GB458675A - Improvements in or relating to metal mesh screens for example for use in cathode ray tubes - Google Patents

Abstract

458,675. Making mesh screens, sieves, etc.; electrodeposition. HOLMAN, H. E., 4, Fairway Avenue, Garden City, Yiewsley, Middlesex. May 23, 1935, Nos. 15103 and 31199. [Class 83 (ii)] [See also Groups XXXVI and XL] A method of forming a metal mesh screen includes the steps of forming a matrix having grooves corresponding to the finished screen, coating the matrix with a layer of metal, removing the metal coating from between the grooves, and removing the matrix. A coating of nickel 41, Fig. 3, or 41<1>, Fig. 7, is electrodeposited on a matrix 40 formed with transverse and longitudinal grooves and the surface is ground or lapped leaving nickel only in the grooves of the matrix 40, Fig. 4, the matrix then being removed to leave a nickel screen. The grooves may be of V-section and the degree of grinding regulated to vary the thickness of the nickel. The copper may be removed electrolytically after applying a resistive varnish to the grooved surface, any residual copper being removed by ferric chloride or ammonium persulphate. Sharp edges produced in grinding are removed by dipping in nitric acid. A screen may be mounted between two rectangular frames of nickel wire, the assembly being secured by resistance welding. Alternatively, the margin of the sheet 40, Fig. 4, may be electroplated with nickel to form a frame, the centre portion being stopped off by a sheet of ebonite or similar material stuck thereon, after which the copper matrix is removed. Supporting wires are welded to the screen. In the production of a screen for a cathode-ray tube, such as used for the transmission of pictures, gold is substituted for nickel, and the copper backing is removed by nitric acid. Before complete removal of the copper, a nickel wire frame is secured by welding, which frame may have glass bead insulation for joining to a mosaic screen. The remainder of the copper is removed by immersion in nitric acid. An alternative method of mounting comprises welding a nickel frame to the gold mesh before complete removal of the copper, applying an asphalt varnish to the grid surface and to the copper backing, placing in a gold-plating bath and applying a resistant coating to the frame and the welds, removing the asphalt by boiling in ether, and finally removing the copper in a nitric acid bath. The copper backing may be removed from a nickel or gold screen by a 20 per cent ammonium persulphate solution at 25‹ C. A nickel screen is coated with enamel after cleaning electrolytically and heating in oxygen to form a blue oxide coating, or applying a light copper deposit and thermally oxidizing it. Commercial vitreous enamel is reground in a ball mill, mixed with additional water, and a suspension of very fine particles is obtained by decantation. The powder is sprayed by a gun using nitrogen at a pressure of 50 lbs. per sq. in., a second coating being applied after drying. The enamel coating may be fused in a vacuum. Screens produced by the method described may be employed in the production of blocks for the photographic reproduction of pictures &c., or as sieves for granular material. Specification 458,736 is referred to.