US2845690A

US2845690A - Electrical components and methods

Info

Publication number: US2845690A
Application number: US451792A
Authority: US
Inventors: Richard I Harrison
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1954-08-24
Filing date: 1954-08-24
Publication date: 1958-08-05
Anticipated expiration: 1975-08-05
Also published as: FR1136479A; GB808282A

Description

Aug. 5, 1958 R. l. HARRISON ELECTRICAL COMPONENTS AND METHODS Filed Aug. 24, 1954 Unite ELECTRICAL COMPONENTS AND METHODS Application August 24, 1954, SerialNo. 451,72

10 Claims. (Cl. 29-2514) The present invention relates to electrical components, such as encased and supported impedance and signaltransmission elements, more particularly to an improved process forfabricating such components and to resultant electrical devices exhibiting enhanced mechanical and electrical properties. Specifically, the present invention is concerned with an improved method of manufacturing traveling wave tubes and like =devices incorporating a helical wire conductor and with traveling wave-devices having improved characteristics, prominently reliability and ruggedness.

The impedance and signal-transmission characteristics of coils, helices and the like, useful as circuit components and asparts of electrical and electronic devices, frequently depend upon-turn distribution and/or the material surrounding and between turns. For example, the inductance of a coil and the signal-transmission properties of a helical conductor change with variations in intertum spacing and the proximity of dielectricmaterial to the respective turns.

Accordingly, it is an object of the present invention to provide an improved method of fabricating electrical components. To advantage, encased and supportedcoils, helices and the like may be constructed having ta (fixed turn distribution-and desirable electrical and mechanical properties.

:In one form, the inventionmay be best demonstrated as applied to the well-known traveling wave tube which is essentially an electron beam tube employing an electronjgun. The electron gun, similar to those commonly .foundin cathode ray tubes, forms and projects an electron beam axially within a surrounding wire helical coniductor which is excited by a high frequency input signal at the inputcnd thereof. During travel of the input signal :along the helical conductor, there is interaction with the electron .beam which results inamplificationof a broad band of input frequencies available .at the output end of the helical conductor.

Suchknown traveling wave tubes :includean elongated wire helix, encased within a vitreous envelope or tube throughout its length and appropriately .assembled with .input and output coupling devices, as well as beam .collecting and focusing electrodes. Such helix assemblies, usually -.of relatively small dimensions, are comparatively .longand include many turns in relation to thediameter of the helix. The accomplishment of entry transfer between the beam and the helix often necessitates the .use of T00-t0 800 turns for a helix length of approximately 15 inches and helix diameters of the order of of an inch.

The support of such a helix within a vitreous sheath or envelope presents a rather troublesome problem, :par-

ticularly since the assembly is rather small and hascritical electrical properties whichmay vary greatly and in a random fashion depending upon the mounting of the helix. Of primary importance is the fixing of the respective :turns of the helix in relation to each other in accordance with the established helix pitch, whether uniform or varied. Such fixing of the turn=distribution of the helix should be accomplished without adversely-affecting theelectrical properties of the helix, as .by establishing microwave mismatches or causingjprohibitive'standing wave ratios.

Numerous approaches have been suggested win the manufacture of traveling-wave devices for formingamencased helix having a fixed turn distributionand desirable electrical properties. Among these approaches has been theformation of aninternal thread on a precisely bored tubing, followed by deposition of metallic materialvin the threads and the removal of any metallic material .in the spaces between successive turns of the thread. The inherent complexity of such procedure is apparent,,;particularly when it is considered that the thread .musP-be formed within a long tubing having --a. relatively :smallwinternal cross-section.

Accordingly, it is another object of thejpresent invention to provide a novel method of fabricating traveling wave tubes which obviates one or more of the aforesaid difiiculties. Specifically, it is within the contemplation of the invention to provide an improved process for mechanically supporting the helix of a traveling wave-device witha particular turn-distribution and without alter- .ing said turn distribution and/ or adversely .afiectingthe electrical properties of the final traveling wave tube'assembly.

As applied to traveling wave tubes, the present invention employs the principle of assembling ahelix within a closely conforming vitreous sheath or tubing, -and.-heat softening and shrinking'the vitreous sheath into supportingrelation with the helix, thus fixing the distributiontof the helix turns. A helix supported by heat shrinking-bf its vitreous sheathing into supporting relation Withith helix turns has been found to be exceptionally rugged;

furthersaid :helix exhibits electrical characteristics compatible with proper functioning of traveling wave devices.

