To provide a form rolling method and a form rolling apparatus by which troubles such as the deterioration of function and discontinuity of a heating wire are prevented since the heating part of a preheating plug is not brought into contact with a plug hole when the plug is mounted onto the plug hole in the case of the preheating plug for diesel engines by preventing occurrence of eccentricity on a worked screw by deflection of a half-finished products in the form rolling (threading) process.
When performing the form rolling stage for working a screw by using a roll die or a flat die in the portion excepting the head part of the half-finished products the head part of which is formed by working it into a hexagon after enlarging the diameter of the upper end part of a base stock which is cut into a fixed length, a guide stage for preventing the deflection of the half-finished products in the screw cutting stage and the occurrence of the eccentricity on the worked screw by supporting the rest portion excepting the portion where the screw is worked by being pressed with the die in the above half-finished products by any of a roll guide, a flat guide or a pipe guide is furthermore included.
CHO REICHIN
KIM KANSHOKU
Yoshinobu Hagino
Naoya Taniguchi
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