JP3118287B2 - Magnetron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetron.
More specifically, the present invention relates to a magnetron in which discharge is prevented by improving the structure of a stem insulator from which a cathode lead is led.

[0002]

2. Description of the Related Art A cathode supporting portion of a conventional magnetron for a microwave oven, for example, has a structure as shown in FIG. That is, in FIG. 5, both ends of a filament 4 wound in a coil shape are fixed to a pair of end hats 5 and 6, respectively. Cathode leads 7, 8 made of molybdenum (Mo) or the like are provided on the end hats 5, 6.
Is fixed. These cathode leads 7 and 8 extend outside through the through holes of the stem insulator 3. On the metallized surface 9 on the outer periphery of the stem insulator 3,
The cylindrical metal container 1 to which the separately assembled anode portion (not shown) is fixed at the upper portion is brazed by silver brazing or the like. The aforementioned cathode leads 7 and 8 are connected to the stem insulator 3.
The metallized surfaces 10a, 10b are hermetically sealed with silver brazing material using the metal bonding plates 2a, 2b as a medium. An annular groove 11 is formed between the metallized surface 9 and the metallized surfaces 10a and 10b to prevent short-circuit and discharge due to brazing material or the like.

In a magnetron having such a structure, generally, a cylindrical metal container 1 integrally joined to an anode portion is set to an earth potential, whereas a cathode portion constituted by a filament 4, cathode leads 7, 8 and the like is provided to a cathode portion. It operates by applying a negative high voltage of, for example, 4 kV. Therefore, the metal joining plates 2a, 2b used for brazing the ends of the cylindrical metal container 1 and the cathode leads 7, 8 brazed to the metallized surface 9 around the stem insulator 3 to the stem insulator 3. Discharge is likely to occur in between. This is because these joints have metallized surfaces 9, 10a, and 10b, respectively, and have a rough peripheral edge, and silver brazing used for hermetic bonding grows on the peripheral edge, and countless needle-like projections 12, 13 ( (See Fig. 6)
Is formed, and it becomes a needle-shaped electrode and the interval becomes narrow.

In particular, in a microwave oven using a leakage transformer, when the power is turned on without preheating the filament 4, an unloaded voltage of 8 to 10 kV is applied to the magnetron in an initial stage in which electrons are not emitted from the filament 4, Discharge occurs in the above-mentioned hermetically sealed metallized portion, which induces a surge voltage and destroys high-voltage components. In order to solve such inconvenience, for example, Japanese Patent Application Laid-Open
As disclosed in Japanese Patent No. 8536, the metal bonding plate 2a,
A structure in which 2b is extended to the annular groove 11 of the stem insulator 3 has been proposed. FIG. 6 is an enlarged explanatory view of the structure.
FIG. 6 is an enlarged view of the metallized surfaces 9 and 10a. By projecting the metal bonding plate 2a on the upper surface of the annular groove 11, the needle-like projections 13 of the brazing material are electrically covered with a conductor. An electric field layer is formed to prevent discharge.

[0005]

However, even with the structure in which the above-described measures are taken, discharge cannot be completely prevented.
The reason is that the needle-like projections 12, 13 of the metallized surfaces 9, 10a, 10b are 0.3 mm more than the metallized surfaces 9, 10a, 10b.
This is probably because the conductor is formed in a low portion of about 0.5 mm (dimension B in FIG. 6), so that it is not possible to form a complete electric field-free layer using only a conductor extending in the same plane.

The present invention has been made in view of such circumstances, and has as its object to provide a highly reliable magnetron that can more reliably prevent discharge from occurring with a simple configuration.

[0007]

According to the present invention, there is provided a cylindrical metal container which is airtightly joined to an anode portion and forms a part of a vacuum container, and an open end of the cylindrical metal container is airtightly joined therearound. A magnetron comprising: a stem insulator; a cathode disposed on a central axis of the anode portion; and a cathode lead supporting the cathode and fixed to a central portion of the stem insulator. The joint of the cylindrical metal container and the joint of the cathode lead are formed on substantially the same plane, and a concave portion is formed between the joint of the tubular metal container and the joint of the cathode lead of the stem insulator. A groove is formed, and an electrical insulator is formed in the groove, which is lower than the joint between the cylindrical insulator of the stem insulator and the joint of the cathode lead, and from the place where the projection of the brazing material is generated. High height Wherein the protruding portion is formed.

[0008]

[0009]

Next, the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a cathode portion and a stem insulator portion according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a fixed portion thereof. In these figures, 1 to 13 indicate the same parts as in FIGS.

In this embodiment, a second concave groove 18 is formed between the metallized surface 9 which is a joint portion with the cylindrical metal container 1 and the annular first concave groove 17 via the projection 14. Further, a projecting portion is also provided between the metallized surface 10a for joining the cathode lead 7 together with the metal joining plate 2a and the first concave groove 17.
A third concave groove 19 is formed via 15. as a result,
The first groove 17, the second groove 18, and the third groove 19 form the groove 11.
Are formed, and protrusions 14 and 15 are formed in the concave groove 11.

