Abstract:
A cathode structure of a magnetron which is used for microwave ovens, industrial microwave heating, and medical purposes is disclosed. One of two leads of the cathode structure of the magnetron, that is, one of a center lead and a side lead is tightly fitted into the spacer, and a metal fixing material is poured into the fitting portion and is fixed thereto. A hole of the spacer for inserting the other of the two leads has looseness with respect to the other of the two leads. The friction between the other of the two leads and the spacer is reduced, and even when the leads are made thin, the strength of the cathode structure is not reduced, and the production of extraneous sounds can be suppressed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a cathode structure of a magnetron for microwave ovens, industrial microwave heating, and medical use. 
     2. Description of the Prior Art 
     FIG. 1A shows a longitudinal sectional view of a tube main body of a magnetron used generally in microwave ovens and the like. In FIG. 1A, reference numeral 1 designates a cathode for emitting electrons, 2 designates an anode having cavity resonators formed therein, and there are provided with magnetic pole pieces 3, 4 for concentrating magnetic line of force applied from the outside of the tube main body into an operating space formed by the cathode 1 and the anode 2. Sealing cylinders 5, 6 abut respectively against opposite ends of a cylindrical portion of the anode 2 to enclose the magnetic poles 3, 4. Further, a ceramic member serving as a sealing member supports the cathode 1, and a stem ceramic 8 is joined with the sealing cylinder 5 together with a cathode terminal 7 which supplies a cathode current. And an exhaust pipe support 11 holding an exhaust pipe 10 enclosing an antenna 9 extending from a specific vane of the anode 2 is joined with an antenna ceramic 12 serving as a radiation window of the generated microwaves, and the antenna ceramic 12 is in turn joined with the sealing cylinder 6. 
     FIG. 1B is a longitudinal sectional view of the prior art cathode structure of the magnetron shown in FIG. 1A. 
     In FIG. 1B, a filament 22 of a spiral shape made of Th-W (thoriated tungsten) constituting the cathode 1 is supported and fixed at its opposite ends respectively to an upper end shield 23 and a lower end shield 24. The upper end shield 23 is secured to a center lead 26, and the lower end shield 24 is secured to a side lead 25, and these leads 25, 26 are respectively inserted into holes 27a, 27a of an insulating ceramic 27 to pass therethrough. Extending ends of the leads 25, 26 are secured air tightly to the cathode terminal 7 made of a metal fixed to a metallized portion formed at an outer end of the ceramic 27. The sealing cylinder 5 made of a metal has one end secured air tightly to the insulating ceramic 27, and the other end of the sealing cylinder 5 is fixed to the anode 2 (FIG. 1A) to mechanically hold the magnetron and to shield from the atmosphere. The reference numeral 28 designates a spacer made of ceramic, and FIGS. 1C and 1D are respectively a plane view and a longitudinal sectional view. In FIGS. 1C and 1D, the spacer 28 has two spacer holes 28a and 28b, and the side lead 25 is inserted into the spacer hole 28a and the center lead 26 is inserted into the spacer hold 28b to suppress the movements of both leads 25, 26 and to reinforce the securing of both leads 25, 26. 
     Such a cathode structure of a magnetron is disclosed, for example in JP-A-54-109364 (Japanese Patent Laid-Open Publication No. 54-109364). 
     Recently, as the microwave ovens are widely used, inexpensive, small sized, and light magnetrons have been needed. In the cathode structure of the magnetron, as shown in FIGS. 1A and 1B, two leads 25, 26 of expensive molybdenum bars have been used as a support of the cathode structure. 
     As a result, when the leads are made thin to save the material, the vibration-resistant property and the high-impact property of the cathode will be degraded. Furthermore, in order to increase the mechanical strength, two leads 25, 26 are inserted into the spacer 28, and thus, when the thermal expansion of the leads 25, 26 occurs, the leads 25, 26 and the spacer 28 move under frictional resistance relative to each other, and extraneous sounds have been produced. 
     In other words, in the prior art structure shown in FIGS. 1B, 1C and 1D, the following drawbacks have been involved. 
     (1) Since the spacer is permitted to rotate relative to the leads, the degree of freedom of movement of the leads is considerably large. 
     (2) When the looseness between the spacer hole and the leads is made small, the breakdown strength of the cathode against vibrations is increased, however, the extraneous sounds are easily produced. 
     (3) The spacer 28 is inclined also in the axial direction about a supporting point, that is, a metal sleeve 29 which is a stopper. Thus, even when the looseness is made large, the frictional resistance between the spacer and the leads is not prevented, and the extraneous sounds are produced. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a cathode structure of a magnetron in which the strength of the cathode structure is not decreased even when the leads are made thin, and in which the production of extraneous sounds due to the movement of the spacer and the leads under the frictional resistance is prevented. 
