Insulator for spark plug, and method for manufacturing spark plug

摘要

A method for manufacturing an insulator includes: preparing a press pin (50) and a forming die (80) having a cavity (83), the press pin (50) including a pin-side spiral portion (54) formed on a first position; filling a raw powder (GP) into the cavity (80); arranging the press pin (50) within the cavity (83); pressing the raw powder (GP) within the cavity (83) along with the press pin (50), and obtaining a green body (PC1) formed with a green body-side spiral portion; releasing the green body (PC1) along with the press pin (50) from the cavity (83); retreating the press pin (50) with respect to the green body (PC1) while rotating the press pin (50) relative to the green body (PC1) around an axis, and extracting the press pin (50) from the green body (PC1) ; and removing an unnecessary portion from the green body (PC1). The first position is positioned such that the green body-side spiral portion is located in the unnecessary portion of the green body (PC1).