Automatic Temperature Measurement for Casting Furnaces Using an Immersion Thermocouple

摘要

Thermocouple fixturing and immersion thermocouple assemblies have been developed to provide a temperature measurement of molten metal in vacuum casting furnaces. The previous thermocouple temperature measurement was inadequate because of sheath breakage and sheath erosion problems. A fixture was developed which uses a welded-metal bellows to retract and insert thermocouples, thus eliminating breakage problems caused during furnace loading. Sheath erosion problems were eliminated by developing a disposable-sheath thermocouple design in which an outer sheath could be replaced periodically. Tests show that the fixture lifetime is > 450 cycles and that the disposable-sheath thermocouple will operate for more than 200 cycles, with not more than +-3.6 exp 0 C drift. Total system error does not exceed +-10 exp 0 C during steady state at 1340 exp 0 C. (ERA citation 08:047236)