US2619438A - Method of making a grid structure - Google Patents

Description

NOV- 25, 1952 s. F. VARIAN ETAL 2,619,438

METHOD OF MAKING A GRID .STRUCTURE Filed April 16, 1945 fav INVENTOR S/GURD E QR/,4N

l ATTORNEY Patented Nov. 25, 1952 METHOD OF MAKING A GRID STRUCTURE Sigurd F. Varian and Russell H. Varian, Garden City, N. Y., assignors to The Sperry Corporation, a corporation of Delaware Application April 16, 1945, Serial No. 588,580

1 Claim. 1

The present invention relates to control electrodes for electron tubes and to methods for producing the same. Cellular grid structures of the type here disclosed are especially adapted for use as the control electrodes in thermionic tubes, such as klystrons, but also have many other uses.

In the past, it has been common practice to make the control electrodes or the grids of electron tubes either from fine Wire screening or by fabrication. In general, such structures have been relatively unsatisfactory for the purpose. Both types of construction lack suicient rigidity when the supporting Wires or interstitial metal or webs are so reduced in size and volume as to permit the development of maximum desired interstices or pores. Neither of these two types of construction provides a grid which has at least one regular geometrical surface. For example, a perforated sheet normally cannot have a regular geometrical surface, since the surface is deformed by the punching operation. An attempt to remove the deformation of the sheet which results from the unilateral burring due to the perforating operation almost invariably causes irregularities in the size and shape of the perforations. When a woven Wire screen is used, the weaving operation bends the wires and thus inherently eliminates the possibility of developing a regular geometrical surface on either side of the screen. This is also true of other types of wire screens. The shape of the openings has also been found to be of importance. Experiments have shown that better collimation of the electron beam is achieved when hexagonal openings than with the previously more readily obtained circular or rectangular configurations.

`Grrids and other control electrodes previously used have been characterized by a relatively high electron interception factor. Too large a portion of the total area occupied by the structure was necessarily utilized to provide proper structural stability and other mechanical properties, so that the area available for the passage of electrons was unduly restricted. As electron density and velocity increase with improvements in electron tubes, it becomes increasingly important to minimize the interception factor of the grid and other control electrodes. At the same time, the necessity for providing a structure which has at least one regular geometrical surface and high structural rigidity is increased, since dimensional tolerances and the tendency toward microphonic effects are increasingly important problems under these conditions.

Accordingly, it is a feature of the present inventon to provide an improved grid member or foraminous disc of multicellular construction which has desirable mechanical properties resulting in reduced microphonic effects and a relatively low interception factor.

It is another feature of the present invention to provide a method of producing such grids or foraminous discs on a quantity basis with eX- tremely good uniformity.

The invention contemplates the formation of cellular grid members, desirably in disc form, and in the following manner. A plurality of wires of a first metal are employed as mandrels which are later removed. Each of the wires is plated or otherwise coated or sheathed with a second metal. In a, preferred form of the invention, the coated wires are bunched and surrounded by a suitable sheath or housing. The resultant assembly is then consolidated, as for example by drawing or swaging, after which wafers of a suitable thickness are cut off. The wafers are then subjected to a chemical `action Which preferentially dissolves or etches the Wires out of their coatings, leaving a cellular, honeycomb-type 1 structure formed from the original coatings or sheaths of the Wires. The adjacent Walls of the coatings, in turn, are autogenously joined or coalesced, as for example by subjecting the wafers to heat treatment such as sintering. If desired, the coalescing may be accomplished before the individual wafers are sliced off, or after slicing but before etching is accomplished.

The foraminous disc or grid member in accordance with the present invention is formed by a, plurality of tubular or tubiform sections or cells having substantially parallel longitudinal axes and with their adjacent wall surfaces joined together. The sections have relatively thin Walls, so the interception factor` of the grid member is desirably low. Since the axial length of the sections is preferably of the order of their opening size, however, the grid member has substantial structural rigidity, each section being supported by, and in turn contributing to the support of, several adjacent sections.

The above features and brief description of the invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawing, in which like components are designated by like reference numerals and in which:

Fig. l is a flow chart, in diagrammatic form, of the method of the present invention;

Figs. 2, 3 and 6 are partial sections taken respectively on lines 2 2, 3 3 and -6 of Fig. 1;

Fig. 4 is a section of a curvilinear grid structure made in accordance with a modification of the method of Fig. 1;

Fig. 5 is a section of a curvilinear grid structure made in accordance With another modication of the method of Fig. 1;

Fig. 'I is a section taken on line 'I-'I of Fig. 6; and

Fig. 8 is a plan view of a foraminous disc. or grid structure in accordance with the present invention.

