degrees Celsius.
Therefore, when a temperature variation of 200 degrees Celsius occurs, there is a concern that the surface hardness after tempering may deviate from the target value.

Therefore, the present inventors further investigated and investigated the cause of the large temperature variation during tempering even though the temperature variation during quenching was small.
As a result, when high-frequency induction heating is performed, if the temperature is raised from room temperature to a temperature exceeding the A1 transformation point, the overall temperature variation becomes small and the temperature rise time variation is small, but the temperature rise from room temperature to less than the A1 transformation point. If attention is paid only to the curve, there is a slight difference between the portion B where the temperature rise is easy and the portion A where the temperature rise is difficult, and this difference in the temperature rise curve causes a large temperature variation during tempering. It has been found.
Hereinafter, this reason will be described.

In the case where induction hardening is performed on the workpiece 100 having the part A in which the external shape and the cross-sectional shape are different depending on the position in the axial direction as shown in FIGS. The induction heating coil 120 having a characteristic that the magnetic line density passing through the part B where the temperature rise is easy and the magnetic line density passing through the part A where the temperature rise is difficult is high.
That is, the induction heating coil 120 having a characteristic that the magnetic line density passing through the part B where the temperature is easily raised is low and the magnetic line density passing through the part A where the temperature is difficult to raise is high so that the temperature of the workpiece is uniform.

More specifically, as shown in FIG. 3, it has a total length L corresponding to the length L of the part desired to be quenched and the length L of the part desired to be reheated, and depends on the part in the axial direction. An induction heating coil having portions with different generated magnetic line densities is used.
That is, the induction heating coil 120 for quenching shown in FIG. 3 is a semi-open saddle coil, and has a shape having straight portions 102 and 103, a large-diameter curved portion 105, and a small-diameter curved portion 106, which are in series. It has a structure connected to.

Further, stepped portions 110 and 111 are provided between the large-diameter curved portion 105 and the straight portions 102 and 103.
Furthermore, the large-diameter curve portion 105 and the step portions 110 and 111 are provided with a plurality of cores 121.
Therefore, the induction heating coil 120 has a high strength of magnetic lines of force generated in the axial direction a region corresponding to the large-diameter curved portion 105 and the step portions 110 and 111, and a low strength of the magnetic force lines generated in the axial direction b region of the linear portions 102 and 103. .
And the induction heating coil 120 for hardening shown in FIG. 3 is adjoined to the workpiece | work 100 so that it may become the positional relationship shown in FIG. That is, the region a where the strength of the generated magnetic lines of force is high covers the portion A of the workpiece 100 where heating is difficult, and the region b where the strength of the generated magnetic lines of force is weak covers the portion B where the heating of the workpiece 100 is easy.

  As a result, at the time of quenching, strong lines of magnetic force pass through the portion A of the workpiece 100 where it is difficult to raise the temperature, and the entire temperature becomes uniform.

However, when the temperature rise curves of the part A where the temperature of the workpiece is difficult to rise and the part B where the temperature is easy to raise are observed in more detail, there are slight differences as shown in FIG.
Here, FIG. 6 shows a case where a workpiece having a part that has a considerable length in the axial direction and has an easy-to-heat up part and a hard-to-heat up part whose outer shape and cross-sectional shape are different depending on the position in the axial direction. Quenching using an induction heating coil having a length corresponding to the length of the portion desired to be reheated and the length of the portion desired to be reheated, and having a portion with different magnetic field density generated by the axial portion. It is the graph which represented typically the temperature change of the workpiece | work at the time of doing.

When the temperature of the workpiece as shown in FIG. 1 is increased using the induction heating coil 120 as shown in FIG. 3, the temperature of the portion A having a high magnetic force line density is increased in advance and supplied with a slight delay. B part with a high magnetic force line density heats up. That is, the inclination of the temperature rise differs between the A part and the B part, and the temperature of the A part having a higher magnetic line density to be supplied rises with a higher inclination than the B part.
However, when the temperature of the portion A that has been heated first exceeds the temperature of the transformation point A1, the ferrite structure in the workpiece is transformed into austenite, and the magnetic permeability is significantly lowered. As a result, the induced current flowing through the part A of the workpiece 100 is abruptly reduced, and the temperature increase curve is blunted.
On the other hand, when the temperature of the portion A that has been raised first exceeds the temperature of the transformation point A1, the induced current flowing in the other portion increases, the temperature rise curve of the portion B becomes upward, and the portion B is within a short time. Also reaches the temperature of the transformation point A1. After that, the temperature rises while drawing the same rising curve in both A part and B part. And it is cooled rapidly and both fall in temperature.
Therefore, the final temperatures of the A part and the B part of the workpiece 100 are substantially the same temperature. There is no great difference in the time required to reach the desired quenching temperature. Therefore, there is no variation in the surface hardness of the workpiece during quenching.

