Apparatus for producing plastic drain pipes

In an apparatus for producing a drain pipe having annular or helical corrugations and having openings for the entry of water in distinct portions being disposed in said pipe at regular repeating intervals between corrugated lengths of pipe, said apparatus comprising an extruder having an extruder head, said extruder head having a generally annular opening defined by a generally circular die disposed about a generally circular mandrel, said apparatus having in general axial alignment with said opening a pair of endless travelling means in the form of a mold train, each of which travelling means carries cooperating mold halves which are in facing relationship generally axial of said opening and joined to define a mold cavity, means operatively associated with said mold cavity for exerting a partial vacuum on the contents of said mold cavity, some of said mold halves having grooves to form transversely corrugated pipe lengths of synthetic plastic extruded through said openings, the improvement wherein some of said mold halves have a cylindrical mold cavity, the internal diameter of the cylindrical sections being slightly less than the internal diameter of the transversely corrugated portions and a fixedly disposed pipe cutter means located inside the pipe and in the direction of travel downstream of the point where the mold halves separate, said fixedly disposed pipe cutter means engaging said cylindrical sections as they pass thereover but being in out of contact relationship with said transverse corrugated sections as they pass over, said mold halves being disposed on opposed sides and urging said pipe over said fixedly disposed pipe cutter to cut an aperture in said pipe no more frequent than every 20 cm of pipe length.