Investigation Of Sodium Silicate Binder Modified By Ultra-fine Powder

As environmental protection becoming our social recognition day by day,technological innovation should be taken as a serious task in many industrial productions which can cause pollution. Specially, the development on the green binder for environmental protection will be the key point in the casting industry. The sodium silicate sand can get a position in green clean casting comparing to other mould sands for its advantages of achromatic color, tastelessness, non-toxic, and so on. Furthermore, the sodium silicate sand process can get rid of irritant odor or harmful gas during mixing, molding, pouring and knocking out. However, the defects, such as bad collapsibility and the difficulty in sand reclamation, restrict the development of the sodium silicate sand process, which cause the used sand pollute the environment heavy. So the sodium silicate sand becomes the"double-edged sword"of the environmental protection, but a new hope is appeared for the ultra-fine material technology (that is nano-meter material technology) development.In this paper, it is discussed that the possibility on the ultra-fine material modified sodium silicate binder at first, and then a series of single factorial experiments (including ultra-fine montmorillonite powder, ultra-fine mica powder,sorbitol, dehydrated borax, and so on) were made to demonstrate the influence on the performance of the sodium silicate sand. The results indicate that the ordinary temperature 24hr strength has increased and the residual strength has decreased by adding ultra-fine mica. Next experiments are made for the sorbitol and the borax, the results show that adding ultra-fine mica powder and sorbitol can get higher 24h strength and lower residual strength, and adding ultra-fine mica powder and dehydrated borax can increase the resisting wet ability. The third are an orthogonal experiments that test the effects of ultra-fine mica powder, sorbitol and dehydrated borax on the sodium silicate binder to get an optimum modified material. Finally, an SEM photos are taken to explain the modifying reason of ultra-fine mica powder.Above experiment results indicate that:(1) The ultra-fine mica powder is a good modifying material for sodium silicate binder, its function is mainly to increase the 24h strength and reduce the residual strength of the sodium silicate sand. When the adding amount of ultra-fine mica powder is about 1.5%, the 24h strength can be increased about 21% and the residual strength be decreased about 34.5%.(2) The sorbitol can help the ultra-fine mica powder to improve the properties of the sodium silicate binder, not only increasing 24h strength but also reducing residual strength. When about 1.5% ultra-fine mica powder and about 1.0% sorbitol are adding to the binder, the 24h strength could be increased about 32.6% and the residual strength would be decreased about 38.2% for the sand.(3) The borax can increase the 24h strength and resisting wet ability of the sodium silicate sand, the dehydrated borax also possesses the abilities of quicking harden velocity of the sand and improving the decentralization of mica powder in the binder.(4) The optimizational proportion of the three materials from the orthogonal test is 1.5% ultra-fine mica powder, 0.5% sorbitol and 3% borax. The 24h strength of the modified sodium silicate sands is increased about 35% and its residual strength is decreased about 34.1%.