Experimental Investigation Of Sodium Silicate Modification Based On Dry Reclamation

The development goal of modern foundry industry is to realize the green casting. Sodium silicate sand is considered the most possible mould sand to realize green casting, but the most difficulty is the reclamation of sodium silicate used sand. The dry reclamation of the used sand has some advantages, such as simple craft, easy realizing and the least secondary pollution, but the reclaimed sand quality is not very good. Improving the dry reclamation effect and the reclaimed sand quality become the hot issures in the technical research of sodium silicate sand process.In this paper, the author analyses the high temperature reactional mechanism of silicate materials and searches the modified materials to reduce the retained strength of sodium silicate sand from the chemical reaction principle. It was studied and tested that the effect of modified sodium silicate binder and modified raw sand was added different modifying power materials. The microstructure of the common sodium silicate sand and the modified sodium silicate sand roasted in high temperature was contrasted by scanning electron microscope (SEM). And the component of the binder film was analyzed by x-ray diffraction (XRD). The results shown that it can improve the used sand collapsibility when the Ax O y? mAl 2 O3 ? nSiO2 and the Na3A1F6 were used as modified materials because the feldspar with high melting point and huge swell coefficient could be formed.It was studied that the measures of improving the collapsibility of dry reclaimed sand after recycling use, and it was analysed the relation between consumption acid value and usefulable time of dry reclaimed sand. Using self-developed modified sodium silicate binder, it can get higher normal temperature intensity and better collapsibility than common binder for dry reclaimed sand. The removing film ratio of"heating-dry"reclaimed modified sodium silicate used sand could be reached 35%, and the ratio could be reached 42% by"freezing-dry"reclaiming. When the added quantity of sodium silicate binder is unaltered it was found that the quantity of residual ester in reclaimed sand increases with the added ester quantity increasing, and more H+ would be generated from the residual ester hydrolysis process. Therefore the acid consumption value of reclaimed sand decreases, and the usefulable time of dry reclaimed sand reduces with the acid consumption value decreasing. When the added quantity of ester is unaltered the quantity of residual Na2O in reclaimed sand increases with the added quantity of sodium silicate, and more OH- would be generated from the reaction of Na2O with H2O. Hence the acid consumption value of reclaimed sand increases, and the usefulable time of dry reclaimed sand reduces with acid consumption value increasing.