Nodular cast iron manhole cover belongs to one of the products of nodular cast iron. After inoculation and spheroidization, nodular cast iron produces spherical graphite, which makes the mechanical properties of cast iron improved. The obvious thing is that it strengthens the plasticity and toughness of cast iron, and its strength is even greater than that of carbon steel. Nowadays, nodular cast iron well cover has grown into a kind of manhole cover which is second only to gray cast iron manhole cover and is widely used in city Road.

There are two shapes of ductile iron manhole covers, round and square. The city road administration usually accepts a round manhole cover, because it is not easy to tilt the round manhole cover, so as to protect the peace of pedestrians and passing vehicles. Another reason for accepting the round plan is that the diameter of each round manhole cover is the same. If so, when the vehicle passes through the manhole cover, regardless of the rolling direction, the diameter of the ductile iron manhole cover is wider than the lower wellhead, so that the ductile iron manhole cover will not fall into the manhole.