JP4171124B2 - Magnetic field generator and permanent magnet manufacturing apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field generator that realizes a magnetic field in a radial direction and a permanent magnet manufacturing apparatus that incorporates the magnetic field generator, and is optimal for manufacturing an anisotropic sintered permanent magnet manufactured by a powder sintering method. is there.
[0002]
[Prior art]
In the manufacturing process of a magnetic material by powder molding, especially a permanent magnet, magnet powder is oriented in a magnetic field, and press molding, that is, orientation pressing in the magnetic field, is performed while the magnetic field is applied to produce an anisotropic magnet.
The generation of the magnetic field is performed with a pair of air cores or electromagnets with an iron core facing each other and sandwiching a gap. Usually, a die press mold is disposed in the gap to generate a unidirectional magnetic field in the gap, and the magnetic field is generated. In the state in which the magnet powder is oriented in the generation direction, press molding is performed to form an anisotropic magnet molded body, and further, sintering heat treatment is performed to manufacture a sintered anisotropic permanent magnet.
[0003]
The magnitude of the magnetic field applied in the magnetic field orientation press varies depending on the type of magnetic powder to be molded, but 2 to 5 kOe for ferrite magnet powder and 10 to 15 kOe for rare earth magnet powder are only a rough guide. The manufactured anisotropic permanent magnet can obtain an energy product about four times that of an isotropic permanent magnet.
[0004]
In sintered anisotropic permanent magnets for motors, in particular, anisotropic magnets having a magnetization easy axis oriented in the radial direction (radial direction) of a ring-shaped magnet, that is, radial oriented magnets are often required.
A radial orientation magnet is used as a rotor magnet of a motor, and the number of poles and skew can be arbitrarily changed by magnetization. Therefore, it is most suitable for a surface magnet type motor. For this reason, there is an increasing demand for a radially oriented ring-shaped magnet that can meet various demands for size and length and has high characteristics and good orientation.
[0005]
Conventionally, as shown in FIG. 2, a radially oriented magnet is oriented by placing a pair of air cores or coils 1a and 1b with iron cores facing each other in the same pole, and die presses in the space region of the magnetic flux 3 generated in the radial direction. A metal mold (not shown) was placed, and the magnetic powder was radially oriented and press-molded.
However, since the spatial region of the magnetic flux 3 generated in the radial direction by this method is particularly narrow in the axial direction, there is a disadvantage that only a ring-shaped magnet having a low height can be manufactured. Even if the magnetic flux 3 is oriented in the radial direction (horizontal direction), it also has a magnetic flux component in the vertical direction, so that the degree of orientation of the magnet powder is inferior to that in the case of a complete radial magnetic field. Furthermore, since the magnetic field strength in the radial direction decreases more rapidly as it approaches the outer periphery, the orientation magnetic field strength is insufficient depending on the size of the ring-shaped magnet to be formed. In order to produce a radially oriented permanent magnet by press molding, there are various problems as described above, and there is a great limitation on the diameter and length of the magnet that can be produced.
[0006]
Various improvements have been attempted to improve these problems. For example, in the case of a relatively large magnet, by incorporating a pair of coils facing the core portion of the mold, the orientation magnetic field strength can be increased and the vertical component of the radial magnetic flux can be reduced. However, the actual incorporation of the coil is restricted by the shape of the magnet, and if the shape is different, the coil portion must be redesigned each time, which is complicated.
[0007]
As another method, there is a method in which a core part of a ring-shaped magnet mold for generating a magnetic field is formed of a ferromagnetic core such as iron, and the magnetic flux of an opposing coil is drawn into the core part and then radiated in the radial direction. As a result, the magnetic field strength of the mold cavity can be increased and the vertical component of the radial magnetic flux can be reduced. However, in this method, the diameter of the core portion is not sufficiently large and magnetically saturated with respect to the amount of magnetic flux generated by the opposing coil, and therefore magnetic flux cannot be drawn into the core portion as expected. In addition, even if the applied magnetic field becomes zero, the ferromagnetic core has a magnetic field in the mold corresponding to the residual magnetization, which hinders filling of the mold powder with magnet powder. Further, the uniformity of the magnetic field in the cavity is also deteriorated, and the magnetic powder tends to be biased toward the core during magnetic field orientation, causing cracks in the magnetic powder molded body.
[0008]
[Problems to be solved by the invention]
As described above, the radial orientation magnet can be manufactured even with a conventional molding apparatus, but the orientation properties and shape arbitraryness of the magnet are not satisfactory.
