US3102180A - Apparatus for making electron tubes - Google Patents

Description

APPARATUS FOR MAKING ELECTRON TUBES Original Filed Dec. 5, 1957 3 Sheets-Sheet 1 IN VEN TOR JACK A. McCULLOUGH WILLIAM R. STUART w/waza AT TORNE YS Aug. 27, 1963 J. A@ M CULLOUGH ETAL 3, 2,

APPARATUS FOR MAKING ELECTRON TUBES Original Filed Dec. 5, 1957 3 Sheets-Sheet 2 IN VEN TORS JACK A. McCULLOUGH Y WILLIAM R. STUART GEM/ 8m ATTORNEYS 1963 J. A. MCCULLOUGH ETAL I 3,102,180

APPARATUS FOR MAKING ELECTRON TUBES Original Filed Dec. 5, 1957 3 Sheets-Sheet 3 IN VEN TORS JACK A. MCCULLOUGH YW/LLIAM R. STUART ATTORNEYS usual exhaust tubulation on tubes.

and this application Sept. 29, 1961), Set. No. 59,265 6 Claims. (Cl. 219-95) This invention relates to apparatu's'for making electron tubes. More specifically, the invention relates to apparatus for making electron tubes having pressure seals made between two metallic surfaces. The term pressure seal is defined for use herein as a permanent, vacuum-tight seal obtained by the application of pressure at temperatures belowthe melting point of any of the metals within the seal or any of the materials around the seal. This invention is a divisional of our application Serial No. 700,853, filed December 5, 1957, noWPatent No. 2,996,347, issued August 15, 1961.

The construction of electron tubes is such that practically all types have a shell or envelope involving at 7 least two sections sealed together along an annular joint. In the past it has been standard practice to join envelope sections by means of fused or melted bonds, such as the conventional braze or weld joint. It has previously been proposed that a vacuum-tight seal could be made at temperatures below the melting point if the surfaces to be joined were given an optical polish. This optical polish technique has never been adopted commercially for a number-of reasons including the fact that optical polishing is'expensive.

The present invention has as a basic object the teaching of an apparatus by which electron tubes can be made with pressure seals on a commercially practical basis.

I A more specific object of the invention is to provide a pressure sealing'apparatus having'a very short processing cycle. An associated object of the invention is to provide a pressure sealing apparatus in which heating of the seal is accomplished by inducing an RF. current directly in the metal surfaces to be sealed together.

A further object of this invention is to provide a pressure sealing apparatus which does not involve the expense of obtaining an optical polish on the surfaces to be joined.

An additional object of the invention is to provide a pressure sealing apparatus which eliminates need for the An associated object is to provide a pressure sealing apparatus which combines into a closely related system the formation of the pressure seal and the normal tube processing procedures such as exhaust, bakeout, and cathode formation.

Another object of the invention is to provide an electron tube having an envelope comprising two members joined together by a pressure seal.

:In essence, the invention resides in the making of electron tube pressure seals by the application of high pressures and high temperatures in a vacuum. Although high temperatures are utilized, they are of course below the melting ,point of any of the materials involved in making the seal. The components of the apparatus remain relatively cool as the metallic sealing surfaces are elevated in temperature.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention.

It is to be understood that the invention is not limited to the disclosed species, as variant embodiments thereof are contemplated and may be adopted within the scope of the claims. A

' ,tabfor which primed reference numerals are employed.

' Referring to the drawings:

FIGUREI is a side view partly in section showing a Va-cuum'chamber and pressure exerting ram in accordance with the invention. An electron tube is shown in the chamber and the ram is positioned in pressure exerting contact therewith;

FIGURE 2 is a cross-sectional view showing the vacuum chamber of FIGURE 1 on an enlarged scale. The tube is shown in cross section, and the position of the ram is such that it is not exerting pressure on the tube;

FIGURE 3 is a view on line 3-3 of FIGURE 1;

FIGURE 4 is an enlarged top view of the tube holding jig of FIGURES 1 and 2; and

FIGURE 5 is aside View of a completed tube of the type shown in FIGURE 2.

Referring to the drawings in more detail, FIGURE 5 shows an example of a tube 10 made by the apparatus of the invention. The particular tube shown in the drawings is cylindrical in shape and has an envelopewall made of a plurality of ceramic rings 11 and a plurality of metal rings 13-22. FIGURE 2 shows the tube 10 in cross-section, and the construction of the tube can be a best understood by viewing both FIGURES 2 and 5. It will be noted that the tube is a double triode so that metal rings 14 and 21 both form anodes at the ends of the tube. Metal rings 15 and 26 form supports for control grids; rings 16 and 19 form cathode supports; and rings 17 and 18 form leads for the single heater which is inside the double cathode. The end rings 13 and 22 are merely to protect the anode rings against damage. Each of the electroderings is provided with a terminal The terminal tabs are arranged in two diametrically positioned rows. l

Although a specific tube has been disclosed for convenience in describing the apparatus, it will be understood that other. tube configurations can {be made by the invention.

