GB959573A - Improvements in and relating to methods and apparatus for shaping thermoplastic foils - Google Patents

Abstract

959,573. Shaping thermoplastic sheet material. W. BAHLSEN. Oct. 14, 1960 [Oct. 16, 1959; April 6, 1960], No. 35349/60. Heading B5A. [Also in Division B8] A method for pneumatically shaping thermoplastic foils to close or seal an article or parts thereof, comprises bringing the foil into contact with a heated surface, e.g. a plate 15, Fig. 1, so that it is heated to the required temperature, disengaging the foil from the plate pneumatically and through the agency of a mould which may or may not be cooled, pneumatically shaping the foil into engagement with the article, e.g. a greasing nipple 24, to effect the desired seal, i.e. produce a closure plug 26, and wherein the mould comprises that part of the article which it is desired to close or seal. The plate 15 has heating elements 18, and by means of ducts 19, 20 a vacuum is applied to the foil sucking it on to the heated plate. Subsequently, compressed air is used to form the closure plug 26. It is sometimes necessary to cause the foil to be heated less in some parts than in others, and in Fig. 3 a foil 41 is shown on a plate 40 which has small grooves 42 and larger grooves 43. Above the grooves 43 the foil will only be heated by heat transfer via the narrow webs 44 and will be heated less than that part of the foil above the grooves 42. These grooves can be arranged in a circular fashion or as a raster or network of grooves which are connected to ducts like those shown as 19 in Fig. 3. An alternative method of producing uneven heating of the foil is to either coat the surface of the plate with a poorly conducting lacquer, or to construct the plate of heated and unheated parts. The invention may be applied to closing the ends of containers, as shown in Figs. 10 and 11. Here the end of the container 109<SP>11</SP> is shown fitted with a central pin 116 to form part of the mould. The foil 107 is clamped between the outer peripheral ring of the mould 108<SP>11</SP> and the dome 103. A vacuum pump is connected to the part 106 and the foil is sucked on to the heated plate 101. By now supplying compressed air to the part 106 the foil takes the shape shown in the right-hand half of Fig. 10. For a snap-fitting lid this is sufficient and the moulded lid may be cut from the foil. If complete sealing is required further moulding may be accomplished by movement of the dome 103 downwards against the springs 115 relative to the parts 109<SP>11</SP>, 116 and 101 to mould the foil as shown in Fig. 11. The end of the container 109<SP>11</SP> may be coated with a thermoplastic glue to effect complete sealing on moulding.