US2661029A

US2661029A - Method of making a fine wire mesh

Info

Publication number: US2661029A
Application number: US55579A
Authority: US
Inventors: Edward J Walsh
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1948-10-20
Filing date: 1948-10-20
Publication date: 1953-12-01
Anticipated expiration: 1970-12-01

Description

Dec. 1, 1953 E. J. WALSH 2,661,029

METHOD OF MAKINQ A FINE WIRE MESH Filed 0011;. 20, 1948 ArroR/vsv intersecting wires.

Patented Dec. 1, 1953 METHOD OF MAKING A FINE WIRE MESH Edward J. Walsh, 'Tenaily, N 3'., assigner toy Bell Telephone Laboratories, Incorporated, New York, N. Y.,v a corporation of New `York Application October 20, 1948', Serial No. 55,579

3 Claims.

This invention relates to a method of making a fine wire mesh and more particularly to a fine wire mesh for electrodes for electron discharge devices.

The main object of this invention is to obtain a ner wire mesh than heretofore available.

Another object is to simplify the method of manufacturing fine wire meshes.

The transconductance of electronic discharge devices, depends on the spacing between the cath- 0de, controlv grid, andv screen grid, the diameter of the grid wire, the spacing thereof, the electrode area and the. potentials applied to the electrodes. In order to. attain a high transconductance certain factors must, be. incorporated in the grid structure including small diameter grid laterals, close spaced adjacent laterals, and mechanically stable laterals. rWhen laterali diameters on the order of 0.0003 inch and less are employed in electrode structures, the. advantages of themechanical stability obtained by the mutual supporting effect of thel intersecting laterals of a mesh electrode are obvious. -Ho,wever, the finest woven Wire meshes heretofore,A commercially available have been limitedv to about 100 x 100 wires per inch using wires of about .0.008 inch diameter. Such coarse meshes and such large diameters of the laterals haveprevented the employment of mesh electrodes, particularly control electrodes, tubes intended for the ve-ry high frequency ranges, since a poor transconductance isattained. Finer meshes have been formed byA electrolytic processes. However, these meshes have had too large a closed area in relation to the open arca to be employed.. in Somer applications in the construction of electron*v tubes..

According to this invention, meshes giving very satisfactoryY resultsv as electrodes for high frequency'tubes have been formed comprising a plurality of parallel lengths of fine wire all in a single plane which lie above and in contact with asecond group of parallel vlengths of fine wire which extends transverse to the rst set and are also in a single plane which is parallel to the rst plane. These wires are coated with a metal fusible below their fusing temperature and they are bonded together at their points of contact with each other by a fused joint of the metal coating. In the magnitudes to which this invention is particularly directed, that is, wires of 0.0005 inch and less diameter, it has been found that gold joints can be conveniently formed between the In one methodv of manufacture gold is maintained adjacent the ends of wires and the mesh is subjected to a brazing tempera- 2 ture sufcient to melt the gold. The fluid gold iiows out along the wiresr to coat themv with a thin film ofV gold which fuses with the coating on the transverse wires to form a secure bond therebetween.

A more complete explanation of the process of manufacturing the mesh of this invention and its application in a typical electrode structure will be forthcoming from the following detailed description when read in conjunction with the accompanying drawings in which:

Fig. 1 represents an elevation of a triode in which the mesh of this invention might be employed as one of the electrodes, portions of the envelope of the tube being c-ut away to more clearly set forth the relationship. of the electrode structure;

Figure 2 is an enlarged cross-section of the electrode structure shown in Fig. I taken along the line 2-2 of' Fig. 1;

Fig. 3 is a perspective of the electrode structure of the tube of Fig. 1 with the anode removed to show the relationship of the mesh to. its support and to the filament;

Fig. 4 shows a perspective of the mesh and an associated frame on which it can readily be formed; and

Fig. 5 shows an enlarged portion of the mesh illustrating the joint formed by the flow of the metal coating at each intersection of the wires.

Referring nowl to the drawings, a triode employing a control grid formed from the mesh of this invention is disclosed in Fig. l. The triode comprises a conventional envelope II housing an electrode structure including an anode I2, a mesh control electrode I 3l and a filament I4. This electrode structure is supported in the envelope by the straps I5 extending from base pins I6 to the various electrodes and bythe spring I'I secured to the upper portion of the electrode structure and frictionally engaging the inner walls of the envelope I I. The electrode structure proper comprises a lamentary cathode It mounted between a pair-of frames I9 made up of a suitable insulating sheet material, such as a mica or a ceramic. These frames are assembled in a pile-up and are separated by quartz filament spacers 20 of slightly greater thickness than the filament. The filament is supported between these frames I9 and along the longitudinal axis of their windowsv ZI by a metal tab 22 formed from a portion of a strap 23 which is bound around extensions 24 on said frames. The otherv end of the filament is tensioned by a spring 26 welded to a strap 2Iv secured around an extension 28 on the lower end of the mica frame. A single sheet of wire mesh 30 is then wrapped around the frame to form an effective mesh grid surface I3 across the frame windows 2|, the grid being spaced from the filamentary cathode the thickness of the sheetI material of the frame. 'I'he mesh 30 is cut, prior to its mounting on the frame I9, so that integral tabs 3| extend from the side to provide an extension to which an electrical conductor, such as the strap I5, may be secured. A second pair of frames 32, each having a critical thickness which determines the grid to anode spacing, is then mounted over the mesh 30 with their Windows aligned with those of the first frames. A sheet anode I2 is formed yaround the assembly and welded upon itself at its projecting tabs 34 to secure the completed electrode structure in its assembled relationship.