Coming now to the novel apparatus of the invention, FIGURE 1 discloses the stand pipe 30 ,of a conventional exhaust pumping system (not shown). At the upper end of pipe 30 a Water cooled mounting disk 33 is attached as by brazing, and a sealing ring 35 is seated in a recess on the upper surface of the disk. A support ring 37 is attached to disk 33 by means of screws 38.

A base member or plate 46 is mounted in the center of encircles plate 40 in the area of seal 47 to permit cooling piston rod 63.

of the seal. I

Aplatform 5th is mounted on support ring 37 'by means of three rods 51 which are attached to ring 37 by screws 52 and the platform 50 by screws 53. ln turmplat-form 50 supports a conventional hydraulic cylinder and piston unit 55 by means of three rods 56 held in place by screws 57. The cylinder and piston unit is connected by pipes 60 and 61 to a conventional hydraulic pumping system (not shown). I

' A piston rod 63 extends down from the unit 53 and is threaded into-a coupling 64 and fixed by lock nut 65. A rod 67 is accurately guided by a bushing 69 which is mounted on platform 511 by screws 70. Rod 67 dits into coupling 64 with considerable playin order to accommodate any misalignment between bushing 69' and'the A coupling 72 is mounted on the end of rod 67 where it is held in place by a screw 73 which engages a recessed wall portion 75 on rod 67. The rod 67 has an accurately machined closed fit in coupling 72, and

Patented Aug. 27, 1963 thereof. 7 coil 85 and cooling water is passed therethrough. The coil is arranged to move up and. down with the cylinder,

the recess 75 is provided sothatthescrew 73 will not 3 roughen the accurately machined portion of the rod.

The lower end of coupling '72 has a recessed portion lined with two sealing rings 77 and 78 (FIGURE 2). A cooling tube "/9 isattached to coupling -72 to prevent heatthe position of ring 1102 to permit easy insertion of the tube and associated ceramic parts 98, 1%, 94 and 102.

ing of the sealing rings. A glass cylinder-30 is held in the end of coupling 72 by frictional engagement with sealing rings 77 and 78. A ram {82 is held wedged between the I recessed end of coupling '72 and the upper end of cylinder 80. Ram 82 is made of ceramic or other dielectric ma-v terial having high strength and low heat conductivity.

I A tubular coil 85 surrounds cylinder 3d about the center Radio frequency current is passed along the as will now be described. A platform -87 cfinsulating material is split at one end and clamped to coupling 72. I

by means of'screw 88. The ends of the coil 85 are attached to platform 87 to support the coil and are provided with fittings 8-9 for connection to'flexible water hoses.

. The ends of coil 85 and the fitting are joined to metal After the tube and associated ceramic parts have been I placed in processing position with stand 98 seated in recess 45','the ends of heater leads 108 and 109 are inserted through slots 196' sothatthe contact fingers. on the leads engage the heater terminals 118" and 117'. Next, the

v cylinder and piston unit 55 .is operated to lower the glass cylinder 80 until its lower end makes sealing contact with sealing ring 471m before ram 82 makes contact Withjring 102, as shown in FIGURE 2. Y

Next, the stand pipe 3tlis. connected, as by suitable valving, to a conventional vacuum system to obtain a vacuum in the cylinder 80 and hence within tube Ill. At this point it should be explainedthat the separate metal and metalized ceramic envelope parts have sealing surfaceswhich are not provided with an optical finish. In fact, the sealing surfaces which are pressed together need not be polished at all, although coining to obtain flatness is desired.

In addition to saving the'expense ofoptical polishing,

the use of sealing surfaces which have a finish rougher plates 90 which are attached to platform 37 and to which flexible copper strap leads- 91 are attached by screws92 (FIGURE 3 The leads 91 are connected to a conventional source of radio frequency power-(not shown).