However, when tempering is performed using the same induction coil 120, a temperature change as shown in FIG. 7 is achieved.
That is, as described above, when the temperature of the workpiece as shown in FIG. 1 is increased using the induction heating coil 120 as shown in FIG. The temperature rise gradient of the B part where the magnetic line density supplied is high is low.
For example, in the graphs of FIGS. 6 and 7, when the temperature on the B portion side is 300 degrees Celsius, the temperature of the part A that is difficult to raise reaches 450 degrees Celsius.
Therefore, even when energization of the induction heating coil 120 is stopped in a state where the temperature on the B part side is 300 degrees Celsius, the temperature of the part A that is difficult to raise is already 450 degrees Celsius, and is heated too much. It is in the state of.

As described in Patent Document 1, a circular one-turn coil is used, and the one-turn coil is brought close to the part A where it is difficult to raise the temperature, and the part A is heated. If the temperature is increased by moving the portion B, the temperature variation during tempering is eliminated and the hardness variation is reduced, but the overall work time is remarkably increased, which is not practical.
That is, a circular one-turn coil is used, and after the one-turn coil is brought close to a portion A where heating is difficult and the portion A is heated, the one-turn coil is moved to a portion B where heating is easy and the B portion is raised. When the temperature is raised, a temperature rise curve as shown in FIG. 8 is drawn, and the temperature of the part B does not increase while the part A is being heated. Therefore, the temperature raising step is substantially repeated twice, and the working time is significantly increased.

  Therefore, the present invention pays attention to the above-mentioned problems of the prior art, performs quenching and tempering with a single induction heating coil, suppresses temperature variation of the workpiece during tempering, and reduces hardness variation, thereby high-frequency induction heating method. It is an issue to provide.

The invention of claim 1 for solving the above-mentioned problem has a part that has a considerable length in the axial direction, has an outer shape and a cross-sectional shape that differ depending on the position in the axial direction, and a part that is difficult to raise. A quenching step in which a region having a considerable length in the axial direction is heated to a predetermined quenching temperature and then rapidly cooled, and then from the quenching temperature. In the method of performing high frequency induction heating having a reheating step of gradually cooling after raising the temperature to a lower temperature, the length of the part desired to be quenched and the total length corresponding to the length of the part desired to be reheated In addition, using an induction heating coil having a part where the magnetic field line density generated by the part in the axial direction is different, in the quenching step and the reheating step , a part having a high magnetic force line density of the magnetic field generated by the induction heating coil , of work NoboriAtsushikoma Is close to a site, induce generated magnetic force line density is lower portions of the magnetic field of the heating coil, in close proximity to the heated easy site of the work, quenching and reheating overall heating a site they wish to work In the reheating process , the temperature rise of the workpiece is preceded by the portion where heating is difficult, and the magnetic field line density of the magnetic field generated by the induction heating coil during the temperature rise of the workpiece in the reheating process. the low sites, while facing the heated easy site of the work, the induction heating coil and the generated magnetic lines dense portion of the magnetic field of the induction heating coil by changing the relative axial position of the workpiece the workpiece Atsushi Nobori This is a high-frequency induction heating method characterized by being separated from a difficult part.

According to the first aspect of the present invention, in the quenching step, a portion where the magnetic field line density of the generated magnetic field is high is brought close to a portion where it is difficult to raise the temperature of the workpiece, and the portion where quenching is desired is raised to the quenching temperature as a whole. Therefore, the temperature of the workpiece is likely to rise uniformly. As a result, the workpiece can be quenched to a uniform depth.
Further, in the reheating process, the same induction heating coil as that used in the quenching process is used, so that it is not necessary to replace the induction heating coil between the quenching process and the reheating process.
Further, in the reheating process, the same induction heating coil as that used in the quenching process is used. Therefore, as described above, the temperature of the part A where it is difficult to raise the temperature of the work is increased in advance. However, in the present invention, during the temperature increase, the relative position in the axial direction of the induction heating coil and the work is changed to separate the part where the magnetic field line density of the magnetic field is high from the part where the temperature increase is difficult. The temperature rise curve of the part B where it is difficult to raise the temperature slows down. As a result, as shown in the graph of FIG. 9, initially, the temperature rise gradient of the part A where the temperature of the workpiece is difficult to rise is high and the temperature of the part A rapidly rises, but the relative position of the induction heating coil and the workpiece in the axial direction. When the region where the magnetic field line density of the magnetic field is high is separated from the region where it is difficult to raise the temperature, the temperature rise curve of A in the region where it is difficult to raise the temperature rapidly dulls. On the other hand, the induction coil has a total length corresponding to the length of the part desired to be hardened and the length of the part desired to be reheated, so the relative position of the induction heating coil and the workpiece in the axial direction is changed. However, the temperature rise curve of B in the part where the temperature can be easily raised does not change. For this reason, the temperature of B in the part where the temperature is easily raised catches up with the temperature of A in the part where the temperature is difficult to rise, and the temperature variation between the two is reduced.
In this state, if the energization to the induction heating coil is stopped, the workpiece can be heat-treated without causing hardness variation.

