Deyang, Mianyang, ductile iron manhole covers manhole covers covers Guangyuan, Mianyang, Deyang cast iron covers cast iron covers Guangyuan ductile cast iron manhole cover covers the production process (a) stringent requirements of chemical composition, carbon and silicon content of the original liquid iron requirements than gray iron, ductile lower cast iron manganese, phosphorus, sulfur content (b) of molten iron tapping temperature higher than gray cast iron, to compensate for the ball, bred loss treatment temperature of molten iron (III) were ball handling, which was added to the iron ball agent (four) were added inoculant inoculation (five) ductile iron poor liquidity, a larger contraction, and therefore requires a higher temperature and larger casting gating system size, rational application of the riser, chills, sequential solidification principles (six) heat treatment