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Abstract

This paper presents initial findings from research into the possibility of using gypsum binders in quartz moulding sand that could be used in the production of casting moulds and cores. For the purposes of the research two commercial types of gypsum were used as binders: building gypsum and gypsum putty. Dry components of moulding sand i.e. medium quartz sand and gypsum were mixed in proportion of 89/11 parts by weight. In order to achieve bonding properties for the binders, 5 parts by weight of water was added to the mixture of dry components. After 24 hours of adding water and mixing all the components, the moulding sand, naturally hardened, was subjected to high temperature. The moulding sand thus produced, i.e. with cheap and environmentally-friendly gypsum binders, was eventually analysed after heating (at temperatures of 300oC, 650oC and 950oC) and cooling in order to determine changes in the following parameters: LOI – loss on ignition, chemical composition and pH. Moreover, investigated were bonding bridges, before and after the moulding sand was roasted. The research results revealed differences in the structure of bonding bridges and the occurrence of automatic adhesive destruction for both types of gypsum binders. For two types of moulding sands under the investigation of the LOI exceeded 2.59wt.% (with building gypsum) or 2.84wt.% (with putty gypsum) and pH increased to ca. 12 as a result of increasing roasting temperature from 300oC to 650oC. Next, roasting at 950oC decrease value of LOI in both types of moulding sands. Moulding sand with builoding gypsum roasted at 950oC revealed a return to the value of pH parameter measured prior to annealing.
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