The paper presents results of initial research on the possibility of applying microwave radiation in an innovative process of making casting

moulds from silica sand, where gypsum CaSO4∙2H2O was acting as a binding material. In the research were compared strengths and

technological properties of moulding mixture subjected to: natural bonding process at ambient temperature or natural curing with

additional microwave drying or heating with the use of microwaves immediately after samples were formed. Used in the research

moulding sands, in which dry constituents i.e. sand matrix and gypsum were mixed in the ratio: 89/11. On the basis of the results of

strength tests which were obtained by various curing methods, beneficial effect of using microwaves at 2.45 GHz for drying up was

observed after 1, 2 and 5 hours since moisture sandmix was formed. Applying the microwaves for hardening just after forming the samples

guarantees satisfactory results in the obtained mechanical parameters. In addition, it has been noted that, from a technological and

economic point of view, drying the silica sand with gypsum binder in microwave field can be an alternative to traditional molding sand

technologies.

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.

The research paper presents the results of testing the strength and technological properties of molding sand with gypsum binder, the bonding process proceeded: naturally or conventionally. The tests included mass containing (parts by weight): 78 pbw. Grudzeń-Las quartz sand, 22 pbw. plaster gypsum "Dolina Nidy” and 9 pbw. water. Measurements of compressive strength, shear, tensile and bending as well as permeability and looseness were carried out on standard cylindrical samples kept in the air for 1 - 96 hours or dried at 110 oC for 1 - 8 hours. The results of the analysis were analyzed in connection with the mass structure and construction binding bridges warp grains observed with a scanning microscope (SEM). The influence of drying intensity on the bonding process and related mass properties has been demonstrated, especially from the point of view of the possibility of selection and / or intensification of a specific curing method for use in the production of gypsum binger molds and cores.

The paper presents the preliminary results of research on determining the possibilities of using available on the market commercial gypsum kinds as a binder for foundry moulding and core sandmixes. Construction gypsum and plaster gypsum, finishing coat and jewelry casting gypsum were tested. Elemental composition of gypsum kinds were carried out using a scanning electron microscope (SEM) with EDS/EDX probe, their crystal structure and phase composition was determined by analyzing the results of X-ray diffraction measurements (XRD) and thermogravimetric studies (TG-DTA). Evaluation of the mechanical properties of selected materials was carried out at the tensile strength test of the dog-bone samples after initial hardening of gypsum mortar at 25 °C for 5 h and drying at 110 °C for 24 hours. The impact of the properties of the used commercial gypsum kinds on the possibility of their use as a valuable binders in the manufacture of the foundry sandmixes for moulds and cores was evaluated. Construction gypsum and finishing coat have the highest tensile strength. Plaster gypsum and finishing coat have the longest setting time. In all tested types of gypsum, the initial water loss during heating occurs at a temperature of about 200 °C. The lowest valuable properties as a binder for sand moulding mixtures has jewelry casting gypsum mass.