EP0742573A1 - Tube with pyrolytic graphite grid and method of making - Google Patents

Tube with pyrolytic graphite grid and method of making Download PDF

Info

Publication number
EP0742573A1
EP0742573A1 EP96400971A EP96400971A EP0742573A1 EP 0742573 A1 EP0742573 A1 EP 0742573A1 EP 96400971 A EP96400971 A EP 96400971A EP 96400971 A EP96400971 A EP 96400971A EP 0742573 A1 EP0742573 A1 EP 0742573A1
Authority
EP
European Patent Office
Prior art keywords
grid
tube
base
graphite
materials
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP96400971A
Other languages
German (de)
French (fr)
Inventor
Olivier Friquet
Christophe Foissard
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Thales Electron Devices SA
Original Assignee
Thomson Tubes Electroniques
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Tubes Electroniques filed Critical Thomson Tubes Electroniques
Publication of EP0742573A1 publication Critical patent/EP0742573A1/en
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J19/00—Details of vacuum tubes of the types covered by group H01J21/00
    • H01J19/42—Mounting, supporting, spacing, or insulating of electrodes or of electrode assemblies
    • H01J19/48—Mountings for individual electrodes

Definitions

  • the invention relates to electronic vacuum tubes, intended for high power amplification.
  • These tubes sometimes use a graphite grid, produced by a hot deposition operation of graphite carbon on a cylindrical mandrel, followed by demolding of the graphite cylinder thus formed, and machining of the cylinder.
  • the machining gives the cylinder a grid configuration allowing the electrons emitted by a cylindrical cathode to pass around which the grid is placed.
  • the grid is made of graphite to take advantage of the excellent temperature resistance of this material, as well as its good electrical conductivity. It is electrically connected to an external connection to the tube, generally located in the base of the tube. This connection is made of metal such as an iron-nickel-cobalt alloy (for example).
  • the present invention aims to propose an industrially much more advantageous solution than known solutions, for producing and mounting a grid of pyrolytic graphite in an electronic vacuum tube.
  • a method for mounting a graphite grid in an electronic vacuum tube comprising an operation consisting in brazing in a furnace the lower part of the grid on a metal base, using a solder comprising at least two materials forming a eutectic, one of the materials having good wetting properties of graphite, and the two materials having vapor pressures below 1.3.10 -11 bar at the maximum temperature of the base during the operation of the tube.
  • the pressure of 1.3. 10 -11 bar corresponds to the maximum admissible value compatible with the life of the tube.
  • the maximum temperature of the base in operation can be around 500 ° to 700 ° C.
  • Soldering can be carried out in an oven, therefore in batches of several tubes at the same time.
  • the oven temperature can remain reasonably low; the brazing materials are preferably chosen such that the temperature of formation of the eutectic is between 800 ° C. and 1300 ° C.
  • the whole of the grid and the base can be fixed to an external connection electrode during the assembly of the grids.
  • Titanium and zirconium are in fact two materials which wet graphite well, but whose use as sole solder material proves to be of little interest industrially; they must be used at very high temperatures and then tend to form with graphite carbides whose presence seems unfavorable.
  • the pairs of materials used for brazing are preferably present in proportions equal to those of the eutectic or very close to the proportions of the eutectic.
  • the invention also relates to an electronic tube with a pyrolytic graphite grid, characterized in that the grid is mounted on a metal base and is linked to this base by a brazing material consisting at least two materials (preferably those mentioned above), one of which wets graphite well and which form a eutectic, the two materials having vapor pressures below 1.3.10 -11 bar at the maximum temperature of the base during operation of the tube.
  • This maximum temperature can be estimated in the range of 500 to 700 ° C in the general case.
  • the tube shown is an amplifier tube, of the triode or tetrode type, but the invention is applicable to any type of tube using a pyrolytic graphite grid.
  • the tube comprises a cylindrical cathode 10 surrounded by a grid 20 concentric with the cathode, and an anode 30 surrounding the grid and the cathode.
  • the view of Figure 1 is a schematic view of the right half of the tube, the dashed axis 40 representing the axis of symmetry of the cylindrical parts. Several concentric grids can be provided.
  • the internal electrodes of the tube i.e. the cathode and the grid, are located in a vacuum part. They are electrically connected to external connection electrodes which each have an internal part to the tube and an external part.
  • the external parts are annular rings intended to fit into a connection socket.
  • the connection electrode is designated by the reference 12; for the grid 20 and the anode 30, the connection electrodes are designated by the references 22 and 32 respectively.
  • the connection electrodes 12, 22, 32 are separated from each other by ceramic rings 21, 31, which on the one hand provide electrical insulation and on the other hand vacuum sealing between the interior and the outside the tube. These rings are soldered to the connection electrodes.
  • the connection electrodes are for example made of an iron-nickel-cobalt alloy.
  • the grid 20, which is the subject of the invention, is made of pyrolytic graphite as regards its active part, that is to say at least the part directly opposite and in the immediate vicinity of the cathode 10.
  • a grid in pyrolytic graphite is conventionally produced by depositing, by a chemical decomposition process in the gas phase at low pressure, carbon on a cylindrical mandrel having the general shape desired for the grid. When a thickness sufficient graphite carbon is deposited (a few tenths of a millimeter) the monolithic piece of graphite thus obtained is removed from the mold. It is a thin-walled cylinder, terminated at its upper part by a bell. The walls are continuous.
  • FIG. 2 represents, in perspective, such a grid in pyrolytic graphite 20.
  • the meshes of the grid are for example formed essentially by close vertical bars 210, with a few horizontal bars 220 to improve the mechanical strength of the assembly.
  • the bottom of the grid remains formed by a continuous cylindrical wall (not perforated) 230.
  • FIG. 3 represents the grid 20 mounted on its metal base 50, also visible in FIG. 1.
  • the base can be made of an iron-nickel-cobalt alloy like the connection electrode 22.
  • the wall of the base at its upper part 52 is thicker than the lower wall 230 of graphite, and these two walls have substantially the same mean diameter, so that the graphite grid can rest directly by its edge on the base. .
  • the graphite wall is joined by a solder to the wall of the base.
  • the lower part of the base also cylindrical, is connected, preferably by welding, to the connection electrode 22.
  • the lower cylindrical part 56 of the base is fitted into an upper cylindrical part 26 (inside the vacuum tube) of the connection electrode 22. And the two fitted parts can be welded, before placing the assembly in the tube.
  • the solder ring consists of a couple of materials, juxtaposed or in alloy.
  • One of the materials preferably titanium, but it can also be zirconium for example, must be able to wet the graphite.
  • the other material preferably nickel, but it could also be iron, or even at least copper or silver, must be able to form with the first an eutectic at a temperature much lower than the temperature of fusion of the first material.
  • the two materials used must have a low tendency to evaporate at the temperatures to which the base will be subjected during the operation of the tube.
  • the proportions of the two materials are close to the proportions of the eutectic, or equal to these proportions.
  • the eutectic melts at around 950 ° C; for the titanium-iron couple, 70% -30%, eutectic at 1085 ° C; for the titanium-copper couple: 25% -75%, eutectic at 870 ° C; and finally titanium-silver: 3% -97%, eutectic at 910 ° C.
  • the eutectic temperatures are low enough to allow the use of conventional ovens working between 1000 ° C and 1200 ° C. At these temperatures, there is no risk of carbides forming from the metals used. Carbides would be likely to form between the grid and the brazing material (for example titanium carbide) if one worked at temperatures close to the melting temperature of titanium (around 1690 ° C) or zirconium, and these carbides would be unfavorable from the point of view of thermal and electrical conduction between the grid and the base. On the other hand, the temperatures used here for the brazing are much more favorable from the point of view of the stresses generated by the differential expansions between the brazed parts. The temperature of the oven during the brazing operation is chosen to be slightly higher than the melting temperature of the eutectic.
  • the saturation vapor pressures for the materials mentioned above are 10 -8 mm of mercury (1.3 x 10 -11 bar) at the following respective temperatures: 1000 ° C for titanium 900 ° C for nickel 880 ° C for iron 550 ° C for copper.
  • nickel, iron and copper are suitable for a association with titanium (with which they all form a eutectic whose melting temperature is much lower than that of titanium). Copper is the most unfavorable since it tends to evaporate more easily. Nickel is the most favorable.
  • the titanium-nickel pair is the preferred pair according to the invention.

