GB910012A - Improvements in or relating to machines for and methods of moulding hollow bodies - Google Patents

Abstract

910,012. Blow moulding hollow articles. PIRELLI S.p.A. June 13, 1960 [June 13, 19591, No. 20752/60. Class 87(2). Thermoplastic material is extruded in tubular form from the extrusion head 17 of an extruder 12, the outlet of a blowing nozzle 76 being positioned to blow into the extruded tube and a mould 65 being closed upon the tube which is blown into the shape of the desired hollow article inside the mould whilst or after this is displaced with respect to the extrusion head by straight line movement. The material is fed by a screw 10 through holes 16 in a plate 15 to a duct 18 and then through an annular inlet part 19 into a homogenising chamber 20 from which it emerges as a tube through a die 22. A spindle 25 having a frusto-conical head 24 is adjustable relative to the die 22 by a worm wheel and screw 32, 34 so as to vary the thickness of the wall of the extruded tube and may be axially aligned by adjusting screws 36 in order to obtain a tube wall of uniform thickness. A double-acting cylinder 38 actuates a horizontal blade 39 for cutting off each extruded tube portion. The mould 65 is a two-part mould, each part being slidably supported on a vertically reciprocatable platform 51 so as to bring the mould parts opposite the extruded tube portion as they are moved towards each other. At the same time, the nozzle 76 is raised through a cylinder 82 to the blowing position. The walls of the nozzle 76, Fig. 6, which has an axial duct 77, are provided with a ring of vertical channels 78 connected to each other for the circulation of cooling water. A flange 81 is designed to form an undercut on the inside of the neck of a container for the retention of a closure or, alternatively, a groove may be provided so as to form a rib for the same purpose. While the tube is being blown to the shape of the mould 65 by compressed air emitted from nozzle 76, the platform 51 is moved away from the extrusion head 17 and when the expansion is complete, the downward motion of the platform 51 is stopped and the nozzle 76 put into communication with the atmosphere. The mould 65 is then opened and the nozzle 76 moved downwardly relatively to the platform 51 so that the cylinder 82 exerts an upward push on the rim of the neck of the finished article and detaches it from the nozzle 76. The article is then blown by jets of compressed air from the tiltable blow-pipes 86, 87 into an inclined shoot which is inclined further to operate a microswitch which causes the next cycle of operation to commence. Cold air blown against the upper portion of the mould 65 from a nozzle 88 cools the sprue which forms and prevents it from adhering to the finished article. In a modification, Fig. 8, a metering device is interposed between the extruder 12 and the extrusion head 17. This comprises a piston 41, which slides within a cylindrical chamber 40, the inlet duct 18 being alternately put into communication through a rotatable valve 47 with the lower part of chamber 40 and with a duct 48 leading to the upper part of chamber 40. Material which has passed through the holes 16 is pushed into the inlet duct 18 and raises the piston 41 until it presses against the lower surface of a second piston 42, the position of which is adjustable by means of the worm wheel and screw 45, 46. The material also causes the valve 47 to rotate to a position in which the entrance to the lower part of chamber 40 is closed and that to duct 48 opened whereupon material is fed to the upper part of chamber 40 urging the piston 41 downwardly and expelling the material previously accumulated in the lower part. The metered material passes through a duct 49 to the extrusion head 17.