In the prior art, as a method and device that can integrally mold a pipe with a synthetic resin, there has been known the method and device that uses a mold in which a cavity has on its one end a floating core, having a diameter corresponding to the inner diameter of the pipe, and a pressure port through which a pressurized fluid is pressure-injected, and the cavity has on its other end an outlet. After the inside of the cavity is filled with a molten resin, the pressurized fluid is pressure-injected through the pressure port to move the floating core to the outlet side, and, thus, to form a hollow in the resin in a main cavity. At the same time, an excess resin is extruded from the outlet, whereby a hollow pipe is integrally molded (Patent Documents 1 and 2).
However, in the method and device described in the Patent Documents 1 and 2, the hollow of the pipe is formed as sort of a moving track of the floating core. Since the floating core moves in only one direction, there is a problem that a pipe with a branch cannot be produced. It is considered to provide a plurality of floating cores and move the floating cores in different directions so that the pipe with a branch can be integrally molded; however, because of the structure of the mold, it is extremely difficult to enable the plurality of floating cores to move in the different directions.
Patent Document 3 discloses a method of manufacturing a pipe with a branch by molding using a floating core.