JPH0410333A - Cathode structural body of magnetron - Google Patents

Abstract

PURPOSE:To prevent the stress-breaking of a sealing part owing to stress by carrying out barring process to a bottom plane penetrating hole in the bottom plane of a stem for a lead wire in the side to be connected electrically to the bottom plane of a stem choke, to project it toward the stem side, butting the tip part of the barring part to a relay terminal plate, and soldering them with a hard solder to support the stem choke. CONSTITUTION:A lead 1 in a high melting point metal tube which supports a cathode filament is intermediately connected to an outer lead 3 through a terminal plate 2 soldered with a metallized part of a plane of a stem insulator 5 in the vacuum side of the tube by a hard solder and here the tube is sealed in vacuum and air-tight condition. Meanwhile, to suppress leakage of microwaves transmitted by the lead 1, the stem choke 4 is connected with only one of the lead 1 in the tube, and a barring part 4a is so formed in a hole of the bottom plane into which the lead 1 penetrates as to project toward the stem side and its tip part and the terminal plate 2 are joined together. Consequently, the relay terminal plate and the sealing part of the stem insulator 5 do not receive thermal stress from the stem choke 4.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention uses materials such as molybdenum with a high melting point for the inside of the tube and inexpensive iron for the outside of the tube as materials for the cathode lead wire, and the cathode stem M! , metallize the inside surface of the tube of the edge body, and braze and secure the relay terminal plate of the dissimilar material part of the lead wire here, and furthermore, prevent the leakage propagation of the microwave fundamental wave on the inside of the tube of the cathode stem. The depth is 1/4 to suppress
The present invention relates to a magnetron cathode assembly in which a bottomed cylindrical stem choke of wavelength is attached so as not to apply thermal stress to the terminal plate fixing surface of the stem insulator.

[Prior Art] In recent years, microwave ovens have been widely used that use a magnetron to oscillate microwaves and use the power to dielectrically heat food, but in the case of household electronics, they not only have good performance but There is a strong need to keep the price as low as possible. For this reason, the lead wires that support the magnetron's cathode and conduct heating current were initially made entirely of molybdenum wire, but now molybdenum is used only on the vacuum side inside the tube, where the temperature is high, and on the atmosphere side outside the tube. Using inexpensive wires or pipes such as iron, these leads made of different materials are metallized on the vacuum side of the tube inside the cathode stem insulator, and the relay terminal board or flanged pipe is soldered here. It is being done to connect via.

Figure 2 is a diagram showing an example in which leads made of different materials are connected via a relay terminal board. In the figure, 1 is an in-pipe lead made of molybdenum, etc., 2 is a relay terminal board, and 3 is a relay terminal board. An external lead made of iron wire, 5 a cathode stem insulator made of alumina ceramics, etc., 6 an upper part connected to an anode part (not shown), and a lower end butt-jointed to the periphery of the stem insulator 5 with hard solder. The cross-section of the metal sealed cylinder shown in Fig. The terminal plate 2 is hard-soldered to a metallized portion of the stem insulator 5 on the vacuum side of the tube.

However, the relay terminal board 2 is usually made of so-called sealing metal furni (iron-nickel alloy) to match the low coefficient of thermal expansion of the ceramic stem insulator 5, but there is a slight difference in the coefficient of thermal expansion. Therefore, the area of the joint surface of the stem insulator 5 with the relay terminal plate 2 (which is metalized) is kept to the minimum necessary, and grooves are carved in the areas not to be metalized to make it lower. In addition, 5a is the above-mentioned groove carved in the surface of the stem II @ edge body 5 on the vacuum side in the tube in order to increase the creepage distance and improve the withstand voltage characteristics.
As the use of many types of electronic devices has become widespread, legal restrictions have gradually been put in place to prevent microwaves from leaking and propagating from the magnetron to the power source through the lead wire that supplies heating power to the magnetron's cathode. Currently, in order to suppress the fundamental wave of microwaves, a cylindrical stem choke with a bottom and a depth of 1/4 wavelength is provided inside the cathode stem.

An example of the structure of a conventional magnetron cathode structure using a stem choke is disclosed in JP-A-63-216243, but as shown in FIG. 3, the stem choke 4 is a cylinder with a bottom that opens toward the cathode. A cup-shaped groove part 7 is further formed on the bottom surface of the stem choke 4 around the penetration part of the side beam 1 which is electrically connected to and penetrates the bottom surface. In order to connect the above-mentioned dissimilar leads to the bottom of the stem M! , to the flange surface 3a of a flanged pipe that is fitted into a through hole of the S body 5 and whose flange is vacuum-tightly brazed to the vacuum-inverted surface of the stem insulator around the through hole.

The surface is fixed and supported with hard solder.

In Fig. 3, 1 is an inner pipe lead made of molybdenum, etc., 3 is an external lead made of iron pipe, and 3a is a lead of a different type connected inside, and the outside is vacuum-tightly connected to the stem insulator. 4 is a stem choke, 5 is a stem insulator made of alumina ceramics, etc., the upper end is connected to an anode part (not shown), and the lower end is connected to the peripheral edge of the stem insulator. It is a metal sealed cylinder that is butt-jointed with solder.

Figure 4 is a cross-sectional view of the main parts of a conventional example in which different types of leads are connected using a terminal board and a stem choke is attached. The lead-out lead 4 is a stem choke, and the periphery of the through-hole connected to one of the glues on the bottom of the stem choke 4 protrudes toward the stem side, and is surface-brazed to the terminal plate 2 here.

