PURPOSE: To upgrade assembly and disassembly efficiency by providing protrudingly a connecting piece facing outside on one side face of adjacent molding disks and a removable connecting piece facing inside on the other side, engaging both connecting pieces together with a looseness in the axial direction and providing an elastic component between two disks.

CONSTITUTION: In the assembly of a mold A, connecting pieces 4 and 5 facing outside and inside respective adjacent molding disks 1a-1c intervened each other into opposite intervals 50 and 40 are provided protrudedly, and both disks are rotated in the reverse direction and engaging pieces 41 and 42 are engaged with and connected. In the case that a ring bead is molded in a duct cylinder by the mold A, the mold A is fixed on a parallel rotating shaft of a bead molding machine by spline fitting of a shaft fixing hole 2, and the mold is rotated while the duct cylinder wall is clamped by the mold A. Both connecting pieces 4 and 5 are engaged with looseness in the normal time of bead molding, and the disks are retained in the state of parallel interval P, and as the bead is being molded, adjacent disks are brought closer through a space 6 resistant to a spring 7 and can correspond to the shrinkage of the duct cylinder in the axial direction.