A G9 halogen capsule costs cents, yet its production line hides more engineering than most buyers expect. Between raw tungsten wire and the finished capsule that lights an oven at 500°C, there are eight distinct steps. Any one of them, done carelessly, produces a lamp that fails in weeks instead of years. For importers and appliance OEMs, understanding this chain is the fastest way to judge a supplier without ever visiting the factory.
Step one is filament fabrication. Tungsten wire is drawn to the exact diameter for the target wattage, then coiled around a mandrel. The coil pitch, diameter and turn count set the operating temperature and light output. A variation of 0.01mm in wire diameter can change lamp life by hundreds of hours. This step runs on automatic coiling machines in serious factories; manual coiling is a red flag.
Step two is quartz tube preparation. The capsule body of an oven-rated lamp must be quartz glass, not ordinary soft glass — quartz survives the thermal shock of rapid heating and cooling. The tube is cut to length, ultrasonically washed and inspected for surface defects. A micro-crack here will propagate under thermal cycling and fracture the lamp inside a hot oven.
Step three is mount assembly. The coiled filament is welded to molybdenum lead wires, chosen because molybdenum’s thermal expansion closely matches quartz. The mount is then centered inside the tube. Off-center filaments produce uneven light and a hot spot that shortens life — a failure mode that is invisible in a sample but appears across a production batch.
Step four is sealing, the most critical step. The quartz tube is heated to its softening point and pinched around the molybdenum leads to form an airtight seal. This is where workshops and factories diverge: manual or semi-automatic sealing produces variable pinch geometry, while automated sealing machines hold pinch width and position within tight tolerances, lamp after lamp. Ask a supplier how sealing is done — the answer tells you more than any certificate.
Step five is halogen gas filling. The sealed capsule is evacuated and back-filled with a precise mixture of inert gas and a halogen compound, typically bromine or iodine. This is the chemical heart of the technology: during operation, evaporated tungsten combines with the halogen and redeposits on the filament instead of blackening the glass. Wrong fill pressure or composition means short life and cloudy glass.
Step six is base and pin attachment. For a G9 capsule, the loop base with two pins is attached to the sealed body. In oven applications, the base must hold pins rigidly through thousands of thermal cycles — a loose base is the classic "worked for a month, then flickered and died" failure. Reinforced or ceramic bases exist specifically for this.
Step seven is aging, or burn-in. Every capsule is lit at rated voltage for a short period to stabilize the filament and expose early failures. A lamp that survives burn-in has a dramatically higher chance of surviving its rated life. Factories that skip burn-in save pennies per lamp and sell failures by the container.
Step eight is final testing and packaging. Sample-based life testing runs lamps until failure to verify the rated life — typically 2,000 hours for oven-rated capsules — while 100% of production passes electrical testing. After inspection, capsules go into anti-static trays and cartons for shipment from ports like Shanghai, Qingdao or Guangdong.
The buyer’s shortcut: ask three questions — is sealing automated, is burn-in done on 100% of production, and is the glass quartz? A factory that says yes to all three, and can show you the process, will consistently outperform a cheaper alternative that skips steps. Shunqi Lighting runs this full eight-step process for its G9 oven capsules in our Lianyungang plant, and we welcome factory inspections before your first order.