     In the present invention, in order to achieve the aforementioned object, one of the two leads of the cathode structure of the magnetron is fitted into the spacer tightly, and a metal fixing material such as a metal solder or the like is poured into the fitting portion to be made secured thereto thereby to inhibit the movement of the lead relative to the spacer, and the other of the holes of the spacer is made to have looseness with respect to the other lead. 
     As described above, in fitting the two leads into the spacer, one lead is relatively secured to the spacer, and the other lead is fitted with large looseness into the spacer. As a result, it is possible to reduce the friction, the strength of the cathode is not decreased even when the leads are made thin, and it is possible to suppress the production of the extraneous sounds. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention will now be described in conjunction with the accompanying drawings, in which: 
     FIG. 1A longitudinal sectional view of a prior art magnetron tube main body; 
     FIG. 1B is a longitudinal sectional view of the cathode structure in FIG. 1A; 
     FIGS. 1C and 1D are respectively a plane view and longitudinal sectional view of the prior art spacer used in the structure of FIG. 1B; 
     FIGS. 2A and 2B are respectively a plane view and longitudinal sectional view of a spacer portion of a first embodiment of the present invention; 
     FIGS. 3A and 3B are respectively a plane view and longitudinal sectional view of a spacer portion of a second embodiment of the present invention; 
     FIGS. 3C and 3D are , respectively, a plane view and longitudinal sectional view of a variation of the second embodiment 
     FIGS. 4A and 4B are respectively plane view and longitudinal sectional view of a spacer portion of a third embodiment of the present invention; 
     FIGS. 5A and 5B are respectively a plane and longitudinal sectional view of a spacer portion of a fourth embodiment of the present invention; 
     FIGS. 6A and 6B respectively a plane view and longitudinal sectional view of a spacer portion of a fifth embodiment the present invention; 
     FIG. 7 is a sectional view of an assembly of a principal part of a, cathode structure in accordance with the present invention 
     FIGS. 8A and 8B respectively a plane view and longitudinal sectional view of a spacer portion of a sixth embodiment of the present invention; 
     FIGS. 9A and 9B are respectively a plane view and longitudinal sectional view of a spacer portion of a seventh embodiment of the present invention; 
     FIGS. 10A and 10B are respectively a plane view and longitudinal sectional view of an eighth embodiment of the present invention; and 
     FIGS. 11A and 11B respectively a plane view and longitudinal sectional view of a spacer portion in which positional relationships of the two leads in FIGS. 2A and 2B are reversed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a cathode structure of a magnetron in accordance with the present invention will be described in detail by way of embodiments. 
     FIGS. 2A and 2B are a plane view and longitudinal sectional view of a cathode structure of a magnetron according to the present invention. 
     In FIGS. 2A and 2B, the fitting of one of the two leads, that is, a side lead 25 into a spacer hole 28a is made to have relatively small looseness enough to strongly tighten the side lead 25, and a metal fixing material 31 including a metal solder material, or a pasty metal powder and the like is poured into or spread on the fitting portion, and it is fixed or sintered. The other spacer hole 28b is made to have a large looseness l&#39; with respect to a diameter of the other lead, that is, a center lead 26, for example, by setting the looseness, l&#39;=0.3-1.0 mm or so, extraneous sounds are not produced. 
     FIGS. 3A and 3B are a plane view and longitudinal sectional view of a spacer portion of a second embodiment of the cathode structure of the magnetron according to the present invention. 
     In FIGS. 3A and 3B, a spacer hole 28c is formed in a polygon shape (or polygon), and a minimum inner diameter of the spacer hole 28c has small looseness l&#39;, for example, l&#39;=0.05-0.15 mm or so with respect to a diameter of a side lead 25. FIGS. 3C and 3D show a spacer hole 28K formed in a rectangular shape. When such a spacer is assembled in the cathode structure shown in FIG. 1B, advantages are obtained including; 
      1○  since the side lead 25 is fitted into the spacer 28 tightly, the inclination of the spacer 28 in the axial direction is small. In addition, since the center lead 26 is fitted into the spacer 28 very loosely, even when the center lead 26 and the spacer 28 move relative to each other under frictional resistance due to thermal expansion, a chance of producing extraneous sounds is very rare, and 
      2○  due to the tight fitting of the side lead 25 into the spacer 28, a relative displacement of the two leads is suppressed, and the strength and a vibration-resistant property are increased. 
     FIGS. 4A and 4B are a plane view and longitudinal sectional view of a spacer of a third embodiment, and FIGS. 5A and 5B are a plane view and longitudinal sectional view of a spacer of a cathode structure of magnetron of a fourth embodiment of the present invention. 
     In FIGS. 4A and 4B, a recess portion 28d is formed in a part of the spacer 28 adjacent to a spacer hole 28a in the lengthwise direction so that the recess portion 28d is connected to the spacer hole 28a at one end thereof. A width of the recess portion 28d is substantially equal to the diameter of the spacer hole 28a. 
