US2499977A - Method of forming grid-like structures - Google Patents

Description

March 7, 1950 w. J. SCOTT METHOD OF FORMING GRID-LIKE STRUCTURES Filed Nov. 14, 1945 Ihventof: William J. SCO tt, M 25% H is Attorney.

Patented Mar. 7, 1950 METHOD OF FORMING GRID-LIKE STRUCTURES William J. Scott, Rugby, England, assignor to General Electric Company, a corporation of New York Application November 14, 1945, Serial No. 628,566

In Great Britain November 3, 194-3 Section 1, Public Law 690, August 8, 1946 Patent expires November 3, 1963 11 Claims. 1

My invention relates to improved methods for producing grid-like structures and is particularly well adapted for producing control grids for high frequency electric discharge, devices.

It is frequently desired to manufacture small grids of honeycomb or like formation for use in electric discharge devices particularly where such devices depend for their effective operation on the accurate control of an electron beam. Considerable difiiculty has been experienced in manufacturing control grids for this purpose in accordance with prior art methods. Both mechanical and thermal problems have existed which have made it extremely difiicult to produce control grids of this character which are mechanically strong and which did not warp out of shape during operation as the result of thermal ex pansion.

It is an object of my invention to provide a new and improved method of manufacturing grid-like structures.

.It is another object of my invention to provide a new and improved method of manufacturing grid-like structures which is adapted for quantity production of very fine grids such as those employed in high frequency electric discharge devices.

The method according to my invention comprises assembling into a bundle a plurality of core rods or strips of deformable metal which have been coated or interleaved with a metal of which the grid has been formed, surrounding the bundle with a coating or a tube having at least the inner surface thereof formed of the coating material, and then reducing the cross sectional area of the bundle to fill all the interstices and bring the coating metal and the metal of the inner surface of the surrounding tube into intimate contact. After the bundle has thus been compacted the core rods are removed by a suitable chemical re-agent which does not attack the grid metal. Either before or after removal of the core rod, sections are cut from the compacted bundle having a thickness corresponding to the desired thickness of the grids to be manufactured.

For a better understanding of my invention reference may be had to the following description taken in connection with theaccompanying drawing, and its scope will be pointed out in the appended claims. In the drawing, Fig. 1 is a cross sectional view showing abundle ofcoated wires assembled in a surroundingtube; Fig. 2 is across sectional view of the structure of Fig. 1 after it has been compacted bysyvaglng the tube to" a substantially smaller diameter; Fig. 3 is a;

side elevational view of the compacted bundle of Fig. 2 showing a section cut from one end to form a grid, and Fig. 4 is an end view of agrid section after the core rods have been removed.

In carrying out the invention, a bundle .of de formable core rods or strips I formed of a suitable metal, such as iron, are coated with a layer of metal 2 which is to constitute the grid. In one embodiment of my invention the grid metalis one of the noble metals such as platinum or gold, or copper plated with silver or gold. A bundle of these coated wires is then assembled within an outer tube 3 which may be formed of iron internally coated with the grid metal or, if desired, it may be formed entirely of the grid metal. The assembly of coated wiresand surrounding tube is then swaged to reduce the external diameter of the assembly and to fill the voids between the various coated wires and to mechanically join the coating of the various wires and the lining of the tube into an integral structure. Instead of inserting the bundle of wires into a tube, it will be readily understood that a surrounding layer of grid metal may be applied directly by a suitable process such as electroplating. .A cross sectional view of the compacted bundle is shown in Fig. 2. It will be noted that the wires may be deformed to an irregular shape which in the illustrated embodiment is somewhat hexagonal, as illustrated by the numeral 4, so that the section as a whole has a honeycombed appearance. In Fig. 3 the compacted tube is shown in elevation and a section 5 of appropriate thickness for a grid disk has been cut from the compacted bundle. Either before or after the sections are cut from the compacted bund1e,the core rods 2 are removed by immersing the sections or the bundle into a suitable chemicalre-agent which dissolves the core rods but which is selected so that it will not appreciably attack the grid metal. The grid structure with the core rods removed and leaving irregular shaped openings 6 is shown in Fig. 4.

. The core rods may be coated with an oxide of a metal such as tungsten or molybdenum inplace of the noble metal coating. In such a case the oxide is reduced to a metal by heating in an atmosphere of reducing gas such as hydrogen.

base metal, nitric acid may be employed for the removal of the base metal.

