Patent Publication Number: US-6989634-B2

Title: Magnetron cathode assembly

Description:
The present invention relates to a cathode assembly of a magnetron used in a microwave heating apparatus such as an electronic oven. 
   Magnetron used in a microwave heading apparatus usually comprises, as shown in  FIG. 6 , a vacuum tube  1  located in the center portion, plural heat radiating fins  2  arranged at the periphery of this vacuum tube  1 , a pair of annular magnets  3  arranged coaxially with the vacuum tube  1 , a pair of frame yokes  4  for connecting these annular magnets  3  magnetically, and a filter circuit portion  5 . 
   Further, the vacuum tube  1  includes a cylindrical anode  6 , a cathode assembly  7  arranged on an axis of the cylindrical anode  6 , plural plate-like vanes  8  arranged in the inner surface of the cylindrical anode  6  radially extending from a center axis of the cylindrical anode  6 , plural strap rings  9  and  10  for electrically connecting these vanes on alternate vanes, and a microwave emission antenna  11  of which one end is connected to any one of the plate-like vanes  8 . 
   The cathode assembly  7 , as shown in  FIG. 7 , includes a metal tube  15  which is joined to one opening end edge of the cylindrical anode  6  coaxially with the cylindrical anode  6  and constitutes a part of the vacuum container, a coil-shaped cathode  17  arranged in the axial portion of the cylindrical anode  6 , a pair of cathode terminal lead wires  23  and  24  which support the cathode  17  through end-hats  19  and  20  joined to the leading ends of the cathode  17 , a stem insulator  29  which is air-tightly joined to an opening end edge of the metal tube  15  and has a pair of through-holes  29   a  and  29   b  that pass through the stem insulator  29  in the axial direction of the metal tube  15 , a pair of external terminals  31  and  32  of which base end axial portions  31   a  and  32   a  are inserted into a pair of through-holes  29   a  and  29   b , and a pair of sealing metal plates  35  and  36  joined to an end surface on the cathode  17  side of the stem insulator  29 . 
   Leading ends  31   b  and  32   b  of the external terminals  31  and  32  are curved so that the filter circuit portion  5  is easily connected to the external terminals  31  and  32 , that is, formed in the shape of a hook. 
   Of the above parts, the cathode  17  is made of thorium/tungsten, the end-hat  19 ,  20  and the cathode terminal lead wire  23 ,  24  are made of molybdenum, the stem insulator  29  is made of ceramic, and the external terminal  31 ,  32  and the sealing metal plate  35 ,  36  are made of general conductive metal such as a steel plate. 
   Each of the sealing metal plates  35  and  36 , as shown in  FIGS. 8 and 9 , includes a terminal fitting hole  35   a ,  36   a  into which the leading end of the base end axial portion  31   a ,  32   a  of the external terminal  31 ,  32  which extrudes to the metal tube  15   a  side from the stem insulator  29  is fitted; and a lead fitting hole  35   b ,  36   b  into which a leading end of the cathode terminal lead wire  23 ,  24  is fitted. 
   In a state where each of the base end axial portions  31   a ,  32   a  and each of the cathode terminal lead wires  23 ,  24  are fitted respectively into the corresponding terminal fitting hole  35   a ,  36   a  or the corresponding lead fitting hole  35   b ,  36   b , they are soldered to the sealing metal plates  35  and  36 , so that the electric connection between the corresponding external terminal and cathode terminal lead wire is carried out. 
   Further, the sealing metal plates  35  and  36  are soldered onto a metalized layer formed on the end surface of the stem insulator  29 , whereby they are fixed onto the end surface of the stem insulator  29  to seal the end surface on the cathode  17  side of the stem insulator  29  air-tightly. 
   The reason why the base end axial portions  31   a  and  32   a  that are inserted into the stem insulator  29  are provided for the external terminals  31  and  32  is to suppress the length of the expensive molybdenum-made cathode terminal lead wire  23 ,  24  to a minimum thereby to reduce cost 
   In the cathode assembly  7 , soldering of the cathode terminal lead wires  23 ,  24  and the external terminals  31 ,  32  to the sealing metal plates  35 ,  36  is performed by the following procedure. 
