Impact of Density Degree and Grade of Inorganic Binder on Behavior of Molding Sand at High Temperature

Abstract

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 (ϱ 0 ). 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/cm 3 . 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.

Archives of Foundry Engineering

“…4), hardened by classical drying (CD), reacted more slowly to the increasing ambient temperature in the vicinity of the samples. These results may contradict a previous study [21] subjected to the impact of moulding sand densification on their behaviour in higher temperature, however in this study was used only one method of SSBS physical curing (MW). The reasons behind this phenomenon cannot be put down to the issue of filling the space between grains with an insulator (air), but to differences in the process of hardening in which atmospheric CO2 participates to a greater (CD) or lesser (MW) degree.…”

“…Previous SSBS studies for the sodium silicate binders with a molar module ranged from 3.4 to 2.9 [21] shown that mould compaction affect the speed of thermoplastic deformation.…”

“…Referring to research [21] the first analysed parameter was average apparent density expressed in g/cm 3 . Changing this parameter in SSBS by 0.1 g/cm 3 causes significant 40% change in strength parameters [22] at ambient temperature, and also affect the rate of thermoplastic deformation [21]. The weight of the samples hardened/dried and cooled for the purposes of mHDT was compared to their capacity of 18 cm 3 .…”

New Possibilities in Thermal Analysis of Molding Materials

“…The behavior of the most commonly used molding mixtures have been thoroughly studied by previous authors on various instruments [1][2][3][4]. However, the variety of organic binder systems is updated time and again based on customer requirements as well as economic and environmental considerations.…”