Foundations Of Key Technology Of The Sodium Silicate Sand Casting Process Curing With Microwave

Sodium silicate sand cured with microwave can exert adequately the bondingpotential of binder and so the sand mould with low binder addition would achieve higherstrength and better collapsibility. Beside these, microwave curing possesses manyadvantages such as fast curing, clean production, and so on.The dissertation had carriedout in order to solve the key problems of this microwave curing process.（1）. The heating, strength and storage characteristics of the traditional microwavecuring process for sodium silicate sand were investigated, and the curing time, microwavepower, binder addition and modulus, storage time and circumstance would influence thesand mould strength. Especially, the mechanism of humidity absorption of sodium silicatesand cured with microwave was analyzed.The temperature field distribution of standardcylindrical sand specimen was studied, and the results showed that there was a positivetemperature gradient from inside to outside within the samples of sodium silicate sandsamples cured with microwave. Furthermore, heat transfer formula was deduced.（2）. Four less-using mould, even non-mould moulding processing were developed tosolve the problem of high-performance mould in the microwave oven, that was the firstcuring for demoulding and the second microwave curing for service strength.1).Twice microwave curing processing: The sodium silicate sand specimens werecured in microwave oven for10-30s to the stripping strength of15KPa, and then the sandand mould were taken out from microwave oven, and the sand specimens were demoulded,after which the sand specimens were cured for90-100s in the microwave oven to the sandservice strength, and this processing could greatly decrease the requirements on the mouldmaterial and increase the efficiency of curing.2).Ester―microwave composite curing: The sodium silicate sand specimens werecured by ester fistly for demoulding. A system research of influence factors, included esteraddition, curing time and power, on the strength and moisture resistance properties of thisnew process were investigated. The humidity resistance of the sodium silicate sand wasimproved after the production of hydrophobic materials, glycerol and sodium acetatetrihydrate and high-modulus sodium silicate from the ester curing process. 3).CO₂―microwave composite curing: The sodium silicate sand specimens werecured by CO₂fistly.The influence factors, included CO₂gassing flow and time, curingtime and power, on the strength and moisture resistance properties of this new processwere investigated. The humidity resistance of the sodium silicate sand was improved afterthe production of hydrophobic materials, sodium carbonate decahydrate and high-modulussodium silicate from the CO₂curing process.4).Hot air―microwave composite curing: The sodium silicate sand specimens werecured by hot air fistly.But the demoulding time was longer and humidity resistance wasworse, and the thermal insulating equipment was complex.（3）.The new modifiers and three coatings were developed to solve the high moistureabsorbability of sodium silicate sand cured with microwave.1).Many modifiers, such as nano Si3N4, SiC, sericite and methyl sodium silicate,methyl silicone oil and sodium dodecyl sulphate, span-80, were used to improve humidityresistance. The results show that: the4h storage strength in humidistat with0.2%nanoSi3N4increased about93.7%in which the modifier was the minimum, and the modifiedsodium silicate sand with15%methyl silicone oil increased about129.52%in which themodified effect was the best.2).The alcohol-based coating made of PbO-ZnO low-temperature ceramic powder（aggregate） was fired to form coating in the sodium silicate sand. The results show thathumidity resistance of the sodium silicate sand had significantly greater improvement aftersurface coating, the4hour storage strength can be increased by2.33times. And three newkinds of phase were produced: Al₂TiO₅, NaAlO₂, and PbTiO₃, which were the mainreasons for humidity resistance of sodium silicate sand increased by surface coating.3).The coating of eutectic lithium salts （0.38LiOH-0.62LiNO₃） were sprayed on thesurface of water glass sand and then sintered by the microwave energy to obtain glassymembrane for its lowest eutectic point of175.7℃，so the humidity resistance of waterglass sand cured with microwave was improved greatly. The results showed that the curingtemperature of coating sand mould was about370℃，which was higher than thetemperature （110℃） of common one by the microwave energy，and the strength of coatingsand mould was higher than common one. The4h storage strength of coating sand mould in humidistat with relative humidity of98-100%increased by two times comparing withthe common microwave curing one.4).The microwave low-temperature coating, which was made of PbO-ZnO ceramicpowder,3.5%V2O₅,2.5%Al₂O₃,2.5%TiO₂,20%0.38LiOH-0.62LiNO₃eutectic lithiumsalts could produce Zn₂TiO₄, Pb₅O₈, PbTiO₃, PbSiO₃, Pb₆Al₂Si6O₂1and Al₂SiO₅in thesurface of the sodium silicate sand mould cured with microwave, and the coatingbeginning sintering temperature was259.6℃, but the curing temperature was390℃. The4h storage strength of coating sand mould in humidistat with relative humidity of98-100%increased by six times comparing with the common microwave curing one.4. A new process of wet reclamation by biologically treating the waste waterproduced during the wet reclamation process of used sand was studied in this dissertation.Comparing three diatom species of Melosira varians, Cyclotella hebeiana and Nitzschiapalae （for short N. palea below）, and N. palea was seleted as the optimum diatom to treatthe waste water. So the domestication was used in the N. palea and many influence factorson the reclaimation were investigated as following: temperature25℃, irradiance5000lux,illumination time14h/d, N concentration80mg/L, P concentration50mg/L, N: P14:1,Fe3+concentration2.28mg/L, Mg2+concentration16mg/L, thus a optimized research wasdone to get the best reclamation effect on basis of these data.And the waste water cyclemethod was tested.