Referring now to Fig. 1, the first step in the method of producing foraminousv discs is the selection of a plurality of wires I'. These wires are of a soft malleable materiaLsuch as zinc or aluminum, although iron may also be employed. The wires preferably have a` substantially circular cross section, but other shapes may be employed if desired. It is not absolutely essential that wires Ill be metallic. Wire-like rods or filaments of other materials, asv for example fibers of. hemp. cotton, etc., may be utilized with satisfactory results.

The second step of the method comprises coating wires I0 with another suitable material, this step being indicatedgenerally by unit I-I. The coating may be accomplished in a number of Ways,jincluding electroplating, dipping in molten metal, anodizing, metalizing, or painting with a fluid mixture ofY powder and binder.v In some cases, the coating may be applied to wires I by Winding avribbon of the coating material spirally around' each wire and spot welding its ends to hbld it inplac'e. Thecoating material may either be al good conductor, such as copper, gold orl silver; 0r metal having a high melting point but being of onlyl fair conductivity may be employed, such for example as nickel, platinum, molybdenum, tungsten or 'rhenium. The coating material need not necessarily be metallic. Graphite grids, for' instance, may be produced by vcoating the Wires with colloidal graphite, such for example as AquadagL Aquadag is a dispersion of water-graphite paste in water, and it comprises ai solution of substantially 22% graphite in water. The essential requirements are that the coating be substantially homogeneousv and that it be malleable and ductile. The thickness of the coating is normally made approximately half the desired grid web thickness. The coated wires are next passed through an assemblying funnel I2 'and into 1a sheath I3. The 'sheath I3 comprises va tube of some material which can be read-ily drawn, as for example copper. The coated Wires need not necessarily complet'ely ll sheath I3. The appearance of the bunch'ed and sheathed wires at this point is indicated in Fig. 2, in which the coatingv on the Wires is designated by the reference numeral I4.

The sheath I3` and its contents are now consolidated, as for example by drawing through a die f5, or by swaging. Although only a single die is shown in Fig. 1, it will be understood that the drawing operation may be repeated as often as necessary to reduce the assembly to the desired outside diameter.

Fig. v3 shows the. mosaic formed as the result of the consolidating operation. It will be observed in this gure that the individual Wire I0 and their respective coatings I4 form a mosaic and have now assumed asubstantial hexagonal cross section With the coatings taking the form of cell walls", due to the lateral pressure exerted upon them during the drawing operation.

The consolidated assembly is now subjected to of colloidal the cutting action of a saw I6 which cuts oif individual wafers I'I. It will be understood that instead of cutting the lassembly in a planeperpendicular to its longitudinal axis, wafers having a surface other than flat may readily be formed by machining off discs of the desired shape. If desired, Wafer I'I may be cut with transverse plane surfaces, and then subjected to modification by a parallel, stepped-displacement of the individual cellular sections to provide an approximation of a desired curvilinear surface. Such a grid structure, after this forming operation, is shown in section in Fig. 4. In this view, the desired geometrical surface contour` is indicated by broken line I9.` If high precision is necessary,

the surface of the grid structure may readily be machined to this line.

In some cases, it may be desired to provide a grid structure having a curvilinear surface but' in which the individualcellular sections are radially disposed. Such a structurev is illustrated in Fig. 5 of the drawing. It may bev producedV by first plating or otherwise coating or encasing aA Wafer having transverse plane surfaces with a. matrix of zinc or other suitable relatively soft material. The coating is made thicker on one face of the Wafer than on the other. The coated wafer is then pressed into the desired curvilinear orspherical shape, the side with the thinner coat.- ing being concave. In this manner, the wafer itself is kept under compression in a transverse direction during the shaping operation, so there is no tendency for the individual elements to sep-f arate as they are displaced. After the coating' material is removed, the resultant` shaped disc` will comprise a plurality of individual sections which have their axes radially disposed with 're-if spect to the center of curvature of the disc.,

The wafers I'I are now subjected to' preferential or selective etching in unit |18. The. .purpose rof this operation is to remove or dissolve the Vmandrel wires I0 while leaving intact their individ-l ual sheaths or coatings I4' to form individual cell walls. If zincwire is used, hydrochloricacid is suitable for performing this operation. vFor aluminum Wire, sodium hydroxide is equally suitable.'

