Injection moulding of large plastic components

A method of injection moulding a plastics article, comprising feeding plastics material from an extruder into an accumulator, and displacing the extrudate from the accumulator into a mould via a valve leading into the mould cavity, the valve having a valve passage with a valve piston which at the end of injection closes the mould cavity substantially at the mould surface of the article whereby the moulding is formed without the presence of a sprue at the site of injection, the valve passage and piston being of a constant diameter of at least several centimeters, and filling of the mould with the required amount of plastics material is determined during moulding by sensing pressure of the plastics material within the mould cavity, the valve being closed in response to a mould-full condition as determined by the same sensing pressure.

An injection moulding system for single shot injection moulding of plastics components, comprising an extruder, an accumulator fed from the extruder, the accumulator leading into the mould via a mould valve operative, when closed, to close the mould cavity substantially at the mould surface whereby the moulding is formed without the presence of a sprue at the site of injection and also to close an outlet from the accumulator, and means for determining that a required amount of plastics material has been fed into the mould by sensing the pressure of injected material at one or more positions within the mould cavity, the valve being closed in response to a mould-full condition as determined by said pressure sensing.

A system for injection moulding plastics articles, comprising an extruder, an accumulator coupled to an outlet from the extruder, the accumulator leading into a mould via a mould valve having a passage of a cross-sectional size such that it will not be blocked by stones or other particulate foreign matter in the extrudate when at least partially composed of post-consumer recycled plastics, and means for determining that a required amount of plastics material has been fed into the mould by sensing the pressure of injected material at one or more positions within the mould cavity, the valve being oDerative to close the mould cavity substantially at the mould surface of the article whereby the moulding is formed without the presence of a sprue at the site of injection in response to a mould-full condition as determined by said pressure sensing.