Organobentonite-Bonded Moulding Sands with Carbon Additives

At the stage of preparing SN/PAA organobentonite-bonded moulding sands (organobentonite-bonded green sands), it was found that a higher proportion of the polymer adversely affected the moulding sand already at the stage of mixing. The high viscosity of the system in contact with water hindered the accurate homogenisation of all the components, which resulted in significant deterioration of the technological and strength properties. Therefore, moulding sands were prepared with organobentonite of the lowest polymer content in the system (i.e., SN/5PAA). In this case, the process of mixing the components occurred effectively. The model moulding sand was bonded with unmodified calcium bentonite (SN).
Due to the risk of insufficient efficiency of the polymer in organobentonite as a carbon additive in the technology of synthetic moulding sand, technological and mechanical tests of SN/5PAA bonded moulding sand with a mixture of popular lustrous carbon carriers: coal dust and synthetic resin were also carried out. In addition, shungite was used as a new carbon additive in the field of foundry engineering, whose effectiveness and reduced environmental footprint were confirmed in the patent application (invention project entitled: “Bentonite-bound moulding sand with carbon additive”, application no: P.439688). Two moulding compounds were prepared: a base compound bond with SN/5PAA modifier and a reference compound bond with SN bentonite.
The moulding compound was prepared by mixing the ingredients in a WADAP LM-1 type rotary mixer: 100 parts by weight of silica sand, six parts by weight of binder material and water. Detailed data on the proportions of the individual components are contained in a collective table providing information on the composition of all the moulding sands analysed in this work (Table 3). The technological and mechanical properties of the moulding sand were assessed depending on the water content, so its share in the moulding sand was not taken into account in Table 4. The composition of the moulding sand was determined on the basis of literature data [4 ,34 ]. Mixing of matrix and free-flowing binder material was carried out for 1 min, then after the introduction of water, the whole mixture was mixed for another 3 min. The moulding sand was sieved through a 4 × 4 mm mesh sieve. After forming standard shapes, a series of determinations of selected technological and mechanical properties were made. Due to the research on changes in the analysed indices of the moulding sands depending on their humidity (by adding water), the moulding sand was put back into the mixer bowl, another portion of water was added and the mixing process was repeated for 3 min. The tests were carried out at air humidity of about 27% and ambient temperature in the range of 24–26 °C.
Two series of moulding sand with carbon additives were prepared. The first, in which SN/5PAA acted as the binding material, was prepared with mixtures of coal dust and hydrocarbon resin (P/HCR), shungite and hydrocarbon resin (Sz/HCR), and coal dust and shungite (P/Sz). The second batch of SN-bond moulding sand constituted the reference moulding sand to the first batch of sand and was prepared with the addition of analogous coal mixtures.
The methodology for preparing the moulding sand was analogous to that described above, except that an appropriate amount of a given mixture of carbon additives was initially introduced into the rotary mixer along with the matrix and binder material. The amount of shungite was determined by the carbon content compared to the coal dust and HCR resin, hence its mass proportion in the moulding sands was proportionally higher than that of the other glossy carbon carriers. Table 4 summarises the compositions of the prepared moulding sands.
Table 4 also includes the composition of the moulding sand, in which the role of the binding material was played by commercial sodium bentonite and the carbon carrier was a bentonite-Kormix mixture. S and S/Kormix bentonite-bonded moulding sands were prepared similarly to moulding sands containing unmodified SN bentonite with carbon carriers and were a real standard of technological and strength properties that should characterise a high-quality material binding grains of mineral matrix in the technology of synthetic moulding sands.