High degree of impregnation of sodium silicate indicates that at lower concentrations moisture in the solution (due to dilution) in a gel form and covers the surface of the surrounding sand, creating a sealer, and a solid shell. Fine-grained, including refractory material in model compositions, such as fireclay powder, Marshall, zirconia well suited for creating a sealing layer and at the same time antiburning. A mixture of powders of different grain angularity and enhances these effects. In the foundry used dozens of compositions of water antiburning coatings, some of which are supplied to TU in the form of a concentrate (powder / paste in bags / drums) for dilution with water. They contain refractory filler and binder (bentonite often), and in one way or another suitable for introduction into the model, then building coverage – impregnated layer forms.
From the viewpoint of hydrodynamics impregnating these solutions and suspensions refer to the polydisperse coagulation plastic-viscous systems, which are different from our usual fluids. They are called non-Newtonian, because they have wronged Newton's law relating the speed shear viscosity and shear friction. For clay solutions and adhesives, the model tracks is important thixotropy – save property originally given shape, do not run away from overhead, vertical and horizontal surfaces with thickening (gel or zheleobrazovanii) after cessation of exposure to mechanical (flow or spraying the melting model). The structure of an elastic gel, or gel is formed as a by dispersion forces, electrostatic and hydrogen bonds (gels of gelatin, agar-agar) and by ordinary chemical bonds (proteins, ion-exchange resins). Thixotropic structure recovery – mechanically reversible isothermal process, which in our case it is possible adjustment of the viscosity of the melt wetting the model – the vacuum dehydration, addition of surfactants, pH change, etc.
The use of a filtering method applied to cavity surface vakuumiruemoy forms a sealing film of the products of melting and binding model of the sheath forms a layer impregnated under vacuum relates to novel methods of forming, in the process Development in the Department of the Institute FHPF FTIMS. 1. Patent UA 80 235 B22t 9/02.- publ. 2007, Bull. 13. Sposb formuvannya vacuum on low-melting models / Shinsky J. A., Doroshenko VS