SPARK PLUG AND METHOD FOR MANUFACTURING SPARK PLUG

摘要

Provided are a compact spark plug which shows favorable ignition performance, and a method for manufacturing the spark plug. The spark plug is provided with a center electrode, an insulator and a main body metal piece, and satisfies: condition (1) wherein the wall thickness (T) of the insulator is 0.3 - 1.1 mm; condition (2) wherein a region of the insulator that corresponds to at least 2 mm from the tip of the insulator is formed of an alumina-based sintered compact, which contains Si component, RE component and at least two Group-2 element components and contains substantially no B component; condition (3) wherein the mass ratio (RRE) of the mass of the rare-earth element component to the total of the masses of the Si component, the Group-2 element components and the rare-earth element component is 0.15 - 0.45; condition (4) wherein the mass ratio (R2) of the total of the masses of the Group-2 element components to the mass of the Si component is at least 0.25; and condition (5) wherein an aluminate crystalline phase containing the RE component is included in a grain boundary phase. The method for manufacturing the spark plug includes a step of preparing raw powder, and fabricating the insulator by molding this raw powder under pressure and then sintering the thus molded raw powder, wherein the grain size distribution ratio (volume diameter at 90 % / volume diameter at 10 %) of the raw powder is 3.6 - 5.2.