Abstract

The assembly method involves brazing of the grid (20) to a base (50) of e.g. Fe-Ni-Co alloy, using a mixture of pref. Ti which is capable of softening the graphite, and Ni which can form an eutectic with it at a temperature well below its melting point. The vapour pressures of both metals must be below 1.3 x 10<-11> bar at the highest operating temperature of the base. The cylindrical wall (230) at the lower end of the grid rests directly on the upper circular section (54) of a corresponding cylinder at the top (52) of the base.

Description

L'invention concerne les tubes électroniques à vide, destinés à l'amplification de forte puissance.The invention relates to electronic vacuum tubes, intended for high power amplification.

Ces tubes utilisent parfois une grille en graphite, réalisée par une opération de dépôt à chaud de carbone graphite sur un mandrin cylindrique, suivie d'un démoulage du cylindre de graphite ainsi formé, et d'un usinage du cylindre. L'usinage donne au cylindre une configuration en grille permettant de laisser passer les électrons émis par une cathode cylindrique autour de laquelle est placée la grille.These tubes sometimes use a graphite grid, produced by a hot deposition operation of graphite carbon on a cylindrical mandrel, followed by demolding of the graphite cylinder thus formed, and machining of the cylinder. The machining gives the cylinder a grid configuration allowing the electrons emitted by a cylindrical cathode to pass around which the grid is placed.

La grille est réalisée en graphite pour profiter de l'excellente tenue en température de ce matériau, ainsi que de sa bonne conductivité électrique. Elle est reliée électriquement à une connexion extérieure au tube, généralement située dans le pied du tube. Cette connexion est en métal tel qu'un alliage de fer-nickel-cobalt (par exemple).The grid is made of graphite to take advantage of the excellent temperature resistance of this material, as well as its good electrical conductivity. It is electrically connected to an external connection to the tube, generally located in the base of the tube. This connection is made of metal such as an iron-nickel-cobalt alloy (for example).

