Copper Cored Electrodes for Automotive Spark Plugs
Description
A spark plug centre electrode, typically around 25mm long and 3mm diameter, with a centre core of copper and a protective sheath of tough nickel, chromium, iron alloy, only 0.3mm thick on the flanks, and 2mm thick at the tip.

Challenge
In the late seventies, the development of engines reached a stage where the ‘heat range’ of conventional spark plugs with solid nickel alloy centre electrodes was unable to cope with their demands. A plug that was ‘cold’ enough to cope with the demands of high speed driving would not be able to burn off the carbon deposits caused by stop-start urban conditions, and would foul in these conditions, making the engine misfire. Similarly, a plug that was ‘hot’ enough to run smoothly in town, could actually melt when called upon to cope with extended high speed running on motorways, causing serious damage to the engine.

The answer to this problem, devised by the spark plug manufacturers, was a centre electrode that carried the heat of combustion away from the tip more effectively than was possible with a solid nickel alloy. Copper was the material chosen for the task. With thermal conductivity 24 times that of nickel alloy, it was ideal for the task of heat conduction, but was totally unable to resist corrosion and spark erosion in the harsh conditions of the combustion chamber. Therefore, it was necessary to specify a copper electrode with a protective nickel-chrome alloy sheath.
With the design solution created, the only problem was making it, not only in sample quantities, but in huge volumes. Moreover, this was a bi-metallic part that needed to have many mono-metallic properties. There could be no dis-continuity in the contact between the copper core and the sheath (or conductivity would be affected), and the protective sheath could not be allowed to get too thin, or there would be a risk of burn through.
Altogether this was a severe challenge that left the spark plug manufacturers looking for help.

Floform’s Response
In response to these challenges, Floform’s engineers developed a new approach, that involved bonding together very small copper and nickel alloy slugs, and then co-extruding this bi-metallic billet. This novel process was subsequently patented. However, there was at the time no proprietary production equipment available that was suitable for high-speed manufacture of these complex small parts in such high volumes. Floform therefore, developed and manufactured it’s own purpose-built machines. Copper cored electrodes remain vital to the spark plug industry. In recent years there has also been a need to develop copper cored side electrodes, and again Floform has developed new manufacturing processes to meet its customers’ needs.

Benefits
Technical: Service and warranty problems have been solved and engine manufacturers given greater design freedom.

Commercial: Spark plug manufacturers are able to rationalise their ranges and cover a greater variety of engines with the same plug. This has resulted in simplified manufacturing, reduced stockholding and improved availability for customers. Considerable cost has been taken out of the whole development, manufacturing, and supply chain.

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