A plasticating apparatus and method for its use including a rotating screw having a helical flight disposed within and cooperating with the inner wall of a heated barrel with said barrel provided with inlet and outlet openings so that particles of resinous material are introduced through said inlet opening to a helical valley extending along said flight to be plasticated by said screw and advanced towards said outlet opening. A barrier extends along said helical valley to divide said helical valley into coextensive side by side helical valley sections. The barrier extends in a path which is non-parallel and alternating with respect to the helical flight so that the pitch of the barrier is alternately greater than and less than the pitch of the helical flight. The height of the barrier is less than the height of the flight so that the resinous material overflows the barrier due to changes in width of said side by side helical valley sections.