Further, in the present invention, the temperature rise of the work is preceded by the portion where it is difficult to raise the temperature before the portion where the temperature is easily raised. Here, the site where it is difficult to raise the temperature means that the heat capacity is large and the amount of heat (inductive current) required to raise the temperature is large. In the case of quenching prior to the temperature increase of the portion where it is difficult to raise the temperature, if the magnetic transformation point at which the composition changes is reached, the induced current is less likely to flow and the method of temperature rise is reduced. And a part of the induced current that should flow to the part where heating is difficult flows to the part where heating is easy, the way of raising the temperature of the part where heating is easy is improved, and the temperature of the part where heating is easy is also relatively early. The magnetic transformation point is reached, and the temperature of the part where heating is easy approaches the temperature of the part where heating is difficult. Therefore, it is possible to uniformly harden the entire region of the workpiece quenching region.

According to the second aspect of the present invention, after a predetermined time has elapsed after starting the heating in the reheating step, the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high is separated from the part where it is difficult to raise the temperature. The high frequency induction heating method according to claim 1 , wherein the method is a high frequency induction heating method.

In the invention of claim 2 , after a predetermined time has elapsed since the start of the heating in the reheating step, the portion where the magnetic field density of the magnetic field generated by the induction heating coil is separated from the portion where it is difficult to raise the temperature, the reheating step The temperature of the heat treatment part of the workpiece being heated is made uniform. As a result, the hardness and tenacity of the heat treatment part of the workpiece can be made uniform.

The invention of claim 3 starts the heating in the reheating step, and when the temperature of the part where heating is difficult reaches a predetermined temperature, the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high The high frequency induction heating method according to claim 1 , wherein the method is separated from the high frequency induction heating method.

In the invention of claim 3 , during the reheating step, when the temperature of the part where heating is difficult reaches a predetermined temperature, the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high is separated from the part where heating is difficult. In the reheating process, the temperature of the heat treatment part of the workpiece being heated is made uniform. As a result, the hardness and tenacity of the heat treatment part of the workpiece can be made uniform.

A fourth aspect of the present invention is the high frequency induction heating method according to any one of the first to third aspects, wherein the axle tube is heated as a workpiece.

In the invention of claim 4 , the axle tube can be well quenched and tempered. That is, the axle tube has a portion having a different diameter depending on the position in the axial direction, and a step is formed. Although stress tends to concentrate on this step portion, when the invention of claim 4 is carried out, the desired hardness and tenacity can be applied to the step portion where stress in the axle tube tends to concentrate by induction heating with the same induction heating coil. Can provide.

According to the invention of claim 5 , induction heating is performed on a workpiece having a considerable length in the axial direction and different in outer shape and cross-sectional shape depending on the position in the axial direction and having a portion where heating is difficult and a portion where heating is difficult. A high-frequency induction heating device having a total length corresponding to the length of a part desired to be quenched and the length of a part desired to be reheated, and a part having a different magnetic line density generated by an axial part. An induction heating coil, a high-frequency power source for supplying high-frequency AC power to the induction heating coil, and a moving means for moving the work and the induction heating coil by a predetermined distance relative to each other in the axial direction. first heating mode is performed heating to a temperature, a second heating mode is automatically executed followed by heating to a temperature lower than the first heating mode in which, according to the first heating mode and a second heating mode During heat generated to the magnetic field lines dense portions of the magnetic field of the induction heating coil, is close to the heated hard sites of the workpiece, the generated magnetic force line density is lower portions of the magnetic field of the induction heating coil, the workpiece temperature Increase the temperature of the part where the workpiece is desired to be hardened and reheated in the vicinity of the easy-to-heat part. During heating in the second heating mode, the moving means moves the work and the induction heating coil by a predetermined distance relative to each other in the axial direction so that the magnetic field generated by the induction heating coil has a low magnetic line density. , while opposed to the heated easy site of the work, the magnetic line density of the generated magnetic field of the induction heating coil by changing the relative axial position of the induction heating coil and the workpiece is high site from heated difficult sites of the workpiece Separate Is a high-frequency induction heating device which is characterized in that the anti operation.

