A nondestructive microwave testing method to control the green compression strength and moisture content was proposed and demonstrated. There are various green moulding sands, both qualitative (bentonite type) and quantitative (bentonite and water content), prepared. The permittivity measurements were performed by cavity perturbation technique (CPT) at 2.45 GHz. Relative complex permittivity of the bentonite bonded moulding sands is proportional to the bentonite and moisture content and is inversely proportional to green compressive strength. It was shown that the obtained permittivity value of the molding sands be used to investigate the green compression strength and moisture content.
The presented research was aimed at searching for an exact and effective method of determining moisture content in traditional moulding sands. By measuring resonance frequency and quality factor of a waveguide resonance cavity, relative permittivity was determined for different synthetic moulding sands. Analysis of the presented results confirms a linear relation between relative permittivity values and moisture content values in the selected traditional moulding sands. The obtained linear relationship can be used as a reference characteristic for evaluation of humidity of moulding sand.
Within the research, selected multilayer technological systems created as combinations of water-glass containing moulding sand with foundry tooling, were characterised on the grounds of their electrical properties. By measuring resonance frequency and quality factor of a waveguide resonance cavity, real component of permittivity εr′ and loss tangent tgδ were determined for multilayer foundry systems with various qualitative and quantitative compositions. It was demonstrated that combination of a sandmix and foundry tooling with known dielectric properties results in a system with different physico-chemical properties, whose relation to the parameters of individual components of the system is undefined at this research stage. On the grounds of measurement results, theoretical value of microwave heating power, dissipated in unit volume of the selected multilayer foundry system, was determined. Knowledge of theoretical heating power and evaluation of physical, chemical and structural changes occurring in moulding sands exposed to microwaves in such a technological system makes a ground for empirical modelling of the process of microwave heating of foundry moulds and cores.
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