During operation of a spark plug in an internal combustion engine, the portions of the center electrode and the ground electrode in the combustion chamber and particularly the portions which define the spark gap are subjected to corrosive combustion gases. Electrode erosion also is caused by the repetitive sparking. In recent years, the exposed surfaces of spark plug electrodes commonly have been produced from nickel alloys which resist corrosion and erosion. When longer life spark plugs are desired, the sparking surfaces of the electrodes may be formed from a precious metal, such as iridium, platinum, gold or silver, or from a precious metal alloy. Due to the extremely high cost of precious metals, manufacturing techniques are being developed to minimize the amount of precious metal required to produce these electrodes while maintaining an adequate bond between the precious metal and the base metal. One process involves welding a small disk or wafer of the precious metal to the base metal on the electrode. In another process, a small hole is formed in the end of an electrode blank, a piece of precious metal wire is inserted into the hole and the electrode blank is extruded. In each of these processes, it is necessary to handle very small pieces of the precious metal. There is a risk that the manufacturing equipment will fail to apply the precious metal to the electrode or that a defective bond will occur and consequently a defective spark plug may be manufactured. In other manufacturing processes, the precious metal is applied to the electrodes as a coating. However, if a gap occurs in the coating at the sparking surface, the electrode may be subject to premature failure.
USPTO Backgrounds
USPTO Backgrounds