The high-frequency induction heating device according to the invention of claim 5 has a total length corresponding to the length of the part desired to be quenched and the length of the part desired to be reheated, and the magnetic line density generated by the part in the axial direction. Since the induction heating coil having different parts is provided, when a high frequency current is passed through the induction heating coil, an induction current according to the magnetic line density flows on the workpiece, and the workpiece can be heated.
In addition, since the workpiece is automatically shifted from the first heating mode in which the workpiece is heated to the quenching temperature or the quenching temperature to the second heating mode in which the workpiece is heated to a temperature lower than the first heating mode, quenching and tempering, etc. Reheating can be performed with the same induction heating coil.
Further, when heating in the second heating mode, the relative position of the induction heating coil and the workpiece in the axial direction is changed by moving the workpiece and the induction heating coil by a predetermined distance in the axial direction by the moving means. Thus, the separation operation is performed to separate the part where the magnetic field density of the magnetic field is high from the part where the temperature rise is difficult. Therefore, for the reasons described above, the temperature of the workpiece can be made uniform, and uneven temperature rise of the workpiece can be prevented.

Invention of Claim 6 provides the temperature detection means which detects the temperature of the said site | part with a difficult temperature rising of a workpiece | work, The temperature detected by the said temperature detection means reaches predetermined temperature in 2nd heating mode, or 6. The high frequency induction heating apparatus according to claim 5 , further comprising a control mechanism that executes the separation operation when a heating time reaches a predetermined time.

In the invention described in claim 6 , the temperature detecting means for detecting the temperature of the part where it is difficult to raise the temperature of the work is provided, and in the second heating mode, when the temperature detected by the temperature detecting means reaches a predetermined temperature, the moving means is Since the control mechanism to be operated is provided, it is possible to avoid an excessive temperature increase in a part where it is difficult to raise the temperature of the work, and to make the temperature of the heated part of the work uniform.

In the sixth aspect of the invention, in the second heating mode, when the time for heating the portion of the induction heating coil in which the magnetic field line density of the generated magnetic field is high and the temperature of the workpiece that is difficult to heat up reaches a predetermined time, the moving means Is provided, the heating time of the part where it is difficult to raise the temperature of the work is restricted, and excessive temperature rise of the part can be prevented, and the temperature of the heated part of the work can be made uniform. .

The invention of claim 7 is the high frequency induction heating apparatus according to claim 5 or 6 , wherein the induction heating coil is a semi-open saddle type coil.

In the seventh aspect of the invention, since the induction heating coil is a half-open saddle type coil, the induction heating coil can be easily disposed opposite to the workpiece, and the apparatus can be miniaturized.

When the high-frequency induction heating method of the present invention is performed, in the quenching process, the part where the magnetic field line density of the generated magnetic field is high is close to the part where the temperature of the workpiece is difficult to raise, and the part desired to be quenched is totally quenched. Since the temperature is raised above the temperature and quenching is performed, the temperature of the workpiece is likely to rise uniformly. As a result, the workpiece can be quenched to a uniform depth.
Further, in the reheating process, the same induction heating coil as that used in the quenching process is used, so that it is not necessary to replace the induction heating coil between the quenching process and the reheating process. In addition, since the relative position of the induction heating coil and the workpiece in the axial direction is changed when the workpiece is heated, the workpiece is easily heated uniformly. Therefore, heat treatment can be performed in a desired state.

In the high frequency induction heating device of the present invention, the length of the portion desired to be quenched and the total length according to the length of the portion desired to be reheated, and the magnetic field line density generated by the axial portion is different. Therefore, when a high-frequency current is passed through the induction heating coil, an induction current corresponding to the magnetic line density flows on the work, and the work can be heated.
Further, since the workpiece is automatically shifted from the first heating mode in which the workpiece is heated to the quenching temperature or higher than the quenching temperature to the second heating mode in which the workpiece is heated to a temperature lower than the first heating mode, quenching and tempering, etc. Can be implemented with the same induction heating coil.
Furthermore, in the second heating mode, since the moving means for moving the workpiece and the induction heating coil by a predetermined distance relative to each other in the axial direction is provided, the portion where the induction heating coil and the workpiece face each other moves. As a result, it is possible to prevent an uneven temperature increase of the workpiece, and it is possible to perform quenching and tempering well.

