Investigation On The Performance Characteristics And Humidity Resistance Of Sodium Silicate Sand Hardened By Twice Microwave Heating Process

The microwave heating sodium silicate sand process has many advantages including fast heating, high compression strength, and it can exert adequately the bonding potential of sodium silicate binder, which makes the sodium silicate binder adding quantity decreased greatly. The collapsibility and reclaim-ability of the used sand are excellent, so the process is considered as the most possible mould sand to realize green casting. But the difficult problems of the process for actual application are high requirements on pattern material and strong moisture absorbability of sodium silicate sand. Therefore, finding ways to solve the pattern material problem and improve the sand's humidity resistance becomes very important, which can make great strides in the practical application of sodium silicate sand hardened by microwave heating.A new―twice microwave heating process‖is used to study the performance characteristics. The results show that: when using―twice microwave heating process‖to harden the sodium silicate sand, the influencing time on pattern is very short, which allows using ordinary wood pattern or plastic mold and greatly decrease the requirements on the pattern material; The properties of sodium silicate sand are affected by many factors such as microwave power, microwave heating time, addition amount of sodium silicate, the modulus of sodium silicate and the experimental atmosphere humidity. The moisture absorbability of sodium silicate sand hardened by microwave heating is quite high, after being exposure in air for 4 hours, the strength of sodium silicate sand hardened by microwave heating decreases by about 40%.Aiming at the problem of high moisture absorbability of sodium silicate sand, the research on improving humidity resistance has been done according to modifying silicate sodium and brushing alcohol-based coating on the sodium silicate sand hardened by microwave heating. The results show that: there are many modifiers can improve the humidity resistance of sodium silicate sand, including polyvinyl alcohol, disodium hydrogen phosphate, xylitol, lithium carbonate, polyethylene glycol, polyurethane, ethyl silicate, silicon hydride coupling agent and diethylene glycol ether. Among these modifiers, polyvinyl alcohol and xylitol are respectively the most obvious one for improving the surface stability and increasing the storage strength, when the adding amount of polyvinyl alcohol is about 3%, the surface stability of the sodium silicate sand can be increased by 8.6% after being laid 4 hours in the humidistat, when the adding amount of xylitol is about 2%, the 4 hours storage strength of the sodium silicate sand can be increased by 64.7%. When the recipe is―100 portions of zircon powder+3 portions of li-bentonite+2 portions of phenolic resin +0.2 portions of PVB+45 portions of alcohol‖, the alcohol-based coating properties are better, and the 1 hour storage strength of the sodium silicate sand has also greater improvement after being brushed coating.This paper also preliminarily studies the temperature field of sodium silicate sand hardened by microwave heating, the temperature of different measuring points are measured under different microwave power, heating time, addition amount of sodium silicate, the modulus of sodium silicate and the heating position of sodium silicate sand. Conclusion can be drawn from the investigation: the temperature of sodium silicate sand change from high inside to low outside, and the factors mentioned have only effected on temperature scale but not on temperature distribution.