Spar plug middle electrode has corrosion and erosion resistant core - with sheath of higher thermal conductivity

摘要

Spark plug has a middle electrode with a core of metal with good resistance to corrosion and erosion, to which is bonded a sheath of metal with higher thermal conductivity than the core. The core pref. extends further than the sheath at the spark gap end. There is no sheath over 10-65 (20-35)% of the surface area along the core. The sheath consists of O2-free Cu (alloy) of high electrical conductivity and the core of Ni(alloy). There is a seal of material contg. Ni in the form of an annular cap between the core and the spark gap end of the refractory body to shield the sheath from the environment. This seal can be made in one piece with the core. There can also be a coating of material resistant to corrosion and erosion on the outside of the sheath, a 0.00254-0.0762 mm Ni coating being pref. Heating transfer is improved, whilst good corrosion and erosion resistance are retained. The mfr. of these spark plugs is economical and compatible with current mfg. techniques.