Pre-painted Galvalume Steel Coils

High-Speed Thermal Curing
Applied coatings undergo instantaneous curing in gas-fired ovens with 6-12 heating zones, where strip temperatures are ramped from ambient to 224-254°C PMT (Peak Metal Temperature) in under 60 seconds. Convection zones (air velocity 15-30 m/s) ensure turbulent heat transfer while IR panels target specific heat absorption by pigment types. Temperature profiling uses 40+ thermocouples with PID control maintaining ±1°C uniformity. For silicone-modified polyesters (SMP), cure schedules target 90% cross-linking at 232°C for 45 seconds, while PVDF systems require 249°C for 30 seconds to achieve crystalline phase fusion. Exhaust gases pass through 85% efficient thermal oxidizers, converting VOCs to CO₂/H₂O while recovering heat.

This rapid curing determines final film properties. Differential Scanning Calorimetry (DSC) confirms Tg (glass transition) temperatures of 105-120°C for fully cured SMPs, ensuring formability without cracking. Quenching zones rapidly cool coils to 50°C in 8 seconds, freezing polymer morphology for consistent gloss. FTIR spectroscopy verifies >95% conversion of reactive groups – critical for chemical resistance. Undercured films show poor MEK resistance (<50 double-rubs), while overcured systems become brittle (impact resistance <40 in-lbs). Oven control prevents "burning" of organics that causes yellowing (b* shift >1.5). The process enables production speeds up to 200 m/min while achieving: pencil hardness 2H-3H (ASTM D3363), adhesion 5B (ASTM D3359), and flexibility passing 1T T-bend on 0.5mm substrates. Thermal efficiency reduces energy consumption to <0.8 kWh/m².