GB1378661A - Extruding - Google Patents

Abstract

1378661 Extruding parisons; blow-moulding JOHN ORME Ltd 11 Feb 1972 [12 Feb 1971] 4529/71 Heading B5A An extruder for the extrusion of parisons of controlled wall thickness to be blow-moulded includes moving means to vary the dimensions of the die orifice and control means connected to the extrusion member so that, as the latter moves to effect extrusion, the control means is correspondingly moved and controls the operation of the moving means which alters the die. As shown in Fig. 1, the extruder comprises an axially reciprocating ram screw 14 to feed plastics from accumulation chamber 12 past screw-threaded mandrel 68 to die 16 which comprises an outer die ring 69 and conical core 66. Mounted on ram 14 and movable therewith is a carrier 80 carrying rack 84 which engages a toothed wheel 88 to turn graduated control wheel 90. Several cams 92 are mounted on the rim of wheel 90 to engage microswitches 94 controlling the pneumatic circuitry supplying fluid to cylinder 52 of eccentric device 18 which adjusts the position of die core 66. Core 66 is mounted on rod 60 which is pivoted to an arm 54 mounted eccentrically on a shaft which is rotated by cylinder 52 through arm 38 between limits set by stop bolts 46. The die ring 69 which may be provided with band heaters is adjustable relative to core 66 by means of screws (71, Fig. 5, not shown). The pneumatic circuitry (Fig. 6, not shown) comprises a thick/thin valve (100), a fast/slow valve (104) and a stop/go valve (102) with pilot valves (106, 108), non-return valves (110, 112), air flow regulator (114) and shuttle valves (116, 118). Air from reservoir may flow from thick/ thin valve (100) to either end of cylinder 52 via either valves 110, 106 or valves 112, 108 and through either valve (116) or (118) to operate the appropriate pilot valve (106 or 108). The position of the piston of cylinder 52 and core 66 are thereby determined for a thick or thin extrudate. Air exhausted from cylinder 52 returns via valve (106) or (108) to fast/slow valve (104) and thence to reservoir either directly for fast movement of core 66 or via regulator (114) for slow movement. The stop/go valve (102) operates to maintain the system as it is at any moment by passing air from reservoir to operate whichever of valves (116, 118) is not receiving air from valve (100) so as to switch the air exhaust from cylinder 52 to either of non- return valves (110 or 112), thereby locking the system with the piston of cylinder 52 stationary. In an alternative arrangement (Fig. 7, not shown) the extruder is a continuously operating, rotating screw type, the eccentric device (140) of which moves the die ring while the core is stationary. The control box (142) includes an electromagnetic clutch to disengage when the blow-mould closes to cut off the parison and a clock weight to return the graduated control wheel to its initial position after the clutch has disengaged for the extrusion of a further parison.