The present invention solves these problems, and provides a magnetic field generator capable of generating a radial magnetic field having a small vertical component and having a magnetic line of force directed in the horizontal radial direction in a wide spatial region. It is an object of the present invention to provide a permanent magnet manufacturing apparatus capable of manufacturing a good radial-oriented permanent magnet by incorporating in a magnetic field oriented press molding apparatus.
[0009]
[Means for Solving the Problems]
The present inventor has solved as a result of diligent research to solve the above problems, that is, the magnetic field generator of the present invention has a magnetic field in which a pair of air cores or coils with iron cores are opposed to each other with a gap interposed therebetween. In the generator, a liner selected from Al, Cu, Ag, Au, or an alloy thereof is arranged symmetrically in contact with each coil across the gap, and a pulse current in the opposite direction is applied to both coils. it is characterized by being configured as electrode face each other. The liner is preferably cylindrical. The circular cylinder shape, and a straight cylindrical shape of objects or different diameters at the upper and lower truncated circular cone trapezoidal shape.
[0010]
In short, in the magnetic field generator of the present invention, a pair of cylindrical liners are arranged symmetrically in contact with each coil of the magnetic field generator facing each other across the gap, and a reverse pulse current is applied to both coils. The magnetic flux is generated by the eddy current generated by the highly conductive liner, and the generated magnetic flux is focused in the cylinder of the liner, and the magnetic flux is radiated radially through the slit-like gap between both liners, A radial magnetic field with little vertical magnetic flux component can be generated in a wide space region.
By incorporating the magnetic field generator into a die press machine, a permanent magnet manufacturing apparatus capable of manufacturing a permanent magnet having excellent radial orientation characteristics can be obtained. The magnetic material that is oriented in the magnetic field direction and press-molded can be applied to all permanent magnet powders, but is particularly preferable in terms of the characteristics of the magnet from which rare earth permanent magnet powders can be obtained.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The magnetic field generator of the present invention will be described in further detail.
FIG. 1 is a schematic cross-sectional view showing an electromagnet portion of the magnetic field generator of the present invention. In the figure, a pair of coils 1a and 1b with air cores or iron cores are arranged to face each other with a gap, and a pair of cylindrical liners 2a and 2b in contact with the coils 1a and 1b have a gap. They are arranged symmetrically. A pulse current in the opposite direction is applied to the coils 1a and 1b to form a magnetic field in which the same poles face each other. The magnetic flux 3 generated by the coils 1a and 1b is focused in the cylinder by the eddy currents of the liners 2a and 2b, is regulated in the cylinder, and radiates in a wide space region through the slit-like gap between the liners 2a and 2b. To generate a radial magnetic field with a small vertical magnetic flux component.
[0012]
The first feature of the magnetic field generator of the present invention resides in that a pulse current is applied to opposing coils instead of a constant current so that the magnetic poles face each other.
Since the magnetic powder is oriented in the order of microseconds (μs) unless the friction between the powders is taken into consideration, a pulse magnetic field having a pulse width of the order of milliseconds (ms) is sufficient for orienting the magnetic powder. Further, since the energization time of the pulse current is extremely short, even when a high peak magnetic field is applied compared to the constant current, the heat generation of the coil is small. Therefore, the magnetic powder can be oriented with a relatively high peak magnetic field.
[0013]
As a pulse current generator, a pulse power source in which capacitors are arranged and discharged simultaneously by a thyristor switch can be used. The time constant of the pulse current or pulse magnetic field is determined by the capacitance of the capacitor, the inductance of the coil, the inductance and impedance of the pulse power supply. The pulse magnetic field needs to penetrate into the mold made of cemented carbide, but it is desirable not to penetrate into the liner. Therefore, the shorter the time constant, the better. As the half-cycle pulse width, a range of 0.1 to 100 ms is appropriate due to the above-mentioned restrictions. If the pulse width is shorter than 0.1 ms, it will not penetrate into the mold, and if it exceeds 100 ms, it will penetrate into the liner.
[0014]
A second feature of the present invention resides in that a pair of cylindrical liners are disposed symmetrically in contact with each coil across a gap between a pair of coils disposed opposite to each other. A gap is interposed between both liners, for example, as shown in FIG.
When a pair of coils 1a and 1b wound in reverse are energized with pulses, the generated pulse magnetic flux 3 collides with the same polarity between the coils 1a and 1b. The colliding magnetic flux spreads as shown in FIG. 2 and tries to close the magnetic flux around the opposite side, but as shown in FIG. 1, it is regulated by the liner due to the action of eddy currents generated in the highly conductive liners 2a and 2b. Thus, it is impossible to leak out of the diameter, and the magnetic flux advances through the diameter of the liners 2a and 2b. Since the gap between the liners 2a and 2b is a slit and is not affected by eddy currents, the magnetic flux 3 radiates radially through the gap and is distributed in the radial direction over a wide space area. A magnetic field is realized in a short time.