It is a perspective view which shows an example of the workpiece | work which quenches and tempers by this invention. It is sectional drawing of the workpiece | work of FIG. It is a perspective view of the induction heating coil employ | adopted by embodiment of this invention. It is the perspective view which observed the induction heating coil of FIG. 3 from the opposite side. It is a perspective view which shows the state which the induction heating coil of FIG.3, 4 adjoined to the workpiece | work shown in FIG. The length of the part that you want to quench for a workpiece that has a considerable length in the axial direction, and that has different parts in the outer shape and cross-sectional shape depending on the position in the axial direction and that has parts that are easy to raise and difficult to raise. And the temperature of the workpiece when quenched using an induction heating coil having a length corresponding to the length of the portion desired to be reheated and having a different magnetic line density generated by the axial portion. It is a graph showing a change typically. FIG. 7 is a graph similar to FIG. 6, schematically illustrating a temperature change when the work is removed after the part where the temperature of the work is easily increased reaches a certain temperature. It is the graph which represented typically the temperature change at the time of quenching and tempering applying the measure disclosed by patent document 1. FIG. It is the graph which represented typically the temperature change at the time of employ | adopting embodiment of this invention, and the workpiece | work is decooled after the site | part with easy temperature rising of a workpiece | work reached fixed temperature. BRIEF DESCRIPTION OF THE DRAWINGS It is a side view of the induction heating coil for implementing this invention, and the workpiece | work which is induction-heated, (a) shows the state at the time of the 1st mode in which a workpiece is hardened, (b) reheats a workpiece | work. (C) shows a cross section of the workpiece after heat treatment. It is a signal system diagram of the high frequency induction heating device of the present invention. It is a flowchart which shows the procedure which implements the high frequency induction heating method of this invention. It is sectional drawing which reprinted FIG. 1 of patent document 2. FIG. (A)-(e) is sectional drawing which reposted FIG. 2 (a)-(e) of patent document 2, respectively.

Embodiments of the present invention will be described below with reference to the drawings.
In the following embodiments, the structure and method of implementation of the present invention will be described by taking an axle tube used as a work 10 for an automobile axle as an example.

  The high-frequency induction heating device 1 includes an induction heating coil 2 that is disposed opposite to a work 10 to perform induction heating, a heating coil moving device 8, a high-frequency power supply device 9, a work rotation driving device 6, a work moving device 7, and a work temperature detection. A device 11, a timer 12, and a control device 13 are provided.

  The workpiece 10 has an axial shape and a portion having a different diameter. That is, the workpiece 10 has a large diameter portion 15 and a small diameter portion 16. A corner portion 10 a is formed at a connection portion between the large diameter portion 15 and the small diameter portion 16. The diameter of the small-diameter portion 16 is substantially the same over the entire length (the length in the left-right direction as viewed in FIG. 10), although there are some differences. As shown in FIG. 10, the small diameter portion 16 has a considerable length in the axial direction.

The corner part 10a is a part where the temperature rise is more difficult than the other part (small diameter part 16) of the workpiece 10. That is, it is considered that the heat of the heated corner portion 10a is less likely to raise the temperature than other portions because it moves toward the inside of the large diameter portion 15.
For this reason, when the work 10 is observed by being divided into axial regions, the region A in FIG. 10A is a region where heating is difficult, and the region B is a region where heating is easy.

  Further, both ends of the work 10 are detachably held by the work support member 5 during heat treatment. A workpiece rotation driving device 6 and a workpiece moving device 7 (FIG. 11) are connected to the workpiece support member 5. That is, when the work rotation driving device 6 is operated, the work 10 rotates integrally with the work support member 5. Further, the workpiece 10 can be moved in the horizontal direction (left-right direction as viewed in FIG. 10) by the workpiece moving device 7. The operations of the workpiece rotation driving device 6 and the workpiece moving device 7 are controlled by the control device 13 (FIG. 11).

  The induction heating coil 2 used in the present invention is a semi-open saddle type coil, and can be moved in the vertical and horizontal directions by a heating coil moving device 8 (FIG. 11) whose operation is controlled by the control device 13. The induction heating coil 2 is composed of a copper tube having good electrical conductivity, and a coolant can flow inside the tube. The induction heating coil 2 can be supplied with a high-frequency alternating current from a high-frequency power supply device 9 (high-frequency power supply). When power is supplied from the high-frequency power supply device 9, an induced current is generated on the surface of the opposing workpiece 10, and the workpiece 10 can be heated (induction heating).

  Moreover, the induction heating coil 2 has semicircular portions 2a and 2b disposed at both ends, and a linear portion 2c disposed between the semicircular portions 2a and 2b at both ends. A plurality of cores 3 are installed at predetermined equal angles in the semicircular portion 2a, and a plurality of cores 4 are arranged at predetermined intervals in the straight portion 2c.

