Theory and Method
Glow wire testing reproduces a specific real-world failure. An internal component such as an overloaded resistor, a degraded connection, or a glowing heating element reaches incandescence and touches nearby plastic. The test asks whether that contact ignites the material and, if it does, how long the flame persists once the heat source withdraws. A loop of nickel-chromium 80/20 wire, 4 mm in diameter, serves as the standardized heat source because its resistivity and oxidation behavior stay stable across repeated heating cycles.
Resistive heating raises the loop to the target temperature. Current passes through the wire, and the power dissipated per unit length sets the equilibrium temperature once radiative and convective losses balance the electrical input. An armored Type K thermocouple embedded at the tip measures that temperature directly rather than inferring it from current alone, which keeps readings accurate as the wire ages and its cross-section shifts slightly. The panel-mounted current control and ammeter let the operator trim the setpoint between runs.
Mechanical variables matter as much as temperature. The carriage advances the specimen at 18 mm/s, applies 0.97 N, and stops travel after 7 mm of penetration so that thin-wall parts do not melt through and end the test prematurely. Observers record time to ignition, flame extinction time after the wire withdraws, and whether burning particles ignite the tissue paper placed on the pine board beneath. Those observations yield the flammability index, the ignition temperature rating, or a pass result.
