JPH10321357A - Induction heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an induction heating device whose end surface can be efficiently heated particularly by welding of metallic bars or the like by arranging plural coils to generate magnetomotive forces in the direction perpendicular to the central axis of the metallic bars, and connecting them so that the magnetomotive forces of the respective coils can be added to each other. SOLUTION: Two coils 21 and 22 are arranged so as to cover a part to which metallic bars 1A and 1B are joined. A reason for being constituted in this way is that a butting end surface of the metallic bars 1A and 1B can also be heated, but they are connected so that respective electromotive forces of the coils 21 and 22 can be added in the direction perdpendicular to the central axis of the metallic bars 1A and 1B. The two coils 21 and 22 are connected in series to each other. In this way, since the coils are divided into two parts, the metallic bars 1A and 1B can be easily mounted on and demounted from the coils 21 and 22. The coils 21 and 22 are desirably excited by a high frequency power source 5 of two phases or four phases.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction heating device for heating a metal with a high-frequency magnetic field, and more particularly to an induction heating device capable of efficiently heating an end face of a metal rod by welding or the like.

[0002]

2. Description of the Related Art FIGS. 7A and 7B are configuration diagrams showing a conventional example of an induction heating apparatus, wherein FIG. 7A is a plan view and FIG. 7B is a side view of a metal rod portion. 1 is a metal rod as a work, 2 is a heating coil (also referred to as a water cooling coil or simply a coil), 3 is a cooling water device for circulating cooling water through the coil 2, 4 is a current transformer, and 5 is a high frequency power supply. . The current transformer 4 includes a high-frequency power supply 5
Is used for current matching when the coil 2 is connected to the coil. That is, a high-frequency current of several kHz to several hundreds kHz flows through the water-cooled coil 2 wound around the portion of the metal rod 1 to be heated, and a high-frequency magnetic flux φ is generated by the magnetomotive force. Heating is performed by flowing a high-frequency eddy current to the surface of the metal rod.

[0003]

In the conventional apparatus,
Compared to those using thermal power or electric heat, it is easier for power to concentrate,
While there are advantages such as high power conversion efficiency, there are the following problems. 1) It is difficult to heat the center of the end face of the rod. Since the magnetic flux φ is generated only in a portion close to the surface of the side surface of the metal rod due to the skin effect, the central portion of the end surface is hardly heated. For example, in the case where the mating surface of the metal rod is heated to a predetermined temperature of 1000 ° C. or more for welding, it is necessary to wait for the heat to be transmitted to the central part with sufficient heating time. At that time, it is effective to make the center part concave in advance, but extra processing is required. Further, if the temperature reaches the predetermined temperature until the center, the heat spreads above and below the rod, so that the required electric energy becomes considerably large.

2) It is difficult to divide and detach the coil. The shape of the coil is simple and easy to manufacture, but it is quite difficult to remove it from the metal rod. It is difficult to manufacture a coil that is water-cooled and can be easily divided. 3) A current transformer is required for the water-cooled coil. A water-cooled coil having a small number of turns has a large current (several thousands of A) and a small electromotive force (several tens of volts). Therefore, to connect to a high-frequency power supply having an output voltage of several hundreds to several thousand volts, a current transformer, A so-called matching transformer (matching transformer) is required.
Therefore, an object of the present invention is to solve the various problems described above.

[0005]

In order to solve such a problem, the present invention is as follows. (1) The direction of the coil magnetic field is perpendicular to the central axis of the metal rod. (2) A plurality of coils are connected so that the magnetomotive force of each coil is added to each other. (3) Heating is performed not only by a single phase but also by a rotating magnetic field using a multiphase high frequency power supply. (4) Use an iron core. (5) An iron core cover (core cover) is used to more effectively use the iron core. (6) Use a spacer.

(1) That is, the direction of the magnetomotive force generated by the coil is changed to a direction perpendicular to the conventional direction, and the coils are arranged on the entrance side and the exit side of the magnetic flux, respectively. Since the magnetic flux penetrates into the inside and creeps along the end face of the metal rod, a magnetic flux is generated, so that heat is also generated at the center of the end face by eddy current. When heating with a single coil as in the prior art, a predetermined portion of the rod could be uniformly heated over one round, but with a plurality of coils, 360 ° per round
Cannot be heated uniformly. (2) Therefore, if the excitation of a plurality of coils is performed in a three-phase coil or a multiple thereof in order from a single phase, and the excitation is sequentially performed at an electrical angle of 120 °, the direction of the composite magnetic field can be changed to a rotating magnetic field.
The possibility of uniform heating over 60 ° increases.
This is the same when the number of coils is a multiple of two, and it is preferable to excite two or four phases.

