JPH0668954B2 - Cathode structure for magnetron - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cathode assembly of a direct heating magnetron.

2. Description of the Related Art A cathode assembly of a direct heating type magnetron used in a microwave oven is constructed as shown in FIG. 2, for example, and a spiral filament 1 made of thorium tungsten is a bottom plate of a cup-shaped stem insulator 2 made of ceramic. First and second lead wires 3 and 4 that penetrate through the airtight portion, and first and second lead wires attached to the tip portions of both lead wires 3 and 4.
Supported by the end hats 5, 6.

The first end hat 5 has an eyelet shape and is fixed to the tip of the first lead wire 3 on the lower surface of the flange portion 5a, and accommodates one end of the filament 1 in the tubular portion 5b. The second end hat 6 is a top plate member 6a.
And a cup member 6b fixed to this,
Is fixed to the tip of the lead wire 4 at the central portion of the top plate member 6a, and the filament 1 is attached to the tubular portion of the cup member 6b.
Accommodates the other end of the.

Problems to be Solved by the Invention In the manufacture of the cathode structure constructed as described above, the first
When the welding points A and B are irradiated with a laser beam in the direction of the arrow in order to weld the second end hats 5 and 6 and the filament 1 by the laser welding method, the laser beam directly hits the filament 1 and the filament 1 concerned. Crystal growth occurs in the portion and weakens to easily cause cracks 7 as shown in FIG. Further, there is also a problem that the metal vapor or the metal fragments generated by welding adheres to the filament surface as foreign matter and deteriorates the electron emission function.

Furthermore, since the first and second end hats 5 and 6 are obtained by press-molding a thin molybdenum plate, the heat capacity is small, the welding condition setting width is small, and delicate adjustment is required. In addition, the cathode temperature during operation of the magnetron reaches about 2000 ° K, and ignition and extinguishing are repeated frequently, so that the tubular parts 5b and the cup member 6b of both end hats 5 and 6 are thermally deformed. There is also a problem that the relative position with respect to the anode vane 8 fluctuates, which adversely affects the tube characteristics.

Means for Solving the Problems The present invention has been made to solve the above-mentioned conventional problems, and according to the present invention, at least one of the first and second end hats facing each other has a facing surface. The central region has a recess for accommodating the end of the spiral filament, and the peripheral region of the facing surface has an annular groove surrounding the recess. Then, the filament and the cylindrical partition wall located between the recess and the groove are welded.

When configured in this way, since the partition wall portion covers the filament end portion, even if a laser welding method is applied to the welding, the laser beam is less likely to directly hit the filament end portion, and the above-mentioned cracks It is possible to reduce the generation and the deterioration of the electron emission function. Further, the overall heat capacity of the end hat becomes relatively large, and even if the cylindrical partition wall undergoes thermal deformation, the outer peripheral wall portion does not overhang to the anode side, and stable characteristics can be obtained. .

Example In FIG. 1 showing an example of the present invention, the first and second end hats 9 and 10 for supporting both ends of the spiral filament 1 made of thorium tungsten are both made of a high melting point metal such as molybdenum. It is a disk-shaped one, and has circular recesses 9a and 10a in the central area of the facing surfaces, and annular recessed grooves 9b and 10b surrounding the recesses 9a and 10a in the peripheral area of the facing surface. Have respectively. The ends of the filament 1 are housed in the recesses 9a and 10a, and the recesses 9a and 10a and the recess grooves 9b and 10b are accommodated.
Cylindrical partition walls 9c and 10c located between and are welded to both ends of the filament 1 by applying a laser welding method.

Irradiation of the laser beam and supply of the reducing gas at the time of laser welding are performed from the direction shown by the arrow in the figure, so that the chamfered inclined surface 9d, on the outer peripheral surface side of the projecting end of the cylindrical partition 9c, 10c. 10d is provided and the annular groove 9b,
The welding efficiency is improved by inclining the outer peripheral surfaces 9e, 10e of 10b in a direction in which the outlet side of the concave groove has a large diameter. The end hats 9 and 10 having such a shape are
It can be obtained by a powder sintering method. Further, the irradiation of the laser beam does not have to be performed over the entire circumference of the end hat, and may be performed at one place. Further, an arc welding method or the like may be applied instead of the laser welding method. Furthermore, one of the first and second end hats 9 and 10 may have a conventional shape.

EFFECTS OF THE INVENTION Since the present invention is configured as described above, the spiral filament can be stably welded to the end hat without causing weakening or adhesion of foreign matter, and even if thermal deformation occurs in the welded portion. The advantage is that the tube characteristics can be stabilized without changing the relative distance between the end hat and the anode.

[Brief description of drawings]

FIG. 1 is a side sectional view of a cathode assembly for a magnetron according to the present invention, FIG. 2 is a side sectional view of a conventional cathode assembly for a magnetron, and FIG. 3 is an example of a crack generated in a filament of the conventional cathode assembly. FIG. 9 and 10 ... end hat, 9a and 10a ... recess, 9
b, 10b ... Recessed groove, 9c, 10c ... Partition part.

Claims (1)

[Claims] 1. At least one of a first end hat and a second end hat provided at both ends of a spiral filament made of thorium-tungsten has a recess for accommodating the end of the filament in a central region of opposite faces. Along with
An annular groove surrounding the recess is provided in a peripheral region of the facing surfaces, and a cylindrical partition wall portion located between the recess and the groove is welded to the filament. A cathode assembly for a magnetron.