Patent ES-377567-A1 (ES)
Title: Friction welding of plastic strapping
IPC: B29C53/00
Filed: 1970-03-16
Abstract: The overlapping end portions 141, 1411, Fig. 6, of a loop of thermoplastic strapping tensioned about an object, are welded together by pressing the portions 141, 1411 together, softening the pressed together portions by imparting a motion to the portion 141 such that a point A approximately on the centre line thereof orbits about a point B approximately on the centre line of the portion 1411, and continuing to press the portions 141, 1411 together until they become welded. The friction welding apparatus comprises a serrated-edge dog 12, Fig. 1, to hold the strapping 14 against a base 10, a tensioning mechanism 16, a sealing head 18 and a cutter 20 to sever the strapping from the supply. The dog 12 is pivoted on a pin 21 and is urged by a spring (26), Fig. 3 (not shown) into engagement with the base 10 or the strapping 14 thereon. The dog 12 may be rocked counterclockwise of Fig. 1 by a lever 28 having an operating portion 30 to facilitate insertion of the strap therebeneath. The mechanism 16 comprises a tensioning wheel 32, Figs. 1 and 4, secured to a shaft 34 mounted in a link 36 pivotably mounted on a fixed shaft 42. A spring 46 urges the link 36 so that the wheel 32 engages a shoe 48 on the base 10. A ratchet 50 is secured to the shaft 34 and its teeth are engaged by a plunger 54 urged by a spring 56 and carried by a member 52 pivotally mounted on the shaft 34. The ratchet 50 is rotated by the plunger upon counterclockwise movement, Fig. 4, of the member 52 and remains stationary upon clockwise movement of the member 52 due to the ratchet 50 normally contacting a spring-urged detent 58 in the base 10. Normal oscillation of a lever 60, see also Fig. 1, secured to the member 52 rotates the knurled or serrated wheel 32 clockwise of Fig. 1 so as to tension the strap 14 about the object. Movement of the lever 60 counterclockwise of Fig. 1 brings a nose 62, Fig. 4, on the member 52 into contact with a ledge 64 on the base 10 and pressure of the nose against the ledge rocks the lever 36 against the spring 46 so that the wheel 32 is lifted so that the strap can be positioned therebeneath. Simultaneously, a cam 66 operates the portion 30 to rock the dog 12 counterclockwise. The arrangement is such that, after positioning of the strap, a slight relaxing of the lever 60 clockwise permits the dog 12 to engage the strap while the wheel 32 is maintained elevated. The cutter 20, Figs. 4 and 5, comprises a fixed blade 68 having a cutting edge 70 and a blade 72 having a cutting edge 74. The blade 72 is pivoted at 78 on a wedge 76 and near the edge 74 is pivoted at 80 to a slide 82 normally urged to the position of Fig. 4 by a spring 84. To actuate the cutter 20, a lever 92, Fig. 1, is moved to rotate a shaft 90, Fig. 4, so that the high portion of a cam 88 thereon engages an arm 86 on the slide 82 to move the slide against the spring 84 to rock the blade 72 about its pivot 78 so that the blades 70, 72 close with a scissors action and sever the strap. Beneath the sealer head 18, there is provided a pad 106, Figs. 1 and 2, mounted on an anvil 98 resiliently mounted by a spring (100) in the base 10. The head 18 comprises a cylindrical device 107 carrying a pad 112 directly above the pad 106. If the strap 14 is made of polypropylene, then the pads 106, 112 may be made of polyurethane. For other materials, the pads may be made of roughened or spiked-surface metal or metal spikes embedded in an elastomer. The drive shaft 114 of an electric motor 116 has a sleeve 120 secured thereto and extends into the device 107. The lower end of the sleeve 120 is eccentric with respect to the shaft 114 but is concentric with respect to the device 107. A needle bearing 124 is mounted between the device 107 and the sleeve 120. A spring 134 acts on a collar 132 surrounding the device 107 and which carries balls 138 in sockets 136 therein to engage the base 108 of the device 107. A retainer 140 is secured to the collar 132. The device 107 is prevented from rotating about the axis of the sleeve 120 and constrained to an orbital motion about the eccentric axis of the shaft 114 by a member 126 secured to a wire (128), Fig. 3 (not shown), and a spring 130 so that the device 107 can effect the movement shown in Fig. 6. To move the device 107 towards and away from the anvil 98, a shifter 148 is pivotally mounted on horizontal pins, e.g. 150, and is pivoted to the collar 132 by pins 154, 156, Fig. 1. Arms (not shown) extend from the body of the shifter 148 and carry a follower 162, Fig. 2, which engages a cam 164 on the shaft 90. Movement of the lever 92 clockwise of Fig. 1 rotates the shaft 90 so that the cutter 20 is actuated and then the low portion of the cam 164 engages the follower 162 so that the spring 134 moves the collar 132 downwardly and a micro-switch (not shown) is tripped by the lever 92 to start the motor 116 and a timer 168 when the strap portions are squeezed between the pads 106, 112. After a predetermined time, the timer 168 stops the motion although the lever still closes the microswitch. The strap portions weld together quickly after the stopping of the motor and then the lever 92 is returned to the position of Fig. 1.