As one practical example of the manner in which the invention may be carried into effect, we may say that we have successfully made grids having a substantially circular shape with an external diameter of inch in the following manner:

Iron wires of circular cross-section and 0.020 inch diameter were electroplated with silver until a coating of 0.001 inch in thickness was deposited thereon. Sixty-one of these silver-coated wires were then assembled into a bundle and inserted in a silver tube to provide a further coating on the outer periphery of the bundle. The assembled bundle then had an external diameter of nearly A inch and was placed in a inch bore tube inch in diameter. The assembly was then mechanically swaged until its external diameter" was reduced to approximately inch. During this swaging. process the bundle was compacted into an integral mass which was then sintered in hydrogen. As indicated in Fig. 3 discs. were cut from the compacted mass having a thickness of 0.040. inch or less. These discs were then immersed. in a solution of hydrochloric acid and the iron was completely dissolved away leaving silver behind in the form of a grid of irregular honeycomb shape. These grids were then washed. to remove all traces of acid and dried.

In an alternative method, a grid suitable for use at very high temperatures is made of tungsten as follows. Nineteen molybdenum wires of 0.040 inch diameter, each overwound with 0.001 inch diameter tungsten wire, were assembled into a compact bundle in. a tube bent up from thin (0.005 inch) tungsten sheet and the spaces between the wires filled with a sludge of fine tungsten powder in water. The bundle was pushed in a close fitting molybdenum tube of about 78 inch external diameter and the end plugged with molybdenum rod. The compound rod was swaged down to give grid diameters of 2 and 2 mm. respectively. Discs varying from 0.100 inch to 0.050 inch thick were sliced from the rod with a thin grinding wheel. They were heated for fifteen minutes or more at a temperature of 1850 C. or higher in wet hydrogen to sinter the tungsten surfaces together, the flat faces cleaned by grinding, and the molybdenum dissolved out in a mixture of nitric acid, sulphuric acid and water. The cell wall thickness was 0.001 inch or less.

Tungsten grids, of still smaller size have been made, but for them a more continuous covering of tungsten on the molybdenum wires is desirable. One method of doing this is to heat the molybdenum wire in an atmosphere of tungsten oxychloride or tungsten hexachloride. which decomposes and. deposits a layer of tungsten on the hot wire.

It will be apparent from the foregoing detailed description and examples of specific materials employed in accordance with the improved method that I provide very workable procedures for producing extremely fine grid-like structures. While these structures are particularly adapted for control grids for use in high frequency discharge devices, it is apparent that. my invention is not limited to the production of grid-like structures for this purpose.

, What. I claim as new and desire to secure by Letters Patent of the United. States, is: 1

1. The method of producing a metal control grid of honeycombed or like form. for controlling an electric discharge in an electric discharge do.

vice which comprises the steps of coating a plurality of core rods of deformable metal with a metal of which the control grid is to be constituted, assembling the coated rods into a bundle with various ones of the coated rods in contact with one another, mechanically reducing the cross sectional area of the bundle to join the coating metal of the contacting rods together and then removing the deformable metal by a chemical re-agent to the action of which the grid metal is essentially chemically inert to form a grid structure of the metal with which the rods are coated.

2. The method of producing a metal control grid of honeycombed or like form for controlling an electric discharge in an electric discharge device which comprises the steps of coating a plurality of core rods of deformable metal with a metalof which the control grid is to be constituted, assembling the coated rods into a bundle with various ones of the coated rods in contact with one another, mechanically reducing the cross sectional area of the bundle to join the coating metal of the contacting rods together, cutting a section from the compacted bundle of the required thickness to form the grid, and removing the deformable metal by a chemical reagent to the action of which the grid metal is essentially inert to form a grid structure of the metal with which the rods are coated.

3. The method of producing a metal control grid of honeycombed or like form for controlling an electric discharge in an electric discharge device Which comprises the steps of coating a plurality of core rods of deformable metal with a metal of which the control grid is to be constituted, assembling the coated rods into a bundle including an overlying layer of the grid metal and with various ones of the coated rods in contact with one another, mechanically reducing the cross sectional area of the bundle to join the coating metal of the contacting rods together and to the overlying layer of the grid metal and removing the deformable metal by chemical reagent to the action of which the grid metal is essentially chemically inert to form a grid struc ture of the metal with which the rods are coated and with a marginal portion formed from the overlying layer.

