Method of injection molding employing multichannel wave screw

A method of injection molding wherein a quantity of synthetic resinous material is prepared for injection into a mold without overheating and with good melt quality, comprising processing resinous material in a feed and transition zone to melt a substantial portion of the material and advance it to a second zone, dividing the flow through said second zone into two parallel channels each of which has restricted cross-sectional areas at a plurality of locations along its length with the restricted areas in one channel being longitudinally offset from the restricted areas in the other channel and with the cross-sectional area of each channel varying cyclically over a plurality of substantially identical cycles, forcing most of the incompletely melted resinous material in each of said channels to pass through said restricted areas in that channel to receive extra energy input for melting the same thoroughly, and filtering a portion of the completely molten resinous material from one channel to the other with minimum energy input just in advance of each of said restricted areas to avoid the extra energy input associated with passage through said restricted areas and thereby to avoid overheating of the melted material, said cycles reinforcing one another and collectively providing a steady material flow rate and pressure at an output end of said second zone, and injecting a charge of the completely molten resinous material at the discharge end of said second zone into a mold cavity.