The structure thus far described provides the operating mechanism for making a tube according to the invention. Theremaining'structure shown within the cylinder 80 in FIGURES 1 and 2 consists of the tube and the jigging for it. The tube 10 has already been described. It-will be seen best in FIGURES 2 and 4 that the tube parts are loadedina cylindrical jig 94 having a central bore 95 and 'longitudinalkgrooves 96. The grooves 96 must be at least equal innumber to the number, of rows of terminal tabs 4 onthe tube, assuming of course that the tube under con- 1 struction has this type of terminal arrangement. Itwill fbe seen'in FIGURE 4 that jig 9'4 has four grooves 96 whereas tube 10' has only two rows of terminal tabs. The two extra grooves are desirable for free passage of air from the tube to the exhaust chamber. Jig 94 is made of dielectric material such as ceramic.

The jig 94is supposed on a cylindrical stand 9% which is received in the seating recess 45 in plate 40. A short 98. A pressure ring 102 rests on the top of the tube and is provided with a central 'bore 103. Ram 82 is provided with a tapered tip 104 which engages the rim of bore 103 I to, assure even application of pressure. Stand 98 and the rings 100 and 102 are made of ceramic or other dielectric material having high strength and low heat conductivity. Ji-g94 isprovided with two apertures 106 opening. into diametrically opposed recesses 96 sothat electrical connection can be made to beater tabs 17' and 18 The connection is made by leads 108 and 109 whichpass through aperture 44 in plate 40 and are connected to terminals 110 and 111 (FIGURE 1) which are mounted on 'elevatingring' 100 is received in the upper end of stand but insulated from standpipe Till. The upper ends of leads 108' and 109 are provided with contact fingers which pass through apertures 106 andengage tabs 18' and 17',-respectively. 1 r

" The method of using the hereinbefore described appa- 1 ratus in the manufacture of a tube will now be explained.

FIGURES 1' and 2 show a tube 10 positioned inside the Vacuumtightchamber formed by the base member 40 in cooperation with the wall structure comprising cylinder 80 and coupling 72. Naturally, the first step is to insert the. tube parts into the'vacuum chamber. Preferably the tube parts, such as par.ts 1322, are loaded into the jig,

such as jig 94, before placing the jig in the vacuum chamber. In practice it is desirable to assemble stand 98,

'ring 100, jig 94, the tube parts, and ring 102 outside the vacuum chamber and insert them as a unit. It will be apparent from FIGURE 1 that by operating the cylinder and pistonunit 55 to raise piston rod 63, the glass cylinder 80 can thereby be lifted so that itsbottom edge is above period commensurate with'its size.

than an .optical'finish permits .the tube to be quickly and fully pumped in a vacuum chamber Without resorting to some means for holding the sealing surfaces separated during pumping. it will be understood by those skilled l1'l the art that if the sealing surfaceshave an optical polish they .will fitso closely-together that the passage of gas therebetween .will be at best so slow as to require,

bond together upon the application ofpressure, the direct induction of radio frequency current eliminates the prolonged heating and cooling period which would be required if a conventional oven type of heating were employed. In this connection it should be understood that one of the reasons for making parts 98, 100, 10-2, $2, and particularly jig 94 out of dielectric material is so that theywill not prevent or diminish the induction of RiF. current in the metal partsof the tube. Similarly,

it will be appreciated that the elimination of metal as the'material for parts which are subject to high temperature makes it possible to raise cylinder immediately after forming the pressure seals. If metal were used it would be necessary to have a cooling period within the vacuum, as otherwise oxides would form and destroy I the tolerances for parts98, 100, 102, 104 and particularly 94. I 4

During the outgassing period any required cathode forming is accomplished. The particular tube shown in the drawings employs a conventional oxide coated cathode. Forming of the cathodeis accomplished by applying power to the leads 108' and 109" which energizes the heater to the extent necessary to raise the cathode to forming temperature;

When forming of the cathode and outgassing has been completed, the next step is to make the pressure seals. 9 v The pressure seals are made by operating the cylinder and piston unit 55 to move piston rod 63 downwardly until ram 82 engages pressure ring 102 with sufficient force to apply to the sealing surfaces a unit pressure I substantially in excess of that which would be provided by exposing the outside of the tube to atmospheric pressure with a vacuum on the inside. It should be understood thatevacuation of the vacuum chamber and induction.

heating of the sealing surfaces are continued when the sealing pressure is applied. After the sealing pressure has been applied and a vacuum'tight seal has been formed, the heating current in coil is cut Offlstand.

pipe 30 is disconnected from the vacuum pump, cylinder 80 is raised, tube and jig 94 are removed from the vacuum chamber, and finallytlie tube is removed from the jig.

