Moulding method and apparatus

Abstract

A method and apparatus are provided for moulding an article by feeding molten plastics material into a metering cavity, feeding a predetermined quantity of the material from the metering cavity into a mould cavity via a transition passage adjacent the mould cavity and urging the molten plastics material from the transition passage into the mould cavity with a working stroke of a packing piston, until the packing piston closes a port defined between the transition passage and the mould cavity and a leading face of the packing piston forms part of the peripheral wall of the mould. Less than ninety percent of the mould cavity is filled with the molten plastics material when the packing piston starts its working stroke and the packing piston starts its working stroke while molten plastics material is still being fed from the metering cavity.

1 . A method of moulding an article, said method comprising: feeding molten plastics material into a metering cavity, feeding a predetermined quantity of molten plastics material from the metering cavity into a mould cavity via a transition passage, the transition passage being defined adjacent the mould cavity, and urging the molten plastics material from the transition passage into the mould cavity with a working stroke of a packing piston, until the packing piston closes a port defined between the transition passage and the mould cavity and a leading face of the packing piston forms part of the peripheral wall of the mould.  
   
   
       2 . A method as claimed in  claim 1 , wherein less than ninety percent of the mould cavity is filled with molten plastics material when the packing piston starts its working stroke.  
   
   
       3 . A method as claimed in  claim 1 , wherein the packing piston starts its working stroke while molten plastics material is still being fed from the metering cavity.  
   
   
       4 . A method as claimed in  claim 1 , wherein the packing piston closes an inlet into the transition passage from the metering cavity, during said working stroke.  
   
   
       5 . A method as claimed in  claim 1 , wherein a predetermined volume of molten plastics material is fed from the metering cavity to the mould, via the transition passage.  
   
   
       6 . A method as claimed in  claim 1 , wherein the molten plastics material is fed from the metering cavity by a working stroke of a metering piston that is displaceable within the metering cavity.  
   
   
       7 . A method as claimed in  claim 6 , wherein the displacement of the metering piston within the cavity is monitored, to control the volume of molten plastics material that is fed from the metering cavity.  
   
   
       8 . A method as claimed in  claim 1 , wherein the molten plastics material is fed from the metering cavity by a working stroke of a reciprocating injection moulding screw that is displaceable within the metering cavity.  
   
   
       9 . Apparatus for moulding an article, said apparatus comprising: a metering chamber and a displaceable member, together defining a metering cavity of predetermined variable volume, said volume of said metering cavity being variable by reciprocal displacement of the displaceable member in the metering cavity and said metering cavity being connectable to a supply of molten plastics material, a packing chamber and a packing piston, together defining a transition passage that is in flow communication with an inner cavity of a mould via a port and that is in flow communication with the metering cavity via a hot runner, a packing piston being reciprocally displacable within the transition passage between a retracted position and a forward position, the packing piston closing said port between the transition passage and the mould cavity and a leading face of the packing piston forming part of the peripheral wall of the mould cavity, when the packing piston is in said forward position.  
   
   
       10 . Apparatus as claimed in  claim 9 , wherein said packing piston is configured to start a working stroke from its retracted position to its forward position when less than ninety percent of the mould cavity is filled with molten plastics material.  
   
   
       11 . Apparatus as claimed in  claim 10 , wherein the displaceable member is a metering piston.  
   
   
       12 . Apparatus as claimed in  claim 10 , wherein the displaceable member is an injection moulding screw.