The manhole cover is the closure on the top of the pipeline opening to the underground facilities. It is necessary to install the manhole cover wherever public facilities such as tap water, telecommunications, electricity, gas, heat, fire protection, sanitation, etc. are installed to facilitate the maintenance of pipeline facilities and timely discharge of sewage. .
According to the technical characteristics of the pipeline project, in order to meet the requirements of equipment installation, daily overhaul and maintenance, inspection wells are set up at certain intervals along the pipeline burying direction in the project.
Inspection manhole covers (commonly referred to as manhole covers and various underground pipeline inspection manhole covers and rainwater grate) are the main supporting products of inspection wells, and their functions are load-bearing, closing and opening inspection wells, which can withstand the large flow of traffic vehicles. High-speed driving can also prevent the entry of vehicles, pedestrians and foreign objects, and ensure the normal operation of underground pipelines and equipment.
Divided by pipeline types: rainwater, sewage, water supply, gas, hot gas, power supply, communications, cable television, traffic signal lines, etc. This type of manhole cover is mostly an underground pipeline type set in road engineering.
Heavy-duty manhole cover: used for municipal road traffic and heavy vehicles.
Light manhole cover: public road traffic and light vehicle traffic.
The carrying capacity of the manhole cover is divided into four levels: A, B, C, and D.
Grade A steel fiber concrete inspection manhole covers are used for special roads and sites such as airports.
Grade B steel fiber concrete inspection manhole covers are used for urban roads, highways and parking lots where motor vehicles run and park.
Grade C steel fiber concrete inspection manhole covers are used for slow lanes, passages and sidewalks in residential quarters,
Class D steel fiber concrete inspection manhole covers are used in green belts and alleys and sites where motor vehicles cannot drive or park.
a. Metal manhole covers: cast iron, ductile iron, bronze manhole covers, etc.
b. High-strength steel fiber cement concrete manhole cover (cement-based composite material)
1. Drainage engineering, applied to rainwater and sewage pipelines.
2. Water supply engineering, applied to tap water, fire fighting engineering, etc.
3. Heating engineering, applied to heating arm line.
4. Power supply engineering, applied to power supply cables, telecommunications engineering, telephone, communication cable pipelines.
5. Garden engineering, applied to supporting integrated pipelines.
6. Gas engineering, applied to gas engineering, natural gas pipelines, etc.
7. Street lamp engineering, applied to power supply, lighting, cable pipeline
Cast iron manhole covers have the advantages of high strength, good rigidity, impact resistance, corrosion resistance, etc. The shortcomings are that the anti-theft problem has not been completely solved; thirdly, the manhole covers are prone to beating and noise when vehicles pass by, and the noise is very loud at night, which affects the lives of residents.
There are three categories: steel fiber concrete inspection manhole cover, recycled resin composite material inspection manhole cover, and glass fiber reinforced plastic inspection manhole cover:
1. The steel fiber concrete inspection manhole cover is an improved product of the original reinforced concrete inspection manhole cover. It is to add steel fibers about 2 cm in length to the concrete, and a large amount of steel fibers are dispersed in the concrete. And the formation of irregular radial distribution. So that the strength of concrete is strengthened. Greatly improve the toughness of concrete. Its flexural and tensile strength, fatigue cracking strength, etc. have been greatly improved, while the crack width can be reduced. In order to reduce the edge collapse of the steel fiber concrete inspection manhole cover during use, a metal frame is generally added to the outer side of the inspection manhole cover. The strength of the steel fiber concrete inspection manhole cover is more than 30% higher than that of the ordinary concrete inspection manhole cover under the same proportion, and its performance is close to that of the cast iron manhole cover. Moreover, the steel fiber concrete inspection manhole cover has the advantages of low production cost, low recycling value, and anti-theft, so it occupies a certain share in the market, but its most obvious defect is its bulkiness and insufficient carrying capacity.
2. Recycled resin composite inspection manhole cover is a synthetic resin-based composite product made of fly ash and waste plastics as raw materials, kneaded in a molten state, and molded by pressing. This composite material inspection manhole cover uses waste materials without any Steel or other recyclable materials, so it has anti-theft function. At the same time, it can digest a large amount of fly ash and waste plastics in manufacturing, which meets the requirements of the national energy-saving and environmental protection policies. Therefore it is called "green manhole cover". At the same time, its compression resistance, bending resistance, impact resistance and other properties are good, and it has the advantages of no corrosion and no rust. Its quality has reached the level of similar cast iron products, and its cost is about 30% lower than cast iron products. The economic benefits are significant, so it has strong market competitiveness. However, the quality and performance of the recycled resin composite inspection manhole cover is unstable during use, especially when the temperature is high. The manhole cover will undergo qualitative changes, causing the middle part of the inspection manhole cover to sink continuously or even fall off, which will cause great safety hazards.
3. FRP inspection manhole cover, which is made of unsaturated polyester resin as raw material, glass fiber as reinforcement material, and added with certain fillers. Due to different processes, different structural materials, and different reinforcing materials. The performance of the manufactured inspection manhole covers varies greatly. The process of domestic production of glass fiber reinforced plastic inspection manhole cover generally includes:
(1) Resin transfer molding process. Due to the high resin content, the manufactured inspection manhole cover is not suitable for use on the roadway due to its insufficient carrying capacity;
(2) Hand lay-up process. The production efficiency is slow, not suitable for mass production, and there is no competitive advantage;
(3) Molding process. The molding process is layered composite compression molding under a certain temperature and pressure. The structure of this product is relatively compact, and it uses different materials for different parts of the inspection manhole cover. Continuous fiber reinforcement is used in the lower part of the manhole cover. To ensure its carrying capacity: use fillers in the middle. To improve the anti-deformation ability of the product and reduce the production cost: use materials with higher hardness and good abrasion resistance in the upper part to improve the compression resistance and abrasion resistance of the upper part of the product. FRP inspection manhole covers are gradually popularized due to their advantages of light material, high strength, fatigue resistance, corrosion resistance, resistance to brittle damage, and easy processing and forming.
The new product quality standard has raised the load requirement of the manhole cover and is in line with the internationally accepted EN124 standard. After the standard was implemented on February 1, 2010, it clarified that the composite manhole cover is a kind of inspection manhole cover, and explained its characteristics: using polymer as the matrix material, adding reinforcement materials, fillers, etc., through a certain process composite The popularization and application of the inspection manhole cover made in the market. The polymer full composite material manhole cover has the advantages of light weight, high strength, good fatigue resistance, good damage safety, superior molding processability, low rolling noise, non-corrosion, acid and alkali resistance, and beautiful appearance, making it an ideal replacement for cast iron manhole covers. Taste.
There are many varieties and formulas of composite inspection manhole covers. There are steel fiber concrete, glass fiber reinforced plastic, recycled resin, silicon-plastic composite material, polymer matrix composite material, polymer composite material and so on. Due to the short development time. intense market competition. Merchants often cut corners and shoddy goods in order to make profits. It is difficult for users to check and judge the quality by simple methods such as appearance and feel. Therefore, the composite inspection manhole cover must not be cheap
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