Although the exact nature of the sealing action may not be known with provable certainty, it seems reasonably clear that the practical success of the pressure sealing method of this invention depends primarily on the fact that the metal surfaces to be sealed together are heated in a vacuum prior to the application of pressure and are. not handled or removed from the vacuum between heating and the application of pressure. The point is that metal surfaces to be pressure sealed must be almost entirely free of'dirt, occluded gases, oxides and other impurities. One of the best ways of accomplishing such cleaning is to heat the surface in a non-oxidizing environment, as for example in a vacuum or inert gas. Incidental to this understanding is the realization that the method of the invention can be used to make gas filled t-ubesemploying one of the inert gases such as helium, or other gases such as hydrogen where the other gas does not form compounds with any of the particular metals out of which the sealing surfaces are made.

Naturally, it is not only necessary that the metallic sealing surfaces be cleaned some time prior to the application of pressure, but they must also be kept clean between the cleaning step and the pressure step. The present invention provides the only practical method of maintaining cleanliness; namely, the method of pressing the metallic sealing surfaces together in the same chamber in which they were cleaned.

Perhaps in theory, perfectly smooth, perfectly clean metallic sealing surfaces would bond together in a vacuum tight seal without the application of any pressure. However, the purpose of the invention being to provide a practical mass production method of making electron tubes does not admit of such perfection. Thus,

it is proposed that substantial pressure be used. One

purpose of the pressure is to overcome the lack of smoothness. Clearly, if metallic sealing surfaces which are not perfectly smooth are brought togethenthey will not he in contact over their entire surfaces but only at a number of separate points. Although the points in contact may bond together to form a joint of appreciable strength, they will very likely not form a continuous wall, or vacuum tight seal. The invention requires, then, that enough pressure he applied to assure sufficient contact between the sealing surfaces to form a vacuum-tight seal. In addition, it has been found that the yield of good seals is increased if sufficient pressure is applied to actually cause radial deformation or extrusion of the metal in the sealing surfaces, or at least of the softer metal in the sealing surface'where the surfaces are of different metals. This improvement is believed to be explainable by the theory that any surface oxides which might not have been removed by the high temperature cleaning can be broken up by deformation to expose clean metal. This theory also provides an additional reason for using metallic sealing surfaces having a finishwhich is rougher than an optical finish, the thought being that surface oxides can be more easily ruptured when relatively rough surfaces are pressed together than when optically smooth surfaces are used.

In connection with the application of pressure, it should be noted that the apparatus provides a very rapidly operating and simple arrangement. More specifically, the apparatus eliminates the need for complicated bellows arrangements by making the pressure exerting means or ram 82'movable with the chamber wall 80. Thus, the movement which initially closes the chamber places ram 82 almost in pressure exerting contact, and the movement which removes the pressure of ram 82 also opens the chamber so a finished tube can be immediately extracted. It is also important to note that when pressure is applied to the tube it is done with poor heat conductors such as meramic pieces 98, 100, 102, and 82. There are two reasons for preventing a good heat conducting path; one is that it would be undesirable to drain heat from the sealing surfaces at the exact period of sealing, and the other reason is that sudden cooling of the tube ceramics would cause them to crack.

Utilizing the basic teachings of the invention, it is possible by experimentation to determine the minimum temperatures, pressures and duration of application which are necessary to obtain satisfactory seals between the various materials which might be used. By way of example, experiments have been made with tubes which comprise the following envelope construction: a high alumina ceramic member such as rings 11, a conventional molybdenummanganese metalizing coating on the ceramic, and a nickel layer forming a sealing surface plated on the metalizing coating; a thin sealing ring of copper; and a metal envelope ring such as rings 13-22 of Kovrar or nickel. The metalizing, the nickel plating, and the copper rings do not appear in the drawing because the invention is not limited to any specific materials and because they are extremely thin. For example, the copper ring is .003 inch thick and the metalizing and nickel plating are each only .0002 inch thick. Tubes having satisfactory seals with these materials have been made according to the following procedure utilizing the apparatus of. the invention: Place the tube parts in the vacuum chamber, exhaust the chamber, induce current in the sealing surfaces for about three minutes to raise the temperature of the surfaces to about 750 0., lower ram '82 with sufficient force to deliver between \l1,000 and 18,000 pounds per square inch pressure at the sealing surfaces, and maintain this pressure for about two and one-half minutes. The cathode must be formed prior to applying pressure and the earlier it is Not only are the method and apparatus of the invention not limited to certain specific materials, they make it possible to effect pressure seals even using easily oxidized metals such as copper. The advantage of being able to use copper, which is a desirable metal in electron tubes, is made possible because the sealing surfaces are not removed from the non-oxidizing environment between the time they are cleaned by heating and the time they are pressed together.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for making pressure seals, said apparatus comprising a base member having an exhaust aperture therethrough, said member having a circular recess on one side thereof into which said aperture opens, sealing ring 1 means in the side wall of said recess, a cylinder coaxial With said recess, said cylinder having one end receivable in said recess in sliding contact with said sealing ring means, a closure member for the other end of said cylinder, said closure member having a recess in which said other end of the cylinder is received, sealing ring means in the side wall of said recess in the closure member, the last mentioned sealing ring means being in contact with said cylinder over a greater area than the area of contact between the cylinder and the first mentioned sealing ring means, means for moving said closure member toward and away from said base member, and a ceramic r-am projecting from said closure member toward said base member inside said cylinder.

