High efficiency injection molding screw

Abstract

A screw for use in the bore of an extruder barrel of a molding machine thermo-plastics material feeder has an intermediate section of circumferentially interrupted helical flights or screw threads with inclined ramps on the leading ends of the interrupted flights or threads effective to flatten unmelted lumps of plastics material for increasing the surface area thereof to enhance heat transfer for expediting melting of the material. The tapered ramps are preferably longitudinally grooved forming shallow pockets gripping the plastics material and shearing the lumps as they are wedged between the ramps and bore of the extruder barrel. The peripheries of the flights or screw threads are spaced from the bore of the extruder barrel to define extrusion gaps therebetween with the gaps diminishing in thickness from the inlet to the outlet ends of the screw section or zone. The screw section or zone is positioned intermediate the ends of the screw to receive the thermo-plastics material in a partially melted condition composed of about 50 percent molten flowable material and about 50 percent of solid material and the flights or screw threads of the section discharge fully melted thermo-plastics material to a cascading mixing section or zone having axially spaced barrier rings with advancing and reversing flight lengths. The reversing flights terminate radially inward from the bore of the extrusion barrel providing shear gaps to mix the molten material with the gaps decreasing in thickness from the inlet to the outlet ends of the mixing section.