The wafers which emerge from u'nit |18 comprise a plurality of 'small tubular sections or cells which arey movable with respect to each other so that the same may tend to separate. The walls ofv these individual sections, therefore, are coalesced or otherwise suitably ljoined or bonded together by use of suitable apparatus as indicated at 20. Oneway of accomplishing this is by sintering in a hydrogen furnace. of copper, a sintering temperature between 800 and 900 C. is appropriate. For nickel, the temperature is about l300 C., and for silver about 500 C. In addition tojoining the individual tubular sections or cell walls together, the coalescing operation tends to bond the walls of the outer gubuar sections to the sheath I3, as indicated in The thickness of wafers I 'I is preferably so chosen vas to be of the order of the individual aperture. size of the cells of the finished grid structure. As clearly shown in Fig. 7, each cell or 'tubular section is substantially square in longitudinal section and has appreciable depth so that the completed grid structure has a maximum structural rigidity reducing microphonic eiects. As also clearly shown in Fig. 7, the thickness of each of the Walls comprising the cells Aof the grid structure is relatively small compared with the width of each opening. Accordingly', the

If the Vgrids are' overall grid structure has a relatively low interception factor when it is interposed in the electron stream of an electron tube.

Fig. 8 indicates the general appearance of the completed grid structure. If desired, the outer sheath I3 may be silver plated, prior to the cutting operation, in order to provide the proper amount of silver to permit the grid structure to be soldered in place in an electron tube, as for example to the resonator of a klystron. If a rimless grid structure is desired, outer sheath I3 may be etched away or otherwise removed following coalescing.

Several modications in the above-described method of producing cellular grid structures may be made without departing from the present invention. For example, the last two operations illustrated in Fig. 1 may be reversed if wires I6 are made of relatively refractory material, such as iron. In this case, the cell walls of the individual tubular sections would be coalesced before their cores were etched or dissolved away. Another modification is to accomplish the steps of etching and coalescing substantially simultaneously. Still another change, which may in some cases be desirable, is to eifect coalescing prior to the cutting operation, this being accomplished, for example, by induction heating of the assembly after drawing.

After the cutting operation, it has been found desirable in some cases to remove the feather edge on each wire. This is especially true if the grid structure is to be bowed or otherwise shaped before the etching step, as described above in connection with Figs. 4 and 5. The removal of these feather edges is conveniently accom.- plished by lapping each wafer with sandpaper or by dropping the wafers into a non-selective reagent which etches the wires and their coatings more or less equally.

In accordance with the method of the present invention, it has been found entirely feasible to make cellular grid structures having webs as thin as 0.0001 inch and to provide such grid structures with at least one highly precise regular geometrical surface. The utility of such cellular grid structures in electron tubes, as for example klystrons, will be readily apparent and their use greatly minimizes the production of secondary electrons due to impact of the primary electrons upon the grid structure.

Instead of cutting oif wafers, longer portions of desired axial length may be utilized as heat exchangers, chemical filters, or the like. The close proximity of adjacent openings of the structure in accordance with the present invention is especially advantageous in such applications of the invention.

The interception factor of a cellular grid structure may, in accordance with the present invention, be varied without changing the size of wire used merely by omitting the coating on a portion of the wires. In this way a grid structure will result in which there are a number of openings substantially larger than the cross section of the wire after consolidation.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

A method of forming curvilinear grid electrodes having a hexagonally shaped mesh comprising individually coating a plurality of wires of a first metallic material with a relatively thin coat of second metallic material, assembling said coated wires in a sheath, drawing said assembly so that said coated wires are deformed into substantially hexagonal cross-sections with the abutting surfaces of said coatings contacting one another and retaining their identities, said coatings being relatively displaceable after said drawing, cutting said drawn assembly transversely to form relatively thin discs, displacing the individual elements of said discs in a direction substantially at right angles to the plane of said discs, removing completely said wires of first material from said discs, and sintering the abutting surfaces among said coatings and said sheath so that they are coalesced, whereby an integral, unitary electrode is formed of curved configuration.

SIGURD F. VARIAN. RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,991,606 Eitel et al Feb. 19, 1935 2,002,148 Klinkert May 21, 1935 2,169,937 Wempe Aug. 15, 1939 2,185,106 Krahl Dec. 26, 1939 2,197,753 Liebmann Apr. 23, 1940 2,217,193 Aronson Oct. 8, 1940 2,217,194 Bryce et al. Oct. 8, 1940 2,261,154 Hansen et al Nov. 4, 1941 2,266,349 Wempe Dec. 16, 1941 2,273,589 Olt Feb. 17, 1942 2,289,897 Balke et al. July 14, 1942 2,297,817 Truxell et al Oct. 6, 1942 2,304,186 Litton Dec. 8, 1942 2,367,615 Rively Jan. 16, 1945 2,379,135 Ekstedt et al June 26, 1945 2,499,977 Scott Mar. 7, 1950 FOREIGN PATENTS Number Country Date 501,660 Germany July 3, 1930

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