In accordance with an illustrative process -.demonstrating .features of the present invention, a wire-helix :is

wound upon a mandrel andpreferably assembledwithdevices for input and output coupling of wave energy to the helix. 'The subassembly of the woundwhelix and coupling devices is then placed within and axially oba glass tube having a bore diameter closely-conformingto the outer diameter of the helix. Theassembly .of the helix and the sheathing or tube is elevated to .a'tempera ture appropriate to heat soften and shrink the gglass-into contact with the respective turns of the helix. :Bycontrol over the shrinking rate, relatively rigid tolerances may be maintained for the degree of contact betweenthc ,g'lass 'of the tube and the helix turns, as well as tthepene- 'tration of glass between the respective turns of the helix.

Preferably the .process is carried out with the mandrel substantially filling out the helix :space and theassembly continuously rotated about the common of 'themandrel and the vitreous tube suchthat'the tube does not bow throughout its length due to gravitational forces.

Additionally, the heat shrinking is preferably-carried out w'i'th'the interior of the .tube at .a reduced pressure with 'resp'ectto "the exterior 'of'the tube. This'pressure differential lowers the shrinking temperature, thus: providing "high viscosity of "the glass at relatively low *control sen- -sitivity--of-glass sagging.

. he- 'above :as we'llasstill further =objects, features and :advantages of the present invention will be-sbc'st appreciated by reference :to :the following detailed description of "-a presently preferred process and :articles attainable thereby, when taken in conjunction with :theaaccompanying drawings, wherein: Figure .1 is an elevational'view with parts broken'taway, showing a traveling wave tube .assemblyprocesseduin accordance with features of the present invention;

Figure 2 is a longitudinal sectional view, enlarged and foreshortened, showing the assembly of a mandrel having a helix and coupling probles with a vitreous sheathing assembled prior to a processing in accordance with the present invention;

. Figure 3 is a sectional view, enlarged and foreshortened, of a sheathed helix and probe assembly processed in accordance with the present invention;

Figure 4 is a fragmentary sectional view on a greatly enlarged and exaggerated scale showing the contact region between the turns of the helix and the encasing vitreous sheath.

In Figure'l there is shown an illustrative traveling wave tube which includes a vitreous body 12 having an enlarged bulb 14 and an elongated sheath or tube 16. Within the bulb 14 is the well-known electron gun assembly 18 which is arranged to produce a beam to be directed axially along the envelope or tube 16 and includes the usual filamentary heater, electron-emitting cathode and beam-forming elements. The electrode assembly within the elongated tube or sheath 16 includes an input probe 20, a helix 22 of variable or uniform pitch having one end electrically connected to the input probe 20, and an output probe 24 electrically connected to the other end of the helix. Beyond the output probe 24 is a collector 26 for the electron beam having an appropriate external terminal or connection. As is well understood appro priate connections are provided for establishing operating potentials and a magnetic field to focus the electron beam. with this broadly old traveling wave tube, further descrlption as to the details of the tube construction will be dispensed with except as is necessary for an understanding of the present improved method.

Referring now specifically to Figure 2, there is shown U the helix 22 which is of tungsten wire wound on a mandrel M of a material having a coefiicient of expansion selected to avoid indenting of the helix material. It has been found that a steel mandrel maybe used successfully with a wire helix of either tungsten or molydenum having a copper coating. Preferably, the helix and its mandrel are fired at a temperature of approximately 900 C. fora period of three to four minutes in a protective atmosphere to set the helix turns.

probes

20, 24 are assembled with the helix 22, as by spot welding or the like. The mandrel M with the assembled helix 22 and energy-

coupling probes

20, 24 is inserted within the vitreous bulb envelope or body 12 which may be of a glass, such as Corning 7052. far as the rate of propagation of electromagnetic wave energy along the helix is critically dependent upon the dielectric medium in the immediate vicinity of the helix 22, the glass of the envelope 12 is selected to have an appropriate dielectric constant for microwave applications. The envelope 12, illustrated in incomplete state with its opposite ends open, includes the tubing 16 pre cisely bored in the region coextensive with the helix and probe assembly, the tubing 16 having an inside diameter approximately equal to the outside diameter of the helix and probe assembly. The envelope 12 maybe preliminarily processed to form an attenuated coating thereon in selected regions, as by evaporating a nichrome film onto the inner walls of the tube 16 as shown in U. S. Patent No. 2,660,690.

