Effect on mold shell drying
Environmental humidity has a great influence on drying rate. With the increase of environmental humidity, the drying rate of shell decreases and the drying time increases. When the ambient humidity exceeds 80%, the drying time will be greatly extended, which must be strictly controlled in production.The environmental humidity of the surface layer should be good at 60%~ 70%, and that of the back layer should be good at 40% ~ 60%.
Wind speed has obvious influence on the drying rate of silica sol shell. As the wind speed increases, the drying time decreases. In order to accelerate the drying time of silica sol shell, the wind speed has been increased to 6-8m /s in foreign countries in recent years, which achieve a good result. The breeze should be rotating, not blowing in one place, not be too long. Some domestic factories pay much attention to the wind speed..
Increasing the ambient temperature can accelerate the evaporation of water and shorten the drying time of shell. However, the ambient temperature will affect the thermal expansion and quenching of the melting module, thus affecting the size precision of the casting and even causing the casting deformation. Therefore, the drying time of mold shell cannot be shortened by increasing the ambient temperature. Shell drying should be under a certain temperature (22 ~ 25 ℃), and the high precision casting production be more narrow temperature range.。
Types of refractory
The drying rate of shell with different refractory materials is also different. Generally speaking, alumina and kaolin clinker shells dry faster, corundum shell comes second, while the zirconium sand shell dries more slowly. This may be because bauxite and kaolin clinker are porous materials with large specific surface area, which can absorb a lot of solvents quickly, thus increasing the concentration of silica sol and accelerating the gelation, that’s the reason why this kind of mold drying rate is faster than others.