Un des problèmes pratiques qui se posent dans la fabrication du tube est la fixation de la grille sur l'électrode de connexion extérieure. Si la grille est entièrement en graphite, on ne peut faire autrement que de la visser sur cette électrode pour assurer le montage définitif. Mais un montage vissé nécessite des opérations d'usinage supplémentaires : perçages, taraudages, ébavurages, etc. Ces opérations sont coûteuses en temps et en main d'oeuvre; elles amènent des copeaux métalliques qui peuvent se retrouver plus tard dans le tube et qui peuvent y créer des dysfonctionnements (dus à des court-circuits, ou à des dépôts de matière sur des pièces sensibles telles que la cathode). De plus, le contact électrique et thermique entre la grille et la connexion extérieure n'est pas très bon avec une fixation par simple vissage.One of the practical problems which arise in the manufacture of the tube is the fixing of the grid to the external connection electrode. If the grid is entirely made of graphite, you can not help but screw it onto this electrode to ensure final assembly. But a screwed assembly requires additional machining operations: drilling, tapping, deburring, etc. These operations are costly in time and in manpower; they bring metal chips which can be found later in the tube and which can create dysfunctions there (due to short-circuits, or to deposits of material on sensitive parts such as the cathode). In addition, the electrical and thermal contact between the grid and the external connection is not very good with fixing by simple screwing.

C'est pourquoi on a déjà proposé de réaliser la grille en deux parties, une partie utile de grille proprement dite, en graphite pyrolytique, et une embase métallique. La grille est soudée à l'embase, et l'embase peut ensuite être soudée à l'électrode extérieure lors du montage définitif du tube.This is why it has already been proposed to produce the grid in two parts, a useful part of the grid proper, in pyrolytic graphite, and a metal base. The grid is welded to the base, and the base can then be welded to the external electrode during the final assembly of the tube.

Le brevet US 4 739 213 décrit une tentative de ce genre. La soudure de la grille de graphite sur l'embase se fait par l'intermédiaire d'un manchon réalisé dans un métal (tungstène, ou molybdène ou tantale) qui forme un carbure avec le graphite de la grille. La grille est emmanchée sur ce manchon qui lui-même est emmanché sur l'embase.US Patent 4,739,213 describes an attempt of this kind. The graphite grid is welded to the base by means of a sleeve made of a metal (tungsten, or molybdenum or tantalum) which forms a carbide with the graphite of the grid. The grid is fitted onto this sleeve which itself is fitted onto the base.

Mais cette solution nécessite une opération de soudure à l'arc ou par plasma tout autour de la grille. Il s'agit d'une opération manuelle, difficilement automatisable pour des productions en série. De plus, la soudure progressive tout autour de la grille crée des contraintes élevées dans celle-ci.However, this solution requires an arc or plasma welding operation all around the grid. It is a manual operation, difficult to automate for mass production. In addition, the progressive welding all around the grid creates high stresses in it.

La présente invention vise à proposer une solution industriellement beaucoup plus intéressante que les solutions connues, pour réaliser et monter une grille de graphite pyrolytique dans un tube électronique à vide.The present invention aims to propose an industrially much more advantageous solution than known solutions, for producing and mounting a grid of pyrolytic graphite in an electronic vacuum tube.

Selon l'invention, on propose un procédé de montage de grille en graphite dans un tube électronique à vide, ce procédé comprenant une opération consistant à braser dans un four la partie inférieure de la grille sur une embase métallique, à l'aide d'une brasure comportant au moins deux matériaux formant un eutectique, l'un des matériaux ayant de bonnes propriétés de mouillage du graphite, et les deux matériaux ayant des tensions de vapeur inférieures à 1,3.10-11 bar à la température maximale de l'embase lors du fonctionnement du tube.According to the invention, a method for mounting a graphite grid in an electronic vacuum tube is proposed, this method comprising an operation consisting in brazing in a furnace the lower part of the grid on a metal base, using a solder comprising at least two materials forming a eutectic, one of the materials having good wetting properties of graphite, and the two materials having vapor pressures below 1.3.10 -11 bar at the maximum temperature of the base during the operation of the tube.

La pression de 1,3. 10-11 bar (environ 10-8 mm de mercure) correspond à la valeur maximale admissible compatible avec la durée de vie du tube. La température maximale de l'embase en fonctionnement peut être d'environ 500° à 700° C.The pressure of 1.3. 10 -11 bar (approximately 10 -8 mm of mercury) corresponds to the maximum admissible value compatible with the life of the tube. The maximum temperature of the base in operation can be around 500 ° to 700 ° C.

La brasure peut être effectuée dans un four, donc par lots de plusieurs tubes à la fois. Cependant, la température du four peut rester raisonnablement faible; les matériaux de brasure sont choisis de préférence tels que la température de formation de l'eutectique soit comprise entre 800°C et 1300°C.Soldering can be carried out in an oven, therefore in batches of several tubes at the same time. However, the oven temperature can remain reasonably low; the brazing materials are preferably chosen such that the temperature of formation of the eutectic is between 800 ° C. and 1300 ° C.

