Method and apparatus for sheathing a structural member with a synthetic thermoplastic material

Claim 1

IN A PROCESS OF SHEATING WITH SYNTHERIC THERMOPLASTIC MATERIAL AN ELONGATED STRUCTURAL MEMBER HAVING A CONCAVE ANGLE IN ITS CROSS-SECTIONAL OUTER PROFILE BY EXTRUDING ON THE MEMBER A SHEATH OF THE MATERIAL IN A SOFTENED CONDITION WHILE ADVANCING THE STRUCTURAL MEMBER LONGITUDINALLY THROUGH AN EXTRUSION ORIFICE, THE IMPROVEMENT WHICH COMPRISES, CLAMPING THE THERMOPLASTIC MATERIAL RADIALLY INWARDLY IN THE DIRECTION OF SAID ANGLE CIRCUMFERENTIALLY OF SAID MEMBER ALONG A NARROW, CIRCUMFERENTIAL ZONE IMMEDIATELY ADJACENT THE LEADING END OF THE STRUCTURAL MEMBER WHEN IT PASSES OUT OF SAID ORIFICE TO FORM A FLUID-TIGHT SEAL BETWEEN THE MATERIAL AND SAID MEMBER THROUGHOUT SAID ZONE, ADVANCING THE STRUCTURAL MEMBER THROUGH SAID ORIFICE TO SHEATH THE STRUCTURAL MEMBER CIRCUMFERENTIALLY AND LONGITUDINALLY WHILE MAINTAINING SAID FLUID-TIGHT SEAL IN SAID ZONE, PROVIDING A SHORT PASSAGEWAY THROUGH SAID ZONE TO PROVIDE COMMUNICATION THROUGH SAID FLUID-TIGHT ZONE UNDERNEATH SAID MATERIAL ALONG SAID CONCAVE ANGLE, APPLYING A VACUUM AT THE LEADING END OF SAID MEMBER TO SAID PASSAGEWAY WHILE ADVANCING SAID MEMBER THROUGH SAID EXTRUSION ORFICE TO EXHAUST AIR LONGITUDINALLY OF SAID MEMBER ALONG SAID CONCAVE ANGLE WHILE CLAMPING THE MATERIAL ALONG SAID ZONE, AND SETTING THE THERMOPLASTIC MATERIAL WHILE APPLYING SAID VACUUM AND MAINTAINING SAID ZOND CLAMPED.