| 摘要 |
In a method of making a spark plug centre electrode, a billet (12) of a first metal which has good thermal conductivity is placed within a cup-shaped billet (10) of a second metal having good corrosion resistance, the first metal being melted within the cup-shaped billet of the second metal and, subsequent to cooling, the composite billet is extruded through an extrusion die (17) to form a composite centre electrode in which a core of the first metal is enclosed substantially entirely within a sheath of the second metal. |
