Raw sand is the main raw material of coated sand, the requirements: high refractoriness.
Natural silica sand is a good raw sand of coated sand with less volatile matter, high strength particle, which is rich reserves, cheap price, meet casting requirements. Only special castings need using special sand (such as zircon sand, chromite, ceramic sand, magnetic iron ore, etc.) as the original sand.
General Requirements for Silica Sand:
A. SiO2: cast iron and non-ferrous foundry sand requires more than 90%, castings require more than 98%.
B. Acidic Sand is better than alkaline sand.
C. Clay content <0.3%.
D. Particle size distribution: centralized 3 screen, 5 sieve dispersion.
E. Grain shape: Choose silica sand with good roundness, angular coefficient should generally be less than 1.3.
Usually silica sand through the secondary scrub to meet the requirements, but in order to improve the performance of coated sand, silica sand can be pickled or high temperature active treatment (900-1200 ℃ roasting).