US2928022A - Metal tube assembly and method - Google Patents

Description

March 8, 1960 P. E. GATES METAL TUBE ASSEMBLY AND METHOD Original Filed Nov. 2, 1949 INVENTOR PAUL E. GATES ATTORNEY -S es Paem r 2,928,022 Patented Mar- 119. 9.

METAL TUBE ASSEMBLY AND METHOD Paul E. Gates, Danvers, Mass., assignor, by mesne Vas-.

sig'nments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Continuation of application'Serial No. 125,055, Novem- I her 2, 1949. This application September 17, 1954,;

Serial No. 456,701

6 Claims. (Cl. 315-39) The present invention relates to metal-walled electrical devices that are at least partially evacuated, and which include a wall portion of glass or like vitreous insulating material. In particular, this invention is concerned with transmitreceive tubes and the like, and to methods of constructing such devices. Other tubes of this general class are anti-transmit-receive tubes, attenuator. tubes, switch tubes and pre-transmit-receive tubes. These have an ionizable gas enclosed in a section of waveguide, and

the first three have electrodes where an ionized discharge may take place. This specification is directed to transmit-receive tubes (or T.-R. tubes briefly) for illustrative purposes, but its application to comparable tubes'will be readily apparent. The present application is a continuation of my application Serial No. 125,055, filed November 2, 1959, and assigned to the assignee of the present application, now abandoned.

.A form of T.-R. tube that is commonly in meat the present time includes a length of metal-walled waveguide that is closed off hermetically at each end'by a metal -frame'having a glass center, this composite structure being commonly termed a window. The waveguide is divided into sections by one or more apertured resonator plates transverse of the waveguide, parallel to the windows. Electrodes affording a discharge gap are provided 'within each aperture. At'the end of the transmit-receive tube and externally thereof is a flange by means of which electrical and mechanical contact is made tov the wave-f guide system where the tube is to be used. The effective distance between the exposed mounting" surface of the flange and the nearest discharge gap (where more than one gap is provided) is of critical importance in the design of the waveguide system, and this distanceis preestablished andstandardized in the commercial production of these tubes. The distance as a. mechanical dimension can be permitted to vary so long as uniform operating characteristics are achieved; buthe'retofore a close tolerance on all physical dimensions has been relied upon to reproduce the desired characteristics from tube to tube. An object of the present invention is to provide a method of constructing these tubes and a novel tube construction-that will enable adjustment of this flange-to-gap distance for optimum electrical standardization after the T.-R. tube has been sufiiciently complete to enable testing.

In a previous practice, the fla' ge is hard-brazed to the end of the waveguide wall before the window is inserted,

the position of the flange-being fixed in, relation to the discharge electrodes according to standardized dimensions; and then the window is soft-soldered across the opening within the flange. This procedure has been followed because hard-brazing of the window frequently re sulted in cracking of the glass when the cooling stresses thinned wall portions or edges at its ends, and a window is hard-brazed to these thinned edges.v The flange is mounted about the window after the T.-R.'tube has been completed sulficiently to enable atest, and the flange is then fixed in place laya soft soldering operation, the place being determined by electrical tests. The resulting tubes are more uniform in performance and more satisfactory as,to life because of the hard-fused-seals that are used inplace of soft-solder joints- Tubes of the interior, and with only one .of the two mounting flanges that are normallyprovided.

Figure 2 is an enlarged detail view of a portion of the tubezin Figural in its condition preliminary to sealing,

being an isometric View, partly in section.

Figures 3 .and '4 are modifications of the seal construction in FigureZ. L j

The tube in Figure .1 that embodies theinvention-incorporates the usual elements of a known type of transrriit-receive tube. It has a longitudinal wall 10 of rectangular waveguide,,.the metal wall thickness being sufltcient to maintain the proper shape despite. the low pressure within the tube-as compared to the external atmospheric pressure. At each end is a window 12 (only'one of which is shown) that has a glass center 14 and a metal frame 16. Tube 18 is provided for exhaust and for fill I purposes,'being sealed off in the completed tube. Plates 20 are spaced apart so that their edges, together with the top and bottom wall, form a resonant aperture. Within each of the two apertures shown is a discharge gap formed imposed by the flange were transmitted to the glass element; but the soft-solder seal is not entirely'satisfactory.

