JPH046788A - Induction heating method by low-frequency ac magnetic field and device thereof - Google Patents

Abstract

PURPOSE:To dispense with a large power facility and perform quick heating by applying the low-frequency AC magnetic field to cores forming a closed loop magnetic path, and generating Joule's heat by the secondary current in a heated object arranged around the cores. CONSTITUTION:A heated metal 7 to be treated is stored in an adiabatic container 6, a yoke 2 is extracted from cores 4, 5, the center hole of the adiabatic container 6 is inserted into the core 4 and mounted on a frame 9, then the cores 4, 5 are fitted to the yoke 2. A low-frequency AC exciting current is fed to a coil 8. The AC magnetic flux (arrow) according to the AC frequency flows in the yokes 2, 3 and cores 4, 5 of a closed loop. A secondary induction current is generated in the heated metal 7 arranged around the magnetic flux, and the metal 7 is self-heated by Joule's heat.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to an induction heating method using a low frequency alternating magnetic field for melting metals and various heat treatments, and an apparatus therefor.

``Prior Art'' Conventionally, various methods and apparatuses have been used for melting metals and subjecting them to various heat treatments, as described below.

First, a method is used in which a carbon electrode is brought into contact with the metal to be heated, and an alternating current or direct current is supplied from the carbon electrode to the metal to be heated, thereby heating the metal by contact resistance loss between the carbon electrode and the metal to be heated. ing.

The second method is indirect heating, in which a heating element such as a heating wire or ceramic is energized to heat a refractory crucible or refractory brick container, and the metal to be heated stored in the refractory crucible or refractory brick container is melted. There is a method that utilizes the radiant heat of the above-mentioned heating element.

The third method is to heat a fireproof crucible or firebrick container by burning fossil fuels such as kerosene, heavy oil, coal, gas, etc.
Similar to the third method, there is a method of melting the metal to be heated in a refractory crucible or a refractory brick container using indirect heating or radiant heat.

A fourth method is a method using a high-frequency heating device, that is, a high-frequency current is supplied to an induction coil, the induction coil generates a high-frequency alternating magnetic field, and the metal to be heated is exposed to the high-frequency alternating magnetic field. There is a method in which a secondary current is generated in the metal to be heated, and the Joule heat is used to heat and melt the metal to be heated, and the metal to be heated can be heated rapidly, and the shape of the induction coil itself can be small. Moreover, because of the skin effect caused by high-frequency induction, it is possible to heat only the surface of the metal to be heated, and it is often used for surface hardening.

"Problems to be Solved by the Invention" However, in the first method, the carbon electrode wears out as it is used, which requires maintenance such as cleaning and replacement, and the consumables of the carbon electrode melt. There is a problem that it mixes into the metal to be heated, and it is not suitable for heating the metal to be heated below the melting temperature.

The second method has limitations such as not being able to heat the metal to a temperature higher than the maximum temperature allowed by the heating element, and the higher the temperature of the heating element, the shorter its life. There's a problem.

The third method has the advantage that the price of fuel is low, but it has problems such as complicated combustion control when controlling the heating temperature of the metal to be heated, and a large loss in the control device. be.

The fourth method has the advantage of being able to rapidly heat the metal to be heated, but it requires a high-frequency power supply that converts the commercial frequency of a commercial power source into a high frequency, and the high-frequency power supply is extremely expensive and has a large shape. They require a large area to be installed, and they also have poor heating efficiency and become a source of noise due to the use of high frequencies, causing noise to be mixed into surrounding equipment.

Moreover, because only the surface of the metal to be heated is heated due to the skin effect, it is not suitable for heating the entire metal, including the inside of the metal to be heated. In particular, in recent years, there has been a demand to uniformly heat not only the surface but also the entire surface of the metal to be heated in order to remove stress inside the metal, but the fourth method is not suitable. However, heating only the surface has problems such as the temperature difference between the surface and the inside causing stress to be applied.

In view of the above-mentioned circumstances, the present invention has been developed so that the metal to be heated generates heat by self-heating by obtaining heating energy from the outside without contact, thereby eliminating the need for maintenance and management of electrodes, etc., and generating noise such as in high-frequency induction heating. Furthermore, the entire object to be heated can be heated uniformly, and it is possible not only to melt the object but also to heat it below the melting temperature. Also, there is no need for costly power supply equipment, and high-frequency induction heating An object of the present invention is to provide an induction heating method using a low-frequency alternating magnetic field, which is capable of rapid heating similar to the method according to the present invention, and an apparatus therefor.

