Patent GB-1174990-A (GB)
Title: Method and Apparatus for Welding Plastics Members
Inventor: MORI EIJI
IPC: B29C65/00
Filed: 1967-10-06
Abstract: 1,174,990. Seaming non-metallic sheet material. E. MORI, M. IDE and S. KANEKO. 6 Oct., 1967 [19 Oct., 1966 (2); 22 March, 1967], No. 45882/67. Heading B5K. Plastics members, e.g. of polyethylene, are ultrasonically welded by focusing ultrasonic vibrations through a void-free liquid medium to reach a focal zone at an interface between the surface of at least one of the plastics members and a liquid layer. In one embodiment, Fig. 2a, a part-spherical vibrator 2 of a magneto-strictive material, e.g. barium titanate or lead zirconate, or a piezoelectric material, e.g. quartz, has electrically conductive coatings, e.g. of silver or nickel, or its surfaces to form electrodes 2a, 2b connected through a cable 14 to a high frequency powder source for excitation of the vibrator 2. The peripheral edge of the vibrator 2 is supported in a body 1 by a snap ring 6. A vessel 3 is connected through a fluid-tight packing 7 to the body 1 by a ring 6 and is closed at the bottom by a cap 4 through a fluid-tight packing 9. The liquid medium 10 completely fills the vessel 3 which is provided with an inlet 1] and an outlet 12 therefor both normally closed by valves (not shown). The bottom of the cap 4 is formed by a thin metal plate 13 which transmits the ultrasonic vibrations propagated through the liquid 10 to an underlying plastics member to be welded. Due to its shape, the vibrator 2 acts as the focusing means for the vibrations. The body 1 is connected to a mounting stub 15 by a screw 16. In modification, Fig. 3 (not shown), the vibrator (2) is cooled by a blower (17) and the body (1) is provided with air outlet holes (18). The body (11) is mounted on a plate (19) instead of the shaft 15 of Fig. 2a. In use, the plate 19 of the apparatus A of Fig. 3 is mounted on a frame 24, Fig. 4, which loosely fits around posts 23 and is urged upwardly by springs 26. Plastics plates P 1 , P 2  or films to be joined are placed on a trolley 22 positioned beneath the apparatus A which is adjusted so that the plate 13 contacts the plate P 1  with light pressure. Previously, a layer or film of liquid, e.g. water or oil, has been applied to the upper surface of the plate P 1  to insure minimum loss in transmission from the plate 13 to the plate P 1 . During the application of the ultrasonic vibrations, the trolley 22 is run on rolls 22a running in grooves in a stool 21 to form a continuous line weld. The weld may be a lap seam, Fig. 10a (not shown), a butt seam, Fig. 10c (not shown), or a stepped seam, Fig. lOb (not shown). In the latter two cases pressure may be applied to hold the plastics members in engagement. A layer or film of liquid, e.g. water, alcohol or oil, may be applied between the surfaces to be welded. In modifications, (a) a planar vibrator 27, Fig. 6, is used and the vibrations are reflected by a conical reflector or prism 28 to a mirror 29 in the form of part of a paraboloid; (b) a planar vibrator (27) is combined with a plano-concave plastics lens (30), Fig. 7 (not shown); (c) a linear focus is produced by a plane-concave lens (31), Fig. 8 (not shown); and (d) a circular focus is produced by a lens 32, Fig. 9. In a further embodiment, Fig. 11, an ultrasonic generating and focusing apparatus is mounted on an adjustable plate 41 in a casing 40 and has an upwardly concave vibrator 2 to focus the vibrations at a point 44 below the level of the void-free liquid in the casing 40. Two hollow cylindrical plastics bodies 45, 46 to be welded are mounted between frustroconical supports 47, 54 so that the point 44 coincides with a stepped junction therebetween. Pressure is applied by a piston and cylinder assembly 49, 50 and a compression spring 52 to hold the bodies 45, 46 in engagement. During excitation of the vibrator 2 a handle at the end of an axle 64 is rotated either manually or automatically to rotate the support 54 through gears 63, 62 and a shaft 55 to form a circular weld line. In another embodiment (not shown), both translational and rotational movement is imparted to the members to be welded to produce a helical weld line.