Ya Aba manhole covers manhole covers well 盖雅安 ductile cast iron covers Ganzi Aba Ganzi cast iron covers cast iron covers manhole covers production process (a) stringent requirements for 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-treated ductile iron manhole covers with a higher ball ductile materials, production processes to implement clear sand processing standards in accordance with national requirements, the asphalt painted galvanized corrosion, rust paint, neat appearance, beautiful, suitable for city roads transformation covers replacement product has the following five anti-function: anti-settling, anti-shifting, noise, anti-theft, anti-bounce.