METHOD FOR PUNCHING AN OPENING IN A SYNTHETIC PLASTIC CONTAINER SECTION BLANK AND FORMING RIBS THEREON
A hole is punched in the base of a cold plastics container blank B, and an outwardly extending curled rim formed around the hole, by a reciprocating punch 11 which co-operates with a stationary platen 17 having an opening 18 which receives the reduced leading section 20 of the punch. The blank B is provided with an inwardly-directed stiffening rib 15 and a curved fold section 16. In operation the punch is forwarded into the opening 18 and severs the bottom wall 14 of the blank. Further movement of the punch causes the shoulder 21 on the punch to engage the rib 15 thereby causing the section 16 to be deformed under the axial pressure as shown in Fig. 5. The punch is then withdrawn and the fold section, due to the inherent elasticity of the cold plastics material, partially regains its former shape to form the desired rim. In a second embodiment (see Figs. 8-14, not shown), the stiffening rib is omitted from the blank, the necessary axial pressure being derived by contact of the platen 10 carrying the punch with the web P surrounding the blank.