Kinetics of Penetration and Drying of Protective Coatings into the sand Mold under Conditions of Variable Porosity of the Mold

This paper presents a study of moisture migration in the surface layer of molding compound during the application and drying of the protective coating. The purpose of the ongoing research is to understand the mechanism of migration, that is, the penetration and drying of moisture from the protective coating applied to the mold or core. Hence, the introduction describes the transport of moisture in porous materials, as well as the process of moisture exchange between the environment and porous materials. In addition, the effects of poor drying of the protective coating applied to the core or mold are presented. In the experiment, a new test rig was used to measure the resistance of the porous medium. The change in resistance of the molding compound occurs due to moisture migration. Test cores were made of molding compound with phenol-formaldehyde resin. To measure the resistance continuously in the mass, electrodes were placed at a depth of 1, 2, 3, 4, 5, 8, 12, 16 and 20 mm. A zirconium alcohol coating was used in the tests. The coating thinner is isopropyl alcohol. The “conventional” viscosity of the coating was determined using a 4mm mesh Ford cup and was 20s. During the study, the course and kinetics of the diluent migration process from the protective coating applied to the core into the top layer of the molding sand were determined, and the effect of the grain size of the sand matrix on the process was determined. Fractionated grain matrix with average grain sizes of 0.20 and 0.63 mm was used to prepare cores. The experiments were conducted under constant climatic conditions. The air temperature was T = 35oC, and the humidity was H = 35%. The research shows that the size of pores has a significant impact on the process of moisture sorption and desorption from porous material. For moulding sand with a grain size of Z=0.20 mm, the drying time is more than four times shorter than for sand with a grain size of Z=0.63 mm.