     In contrast in FIGS. 5A and 5B, a recess portion 28e is formed in a part of the spacer 28 adjacent to a spacer hole 28a in a direction at right angles to the lengthwise direction so that the recess portion 28e is connected to a spacer hole 28a. Also in this case, a width of the recess portion 28e is equal to the diameter of the space hole 28a. These recess portions 28d and 28e limit the coating area of a metal fixing material 31, and easily prevent the electrical short-circuit between the leads. 
     FIGS. 6A and 6B are a plane view and longitudinal sectional view of a spacer portion of a fifth embodiment of the present invention, in which a recess portion 28f is formed in the upper surface of the spacer 28 so that one side of the recess portion 28f passes through the center of a spacer hole 28a in a direction at right angles to the lengthwise direction. In this case, as is the case in FIGS. 4A and 4B, the flowing out of a metal fixing material 31 is prevented, and further, the short circuiting between a side lead 25 and a center lead 26 due to the metal fixing material 31 is prevented. 
     FIG. 7 is a sectional view of the cathode structure in which the spacer 28 having the recess portion 28d, 28e, or 28f in FIGS. 4,5, and 6 is used. 
     In FIG. 7, a solder material such as a Ru-Mo material, a Ru-Mo-Ni material, or a Ni material is pasted and spread on the recess portion 28d, 28e, or 28f, and then the solder material is fused and fixed. Alternatively, a pasted Mo powder is spread on the recess portion and it is sintered. By pouring such a metal fixing material 31 on the outer surface of the side lead 25 at the position of the recess portion 28d, a gap between the spacer hole 28a and the side lead 25 is filled with the metal fixing material 31, and it is possible to inhibit the relative movement between the spacer 28 and the side lead 25. 
     In this case, if the spacer holes 28c and 28k are in the polygon shape or rectangular shape as shown in FIGS. 3A and 3B, and FIGS. 3C and 3D, respectively, the rotation of the spacer 28 can be suppressed more firmly. The metal fixing material 31 may naturally be applied to the spacer 28 shown in FIGS. 3A and 3B, however, if the recess portion is formed in the spacer as shown in FIGS. 4A, 4B-6A, 6B, the metal fixing material 31 can be poured more easily into an optimum portion, and thus, there is little fear of causing short-circuiting between both leads 25 and 26 due to excessive spreading of the metal fixing material 31 on an unrequired portion on the surface of the spacer 28. 
     Further, the spacer hole 28a shown in FIGS. 4A, 4B-6A, 6B may be formed in the rectangular shape (or polygon), and the spreading of the metal fixing material 31 on the fitting portion of the side lead 25 with respect to the spacer 28 shown in FIG. 7 and the sintering of the metal fixing material 31 may be carried out simultaneously with the assembling of a filament, etc., or the spreading and sintering of the metal fixing material 31 may be carried out beforehand in relation to the side lead 25 and the spacer 28. 
     Lastly, FIGS. 8A, 8B, -10A, 10B show various recess portions formed in the spacer 28. In other words, FIGS. 8A and 8B are a plane view and longitudinal sectional view of a spacer portion of a sixth embodiment of the present invention, a recess portion 28g is formed in the upper surface of the spacer 28 from one side thereof adjacent to a spacer hole 28a downwardly towards the center of a spacer hole 28a. That is, the bottom surface of the recess portion 28g is inclined from the one side of the spacer 28 towards the center of the spacer hole 28a. 
     Next, FIGS. 9A and 9B are a plane view and longitudinal sectional view of a spacer portion of a seventh embodiment of the present invention, in which a recess portion 28h is formed in the upper surface of the spacer 28 circularly and coaxially with a spacer hole 8a. 
     Further, FIGS. 10A and 10 are a plane view and longitudinal sectional view of a spacer portion of an eighth embodiment of present invention, in which a recess portion 28i is formed in the upper surface of a spacer 28 in a countersink shape coaxially with a spacer hole 28a, and in the longitudinal section of spacer, the recess portion 28i is in an arcuate shape. 
     Further, in the embodiments described in the foregoing, the description of the fixing is made only in relation to the spacer and the side lead. However, the present is not limited to this, and as shown in FIGS. 11A and l1B, the center lead 26 may be fixed, and the side lead 25 may be fitted into a spacer hole 28a with looseness therebetween. 
     As described in the foregoing, the present invention provides advantages in that since the engagement between one of the two leads and the spacer is tightened, the cathode structure is good in the vibration resistant property and the high-impact property. Moreover, since the other lead and the spacer hole have large looseness therebetween, there is no portion causing the friction therebetween, the extraneous sounds are not produced, and even when the diameter of the leads is reduced, sufficient strength can be insured. Thus, a magnetron which is inexpensive and which exhibits high performance can be obtained.