In practicing the present invention as applied to one form of T.'-R. tubes, a waveguide of adequate wallthickness to support a partial vacuum is provided with by conical electrodes: 26. One of these, 2611, is hollow and open at its apex, and contains a coaxial, glass-sheathed j k'eep-alive electrode (not shown) that terminates just short of the apex opening and has an external; terminal 28. In operation this is appropriately energizedto maintain a limited volume of ionized gas at the tip of electrode 26a.

a "The equipment in which this tube is typically intended to be used includes a transmitter and a receiver that operate into a waveguide system having a common antenna, and when the transmitter :is-pulsed-to send a burst of energy into the antenna the transmit-receive tube is to fire. This discharge is expedited by the action of the keep-alive. The discharge, occurring at a definite point in the waveguide system, so changes its electrical configuration that substantially, none of the transmitter energy reaches the receiver where it might otherwise have damaging effect. Thus, the location of the discharge gap in its electrically effective spacing from the flangevof the tube is a very critical matter.

The configuration of the resonators formed by plates 20 and by walls 10, the form and spacing of the conical electrodes 26, the thickness of the glass portion 14, and

the spacing of the discharge gap from thewindow are all factors affecting the tube operation. These are all cumulatively resolved by preserving the ad justabilityof flange 30, so as to permit adjustment toward and from the gap between cones 26, 26a, until the tube can-be tested electrically; that is, after sealing evacuation andproper filll 'Windows 12 are hard-soldered or brazed (both being high temperature fusing operations) to the end of walls 10 v of the waveguide. These walls have end portions 10a of v wall.

reduced thickness. Thin ribbons 32 of nickel or the like are secured as by spot welding to act as a frame for centering the'window l2. during'assembly, and to conduct the flow of sealing metal by capillary action to the abutt ed surfaces of wall portions Illa and the frame 16 (Figure 2). A pre formed shape 34 of silver-solder or like high temperature soldering or brazing alloy is applied to' the outsidesurface of the window. This is secured in place by bending the ribbon 32 as illustrated at 32a. Thereafter, the assembly of the waveguide and the windows is passed in a soldering jig through a hydrogen furnace, for a heating cycle and a subsequent gradual cooling cycle. In this cycle the silver-solder or like sealing metal forms ahermetic seal between frame 16 and'thinned wallportionsllla, and also runs into the space between the nickel strip and portions lilo to constitute a firm hermetic seal at the periphery of thewindow. It is inadvisable to assemble the windowand the wall withthe silver-solder preform interposed between frame 16 and edge portions a, because this arrangement has the tendency of causing the solder to flow mainly along'the inside surface of portions 16a and to build up its thickness excessively while affording inadequate flow of the alloy where the joint is to be formed.

The hard-soldering or brazing operation is accomplished at high temperatures and the cooling cycle extends over a half-hour period or longer. When in the subsequent operation flange Bills secured to the sealed tube, it is secured in a. low temperature operation which does not have any great tendency to impose large contraction stresses on. the window. Any moderate stress that might develop because of the soldering temperature as well as the stress resulting. from the operation in whichthe win dow is sealed to the rectangular waveguide wall are absorbed by the resilience of the thinned wall portions ltla. The location at'which the flange is to-be secured 'is determined by inserting the tube and fiangecin a typical operat- What is claimed is:

1. The method of fabricating a waveguide structure having a window including a metallic frame and an external flange, including the steps of reducing the thickness of the walls throughout a short end portion of a length of Waveguide having walls of otherwise substantial uniform wall thickness whereby said end portion has greater flexibility than the remaining length of the waveguide, placing a thin ribbon of metal around said waveguide to surround said end portion and to extend beyond the. outer end thereof, placing said window traversely across the end of said waveguide with the frame in abutting relationship with the outer end of said portion of reduced thickness, bending the extending portion of said ribbon of metal inwardly to hold said frame in place, sealing said frame its length inwardly from one end whereby said short portion of the wall has greater flexibility than the remaining length of the waveguide, sealing a window across said one end of said waveguide by high temperature fusion of the window frame to the outer end of said portion of reduced wall'thickness, and securinga mounting flange around said one end of said waveguide at a position spaced from said discharge-gap structure.

