| 摘要 |
849,222. Seaming. ARTHUR, J. March 17, 1958 [March 18, 1957], No. 8875/57. Class 42 (1). Two surfaces of a polyethylene terephthalate are welded together by heating them, while they are in contact, at a temperature which is below that at which embrittlement takes place (about 350‹ C.) and at or above the softening- point (i.e. minimum welding temperature) by directing a stream of heated gas on to the surfaces. A temperature between 200‹ and 300‹ C., and in particular 260‹ C., is stated to be satisfactory. As shown, a ribbon A of polyethylene terephthalate from a reel 11 is folded longitudinally at 13, 14 and the abutting edges are seamed together by a jet of heated nitrogen from a nozzle 17 to form a tube B. The nitrogen jet impinges on the edges as they protrude slightly from the jaws of a welding block 15. The jaws are cooled by water &c. supplied via pipes 25, 26, and their spacing is adjusted by means of a screw 21 so that the ribbon is just able to move freely. The nitrogen is heated to a controlled temperature by an electrically-heated jacket 20. Extraction rollers 16 maintain the ribbon under slight tension to prevent contraction of the ribbon edges. The tube may be subsequently divided into sachets, the ends of which are sealed by a further welding. Preferably the nitrogen is dry and oxygen-free. The material may be preliminarily heat-treated to avoid contraction during welding. |
