| 摘要 |
PURPOSE:To make a plurality of lines of protrusions to be formed among a plurality of lines of spiral grooves into a radial state precisely, by a method wherein a plurality of lines of molding grooves are tilted at a fixed angle in a turning direction of a die to a shaft center direction extending to resin outlet side from a resin inlet side. CONSTITUTION:A molding groove 2 of a rotary die 1 for extrusion molding is tilted in a turning direction of the rotary die 1 for extrusion molding to a shaft center extending to a resin outlet 1b side from an inlet 1a side. When the tilting angle is alpha, since the rotary die 1 for extrusion molding is turning, a speed of resin of a top part of the molding groove 2 in the resin outlet 1b becomes Vb obtained by compounding v1 and V1. Since the alpha can be set up so that an ingredient of a circumferential direction of the Vb becomes equal to V'1, a protrusion can be formed precisely radially by eliminating a twist of the protrusion. A matter where the ingredient of a circumferential direction of the Vb becomes equal to the V'1 means that a difference V between the V'1 and V1 becomes equal to an ingredient of the circumferential direction of the V'1. |
