Shadow mask frame construction

Claim 1

A shadow mask of a color television receiving tube of the class comprising: a rectangular mask plate including a curved rectangular face having at least one centre of curvature on the side of a source of electron beams contained in the envelope of said tube, and a peripheral flange surrounding said curved rectangular face and bent toward said source of electron beams, said curved rectangular face being provided with a plurality of small perforations therein for controlling the passage of said electron beams; and a rectangular frame member having two shorter side walls and two longer side walls adapted to receive said peripheral flange inclined toward said source of electron beams and a reinforcing flange bent inwardly of said rectangular frame and away from said side walls, each of said side walls having a curved free edge and a stationary edge opposite said curved free edge, said curved free edge having the same radius of curvature as the periphery of said mask plate, the radius of curvature of said stationary edge opposite to said free edge of each side wall differing from that of said free edge, the angle between said side wall and said reinforcing flange equaling 90*+ Alpha 1, 90*+ Alpha 2 and 90*+ Alpha 3 at the corner, at the longitudinal centre of said shorter side wall and at the longitudinal centre of the longer side wall, respectively, and said angles Alpha 1, Alpha 2 and Alpha 3 having a relation Alpha 1< Alpha 2<3, the angles Alpha 2 and Alpha 3 gradually decreasing from the longitudinal centres of said shorter and longer side walls toward the corner of said rectangular frame member wherein Alpha 1 5 to 15*, Alpha 2 10 to 45*, and Alpha 3 15 to 55*.