Patent GB-1536867-A (GB)
Title: Strapping joints
IPC: B65B51/22
Filed: 1975-11-25
Abstract: 1536867 Seaming non-metallic sheet material SIGNODE CORP 25 Nov 1975 [25 Nov 1974] 48476/75 Heading B5K Overlapping inner and outer end portions 20a, 20b of molecularly oriented thermoplastic strap, e.g. of polypropylene, polyester or nylon, formed into a loop and tensioned about an article P, are fused to one another by a resolidified thin layer 26 of formerly melted material from each portion 20a, 20b, the portion' 20b having a tapered section 27 producing a reducing taper towards the portion 20a, the reducing taper having an outer end that forms part of the layer 26, the resolidified material extending completely to the end of the tapered section 27. In one embodiment, Fig. 4, the portions 20a, 20b are positioned between jaws 21, 22 so that the end 30 of the portion 20a projects beyond an edge 40 of the jaw 21 and-the end of the portion 20b extends only up to an edge 41 of the jaw 22. To prevent strap slippage, teeth 35 are provided on the gripping surfaces 23, 24 of the jaws 21, 22. On the jaw 22, a protrusion 25 extends outwardly of the surface 24 and has a curved surface 31 tapering to an edge 33 above the edge 41. The protrusion 25 faces a smooth portion 44 of the jaw 21 and may be formed integrally with the jaw 22 or may be a separate part. The jaws 21, 22 are moved together to compress the portions 20a, 20b and the jaw 21 is vibrated at high speed in a direction parallel to the surfaces 23, 24. This vibration causes melting at the compressed interface 26, Fig. 6, and the pressure concentration caused by the protrusion 25 turns inwardly the outer edge 27 of the portion 20b. A mass of molten material 28 is forced outside the interface 26 which becomes uneven adjacent the protrusion 25. After cessation of the vibrations, the molten material resolidifies. The inner end of the portion 20a may provide a manually grippable tab 30 for pulling the joint apart. Other movements between the jaws 21, 22 to friction fuse the strap may be used, e.g. rotary, lateral or reciprocal movement. In a modification, Fig. 7, the portion 20b terminates beyond the protrusion (25) so that there is formed a brittle loose end 51 which, if snagged, breaks off to leave a snag resistant tapered end 52 similar to the end 27 of Fig. 6. Alternatively, the protrusion 25 may be shaped to sever the strap portion leading to the supply so that a separate cutter is not required. In another modification Fig. 8, the protrusion 25 includes a flat surface 32 terminating in a sharp edge 34 which may act as a cutting edge. In a further modification, Fig. 9, welding jaws 60, 61 having complementary arcuate gripping surfaces 62, 63 with teeth 68 are provided. A protrusion 64 extends from the surface 62 and to effect welding the jaw 61 is rocked at high speed.  A machine similar to that described in Specification 1,225,992, Fig. 10, comprises a vibrator 50, a temporary holding gripper 53 and a tandem pair of gripping jaws 128, 144 with a protrusion 25 on the jaw 144. In use, an end 20a of thermoplastic strap is clamped to the vibrator 50 by the gripper 53. The strap is drawn around a package and an end 20b passes under the vibrator 50 and extends to a tensioner (not shown). A toggle plate 104 is moved upwardly and the jaw 128 first moves to clamp the ends 20a, 20b against the vibrator 50. The jaw 144 moves to a position, Fig. 12 (not shown), in which a sharp edge 33 of the protrusion 25 in conjunction with a cutter 42 severs the strap from the end 20b. A sloping surface (142), Fig. 12 (not shown), of the plate 104 moves a rod 57 to the right of Fig. 10 against the action of a spring 58 so that, with the assistance of a spring 69, a link 56 is moved counterclockwise of a pivot 59 to move the gripper 53 out of engagement with the end 20a. At the completion of the stroke of the plate 104, the jaw 144 clamps the ends 20a, 20b, Fig. 14 (not shown). The vibrator 50 is oscillated to move the end 20a relative to the end 20b and form a joint similar to that of Fig. 6. In another embodiment (not shown), to form a joint by a hot-knife process similar to that described in U.S.A. Specification 3,368,323, the strap end portions with a heated knife blade therebetween are compressed between a pair of jaws similar to those described above. After melting of adjacent strap portions, the knife is withdrawn in a plane parallel to the strap surfaces and a joint is formed as the melted interface material resolidifies. Alternatively, the protrusion is formed on the knife instead of one of the jaws.