Thermal System Prevents Stress Cracking in Refractory
To prevent thermal stress cracking a refractory materials processor required pre-heating refractory materials to a minimum 1000°F (540°C) before processing. The heater had to fit inside an 8-inch (20 cm) wide by 54-inch (137 cm) deep refractory, and be capable of keeping the heating profile on a precalculated ramp to prevent thermal shock. A built-in thermocouple was needed to sense inside sheath temperatures.
Watlow provided a thermal system solution HT FIREROD® cartridge heaters, a Series 920 ramp and soak temperature controller, a Series 140 high-limit temperature controller, mercury displacement relays, and a Type K thermocouple. The 10 W/in2 (1.5 W/cm2) heaters were spaced three inches (75 mm) center to center to avoid cross radiation. Using Watlow's thermal system kept the refractory heating profile within ±12°F (±6.6°C), eliminating thermal cracking of the refractory.