Effect of Silica Fume on Humidity Resistance of Sodium Silicate Binder for Core-making Process
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Copyright Ó 2020 American Foundry Society https://doi.org/10.1007/s40962-019-00405-1
Abstract In this study, an inorganic sand core that exhibited high tensile strength was fabricated by sodium silicate, silica sand, as well as silica fume. The effects of the silica fume on the properties of the sand core were studied. According to the optimal hardening process of sand core material, the mold was first heated to 175 °C and the compressed air purging continuously for 30 s at 150 °C. According to the results, silica fume is capable of enhancing the hardening speed, tensile strength and humidity resistance of sand core. The results of SEM analysis suggested that the humidity resistance of the sand core after the addition of silica fume was noticeably enhanced, and the quality of bonding bridge was better than that without silica fume at
the identical environment humidity. The results of TG/DTG test suggested that the mass loss rate of the bonded material was the fastest at 175 °C, and the mass loss tended to be stable after 600 °C. The results of infrared spectrum analysis revealed that the types of Si–O–Si characteristic peak increased when containing silica fume, which suggested that silica fume can promote the polymerization of sodium silicate.
Introduction
to fill the pores between sand particles in the core-making process, and the SiO2 content in the silica fume reaches nearly 92%. Besides, silica fume and sodium silicate binder are capable of cementing products under alkaline condition, enhancing the later strength of sand core, improving the micro-structure of sand core and enhancing the mechanical properties and humidity resistance of sand core. Compared with air hardening and self-hardening, the heat-hardening process exhibits faster hardening speed. Compared with microwave hardening, metal mold can ensure the dimensional accuracy of the sand core and reduce the wastage of mold. In this study, the performance of sand core was enhanced using a sodium silicate as binder and adding silica fume in the core-making process. As impacted by the hardening process, the reaction of sodium silicate and silica fume consumed –OH. The effect of the amount of silica fume on the properties of sodium silicate sand core was analyzed, the microstructure was tested and then delved into, and subsequently the moisture absorption mechanism of binder was analyzed. The advantages of this study are the simple preparations of binder and powder additives, the low cost of raw materials
As fueled by the advancement of casting technology, castings are developed to be more lightweight, complex and environmental friendly. Over the years, the application of organic binder sand core casting technology has suggested that organic binder sand core has high production cost and causes serious environment pollution, while the investment in workshop labor protection and production environmental hygiene has been relatively large (e.g., the use of phenolic resin and furan resin).1,2 Inorganic binder has the advantages of improving working environme
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