Preliminary to processing in accordance with the present invention it may be further desirable to cold match .the inserted helix and probes to obtain an appropriate radio frequency match and to determine whether the assembly meets other predetermined standards of electrical performance. The cold match is carried out by making appropriate connections to the input and output ends of the assembly and testing on a radio frequency bench. Acceptable assemblies are then completed by fitting the collector 26 on the reduced end m of the In that the present invention is not concerned The input and output I Insomandrel M, the mandrel M serving to align the

respective probes

20, 24, the helix 22 and the collector 26.

To preclude lengthening and foreshortening of the helix 22 during heat treatment, the

probes

20, 24 are secured to the vitreous sheath or tubing 16. This may be accomplished by dimpling the tubing 16 or by application of a cold ceramic cement, such as Sauereisen #29 at the locations 30, 32. The mandrel M is fixed in relation to the envelope or bulb 12 by pinching down on the envelope or blank at its opposite ends, as illustrated at the left in Figure 2 and designated by the numeral 34. The right end of the tube 12 beyond the collector 26 may likewise be secured in relation to the mandrel M by pinching down on the glass tubing. At points beyond the region of support of the tube 16 by the mandrel M, it may be desirable to provide extension tubings which have a sufiiciently high melting and softening point as compared to the glass of the envelope for convenience in working and to preclude bowing of the assembly.

The assembly of the mandrel M and the envelope 12 is then supported between the chucks C C The chuck C is a vacuum chuck connected to an appropriate exhaust pump, while the chuck C is an ordinary mechanical chuck. The end of the envelope-mandrel assembly supported in chuck C which may be an extension of a high melting and softening point glass, is appropriately sealed, as by a stopper (not shown). The use of the mandrel M for centering the

probes

20, 24, the helix 22 and the collector 26 assures perfect coaxial relation between the respective components of the final tube assembly; while the use of the low-expansion cold cement having good electrical properties and capable of withstanding rela' tively high vacuum assures that the helix 22 will not change length.

The assembly of Figure 2, while under vacuum and rotating, is heated, as by application of a flarne directly thereto or by placing the assembly within an oven. The heating, whether in a localized area or throughout the length of the assembly, is continued for a period and at a temperature to sofeten and shrink the tubing 16 onto the probe-helix assembly. The shrinking temperature is dependent upon the type of vitreous material used and on the pressure differential existing between the inner and outer walls of the sealed-off envelope 12. Slow shrinkage is preferred to facilitate accurate control over the depth of sagging or penetration of the vitreous material between the respective turns of the helix 22. To this end, the use of a relatively high vacuum and lower shrinking temperatures assures low flow rates of the vitreous material due to the high viscosity of the glass. The use of reduced temperatures besides providing for easier control over glass sagging, minimizes the risk of oxidizing the metal tube parts as well as fusing copper from the plating of the helix wire onto the adjacent vitreous walls. Such fusing of copper onto the glass walls increases the attenuation of microwave power and is appreciably reduced by lowering the shrinking temperature. By careful control of the shrinking temperature and by operating at vacuums on the order of one-tenth of an atmosphere or less, it has been found possible to obtain uniform shrinkage of the vitreous material between respective turns of the helix 22 to fix the preestablished turn distribution of the helix 22. Although it is preferable to obtain the pressure difierential between the inside and outside walls of the envelope 12 by drawing a vacuum therein, it is equally within the scope of the invention to apply pressure externally of the envelope 12.

When the required glass sagging is obtained, the temperature of the assembly is reduced to stop the sagging action. During the reverse cycling of the heat-shrunken assembly, it is preferable to continue rotation and operation under vacuum. By slow cooling, it is possible to anneal the tubing with attendant advantages.

The helix and probe assembly within the envelope 12 is then prepared for incorporation into the final traveling wave tube by removing the extension portions of the euvelope by cutting at the parting planes P P illustrated in'Figure 2. The final helix and probe assembly with the mandrel removed is shown in Figure 3. Preliminary to removal of the mandrel M, the lead or extension 28 for the collector 26 is sealed to the envelope, as indicated at 36.