   Firstly, the cathode terminal lead wires  23 ,  24 , the sealing metal plates  35 ,  36 , the metal tube  15 , and the stem insulator  29  are set to a solder reception jig (not shown) that keeps the position of each part shown in  FIG. 7 . Next, the external terminals  31 ,  32  are inserted into a pair of through-holes  29   a ,  29   b  of the stem insulator  29  and further into the terminal fitting holes  35   a ,  36   a  of the sealing metal plates  35 ,  36 . Under this state, soldering is executed. At this time, the state among the cathode terminal lead wires  23 ,  24 , the external terminals  31 ,  32  and the sealing metal plates  35 ,  36  is as shown in  FIG. 8 . 
   Since the base end axial portions  31   a ,  32   a  of the external terminals  31 ,  32  in the cathode assembly  7  is round rod-shaped, and the terminal fitting holes  35   a ,  36   a  are also round, there is fear that the external terminals  31 ,  32  turn in soldering and the directions of the leading ends  31   b ,  32   b  are shifted. Therefore, conventionally, as shown in  FIGS. 10 and 11 , a pair of bulge portions  39   a ,  39   b  are additionally equipped for a top portion of a jig  39  covering the stem insulator  29  in assembly, the leading ends  31   b ,  32   b  of the external terminals  31 ,  32  are fitted into a groove  39   c  formed by these bulge portions  39   a ,  39   b , and turning of the leading ends  31   b ,  32   b  is stopped, whereby the directions of the external terminals  31 ,  32  can be kept constant. 
   However, in case that turning of the external terminals  31 ,  32  is stopped by the jig  39  covering the outside of the stem insulator  29 , the volume of the jig  39  increases because of equipment of the bulge portions  39   a ,  39   b , so that quantity of heat in a furnace absorbed by the jig  39  in soldering increases. Consequently, due to a short of heat transmission to each part to be soldered, there is fear that bad joint at the soldering portions is produced. 
   In order to compensate for the heat absorbed by the jip  39 , it is thought that the temperature in the furnace is increased in soldering. However, in this case, consumption of electrical energy increases, and increase of a manufacturing cost is caused. 
   Because of such the background, as shown in  FIGS. 12 and 13 , a cathode assembly has been proposed in which the leading ends of the external terminals  31 ,  32  inserted into the stem insulator  29  include radial direction-extensions  31   c ,  32   c  which extend in the radial direction of the stem insulator  29 , and axial direction-extensions  31   d ,  32   d  which extend from the leading ends of these radial direction-extensions  31   c ,  32   c  in the axial direction of the stem insulator  29 , and in which on the outer side end surface of the stem insulator  29 , grooves  29   c ,  29   d  for housing and retaining the radial direction-extensions  31   c ,  32   c  therein are provided, communicated with each of the through-holes  29   a ,  29   b  (for example, refer to Japanese Postexamined Publication 6-73275). 
   In the structure shown in  FIGS. 12 and 13 , components other than the stem insulator  29  and the external terminals  31 ,  32  are common to those in the cathode assembly  7  shown in  FIGS. 6 and 7 . Parts common to those in  FIGS. 6 and 7  are denoted by the same reference numerals, and their description is omitted. 
   In the cathode assembly shown in  FIGS. 12 and 13 , it is prevented, by fitting the radial direction-extensions  31   c ,  32   c  into the grooves  29   c ,  29   d , that the external terminals  31 ,  32  inserted into the through-holes  29   a ,  29   b  of the stem insulator  29  turn. 
   Therefore, it is not necessary to add the bulge portions for preventing the turn of the external terminals  31 ,  32  to the jig used when the external terminals  31 ,  32  and the cathode terminal lead wires  23 ,  24  are soldered to the sealing metal plates  35 ,  36 , and the volume of the jig can be made necessarily minimum, so that the above problems due to the increase of the volume of the jig can be solved. 
