| 摘要 |
PURPOSE: A double-bellows combined pipe for a heating pipe is provided to reduce flow velocity by a corrugated inner peripheral surface and prevent noise by attaching the outer surface of a plastic pipe to the inner circumference of a metal bellows pipe. CONSTITUTION: A double-bellows combined pipe for a heating pipe comprises following steps. A first plastic pipe(10) is inserted into a metal bellows pipe(1)(S100). The pipes are heated, the inside of the first plastic pipe is pressurized, and a second plastic pipe(11) is shaped(S200). The metal bellows and the second plastic pipe are frozen, and a third plastic pipe(12) is shaped(S300).
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