[Problems to be Solved by the Invention] However, the above method of supporting the stem choke was designed to increase the area of the support part in order to stably support the stem choke, but it , and the heat and thermal expansion of the stem choke, which becomes a parallel resonant circuit and is heated to a high temperature due to the flow of a large current, passes through the hard soldering part of the large-area surface mounting, and in the conventional example shown in Figure 3, The heat and thermal expansion of the stem choke is transmitted to the wide flange of the flanged cylinder for connecting dissimilar leads, and in the conventional example shown in Figure 4, the heat and thermal expansion of the stem choke is transmitted to the relay terminal plate, causing stress concentration on the stem made of alumina ceramics, etc. The problem arose of cracking the insulation.

Note that in the past, flanged cylinders and relay terminal plates that were directly brazed to the stem insulator were made of iron-nickel alloys such as Fur 2, which had a relatively low coefficient of expansion, but materials with large areas were used. Stem chokes have no choice but to be made from steel plates in order to be made inexpensively.

When a stem choke made of a steel plate becomes hot, it thermally expands significantly, so the large elongation of the stem insulator directly applies mechanical force to the flange and terminal plate via the wide fixed area.

As described above, the present invention is designed to prevent the flanged pipe and relay terminal board for relaying dissimilar lead connections from becoming hot due to the influence of the stem choke, and being pulled by the large elongation of the stem choke, causing the ceramic surface of the stem insulator to It is an object of the present invention to provide a cathode structure for a magnetron that can prevent the occurrence of cracks.

[Means to solve the problem] In order to achieve the above object, the present invention.

The surface of the vacuum side inside the tube of the cathode stem insulator that supports the cathode and supports the cathode via the lead wire through which the heating current is applied is metalized, and different materials are applied here to the vacuum side inside the tube and the atmosphere side outside the tube. In a magnetron, the parts of different materials of the lead wires used are connected and fixed in separate locations, and the relay terminal plate is brazed to support the cathode and seal the vacuum. A bottomed cylindrical stem choke for suppressing microwave leakage is provided, which opens toward the cathode, and a lead wire passes through its bottom surface, and a bottom through hole for the stool lead wire is electrically connected to the bottom surface. A burring process was applied to the burring part to protrude toward the stem side, and the tip of the burring part and the above-mentioned relay terminal plate were butted together and hard soldered to support the stem choke.

[Function] Since the tips of the thin burring portions are only butt-jointed, the relay terminal board is not subjected to thermal stress from the stem choke. Further, when the stem choke is connected to the cathode lead, the influence of thermal stress on the terminal board is almost negligible. Note that connecting different types of leads using a relay terminal board is more reliable and easier than connecting them inside a flanged pipe.

[Embodiment Fig. 1(a) is a vertical sectional view of the main part of an embodiment of the present invention.
Figure (b) is a cross-sectional view taken along the line ○-O'' in Figure 1 (a).The tube lead 1 made of a high melting point metal such as molybdenum that supports the cathode filament is connected to the tube inside the stem insulator 5. Terminal board 2 hard-soldered to the metalized part on the side surface
It is relay-connected to the external lead-out lead 3 made of iron through the pipe, and at the same time, the inside of the pipe is vacuum-tightly sealed here. On the other hand, the stem choke 4 for suppressing the leakage of the fundamental wave in the 2450 MHz band through the lead 1 is connected to the pipe lead l.
In order to make this connection, insert a burring part of 0.3 to 0.5 mm into the hole through which the lead 1 passes through the bottom of the stem choke 4 so that it protrudes toward the stem side. 4a is provided, and its tip portion is butted and joined to the terminal plate 2.

The joining means is a silver solder connection at the butt portion, but if the inner diameter of the burring part 4a and the diameter of the lead 1 are made to fit lightly, when the silver solder melts, the lead and the burring will separate due to capillary action. Silver solder accumulates between the inner diameter surfaces, and the lead 1 and stem choke 4 are electrically connected.

[Effects of the Invention] As explained above, according to the present invention, the stem choke is butt-jointed to the terminal board, and the burring part of the stem choke and the lead are connected with silver solder. Since thermal stress applied to the sealed portion between the terminal plate and the edge of the stem M can be reduced, it is possible to prevent stress failure of the sealed portion due to thermal stress.

[Brief explanation of drawings]

FIG. 1(a) is a longitudinal cross-sectional view of the main part of one embodiment of the present invention.
Figure (b) is a sectional view taken along the line 0-o' in Figure 1 (a), Figure 2 is a diagram showing a conventional example in which leads of different materials are connected via a relay terminal plate, and Figure 3. Figure 4 shows a conventional example in which leads of different materials are connected inside a flanged pipe and a stem choke is attached. Figure 4 is a conventional example in which leads of different materials are connected with a relay terminal board and a stem choke is attached. FIG. 1...Inner pipe lead, 2...Terminal board, 3...External impulse lead, 3a...Flanged pipe,
4... Stem choke, 4a... Burring part,
5... Stem insulator, 5a... Groove carved on the vacuum side surface of the stem insulator, 6... Metal sealing cylinder, 7... Cup around the lead penetration part on the bottom of the stem choke. shaped protrusion.

Claims (1)

[Claims] 1. Metalize the surface of the vacuum side inside the tube of the cathode stem insulator that supports the cathode and supports the cathode via the lead wire through which the heating current is applied, so that different parts are formed on the vacuum side inside the tube and the atmosphere side outside the tube. The different material parts of the lead wire are connected and fixed to different parts, and the relay terminal plate is brazed.
In a magnetron with cathode support and vacuum sealing, a cylinder surrounding two lead wires opens toward the cathode, and the lead wires penetrate through the bottom of the cylinder to suppress microwave leakage. A stem yoke is provided for the stem yoke, and the bottom through hole of the electrically connected lead wire is burred to protrude toward the stem side, and the tip of the burred portion is butted against the terminal plate and hard soldered to form the stem yoke. A magnetron cathode structure characterized in that it supports a magnetron cathode structure.