Patent GB-1507714-A (GB)
Title: Apparatus for tensioning and fusing or welding strips of thermoplastics material
IPC: B65B51/14
Filed: 1975-06-04
Abstract: 1507714 Strap tensioners STRAPEX AG 4 June 1975 [24 June 1974] 24048/75 Heading F2G [Also in Division B5] Apparatus for tensioning and welding overlapping ends of thermoplastics strapping 44 looped about an article 45 comprises a pair of clamping jaws 12, 17 between which the overlapping ends are clamped, a drive 6, 9 for reciprocating the jaw 12 to tension the strapping about the article and then to friction weld the overlapping ends as soon as a predetermined tension is reached, the drive including coupling means to engage the jaw 12 and press it against the overlapping ends in a tensioning direction during a work stroke and for partially relieving this pressing during its return stroke, and stop means 18, 19 to engage the overlapping ends for preventing return movement of the tensioned end during the return stroke of the jaw 12 until the predetermined tension in the strapping is reached. As shown, a drive shaft 6 is provided with an eccentric 7 and, via a needle bearing, drives a lever 9 having an edge 10 engaging in a notch 11  of the jaw 12 which has teeth 13, Fig. 3. The lever 9 has part-circular grooves 14 in which shaped segments 15 of the jaws 12 engage. A compression spring 16 acts on the lever 9. The jaw 12 co-operates with a fixed toothed jaw 17 and toothed clamping jaw 19 co-operates with a fixed toothed jaw 18. A tension spring 20 urges the jaw 19 to the left of Fig. 1. Inclined levers 22 engage in notches 21 in the jaw 19 and in notches 24 in a plate 25 urged towards the jaw 19 by a tension spring 23. A bolt 26 on the plate 25 slides in a sleeve 27 adjustable by a hand wheel 28 to adjust the tension of a plate spring assembly 29 to pre-select the tension of of the strapping. Pins 251 determine the lower position of the plate 25. A side portion 2 of the frame of the apparatus has an extension 30 acting as a grip. A hand lever 31 is pivoted at 32 on the extension 30 and is held in its lower position by a compression spring 33. A slider 36 is connected by a pivot 35 to an extension 34 of the lever 31 and has an inwardly bent projection 37 to act on the jaw 19 and a lug 38 having an inclined flank 39 to co-operate with a pin 40 on the lever 9. A pivoted severing blade 42 is kept in contact with the upper end of the strapping 44 by a spring 43. In operation, with the lever 31 raised, the free end of the strapping 44 is passed from the supply below the jaws 12, 19, looped around the article 45 and passed over the jaws 17, 18. The lever 31 is lowered and the strapping is tensioned by displacing the upper end thereof to the right of Fig. 1. The shaft 6 is driven by an electric motor (8), Fig. 2 (not shown), so that the eccentric 7 actuates the lever 9 and the jaw 12 is reciprocated so that the upper end of the strapping slides beneath the jaw 19 and is carried along to the right. The strapping tends, during the return movement of the jaw 12, to move to the left therewith but this movement is prevented by the jaw 19 being unable to raise the plate 25. When a considerable tension is attained, the plate 25 is raised against the action of the springs 29 and a toggle action occurs quickly and the strapping returns to exactly the same extent as it had been advanced by the last stroke of the jaw 12. When this stage is attained and the upper end of the strapping is only being reciprocated and slides along the lower end, welding of the strapping ends occurs below the jaw 12 and, possibly, below the jaw 19. Before this stage has been reached, the blade 42 severs the upper end of the strapping from the supply when the strap return has attained an amount of, for example, 2 mm. After welding, the motor (8) is switched off and, after a delay to allow cooling and solidification, the lever 31 is raised to move the slide 36 to the right so that the projection 37 moves the jaw 19 to the right to relieve the tension of the spring 20 so that the spring 23 lifts the jaw 19 off the strapping. The flank 39 engages the pin 40 to lift the jaw 12 off the strapping and raise the blade 42. The apparatus is pulled laterally from the loop and is ready for re-use.