The core 3 and the core 4 have a function of increasing the density of magnetic lines of magnetic force generated around when the current flows through the induction heating coil 2. That is, a particularly large induction current flows through a portion of the work 10 facing the induction heating coil 2 that is close to the core 3 or the core 4.
In this embodiment, the space | interval of the core 3 of the semicircle part 2a is narrower than the space | interval of the core 4 of the linear part 2c, and the core 3 is more closely attached to the semicircle part 2a. Further, the core 3 is set to have higher magnetic permeability than the core 4. Therefore, when the induction heating coil 2 is observed by dividing it into the axial region, the region a in FIG. 10A has a large magnetic field line density and the region b has a small magnetic field line density.

  The high frequency power supply device 9 is controlled by the control device 13 to supply power to the workpiece 10. That is, the amount of power to be supplied and the power supply time are set and controlled by the control device 13 in a first heating mode (quenching process) and a second heating mode (reheating process) described later.

  The control device 13 (control mechanism) is composed of a computer having a CPU and a memory (not shown), receives signals from the work temperature detection device 11 and the timer 12 as appropriate, and supplies the heating coil moving device 8 and high-frequency power supply. Control signals are transmitted to the device 9, the workpiece rotation driving device 6 and the workpiece moving device 7 to operate each device.

  Next, a method of induction heating (heat treatment) of the workpiece 10 will be described with reference to FIG. As shown in FIG. 12, the high-frequency induction heating method of the present invention includes steps 1 to 5.

  First, in step 1, the workpiece 10 is supported by the workpiece support member 5, and is transported to a predetermined position by the workpiece moving device 7 and waits. Further, the induction heating coil 2 is transported to a predetermined quenching execution position by the heating coil moving device 8 and is disposed opposite to the workpiece 10. At that time, the core 3 of the induction heating coil 2 is close to the corner portion 10a of the workpiece 10 as shown in FIG. That is, the region a where the magnetic field density of the induction heating coil 2 is large is brought close to the region A that is a region where it is difficult to raise the temperature. Further, a region b where the magnetic field line density of the induction heating coil 2 is small is close to the region B which is a region where temperature rise is easy.

Next, the process proceeds to step 2, and the work 10 is rotationally driven by the work rotation driving device 6, and the induction heating coil 2 is supplied with electric power from the high-frequency power supply device 9. In step 2, the workpiece 10 is induction-heated and quenched in the first heating mode (quenching process). That is, in the first heating mode, the temperature of the workpiece 10 is increased until it exceeds the A1 transformation point. At that time, since the core 3 is close to the corner portion 10a, more induced current flows in the corner portion 10a than in other parts, and a part of heat moves toward the large diameter portion 15 or in the inner direction. Quenched well. That is, the region A where the magnetic field lines of the induction heating coil 2 are strong (the magnetic field line density is large) is close to the part A which is difficult to raise the temperature, and the magnetic field lines of the induction heating coil 2 are weak to the part B which is a part where the temperature increase is easy ( Since the b region (which has a high magnetic force line density) is close, the workpiece 10 is heated substantially uniformly. However, when the temperature rise state of each part of the workpiece 10 is observed in detail, as shown in the graph of FIG. 6 described above, the temperature rise gradient of the part A, which is a part where heating is difficult, is large. The temperature rise curve becomes dull, and at the same time, the temperature rise curve of the part B rises and the temperature of the workpiece 10 becomes uniform.

  When the induction heating is completed, the control device 13 stops the power supply of the high-frequency power supply device 9 and jets a coolant from a cooling jacket (not shown) to rapidly cool the workpiece 10. Thereby, the first heating mode (quenching process) is completed, and the quenching of the workpiece 10 is completed.

  Next, it transfers to step 3 and 2nd heating mode (reheating process) is implemented. In the second heating mode, control is performed by the control device 13 so that the power supplied from the high-frequency power supply device 9 is smaller than in the first heating mode, and the heating amount of the workpiece 10 is small. That is, in the second heating mode, the workpiece 10 is reheated in step 3, but the temperature rise of the workpiece 10 is controlled so that the hardness and tenacity of the workpiece 10 become desired values (or desired levels). The

  Even during reheating in step 3, the work 10 is driven to rotate by the work rotation driving device 6, and the core 3 of the induction heating coil 2 is close to the corner portion 10 a of the work 10.

  Then, the process proceeds to step 4, whether or not a predetermined time has elapsed since reheating is started, or whether or not the temperature of the corner portion 10 a of the workpiece 10 (part A, which is difficult to raise) reaches the predetermined temperature. Is determined. The control device 13 receives signals from the timer 12 and the workpiece temperature detection device 11 and performs the determination in step 4.

