Extruder with short cycle multichannel wave screw

A plasticating apparatus of the type in which a rotating screw is disposed within and cooperates with the inner wall of a barrel provided with inlet and outlet openings and wherein synthetic resinous material is introduced through the inlet opening, plasticated by said rotating screw and advanced toward said outlet opening;

• said screw including a section comprising a helical conveying flight having an effective outer width and cooperating with the inner wall of said barrel to form a helical passage, a helical outwardly extending barrier flight disposed axially between adjacent turns of the conveying flight and dividing the helical passage into two flow channels extending side by side, each of said channels having a base surface whose radius from the screw axis of rotation varies cyclically through at least four cycles along the helical length of the channel to provide a channel of varying depth, with the variations of said cycles being arranged so that the combined cross-sectional area of said channels is not constant entirely throughout a cycle, said barrier flight adjacent each area of increasing radius being undercut to provide sufficient clearance between its outermost surface and the barrel inner wall to permit the flow thereover of molten resinous material from the channel containing an area of increasing radius to an axially adjacent area of the same channel of the pair;
• the improvement wherein said screw section is a mixing section wherein each cycle has a helical length which extends less than 360 degrees about the axis of the screw whereby pumping of molten resinous material back and forth across said barrier flight in rapid succession occurs.

A plasticating apparatus of the type in which a rotating screw is disposed within and cooperates with the inner wall of a barrel provided with inlet and outlet openings and wherein synthetic resinous material is introduced through the inlet opening and plasticated by said rotating screw and advanced toward said outlet opening;

• said screw including a section comprising conveying flight means, outwardly extending barrier flight means disposed intermediate said conveying flight means to divide said passage into channels extending side by side helically along said screw section, each of said channels having a depth which varies cyclically through a plurality of cycles along the helical length of such channel, the minimum depth portions of the channels on opposite sides of said barrier flight means defining wave crests which are displaced helically from each other, a substantial portion of each channel situated between successive wave crests in the channel being of substantially constant depth, the barrier flight means adjacent each wave crest being undercut to provide sufficient clearance between its outermost surface and the inner wall of the barrel to permit the flow thereover of molten resinous material from the channel containing an area of decreasing depth to an adjacent area of the other channel, the outer width of said barrier flight means being shorter than that of said conveying flight means so that the shear energy imparted to molten material flowing over said barrier flight means is low;
• the improvement wherein said screw section is a mixing section wherein each cycle has a helical length which extends less than 360 degrees about the axis of the screw whereby pumping of molten resinous material back and forth across said barrier flight means in rapid succession occurs.