Effect of Core Box Temperature, Hot-Air Parameters and Micro-Silica Powder on Tensile Strength of Sand Core

Abstract

A study was conducted on the effects of various influencing factors in the compound hardening process, including core box temperature, such hot-air parameters as temperature, pressure and blowing time, as well as micro-silica powder, on the tensile strength denoted as σ0 of the prepared sand core after cooling to room temperature, on the basis of which the hardening mechanism of the micro-silica powder was revealed. The sand core was bonded using modified water glass. The single factor test was conducted to achieve the optimal compound hardening process for the sand core. According to the research results, the introduction of hot air improved the σ0 of sand core significantly from 1.89 MPa to 2.20 MPa, in comparison with that hardened only by heating the core box. After the addition of micro-silica powder, the σ0 of sand core was further improved to 2.58MPa. According to the results of SEM analysis, the Si atoms in the water glass contributed to improving the modulus of the water glass after the addition of micro-silica powder, thus promoting the water glass to gel when heated. As indicated by FT-IR analysis, the concentration of Si–O–Si bonds was increased as a result of the reaction occurring between micro-silica powder and water glass in the hardening process, implying that micro-silica powder can be effective in enhancing the polymerization of water glass.