Après cette brasure, l'ensemble de la grille et de l'embase peut être fixé à une électrode de connexion extérieure lors de l'assemblage des grilles.After this soldering, the whole of the grid and the base can be fixed to an external connection electrode during the assembly of the grids.

Les matériaux préférés pour la brasure sont :

  • brasure titane-nickel
  • brasure titane-fer
  • brasure titane-cuivre, ou titane-argent
  • brasure zirconium-nickel, ou zirconium-fer
The preferred materials for brazing are:
  • titanium-nickel solder
  • titanium-iron solder
  • titanium-copper, or titanium-silver solder
  • zirconium-nickel solder, or zirconium-iron

Le titane et le zirconium sont en effet deux matériaux qui mouillent bien le graphite, mais dont l'utilisation comme matériau unique de brasure s'avère peu intéressante industriellement; ils doivent être utilisés à très haute température et tendent alors à former avec le graphite des carbures dont la présence semble défavorable.Titanium and zirconium are in fact two materials which wet graphite well, but whose use as sole solder material proves to be of little interest industrially; they must be used at very high temperatures and then tend to form with graphite carbides whose presence seems unfavorable.

Les couples de matériaux utilisés pour la brasure sont présents de préférence dans des proportions égales à celles de l'eutectique ou très proches des proportions de l'eutectique.The pairs of materials used for brazing are preferably present in proportions equal to those of the eutectic or very close to the proportions of the eutectic.

Les contraintes engendrées pendant la brasure s'avèrent beaucoup plus faibles que celles que créeraient des opérations de soudure de la grille sur l'embase.The stresses generated during soldering are found to be much lower than those that would be created by welding operations on the grid on the base.

Outre le procédé de fabrication résumé ci-dessus, l'invention a pour objet également un tube électronique à grille en graphite pyrolytique, caractérisé en ce que la grille est montée sur une embase métallique et est liée à cette embase par un matériau de brasure constitué d'au moins deux matériaux (de préférence ceux mentionnés ci-dessus) dont l'un mouille bien le graphite et qui forment un eutectique, les deux matériaux ayant des tensions de vapeur inférieures à 1,3.10-11 bar à la température maximale de l'embase lors du fonctionnement du tube. Cette température maximale peut être estimée de l'ordre de 500 à 700°C dans le cas général.In addition to the manufacturing process summarized above, the invention also relates to an electronic tube with a pyrolytic graphite grid, characterized in that the grid is mounted on a metal base and is linked to this base by a brazing material consisting at least two materials (preferably those mentioned above), one of which wets graphite well and which form a eutectic, the two materials having vapor pressures below 1.3.10 -11 bar at the maximum temperature of the base during operation of the tube. This maximum temperature can be estimated in the range of 500 to 700 ° C in the general case.

D'autres caractéristiques et avantages de l'invention apparaîtront à la lecture de la description détaillée qui suit et qui est faite en référence aux dessins annexés dans lesquels :

  • la figure 1 représente un tube électronique à vide selon l'invention;
  • la figure 2 représente un exemple de constitution de grille en graphite;
  • la figure 3 représente la grille selon l'invention, constituée de la grille de la figure 2 montée sur une embase métallique.
Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:
  • FIG. 1 represents an electronic vacuum tube according to the invention;
  • FIG. 2 represents an example of constitution of a graphite grid;
  • 3 shows the grid according to the invention, consisting of the grid of Figure 2 mounted on a metal base.

Le tube représenté est un tube amplificateur, du genre triode ou tétrode, mais l'invention est applicable à tout type de tube utilisant une grille en graphite pyrolytique.The tube shown is an amplifier tube, of the triode or tetrode type, but the invention is applicable to any type of tube using a pyrolytic graphite grid.

Le tube comporte une cathode cylindrique 10 entourée par une grille 20 concentrique à la cathode, et une anode 30 entourant la grille et la cathode. La vue de la figure 1 est une vue schématique de la moitié droite du tube, l'axe tireté 40 représentant l'axe de symétrie des pièces cylindriques. Plusieurs grilles concentriques peuvent être prévues.The tube comprises a cylindrical cathode 10 surrounded by a grid 20 concentric with the cathode, and an anode 30 surrounding the grid and the cathode. The view of Figure 1 is a schematic view of the right half of the tube, the dashed axis 40 representing the axis of symmetry of the cylindrical parts. Several concentric grids can be provided.

Les électrodes internes du tube, c'est-à-dire la cathode et la grille, sont situées dans une partie sous vide. Elles sont reliées électriquement à des électrodes de connexion extérieure qui comportent chacune une partie interne au tube et une partie externe. Les parties externes sont des bagues annulaires destinées à s'emboîter dans un socle de connexion. Pour la cathode 10, l'électrode de connexion est désignée par la référence 12; pour la grille 20 et l'anode 30, les électrodes de connexion sont désignées par les références 22 et 32 respectivement. Les électrodes de connexion 12, 22, 32 sont séparées les unes des autres par des bagues en céramique 21, 31, qui assurent d'une part l'isolement électrique et d'autre part l'étanchéité au vide entre l'intérieur et l'extérieur du tube. Ces bagues sont brasées aux électrodes de connexion. Les électrodes de connexion sont par exemple réalisées dans un alliage fer-nickel-cobalt.The internal electrodes of the tube, i.e. the cathode and the grid, are located in a vacuum part. They are electrically connected to external connection electrodes which each have an internal part to the tube and an external part. The external parts are annular rings intended to fit into a connection socket. For cathode 10, the connection electrode is designated by the reference 12; for the grid 20 and the anode 30, the connection electrodes are designated by the references 22 and 32 respectively. The connection electrodes 12, 22, 32 are separated from each other by ceramic rings 21, 31, which on the one hand provide electrical insulation and on the other hand vacuum sealing between the interior and the outside the tube. These rings are soldered to the connection electrodes. The connection electrodes are for example made of an iron-nickel-cobalt alloy.