4. The method of producing a metal control grid of honeycombed or like form for controlling an electric discharge in an e ectric discharge device which comprises the steps of coating a plurality of core rods of deformable metal with a metal of which the control grid is to be constituted, assembling the coated rods into a bundle with variousv ones of the coated rods in contact with one another, inserting the bundle into a tube having at least the inner surface thereof formed of the grid metal, mechanically reducing the cross sectional area of the bundle to join the coating metal of the contacting rods together and to the inner surface of said tube, and removing the deformable metal by a chemical re-agent to the action of which the grid metal is essentially inert to form a grid structure of the metal with which the rods are coated.

5. The method of producing a metal grid which comprises the steps of coating a plurality of core rods with a metal of which the grid is to be constituted assembling the coated rods intov a bundle with various ones of the coated rods in contact with one another, filling the interstices between the coated core rods with a sludge of the powdered grid. metal, sinteringthe assembly to. cause '9 the powdered metal to adhere to the remainder of the grid metal, cutting a section from the compacted bundle of the required thickness to form the grid, and removing the core rods by a chemical re-agent.

6. The method of producing a metal control grid for controlling an electric discharge in an electric discharge device which comprises the steps of coating a plurality of iron core rods with a noble metal which is to constitute the control grid, assembling the coated rods into a bundle with the noble metal coating with various ones of the rods in contact, mechanically reducing the cross sectional area of the bundle to join the noble metal coatings of the contacting rods and then removing the iron by chemical re-agent which does not attack the noble metal to form a control grid of the noble metal.

7. The method of producing a metal control grid of honeycombed or like form for controlling an electric discharge in an electric discharge device which comprises the steps of wrapping a layer of wire formed of the metal of which the control grid is to be constituted on each of a plu rality of core rods of deformable metal, thereafter assembling the coated rods into a bundle with the wrapped layers of various ones of the rods in contact, mechanically reducing the cross sectional area of the bundle to join together the contacting layers of wire and then removing the deformable metal by chemical re-agent to the action of which the grid metal is essentially chemically inert to form a grid of the metal provided by the wrapped layers.

8. The method of producing a metal grid of honeycombed or like form which comprises the steps of Wrapping a layer of tungsten wire on each of a plurality of molybdenum core rods, assembling the coated rods into a bundle with the layers of tungsten wire of various ones of the rods in contact with one another, mechanically reducing the cross sectional area of the bundle to join the layers of tungsten wire together, and then removing the deformable metal by a chemical re-agent to which tungsten is substantially chemically inert.

9. The method of producing a metal grid of honeycombed or like form which comprises the steps of coating a plurality of molybdenum core rods with a tungsten coating by heating the rods in an atmosphere containing a compound of tungsten which decomposes to deposit metallic tungsten on the rods, assembling the coated rods into a bundle with various ones of the coated rods in contact with one another, mechanically reducing the cross sectional area of the bundle and then removing the deformable metal by chemical reagent to the action of which the grid metal is essentially chemically inert.

10. The method of producing a grid of honeycombed or like formation which comprises the steps of coating an iron wire with an oxide of a refractory metal selected from the group consisting of tungsten and molybdenum, assembling a plurality of lengths of the coated wire into a bundle with various ones of the coated rods and in contact with one another, encasing the bundle in an outer iron tube, swaging the composite body to reduce materially its diameter, heating the compacted bundle in an atmosphere of hydrogen so as to reduce the oxide to its metallic state, and immersing the disks in nitric acid to remove the iron and leave the refractory metal in the desired grid-like formation.

11. The method of producing a grid of honeycombed or like formation which comprises the steps of coating an iron wire with an oxide of a refractory metal selected from the group consisting of tungsten and molybdenum, assembling a plurality of lengths of the coated wire into a bundle with various ones with the coated rods in contact with one another, encasing the bundle in an outer iron tube, swaging the composite body to reduce materially its diameter, heating the compacted bundle in an atmosphere of hydrogen so as to reduce the oxide to its metallic state, cutting the compacted bundle into disks, and immersing the disks in nitric acid to remove the iron and leave the refractory metal in the desired grid-like formation.

WILLIAM J. SCOTT.

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

UNITED STATES PATENTS Number Name Date 1,286,089 Pfanstiehl Nov. 26, 1918 2,047,555 Gardner July 14, 1936 2,169,937 Wempe Aug. 15, 1939 2,197,753 Liebmann Apr. 23, 1940 2,266,349 Wempe Dec. 16, 1941 FOREIGN PATENTS Number Country Date 501,660 Germany July 3, 1930

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