[0015]
According to the onset bright, then led electromagnet i.e. coils 1a, the magnetic flux 3 exiting from 1b to the spatial area required by liners 2a, 2b, obtained since it is caused to diverge, less radial distribution field of the vertical component of the divergence flux It is done. By adopting various shapes for the liner, the pulse magnetic flux can be narrowed or expanded, and a spatial region in which a radial magnetic field is generated can be freely set. Further, the radial magnetic flux generation space region in the axial direction can be freely set by increasing or decreasing the gap interval between the liners. Therefore, by appropriately selecting the shape of the liner without changing the coil each time according to the magnetic field region to be generated, it is possible to widely correspond to various magnetic field regions with one coil. Also, if the gap between the liners is structurally variable, the mold cavity is placed in the gap between the liners, filled with magnetic powder in the mold cavity to generate a magnetic field, and oriented. After molding, the liner spacing is increased, and the mold cavity can be filled again with magnetic powder, magnetic field orientation, and molding again to produce a longer molded body.
[0016]
As the material of the liner, a material having high electrical conductivity is preferable, and examples thereof include Al, Cu, Ag, Au, and alloys thereof. If it is possible to cool the liner part to a low temperature, the use of a superconductor for the liner enables the use of the complete diamagnetism of the Meissner effect, which requires a magnetic flux more effectively even in a static magnetic field. It can be guided to space. In this way, by attaching a highly conductive liner to the magnetic field generator and generating a pulsed magnetic field by flowing a pulse current through the coil, it is guided radially to the space where the magnetic flux is required using the action of the eddy current. It became possible to diverge.
[0017]
Further, the magnetic field generator of the present invention can be incorporated into a die press capable of powder molding to form a permanent magnet manufacturing apparatus.
Specifically, a die mold is incorporated into the slit (gap) between the upper and lower liners attached to the magnetic field generator to form a radial magnetic field orientation press molding device, generating a radial magnetic field and orienting the magnetic powder in the magnetic field direction. . That is, in the state where the die mold cavity is filled with magnetic powder, the upper punch is lowered to the die surface position and the lid is closed, the upper and lower coils are pulsed to generate a pulse magnetic field and the magnetic powder is directed in the radial magnetic field direction. It may be oriented and then press-molded.
[0018]
The magnetic powder orientation by the pulsed magnetic field of the present invention is significantly different from the normal constant current magnetic field orientation press, which eliminates the need for applying a magnetic field during press molding and further simplifies the structure as a permanent magnet manufacturing apparatus. be able to.
Since the radial orientation direction of the magnetic flux of the present invention is orthogonal to the pressing direction of press molding and is a kind of transverse magnetic field molding, even if no magnetic field is applied during molding, disorder of orientation hardly occurs in the magnetic powder. Absent.
[0019]
The permanent magnet manufacturing apparatus of the present invention can be employed for all magnetic powders, but is particularly suitable for manufacturing a radially oriented magnet by applying it to ferrite magnet powder or rare earth magnet powder.
In particular, rare earth magnets are compact and can generate high torque, and are increasingly used in surface magnet type AC servo motors and DC brushless motors in which a proportional relationship exists between current and torque.
In the case of using a high-performance magnet, a radial oriented magnet capable of skew magnetization is required because of the need to reduce the cogging torque. Therefore, the permanent magnet manufacturing apparatus of the present invention is suitably used for manufacturing rare earth magnets.
[0020]
【Example】
Next, examples of the present invention will be given.
(Example 1, Comparative Example 1)
A pair of air core coils with an inner diameter of 200 mm produced by winding copper wire square wires (5 mm x 2 mm) are placed facing each other across a 200 mm gap, and the coil side inner diameter is 200 mm and the gap side inner diameter is placed in this gap. A pair of Cu liners having a uniformly narrowed truncated conical shape of 100 mm, height 50 mm, and thickness 3 mm were inserted.
There is a 100 mm gap between both liners. Both coils were wound in opposite directions, and a pulse power source was connected in series at both ends. The pulse power supply is composed of a total of 4000 V and 5000 μF capacitors, and the electric charge stored in the capacitors is instantaneously discharged by a thyristor switch. As a result, magnetic fluxes of the same polarity collide between the coils wound in the opposite directions, and the magnetic flux coming out of the air core of the coil tries to close the magnetic flux around the opposite side, but occurs in the Cu liner. It cannot leak out of the liner due to the action of eddy current, and when it moves through the 50 mm liner, magnetic flux radiates radially from the gap between the liners.
