Detailed explanation of ductile iron manhole cover
Nodular cast iron manhole cover is a kind of nodular cast iron product。 Through spheroidizing and inoculation, nodular graphite is obtained, which effectively improves the mechanical properties of cast iron, especially the plasticity and toughness, so as to obtain higher strength than carbon steel。 Nodular cast iron is a kind of high-strength cast iron material developed in the 1950s。 Its comprehensive properties are close to that of steel。 It is based on its excellent properties that nodular cast iron has been successfully used to cast some parts with complex stress, high strength, toughness and wear resistance requirements。 Nodular cast iron has developed rapidly into a widely used cast iron material next to grey cast iron。 The so-called "replacing steel with iron" mainly refers to ductile iron。
Nodular cast iron manhole covers are generally divided into round and square. In urban road administration, round manhole covers are generally used because they are not easy to tilt and can better protect the safety of pedestrians and vehicles. The use of a circle is mainly due to the fact that the length of each diameter of the round well cover passing through its center is the same, so that if the well cover is rolled up by the passing vehicle, the diameter of the well cover will be slightly wider than that of the lower wellhead no matter how it is rolled up, and the well cover will not fall into the wellhead.
If the square is used, because the diagonal of the square is obviously longer than each side, such a well cover can easily fall into the well along the diagonal direction of the wellhead when it is rolled up, causing potential safety hazards. If the wellhead is round or obviously smaller than the well cover, the square well cover will not fall into the well. Here is a matter of maximum utilization and saving of materials. The use of the well cover depends on the size of the wellhead. If a square well cover with an area far larger than the wellhead has to be installed on it, then the utilization and practical value of the materials are not more effective than using the round well cover directly, which not only saves the material of the well cover, but also ensures the safety of the wellhead.
In the countryside and cable wells, the square is generally used, which can better prevent rainwater and other liquids from entering.
Nodular cast iron manhole cover is mainly made of nodular cast iron. The quality of this kind of manhole cover is related to the spheroidization rate. The common coating used to treat castings is antirust asphalt paint. Of course, the surface of nodular cast iron manhole cover is also treated by spraying antirust asphalt paint. The advantages of ductile iron well cover are that it is 30% lighter than the same type of gray iron well cover due to its high strength and toughness.
Features of ductile iron manhole cover:
Good toughness. The impact value is similar to that of medium carbon steel, more than 10 times of that of gray iron.
Strong corrosion resistance. In the water spray corrosion test, the corrosion amount in 90 days is only 1 / 40 of the steel pipe and 1 / 10 of the gray iron pipe. Its service life is twice that of grey iron pipe and five times that of ordinary steel pipe.
Good plasticity. Elongation ≥ 7%, similar to that of high carbon steel, while the elongation of gray iron material is zero.
High strength. The tensile strength is not less than 420MPa, and the yield strength is not less than 300mpa.
Because of the microstructure of spheroidal graphite, spheroidal graphite cast iron is better than cast steel in reducing vibration capacity, so it is more conducive to reducing stress. One of the important reasons for choosing nodular cast iron is that the cost of nodular cast iron is lower than that of cast steel. The low cost of nodular cast iron makes the material more popular, the casting efficiency is higher and the machining cost of nodular cast iron is reduced.
The strength of nodular cast iron is comparable to that of cast steel. Ductile iron has higher yield strength, the lowest yield strength is 40K, while the yield strength of cast steel is only 36K. In most municipal applications, such as water, salt water and steam, the corrosion resistance and oxidation resistance of nodular cast iron are higher than that of cast steel.
Ductile iron castings have been applied in almost all major industrial sectors, which require high strength, plasticity, toughness, wear resistance, severe thermal and mechanical impact resistance, high or low temperature resistance, corrosion resistance and dimensional stability. In order to meet these changes of service conditions, there are many brands of nodular cast iron, which provide a wide range of mechanical and physical properties.
