The manhole cover is a closure at the top of the pipeline opening to underground facilities. Every place where public facilities such as tap water, telecommunications, electricity, gas, heat, fire, sanitation and other public facilities are installed needs to install a manhole cover to facilitate the maintenance of pipeline facilities.
I. Classification of Manhole Covers
According to the technical characteristics of pipeline engineering, in order to meet the requirements of installation equipment, daily inspection and maintenance, inspection wells are set at a certain distance along the pipeline buried direction in the project.
Inspection manhole covers (commonly known as manhole covers and various types of underground pipeline inspection manhole covers and gullies) are the main supporting products of inspection wells. Their functions are load-bearing, closed, and open inspection wells. High-speed driving can also prevent the entry of vehicles, pedestrians and foreign objects, and ensure the normal operation of underground pipelines and equipment.
According to the type of pipeline: rainwater, sewage, water, gas, hot gas, power supply, communication, cable television, traffic signal lines, etc. This type of manhole cover is mostly installed in road engineering underground pipeline types.
Divided by carrying capacity:
Heavy manhole cover: used for municipal road traffic and heavy vehicles.
Light manhole cover: public road traffic and light vehicle traffic.
The bearing capacity of the manhole cover is divided into four levels of A, B, C and D.
Class A steel fiber concrete inspection covers are used for special roads and sites such as airports.
B-grade steel fiber concrete inspection manhole covers are used for motor vehicles, parked urban roads, highways and parking lots,
C-grade steel fiber concrete inspection manhole cover is used for slow lanes, passages and sidewalks in residential residential areas,
D-level steel fiber concrete inspection manhole covers are used for green belts and alleys and sites where motor vehicles cannot drive or park.
Distinguish by material
a. Metal manhole cover: cast iron, ductile iron, bronze manhole cover, etc.
b. High-strength steel fiber cement concrete manhole cover (cement-based composite material)
Application range of manhole cover
1. Drainage works, applied to rainwater and sewage pipelines.
2. Water supply engineering, applied to tap water, fire protection 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 light engineering, applied to power supply, lighting, cable pipeline
Advantages and disadvantages of metal manhole covers
The cast iron manhole cover has the advantages of high strength, good rigidity, impact resistance, corrosion resistance, etc. The disadvantages are that the theft prevention problem has not been completely solved; again, the manhole cover is prone to bouncing and sound when the vehicle passes by, and it is very noisy at night, which affects residents' lives.
Advantages and disadvantages of composite manhole covers
There are three categories of steel fiber concrete inspection manhole covers, recycled resin composite material inspection manhole covers, and glass steel inspection manhole covers:
1. Steel fiber concrete inspection manhole cover is an improved product of the original reinforced concrete inspection manhole cover. It is made by adding steel fibers with a length of about 2 cm, and a large amount of steel fibers are dispersed in the concrete. An irregular radial distribution is formed. Thereby, the strength of concrete is strengthened. Greatly improved the toughness of concrete. Its flexural tensile strength and fatigue cracking strength have been greatly improved, and at the same time, the crack width can be reduced. In order to reduce the edge collapse phenomenon 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 at the same proportion, and its performance is close to that of the cast iron inspection manhole cover. Moreover, the steel fiber concrete inspection manhole cover has the advantages of low production cost, small recycling value, anti-theft, etc., so it has a certain share in the market, but its most obvious defects are bulky and insufficient bearing capacity.
2. Recycled resin composite material inspection manhole cover is made of fly ash and waste plastic as raw materials. It is a synthetic resin-based composite material product that is mixed and pressed in a molten state. This composite material inspection manhole cover uses waste materials without any Steel or other recyclable materials are therefore anti-theft. At the same time, it can digest a large amount of fly ash and waste plastic in manufacturing, which meets the requirements of national energy conservation and environmental protection policies. Therefore it is called "green manhole cover". At the same time, its compressive, bending, impact strength and other properties are better, and has the advantages of no corrosion, no rust, etc., its quality has reached the level of similar cast iron products, the cost is about 30% lower than cast iron products. The economic benefits are significant, so it has strong market competitiveness. However, the quality performance of the recycled resin composite inspection manhole cover is unstable during use, especially when the vehicle is continuously rolled under high temperature. The manhole cover will undergo qualitative changes, which will cause the middle part of the inspection manhole cover to sink continuously or even fall off. This will cause a great safety hazard.
3. FRP inspection manhole cover is an inspection manhole cover made of unsaturated polyester resin as the raw material, glass fiber as the reinforcing material, and a certain filler. Due to different processes, different structural materials, and different reinforcing materials. The performance of the manufactured inspection manhole cover products also varies greatly. The domestic technology for producing FRP inspection manhole covers is generally as follows:
(1) Resin transfer molding process. Due to the high resin content, the manhole cover produced is not suitable for use on the carriageway due to insufficient bearing capacity;
(2) Hand lay-up process. Slow production efficiency, not suitable for large-scale production, and no competitive advantage;
(3) Molding process. The molding process is a layered composite compression molding under a certain temperature and pressure. The structure of this product is relatively compact. It uses different materials in different parts of the inspection cover. Use continuous fiber reinforcement under the manhole cover. To ensure its carrying capacity: use fillers in the middle. To improve the product's resistance to deformation and reduce production costs: use a higher hardness and good wear resistance in the upper part to improve the compression resistance and wear resistance of the upper part of the product. FRP inspection manhole covers are gradually popularized due to their advantages such as light material, high strength, fatigue resistance, corrosion resistance, non-brittle damage, and easy processing and forming.
With the GB / T23858-2009 inspection cover standard issued by the country in 2009, the new product quality standards have increased the load requirements of the cover and are in line with the internationally accepted EN124 standard. After the implementation of this standard on February 1, 2010, composite manhole covers were specified as a type of inspection manhole cover, and their characteristics were described: using polymers as matrix materials, adding reinforcement materials, fillers, etc., and compounding them through a certain process The popularity and application of the inspection manhole cover in the market. Polymer all-composite manhole covers have the advantages of light weight and high strength, good fatigue resistance, good breakage safety, superior molding process, low rolling noise, non-corrosion, acid and alkali resistance, and beautiful appearance. They are an ideal replacement for cast iron manhole covers. Product.
Problems found in the use of composite manhole covers:
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 materials, polymer-based composite materials, polymer composite materials and so on. Due to the short development time. intense market competition. Businesses often cut corners for the sake of profits. It is difficult for users to check and judge the quality of the product by simple methods such as appearance and feel. Therefore, the composite inspection manhole cover must not covet the cheap choice of non-standard products.