Upon inspection of Figure 4,.it will be appreciated that intermediate the respective turns of the helix 22, there are integral portions of the tube 16 which provide peripherally-extending and circiunferentially-extending area contact to the respective turns of the helix '22. The area contact embraces the outer surface ofthe wire of the helix throughout the length of the wire. Such embracing arcuate contact, providing a helical groove mating with the outer surface of the wire of the helix, contrasts markedly to constructions in which the helix is snugly received in its supporting envelope. The showings of Figures 2 to 4 inclusive are exaggerated dimensiona'lly such that the physical configurations attainable in accordance with the present invention may be fully appreciated. However, a typical traveling wave tube assembly includes a helix having an inside diameter of approximately .1 inch which helix is fabricated of a tungsten wire of mils diameter and having an electroplated copper Coating of approximately .5 mil. The outside diameter of the helix is approximately .11 inch, the helix being received within a precisely bored tubing having aninside diameter of .12 inch and an outside diameter .of..210 .inch. A typical assembly includes 770 turnsin a length of approximately 15% inches. Approximately .2 mil of total sagging, that is .07% of the wirec'ircumference, has been found 'to'be sufiicient to secure the'turns of the helix in relation to each other without significant interference with the electrical characteristics of the tube due to the presence of prohibitive amounts of diel'ectric material between the respective turns. Traveling wave tubes with desirable characteristics have been constructed having 3% circumferential wetting of the helix turns by the dielectric material of the sheath. The aforesaid dimensions are purely illustrative and are set forth such that the relative proportions of one such typical structure may be more fully appreciated.

Following processing of the probe and helix assembly, the electron gun 18 is placed within the bulb 14 and the remaining electrodes and leads connected in accordance with techniques which are well understood. Thereafter the envelope 12 is evacuated and sealed.

The wide variety of modifications as well as further details will be apparent to those skilled in the art. For example, the helix 22 may be wound on a variable pitch throughout selected regions of its length, to advantage in certain types of microwave applications. Still further refinement may be made in control of the temperature throughout the various portions of the helix and probe assembly. For example, in the regions adjacent to the probes 2t 24 more localized heating may be required in that a large area of heat conduction is provided to the vitreous wall or sheath 16; while in the regions occupied by the helix 22, such large areas of heat conduction are not present.

Although the invention has been described as applied to traveling wave amplifying devices, application of the principles herein to manufacture of precise inductance coils and tube electric components is likewise intended.

Further modifications and varied applications of the foregoing invention will occur to those skilled in the art. Accordingly, the appended claims should be construed broadly, consistent with the spirit and scope of the present invention.

What I claim is:

1. In the manufacture of traveling wave tubes, the steps including subassembling a helix and probes concentrically of a mandrel, placing said mandrel in a vitreous g t tube, fixing said probes to said =vitreoustube :to prevent elongation and foreshortening of said helix, drawing a vacuum in said vitreous tube, axially rotating the assembly of said mandrel and vitreous tube, and heating said assembly while rotating to shrink said vitreous tube 'onto said helix .to permanently .fixthe helix turns in place.

2. In the manufacture of traveling wave tubes, the steps including subassemblingahelix and probes concentrically of a mandrel, .placing-saidrnandrel in a vitreous tube, fixing said probes in :relation to said vitreous tube to prevent elongation and .foreshortening of said helix, and heating said assembly while rotating to shrink .said vitreous tube onto said helix to permanently fix1the helix turns in place.

3. In the manufacture of traveling wave tubes, the steps including subassembling a helix .and probes "concentrically of a mandrel, placing said smandrel in a vitreous tube, fixing said probes to said vitreous tube to prevent elongation and foreshortening of said helix, drawing a vacuum in said vitreous tube, axially rotating the assembly of-said mandre'land vitreous tube, 'andheating said assembly whilerotating toa temperature sufil :cient to shrink said vitreous :tube at a low :fiow rate to uniformly engage the helix turns circumferentially and along their length.

4. In the manufacture of .traveling wave tubes, the steps including subassembling a helix and probes sconic'entrically :of a mandrel, placing said mandrel in a vitreous tube, fixing said :probes to said vitreous tube to prevent elongation and *foreshortening of said helix, drawing a vacuum of the 'order of one-tenth of an atmosphere in said vitreous tube,'axi'ally rotating the assembly of said mandrel and vitreous tube, and heating said assembly while rotating to a temperaturesufficient toshrink said vitreous tube at a low flow' r'ate to uniformly. engage the helixturns circumferentially and along their length.

