GB575320A - Process for forming honeycomb or like grids for electric discharge devices - Google Patents

Abstract

575,320. Electric discharge apparatus. BRITISH THOMSON-HOUSTON CO., Ltd., and SCOTT, W. J. Nov. 3, 1943, No. 18184. [Class 39 (i)] [Also in Group XXII] A metal grid of honeycomb or like form is made by assembling wires or strips of deformable metal coated or interleaved with the metal of which the grid is to be made, compacting to reduce the cross-section of the assemblage, and removing the wires by a chemical which will not attack the grid metal. A section is preferably cut from the assemblage having the required thickness to form a grid, before removing the wires, but this may be done after; The assemblage may be placed before compacting in a metal tube of or lined with the grid metal. Iron wires electro-plated with platinum, silver or gold may be placed in an iron tube, electroplated inside with the same noble metal, or copper-plated with silver or gold, may be used. In another modification the compacted wires may be electro-plated to form an outer tube. The iron could be removed by hydrochloric or nitric acid. In another modification the wires are coated with tungsten or molybdenum oxide which is then reduced to metal by hydrogen. The compact mass or the discs cut therefrom may be sintered in hydrogen. A grid for high temperatures is made by winding tungsten wire, 0.001" in diameter, on molybdenum wires 0.04" in diameter. Nineteen of these are placed in a tube of tungsten 0.005" thick, spaces being filled by a sludge of fine tungsten powder 'in water. The bundle is pushed into a tube and the end plugged with a rod, both of molybdenum. The whole is swaged till the diameter is 2 to 2¢ mm. and discs 0.01 to 0.05" are cut off by a thin grinding wheel. These are heated for over 15 minutes to over 1850‹ C. in wet hydrogen, the flat faces are ground and the molybdenum dissolved out with a mixture of nitric and sulphuric acids and water. In a modification, the molybdenum wires are coated with tungsten by heating them in tungsten oxy- or hexa-chloride vapour. The method enables fine grids to be made, for use in valves for still shorter wavelengths, and also successive grids with all their holes in alignment to give maximum transmission of an axial electron beam.