Injection unit for an injection molding machine

An injection unit for injection molding machines used in the molding of plastic objects, said unit comprising a material feed system for supplying a flow of plastic material, a cylinder-piston unit in selective communication with said material feed system and comprising a cylinder and a piston, said piston having an axial bore for the passage of flowable plastic material, said axial bore communicating with the interior of the cylinder and communicating with a nozzle element at an outer end of said bore, said nozzle element including a nozzle channel in alignment with the axial bore in the piston, a valve-controlled passage between the cylinder and the material feed system for providing the selective communication between said material feed system and the cylinder, means for moving the nozzle element to the edge of a gate of an injection molding mold, and means for reciprocating the cylinder toward and away from said nozzle element along the longitudinal axis of the piston, wherein

• said valve-controlled passage interrupts the communication between the material feed system and the cylinder to prevent the flow of plastic material from the cylinder in the direction of said material feed system when the cylinder is moved toward the piston, and said valve-controlled passage provides a communication between the material feed system and the cylinder during movement of the cylinder away from the piston to enable a flow of plastic material from the material feed system to the cylinder.