2. Apparatus for making pressure seals, said apparatus comprisinga base member having an exhaust aperture therethrough, said member having a circular recess on one side thereof into which said aperture opens, sealing ring means in the side wall of said recess, a cylinder coaxial with said recess, said cylinder having one end receivable in said recess in sliding contact with said sealing ring means, a closure member for the other end of said cylinder, said closure member having a recess in which said said cylinder over a greater area than the area of contact between the cylinder and the first mentioned sealing ring means, and a ram positioned within said cylinder, said ramh-aving a rim portion clamped between the end of said cylinder and the end of said recess in the closure chamber. v p v I 3. Apparatus for making pressure seals comprising a base member, a dielectric wall structure engageab'le with said base to fornr a vacuum chamber having an exhaust aperture therein, means for moving said wall structure toward and away from said vbase member, a sealing ring engaging said base member and the side of said wall structure and forming a vacuum tight seal between said base member and said wall structure during theterminal portion of said movement of the. wall structure toward said base member, a ceramic ram positioned within said wall structure and movable therewith, and said ram and wall structure being so connected that any movement of said ram toward said base member is necessarily accompanied by movement of said wall structure toward said basemember, and an induction heating coilsurrounding said well structure. I

4. Apparatus as claimed in claim; 3 in which said means .for moving the wall structure relative to said base member comprises an actuating unit having a cylinder element and 1a piston element, and-connecting means joining said wall structure and ram to oneof said actuating elements and joining said'base' member to the other of said actuating elements. Y

5. Apparatus as claimed in cbaim 3 further compris ing a ceramic work supporting member seated on said base member and projecting toward said ram insidesaid wall structure. m

6. Apparatus as claimed in claim 5 fiurthe-r comprising a cylindrical ceramiework holding jig mounted on. said I work supporting member.

References Cited in the file of this patent UNITED' STATES PATENTS 2,279,854 Whitney'. Apr. 14, 1942. 2,397,263 Hunter'et al. Mar. 26,1946 2,439,246 'Gibian Apr; 6, 1948 2,629,093 Pask et al. Feb. "17, 1953; 2,654,822 A-gule Oct. 6, 1953" v 2,730,599 Ronay' Jan. 10, 1956' 2,920,786 Duran et all Jan. 12, 1960 2,966,571

Markert Dec. 27,1960

Claims (1)

1. APPARATUS FOR MAKING PRESSURE SEALS, SAID APPARATUS COMPRISING A BASE MEMBER HAVING AN EXHAUST APERTURE THERETHROUGH, SAID MEMBER HAVING A CIRCULAR RECESS ON ONE SIDE THEREOF INTO WHICH SAID APERTURE OPENS, SEALING RING MEANS IN THE SIDE WALL OF SAID RECESS, A CYLINDER COAXIAL WITH SAID RECESS, SAID CYLINDER HAVING ONE END RECEIVABLE IN SAID RECESS IN SLIDING CONTACT WITH SAID SEALING RING MEANS, A CLOSURE MEMBER FOR THE OTHER END OF SAID CYLINDER, SAID CLOSURE MEMBER HAVING A RECESS IN WHICH SAID OTHER END OF THE CYLINDER IS RECEIVED, SEALING RING MEANS IN THE SIDE WALL OF SAID RECESS IN THE CLOSURE MEMBER, THE LAST MENTIONED SEALING RING MEANS BEING IN CONTACT WITH SAID CYLINDER OVER A GREATER AREA THAN THE AREA OF CONTACT BETWEEN THE CYLINDER AND THE FIRST MENTIONED SEALING RING MEANS, MEANS FOR MOVING SAID CLOSURE MEMBER TOWARD AND AWAY FROM SAID BASE MEMBER, AND A CERAMIC RAM PROJECTING FROM SAID CLOSURE MEMBER TOWARD SAID BASE MEMBER INSIDE SAID CYLINDER.

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