How spark plugs are made

A spark heats its path through the cylinder to 60,000 kelvins, while ceramic keeps the voltage inside the plug.

stations: 8
things upstream: 33
raw sources: 16
steps from the ground: 5

The short version

A spark plug has a threaded steel shell, a ceramic insulator and a central electrode. The insulator is pressed from ceramic powder and fired hard. Steel is pressed through dies into a shell, a nickel alloy tip is added, and threads are rolled on. The shell is shrunk tight around the insulator and the tip is bent over to set the gap.

Press the insulator

Ceramic powder is packed in a mold under pressure and ground to the long shape of the insulator. It will have to stand thousands of volts and high heat.

Goes in
Alumina
Fire it hard

The insulators are fired in a kiln to a dense ceramic body that does not conduct electricity.
Form the steel shell

Raw steel is pressed repeatedly into dies until it reaches the final hex-topped shape.

Goes in
Steel
Attach the side tip

A straight nickel alloy tip is fixed to the end of the shell. It will become the side electrode.

Goes in
Nickel
Roll the threads

The shell passes through threaded rollers that emboss the threads that screw into a cylinder head.
Seat the center electrode

An electrode running the whole length of the insulator is pressed in, with a nickel-alloy skin and a copper core.

Goes in
Nickel Copper
Shrink the shell on

Oil helps the shell slide over the insulator. A shrinking tool then passes electric current through the metal so it grips the ceramic tight.
Bend the tip over

Bending brings the nickel tip within a few thousandths of an inch of the center electrode, and the spark jumps this space.

End of the lineSpark plug

Worth repeating

The spark channel inside the cylinder reaches a temperature of 60,000 K.
NGK, which describes itself as the world's leading spark plug maker, began as a company that made ceramics.