Patent GB-1071454-A (GB)
Title: Strap sealing method and apparatus
IPC: B65B13/32
Filed: 1965-02-05
Abstract: 1,071,454. Seaming non-metallic sheet material. FMC CORPORATION. Feb. 5, 1965 [Oct. 12, 1964], No. 5136/65. Heading B5K. [Also in Division F2] In a method of heat sealing together in overlapping relationship opposite end portions 10, 11, Fig. 2, of an oriented polymeric strap by positioning the portions 10, 11 in face-to-face spaced apart relationship, inserting a heating element 14 between the portions 10, 11 to soften the face-to-face surfaces thereof, sliding the element 14 from between the portions 10, 11 and then pressing the softened surfaces together, the element 14 is constantly urged, e.g. by a spring 15, to slide out from between the portions 10, 11 which are pressed, e.g. by a block 12, against the element 14 while it is hot to cause the face-to-face surfaces to soften and the pressing force is sufficient to produce frictional engagement between the portions 10, 11 and the element 14 whereby the element 14 is prevented from moving until the softening of the surfaces reduces the friction between the element 14 and the portions 10, 11. A device for tensioning a polypropylene strap about an article and heat sealing the ends thereof, Fig. 5, rests upon the article being strapped and a strap 20 extends from a gripper 18 around the article and is inserted beneath a gripper 26 which permits the strap to be drawn tight about the article but prevents retrograde movement thereof. The grippers 18, 26 are pivotally mounted in a housing 16 and grip the strap against ledges 22, 30, respectively. Oscillation of a lever 40 causes a member 34, carrying a gripper 38 to grip the strap against a ledge 36 in the plane of the ledge 30, to move between the full and dotted line positions of Fig. 5 to tighten the strap about the article. The strap end held by the gripper 18 passes under a heat shield 42. A carriage 48 is slidably mounted in grooves in the housing 16 and is resiliently urged rearwardly by a spring 50. A smooth surfaced flat blade heating element 52 and a rigid strap severing wire 62 are mounted on the carriage 48. An operating lever 74 is secured to one end of a shaft 72 carrying a ratchet wheel 76 engaging a pawl 78 pivoted on a cam 80 loosely mounted on the shaft 72. The cam 80 has adjoining flats 82, 84 on its periphery the latter of which lies adjacent to an arm 86 on the carriage 48 when the lever 74 is in the position of Fig. 5. To effect heat sealing of the strap portions, the lever 74 is swung clockwise so that the flat 84 engages the arm 86 and slides the carriage 48 forward against the spring 50 to position the element 52 between the strap end portions overlying a ledge 24. When the carriage 48 reaches its forward position determined by the flat 84 moving past the arm 86, a cam 91 engages a leaf spring 90, which extends through a slot in a pressing element 88 mounted to slide vertically, to move the element 88 downwardly to press the overlapping strap portions against the element 52. The friction exerted between the strap 20 and the element 52 is sufficient to prevent the spring 50 returning the carriage 48 when the circular periphery of the cam 80 bears against the arm 86. As the element 88 moves the upper run of the strap 20 downwards the strap engages an arm 70 on a leaf spring 68, Fig. 7 (not shown), to close contacts 64, 66 and close the circuit to the severing wire 62 and heat it rapidly to a temperature at which it melts through the strap in contact therewith. As soon as the strap is severed, pressure is removed from the arm 70 and the contacts 64, 66 open to de-energize the wire 62, Fig. 6 (not shown). At about the time the wire 62 is energized or immediately thereafter, a lobe 99 on a cam 98 secured on the shaft 72 contacts a member 93, pivotally mounted on a stub shaft 92 secured to the housing 16, to push it downwards to cause a foot portion 94 thereof to engage a tab 95 to depress a leaf spring 60 and close contacts 54, 56 to energize the elements 52, Fig. 7 (not shown). After the facing strap portions have softened to a depth of only a few hundredths of a millimeter the spring 50 becomes effective to move the carriage 48 to its home position. The tab 95 slides from beneath the foot 94 and contacts 54, 56 open to de-energize the element 52. The element 88 squeezes the melted strap portions together and is raised by the spring 90 when the lever 74 is swung back to its original position. Finally the grippers 18, 26, 38 are released.