(3) The use of an iron core rather than an air core saves the magnetomotive force of the coil. In other words, if the magnetic flux is guided by the iron core and the magnetic circuit is extended, not only a small magnetomotive force is required but also the cross section of the coil can be enlarged, so that the number of turns can be increased, and as a result, the current transformer and cooling water device Sometimes it can be omitted. (4) A considerable amount of leakage magnetic flux is generated on the surface and side surfaces of the iron core, and a magnetic flux is generated that does not pass through the end of the iron core close to the metal rod where the magnetic flux is to be concentrated. This leakage magnetic flux causes problems such as hastening saturation of the central portion of the iron core, causing local heating on the surface of the iron core, and heating a part of the coil.

(5) A core cover made of a good conductor such as copper or aluminum is effective in blocking the above-mentioned leakage magnetic flux. Although loss occurs due to the core cover, it is advantageous as a whole. (6) In the heating method according to the present invention, if there is no gap between the butted portions of the two metal rods and they are in good electrical contact, no magnetic flux is generated along the end surfaces of the rods and no heat is generated. It is important to have For example, when welding the ends with high speed and low energy,
A gap is required until the end face of the iron bar becomes nonmagnetic beyond the Curie point of about 700 ° C. In the case of a method in which the heat generated by heating the side surface is transferred to the center, the gap is not so necessary.

[0009]

FIG. 1 is a structural view showing a first embodiment of the present invention. FIG. 1 (a) is a plan view, FIG. 1 (b) is a side sectional view, and FIG. 1 (c) is a side view. It is. In this case, the coil covers the portion where the metal rods 1A and 1B are joined, as shown in FIG.
(A) and (b) are provided two as indicated by reference numerals 21 and 22. This is to make it possible to heat the butted end faces of the metal rods 1A and 1B. However, the magnetomotive forces of the coils 21 and 22 are added in a direction perpendicular to the central axes of the metal rods 1A and 1B. Connected as they are. FIG.
In (a), they are connected in series. As described above, since the coil is divided into two, it is easy to attach and detach the metal rod to and from the coil. Note that the number of turns of the coil cannot be increased so much that the cooling water device 3 and the current transformer 4 cannot be omitted.

In the case of FIG. 1, it is convenient to excite the coils 21 and 22 with a two-phase or four-phase high-frequency power supply. However, in the case of three coils, the arrangement is as shown in FIG. Here, since the magnetic fluxes φu, φv, φw from the coils 21, 22, 23 are generated with a 120 ° spatial and temporal shift, the combined magnetic field becomes a high-frequency rotating magnetic field, and It is possible to eliminate uneven heating due to the position.

FIG. 3 is a structural view showing another embodiment of the present invention. FIG. 3 (a) is a plan view and FIG. 3 (b) is a side sectional view. This is because iron cores 6A and 6B made of a magnetic material having high magnetic permeability are used.
The magnetic flux path and magnetic path are extended using
, The required magnetomotive force can be reduced, and the cross section of the coil can be increased. In this case, by increasing the number of turns and the surface area of the coil to efficiently release the heat, the current transformer and the cooling water device can be omitted.

By the way, if an iron core is used as shown in FIG.
As shown in FIG. 4, a leakage magnetic flux is generated on the surface of the iron core inside the coil as shown by a curved arrow. The leakage magnetic flux causes various inconveniences as described below. 1) A maximum magnetic flux density Bm as shown in the figure is generated in the central portion of the iron core immediately below the coil, which is magnetically saturated ahead of other portions, and no output can be output. 2) When the core is a laminated type (laminate core), high-frequency magnetic flux passes through the laminated surface, so that a local loss is extremely large and a local overheating is caused to cause a local burning of the core. 3) Unnecessary high-frequency magnetic flux heats a part of the heating coil, so that unnecessary loss occurs and lowers the thermal efficiency of the device.