3. The method of fabricating an electric discharge device including the steps of forming a discharge gap strucing system or simulated system, and adjusting the flange dow has been sealed in place, the tube can be completed in readiness for test while the flange is still adiustable. While dimensional standards, are still followed, performuntil standardized results are achieved' Because the winance of the tubes no longer depends on conformity to that-retains solder pre-form 134 in place against frame.

portion of window. By virtue of this modification the outside surface of the completed tube is smooth, unlike that'in Figure l where a slight step is produced. The step as" shown is somewhat exaggerated, ribbon 32 actually being very thin.

The form in Figure 4 is similar to that in Figure 3 inthat wall ass with thinned portion 206a is provided with a further recess Zildb to locate frame 216 of the window accurately during the soldering or brazing operation and.

the pro-form 234 is held in position in the hydrogenfuruace by means not shown. Figure 4 like Figure 3 produces a transmit-receive tube having a smooth external This typeof construction is applicable to tubes other than the transmit-receive tube illustrated, in which excessive stress-might be applied to a fragile portion of the tube V wall due to expansion and contraction of the metal parts ture within a length of metallic. rectangular waveguide having walls of substantial uniform thicknesa uniformly reducing the thickness of the walls of said Waveguide for a short'portion of its length inwardly from one end by removing metal from the inner surfaces of said'walls,

flange by low temperature soldering around said portion of reduced thickness at a position spaced from said discharge-gap structure.

4. The method of fabricating an electric dischmge device including the steps of forming a discharge gap structure Within a length of metallic rectangular waveguide.

having walls of substantial uniform thickness, uniformly reducing the thickness of the walls of said waveguide for a short portion of its length inwardly from one end by removing metal from: the inner surfaces of said walls, placing a thin ribbon of metal around said waveguide to surround said end portion and to extend beyond the outer end thereof, placing a window including a metallic frame transversely across said. one end of said waveguide in abutting relationship with the outer end of said portion of reduced thickness, bending the extending portion of said ribbon of metal inwardly to hold said frame in place, sealing said frame by high temperature fusion to said waveguide, and securin an external mounting flange by low temperature soldering around said portion of reduced thickness at a position spaced from said discharge-gap and a relatively fragile center portion sealed at its outer periphery to the outer'end of said portion of reduced thickness by a high-temperature-fusion material, and an device. t g I -6. An electric discharge device comprising, a-section of rectangular waveguide having walls of substantial uniform thickness throughout its length except'for ,a short portion of uniformly reduced thickness at one end of said section, the wall of said short portion thereby having greater flexibility than the remaining length of said section, discharge-gap electrodes mounted within said waveguide, a ribbon of metal secured to said one end of said waveguide and extendingslightly beyond said one end, a window structure including a rectangular metallic frame and a relatively fragile center portion arranged transversely in abutting relation with the outer end of said short portion and sealed thereto by a high-temperature-fusion material, and an external flange surrounding said ribbon of metal and secured thereto at a distance from said discharge-gap electrodes critical to the operation of the device.

References Cited in the fileof this patent UNITED STATES PATENTS 2,409,913 Tonks Oct. 22, 1946 2,421,912 Spooner June 10, 1947 2,454,741 McCarthy Nov. 23, 1948 2,456,563 McCarthy Dec. 14, 1948 2,496,865 Fiske Feb. 7, 1950 2,533,512 Samuel Dec. 12, 1950 2,680,827 Randall et al. June 8, 1954 2,697,800 Roberts Dec. 21, 1954 2,709,294 Jimenez May 31, 1955 2,748,351 Varnerin May 29, 1956

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