   However, the stem insulator  29  is usually made of ceramic. After ceramic is press-molded with a predetermined molding die, it is fired to form the stem insulator. Generally, in this method, dimensional accuracy is bad. Therefore, it is necessary for the grooves  29   c ,  29   d  to provide a large gap between the external terminals  31 ,  32  and the grooves  29   c ,  29   d . Accordingly, there is a problem that accuracy of turning stop of the external terminal  31 ,  32  becomes bad. 
   SUMMARY OF THE INVENTION 
   An object of the invention is, in view of the above problems, to provide a magnetron cathode assembly which can realize stopping of turn of an external terminal inserted into a stem insulator without requiring a jig that causes the increase of a manufacturing cost and improvement of the stem insulator, and which can improve soldering performance of the external terminal and simultaneously can reduce the manufacturing cost. 
   The above object is achieved by the following constitution. 
   (1) In a magnetron cathode assembly, a sealing metal plate which includes a terminal fitting hole into which a leading end of an external terminal is fitted, and a lead fitting hole into which a leading end of a cathode terminal lead wire is fitted, thereby to connect electrically the external terminal and the cathode terminal lead wire is joined to a stem insulator. The magnetron cathode assembly is characterized in that the external terminal has a non-circular section by providing a flat surface in at least one position on its peripheral surface, and a stop edge that fits to the flat surface thereby to carry out stopping of turn of the external terminal is provided for the terminal fitting hole. 
   (2) In the above (1), the magnetron cathode assembly is characterized in that the flat surface of the external terminal that comes into contact with the stop edge of the terminal fitting hole is formed into a slant surface in which the contact strengthens more as fitting into the terminal fitting hole becomes deeper. 
   In the magnetron cathode assembly described in the above (1), when the leading end of the external terminal is fitted into the terminal fitting hole of the sealing metal plate, the flat surface provided for the leading end of the external terminal is fitted to the stop edge of the terminal fitting hole. By only fitting of the external terminal into the terminal fitting hole, stopping of turn of the external terminal is achieved. 
   Accordingly, without requiring the jig that causes the increase of a manufacturing cost and improvement of the stem insulator, stopping of turn of the external terminal inserted into the stem insulator can be realized, soldering performance of the external terminal can be improved, and simultaneously the manufacturing cost can be reduced. 
   In the magnetron cathode assembly described in the above (2), the contact strengthens more as fitting into the terminal fitting hole becomes deeper, which is different from the case in that the flat surface provided for the external terminal is a simple vertical surface in the through-direction of the terminal fitting hole, Therefore, positioning accuracy of fitting improves, and firm fitting in which unstableness is not produced is obtained, so that joint strength by soldering and air-tightly sealing performance can be improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view of a magnetron cathode assembly in one embodiment according to the invention; 
       FIG. 2  is a perspective view showing a fitting state between each sealing metal plate located on the cathode-side end surface of a stem insulator shown in  FIG. 1  and each external terminal; 
       FIG. 3  is an exploded perspective view showing the structure of a fitting portion between each sealing metal plate shown in  FIG. 2  and each external terminal; 
       FIG. 4  is an enlarged view of the fitting portion between the sealing metal plate shown in  FIG. 1  and the external terminal; 
       FIG. 5  is a sectional view showing a leading end shape of an external terminal used in another embodiment of the magnetron cathode assembly according to the invention; 
       FIG. 6  is a longitudinal sectional view showing the constitution of a conventional magnetron cathode assembly; 
       FIG. 7  is an enlarged view of the magnetron cathode assembly shown in  FIG. 6 , shown in the inverse direction; 
       FIG. 8  is a perspective view of the surroundings of the stem insulator shown in  FIG. 7 ; 
       FIG. 9  is an exploded view showing a connecting relation among a cathode terminal lead wire, an external terminal, a sealing metal plate shown in  FIG. 6 ; 
       FIG. 10  is a perspective view of a jig used in soldering of the magnetron cathode assembly shown in  FIG. 7 ; 
       FIG. 11  is a perspective view showing a state where the external terminal is positioned by the jig shown in  FIG. 10 ; 
       FIG. 12  is a longitudinal sectional view of the conventional magnetron cathode assembly that has been improved; and 
       FIG. 13  is a perspective view of the magnetron cathode assembly shown in  FIG. 12 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The preferred embodiment of a magnetron cathode assembly according to the invention will be described below in detail with reference to drawings. 
