A cast iron manhole cover is a closed structure at the top of the entrance and exit to underground facilities.It is necessary to install manhole covers in places where public facilities such as tap water,telecommunications,electricity,gas,heating,fire protection,and sanitation are installed.Next,let's talk about the types of cast iron for cast iron manhole covers.

　　With the rapid development of the economy,cast iron can be divided into:

　　1.Grey cast iron.The carbon content is relatively high(2.7%~4.0%),and the carbon mainly exists in the form of flake graphite,with a gray fracture surface,abbreviated as gray iron.

　　2.White cast iron.The content of carbon and silicon is relatively low,and carbon mainly exists in the form of cementite,with a silver white fracture surface.

　　3.Malleable cast iron.Obtained after annealing treatment of white cast iron,graphite is distributed in a cluster like manner,abbreviated as ductile iron.

　　4.Ductile iron.After spheroidizing the gray cast iron molten iron,the precipitated graphite is spherical,abbreviated as ductile iron.

　　5.Vermicular graphite cast iron.The graphite precipitated from gray cast iron molten iron after vermiculization treatment is in the form of vermiculites.

　　6.Alloy cast iron.Ordinary cast iron is obtained by adding an appropriate amount of alloying elements(such as silicon,manganese,phosphorus,nickel,chromium,molybdenum,copper,aluminum,boron,vanadium,tin,etc.).