US2878549A

US2878549A - Manufacture of delicate grids

Info

Publication number: US2878549A
Application number: US622345A
Authority: US
Inventors: Willner Ernst
Original assignee: Telefunken AG
Current assignee: Telefunken AG
Priority date: 1955-11-18
Filing date: 1956-11-15
Publication date: 1959-03-24
Anticipated expiration: 1976-03-24

Description

March 24, 1959 E. WILLNER 2,378,549

MANUFACTURE OF DELICATE GRIDS Filed NOV- 15, 1956 F/G. F/GZ F/6.3

INVENTOR ERNST WILLNER PATENT AGENT Unite MANUFACTURE OF DELICATE GRIDS Ernst Willner, Berlin-Frohnau, Germany, assignor. to Telefunken G.m.b.H., Berlin, Germany The invention relates to grid electrodes for electron tubes and the manufacture thereof.

Many types of electron tubes have been known, particularly tubes of small dimensions, having characteristic curves of steep slope and/or designed for high frequencies. These tubescontain grid electrodes comprising very thin'wires, the electrodes being mounted at small distances from other electrodes. Care must be taken that such grids, even when heated during degassing or during operation, maintain their shape. Since grids formed by wire helixes do not meet such requirements, flat parallel wire grids have been proposed wherein the wire is wound under tension on a frame having spaced opposed hooks, the wires zigzagging back and forth therebetween. tion and does not permit the manufacture of grids spaced at verysmall distances between adjacent wires. more, it has been known to make flat or arched grids from a mesh of crossed wires and to secure the same to supporting elements or to a metal frame. Due to the relatively large amount of metal present, grids of the above type have a considerable capacity with respect to the adjacent electrodes, which capacity excludes the application of such tubes to high frequencies. Consequently, in the latter cases, grids comprisingonly a number of parallel wires are preferred, the ends of' these wires being mounted either on supporting elements or on a metal frame.

According to a known method of producing delicate parallel-wire grids, a fabric of weft and warp threads of different metals is first made and is secured to either metallic supports or to a frame, and, thereafter, one kind of wire is attacked and removed byv immersing the electrodes in an. acid. This method has certain disadvantages which. will be explained in the following.

The range of suitable material is restricted because the wires of said one metal have to be rapidly and entirely removed by an inorganic acid, while the wires of the other metal must not be attacked by said acid.

Thus, it is necessary to make the unattacked elements and wires of an insoluble metal, such as molybdenum or tungsten, while the wires to be removed have to be made of metals which are readily attacked by the acid used. Tungsten and molybdenum wires have the undesirable property that they are readily oxidized. The oxide layers thus formed on the grid wire may interfere with proper operation of the tube. In order to eliminate such layers, nickel wire is frequently employed in place of tungsten or molybdenum wire, or a nickel or silver-plated tungsten or molybdenum wire is used. In such cases, the dissolving step of the mesh wires, temporarily serving as supporting wires, can be carried out, if at all, only with difficulty, since the nickel or silver layer will be, likewise, attacked by the acid. In addition to this, the abovementioned acid application is disadvantageous because the grids have to be thoroughly cleaned after the acid treatment to remove any traces of anions which might impair the operation of the tube. Deformations This method is not suitable for mass produc-- F urther-- ttes Patent this step.

It is an object of the present invention to overcomethese disadvantages.

It is another object of the invention tormanufacture' grid-shaped electrodes for electrical discharge devices by. first making a mesh or fabric having eitherits warp' or its weft made of an organic material, and the weft or warp made of a metallicmaterial. The metallic elements of this mesh are then attached to a grid support or frame and, finally, the organic threads are destroyed by dissolving or by burning. Organic'materials suitable for this purpose are for instance, cotton, silk, cellulose and synthetic resins.

The method according to the present invention has several advantages. Since organic threads have a higher resiliency than metal wires, the latter will more readily lie in one plane and, thus, in operation will define an, equipotential plane, while the organic threads will meand'er about said plane on both sides. When such fabric is set by rolling, the organic threads and; the metal wires will retain their mentioned positions. There are no basic restrictions as to the selection of the metal for the wires. These Wires may be of nickel, copper or any of their alloys, because these metals are attacked neither during the burning of the organic threads nor during the dissolving of thev same.

It is a still further object of this invention to provide a machine for manufacturing grid electrodes in accord,- ance with the-new method.

Still further objects and the entire scope of applicabilityof the present invention will, become apparent from the; detailed description given hereinafter; it'should beunderstood, however, that the. detailed description and;

specific examples, while indicating preferred embodiments of, the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

In the drawing:

Figure l is, a. plan view on a considerably enlarged scale of a fabric strip to be used in the manufacture of a grid electrode according to the invention;

Figure 2 shows aplan view of a single frame for the; electrode to be made according to the invention with the; fabric strip assembled;

Figure 3 illustrates a plan view of a finishedigridelectrode according to this invention;

Figure 4 shows schematically in plan view'the essential parts of a machine for manufacturing grid electrodes according to the invention;

Figure 5 illustrates schematically a front view, partially in section, of the machine shown in Figure 4.

