The part is made by the mathod of precoated sand casting.  The precoated sand casing also called shell casting, suitable for casting small size products in large quantity.  It has the advantage of high accurancy and smooth surface, thus saving a lot of machining cost.  The shell is shaped with high temperature by machine, increasing the effiency greatly and reduce the cost.  The material applies for grey casting iron and ductile casting iron including GG20, GG30, GGG50 etc.