Apparatus for producing double-walled composite tubes

An apparatus for producing a double-walled composite tube, wherein the tube has least one finned tube longitudinal portion with an outer wall having wave valleys and wave peaks, smooth inner wall integrally joined to the wave valleys of the outer wall, and at least one tube socket portion along which the outer wall and the inner wall are integrally joined to each other, the apparatus comprising;

• two rows of first and second shaping-jaw halves forming, along a common shaping section, a shaping tunnel, wherein the first shaping-jaw halves of the two rows lie opposite each other in the shaping section and have an inner contour for producing a tube socket portion, wherein the second shaping-jaw halves of the two rows lie opposite each other and include transverse grooves alternating with transverse fins for producing, respectively, the wave peaks and the wave valleys of the finned tube longitudinal portion;
• a sizing mandrel having an outer lateral surface adapted for application of a controlled subatmospheric pressure and projecting into the shaping tunnel for forming the smooth inner wall of the composite tube, wherein the sizing mandrel defines a plurality of narrow vacuum grooves spaced apart from one another in the axial direction and extending, continuously in the circumferential direction around the outer lateral surface;
• a vacuum control valve device defining a plurality of vacuum holes respectively corresponding to the plurality of vacuum grooves of the sizing mandrel;
• and
• a control member connected to a drive device and operable for closing the vacuum holes corresponding to the vacuum grooves located at the tube socket portion and simultaneously opening the vacuum holes corresponding to the vacuum grooves located at the finned tube longitudinal portion.