| 摘要 |
943,457. Seaming non-metallic sheet material. FR. HESSER MASCHINENFABRIK-A.G. April 5, 1962 [April 28, 1961], No. 13194/62. Heading B5K. [Also in Division B8] In forming a seam between unsupported thermoplastic sheets the sheets are applied together and a seam is made by continuously heated welding jaws whereafter a part of the width of the seam is given a second hot pressing by means of further pressing jaws. The embodiment shown is applied to the closure of bags made of polythene. The walls 1, 2 of the bag are first brought into face-to-face contact and are pressed together by heated jaws 3, 4. After the fused condition is achieved jaws 3, 4 are moved apart and the seam 6 is left for a short period during which it contracts widthways as shown in Fig. 2. The seam 6 is then pressed again, approximately over half its width nearest the top end of the bag, and whilst still warm, by means of a further pair of jaws 7, 8 (Fig. 3) each provided with a resistance strip 9 whereby they can be heated. The surplus bag material above the seam may be folded over and additionally seamed. In a second embodiment, the jaws 3, 4 are formed with two contact areas with a space therebetween so as to form spaced apart seams and the jaws 7, 8 are arranged to cover the whole of the top seam and approximately the top half of the bottom seam. U.S.A. Specification 2,460,460 is referred to. |
