Abstract
Sand binding systems can have a significant impact on the nature of the casting skin formation. In particular, the binder containing elements such as S, O and N may adversely affect the structure of the layer. As in the case of spheroidal graphite cast iron (SGI) and compacted graphite cast iron (CGI) main factor causing the degeneration of graphite in the surface layer of the casting is sulfur, therefore these binding systems (binder) which contain sulfur have been thoroughly discussed here. The following are sand mold technologies: furan, acid catalyzed, phenolic, acid catalyzed, hot box, warm box and Shell (Croning) process. Sand molding with the use of furfuryl resins technology is presented in detail due to their widespread use in casting both cast iron and cast steel. To reduce the thickness of the surface layer, which may be the adverse effect of sulfur on the degeneracy of the graphite, S content in molding sand should be less than 0.15 % mass, and even below 0.07 % mass. Sand binding systems can have a significant impact on the nature of casting skin formation. In the case of green sand, moisture promotes the formation of the ferritic rim (Reisener, Br Foundryman 55:362–369, 1962; Matijasevic et al. Trans AFS 82:571–622, 1974; Narasimha and Wallace, AFS Trans 83:531–550, 1975). Research carried out for sand mold with sodium silicate and phenolic urethane has shown that SGI and CGI castings made in the first sand mold is pearlitic rim occurred, and in the second sand mold this occurrence is not found (Boonmee and Stefanescu, Foundry Trade J 186:225–228, 2012). Regarding the effect of the molding sand on the nature of the casting skin formation, they can be divided into molding sand: with binders containing sulfur (i.e. furfuryl alcohol and urea-formaldehyde resin) and the molding sand that are not bound with binders not containing sulfur (i.e. phenol-urethane resin ). From the point of view of the top layer the sulfur-containing molding sand is much more important, due to its adverse effect on the formation of spheroidal graphite.
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Holtzer, M., Dańko, R. (2015). Molds and Cores Systems in Foundry. In: Microstructure and Properties of Ductile Iron and Compacted Graphite Iron Castings. SpringerBriefs in Materials. Springer, Cham. https://doi.org/10.1007/978-3-319-14583-9_2
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