Investigating On The Composite Hardening Processes And Humidity Resistance Of The Sodium Silicate Sand Hardened By Microwave Heating Process

The microwave heating hardening process can make full use of the binding efficiencyof sodium silicate and obtain high strength with low addition of sodium silicate, due to theadvantages of fast speed, even heating, extreme efficiency and environmental protection.However, the development of the application is slowed down by mould materials withhigh requirements and strong moisture absorbability of sodium silicate sand cured bymicrowave heating.Three composite curing processes were researched in order to solve the problem ofhigh requirements on the pattern material.(1) The performance characteristics of composite hardening process by combiningester curing and microwave heating were investigated. The results showed that theproblem of high requirements on the pattern material could be solved and the humidityresistance of the sand samples was improved simultaneously, to some extent, by thisprocess. The4hours storage strength of the sand samples in the humidistat was increasedby70%, the hygroscopicity was decreased by14.4%, and the surface stability wasimproved significantly. Through comparing with ester curing process, the process exhibitsthe advantages of low amount added by sodium silicate, fast hardening speed and highstorage strength.(2) The performance characteristics of composite hardening process by combiningblowing hot air and microwave heating were studied. In comparison to the twicemicrowave hardening process, this process was simple and could achieve microwaveheating hardening without mould. Nevertheless, it took a longer time to reach the ejectionstrength than blowing CO2curing process and microwave hardening process, which wouldreduce the productive efficiency in the practical production. Furthermore, the measure anddevices of production, transportation and temperature maintenance of hot air wouldincrease the cost of production.(3) The performance characteristics of composite hardening process by combiningblowing CO2gas and microwave heating were studied. The results showed that thisprocess not only solved the problem of pattern material well, but also has higher storage strength of sand samples compared with ordinary microwave hardening process. When theamount of sodium silicate was1.5%weight of raw sand, the optimal technologicalparameters of the process were as follows: the experimental sand samples were blew CO2gas for5s with a10L/min flow and then heated for180s with a700W power microwave.Under the optimal condition, the compressive strength of the composite hardening sandsamples was increased by about80%compared with that by twice microwave heatingprocess.To the problem of strong moisture absorbability of sodium silicate sand bymicrowave heating hardening, the humidity resistance was improved by modifyingsodium silicate or raw sand. The results showed that there were many modifiers couldimprove the humidity resistance of sodium silicate sand, including methyl silicone oil,methanesiliconic acid sodium salt, span-80, SDBS, AEO-25, superfine sericite powder,nano SiC powder and so on. Among these modifiers, methyl silicone oil, methanesiliconicacid sodium salt, span-80, SDBS had remarkable effect on improving the humidityresistance, and the4hours storage strength of sodium silicate sand could be increased by129%,100%,102%and105%respectively when amount of addition were about15%,15%,3%and7.5%.