PURPOSE: To enable formation of a specifically corrugated working part immediately after the start of corrugation by basing as reference on a difference in eccentric quantity at the time of corrugation reaching a steady state and setting such difference in the early stage of corrugation for a specific number of times of the reference value.
CONSTITUTION: An eccentric die 1 is moved upward from its original position and made to be eccentric ; and corrugation working is performed on a tube stock 2 by means of a projected line 3. Assuming as Δ an eccentric quantity at the time of corrugation reaching a steady state; corrugation working is performed with the eccentric quantity in the early stage of corrugation set as from 1.1 to 1.3×Δ. When working is performed with a standard eccentric quantity of Δ in the early stage of corrugation, a restraint of a non-forming part of the tube stock 2 affects the corrugated working part in the early stage, forming a shallow corrugation. Therefore, a large eccentric quantity of the eccentric die 1 cancels the restraint of the non-forming part of the tube stock 2, forming a prescribed corrugation.
DEN TATSUHIRO
NAKAMOTO KAZUNARI
