An injection moulding system for plastic material, comprising:
- a press having a first and a second pressure plate associated respectively with a first side and a second side, opposite to the first one, of a mould, said two pressure plates being suitable for moving one of said pressure plates with respect to the other pressure plate in order to close, between them, said mould during an injection and moulding step of a piece, so as to apply a closing force to said mould, and
- a distribution and injection assembly suitable for distributing and injecting, into said mould, a fluid plastic material during said injection and moulding step, said distribution and injection assembly being arranged adjacently to and extending along a third side of said mould, different from said first and second side, so that said distribution and injection assembly is not associated with said first and second pressure plate and thereby said distribution and injection assembly is not subjected to the closing force that is applied by the two pressure plates of said press on said first and second side, opposite each other, of said mould, for closing said mould,
- wherein said distribution and injection assembly in turn comprises:
- a first bottom plate;
- a second nozzle-bearing plate bearing one or more injection nozzles provided for cooperating with said mould, along the respective third side, in order to inject into said mould the fluid plastic material;
- and
- a third intermediate hot distribution plate, which is interposed between said bottom plate and said nozzle-bearing plate, said third intermediate hot distribution plate defining a network of flow hot channels suitable for distributing to said one or more injection nozzles the fluid plastic material to be injected into said mould, during said injection and moulding step, said third intermediate hot plate being coupled and provided for cooperating into contact, along a respective sliding and contact plain surface, with said one or more injection nozzles, in order to distribute to said nozzles the fluid plastic material to be injected into the mould, said third intermediate hot plate being arranged between said bottom plate and said nozzle-bearing plate in such a way to be free, when it is heated during use, to expand thermally, in a longitudinal sense, with respect to said bottom plate and to said nozzle-bearing plate, by sliding, in the zone of said sliding and contact plain surface, relatively to said one or more injection nozzles, and
- wherein the first bottom plate, second nozzle-bearing plate and third intermediate hot distribution plate, cooperate each with other, in such a way to ensure the sealing against any outflow or leakage, towards the outside, of the fluid plastic material which passes across said sliding and contact plain surface, from said third intermediate hot plate to said one or more injection nozzles, despite said distribution and injection assembly not subjected to the action of said closing force, applied by the pressure plates of said press on said mould.