This paper discusses the impact of high temperatures (up to 900°C) on molding and core sand with inorganic binders selected
from among the group of unmodified grades of hydrated sodium silicate (water-glass). Molding sands with medium
quartz sand were made under laboratory conditions and compacted at the different energy inputs necessary for obtaining
various apparent densities (ϱ0). Due to the different composition and apparent density of molding mixtures hardened via
microwaves at a frequency of 2.45 GHz, it was possible to assess their deformation (L) at a high temperature above the
binder’s eutectic temperature. For this purpose, an apparatus for hot distortion tests was used whose construction and
equipment allows us to measure the thermoplastic deformations in molding sand in many aspects; i.e., in its time of annealing.
The article proposes new possibilities of interpreting the hot distortion phenomena in comparative studies of molding
materials and mixtures. The application of this new measurement method revealed the differences between molding mixtures
made with five inorganic binders with a molar module ranging from 2.0 to 3.4 and apparent density ranging from
1.34 to 1.57 g/cm3. It was established that distortions under the influence of high temperatures last the longest in molding
sand with a binder with the highest molar module (3.4). Research also revealed that the density of molding sand is significant
for increasing/decreasing the rate of thermoplastic deformations following the heating of samples only if the molding
sand includes binders with a molar module of between 3.0 to 3.4. For molding sand with binders with molar modules from
2.0 to 2.5, it was established that this is excessively susceptible to thermoplastic deformation.
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