Effect of Powder Breakdown Additives on Properties of Ester-Hardened Sodium Silicate Bonded Ceramic Sand
- PDF / 1,617,356 Bytes
- 9 Pages / 595.276 x 790.866 pts Page_size
- 38 Downloads / 245 Views
Copyright 2020 American Foundry Society https://doi.org/10.1007/s40962-020-00517-z
Abstract The sand systems containing sodium silicate binder have excellent casting quality and eco-friendly advantages. However, the poor collapsibility of sodium silicate bonded sand (SSBS) makes it difficult for foundries to recycle used sand. Thus, many investigations have been performed recently to improve the collapsibility of SSBS. In this study, the powder breakdown additives alumina (Al2O3), silicon carbide (SiC) and boron nitride (BN) were used as modifiers to further improve the collapsibility of ester-hardened sodium silicate bonded ceramic sand (SSBCS) on the basis of modified sodium silicate, and the specific parameters were optimized by orthogonal experiments. The results of orthogonal experiment showed the optimum additive amount of Al2O3, SiC and BN were 0.4%, 0.3% and 0.1% of ceramic sand, and the addition of modifiers effectively
increased the 1h tensile strength and further reduced the residual strength of the SSCBS. The experimental results indicated that the difference of the linear expansion coefficient between the modifiers, the new phase AlN formed by the modified sand sample and the phases Na3PO4, Na4B2O5 formed by the unmodified sand sample effectively accelerated the generation of many coarse pores and very big cracks on the bonded bridge in the process of heating at 950 C and cooling, thereby resulting in the improvement in the collapsibility of SSBCS.
Introduction
et al.16 investigated the modification mechanisms of Na5P3O10 on SSBS. The results of their study confirmed that the adhesive film of sand sample was prone to crack in the hot and cold change process, which was attributed to the difference in the shrinkage capacity between phosphate and silicate, thereby leading to a remarkable improvement in the high-temperature collapsibility of SSBS. Yang17 modified sodium silicate with four different ultra-fine powders Al2O3, ZnO, TiO2 and MgO, and the addition amount of the powder was 3.5% of sodium silicate binder. They found that the different expansion rate of ultra-fine powder and sodium silicate system could tear the vitreous body and reduce the residual strength of moulding sand. And, ZnO had the most obvious modification effect due to its small particle size and better particle distribution.
The foundries renewed interest in inorganic binders with the increasing demands for the protection of the environment and the growing lack of raw materials available for casting production.1–4 Sodium silicate binder is considered to be the most likely inorganic binder for achieving green production. Therefore, it is important to develop and implement new methods or processes of modified sodium silicate binders for meeting the requirements of casting production.5–7 The sodium silicate bonded sand (SSBS) prepared with this binder is used mainly in the production of moulds and cores due to its good strength and simple processing operation.8–11 However, there are some obvious disadvantages in the application
Data Loading...
