Method for manufacturing tapered rods

摘要

Method for manufacturing a tapered rod for a coil spring from a metallic material of mainly steel in a linear state, by imparting heating to the same with a predetermined temperature gradient pattern in the axial direction thereof while or before pulling by tensile force the metallic material chucked at two axially distant points in either direction in a gradually decreasing or stepwise decreasing speed, until a desired tapered portion is formed. An apparatus preferably employed for this method comprises a pulling mechanism for chucking and pulling the material, an electric current supplying mechanism for supplying predetermined amount of current to the material between the two chucked points, a plurality of cooling units arranged axially along the material for positionwise cooling the material so as to make the temperature gradient thereon, a temperature detecting device for detecting the surface temperature of the material for feeding back the detected data to the current supplying mechanism, and a heating temperature controlling device for controlling the amount of the current flowed there.