     FIG. 1  shows one embodiment of the magnetron cathode assembly according to the invention. 
   A magnetron cathode assembly  51  in this embodiment is used for magnetron used in a microwave heating apparatus such as an electronic oven. The magnetron cathode assembly  51  includes a metal tube  15  which is joined to one opening end edge of an anode block coaxially with the anode block and constitutes a part of a vacuum container, a coil-like cathode  17  arranged in the axial portion of the anode block, a pair of cathode terminal lead wires  23  and  24  which support the cathode  17  through end hats  19  and  20  joined to the leading ends of the cathode  17 , a stem insulator  29  which is air-tightly joined to an opening end edge of the metal tube  15  and has a pair of through-holes  29   a  and  29   b  that pass through the stem insulator  29  in the axial direction of the metal tube  15 , a pair of external terminals  53  and  54  of which base end axial portions  53   a  and  54   a  are inserted into a pair of through-holes  29   a  and  29   b , and a pair of sealing metal plates  57  and  58  joined to an end surface on the cathode  17  side of the stem insulator  29 . 
   Leading ends  53   b  and  54   b  of the external terminals  53  and  54  are so curved, as shown also in  FIG. 3 , that a filter circuit portion is easily connected to the external terminals  53  and  54 , that is, formed in the shape of a hook. 
   Of the above parts, the cathode  17  is made of thorium/tungsten, the end hat  19 ,  20  and the cathode terminal lead wire  23 ,  24  are made of molybdenum, the stem insulator  29  is made of ceramic, and the external terminal  53 ,  54  and the sealing metal plate  57 ,  58  are made of general conductive metal such as a steel plate. 
   In the magnetron cathode assembly  51  in this embodiment, components other than the external terminals  53 ,  54  and the sealing metal plate  57 ,  58  are common to the components in the cathode assembly  7  shown in  FIG. 7 . 
   Each of the sealing metal plates  57  and  58 , as shown in  FIGS. 2 and 3 , includes a terminal fitting hole  57   a ,  58   a  into which a leading end of the base end axial portion  53   a ,  54   a  of the external terminal  53 ,  54  which extrudes to the metal tube  15   a  side from the stem insulator  29  is fitted; and a lead fitting hole  57   b ,  58   b  into which a leading end of the cathode terminal lead wire  23 ,  24  is fitted. 
   In a state where the base end axial portions  53   a ,  54   a  and the cathode terminal lead wires  23 ,  24  are fitted respectively into the corresponding terminal fitting holes  57   a ,  58   a  or the lead fitting holes  57   b ,  58   b , they are soldered to the sealing metal plates  57  and  58 , so that the electric connection between the corresponding external terminal and cathode terminal lead wire is carried out. 
   Further, the sealing metal plates  57  and  58  are soldered onto a metallized layer formed on the end surface of the stem insulator  29 , whereby they are fixed onto the end surface of the stem insulator  29  to seal the end surface on the cathode  17  side of the stem insulator  29  air-tightly. 
   The reason why the base end axial portions  53   a  and  54   a  that are inserted into the stem insulator  29  are provided for the external terminals  53  and  54  is to suppress the length of the expensive molybdenum-made cathode terminal lead wire  23 ,  24  to a minimum thereby to reduce cost 
   In case of this embodiment, the base end axial portion  53   a ,  54   a  fitted into the terminal fitting hole  57   a ,  58   a  is round rod-shaped. However, the leading end of this base end axial portion  53   a ,  54   a , as shown also in  FIG. 4 , has a non-circular section by forming a pair of opposing portions on the peripheral surface into a flat surface  61 . It is good for formation of a pair of flat surfaces  61  to utilize press molding that is superior in working performance. 
