Patent GB-1130443-A (GB)
Title: Methods and apparatus for forming ultrasonic seals
IPC: B29C65/78
Filed: 1966-01-13
Abstract: 1,130,443. Ultrasonic vibrators. UNION SPECIAL MACHINE CO. 13 Jan., 1966 [13 Jan., 1965], No. 1567/66. Heading H4J. [Also in Division B5] Pieces of material are ultrasonically bonded by heating an ultrasonic vibratory horn 11 to a predetermined temperature, arresting the application of heat to the horn and thereupon vibrating this horn at an ultrasonic frequency to transmit vibratory energy to the pieces to bond them together, the vibratory motion of the horn 11 tending to produce additional heating thereof, and cooling the horn as it vibrates to maintain the horn at a controlled temperature during the application of vibratory energy to the pieces. The horn 11 comprises a tapered exponential horn flared at its upper end to provide at an antinode, a surface 14 which faces a surface 15 on an anvil 12. Small protrusions may be formed on the surfaces 14, 15 to form discrete bonded areas. A disc-like transducer 20, preferably comprising a piezo-electric crystal coated with silver on its opposed faces, is secured to the horn 11, e.g. by an epoxy resin cement containing silver granules. Alternatively, a magneto-strictive transducer may be used. The horn 11 is supported at a node by three screws 24 provided on a plate 23, see also Fig. 3 (not shown). A blower unit 40 controls the temperature of the horn 11 and includes a conduit 45 having the discharge end thereof positioned adjacent the horn 11. A heating element 50 is situated in the conduit 45. Apertures (48), Fig. 2 (not shown), are provided on a side panel 39 to allow free circulation of air across the horn 11. Prior to bonding, the apparatus is adjusted to form an appropriate gap between the horn 11 and the anvil 12. A coarse adjustment is first effected by releasing locking members 93, Figs. 1 and 2 (the latter not shown), which mount the anvil 12 on a standard (43) by an arm (91) on a bracket assembly 90. The arm (91) is slid vertically on the standard (43) to move a rack (95), a C-shaped head 102, a spring 112 which, in use, permits limited upward movement of the anvil 12, a rod 108 and the anvil 12 with respect to the horn 11. A precise adjustment of the gap is then effected by loosening wing screws 98 and rotating a knurled knob 97 to move the rack (95) and the anvil 12 vertically, a pinion (not shown) which meshes with the rack (95) being connected to the knob 97. A threaded stop member 100 which limits downward movement of the rack 95 with respect to the arm 91 is then adjusted to prevent the anvil 12 from approaching the horn 11 closer than the desired gap setting. In use, the blower is operated to direct air across the horn 11 and current is supplied to the element 50 to heat this air to maintain the horn at a predetermined elevated temperature. Then, the pieces to be bonded are either positioned manually between the horn 11 and the anvil 12, or, alternatively, they are advanced by endless belts, 120, 121. The supply of current to the element 50 is stopped and, simultaneously, the horn is vibrated at its ultrasonic resonant frequency to effect bonding. The blower 40 remains in operation and directs a stream of cooling air against the horn 11 to maintain it at the desired temperature and prevent overheating and expansion thereof. After bonding, the vibration of the horn is stopped and the element 50 is again heated to maintain the horn at its elevated temperature. The pieces to be bonded may be preconditioned by the application of heat by passing between either heated elements 125, 126, Fig. 1, or U-shaped members (128), (129), Fig. 6 (not shown), the legs of which are interconnected by resistance wires (131), (132). The apparatus may be used to bond synthetic thermoplastic polymeric materials in film or woven form, e.g. polyethylene terephthalate, polyamides, polyvinyl fluoride, polytetrafluoroethylene, polymers of vinylidene bromide, vinylidene chlorobromide, vinylidene cyanide and vinylidene halocyanide, and vinylidene chloride-vinyl chloride copolymer. Cotton fabrics may be bonded by using thermoplastic inserts.