JPH0695490B2 - Manufacturing method of annular permanent magnet for magnetron excitation - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an annular permanent magnet provided on an outer end surface of a magnetic pole piece in order to generate a magnetic field between the pair of magnetic pole pieces. .

2. Description of the Related Art In general, a magnetron incorporated in a microwave heating device such as a microwave oven is integrally formed with a magnetic circuit member including an annular permanent magnet for generating a magnetic field between the pair of magnetic pole pieces. This will be described with reference to FIG. 3. The anode cylinder 1 of the magnetron has a large number of anode vanes 3 protruding from its inner peripheral surface toward the cathode 2, and has a mortar-shaped first and second magnetic pole piece 4. , 5 are provided at both open end portions of the anode cylinder 1 so that the small-diameter end faces face each other. And
The microwave output terminal 7 is provided on the small-diameter end portion of the eyelet-shaped first metal tube 6 sealed to the anode cylinder 1 so as to cover the first magnetic pole piece 4 with the flange portion through the ceramic ring 8. It is projected. Further, the stem 10 for leading out the cathode terminal is sealed to the small-diameter end portion of the eyelet-shaped second metal tube 9 sealed to the anode cylinder 1 so as to cover the second magnetic pole piece 5 with the flange portion. Has been done.

The first annular permanent magnet 11 provided on the outer end face of the first magnetic pole piece 4 so as to surround the first metal tube 6 of the magnetron thus configured surrounds the second metal tube 9. The second annular permanent magnet 12 provided on the outer end face of the second magnetic pole piece 5 and the frame-like yoke 13 for magnetically coupling the outer end face side magnetic poles of both permanent magnets 11, 12 with the pipe. It constitutes the external magnetic circuit. A large number of heat radiating fans 14 are attached to the outer peripheral surface of the anode cylinder 1 in multiple stages, and a choke coil and a capacitor are connected to the cathode terminal lead-out stem 10 and the cathode terminal of the stem to form an LC filter circuit. However, it is housed in the shield case 15.

The first and second annular permanent magnets 11 and 12 are so-called isotropic ferrite magnets, and are usually barium ferrite (BaFe ₁₂ O ₁₉ ) or strontium ferrite (SrF).
It is obtained by press-molding a fine powder of e ₁₂ O ₁₉ ) into a ring shape in a magnetic field, and subjecting the obtained ferrite molded product to a sintering treatment and a magnetizing treatment.

Such ferrite magnets have an outer diameter of 45 mm to 75 mm and a diameter of 15 mm to 35 mm.
It has an inner diameter of mm and a thickness of 8 mm to 20 mm, and its magnetization direction is inclined with respect to the central axis as indicated by an arrow in the figure.
This magnetization direction is determined by the crystal orientation of the ferrite molded product, and this crystal orientation is determined by the magnetic field given at the stage of the heat molding. Since the magnetization direction is inclined in the direction in which the magnetic pole pieces are closed, it is possible to generate a magnetic field having a high magnetic flux density in the action space between the first and second magnetic pole pieces.

FIG. 4 shows the main part of the pressure molding. The cylindrical lower punch 17 provided on the upper part of the pedestal 16 is a pedestal.
As the 16 and the upper punch 18 move in the direction of the arrow in the figure, they enter the center hole of the die 19 as shown in the figure. That is, the ferrite fine powder 20 on the molding surface for the top surface of the lower punch 17 is pressure-molded between the flat upper surface of the lower punch 17 and the flat lower surface of the upper punch 18, which are molding dies. A die rod 21 for molding the ferrite fine powder 20 into an annular shape projects in the center of the lower punch 17, and electromagnetic coils 22 and 23 are provided around the upper punch 18 and on the lower surface of the die 19. Has been. Both electromagnetic coils 2
2,23 is a pedestal 16 made of a magnetic material such as iron, a lower punch 1
7. A magnetic circuit is configured with the upper punch 18 and the struts 24, 25, and this magnetic circuit applies a magnetic field to the ferrite fine powder 20 under pressure molding. By making the magnetic field distribution of this magnetic field appropriate, the crystal orientation of the ferrite molded product can be made to be tilted with respect to the central axis, and the magnetization direction subsequently applied causes the magnetization direction to be tilted as described above.