FIGS. 5A and 5B are configuration diagrams showing still another embodiment of the present invention for avoiding the above-mentioned disadvantages of the leakage magnetic flux. FIG. 5A is a plan view, and FIG. FIG. 1C is a side view. This is because the surface of the iron core 6 from the bottom of the coil to the tip close to the metal rod is made of a good conductor (referred to as a core cover) 7 such as copper or aluminum having good thermal conductivity and electric conductivity.
It is covered with. In other words, at a high frequency of several tens of kHz,
The penetration depth due to the skin effect of a good conductor is 0. Because it is several mm,
If the core cover 7 having a thickness of about 1 mm is provided, the leakage magnetic flux cannot penetrate the core cover 7. At this time, the core cover does not become a single short-circuit coil,
It is necessary to divide as shown by reference numerals 7A and 7B in FIG.

FIGS. 6A and 6B are configuration diagrams showing still another embodiment of the present invention, wherein FIG. 6A is a plan view and FIG. 6B is a side view. The gap is important for effectively heating the end face of the metal rod. In particular, in order to efficiently join the two metal bars by heating, appropriate values are required for the pressing force F and the gap g shown in FIG. However, the gap g is shaded by the heating coil and the iron core and is difficult to see from the outside, so that its management is difficult. Therefore, it is effective to heat-bond several spacers having the following functions (three spacers 8 are used in FIG. 6A) with a gap therebetween.

1) The temperature at which the gap is required (for example, 80
Up to 0 ° C. or lower), above which melting and spillage occur and the bonding temperature (for example, 1250 ° C.) is no longer maintained. 2) A small-sized, harmless material that bites into the metal rod while maintaining a constant shape up to the joining temperature, and does not significantly reduce the joining strength even after the joining is completed. For such a material, a heat-resistant insulator such as a ceramic is effective. Alternatively, heat-resistant alloys such as nickel, chromium, titanium, and tungsten are also conceivable. 3) A material that has almost the same configuration as the base material of the metal rod and melts harmlessly when pressed.

When the above-mentioned gap is managed on a production line to which a precision drive welding robot or the like is applied, the above-described gap spacer is unnecessary, but can be used in some cases. The shape of the spacer is not limited to a columnar shape as shown in the figure, but may be various shapes such as a spherical shape, a ring shape, a quadrangular prism, and a star-shaped column depending on the purpose.

[0017]

According to the present invention, the following effects can be expected. 1) The end face of the metal rod can be efficiently heated to a required (joining) temperature in a short time and with a small amount of power. 2) A coil or a work can be easily attached and detached. 3) The surroundings can be uniformly heated by induction heating using a multi-phase high-frequency power supply. 4) By using an iron core, more effective heating becomes possible. 5) When an iron core is used, it is more effective to use a core cover together. 6) It is often effective to use a gap spacer when joining metal bars.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a configuration diagram showing a third embodiment of the present invention.

FIG. 4 is an explanatory view of a leakage magnetic flux in FIG. 3;

FIG. 5 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a conventional example.

[Explanation of symbols]

1, 1A, 1B: metal rod, 2, 21, 22, 23: coil, 3: cooling water device, 4: current transformer, 5: high frequency power supply, 6
... iron core, 7 ... core cover, 8 ... spacer.

Claims (8)

[Claims] In order to mainly heat an end face of a metal rod, a plurality of coils for generating a magnetomotive force in a direction perpendicular to a central axis of the metal rod are provided, and the coils are connected so that the magnetomotive forces of the coils are added to each other. An induction heating device characterized in that: 2. The induction heating apparatus according to claim 1, wherein the number of the plurality of coils is a multiple of three, and the coil is excited by a three-phase or multi-phase high-frequency power supply. 3. The induction heating apparatus according to claim 1, wherein the number of the plurality of coils is a multiple of two, and the coil is excited by a two-phase or four-phase high-frequency power supply. 4. The induction heating apparatus according to claim 1, further comprising an iron core that covers an inner surface of each of the coils and an outer surface farthest from the metal bar. 5. The induction heating apparatus according to claim 4, wherein the cross-sectional area of each coil is increased to increase the number of windings, and the matching transformer can be omitted. 6. The induction heating apparatus according to claim 4, wherein a cross-sectional area of each coil is increased to increase the number of turns, and a cooling water device can be omitted. 7. The induction heating apparatus according to claim 4, wherein a core cover made of a metal having a small electric resistance is provided between the iron core and the coil. 8. The induction heating apparatus according to claim 1, wherein a gap spacer is previously sandwiched between the joints for induction heating.