La grille 20, qui fait l'objet de l'invention, est en graphite pyrolytique pour ce qui concerne sa partie active, c'est-à-dire au moins la partie directement en regard et à proximité immédiate de la cathode 10. Une grille en graphite pyrolytique est classiquement réalisée en déposant, par un procédé de décomposition chimique en phase gazeuse à basse pression, du carbone sur un mandrin cylindrique ayant la forme générale désirée pour la grille. Lorsqu'une épaisseur suffisante de carbone graphite est déposée (quelques dixièmes de millimètres) on démoule la pièce monolithique de graphite ainsi obtenue. C'est un cylindre à parois fines, terminé à sa partie supérieure par une cloche. Les parois sont continues. Il faut ensuite les amincir aux endroits désirés et les ajourer pour constituer une grille laissant passer les électrons; ceci est fait par usinage au sable, à travers un masque fixe ou mobile délimitant les ouvertures à réaliser. La figure 2 représente, en perspective, une telle grille en graphite pyrolytique 20. Les mailles de la grille sont par exemple formées essentiellement par des barreaux verticaux rapprochés 210, avec quelques barreaux horizontaux 220 pour améliorer la tenue mécanique de l'ensemble. Le bas de la grille reste constitué par une paroi cylindrique continue (non ajourée) 230.The grid 20, which is the subject of the invention, is made of pyrolytic graphite as regards its active part, that is to say at least the part directly opposite and in the immediate vicinity of the cathode 10. A grid in pyrolytic graphite is conventionally produced by depositing, by a chemical decomposition process in the gas phase at low pressure, carbon on a cylindrical mandrel having the general shape desired for the grid. When a thickness sufficient graphite carbon is deposited (a few tenths of a millimeter) the monolithic piece of graphite thus obtained is removed from the mold. It is a thin-walled cylinder, terminated at its upper part by a bell. The walls are continuous. It is then necessary to thin them in the desired places and to perforate them to constitute a grid letting pass the electrons; this is done by machining with sand, through a fixed or movable mask delimiting the openings to be made. FIG. 2 represents, in perspective, such a grid in pyrolytic graphite 20. The meshes of the grid are for example formed essentially by close vertical bars 210, with a few horizontal bars 220 to improve the mechanical strength of the assembly. The bottom of the grid remains formed by a continuous cylindrical wall (not perforated) 230.

Pour des raisons de réduction des coûts de fabrication et d'amélioration des propriétés de conduction thermique et électrique, ainsi que de suppression de causes de dysfonctionnement, on propose ici de fixer la grille en graphite à une embase métallique avant de souder cette embase sur l'électrode de connexion 22.For reasons of reducing manufacturing costs and improving thermal and electrical conduction properties, as well as eliminating causes of malfunction, it is proposed here to fix the graphite grid to a metal base before welding this base on the connection electrode 22.

La figure 3 représente la grille 20 montée sur son embase métallique 50, visible également sur la figure 1.FIG. 3 represents the grid 20 mounted on its metal base 50, also visible in FIG. 1.

L'embase peut être en un alliage fer-nickel-cobalt comme l'électrode de connexion 22.The base can be made of an iron-nickel-cobalt alloy like the connection electrode 22.

L'extrémité inférieure de la grille de graphite 20, terminée par une paroi cylindrique continue fine 230, repose directement sur la tranche circulaire supérieure 54 d'une paroi cylindrique correspondante située à la partie supérieure 52 de l'embase. La paroi de l'embase à sa partie supérieure 52 est plus épaisse que la paroi inférieure 230 de graphite, et ces deux parois ont sensiblement le même diamètre moyen, de sorte que la grille de graphite peut reposer directement par sa tranche sur l'embase. La paroi de graphite est solidarisée par une brasure à la paroi de l'embase. Par ailleurs, la partie inférieure de l'embase, également cylindrique, est reliée, de préférence par soudure, à l'électrode de connexion 22. Par exemple, la partie inférieure cylindrique 56 de l'embase s'emmanche dans une partie cylindrique supérieure 26 (à l'intérieur du tube à vide) de l'électrode de connexion 22. Et les deux parties emmanchées peuvent être soudées, avant mise en place de l'ensemble dans le tube.The lower end of the graphite grid 20, terminated by a fine continuous cylindrical wall 230, rests directly on the upper circular edge 54 of a corresponding cylindrical wall located at the upper part 52 of the base. The wall of the base at its upper part 52 is thicker than the lower wall 230 of graphite, and these two walls have substantially the same mean diameter, so that the graphite grid can rest directly by its edge on the base. . The graphite wall is joined by a solder to the wall of the base. Furthermore, the lower part of the base, also cylindrical, is connected, preferably by welding, to the connection electrode 22. For example, the lower cylindrical part 56 of the base is fitted into an upper cylindrical part 26 (inside the vacuum tube) of the connection electrode 22. And the two fitted parts can be welded, before placing the assembly in the tube.

