Apparatus for producing double-walled corrugated pipes

An apparatus for producing helically wound double-walled thermoplastic pipes having a corrugated outer wall and a smooth inner wall, both the walls being fused together, the apparatus comprising:

• extruder means communicating respectively with first and second dies having extrusion orifices for extruding accordingly the first and second bands of a thermoplastic material for forming appropriately the outer and inner walls of the produced double-walled pipe;
• a former located between said dies, downstream of the first die and upstream of the second die, their extrusion orifices being situated substantially along the former, the same having a lateral surface adapted to receive the first extruded band, to shape the corrugated configuration of the latter and to helically wind the same into the outer corrugated tube of the produced pipe, the inside of said outer tube receiving the second band helically wound into the inner smooth tube of the pipe;
• an elongate tubing mounted inside the former and connecting the second die with its extruder means;
• a cooled pressing element conforming to the inner wall and engaging the second band as it emerges from the second die and pressing the same to the outer wall to fuse them together;
• the improvement, wherein said pressing element has passages communicating with the second band and with a vacuum means.