## 3 Results
### Sieve Analysis of Perlite Ore  
Table 3 showcases the outcomes of the sieve analysis, while Table 4 outlines the fundamental parameters of the perlite ore employed in the experiments. The sieve analysis revealed that, for the perlite ore with the largest grain size, the primary fraction accumulates on 0.80/0.63/0.40 sieves, constituting 99.34% of the total sample (Table 4). This sample exhibits a homogeneity degree of 76%, which is the highest among the perlite ones used. The remaining samples (PO2, PO3, PO4) share the same main fraction, collected on 0.40/0.32/0.20 sieves. The PO3 perlite ore has the largest share of the 0.40 mm fraction, the PO2 perlite ore has the largest fraction of 0.32 mm, and the PO4 perlite ore has the largest number of grains collected on a 0.20 mm sieve among the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Mesh Size Sieve**} & \multicolumn{3}{c}{**Residue on Sieves, \%**} \\ \cline{2-4}  & **QS 1** & **QS 2** & **QS 3** \\ \hline
1.600 & 0.00 & 0.00 & 0.00 \\ \hline
0.800 & 0.02 & 0.64 & 8.00 \\ \hline
0.630 & 0.13 & 7.54 & **52.65** \\ \hline
0.400 & 3.52 & **47.93** & **34.48** \\ \hline
0.320 & **13.13** & **20.60** & **2.03** \\ \hline
0.200 & **60.17** & **19.01** & 2.17 \\ \hline
0.160 & **13.95** & 2.84 & 0.42 \\ \hline
0.100 & 8.78 & 1.42 & 0.25 \\ \hline
0.071 & 0.28 & 0.02 & 0.00 \\ \hline
0.056 & 0.02 & 0.00 & 0.00 \\ \hline Bottom & 0.00 & 0.00 & 0.00 \\ \hline Sum & 100.00 & 100.00 & 100.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Sieve analysis of quartz sands. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Mesh Size Sieve**} & \multirow{2}{*}{**Unit**} & \multicolumn{3}{c}{**Material**} \\ \cline{3-5}  & & **QS 1** & **QS 2** & **QS 3** \\ \hline Number of grains, AFS & & 56.10 & 37.29 & 22.95 \\ \hline Average grain size & mm & 0.23 & 0.34 & 0.55 \\ \hline Geometric average & mm & 0.25 & 0.41 & 0.64 \\ \hline Aritmetic average & mm & 0.26 & 0.44 & 0.66 \\ \hline Harmonic average & mm & 0.24 & 0.38 & 0.60 \\ \hline Median & mm & 0.25 & 0.43 & 0.66 \\ \hline Average grain size & mm & 0.25 & 0.43 & 0.66 \\ \hline Main fraction & \% & 87.25 & 87.54 & 95.13 \\ \hline Separation factor & - & 1.22 & 1.27 & 1.12 \\ \hline Inclination indicator & - & 0.96 & 0.95 & 0.87 \\ \hline Degree of homogeneity & \% & 75.00 & 63.00 & 84.00 \\ \hline Surface area & m\({}^{2}\)/kg & 9.59 & 5.92 & 3.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Characteristic indicators of the tested quartz sands. As depicted in Figure 1, the introduction of perlite ore PO1 and PO2 to the molding sand with an inorganic binder does not lead to a reduction in tensile strength after 24 h of hardening when compared to the molding sand without additives. However, the addition of a finer fraction results in a decrease in strength from 0.71 MPa to 0.44 MPa, attributed to the increased specific surface area with the same binder content. Remarkably, the molding sand with the addition of Hungarian perlite (PO4), despite having the smallest medium-sized grains, achieves tensile strength of 0.55 MPa. Heating samples at temperatures of 100 \({}^{\circ}\)C and 200 \({}^{\circ}\)C reduces their strength by approximately 200-300%, which is the result of the hardening of the molding sand by removing moisture. Further heating to 500 \({}^{\circ}\)C reveals that the samples achieve similar strength (0.16-0.18 MPa), irrespective of the type of additive used. At 700 \({}^{\circ}\)C, it becomes evident that the sands with additives exhibit strength that is half that of the molding sand made without the loosening additive. As the samples are heated in the range of 800-900 \({}^{\circ}\)C, the positive effect of the perlite ore in reducing the final strength becomes apparent. The molding sand without additives reaches strength of 1.26 and 1.08, respectively.