PURPOSE: To prevent the breakage of active substance holding ribs of the grids, and to obtain titled grids of excellent voltage characteristics, by rendering the angle of the blade edge of the cutting part of the second die which form nearly triangular and easy to break ribs of the grids duller than that of the third and thereafter, and notching the thin plate and expanding it to form a net.
CONSTITUTION: A lead alloy thin plate 9 is placed between a group 2 of cutters which are fixed stepwise at the left and right side of a base with gradually narrowing spaces and a group 1 of dies which reciprocate upward and downward, and it is expanded. The first die 1A among these has its edge part 10 make almost flat to notch the thin plate 9, and the second die 1b make its blade edge angle θ1 of the cutting part 11 130W150° to effectively prevent the breakage of ribs when expanding them. The blade angle θ2 of the edge part of the third die 1c and thereafter are made 90W120°. As a result, th slipping off the penetrating direction of the die 1b and the direction of expanding of the thin plate 9 during expansion is reduced to make ribs scarcly break. In the figure, 3 net part, 4 upper rim, 5 lug, 6 lower rim, 7 grid ribs.
YASUDA HIROSHI
AOKI NOBUYUKI
