| 摘要 |
PURPOSE:To smooth the inner surface of a tube by providing small outer diameter extension section in the end section of an outer tube, turning over this at the end section of the inner tube, and forming a sealed bead retainer at the joining section out of the end projected and a socket. CONSTITUTION:A double tube consists of an inner tube 2 of PFA thin wall and an outer tube of polybutene(PB) whose a coefficient of thermal expansion is equal to that of PFA, and the end section of the outer tube 1 is provided with a small diameter thin wall extension section 3, or a thin wall metallic ring 8, whose inner diameter is the same as that of the extension section 3, is plugged, and the PFA inner tube 2 is turned over and coated and fixed at this section. When the outer tube 1 and a socket 5 are joined by welding in heating process said section is fixed to a fixed position without being restored. In addition, since all of the beads (a) and (b) are completely contained in a sealed bead retaining chamber 6 appearing at the outer periphery of the head section of a double tube in joining process, the surface of flow passage is smoothed. As a result, the drift and break in the inner tube due to the heat cycle will not occur, and fluid retaining places on joining sections are eliminated. |