"Means for Solving the Problems" The present invention has been made to achieve the above object, and in claim (1), a low frequency alternating magnetic field is applied to an iron core forming a closed loop magnetic path, and the area around the iron core is This method is characterized by an induction heating method using a low frequency alternating magnetic field, in which Joule heat is generated by inducing a secondary current in a disposed object to be heated based on the low frequency alternating magnetic field. In claim (2), a low-frequency alternating magnetic field generator comprising an alternating magnetic field generation source that provides a low-frequency alternating magnetic field to an iron core forming a closed loop magnetic path, and a heated object detachably disposed around the iron core. It is characterized by an induction heating device using an alternating magnetic field.

"Embodiments" Below, embodiments of the induction heating method using a low frequency alternating magnetic field and its apparatus according to the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment, and 1 in the figure is a base. On the base 1, joints 2 and 3 and a core 4.5 are installed as iron cores to form a closed loop magnetic circuit. The yoke 2.3 and the core 4.5 are made of a soft magnetic material such as nickel steel plate, soft magnetic ferrite, silicon steel plate, etc., and are resistant to iron loss and eddy current loss even when magnetized in an alternating magnetic field. It is preferable to use laminated steel sheets. The yoke 2 is detachably attached to the upper ends of the cores 4 and 5. That is, the heat insulating container 6 having a doughnut-shaped cross section is fitted into the core 4 so as to be removable by removing the yoke 2. At this time, the insulation container 6 is
When inserted into the core 4, it is placed on a pedestal 9.

Inside the heat insulating container 6, a metal to be heated 7 is housed. The metal to be heated 7 may be any metal with relatively good conductivity and low specific electrical resistance, such as iron or non-ferrous metal 9 alloys, and the shape may be a thin plate lump, a plate, a single small lump, powder, molten metal, etc. A wire, coiled thin plate, etc. are possible. A coil 8 is wound around the core 5.

Next, to explain the induction heating method in the first embodiment with the above configuration, first, the metal to be heated 7 to be treated is stored in the heat insulating container 6, the yoke 2 is removed from the cores 4 and 5, and the
After fitting the center hole of the heat insulating container 6 and placing it on the pedestal 9, the yoke 2 is attached to the cores 4 and 5. Next, an excitation current of a low frequency alternating current is supplied to the coil 8. When an excitation current is applied to the coil 8, an alternating magnetic flux according to the alternating frequency of the excitation current flows through the closed loop yokes 2, 3 and cores 4, 5, as shown by arrows in FIG.

Therefore, a secondary induced current is generated in the heated metal 7 disposed around the magnetic flux. Of course, if there is no heated metal 7 in the heat insulating container 6, no secondary induced current will occur. When the secondary induced current flows into the heated metal 7, the heated metal 7 self-heats due to Joule heat. Therefore, the metal to be heated 7 is heated by induction by the excitation current supplied to the coil 8, and the heating temperature can also be adjusted by controlling the value of the excitation current.

In other words, by controlling the value of the excitation current supplied to the coil 8 and adjusting the heating temperature according to the material of the metal to be heated 7 in the heat insulating container 6, even metals to be heated with various melting points can be melted. can be done. Moreover, heating the metal to be heated 7 at a temperature below the melting point for annealing or the like can be performed by controlling the value of the excitation current supplied to the coil 8. When the heating and melting process of the heated metal 7 in the heat insulating container 6 is completed, the yoke 2 is removed from the upper end of the core 4.5, the heat insulating container 6 is pulled out from the core 4, and the heated metal 7 is removed. Take it out. When taking out the heated metal 7 in a molten state from inside the heat insulating container 6, it is also possible to tilt the entire apparatus and pour out the molten heated metal 7 from inside the heat insulating container 6 into another container.

FIG. 2 shows a second embodiment, in which the core 4 of the first embodiment is
A rotating electromagnetic device 10 is provided instead. The rotating electromagnetic device 10 has fixed cores 11.12 magnetically connected to the yoke 2.3, and a movable core 13 located between the fixed cores 11.12 and rotating. The movable core 13 is rotatably supported by a stay 14 with a bearing 15 interposed therebetween. Also, the stay 14 is connected to the fixed core 1
It also supports 1°12. Coil 1 is attached to the movable core 13.
6 is wrapped. The movable core 13 can be made of the same material as the yoke 23 or a steel ring ferromagnetic material, does not necessarily have to be a soft magnetic material, and is formed by supplying an excitation current to the coil 16. The number of magnetic poles can be freely selected from two or more as appropriate. Further, the coil 16 is supplied with an excitation current from an external DC power source via a slip ring 17 and a brush 18. A drive device 21 is connected to the rotating shaft 19 of the movable core 13 via a coupling 20. The drive device 21 is installed on the base 1 on the base 22.
It is installed via. The other configurations are the same as those of the first embodiment.

