A spark plug looks simple — a metal shell with a ceramic insulator and a small electrode. But the engineering and manufacturing behind modern iridium spark plugs is remarkably sophisticated. Here's how they're made.
The Center Electrode
On an iridium plug, the center electrode is a composite of materials. A copper core (for excellent heat conductivity) is surrounded by a nickel alloy, and the tip is laser-welded with an iridium alloy cap measuring as little as 0.4mm in diameter. The laser welding process bonds the iridium to the electrode base with a metallurgical bond stronger than any mechanical fastening.
The Insulator
The white ceramic insulator (alumina — Al₂O₃) is pressed and sintered at temperatures exceeding 1,600°C. The insulator must withstand thermal shock as temperatures swing from ambient to over 800°C with each ignition cycle. It must also provide perfect electrical insulation while conducting heat efficiently to prevent pre-ignition.
The Shell
The steel shell is machined to precise thread tolerances (typically M14 x 1.25mm pitch). The thread profile must maintain a gas-tight seal under cylinder pressures exceeding 1,000 PSI. The shell is then plated with trivalent zinc or nickel for corrosion resistance.
Quality Control
Leading manufacturers like NGK test every plug for electrical resistance, electrode gap, and structural integrity. High-voltage flash testing verifies the insulator integrity under conditions more demanding than real-world operation.
Why Cheap Plugs Fail Faster
Budget plugs cut corners on electrode metallurgy, insulator quality, and shell plating. The result is faster electrode wear, cracked insulators, and corrosion — all of which shorten plug life significantly.
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