Temperature influence on electrical impedance spectra used to monitor dry molding materials in the foundry industry

Abstract Condition monitoring of molding material preparation processes in foundries can help to improve the processes in terms of energy consumption and use of resources. Electrical impedance spectroscopy is a suitable method for this purpose but influence effects must be carefully taken into account in field applications. Temperature, in particular, plays an important role in foundry processes and can be expected to strongly interfere with the extraction of condition information from impedance spectra. To shed light on the details of this temperature influence, we have recorded impedance spectra of measuring cells filled with molding material (quartz sand, used core sand, and regenerated material) in the frequency range from 500 Hz to 1 MHz and have evaluated the spectra with respect to their reproducibility and the quantifiability of their temperature dependence. It was found that the impedances could be measured reproducibly across the entire frequency range, with reproducibility increasing with frequency. In addition, the temperature dependence was observed to be a function of both of the molding-material composition and the frequency. Numerically, the temperature caused impedance magnitude changes of up to 34 % in the worst cases. This suggests that one should either control the temperature of molding-material samples during measurement or that the feature combination of impedance spectrum plus temperature should be used in data interpretation.