Next, to explain the induction heating method of the second embodiment, a DC excitation current is supplied from an external DC power source to the coil 16 via the brush 18 and the slip ring 17, and the drive device 21 is driven to generate the movable core I3. rotate at a predetermined speed. When an excitation current is applied to the coil 16, a predetermined number of magnetic poles are generated in the movable core 13, and the movable core 13 is connected to the drive device 2.
1, the movable core 13 rotates by the fixed cores 11, 12, . Low frequency alternating magnetic flux flows through the yokes 2 and 3 and the core 4. The alternating magnetic flux exhibits a frequency corresponding to the number of magnetic poles of the movable core 13 and the number of rotations of the movable core 13. Therefore, as in the first embodiment, a secondary induced current is generated in the metal to be heated 7 in the heat insulating container 6, and the metal is heated by Joule heat. In this embodiment, the drive device 2
Since the frequency of the alternating magnetic flux flowing through the core 4 can be adjusted by changing the rotation speed of the movable core 13 according to 1, the optimum conditions for induction heating are selected depending on the material of the metal 7 to be heated. Further, the driving device 21 can be a gasoline engine, a rivet, a motor, or other various devices. Furthermore, it is also possible to use permanent magnets in place of the movable core 13 and coil 16.

FIG. 3 shows a third embodiment, in which cores 4 and 5 are each divided at the center in place of the cores 4 and 5 in the first embodiment.
3 to 26 are used. One end of the fixed intermediate core 27 is fitted between the cores 23 and 24. A coil 29 is wound around the fixed intermediate core 27, and a receiving recess 28 is provided at the other end. A fitting shaft portion 31 of a movable intermediate core 30 can be fitted into the receiving recess 28 . The fitting shaft portion 31 is provided to protrude from one end of the movable intermediate core 30 . The movable intermediate core 30 is slidably inserted between the cores 25 and 26, and a protruding portion from between the cores 25 and 26 is supported by a bearing 32 so as to be able to reciprocate. The other end of the movable intermediate core 30 is connected to a piston rod 34 of an air cylinder 33. Movable intermediate core 3
A coil 35 is also wound around the coil 35. Above receiving recess 2
The ring-shaped metal to be heated 37 is removably attached to the base of the fitting shaft portion 31 which is not inserted into the ring-shaped metal to be heated 37, with a heat insulating material 36 interposed therebetween except for a portion other than the peripheral surface of the ring-shaped metal to be heated 37. It goes without saying that all components such as the yokes 2 and 3 as well as the air cylinder 33 are installed on the base 1.

Next, to explain the induction heating method of the third embodiment, first, the air cylinder 33 is operated to separate the movable intermediate core 30 from the fixed intermediate core 27, and the ring-shaped metal to be heated is heated with a heat insulating material 36 interposed therebetween. 37 to the fitting shaft part 31,
The movable intermediate core 30 is moved by the air cylinder 33 to fit the fitting shaft part 31 into the receiving recess 28, and set it in the state shown in FIG. In this set state, fixed intermediate core 27 and movable intermediate core 30 are magnetically connected. The fixed intermediate core 27 and the movable intermediate core 30 are connected to the yoke 2
．． The same ferromagnetic material as in 3 can be used, and as the ring-shaped heated metal 37, the inner race, outer race, gear, etc. of a bearing can be used. Next, when a low frequency alternating excitation current is applied to each coil 29, 35, an alternating magnetic flux is generated in the fixed intermediate core 27 and the movable intermediate core 30, as shown by the arrows in FIG. Alternating magnetic flux flows from the intermediate core 30 in a divided manner toward each of the yokes 2 and 3. Due to the alternating magnetic flux flowing through the fixed intermediate core 27 and the movable intermediate core 30, a secondary induced current flows in the metal to be heated 37 in a circular manner, and the metal is heated by Joule heat as in the first embodiment. As in the first embodiment, the heating temperature can be adjusted by controlling the value of the excitation current supplied to the coils 29, 35. On the other hand, the fixed intermediate core 27 and the movable intermediate core 30 have an outer diameter equal to that of the heated metal 11.
The fixed intermediate core 2 is formed to have a larger diameter than that of the fixed intermediate core 2.
7 and the movable intermediate core 30, the alternating magnetic flux flows directly into the heated metal 37 as shown by the arrow in FIG. Heating occurs due to heat generation due to iron loss and eddy current loss. After the heat treatment is completed, air cylinder 3
3, the movable intermediate core 30 is separated from the fixed intermediate core 27 and the metal to be heated 37 is taken out from the fitting shaft portion 31. It goes without saying that the metal to be heated 37 can be attached and detached from the fitting shaft portion 31 either automatically or manually. In this case, as shown in FIGS. 4 and 5, a donut plate-shaped heat insulating material 36a having a hole with the same diameter as the receiving recess 28 is attached to the end face of the fixed intermediate core 27, and the movable intermediate core 30 A donut plate-shaped heat insulating material 36b having a hole with the same diameter as the fitting shaft 31 is attached to the end face of the shaft, and a cylindrical heat insulating material 36c is attached to the fitting shaft 31. Insulating material 36a
36c blocks heat from the heated metal 37, and can be attached and detached very easily.

