About cast iron frame and manhole
Cast iron is an alloy of iron, carbon, and silicium. Most of it has been made of iron (more than 95 percent of weight), almost 2.1 to 6.2 percent from carbon, and almost 1 to 3 percent from silicium. However, steel is made like cast iron by adding carbon to iron but its main difference is in the amount of applied carbon. Steel has less than two percent carbon but there is more than 2 percent carbon in cast iron.
Cast iron frames and manholes have been the primary option for covering the open manholes to prevent the falling of people into them for many years. They are used for different applications such as electricity, telecommunication, water and sewage, gas manholes, and urban applications. The popularity of cast iron has roots in the capability of casting different shapes with the appropriate final price and also their high durability. The main application of cast iron manholes is covering the manhole openings, access holes to underground lines. Another application of cast iron frames and manholes is their role in conveying the rainwater and surface runoff to urban sewage systems. The cast iron manholes are produced and used in different dimensions and shapes (square, rectangular, and circular) due to broad application in different industries and the easiness of casting.
Cast iron manholes are usually made of two groups of gray cast iron and ductile cast iron. Ductile cast iron manholes have higher strength compared to gray cast iron. A gray cast iron manhole has more weight than a ductile cast iron manhole with the same dimensions. The lower weight of ductile manholes makes their transportation and installation easier. Also, the length change and higher tensile strength are some other advantages of ductile cast iron manholes relative to the gray type. However, gray cast iron is cheaper than ductile cast iron.
The weight and price of cast iron manhole
The weight and price of sewage manholes are the most important parameters that should be considered in the selection of manholes. The weight of manholes should not be too low because there is a chance of theft. Also, due to not fully covering and touching the underframe, they produce noise when motor vehicles pass over it. The high weight of manholes is considered one of their disadvantages too due to the difficulty of transportation, installation, and opening of them.
Generally, the weight and price of cast iron manholes do not have a stable value and are functions of shape, dimension, and bearing capacity. For example, circular cast iron with a diameter of 80 centimeters which is going to be used only in the regions used by pedestrians and bicycles, has a different weight and price compared to a square iron cast with 50 centimeters side which is going to be used in an airport. But, this point is generally true about cast iron manholes that these manholes have more weight compared to other manhole types which cause more expenses in their transportation and installation. Besides more weight, higher prices of them compared to other types in the market are considered another main disadvantage of cast iron manholes. These factors cause cast iron manholes to lose the competition in the market to other types of manholes.
Standards
European standard of EN 124 is the most recognized standard for the production of cast iron manholes. Also, the ISO1083 standard is used for the production of ductile cast iron manholes.
