Organobentonite Binder for Binding Sand Grains in Foundry Moulding Sands

Abstract

A series of studies related to the production of organobentonite, i.e., bentonite-poly(acrylic acid), and its use as a matrix grain-binding material in casting moulding sand is presented. In addition, a new carbon additive in the form of shungite was introduced into the composition of the moulding sand. Selected technological and strength properties of green sand bond with the obtained organobentonite with the addition of shungite as a new lustrous carbon carrier (Rcw, Rmw, Pw, Pw, PD) were determined. The introduction of shungite as a replacement for coal dust in the hydrocarbon resin system demonstrated the achievement of an optimum moulding sand composition for practical use in casting technology. Using chromatographic techniques (Py-GC/MS, GC), the positive effect of shungite on the quantity and quality of the gaseous products generated from the moulding sand during the thermal destruction of its components was noted, thus confirming the reduced environmental footprint of the new carbon additive compared to the commonly used lustrous carbon carriers. The test casting obtained in the mould of the organobentonite moulding sand and the shungite/hydrocarbon resin mixture showed a significantly better accuracy of the stepped model shape reproduction and surface smoothness compared to the casting obtained with the model moulding sand.

Thermostability of Organobentonite Modified with Poly(acrylic acid)

“…As the temperature increases, the decomposition of poly(acrylic acid) chains proceeds (230-300 • C). In the temperature range of 300-500 • C, PAA completely decomposes with the release of gaseous decomposition products from a group of organic compounds, including BTEX, as confirmed in the authors' publication [24]. The part of the polymer that has not decomposed at about 550 • C may contain carbonized carbon, which is important for the use of organobentonite as a binder from generating lustrous carbon.…”

“…The focus was on determining the emission of CO 2 and volatile compounds from the BTEX group, as the determination of BTEX compounds is a standard for evaluating the quality and environmental protection aspects of the materials used in foundries. However, in publication [ 24 ], the authors’ team provides additional knowledge in this area. Figure 5 shows the Py–GC/MS results of the PAA and samples (for retention data and peak identification, see Table 2 ).…”

“…The authors conducted technological tests of SN/PA organobentonite-bonded masses and confirmed the positive effect of PAA on casting quality. The made casting had a better surface quality than a casting made in the classical way, i.e., in a mold made of sodium bentonite-bonded molding sand [ 24 ]. It was found that the dehydroxylation of montmorillonite (MMT) in bentonite starts at a temperature of about 500 °C.…”

“…After separation from the unreacted polymer, each organobentonite precipitate was dried to a constant weight at 105 °C and then milled in an agate mortar. The first series of organobentonites were obtained: SN/5PAA, SN/15PAA and SN/25PAA [ 13 , 24 ].…”

“…The research results in this area conducted for the new binding material under consideration (organobentonite MMT-PAA) have already been largely published. They found that the produced organobentonite meets the requirements for binding materials, and the resulting casting has no surface defects [ 13 , 17 , 24 ]. The only remaining issue is to discuss the research topic related to its thermal stability.…”