Nodular cast iron has high strength and good toughness, so nodular cast manhole covers are about 30% lighter than gray cast iron manhole covers of the same type. The grade of nodular cast iron is QT500-7, the molten iron temperature is not lower than 1456℃, and the rare earth ferrosilicon-magnesium alloy and coke with low sulfur content are added during the spheroidizing treatment, and the spheroidizing level is above grade 3. The mechanical properties of the nodular cast iron specimens are as follows:

　　 Tensile strength: 500N/MM 2

　　 Elongation rate: 7%

　　The pressure test failure load of the manhole cover exceeds the national industry standard;

　　The adoption standards are as follows:

　　 CJ/T3012-93 "Cast iron inspection manhole cover" stipulated standard

　　EN124 "Sluice Cover and Manhole Cover for Driveway Walkway"

　　The size deviation of the manhole cover and the base complies with the national standard