The main bulk density representation in the molding material is opening material, refractory granular material with a particle size of 0.02

mm. It forms a shell molds and cores, and therefore in addition to activating the surface of the grain is one of the most important features

angularity and particle size of grains. These last two features specify the porosity and therefore the permeability of the mixture, and

thermal dilatation of tension from braking dilation, the thermal conductivity of the mixture and even largely affect the strength of molds

and cores, and thus the surface quality of castings. [1]

Today foundries, which use the cast iron for produce of casts, are struggling with surface defects on the casts. One of these defects are

veining. They can be eliminated in several ways. Veining are foundry defects, which arise as a result of tensions generated at the interface

of the mold and metal. This tension also arises due to abrupt thermal expansion of silica sand and is therefore in the development of

veining on the surface of casts deal primarily influences and characteristics of the filler material – opening material in the production of

iron castings.

This paper describes the technology for the production of precursors (space holder material) used to form the complex internal structure of cast metal foam. The precursor material must exhibit sufficient refractoriness, resist contact with liquid metal and at the same time should exhibit good collapsibility after casting. With regard to the greening of foundry production, the focus of this paper was on materials that could exhibit the above properties and at the same time do not have a negative impact on the environment. In this paper, the technology for the production of spherical precursors from a self-hardening mixture with a geopolymer-based binder system is described and verified. The motivation for the choice of material and all the sub-steps of the process – molding into the core box, tumbling, including the necessary accompanying tests of the mechanical properties of the core mixture being verified – are described.