Les opérations de fabrication sont les suivantes :

  • réalisation de la grille en graphite, par dépôt pyrolytique et usinage par sablage;
  • réalisation de l'embase métallique, par emboutissage et usinage;
  • mise en place d'un jonc de brasure annulaire sur la partie supérieure 52 de l'embase; on définira ci-après la constitution de ce jonc;
  • mise en place de la grille de graphite sur l'embase avec le jonc séparant les deux pièces; l'ensemble est placé dans un four de brasure, dont la température est d'environ 1000°C (en fonction de la nature de la brasure utilisée);
  • brasure dans le four, une série de pièces pouvant être traitées simultanément;
  • soudure de l'embase (partie inférieure 56) sur l'électrode de connexion 22;
  • montage de l'ensemble dans le tube.
The manufacturing operations are as follows:
  • realization of the graphite grid, by pyrolytic deposition and sandblasting machining;
  • production of the metal base, by stamping and machining;
  • placing an annular solder ring on the upper part 52 of the base; the constitution of this rod will be defined below;
  • placement of the graphite grid on the base with the rod separating the two parts; the assembly is placed in a brazing furnace, the temperature of which is approximately 1000 ° C. (depending on the nature of the brazing used);
  • brazing in the oven, a series of parts which can be treated simultaneously;
  • soldering of the base (lower part 56) on the connection electrode 22;
  • assembly of the assembly in the tube.

Le jonc de brasure est constitué d'un couple de matériaux, juxtaposés ou en alliage. L'un des matériaux, de préférence du titane, mais ce peut être aussi du zirconium par exemple, doit être capable de mouiller le graphite. L'autre matériau, de préférence du nickel, mais ce pourrait être aussi du fer, ou même à la rigueur du cuivre ou de l'argent, doit être capable de former avec le premier un eutectique à une température bien inférieure à la température de fusion du premier matériau. Les deux matériaux utilisés doivent avoir une faible tendance à l'évaporation aux températures auxquelles l'embase sera soumise lors du fonctionnement du tube. Il s'agit en effet de tubes de forte puissance, dans lesquels les températures peuvent être très élevées; et il s'agit de tubes à vides dans lesquels l'évaporation de matériaux conducteurs peut avoir des effets très néfastes (pollution de la cathode, court-circuits, flashes, etc.). Pour donner une indication chiffrée, on peut considérer que la grille risque d'être soumise à des températures de l'ordre de 500°C à 600°C à l'endroit de la brasure (beaucoup plus au milieu de la grille de graphite). Les matériaux utilisés pour la brasure ne devraient pas avoir une tension de vapeur supérieure à 1,3. 10-11 bar à cette température. Le titane, le zirconium, le nickel, le fer, le cuivre, l'argent conviennent sur ce point.The solder ring consists of a couple of materials, juxtaposed or in alloy. One of the materials, preferably titanium, but it can also be zirconium for example, must be able to wet the graphite. The other material, preferably nickel, but it could also be iron, or even at least copper or silver, must be able to form with the first an eutectic at a temperature much lower than the temperature of fusion of the first material. The two materials used must have a low tendency to evaporate at the temperatures to which the base will be subjected during the operation of the tube. These are indeed high-power tubes, in which the temperatures can be very high; and these are empty tubes in which the evaporation of conductive materials can have very harmful effects (pollution of the cathode, short circuits, flashes, etc.). To give a numerical indication, we can consider that the grid risks being subjected to temperatures of the order of 500 ° C to 600 ° C at the place of the brazing (much more at middle of the graphite grid). The materials used for soldering should not have a vapor pressure greater than 1.3. 10 -11 bar at this temperature. Titanium, zirconium, nickel, iron, copper, silver are suitable on this point.

De préférence, mais sans que ce soit absolument obligatoire, les proportions des deux matériaux sont proches des proportions de l'eutectique, ou égales à ces proportions.Preferably, but without this being absolutely compulsory, the proportions of the two materials are close to the proportions of the eutectic, or equal to these proportions.

Notamment, pour le couple titane-nickel : 72%-28%, l'eutectique fond à 950°C environ; pour le couple titane-fer, 70%-30%, eutectique à 1085°C; pour le couple titane-cuivre : 25%-75%, eutectique à 870°C; et enfin titane-argent : 3%-97%, eutectique à 910°C.In particular, for the titanium-nickel couple: 72% -28%, the eutectic melts at around 950 ° C; for the titanium-iron couple, 70% -30%, eutectic at 1085 ° C; for the titanium-copper couple: 25% -75%, eutectic at 870 ° C; and finally titanium-silver: 3% -97%, eutectic at 910 ° C.

