Injection molding apparatus having low shear screw

An injection molding machine for injecting plastics material into a mold cavity comprising:

• a barrel having a discharge opening at the forward end thereof,
• a screw longitudinally received in said barrel, said screw having a front end and a rear end,
• rotation means operatively connected to said screw to rotate said screw to displace plastics material forwardly of said screw,
• translation means operatively connected to said screw to produce translation of said screw relative to said barrel to displace the plastics material through said discharge opening,
• said screw comprising a flighted conveying portion and an unflighted conveying portion of substantial length forwardly of said flighted portion and adjacent the front end of said screw, said unflighted portion having a generally cylindrical periphery along nearly its entire length so as to define a generally unobstructed annular flow passage between the barrel and cylindrical periphery of said unflighted portion adapted to produce a gentle wiping action with a minimal amount of shear on the plastics material flowing therethrough,
• said screw having a feed section and the diameter of said unflighted portion being less than the diameter of the root of said feed section.

An injection molding machine for injecting plastics material into a mold cavity comprising:

• a barrel having an inner wall and a discharge opening at the forward end thereof,
• a screw longitudinally received in said barrel, said screw having a front end and a rear end,
• rotation means operatively connected to said screw to rotate said screw,
• said screw including conveying means on the rear portion thereof to displace the material forwardly as the screw is rotated,
• said screw including low shear means on the forward portion thereof to permit the material displaced forwardly by the conveying means to flow between the inner wall of the barrel and the screw forwardly of the screw with a minimal amount of mixing of material and with a minimal amount of shear being imparted to the material by the screw,
• said low shear means comprising an unflighted portion of said screw defining an annular passageway between the barrel inner wall and the screw forward portion and extending along a substantial portion of the length of said barrel, and
• translation means operatively connected to said screw to produce translation of said screw relative to said barrel to displace the softened material through said discharge opening,
• said screw including a feed section on the rear portion thereof, and the diameter of the unflighted portion is less than the diameter of the root of the feed section.