  When the predetermined time has not elapsed since the reheating was started, or when the temperature of the corner portion 10a of the workpiece 10 has not reached the predetermined temperature, or until the predetermined time has elapsed since the reheating was started, or It stays at step 4 until the temperature of the corner portion 10a of the workpiece 10 reaches a predetermined temperature.

  As described above, the temperature rise curve of each part in the reheating is preceded by the corner part 10a of the work 10 (part A which is a part where the temperature rise is difficult). Accordingly, the temperature of the small diameter portion 16 (part B) of the workpiece 10 when the temperature of the corner portion 10a of the workpiece 10 reaches a predetermined temperature is lower than that of the corner portion 10a.

  Then, when the predetermined time elapses from the start of reheating or the temperature of the corner portion 10a of the workpiece 10 detected by the workpiece temperature detection device 11 reaches the predetermined temperature, the control device 13 If determined, the process proceeds to step 5.

In step 5, the control device 13 sends a control signal to the workpiece moving device 7 to move the workpiece 10 by a predetermined distance. That is, the workpiece 10 is moved by a predetermined distance in the direction indicated by the arrow A from the position shown in FIG. 10A to the position shown in FIG. 10B by the workpiece moving device 7 while being subjected to heat treatment (induction heating). The semicircular portion 2a (region a where the generated magnetic lines of magnetic force are generated) of the induction heating coil 2 is separated from the ten corner portions 10a (the portion A that is difficult to raise the temperature) (separation operation).
Here, instead of moving the workpiece 10 in the direction indicated by the arrow A, the induction heating coil 2 may be moved in the direction opposite to the direction indicated by the arrow A by the heating coil moving device 8.

  If the determination in step 4 is YES, the workpiece 10 is induction heated while moving to the position shown in FIG. As a result, the temperature rise is slowed at the corner portion 10a having the highest temperature. On the other hand, since the induction heating coil 2 has a considerable length, even if the relative position in the axial direction with respect to the workpiece 10 slightly changes, the temperature of the small-diameter portion 16 (part B) of the workpiece 10 continues to be raised at the same pace. .

  The movement of the workpiece 10 is performed over a preset time. At the same time as the movement is completed, the power supply by the high-frequency power supply device 9 is stopped and the induction heating is also terminated. Then, the workpiece | work 10 is cooled gradually and the 2nd heating mode (reheating process) which is a reheating process is completed.

  As a result, in FIG. 10C, a good quenching pattern 14 shown by a hatched area inclined from the upper left to the lower right is obtained. That is, the corner portion 10a where stress is likely to concentrate is also quenched to a sufficient depth.

  The predetermined time and predetermined temperature in step 4 in FIG. 12 and the moving distance and moving time of the workpiece 10 in step 5 can be arbitrarily set according to the shape and size of the workpiece 10. For example, when the inner diameter of the workpiece 10 is 50 mm, the diameter (outer diameter) of the large diameter portion 15 is 120 mm, and the diameter (outer diameter) of the small diameter portion 16 is 90 mm, the predetermined time in step 4 is, for example, 1 to 3 seconds. Yes, the predetermined temperature may be, for example, 200 degrees Celsius to 300 degrees Celsius.

  Further, the moving distance of the workpiece 10 in step 5 is about half of the arrangement interval of the cores 4 (for example, 30 mm to 50 mm), and the moving time can be 6 to 10 seconds. For example, the time for induction heating of the workpiece 10 when the core 3 is close to the corner portion 10a is 2 seconds, the moving time is 8 seconds, and the total reheating time is 10 seconds (2 seconds + 8 seconds). By reheating the workpiece 10 with the induction heating coil 2 in this way, the workpiece 10 is subjected to good quenching and tempering.

  As a result of experiments conducted by the inventor, the allowable range of the surface hardness of the workpiece is 550 Hv to 720 Hv. When reheating is performed without moving the workpiece 10 in Step 5 of FIG. 12, the surface hardness of the workpiece 10 is 570 Hv to It was 700 Hv, and the variation of what was within the allowable range was large. However, when the present invention was carried out and the workpiece 10 was moved in step 5, a very good result was obtained that the surface hardness of the workpiece 10 was within the range of 610 Hv to 670 Hv.

  That is, when the present invention is carried out, the surface hardness of the workpiece is not only within the allowable range, but can be finished to a value within a narrower range within the allowable range. The results of experiments conducted by the inventor are as described above, but better results can be obtained by tuning the predetermined time in step 4, the predetermined temperature, the moving time in step 5, and the moving distance in FIG. 12 for each work. Can be expected.

