Alumina Spark Plug Insulator

A modern vehicle is a highly complex technical commodity that can only function correctly if all its components work in harmony. One of the most important components is the spark plug, whose performance determines the reliability and service life of the engine.

The insulator, the section of the spark plug that conducts electricity from the centre electrode to the side electrode, is made of an aluminium oxide ceramic material. The material is mined as bauxite and processed, formed, sintered and glazed, providing excellent insulation, resistance to chemical attack and extreme hardness, among other properties.

Today, most spark plugs feature an insulator of an aluminium oxide ceramic. This material is a result of the need for advanced Otto-cycle engines to be fitted into increasingly compact combustion chambers, which means that the spark plug must have a smaller diameter than in the past. This places a greater emphasis on the mechanical strength and dielectric properties, especially the electric breakdown strength, of the spark plug.

Alumina has a high electrical breakdown strength and also has good thermal endurance. Its thermal conductivity is also higher than that of conventional insulators. Alumina can be produced with a density of at least 3.85 g cm3. This can be achieved by using a fine alumina powder, compressing it prior to sintering, especially by isostatic pressing, and adjusting the sintering temperature and time so that 90% by weight of the insulator blanks have particle sizes of less than 1 mm.

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