In Figure l, warp threads 1, lying in the longitudinal direction of the fabric strip, are of metal, such as nickel, while the weft threads 2, crossing the warp threads 1 and being interwoven therewith, are made of an organic material, for example, a natural animal or vegetable fiber, such as silk or cotton, or of a synthetic resin or of cellulose or a cellulose derivative. Metal wires having a diameter in the order of 10 microns or less are used for fine-meshed grids. The organic threads may have the same or larger diameters.

In order to manufacture a grid electrode from such a fabric, the fabric piece, cut to a suitable size, is mounted on a metal frame 3, as shown in Figure 2. This frame 3, made for example of nickel, is either punched out of a metal sheet or assembled from four wire pieces, or bent from a single wire piece. The ends of the metal warp threads 1 are cemented, soldered or welded to said frame 3. During this step or thereafter, the weft threads. 2 are Patented Mar. 24, 1959 removed. The removing operation is carried out by burning the organic weft threads 2 by means of a flame or by placing the frame 3 together with the fabric secured thereon in a furnace filled with air, oxygen or a protective gas and heated to the melting or burning temperature of the organic material of the weft threads 2, or by passing said frame 3 through such furnace. The organic threads are either burned, dissolved or otherwise disintegrated to produce a grid, as shown in Figure 3. The remaining ashes may be easily and completely removed by tapping, brushing or by means of a blower. If the grid electrode is to obtain an arched or curved form, it may be shaped as desired either prior to or after removing of the organic weft threads 2. The frame 3 may be designed so that the wires after being fastened thereto can be tightened.

Another method of removing the organic weftthreads 2 consists in immersing the metal frame 3 with the fabric attached thereto into a liquid which decomposes or dissolves the organic weft threads 2 without attacking the metal warp wires 1. Suitable baths for this purpose may include, for instance, formic acid or dimethylic formamide in case of organic threads of Perlon or nylon.

The fabric is secured to the metal frame 3 and the wires 1 are soldered or welded thereto suitably in an automatic machine to which the fabric and the frames are supplied by means of conveyors.

In the machine according to Figures 4 and 5, 4 denotes a fiat, rectangular metal plate constituting the lower electrode of an electrical welding machine to which the metal frames 3 are successively fed from one side. The metal frames 3 are made by stamping rectangular cutouts 5 in a metal strip 6 integral along the edges denoted by dashlines 7. When such a metal frame 3 forming part of the strip 6 is brought to the proper working position on the metal plate 4, a fabric strip 8, fed successively from the left, is placed thereon so that the front edge 9 of the fabric strip 8 is seated on the side 10 of the frame 3. Thereupon, an upper welding electrode 11, shown only in Figure 5 and having two shoulders 12 extending transversely to the metal wires 1 of the fabric strip 8, is placed on the fabric strip edges and the joining step is carried out by applying a welding current flowing through the frame 3 and the portions of the metal wires 1 seated thereon. Simultaneously or subsequently, the grid electrode thus obtained is separated along dash-line 7 from the metal strip 6, and at the other side from the fabric tape 8 by means of

knives

14 and 13, respectively. After lifting of the upper welding electrode 11, the grid electrode is ejected from the machine. The electrode is then ready for a succeeding working step, leaving the two

strips

6 and 8 to be advanced to repeat the welding operation. The work piece thus obtained will now be shipped of the 1 being in parallel.

organic weft threads 2, as mentioned in the foregoing and, if necessary, may be subsequently tensioned, bent or otherwise shaped. 1

The joint formed between the wires of the fabric and the metal frame may be obtained in such a manner, that the fabric strip 8 and the metal strip 6 are fed to the welding machine with their respective longitudinal edges In this case, only a single knife is necessary to cut off the welded work piece.

I claim:

1. The method of manufacturing grid electrodes for electron tubes comprising the following steps: preparing pieces of fabric of warp and weft threads, of which theone is made of metal and the other of organic material; mounting said fabric pieces on supports; and destroying said threads of organic material in said mounted fabric pieces.

2. The method of manufacturing grid electrodes according to claim 1, wherein said threads of organic material are destroyed by chemical action.

3. The method of manufacturing grid electrodes according to claim 1, wherein said threads of organic material are destroyed by thermal action.

4. The method of manufacturing grid electrodes according to claim 1, wherein said warp threads are made of metal and said weft threads of organic material.

5. The method of manufacturing grid electrodes according to claim 1, wherein said warp threads are made of organic material and said weft threads of metal.

6. The method of manufacturing grid electrodes according to claim 1, wherein said supports are metal frames on which said fabric pieces are to be mounted.

7. The method of manufacturing grid electrodes according to claim 6, wherein said metal threads are cemented to said metal frames.

8. The method of manufacturing grid electrodes according to claim 6, wherein said metal threads are welded to said metal frames.

9. The method of manufacturing grid electrodes according to claim 6, wherein said metal threads are soldered to said metal frames.

10. The method of manufacturing grid electrodes according to claim 6, wherein said metal frames with said mounted fabric pieces are placed in a heating chamber to destroy said threads of organic material.

References Cited in the file of this patent UNITED STATES PATENTS 2,002,148 Klinkert May 21, 1935 2,577,103 Brian Dec. 4, 1951 2,606,822 Pakswer Aug. 12, 1952