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The Technology of FRP Manhole Cover

The Technology of FRP Manhole Cover
The production methods of FRP are basically divided into two part: namely wet contact type and dry pressure forming. According to the characteristics of the process, there are hand lay-up, lamination, RTM, pultrusion, compression molding, and winding molding. Hand lay-up includes hand lay-up, bag press, spray, wet paste low pressure and moldless paste.
There are currently four types of molding methods that are most used in the world.
1) hand paste method: the main countries used are Norway, Japan, the United Kingdom, Denmark and so on.
2) injection method: the main countries used are Sweden, the United States, Norway and so on.
3) molding method: the main use of the country is Germany.
4) RTM method: The main countries used are Europe and the United States, Japan.
More than 90% of FRP products in China are produced by hand-paste method, and others have molding methods, winding methods, lamination methods, and the like. Japan’s hand-paste method still accounts for 50%. From the perspective of countries around the world, the hand-paste method still accounts for a considerable proportion, indicating that it still has

vitality. The hand-paste method is characterized by molding with a wet resin, simple equipment, low cost, and an overall product that can be pasteed for more than 10 m at a time. The disadvantages are low mechanization, long production cycle and unstable quality. China has introduced process equipment such as squeezing, spraying and winding from abroad.

With the development of FRP industry, new methods will continue to emerge.
Frp scientific name glass fiber reinforced plastic. It is a composite material of glass fiber and its products (glass cloth, belt, felt, yarn, etc.) as a reinforcing material and synthetic resin as a base material. The concept of composite material means that one material cannot meet the requirements of use, and it is necessary to combine two or more materials to form another material that can meet people's requirements, that is, composite material. For example, a single type of glass fiber, although high in strength, is loose between fibers, can only withstand tensile forces, cannot withstand bending, shearing, and compressive stress, and is not easily formed into a fixed geometry, and is a soft body.

If they are bonded together with synthetic resin, they can be made into a variety of rigid articles with a fixed shape that can withstand tensile stress and withstand bending, compression and shear stress. This constitutes a glass fiber reinforced plastic matrix composite. Because its strength is equivalent to steel, it also contains glass components, it also has the color, shape, corrosion resistance, electrical insulation, heat insulation and other properties of glass. Like glass, it has historically formed this easy-to-understand name "FRP". This term was proposed by the former Minister of Construction Materials Industry Lai Jifa in 1958. It was expanded from the building materials system to the whole country and is still widely used. It can be seen that the meaning of FRP refers to the reinforced plastics made of glass fiber as reinforcing material and synthetic resin as binder, and abroad is called glass fiber reinforced plastic. With the development of China's FRP industry, as a plastic-based reinforcement material, it has been expanded from glass fiber to carbon fiber, boron fiber, aramid fiber, alumina fiber and silicon carbide fiber. Undoubtedly, these new fiber made of reinforced plastic It is a high-performance fiber reinforced composite material, which can not be summarized by the common name of FRP.

Considering the origin and development of history, FRP composites are usually used, so the name is more comprehensive.

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