Apparatus for the manufacture of hollow bodies from a thermoplastic by the blow-moulding process

Claim 1

Blow-moulding apparatus for the manufacture of hollow bodies from parisons formed from a thermoplastic material, said apparatus comprising in combination: (a) a screw extruder receiving and extruding a charge of thermoplastic material at a controllable rate; (b) an extrusion head having an accumulator chamber of predetermined size having an inlet positioned to receive thermoplastic material from the screw extruder and means indicating said accumulator is filled; (c) a gap-like outlet orifice for passing said material from the accumulator chamber; (d) a piston within said chamber movable to discharge through said outlet orifice a batch of the thermoplastic material of substantially predetermined size for forming a parison; (e) means to move the piston in the chamber to force thermoplastic material therein through said outlet orifice to form a parison while said screw extruder is extruding material into said head and out of said outlet orifice along with the material accumulated in said chamber to form the parison; (f) a blow-mould consisting of at least two openable parts, the open mould encompassing the parison; (g) means for sensing the length of each parison; (h) means responsive to change in parison length sensed by (g) for adjusting the width of the gap-like outlet orifice to correct for changes in length of the parisons; and (i) control means responsive to said means indicating the accumulator chamber is filled for controling the rate of extrusion of the material from the extruder during formation of a parison to affect the amount of material per unit time extruded into the accumulating chamber and parison by the extruder and keep the time for producing the parison substantially constant.