Les températures des eutectiques sont suffisamment basses pour permettre l'utilisation de fours classiques travaillant entre 1000°C et 1200°C. A ces températures, il n'y a pas de risque de formation de carbures des métaux utilisés. Des carbures risqueraient de se former entre la grille et le matériau de brasure (par exemple du carbure de titane) si on travaillait à des températures proches de la température de fusion du titane (vers 1690°C) ou du zirconium, et ces carbures seraient défavorables du point de vue de la conduction thermique et électrique entre la grille et l'embase. D'autre part, les températures utilisées ici pour la brasure sont beaucoup plus favorables du point de vue des contraintes engendrées par les dilatations différentielles entre les pièces brasées. La température du four lors de l'opération de brasage est choisie légèrement supérieure à la température de fusion de l'eutectique.The eutectic temperatures are low enough to allow the use of conventional ovens working between 1000 ° C and 1200 ° C. At these temperatures, there is no risk of carbides forming from the metals used. Carbides would be likely to form between the grid and the brazing material (for example titanium carbide) if one worked at temperatures close to the melting temperature of titanium (around 1690 ° C) or zirconium, and these carbides would be unfavorable from the point of view of thermal and electrical conduction between the grid and the base. On the other hand, the temperatures used here for the brazing are much more favorable from the point of view of the stresses generated by the differential expansions between the brazed parts. The temperature of the oven during the brazing operation is chosen to be slightly higher than the melting temperature of the eutectic.

Les tensions de vapeur saturante pour les matériaux cités ci-dessus sont de 10-8 mm de mercure (1,3 x 10-11 bar) aux températures respectives suivantes :
   1000°C pour le titane
   900°C pour le nickel
   880°C pour le fer
   550°C pour le cuivre.The saturation vapor pressures for the materials mentioned above are 10 -8 mm of mercury (1.3 x 10 -11 bar) at the following respective temperatures:
1000 ° C for titanium
900 ° C for nickel
880 ° C for iron
550 ° C for copper.

On peut donc considérer que le nickel, le fer et le cuivre (dans l'ordre de préférence décroissante) conviennent pour une association avec le titane (avec lequel ils forment tous un eutectique dont la température de fusion est largement inférieure à celle du titane). Le cuivre est le plus défavorable puisqu'il tend à s'évaporer plus facilement. Le nickel est le plus favorable. Le couple titane-nickel est le couple préféré selon l'invention.We can therefore consider that nickel, iron and copper (in decreasing order of preference) are suitable for a association with titanium (with which they all form a eutectic whose melting temperature is much lower than that of titanium). Copper is the most unfavorable since it tends to evaporate more easily. Nickel is the most favorable. The titanium-nickel pair is the preferred pair according to the invention.

Claims (8)

Procédé de montage de grille en graphite dans un tube électronique à vide, ce procédé comprenant une opération consistant à braser dans un four la partie inférieure (230) de la grille (20) sur une embase métallique (50), à l'aide d'une brasure comportant au moins deux matériaux formant un eutectique, l'un des matériaux ayant de bonnes propriétés de mouillage du graphite, et les deux matériaux ayant des tensions de vapeur inférieures à 1,3.10-11 bar à la température maximale de l'embase lors du fonctionnement du tube.A method of mounting a graphite grid in an electronic vacuum tube, this method comprising an operation consisting in brazing in a furnace the lower part (230) of the grid (20) on a metal base (50), using 'a solder comprising at least two materials forming a eutectic, one of the materials having good wetting properties of graphite, and the two materials having vapor pressures lower than 1.3.10 -11 bar at the maximum temperature of the base during tube operation. Procédé selon la revendication 1, caractérisé en ce que le premier matériau de brasure est du titane ou du zirconium, et le deuxième matériau est du nickel, du fer, du cuivre, ou de l'argent.Method according to claim 1, characterized in that the first brazing material is titanium or zirconium, and the second material is nickel, iron, copper, or silver. Procédé selon l'une des revendications 1 et 2, caractérisé en ce que les deux matériaux de brasure sont présents dans des proportions égales à, ou proches de, celles de l'eutectique.Method according to one of claims 1 and 2, characterized in that the two brazing materials are present in proportions equal to, or close to, those of the eutectic. Procédé selon l'une des revendications 1 à 3, caractérisé en ce que la température du four est légèrement supérieure à la température de fusion de l'eutectique.Method according to one of claims 1 to 3, characterized in that the temperature of the furnace is slightly higher than the melting temperature of the eutectic. Procédé selon l'une des revendications 1 à 4, caractérisé en ce que plusieurs grilles à la fois sont brasées dans le four.Method according to one of claims 1 to 4, characterized in that several grids at the same time are brazed in the oven. Procédé selon l'une des revendications 1 à 5, caractérisé en ce que l'ensemble de la grille et de l'embase est fixé à une électrode de connexion extérieure (22), avant installation dans le tube à vide.Method according to one of claims 1 to 5, characterized in that the assembly of the grid and the base is fixed to an external connection electrode (22), before installation in the vacuum tube. Tube électronique à grille en graphite pyrolytique, caractérisé en ce que la grille (20) est montée sur une embase métallique (50) et est liée à cette embase par un matériau de brasure constitué d'au moins deux matériaux dont l'un mouille bien le graphite et qui forment ensemble un eutectique, les deux matériaux ayant des tensions de vapeur inférieures à 1,3.10-11 bar à la température maximale de l'embase lors du fonctionnement du tube.Electronic tube with a pyrolytic graphite grid, characterized in that the grid (20) is mounted on a metal base (50) and is linked to this base by a solder material made of at least two materials, one of which wets graphite well and which together form an eutectic, the two materials having vapor pressures below 1.3.10 -11 bar at the maximum temperature of the base during operation of the tube. Tube selon la revendication 7, caractérisé en ce que le premier matériau de brasure est le titane ou le zirconium, et le deuixième est le nickel, le fer, le cuivre ou l'argent.Tube according to claim 7, characterized in that the first brazing material is titanium or zirconium, and the second is nickel, iron, copper or silver.
EP96400971A 1995-05-09 1996-05-07 Tube with pyrolytic graphite grid and method of making Withdrawn EP0742573A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9505479A FR2734081B1 (en) 1995-05-09 1995-05-09 PYROLYTIC GRAPHITE GRILLE TUBE AND MANUFACTURING METHOD
FR9505479 1995-05-09

