The aim of the hereby paper is to present the developed model of determining the volume and surface porosity based on the main fraction

of polifractional materials, its experimental verification and utilisation for the interpretation of effects accompanying the formation of a

moulding sand apparent density, porosity and permeability in the blowing processes of the core and moulds technology.

The results of researches of sorption processes of surface layers of components of sand moulds covered by protective coatings are

presented in the hereby paper. Investigations comprised various types of sand grains of moulding sands with furan resin: silica sand,

reclaimed sand and calcined in temperature of 700oC silica sand. Two kinds of alcoholic protective coatings were used – zirconium and

zirconium – graphite. Tests were performed under condition of a constant temperature within the range 30 – 35oC and high relative air

humidity 75 - 80%. To analyze the role of sand grains in sorption processes quantitavie moisture sorption with use of gravimetric method

and ultrasonic method were used in measurements. The tendency to moisture sorption of surface layers of sand moulds according to the

different kinds of sand grains was specified. The effectiveness of protective action of coatings from moisture sorption was analyzed as

well.

Knowledge of the role of sand grains from the viewpoint of capacity for moisture sorption is important due to the surface casting defects

occurrence. In particular, that are defects of a gaseous origin caused by too high moisture content of moulds, especially in surface layers.

The paper presents the results of basic research on the influence of the properties of sand grains on electrical properties of water glass

moulding sands. It shows electrical properties of the main component – sand grains, crucial to the kinetics of moulding sands heating, such

as permittivity εr and loss factor tgδ. Measurements were carried out with the use of the perturbation method for silica, chromite and

olivine sands of different mineral, chemical composition and particle size distribution, as well as for moulding sands with water glass

grade 145. Analysis of the results of measurements of electrical properties shows that all moulding sands are characterized by a similar

permittivity εr and loss factor tgδ. It was found that the electrical properties and the quantity and quality of other components may have

a decisive influence on the effectiveness and efficiency of the microwave heating of moulding sands with sand grains. In determining the

ability to efficiently absorb the microwave radiation for mixtures which moulding sands are, the impact of all components influencing their

individual technological parameters should be taken into account.