Experimental validation of error in temperature measurements in thin walled ductile iron castings

Abstract

An experimental analysis has been performed to validate the measurement error of cooling curves measured in thin walled ductile cast iron. Specially designed thermocouples (TCs) with Ø0·2 mm TC wire in Ø1·6 mm ceramic tube were used for the experiments. Temperatures were measured in plates with thicknesses between 2 and 4·3 mm. The TCs were accurately placed at the same distance from the surface of the casting for different plate thicknesses. It is shown that when measuring the temperature in plates with thickness between 2 and 4·3 mm the measured temperature will be parallel shifted to a level ∼20°C lower than the actual temperature in the casting. Factors affecting the measurement error (oxide layer on the TC wire, penetration into the ceramic tube and variation in placement of TC) are discussed. Finally, it is shown how useful cooling curve may be obtained in thin walled castings.