However, when the crystal orientation of the isotropic ferrite magnet is tilted with respect to the central axis by such a method, the shrinkage ratio based on the difference in crystal orientation between the lower surface and the upper surface of the ferrite molded product The ferrite molded product after the sintering treatment is not the same as the one shown in FIG. 5 (a), but it is warped to the higher crystal orientation degree as shown in FIG. 5 (b). Therefore, both sides of the ferrite molded product are polished to increase the parallelism between the front and back sides and have a predetermined thickness as shown in (c) of the figure, but this requires a considerable amount of labor. Not
Waste about 15 to 20% of material. In addition, since one end face having a higher degree of crystal orientation is also scraped off, the efficiency is greatly reduced.

Means for Solving the Problems According to the present invention, the first stage of obtaining an annular ferrite molded product in which a fine ferrite powder is pressure-molded in a magnetic field and the crystal orientation is inclined with respect to the central axis, and this ferrite molding A second step of subjecting the product to a sintering treatment, and a warp in the opposite direction for canceling the warp that occurs in the ferrite molded product by passing through the second step, the upper part of the molding die in the first step. It is provided on each molding surface of the punch and the lower punch.

Function With this configuration, the deformation (reverse warpage) sufficient to offset the warpage that occurs in the ferrite molded product after the sintering process is given to the ferrite molded product before the sintering process in advance. Due to the warpage generated in the ferrite molded product by the treatment, a sintered ferrite molded product having a high flatness can be obtained, and the polishing treatment is not necessary.

Example Next, the present invention will be described with reference to the illustrated example.

1 differs from the structure shown in FIG. 4 in that the molding surface 26a at the top of the lower punch 26 has a concave spherical shape or a shape similar to this, and the bottom surface of the upper punch 27 is The molding surface 27a is curved in a convex spherical shape or a shape similar thereto, and other configurations are the same. However, the degree of warpage of both molding surfaces 26a, 27a is determined according to the degree of warpage caused by the sintering process.

According to this structure, the ferrite molded product of FIG. 2 (a) taken out from the pressure molding machine becomes the flat product of FIG. 2 (b) by undergoing the sintering process.

EFFECTS OF THE INVENTION As described above, according to the present invention, there is no need to perform double-side polishing on a ferrite molded product after sintering, and even if polishing is performed, the amount thereof can be small. Moreover, not only can the utilization rate of the material be increased, but there are no cracks or chips that are likely to occur during the polishing process, and there is no waste of thickly scraping off one end face with a high degree of orientation. The excellent effect can be obtained.

[Brief description of drawings]

FIG. 1 is a side sectional view of a main part of a pressure molding machine used in the manufacturing method of the present invention, and FIGS. 2 (a) and 2 (b) are ferrite molded products after pressure molding and after sintering. 3 is a side sectional view of the magnetron and its accessory parts, and FIG. 4 is a side sectional view of a part of a pressure molding machine used in the manufacture of conventional annular permanent magnets. 5 (a), (b), and (c) are side cross-sectional views of each ferrite molded product after pressure molding, sintering treatment, and polishing treatment when the conventional annular permanent magnet manufacturing method is applied. Is. 20 …… Fine ferrite powder, 21 …… Die rod 22,23 …… Electromagnetic coil, 26 …… Lower punch, 27 Upper punch, 26a, 27a
…… Molding surface.

Claims (1)

[Claims] 1. A ferrite fine powder is pressure-molded in a magnetic field,
The ferrite has a first step of obtaining an annular ferrite molded product whose crystal orientation is tilted with respect to the central axis, and a second step of subjecting this ferrite molded product to a sintering treatment. A warping in the opposite direction for canceling the warpage generated in the molded product is provided in each molding surface of the upper punch and the lower punch of the molding die in the first step, and the magnetron exciting annular permanent magnet of Production method.