FIG. 6 shows a fourth embodiment, in which the yoke 2 and core 23.25 of the third embodiment are removed, and the fixed intermediate core 27 is replaced with the core 2.
4, and the movable intermediate core 30 is fixedly installed in the fitting hole 39 of core 2.
The coil 3 is slidably passed through the guide hole 40 provided in the yoke 3 to form a closed loop shape in which the magnetic path does not separate.
8 wrapped around it. If a low frequency alternating excitation current is applied to the coil 38, the yoke 3 will move as shown by the arrow in FIG.
゜Core 24. Fixed intermediate core 27. An alternating magnetic flux flows through the movable intermediate core 30° to the core 26, and the other third
It is the same as the example.

FIG. 7 shows a fifth embodiment, in which the coil 38 of the fourth embodiment is removed, and the rotating electromagnetic device 10 of the second embodiment is provided in place of the core 24. The configuration is the same as the fourth embodiment.

be.

"Effects of the Invention" As described above, according to the induction heating method using a low-frequency alternating magnetic field and its device according to the present invention, heating is performed using Joule heat generated by the secondary induced current caused by the low-frequency alternating magnetic field. Heated single heavy oil.

They are forced to work in harsh environments such as batch furnaces and tunnel furnaces that use gas, etc., and when using electrical resistance heating elements, the heating temperature of the metal to be heated is limited by the maximum temperature of self-heating, and There are no problems such as shortened lifespan of electrical resistance heating elements. Furthermore, there is no problem of low conversion efficiency or complicated combustion control when heating a metal to be heated using combustion energy such as conventional fossil fuels, and there is no problem of major damage to the device. In particular, because it uses low frequencies, it does not require large and expensive power supply equipment like high-frequency induction heating, there is less problem of noise intrusion into other equipment, and only the surface is heated due to the skin effect caused by high frequencies. There is no situation where the inside is not heated. Moreover, in the present invention, not only can the metal to be heated be melted, but also heat treatment below the melting point, such as annealing, can be performed, which is very convenient for use.

[Brief explanation of drawings]

The drawings show an embodiment of the induction heating method using a low-frequency alternating magnetic field and its device according to the present invention, FIG. 1 is a block diagram of the first embodiment, FIG. 2 is a block diagram of the second embodiment, and FIG. is a block diagram of the third embodiment, FIGS. 4 and 5 are explanatory diagrams of main parts showing the attachment and detachment of the heated metal in FIG. 3, FIG. 6 is a block diagram of the fourth embodiment, and FIG. 7 is a block diagram of the fourth embodiment. It is a block diagram of 5th Example. 2.3...Yoke 4.5.23-26...Core 7.37...Metal to be heated 16, 29. 35°... Rotating electromagnetic device, 12... Fixed core... Drive device... Receiving recess... Fitting shaft portion 38... Coil 13... Movable core 27... Fixed intermediate core 30 ...Movable intermediate core 33...Air thin lidar Fig. 4 Fig. 5

Claims (2)

[Claims] (1) A low-frequency alternating magnetic field is applied to an iron core forming a closed-loop magnetic path, and a secondary current is induced in an object to be heated arranged around the iron core based on the low-frequency alternating magnetic field, thereby generating Joule heat. An induction heating method using a low frequency alternating magnetic field. (2) It consists of an iron core that forms a closed loop magnetic path, an alternating magnetic field generation source that provides a low-frequency alternating magnetic field to the iron core, and a heated object that is detachably disposed around the iron core. An induction heating device that uses a low-frequency alternating magnetic field.