INSULATOR FOR SPARK PLUG, PROCESS FOR PRODUCING THE INSULATOR, SPARK PLUG, AND PROCESS FOR PRODUCING THE SPARK PLUG

摘要

An object of the present invention is to improve withstand voltage properties of a ceramic insulator by making the ceramic insulator dense. A spark plug 1 is provided with a ceramic insulator 2 having therein an axial bore 4 in an axis CL1 direction. A method for manufacturing the ceramic insulator 2, comprising: preparing a slurry by mixing base powder into a solvent, the base powder containing aluminum oxide as a principal component and at least one or more sintering aid including silicon oxide; granulating the-thus formed slurry by spray drying to form granulated base powder PM; filling the granulated base powder PM into a cavity 42 of rubber dies 43, 44 where a press pin 51 is provided; compressing the granulated base powder PM from a circumferential direction of the rubber dies 43 and 44 to form a molded body CP; and cutting the molded body CP into an insulator intermediate body IP assuming a predetermined insulator shape. A mean particle size of the granulated base powder PM falls within a range from 60 micrometers or more to 120 micrometers or less, and granule strength of the granulated base powder PM is 1 MPa or less.