The mesh employed in the above-described tube is disclosed in Figs. 4 and 5. It comprises a plurality of coplanar parallel lengths of fine Wire 36 parallel to and in contact with which is mounted a second group of coplanar parallel lengths of ne wire 38 transverse the first group. The wires are coated with a fine layer of a metal having a fusing temperature below that of the wires, the coating preferably being one of the noble metals, such as gold, when the mesh is to be employed as an electrode. This coating serves to braze the wires of the diiferent groups together at their points of contact 39 with each other thereby stabilizing the mesh structure, and when this coating is of gold it also serves to prevent excessive primary emission when the mesh is employed as an electrode in vacuum tubes.

The following method has been employed in manufacturing a 500 x I700 gold brazed mesh of 0.0003 inch tungsten wire, such as might be employed in the tube of Fig. l. A square frame is formed of tungsten wire, the ends of which are welded or brazed together at one corner. Tungsten is employed as the material of the frame in order to avoid any differential in the temperature coefficients of expansion of the Wires of the mesh and frame. The frame faces are then ground down so that the upper and lower winding surfaces of each side of the square are coplanar with the upper and lower surfaces of the remaining sides. After cleaning, the frame is electroplated with gold, and is then placed in an oven and heated to about 1050 C. and held in that temperature range for a time sufiicient to allow the gold to flow, thereby providing a microscopically smooth surface. This smoothing step is included in order to remove any small irregularities in the gold surface produced in the plating process which might throw olf the position of the extremely fine wires of the mesh thereby causing variations in the spacing between adjacent wires. Next, the frame is mounted in a winding machine, for example, a machine employed for winding very high pitch grids for electronic discharge devices, and wound with fine wire to provide a group of parallel wires 36, as disclosed in Fig. 4, extending over the sides 31 of the frame. A spot of reducible cement, such as nitrocellulose cement 40, is applied to the ends of the winding to tack it to sides of the frame. Then the frame is removed from the winding machine and is placed in an oven containing a hydrogen or other noncxidizing atmosphere and heated to about 1070 C. for a time sufcient to partially braze the wires to the frame with fused gold and evaporate the cement 40. This operation also allows the gold to flow out along the fine wires thus preparing the way for the final joining of the second winding. A second winding 38 is then put on the frame, extending transverse to and over the rst winding and secured thereto by cement 40. The mesh and frame at this stage of construction appear as disclosed in Fig. 4. The mesh and frame are then placed in an oven containing a hydrogen or other non-oxidizing atmosphere and heated to about 1070 C. for a period sufficient to braze the second winding to the frame and complete the brazing of the rst winding. It has been found that molten gold will flow along wires having diameters of less than 0.0005 inch. This phenomena is taken advantage of to cause the adherence of the wires of winding 36 to those of winding 38 at their intersections. The gold which is plated on the frame flows out on the wires of the windings and on cooling, the coating of one winding coheres tc the coating of the other to provide a gold joint at their points of contact 39 as shown in Fig. 5. The mesh forme-d on the upper and lower surfaces of the frame 35 is cut away from the frame near its side and may be utilized in a structure such as the control electrode I3 shown in Figs. l, 2 and 3.

A modiiication of the method of manufacturing this mesh includes the following steps. The frame is prepared as above but the plating step is omitted. nstead the wire to be used in the mesh is coated as by plating or evaporation with the metal it is desired to use as a bond. This coated wire is wound in two separate groups of transverse windings on the frame and is red in a non-oxidizing atmosphere at a temperature suicient to fuse the coating. The coatings of the wires at their points of Contact adhere to each other on solidifying to bond the intersecting wires t0- gether. The mesh can then be cut away from the frame.

As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. The method of manufacturing a iine wire mesh which comprises winding a series of coplanar turns of ne wire on a gold-plated supporting member, winding a second coplanar series of turns of fine wire on said support transverse and in contact with said first series of turns, placing said support member and said windings in a non-oxidizing atmosphere, subjecting said windings and said support to a temperature sufficient to fuse said gold and permit it to flow along and coat said windings, and cooling said windings whereby the coating of one winding adheres to the coating of the other winding bonding the intersecting wires together.

2. The method of manufacturing ne wire mesh, comprising coating a support member with gold, heating said support member to cause the gold to form a smooth surface on said support member, winding a series of parallel turns of fine wire about said support member, winding a second series of parallel turns of fine wire over and at an angle to said first series of turns and in contact therewith, heating said support member and turns to the fusion temperature of gold in a reducing atmosphere, cooling said support member and turns to cause the gold to bond the wires at points of intersection, and removing the resulting bonded meshes from said support member.

3. The method of manufacturing ne wire mesh comprising winding a series of turns of ne wire on a gold-coated frame, heating said frame and turns to the fusion temperature of gold, allowing the gold to flow over said turns, cooling said frame and turrm, winding a second series of turns of ne wire transverse to said rst series of turns and in contact therewith, heating said frame and turns to allow the gold on said first series of turns to bond with the second series of turns at the points of intersection, cooling said frame and removing the resulting mesh from said frame.

EDWARD J WALSH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 600,250 Reese Mar. 8, 1,898 827,365 Harris July 31, 1906 Nun'lbel' 6 Name Date Storey Sept. 2, 1913 Coolidge May 2, 1916 Eldred June 27, 1916 Barnes Oct. 22, 1918 Stoekle` Sept. 28, 1920 Trimble Aug. 21, 1923 Schottky May 12, 1925 Bracker Sept. 1, 1925 Leblanc Sept. 29, 1925 Woerner Feb. 8, 1927 Kelley Jan. 3, 1928 Farr Mar. 26, 1929 Welkovitz July 25, 1933 Pdgeon Aug. 22, 1933 Ingouf Aug. 22, 1939 Schade Oct. 10, 1939 Garbe May 13, 1941 Eitel Oct. 3, 1944 Ehrhardt Oct. 21, 1947