Energy efficient extruder screw

Claim 1

A screw used for a single screw extruder which houses said screw rotatably in a cylindrical barrel for plasticating or melting solid plastic material, said screw having a feed end and a discharge end: said screw embodying a novel mixing section between the feed end and discharge end of said screw comprising: at least one pair of substantially parallel, helical, first and second threads integral with the core of said screw; said first thread of the pair originating at the feed end of said screw creating a helical channel and having a minimum clearance to said barrel; said second thread of the pair originating at a location about one third to two thirds of the length of said screw from the feed end of said screw by rising from the core of said screw and having a large clearance to said barrel comparable to or greater than the size of the components of said solid plastic material; said second thread of the pair dividing said helical channel created by said first thread into two sub-channels of substantially equal width, one located toward the feed end of said screw from said second thread hereinafter called a front sub-channel and the other located toward the discharge end of said screw from said second thread hereinafter called a back sub-channel; the depth of said front sub-channel gradually increasing to a maximum comparable to the depth of said helical channel at the feed end of said screw accompanied by gradual decrease of the depth of said back sub-channel to a minimum comparable to or greater than the size of the components of said solid plastic material over about one half to one turn of said second thread around the core of said screw, the gradual change being linear, cyclical or any other type as long as the change is gradual; at the end of the depth reversal of said front sub-channel and said back sub-channel, said second thread converting to become said first thread with a minimum clearance to said barrel and said first thread converting to become said second thread with a large clearance to said barrel, and the maximum depth of said front sub-channel being maintained over about one half to one turn of said first thread around the core of said screw such that at this point the structural features of said screw become substantially similar to those at the beginning of the depth reversal; then, duplicating the depth reversal between said front sub-channel and said back sub-channel; the conversions of said first thread to said second thread and said second thread to said first thread followed by the depth reversal, being repeated as many times as desired but at least once; and finally, said front sub-channel and said back sub-channel being merged to a single channel with a common depth by gradually changing their depths and eliminating said second thread.