Abstract: A system for the injection molding of plastic material is described. The system has an injection device of the hot runner type for the injection of a plastic material, in a molten state, into a mold, a circular diaphragm to distribute evenly and circularly in a cavity of the mold, through a circular injection gate or port, the plastic material injected by the injection device, and control means adapted to control an operation of the molding system an including a heating inductor and heating means provided to heat and keep at a hot temperature the injection device, and a thermocouple being arranged in an area of the circular injection gate. The control means are adapted to control through the heating inductor a molding cycle of a piece.