TENDSTIFT JEMTE FORFARANDE FOR DESS FRAMSTELLNING

摘要

In a spark plug including an insulator mounted in a tubular shell and an electrode assembly mounted within a bore through the insulator and projecting from a nose portion of the insulator to define a spark gap with a ground electrode, a method for improving the resistance of the nose portion to cracking caused by thermal stresses. The electrode assembly includes a high heat conducting portion in close proximity with the wall of the portion of the bore extending through the nose portion of the insulator. The method comprises applying a coating of a glaze slip to the interior wall of the portion of the insulator bore which will be in proximity with the heat conducting portion of the electrode and then firing the glaze at a controlled time and temperature to form an uninterrupted glassy coating on at least the portion of the nose bore adjacent the end of the insulator. The fired glaze must have a lower coefficient of thermal expansion than the insulator, an appreciably lower thermal conductivity than the insulator and a softening temperature above the highest operating temperature encountered by the glazed bore wall.