Patent ID: 7172333

Claim:
In combination: (a) an injection molding screw barrel including: (1) at least one gas injection port; and (2) a nozzle including a shut-off valve; and (b) an injection molding screw in the barrel, the injection molding screw comprising: a first end adapted for engagement with drive means; a second end adapted for engagement with a screw tip; a longitudinal body extending axially along a length of said screw between said first end and said second end, said body comprising a first stage portion and a second stage portion, said first stage portion being adapted for first receiving at least one substance and for transporting the at least one substance to said second stage portion, said first stage portion including at least one flight extending helically along said first stage portion, said at least one flight forming at least one channel through which the at least one substance is transported along said first stage portion to said second stage portion, said second stage portion including at least one mixing section, and being adapted for transporting the at least one substance transported from said first stage portion to the screw tip, said at least one mixing section being adapted for mixing the at least one substance transported from said first stage portion and for transporting the at least one substance that has been mixed to the screw tip for extrusion wherein at least one fluid is introduced to the at least one substance transported from said first stage portion by at least one injection port of a processing system; and a pressure retention element adapted for being positioned between said first stage portion and said second stage portion for reducing loss of pressure in said second stage portion; wherein said at least one gas injection port is positioned proximate said second stage portion of said screw.