5. A method of constructing a helix assembly for a traveling wave tube including an envelope of thermoplastic material having an enlarged bulb and an elongated tube including the steps of placing the assembly of a wire helix on a supporting mandrel Within said tube with said helix in contact with the inner wall of said tube, creating a pressure differential between the inside and outside walls of said tube, heating said tube to shrinking temperature suflicient to soften said thermoplastic material, and correlating the relationship between said pressure differential and said shrinking temperature whereby said thermoplastic material sags into substantially continuous embracing contact both circumferentially and lengthwise of said wire and at a low flow rate allowing for accurate control over and the limited penetration of said thermoplastic material between the of said helix.

6. A method for constructing a helix assembly including the steps of winding wire in a helical configuration on a supporting mandrel, surrounding said wire by a snugly fitting vitreous envelope, creating a pressure differential between the inside and outside of said envelope, heating said envelope to a shrinking temperature suflicient only to soften said vitreous material, and correlating the relationship between said pressure difierential and said shrinking temperature to cause said vitreous material to sag into substantially continuous circumferential embracing contact throughout the length of said wire and at a low fiow rate assuring accurate control over and the limited penetration of said vitreous material between the respective turns of said wire.

7. A method for constructing a helix assembly including the steps of winding wire in a helical configuration on a supporting mandrel, heat treating said wire to set said Wire in said helical configuration, surrounding said wire by a snugly fitting vitreous envelope, creating a pressure differential between the inside and outside of said envelope, heating said envelope to a shinking temperature respective turns sufficient only to soften said vitreous material, and correlating the relationship between said pressure difierential and said shrinking temperature to cause said vitreous material to sag into substantially continuous circumferential embracing contact with said Wire throughout the length thereof and at a low flow rate assuring accurate control over and the limited penetration of said vitreous material between the respective turns of said wire.

8. A method for constructing a helix assembly including the steps of winding wire in a helical configuration on a supporting mandrel, surrounding said wire by a snugly fitting vitreous envelope, creating a pressure dilferential between the inside and outside of said envelope, axially rotating the assembly of said supporting mandrel and en velope, heating said envelope to a shrinking temperature sufiicient only to soften said vitreous material, and correlating the relationship between said pressure ditferential and said shrinking temperature to cause said vitreous material to sag into substantially continuous circumferential contact with said Wire throughout the length thereof and at a low flow rate assuring accurate control over and the limited penetration of said vitreous material between the respective turns of said wire.

9. A method for constructing a helix assembly for a traveling wave tube including an envelope having an enlarged bulb and an elongated tube including the steps of winding a wire helix on a supporting mandrel, heat treating said helix to fix the turn distribution thereof, assembling said mandrel within said elongated tube with said helix in contact with the inner wall of said elongated tube, creating a pressure difierential between the inside and outside walls of said helix, heating said elongated tube to a shrinking temperature sufficient only to soften said vitreous material while rotating the assembly, and correlating and maintaining the relationship between said pressure differential and said shrinking temperature to cause said vitreous material to sag into substantially continuous embracing contact both circumferentially and axially of said helix and at a low flow rate assuring for accurate control over and the limited penetration of said vitreous material between the respective turns of said helix.

10. A method for constructing a helix assembly for a traveling wave tube including an envelope an enlarged bulb and an elongated tube including the steps of winding a wire helix on a supporting mandrel, heat treating said helix to fix the turn distribution thereof, assembling said mandrel within said elongated tube with said helix in contact with the inner wall of said elongated tube, fixing both said mandrel and said helix in relation to said elongated tube, creating a pressure differential between the inside and outside walls of said helix, heating said elongated tube to a shrinking temperature sufficient only to soften said vitreous material while rotating the assembly, and correlating and maintaining the relationship between said pressure diiierential and said shrinking temperature to cause said vitreous material to sag into substantially continuous embracing contact both circumfer-- entially and axially of said helix at a low flow rate allowing for accurate control over and the limited penetration of said virteous material between the respective turns of said helix.

References Cited in the file of this patent UNITED STATES PATENTS 2,338,336 Koch Ian. 4, 1944 2,457,218 Ferrell Dec. 28, 1948 2,611,101 Wallauschek Sept. 16, 1952 2,619,706 Vause Dec. 2, 1952 2,706,366 Best Apr. 19, 1955 FOREIGN PATENTS 985,536 France Mar. 14, 1951