DESCRIPTION OF SYMBOLS 1 High frequency induction heating apparatus 2 Induction heating coil 3 Core provided in the semicircle part of induction heating coil 4 Core provided in the linear part of induction heating coil 7 Work moving apparatus 8 Heating coil moving apparatus 9 High frequency electric power supply apparatus (high frequency power supply)
10 Work 11 Work temperature detector 12 Timer

Claims (7)

A method of performing high-frequency induction heating on a workpiece having a part that has a considerable length in the axial direction, has an outer shape and a cross-sectional shape that differ depending on the position in the axial direction, and has a part that is easily heated and a part that is difficult to raise. ,
A quenching step in which a region having a considerable length in the axial direction is heated to a predetermined quenching temperature and then rapidly cooled, and then a reheating step in which the temperature is gradually lowered after being heated to a temperature lower than the quenching temperature. In the method of performing high frequency induction heating having,
Use an induction heating coil having a length corresponding to the length of the part desired to be hardened and the length of the part desired to be reheated, and having a part having a different magnetic line density generated by the part in the axial direction,
In the quenching process and the reheating process , a part where the magnetic field line density of the magnetic field generated by the induction heating coil is close to a part where it is difficult to raise the temperature of the work, and a part where the magnetic field line density of the magnetic field generated by the induction heating coil is low Close to the part where the temperature of the workpiece is easily raised , and raise the overall temperature of the part where the workpiece is desired to be quenched and reheated .
The temperature rise of the workpiece is preceded by the part where heating is difficult, and the part where heating is easy,
During the heating of the workpiece in the reheating process, the part of the induction heating coil and the workpiece in the axial direction is relatively opposed to the part where the magnetic field line density of the magnetic field generated by the induction heating coil is low and the part where the heating of the workpiece is easy. A high frequency induction heating method characterized by changing a position and separating a portion where the magnetic field line density of a magnetic field generated by an induction heating coil is high from a portion where it is difficult to raise the temperature of a workpiece . 2. The part according to claim 1, wherein after a predetermined time has elapsed since the start of the heating in the reheating step, the part having a high magnetic force line density of the magnetic field generated by the induction heating coil is separated from the part where it is difficult to raise the temperature . High frequency induction heating method. The heating of the reheating process is started, and when the temperature of the part where heating is difficult reaches a predetermined temperature, the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high is separated from the part where heating is difficult. The high frequency induction heating method according to claim 1 . High-frequency induction heating method according to any one of claims 1 to 3, wherein that you heat the axle tube as a work. A high-frequency induction heating apparatus that induction-heats a workpiece that has a considerable length in the axial direction, has an outer shape and a cross-sectional shape that differ depending on the position in the axial direction, and has a part that is easily heated and a part that is difficult to raise. ,
An induction heating coil having a length corresponding to the length of the part desired to be quenched and the length of the part desired to be reheated, and having a part having a different magnetic line density generated by the part in the axial direction; A high-frequency power source for supplying high-frequency AC power to the heating coil, and a moving means for moving the work and the induction heating coil in a relative distance in the axial direction,
A first heating mode for heating the workpiece to a predetermined quenching temperature is executed, and subsequently, a second heating mode for heating to a temperature lower than the first heating mode is automatically executed.
During heating in the first heating mode and the second heating mode,
Place the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high near the part where it is difficult to raise the temperature of the work, and place the part where the magnetic field line density of the magnetic field generated by the induction heating coil is low close to the part where the temperature of the work is easy to heat up. Let the temperature of the part you want to quench and reheat the workpiece,
The temperature rise of the workpiece is preceded by the part where heating is difficult, and the part where heating is easy,
During heating in the second heating mode, the moving means moves the work and the induction heating coil by a predetermined distance relative to each other in the axial direction so that the magnetic field generated by the induction heating coil has a low magnetic line density. By changing the relative position of the induction heating coil and the workpiece in the axial direction while facing the part where the workpiece is easy to heat up, the part where the magnetic field line density of the magnetic field generated by the induction heating coil is high is A high frequency induction heating apparatus characterized by performing a separating operation. Provided with temperature detection means for detecting the temperature of the part of the workpiece that is difficult to raise temperature, in the second heating mode, when the temperature detected by the temperature detection means reaches a predetermined temperature, or when the heating time reaches a predetermined time, The high-frequency induction heating apparatus according to claim 5, further comprising a control mechanism that performs the separation operation. The high-frequency induction heating apparatus according to claim 5 or 6, wherein the induction heating coil is a semi-open saddle type coil .

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