METHOD AND DEVICE FOR MANUFACTURING BOLT, SCREW ROLLING DIE USED THEREFOR, AND MULTIPLE SCREW BOLT

摘要

A method and a device for manufacturing bolts capable of mass-producing multiple screw bolts such as double screw bolts at low cost and a screw rolling die used therefor, the bolt manufacturing device comprising a pair of screw rolling dies (1) disposed opposite to each other at a specified interval and bolt supporting parts (2) supporting a cylindrical bolt material (3) at specified positions. The screw rolling dies (1) further comprise transfer patterns (4) having coarse screw thread ridge parts (5) as a part of the coarse screw threads formed by expanding a coarse screw and projections (6) as a part of fine screw threads (6a) cyclically formed at the thread root parts (5a) of the coarse screw threads according to the phase shift of the fine screw threads (6a) shown by imaginary lines formed by expanding a fine screw from the coarse screw threads.