Spark plug
A spark plug includes a metallic housing, an insulator fixed in the metallic housing, a center electrode fixed in the insulator, a ground electrode opposed to the center electrode via a spark discharge gap, and a protective coat formed on the surfaces of a metallic housing and a gasket. The protecti...
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Main Authors | , |
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Format | Patent |
Language | English |
Published |
19.09.2006
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Online Access | Get full text |
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Summary: | A spark plug includes a metallic housing, an insulator fixed in the metallic housing, a center electrode fixed in the insulator, a ground electrode opposed to the center electrode via a spark discharge gap, and a protective coat formed on the surfaces of a metallic housing and a gasket. The protective coat includes a galvanized film formed on the surfaces of the metallic housing and the gasket and a chromate film successively laminated on the galvanized film. The chromate film is hexavalent chromium-free and contains trivalent chromium as a major component. The chromate film has a film thickness not smaller than 0.05 μm and not greater than 0.18 μm, and the chromate film contains a metallic component which is robust against oxidation compared with zinc. Furthermore, the chromate film has a film hardness equal to or less than 1 GPa in the temperature range from a room temperature to 180° C. |
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