The reciprocating screw injection moulding machine is the most common machine
found in today’s injection moulding operations.
This machine uses a reciprocating screw that rotates counterclockwise while moving backward and forward. This rotating action causes a shearing of the plastics pellets between the barrel and screw by creating the friction that melts the material. Seventy to ninety percent of the heat needed to melt the plastics comes from this shearing action.
The reciprocating screw injection moulding machine follows this sequence of operation:
(i) As the screw rotates it transfers the melted material to the front of screw.
(ii) As the melted plastics builds up in front of the screw, it forces the screw to move back toward the rear of the injection unit.
(iii) The screw stops turning once it reaches the preset distance or shot size.
(iv) The screw moves forward, acting as an injection ram and forcing the melted plastics material into the closed mould.
