What is a Manhole Cover
Chances are you regularly walk over manhole covers on a daily basis, especially if you are a city dweller. Manhole covers are simply the removable cover that serves as a lid to a manhole. This cover serves several purposes, the most obvious of which, is preventing pedestrians from falling into these oftentimes quite deep access points.
Manhole covers also serve the purpose of keeping unauthorized personnel from accessing manholes and, in turn, keep sewer or stormwater systems safe. Manhole covers also function as a source of ventilation to prevent sewer or stormwater gases from entering residences and as an easy entry point for maintenance workers to access sewage and stormwater lines.
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Manhole Cover Materials
Traditionally, manhole covers have been constructed of either cast iron, concrete, or even some combination of the two. This is because both of these materials are inexpensive, durable, and heavy enough to stay in place. However, similarly to manholes, technology has led to a variety of alternative manhole cover materials, including composite, fiberglass, and plastic. In this section, we discuss the many different types of manhole covers including cast iron manhole covers, plastic manhole covers, and composite manhole covers.
Cast Iron Manhole Covers
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Historically manhole covers have been manufactured from cast iron [3], which is iron that is melted down and poured into a mold. When it comes to manhole cover material, gray cast iron and ductile cast iron are preferred as they are both economical and extremely durable. Gray cast iron is made up of iron alongside alloys including carbon and silicon. It is the carbon that results in the strength associated with cast iron. Ductile cast iron differs from gray cast iron because manganese is added to the molten iron during the casting process, which influences the formation of the carbon, resulting in an even stronger finished product.
Common Issues with Cast Iron Manhole Covers
In more recent years a variety of alternative materials have increased in popularity when it comes to manufacturing manhole covers. This is due to many issues associated with cast iron manhole covers. Some of the top drawbacks of cast iron manhole covers include scrap metal theft, injury to workers associated with the weight, and corrosion.
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