Publications (1)

Publication Number Publication Date
EP0742573A1 true EP0742573A1 (en) 1996-11-13

Family

ID=9478803

Family Applications (1)

Application Number Title Priority Date Filing Date
EP96400971A Withdrawn EP0742573A1 (en) 1995-05-09 1996-05-07 Tube with pyrolytic graphite grid and method of making

Country Status (2)

Country Link
EP (1) EP0742573A1 (en)
FR (1) FR2734081B1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE727337C (en) * 1936-08-01 1942-10-31 Aeg Outer electrode for electrical discharge vessels, which forms part of the wall of the discharge vessel
US4728852A (en) * 1984-06-29 1988-03-01 Thomson-Csf Device for fixing a pyrolytic graphite grid onto the base of an electron tube
FR2695340A1 (en) * 1992-09-04 1994-03-11 Thomson Tubes Electroniques Sealing graphite part to support using solvent metal - esp. in electron tube grid assembly, ensures good thermal and electrical contact and does not require machining other than for alignment

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE727337C (en) * 1936-08-01 1942-10-31 Aeg Outer electrode for electrical discharge vessels, which forms part of the wall of the discharge vessel
US4728852A (en) * 1984-06-29 1988-03-01 Thomson-Csf Device for fixing a pyrolytic graphite grid onto the base of an electron tube
FR2695340A1 (en) * 1992-09-04 1994-03-11 Thomson Tubes Electroniques Sealing graphite part to support using solvent metal - esp. in electron tube grid assembly, ensures good thermal and electrical contact and does not require machining other than for alignment

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
IBM TECHNICAL DISCLOSURE BULLETIN, vol. 17, no. 9, February 1975 (1975-02-01), pages 2620, XP002008172 *

Also Published As

Publication number Publication date
FR2734081A1 (en) 1996-11-15
FR2734081B1 (en) 1997-06-06

Similar Documents

Publication Publication Date Title
EP0289423B1 (en) Tubular electrode for use in a plasma torch, and plasma torch equipped with such an electrode
FR2929754A1 (en) COLLECTOR AND ELECTRONIC TUBE
EP0742573A1 (en) Tube with pyrolytic graphite grid and method of making
EP0037309B1 (en) Travelling-wave tube with coupled cavities and with periodic permanent magnet focussing, and amplifier unit with such a tube
US20090134800A1 (en) Electrode System for a Lamp
EP0076724B1 (en) Method of manufacturing a heat exchanger with annularly mounted water tubes
KR100980446B1 (en) electrode arc of plasma cutting machine
EP0191664B1 (en) Envelope under vacuum for an x-ray image intensifier tube
EP0117804B1 (en) Manufacturing method of a microwave cavity, and cavity obtained thereby
FR2498503A1 (en)
FR2520265A1 (en) WICK FOR HEAT TUBE
FR2480496A1 (en) CATHODE FOR ELECTRONIC TUBES COMPRISING TWO HOLLOW BODIES
BE1001637A4 (en) Method for ceramic bulb close of discharge lamps high pressure and in particular of sodium lamps, lamps and made following this process.
FR2475797A3 (en) VOLTAGE LIMITER AND MANUFACTURING METHOD THEREOF
EP0002406B1 (en) Ion source, in particular for an ion implantation device
US4725510A (en) Source for vapor-depositing manganese
EP0009444A1 (en) Process for making pyrolytic graphite grid electrodes for electron tubes
FR2553688A1 (en) Method for attaching a capillary tube and device for the implementation of the method
BE418022A (en)
FR2638281A1 (en) ELECTRONIC BUILDING TUBE COMPACT
BE396165A (en)
BE499435A (en)
FR2729322A1 (en) Brazing carbon@ parts to each other or to metal or ceramic
FR2741997A1 (en) CATHODE STRUCTURE FOR CATHODE RAY TUBE
FR2556123A1 (en) Method for producing a sealed electrical penetration through a wall

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): DE FR GB

17P Request for examination filed

Effective date: 19961022

17Q First examination report despatched

Effective date: 19971203

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19980616