The protruding portions 14 and 15 are formed integrally with the ceramics forming the stem insulator 3 by molding or the like, are not metallized, and are formed so that the brazing material does not adhere. ing. The height of the projections 14 and 15 is 0.2 to 0.3 mm from the metallized surfaces 9 and 10 of the stem insulator 3.
(Dimension A in FIG. 2). This is when metallizing the surface of the stem insulator 3
In order to prevent metallization on the surfaces of the protruding portions 14 and 15, consideration is given not to complicate the process. As described above, the location where the needle-like projections 12 of the brazing material due to the metallized ends are generated is 0.3 to 0.5 mm from the surface of the stem insulator 3 (dimension B in FIG. 2). Because it was found, the protruding part 14,
It is based on the fact that 15 should be formed.

With this configuration, the cylindrical metal container 1 and the cathode leads 7, 8 are brazed together with the metal bonding plates 2a, 2b, so that the brazing material is attached to the metallized end portion of the cylindrical metal container 1 at the needle-like side. Projection 12 and needle-like projection on cathode lead side
The projection 12 is completely isolated from the projections 14 and 15 and functions to suppress discharge.

As a result, without preheating the filament 4, even if a high voltage is applied between the anode and the cathode, the discharge by the needle-shaped projections based on the brazing material is cut off by the projections 14, 15 which are electrical insulators. Being prevented.

FIG. 3 is an enlarged sectional view of a groove portion according to another embodiment of the present invention. In the above-described embodiment, an example has been described in which the protrusions 14 and 15 are formed on both the joint side of the concave groove 11 with the cylindrical metal container 1 and the joint side with the cathode leads 7 and 8. In the example, one protrusion 14 is provided in the middle of the groove 11.
Is formed. In this example, when the needle-shaped protrusions 12 extend from both sides, it is necessary to provide pressure resistance only with the protrusions 14, so that the thickness of the protrusions 14 is increased or the height is increased as much as possible. You need to earn more distance.

In the embodiment described above, the concave groove is described as an annular example. However, as shown in a plan view of the stem insulator, the cathode leads 7 and 8 are concentric with the stem insulator 3. Therefore, the distance (C in FIG. 4) between the metallized surfaces 10a and 10b for the metal bonding plates 2a and 2b for the cathode leads 7 and 8 and the metallized surface 9 for the cylindrical metal container 1 is not constant. Since there is no danger of short-circuiting or electric discharge at the place where the interval is large, the concave groove and the protrusion of the present invention need not be formed in an annular shape, but it is sufficient to form at least a portion where the interval C is small.

Further, in the above-described embodiment, the example has been described in which the protrusions 14 and 15 are integrally formed of ceramics which is the material of the stem insulator 3. However, the ceramics need not be ceramics but may be an electrical insulator. A protruding portion can be formed in the groove 11 from a resin or the like.

[0017]

As described above, according to the present invention, there is provided a stem insulator which electrically insulates and tightly joins a cylindrical metal container joined to an anode portion and a cathode lead constituting a cathode portion. Since a groove is formed between the two joints to prevent short-circuiting or short-circuiting due to the brazing material during brazing and to prevent discharge due to proximity, a protruding portion is further formed in the groove, so that the metallized end is formed. Even if the needle-like projections of the brazing material based on the rough surface are formed in the concave grooves, they are isolated by the projections, and the discharge can be suppressed even when a high voltage is applied.

As a result, even if the cathode is not preheated and a high voltage is applied, discharge can be prevented, and generation of a surge voltage due to the discharge at the time of starting the magnetron is completely prevented.
Along with protecting high-voltage components, a highly reliable and long-lasting magnetron can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a cathode portion and a stem insulator portion of a magnetron according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is an enlarged cross-sectional explanatory view of a groove portion according to another embodiment of the present invention.

FIG. 4 is an explanatory plan view of a stem insulator.

FIG. 5 is an explanatory sectional view of an example of a cathode section and a stem insulator section of a conventional magnetron.

FIG. 6 is an explanatory cross-sectional view showing another example of a conventional joining of a cathode portion and a stem insulator portion.

[Explanation of symbols]

 Reference Signs List 1 cylindrical metal container 3 stem insulator 4 filament 7, 8 cathode lead 11 concave groove 14, 15 protrusion

Claims (1)

(57) [Claims] 1. A cylindrical metal container hermetically joined to an anode portion and constituting a part of a vacuum container, a stem insulator having an opening end portion of the cylindrical metal container hermetically joined therearound, and the anode portion A magnetron comprising: a cathode disposed on a central axis of a cathode insulator; and a cathode lead supporting the cathode and fixed to a central portion of the stem insulator .
Joint of the tubular metal container of the tem insulator and the cathode
The joint portion of the lead is formed on substantially the same plane, and a groove is formed between the joint portion of the cylindrical metal container of the stem insulator and the joint portion of the cathode lead. An insulator, the tubular metal container of the stem insulator;
Lower than the junction between the heater and the cathode lead, and
A magnetron, characterized in that a protruding portion having a height higher than a position where the protruding portion of the brazing material occurs is formed.