GB1300900A - Shadow masks for colour television receiving tubes - Google Patents

Abstract

1300900 Making shadow mask frames TOKYO SHIBAURA ELECTRIC CO Ltd 29 July 1971 [30 July 1970] 35631/71 Heading B3A [Also in Division H1] A shadow mask is supported by a rectangular frame 14, Fig. 3, formed of strip of L-shaped cross-section, and characterized by the provision of apertures 19 in the angle of the L. The frame is initially plane and then bent to conform to the curvature of the mask portion, and the apertures prevent excessive strains being set up by this process. Also if the mask is etched to enlarge its mask apertures after processing the screen of the tube, the frame apertures allow proper draining of the etching fluid, especially at the corners. The mask may be provided with a foil surround (Figs. 4 and 5, not shown) to trap electrons escaping round the edges of the mask, and this may be secured to the frame by means of clamps which extend through the apertures. Making shadow masks. A metal strip for the frame is prepared to the correct length and width and a plurality of rectangular perforations are punched out along a longitudinal line along which the strip is to be bent. The strip is then bent longitudinally in a machine and further bent into a rectangular configuration, the ends being butt welded. The resulting frame is bent to conform to the periphery of the mask portion which is fitted over it and welded to it.