   Further, for the terminal fitting hole  57   a ,  58   a  of the sealing metal plate  57 ,  58 , a straight stop edge  63  that carries out stopping of turn of the external terminal  53 ,  54  is provided. 
   In case of this embodiment, each of the terminal fitting holes  57   a  and  58   a  has a pair of straight stop edges  63  opposed to each other correspondingly to a pair of flat surfaces  61  provided for the leading end of each external terminal  53 ,  54 . In result, the terminal fitting hole  57   a ,  58   a  shows a rectangular opening shape. 
   In the above cathode assembly  51 , soldering of the cathode terminal lead wire  23 ,  24  and the external terminal  53 ,  54  to the sealing metal plate  57 ,  58  is performed by the following procedure. 
   Firstly, the cathode terminal lead wires  23 ,  24 , the sealing metal plates  57 ,  58 , the metal tube  15 , and the stem insulator  29  are set to a solder reception jig (not shown) that keeps the position of each part shown in  FIG. 1 . Next, the external terminals  53 ,  54  are inserted into a pair of through-holes  29   a ,  29   b  of the stem insulator  29  and further into the terminal fitting holes  57   a ,  58   a  of the sealing metal plates  57 ,  58 . Under this state, soldering is executed. At this time, the state among the cathode terminal lead wires  23 ,  24 , the external terminals  53 ,  54  and the sealing metal plates  57 ,  58  is as shown in  FIG. 2 . 
   In the magnetron cathode assembly  51  described above, when the leading end of the base end axial portion  53   a ,  54   a  protruding from the cathode-side end surface of the stem insulator  29  is fitted into the terminal fitting hole  57   a ,  58   a  of the sealing metal plate  57 ,  58 , the flat surface  61  provided for the leading end of the base end axial portion  53   a ,  54   a  is fitted to the stop edge  63  of the terminal fitting hole  57   a ,  58   a . By only fitting of the external terminal into the terminal fitting hole  57   a ,  58   a , stopping of turn of the external terminal inserted into the stem insulator  29  is achieved. 
   Accordingly, without requiring the jig that causes the increase of a manufacturing cost and improvement of the stem insulator  29 , stopping of turn of the external terminal  53 ,  54  inserted into the stem insulator  29  can be realized, soldering performance of the external terminal  53 ,  54  can be improved, and simultaneously the manufacturing cost can be reduced. 
   It is preferable that the flat surface  61  of the external terminal  53 ,  54  coming into contact with the stop edge  63  of the terminal fitting hole  57   a ,  58   a  has a slant surface  65  in which the contact strengthens more as fitting into the terminal fitting hole  57   a ,  58   a  becomes deeper. 
   This case is different from the case shown in  FIG. 4  where the flat surface  61  provided for the leading end of the base end axial portion  53   a ,  54   a  of the external terminal  53 ,  54  is a simple vertical surface in the through-direction of the terminal fitting hole  57   a ,  58   a , because the contact strengthens more as fitting of the base end axial portion  53   a ,  54   a  into the terminal fitting hole  57   a ,  58   a  becomes deeper, whereby a gap s is not produced between the slant surface and the flat surface. Therefore, positioning accuracy of fitting improves, and firm fitting in which unstableness is not produced can be obtained, so that joint strength by soldering and air-tightly sealing performance can be improved. 
   In the above embodiment, at the leading end of the base end axial portion  53   a ,  54   a  of the external terminal  53 ,  54 , the flat surfaces  61  for preventing the turn are formed in two opposing positions. However, it is sufficient that the flat surface  61  for preventing the turn is arranged in at least one position, and the number of the flat surfaces  61  for preventing the turn is not limited to that in the above embodiment.