JPS6328514Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement of a magnetron for a microwave oven.

Recently, magnetrons that use ferrite magnets as permanent magnets are being put into practical use.This type of magnetron has a pair of pole pieces attached to both ends of an anode cylinder, and a pair of pole pieces arranged coaxially on these pole pieces. A pair of ferrite magnets and a ferromagnetic yoke connecting these magnets are magnetically coupled.

However, in such magnetrons, the thermal demagnetization characteristic of ferrite magnets is approximately 0.2%/℃.
Since there is thermal demagnetization of about 10%, there is a drawback that the anode voltage (bm) decreases by about 10%. Therefore, in order to compensate for the temperature characteristics of a magnetic circuit using ferrite magnets, it has been proposed to arrange a magnetic shunt ring around the outer or inner circumference of the magnet to change the leakage magnetic flux. Since then, the leakage magnetic flux is not so large, and there is a drawback that the volume of the magnetic shunt steel ring becomes large in order to perform temperature compensation. It has also been proposed that the anode cylinder itself be made of magnetic shunt steel, but this has the disadvantage that it is difficult to obtain the necessary magnetic field in the working space.

This invention has been made in view of the above circumstances, and aims to provide a magnetron which eliminates the drawbacks of the conventional magnetron and also provides sufficient temperature compensation for the ferrite magnet.

Hereinafter, embodiments of this invention will be described in detail with reference to the drawings. The magnetron of this invention is constructed as shown in FIGS. 1 and 2, and a magnetron oscillating section main body 1 has an anode cylinder 2 containing a pane and a cathode, a cathode stem 3, and an output section 4. A pair of annular ferrite magnets 5 and 6 are arranged on both sides of the anode cylinder 2 in the axial direction so as to coaxially surround a part of the cathode stem 3 and the output part 4, respectively, and a magnetic flux concentration plate They are magnetically connected via 7 and 8. Furthermore, frame-shaped yokes 9 and 10 are arranged to surround the anode cylinder 2, magnetic flux concentration magnetic plates 7 and 8, and magnets 5 and 6, and the screws 1
1 and 12, and are magnetically coupled in contact with the outer magnetic pole surfaces of magnets 5 and 6, respectively. A vertically blown radiator 21 consisting of a plurality of cooling fins is fixed to the outer periphery of the anode cylinder 2 . A space S without a radiator fin is formed in a portion of the yokes 9, 10 that is blocked from the road by the cooling air, particularly by the upper plate portion 9a. Further, a filter consisting of a choke coil 22 and a capacitor 23 is connected to the cathode stem 3, and a shield box 24 is disposed to cover the filter and the cathode stem 3. In addition, the reference numeral 25 in the figure is an insulating cylinder, 2
6 is a cover for wind guidance, 27 is a gasket, 28,
29 is a mounting screw. Cooling air is introduced into the cover 26 from above as indicated by an arrow f, and is guided to the radiator 21.

Therefore, in the space S on both sides that is blocked by the upper plate part 9a of the yoke and has no radiator fin, a ferromagnetic material having a property that the magnetic flux decreases as the temperature rises, that is, the rectangular magnetic shunt steel plate 1 shown in FIG.
3 and 14 are arranged parallel to the axial direction between the two magnets 5 and 6 and near the outer periphery on both sides of the anode cylinder 2. These magnetic shunt steel plates have metal support pieces 15, 16 and rivets 17, 18, 1, respectively.
It is thermally supported by the yoke 9 by 9 and 20. In addition, magnetic shunt steel has a temperature range from room temperature to approximately 400℃.
It is a high magnetic permeability material whose magnetic permeability decreases as the temperature rises.

As described above, the magnetron of this invention has a space inside the yoke that is in contact with and surrounds the ferrite magnet, which is blocked from the cooling air path by the yoke upper plate and has no vertically blown radiator. A plate-shaped magnetic shunt steel plate is positioned near the anode cylinder in parallel with the axis, and is thermally supported on the inner wall of the yoke by a metal support piece. As a result, almost no cooling air enters the space where the magnetic shunt steel plate is placed, and therefore, regardless of the strength of the cooling air, the magnetic shunt steel plate receives radiant heat from the anode cylinder and passes through the yoke and metal support piece. The temperature changes relatively well following the temperature change of the ferrite magnet due to the heat conducted by the ferrite magnet. Therefore, the magnetic permeability of the magnetic shunt steel plate changes, and the magnetic flux density supplied to the anode cylinder becomes constant. In this way, the vertical blow type magnetron using ferrite magnets can sufficiently compensate for the temperature characteristics of the magnetic circuit. The temperature compensation value can be arbitrarily selected depending on the position and size of the magnetic shunt steel plate, and a relatively small volume of magnetic shunt steel is sufficient. For example output
Compensating magnetic field with 600W microwave magnetron
The amount of magnetic shunt steel required for 100G (equivalent to 250V with EBM change) is 20g or less.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a magnetron according to an embodiment of this invention, and FIG. 2 is a perspective view showing a magnetic shunt steel plate used in the magnetron of FIG. 1. 2...Anode cylinder, 5,6...Ferrite permanent magnet, 9,10...Yoke, 13,14...Magnetic shunt steel plate, 15,16...Metal support piece, 21...Radiator, S...Radiator No space.

Claims (1)

[Scope of utility model registration request] In a magnetron, a ferrite permanent magnet is arranged on both sides of an anode cylinder in the axial direction, a vertically blown radiator is attached to the outer periphery of the anode cylinder, and a frame-shaped yoke is provided to connect both the magnets. A space without the vertical blow type radiator is formed inside, and a magnetic shunt steel plate having a characteristic that magnetic permeability decreases as the temperature rises is placed in the space without the radiator, the longitudinal direction of which is parallel to the axial direction of the anode cylinder. A magnetron characterized in that the magnetron is disposed so as to be thermally supported by a metal support piece on the inner wall of the yoke.