For example, most of the ductile iron castings specified by ISO 1083 are mainly produced in non alloy state. Obviously, this range includes high strength grades with tensile strength greater than 800 n / mm and elongation of 2%. The other extreme is the high plasticity grade, with an elongation of more than 17% and a corresponding low strength (370 n / mm minimum). Strength and elongation are not the only root for designers to choose materials, while other decisive and important properties include yield strength, elastic modulus, wear resistance and fatigue strength, hardness and impact performance. In addition, corrosion resistance, oxidation resistance and electromagnetic properties may be key for designers. In order to meet these special applications, a group of Austenitic Ductile Iron, usually called Aoni - Reis dead ductile iron, has been developed. These Austenitic Ductile Irons are mainly alloyed with zinc, chromium and manganese and are listed in international standards.
（1） The chemical composition is strictly required. The carbon and silicon content of the original liquid iron is higher than that of gray iron. The content of manganese, phosphorus and sulfur in nodular iron is reduced
（2） The temperature of molten iron is higher than that of gray iron to compensate for the loss of molten iron temperature during spheroidization and inoculation
（3） Spheroidizing treatment, i.e. adding spheroidizing agent to molten iron
（4） Inoculant treatment
（5） Because of the poor fluidity and large shrinkage of nodular cast iron, higher pouring temperature and larger pouring system size are needed. The riser, cold iron and sequential solidification principle are adopted
（6） Heat treatment
The main application fields of nodular manhole cover: municipal roads, expressways, communication, electric power, tap water, communities, schools and other parks.
In order to ensure the normal use of cast iron manhole cover, attention shall be paid to the installation quality, accurate size, firm installation, convenient opening, clean and beautiful appearance. According to the technical standards for inspection of cast iron manhole cover, the following installation rules are specially formulated:
For the brick masonry of cast iron well cover, the inner diameter, length * width and square circle (if the construction is based on the actual sample, it is best) shall be determined according to the well cover size designed by the Design Institute, which can also be executed according to the corresponding standards. When building a well, it must be noted that the inner diameter of the wellhead shall be consistent with the inner diameter of the well cover grate, and the well cover installed shall be flush with the road surface. After pouring and laying the well seat with concrete or asphalt, the cover shall be opened and cleaned in time to avoid mortar or asphalt pouring the manhole cover and the seat into one, so as to avoid affecting the opening in the future.
When installing the well seat on the cement road, use C25 concrete to cast 20cm thick ring beam on the brick masonry at the wellhead to level, make sure that the well seat is square and solid, and the whole is flat without looseness, and cast a 40cm wide concrete protection ring on the well cover (if it is a cement road, it can also cast a 20cm wide concrete protection ring, and strengthen it with steel bars) with a maintenance period of more than 10 days.
In order to keep the appearance of the cover beautiful and the surface pattern and handwriting clear, a thin iron sheet shall be used to cover the well cover or waste oil to brush the cover during the construction of asphalt pavement to prevent the asphalt oil from spraying on the well cover; in the construction of cement pavement, a plastic film shall be used to cover the well cover to prevent the water stop mud mortar from contaminating the well cover surface, damaging the surface pattern and handwriting, and water can also be used after the construction of the same day Clean the well cover surface.
When installing the cast iron well cover on the asphalt pavement, it is necessary to avoid the direct rolling of the well seat by the construction machinery. During the overall casting of the pavement, the hole slightly larger than the well seat shall be reserved on the pavement and placed after the asphalt pavement is completed. (the whole concrete pavement shall be installed after two stones are paved and compacted) ensure the quality of well cover placement to extend the service life.
The above is provided by Shandong ductile iron manhole cover rainwater outlet - ductile iron manhole cover manufacturer, Jinan Wanshun Casting Co., Ltd. What we have introduced is the main reason why the surface of nodular cast iron manhole cover is mottled when planning. It is very important to pay attention to these problems. I hope the above introduction can bring you some hints and help. Shandong ductile iron manhole cover rainwater outlet - ductile iron manhole cover manufacturer by Jinan Wanshun Casting Co., Ltd. Welcome to http://www.zgcjxdw.com/