GB744895A - Improvements in the extrusion-moulding of plastics - Google Patents

Abstract

744,895. Extrusion machines, e.g. for blowmoulding containers. INJECTION MOLDING CO. Oct. 11, 1951 [Oct. 19, 1950], No. 23743/51. Class 87 (2). [Also in Group XVII] A machine for moulding containers or other articles comprises a plurality of die heads 21, 22, Fig. 1, and an extruder 11 having a plurality of outlet ducts connected with the die heads by means of valves 23 and 24 and passages 14, 15. The extruder is screw-operated, and by feeding each die head in turn the screw can be kept turning continuously. Thus, the valve 23 may be closed, the extruder supplying only the die head 21 through valve 24 and passage 15; then the valve 24 may be closed and valve 23 opened, whereby die head 22 is supplied via passage 14. 'As shown, there is a second extruder 12 similarly connected to the die heads through valves 25, 26 and passages 17, 18, and the two screws turn continuously together to supply each die head from both sides, each die head being supplied in turn. The valves 23 ... 26 are controlled by a timer 40a via air pressure tubes 23a, 24a, 25a, 26a. The plastic delivered by extruder 12 may differ in colour or type from that delivered by extruder 11; thus, the extruder 11 alone may first supply plastic to a die-head to form the lower part of a container, and then the extruder 12 alone may supply plastic of a different type to form the upper part of the container. More than two extruders may be used. The invention is described in connection with the blow-moulding of containers, which may be filled during moulding. Fig. 2 shows the die 22 in association with a two-part mould 42, 43. The die includes a central core 32 and a nozzle 39 formed of a plurality of rings, and the material may be extruded in tubular form between these two parts. The thickness of the extruded tube may be altered by raising or lowering the core 32, this being effected by movement of a rack 54 meshing with a nut 51 threaded on the core, the core being constrained to move vertically by a spline 35. A spring 56 tends to hold the core up. In operation a tube is extruded between the open mould halves, the halves close on the tube to seal the end of the tube, and compressed air is blown into the tube through conduits 40 and 37 to expand the tube against the mould walls. In a modified method the core is raised to such a height that a solid mass of material is extruded to form the base of the container, then the core is lowered to form a tube, then the tube is blown. The movement of the core may be such as to produce a tube of the form shown in dotted lines in Fig. 2, this tube having thickened central portions 44 which are thinned by subsequent blowing. The movement of the rack is controlled by pneumatic, hydraulic or electrical mechanism in synchronism with the operation of valve. 23 and the opening and closing of the mould halves 42, 43. A transparent printed sheet 91 may be applied to the article by. initially placing it on the wall of the mould or in a recess in the wall. A modified die is described, Fig. 3 (not shown, in which a tube extends through the compressed air conduit 37, this tube being used to fill the blown container with liquid; the mould is then opened and the upper end of the container sealed by a solid slug of plastic or by twisting or welding. Fig. 4 shows another modified die in which the movement of the core is effected by a cam 262 and spring 256. Reference has been directed by the Controller to Specification 700,984, [Group XVII].