Using the radial magnetic field generator configured as described above, the horizontal pulse magnetic field intensity at a position 70 mm in radius from the axial center position between the liners was measured, and a value of 11 kOe was obtained. The pulse width of this pulse magnetic field was 1.5 ms.
As Comparative Example 1, when the pair of Cu liners were removed and the horizontal pulse magnetic field strength was measured at the same position using the same coil, only a value of 5.2 kOe was obtained.
[0021]
(Example 2, comparative example 2)
The radial magnetic field generator of Example 1 was incorporated into a hydraulic press with a pressurizing force of 30 tons. Further, a WC mold having an inner diameter of 60 mm and an outer diameter of 100 mm was disposed between both liners, and NdFeB permanent magnet powder was filled in the mold cavity. Pulse discharge was performed at 4000 V and 5000 μF from a pulse power source, and the magnetic powder was oriented in the radial direction, and then press-molded at a pressure of 30 tons. The magnetic powder compact was sintered to form a sintered magnet, and the magnetic properties of the obtained sintered magnet were measured. As a result, Br was 12.8 kG and iHc was 16.5 kOe. As Comparative Example 2, the Cu liner was removed from the radial magnetic field generator of Example 1, and the NdFeB-based permanent magnet powder was subjected to pulsed magnetic field orientation under the same conditions using the same mold as in Example 2, and after press molding, When the sintered heat treatment was performed and the magnetic properties of the sintered body were measured, Br was 11.4 kG and iHc was 17.0 kOe. The reason why iHc of Comparative Example 2 is slightly higher is that the degree of orientation of the magnetic powder is poor.
Thus, by incorporating the magnetic field generator of the present invention into a permanent magnet manufacturing apparatus, the magnetic properties of the radially oriented magnet could be greatly improved.
[0022]
(Comparative Example 3)
In Comparative Example 1, the same procedure as in Comparative Example 1 was conducted except that a constant current was connected instead of the pulse power source. As a result, Br was 9 kG and iHc was 11 kOe.
[0023]
【The invention's effect】
The magnetic field generator of the present invention uses the action of the eddy current of the highly conductive liner attached to the opposing coil to guide the pulse magnetic flux generated by passing the pulse current through the coil to the required space. It is possible to diverge in the radial direction, and by adopting various shapes for the liner, the pulse magnetic flux can be narrowed or expanded, and the space region where the radial magnetic field is generated can be freely set. Further, the radial magnetic flux generation space region in the axial direction can be freely set by increasing or decreasing the gap distance between the liners. Therefore, by appropriately selecting the shape of the liner without changing the coil each time according to the magnetic field region to be generated, it is possible to widely correspond to various magnetic field regions with one coil.
In addition, by applying a pulse current instead of a constant current to the coil and making the magnetic poles face each other, the coil generates little heat even when a high peak magnetic field is applied, and magnetic powder is generated with a relatively high peak magnetic field. Can be oriented.
By incorporating the above magnetic field generator into a die press machine, a permanent magnet manufacturing apparatus that can produce a permanent magnet having excellent radial orientation characteristics and a desired shape is obtained, and there is no need to apply a magnetic field during press molding. Therefore, the structure is simple compared with the conventional apparatus.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an electromagnet portion of a radial magnetic field generator of the present invention.
FIG. 2 is a schematic cross-sectional view showing an electromagnet portion of a conventional radial magnetic field generator.
[Explanation of symbols]
1a, 1b ... Coil (electromagnet)
2a, 2b ... Liner 3 ... Magnetic flux

Claims (4)

In the magnetic field generating apparatus made to face each other across a gap of a pair of air core or iron core with a coil, across the void, in contact Al, Cu, Ag, Au or La Inner selected from these alloys in the coil A magnetic field generator characterized in that the magnetic poles are arranged symmetrically and configured to apply opposite pulse currents to both coils so that the same poles face each other. It said liner, a magnetic field generator according to 請 Motomeko 1 is a cylindrical shape. A permanent magnet manufacturing apparatus comprising the magnetic field generator according to claim 1 or 2 incorporated in a die press machine. 4. The permanent magnet manufacturing apparatus according to claim 3, wherein the magnetic material oriented in the magnetic field direction and subjected to press molding is rare earth permanent magnet powder.

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