| 摘要 |
775,061. Seaming. GRACE & CO., W. R. Aug. 29, 1955 [Aug. 30, 1954], No. 24735/55. Class 42 (1). A fused seam is formed between two sheets of thermoplastic material by placing the sheets between two relatively movable sealing jaws 13, 44, closing the jaws so that they firmly contact the sheets and then arresting the closing movement, heating the seam area of the sheets until the material becomes plastic and thereafter closing the jaws further so as to apply full sealing pressure to the sheets. As shown, Fig. 1, the jaws 13, 44 are conductively heated by elements 16, 47 respectively and are covered with an antisticking material such as " Teflon " (Registered Trade Mark); radio-frequency electrodes may, however, be substituted. The lower jaw 13 is provided with a heat-resistant compressible pad 14 and is mounted on a frame plate 12, with an interposed layer 17 of insulating material. An air cylinder 18, suspended from plate 12, acts through a bar 24 and rods 33, 34 to raise and lower a top plate 43 carrying the upper jaw 44. The closing movement of the jaws is limited by engagement of adjustable stop screws 62, 63 with stops 58 projecting from the pistons 57, Fig. 2, of air cylinders 49, 51. A control system provides the following operational sequence : (a) low pressure air is applied to the top of cylinder 18 to lower jaw 44 until stops 62, 63 meet stops 58 which are maintained in their raised positions by high pressure air supply; in this position, pad 14 is slightly compressed ; (b) after a predetermined short heating. period, cylinders 49, 51 are exhausted, permitting stops 58 to fall to their lower positions, and high pressure air is applied to the top of cylinder 18, so that jaw 44 descends a further short distance under full sealing pressure; (c) after a short dwell of predetermined duration jaw 44 is raised from the seam by low pressure air applied to the bottom of cylinder 18. The sealing surface of jaw 44 is formed with a radius or bevel to provide a wedging action which forces plastic material inwardly of the seam to form a convex portion 104, Fig. 3; the sheets 101, 102 shown are of a vinylidene copolymer oriented film, the increased thickness at 103 resulting from shrinkage due to disorientation of the film by the applied heat. |
