JPS61285637A - Cathode structure of directly heated magnetron - Google Patents

Abstract

PURPOSE:To prevent crack and misalignment by providing 1st and 2nd end hats with a cylindrical part each, of wall thickness nearly equal to the wire diameter of a filament, and positioning both points where the cylindrical parts of the end hats and the ends of the filament are laser-welded, at opposite sides of the center axis. CONSTITUTION:Wall thickness t1 of a cylindrical part 8b of 1st end hat 8 and wall thickness t2 of a cup member 9b of 2nd end hat 9 are set to both 0.6mm which is nearly equal to the wire diameter phif of a filament 1. Centers of laser- welded points A, B are placed at distances d1 and d2 inward from the opening ends of the respective cylindrical parts, provided that two laser beam-welded points A, B are positioned at opposite sides from the center axis Y of the filament 1, distances d1, d2 are 0.1mm or over, and welded parts of the filament 1 are shadowed by respective cylindrical parts from the laser beam. When the welded parts A, B are exposed to a laser beam under such a construction, the cylindrical part 8b is melted at the welded point A to cover the end of the filament 1.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a cathode structure for a directly heated magnetron.

BACKGROUND ART The cathode structure of a directly heated magnetron used in a microwave oven, etc. is constructed, for example, as shown in FIG. first and second lead wires 3, 4 which hermetically penetrate through the bottom plate of the device, and first and second lead wires 5, 6 made of molybdenum and attached to the tops of the lead wires 3゜4. supported at both ends. The first end knot 6 is in the form of an eyelet, and is fixed to the top of the first lead wire 3 at the lower surface of the flange portion 52L, into which one end of the filament 1 is inserted into the cylindrical portion 5b.

The second entrant 6 consists of a top plate member 6a and a cup member 6b fixed to the top plate member 6a, and the top of the second lead wire 4 is fixed at the center of the top plate member 6a, and the cup member 6b is fixed to the top plate member 6a. The other end of the filament 1 is inserted into the cylindrical portion of the member 6b.

Problems to be Solved by the Invention However, when applying the laser welding method to welding the filament 1 to the first and second knots 5.6,
When welding points A and B are irradiated with a laser beam from the direction of the arrow, the laser beam directly hits the filament 1, causing crystal growth in that part of the filament 1, weakening it and causing a crack 7 as shown in Figure 2. It becomes easier. Also, since there is a slight gap between the end of the filament and the cylindrical part into which it is inserted, if the contact points M and B are biased to one side with respect to the filament center axis, the center of the filament 1 will be shifted. , which has an adverse effect on tube properties.

Therefore, it is an object of the present invention to provide a cathode structure that does not cause cracks or center deviations as described above even though laser welding is applied.

Means for Solving the Problems According to the present invention, first and second end hats supporting a helical filament made of thorium tungsten at both ends thereof are provided with a cylindrical portion having a wall thickness approximately equal to the wire diameter of the filament. At the same time, laser welding points between the cylindrical portion of both end hats and the filament end inserted into the core portion are located on both sides of the central axis of the filament, and the center of each laser welding point is is set at a position inserted from the open end of the cylindrical portion.

With this structure, the laser beam during welding selectively heats and melts the cylindrical portion of the end hat without directly irradiating the filament, thereby making it possible to prevent the ends of the filament from weakening due to the direct irradiation. In addition, since the welding points between both end hats and the filament are located on both sides of the filament central axis, it is possible to prevent the filament from shifting its center due to the welding points being biased to one side.

Embodiment In FIG. 1 showing an embodiment of the present invention, a helical filament 1 made of thorium tungsten is supported at both ends by first and second end hats 8 and 9 made of molybdenum. Unlike conventional models, the first end hat 8 is fixed to the top of the first glue wire 3 made of molybdenum on the lower surface of the flange portion 8IL, and one end of the filament 1 is inserted into the cylindrical portion 8b. It is. The second end hat 9 is made up of a top plate member 9& and a cup member 9b fixed thereto, and is fixed to the top of the second lead wire 4 made of molybdenum at the center of the top plate member 9a. The point that the other end of the filament 1 is inserted into the cylindrical portion 9b is also the same as before.

However, the wall thickness t1 of the cylindrical portion 8b of the first end hat 8 and the wall thickness t2 of the cylindrical portion of the cup member 9b in the second end hat 9 are the wire diameter φf of the filament 1, respectively.
The distance d1. is set to approximately equal to 0.6, and the distance d1. The centers of laser welding points M and B are set at positions that extend by d2. However, the two laser beam welding points M and B are located on both sides of the central axis Y of the filament 1, and the distance is d1 + d.
2 is 0.1 or more birds. Further, the welded portion of the filament 1 is located in the shadow of each cylindrical portion with respect to the laser beam.

Welding black in the assembled state as shown in Figure 1.

When the laser beam is irradiated to B, the cylindrical part 8b of the welding part melts and covers the end of the filament 1, as shown in FIG. 2, and a good welding effect is achieved without directly exposing the filament 1 to the laser beam. can be obtained. In particular, since the thickness of the cylindrical portion 8b is made approximately equal to the wire diameter of the filament 1, there is no excess or deficiency in the amount of melting in the cylindrical portion, and crystal growth occurs at the end of the filament 1. Therefore, the fear of cracks occurring due to weakening can be eliminated.

Effects of the Invention Since the present invention is configured as described above, it is possible to stably laser weld the helical filament to the first and second knots without fear of center shift or weakening.
A cathode structure with good characteristics can be obtained.

[Brief explanation of drawings]

Fig. 1 is a side sectional view of a cathode assembly according to the present invention before laser welding, Fig. 2 is a sectional view of the main parts of the same cathode assembly after laser welding, and Fig. 3 is a side sectional view of a conventional cathode assembly. ,
FIG. 4 is a sectional view of a portion of the cathode assembly. 1...Filament, 8,9... Entnot\t, 8b...Cylindrical part, A, B...
...Laser welding point. Name of agent: Patent attorney Toshio Nakao and 1 other WJ
Figure 1 Figure 2 Figure 3 α Figure 4

Claims (1)

[Claims] first and second end hats supporting a helical filament made of thorium tungsten at both ends;
The cylindrical portion has a wall thickness that is approximately equal to the wire diameter of the filament, and the laser welding point between the cylindrical portion of both end hats and the end of the filament inserted into the portion is centered on the central axis of the filament. A cathode assembly for a directly heated magnetron, characterized in that the cathode assembly is located on both sides of the cylindrical part, and the center of each laser welding point is set at a position inserted from the open end of the cylindrical part.