| 摘要 |
690,614. Seaming non-metallic sheet material. RADIO HEATERS, Ltd., and STANLEY, E. C. April 28, 1950. [May 2, 1949] No. 11694/49. Class 42 (i). [Also in Group XVII] In forming a packet or container from thermoplastic tube or sheet by radio-frequency welding and providing a web portion therein by welding together parts of two adjacent walls to receive a tearing-slit which initially does not extend into the container but can be extended thereinto by tearing, the welding of the tearable web portion is effected by parts of electrodes 16, 17, Fig. 5, that are progressively relieved to avoid forming a thickened inside edge 13 to the weld, thereby facilitating the tearing to extend the slit 7 into the interior of the bag. The progressively relieved portions of the welding- electrodes may provide a tearing web 4 of semicircular shape, as shown in Fig. 1. |
