Method for electrically operated plastics injection

A method of supplying molding material to a mold cavity under pressure by means of an injection system that includes (i) a plastication barrel, (ii) a tubular accumulator barrel separate from the plastication barrel, the accumulator barrel having an inlet that communicates with the plastication barrel and outlet that communicates with the mold cavity, the inlet and outlet being adjacent the same end of the accumulator barrel, and (iii) a plunger positioned within the accumulator barrel for axial sliding movement, the plunger having a head portion with an external helical ridge at the forward end of the plunger, said method comprising the steps of:

• a. plasticating a quantity of molding material in the plastication barrel;
• b. conveying the plasticated molding material from the plastication barrel to the inlet of the tubular accumulator barrel with the plunger fully advanced, such that the molding material initially entering into the accumulator barrel passes over the head portion of the plunger and travels along the external helical ridge, carrying with it any residual molding material on the plunger head toward the outlet,
• c. simultaneously rotating and retracting the plunger as the molding material is conveyed into the accumulator, so that after the plunger has retracted a given distance, subsequent molding material enters the inlet in front of the plunger without passing over the plunger head, wherein the rotation and retraction of the plunger are effected by an electric-motor-powered drive system,
• d. advancing the plunger during an injection stroke to inject the molding material through the outlet of the accumulator barrel and into the mold cavity at a predetermined injection pressure, wherein advancing the plunger is effected by the electric-motor-powered drive system.