Method of making color picture tube shadow mask having improved tie bar

Abstract

An improved method of making a color picture tube shadow mask includes first constructing an apertured flat mask which is formed into a domed contoured mask. The mask has a rectangular periphery with two long sides and two short sides. The mask has a major axis, which passes through the center of the mask and parallels the long sides, and a minor axis, which passes through the center of the mask and parallels said short sides. The mask includes slit-shaped apertures aligned in columns that essentially parallel the minor axis. Adjacent apertures in each column are separated by tie bars in the mask, with the spacing between tie bars in a column being the tie bar pitch at a particular location on the mask. The improvement comprises a first step of calculating the desired tie bar shadow locations at several discrete areas, for a given scan line pitch, as viewed from a distance in front of a viewing screen of a tube. The desired tie bar shadow locations are those locations that will give an optimized compromise for moire at each of the discrete areas. Next, the corresponding tie bar shadow locations on the screen are determined, taking into account the angles of the screen slope at the discrete areas. The corresponding tie bar pitches are then determined on a formed contoured shadow mask, taking into account the mask to screen spacing at each of the discrete areas. Then, the tie bar pitches on the unformed flat mask are calculated, by subtracting the stretch caused by the mask formign step. The stretch is determined by actual measurements of vertical pitch at the discrete areas on the apertured formed mask and by comparing these measurements with measurements made on the flat mask prior to forming. Finally, a least squares fitting is performed on the calculated flat mask tie bar pitches, to obtain the locations of tie bars at all areas on the flat mask.