Author:Site Editor Publish Time: 2021-11-15 Origin:Site
Manholes (alternatively personholes, utility holes, maintenance holes, or sewer holes) are generally found in urban areas, in streets and occasionally under sidewalks. A manhole is an opening to a confined space, allowing maintenance workers to reach underground public utilities like sewers, storm drains, gas pipelines, etc. Manholes are required so that workers can inspect, maintain and upgrade these units. Manholes are always companied by manhole covers as the covers prevent people from falling into manholes.
It is said in the early nineteenth century those manholes for water or town gas pipelines were the first to be constructed with the cover. Sadly, none of them were lucky enough to survive the long history.
Over the years, the construction of the manhole covers has changed. Here's a brief introduction of the manhole cover manufacturing process.
Cast iron takes the largest proportion of all the materials made into a manhole cover. The iron melted and then cast in a mold comes out what we called cast iron. Typical manhole covers are cast using gray cast iron which contains the element iron and the alloying elements carbon and silicon. The addition of alloying elements aims to increase the strength and durability of cast iron. In addition to cast iron, green sand is another indispensable material. Different from what most people might think, "green" is actually not the green color or the environmentally-friendly concept. It describes the feature of remaining wet during the casting process.
Most of the manhole covers are round-shaped as a round object cannot pass through a round hole of the same diameter. This is quite important because the manhole cover is so heavy that it could easily kill a worker standing underneath it.
The Manufacturing Process
The casting process consists of five steps, pattern making, mold preparation, melting/pouring, and cooling and finishing.
Patterns are sculptured on wood or aluminum. Usually, aluminum patterns are suitable for large projects that require long-term use.
Mold-making is an important step. The molds often used are Sand Moulding and Resin Bonded SandMoulding. Sand must be processed in advance so that composition meets the standard printing and is able to withstand the high temperature of the liquid metal. Process sand in the mixer then add a 10% new sand, bentonite, and carbon powder.
Scrap steel is melted in furnaces and then required alloying metals and flux are then added to the molten iron. The flux helps to remove impurities from the iron. Then, the metal liquid will be poured into the mold.
To remove the manhole from the mold, it should be cooled down first. Usually, one and a half hours of cooling is needed for separating the metal from the mold but complete cooling always take around 24 hours
Manholes covers are simple castings that do not require intricate finishing. The finishing involves mashing, grounding and painting and cleaning. Removing the sand left on the manhole cover is the main part of this step.
Before shipment, the finished manhole cover should be tested to ensure the right dimension, right chemical composition and good mechanical and physical properties.
As a sophisticated manhole cover manufacturer, Jinmeng is able to provide you with customized manhole covers and answer all your questions about manhole covers!