Manhole covers are mostly used in towns, factories, mines and large-scale material distribution centers, etc., and the operating conditions are different, and corresponding operating levels should be determined. The preparation of corresponding manhole cover products according to different operating conditions can not only meet the requirements of various journeys and places, ensure the safety and reliability of the manhole cover during the use process, but also maximize the reasonable use of materials to prevent resource waste and decline. Production and use costs of manhole covers. Existing recommendation standards for founding department operations [10J divides the load-bearing grades of cast iron manhole covers into heavy and light grades. Study cast iron to check manhole cover operating standards, fully consider many factors such as traffic flow, durability requirements, saving raw materials, and convenient production equipment for the manhole address journey. Compound manhole covers should be divided into three different application levels to learn the journeys and places with different conditions . Production of manhole covers according to load levels is conducive to the safe use of manhole covers and the rational use of materials, and good economic and social benefits will occur.
Now there are many patented technologies related to composite manhole covers, and more and more companies are engaged in the development and production of composite manhole covers. With the continued rapid opening of China's economy, manhole covers have become more and more widely used in urban planning and journey creation. This heralded the rise of a new material manhole cover industry. Technically speaking, different composite manhole covers can completely replace cast iron manhole covers under different conditions, and Shangyang Energy FRP manhole covers can replace cast iron manhole covers under various conditions. There is reason to trust that as the further progress of the function of composite manhole covers involves the promotion of promotion, its spring will definitely come. Let's talk about the composition of composite manhole covers.
Status of composite manhole covers
There are three main types of composite manhole covers, namely steel fiber concrete manhole covers, recycled resin composite manhole covers, and fiber reinforced resin-based composite manhole covers. All three types of manhole covers do not contain or contain a small amount of metal and have no recycling value.
1. Steel fiber concrete manhole cover: The steel fiber concrete manhole cover is improved based on the original reinforced concrete manhole cover. It participates in steel fibers with a length of 10 to 20 ram in the concrete. Because many fine steel fibers are evenly dispersed in the concrete, the contact surface between the steel fibers and the concrete is large and distributed irregularly, which is almost in all directions. Enhancing concrete, that is, isotropic strengthening, greatly improves the various functions of concrete.
Compared with plain concrete (general concrete), steel fiber reinforced concrete has the benefits of obvious resistance to trekking and excellent crack resistance. Its tensile strength, flexural strength, and fatigue strength all have a large trek, and it can reduce the crack width. On the other hand, the great resistance to trek means that when applied to a structure that is bent or stretched, it has an excellent resistance to impact. It can be seen from the functional comparison that the strength of steel fiber concrete manhole covers is 30% higher than that of ordinary concrete manhole covers at the same ratio. The strength and surface crack resistance are close to those of cast iron. Under the condition that the weight of the components is basically the same, Approaching or exceeding the cast iron. The most obvious defects of steel fiber concrete manhole covers are heavy weight, difficult to open, and severe chipping during use. Generally, the improvement method selected is to add a metal frame edge to the outside of the manhole cover, and the edge collapse phenomenon has been improved. Because steel fiber concrete manhole covers have the advantages of low manufacturing cost, low recovery value and anti-theft, they can replace cast iron manhole covers in residential areas and green belts.
2. Fiber-reinforced resin-based composite manhole cover: Fiber-reinforced resin-based composite manhole cover is a glass fiber reinforced plastic (FRP) manhole cover. It is made of unsaturated polyester resin as the base material, glass fiber as the reinforcing material, and supplemented with certain fillers. Manhole cover. Due to different processes, different structures, and different reinforcement methods, the functions of the finished manhole cover products are also very different. In general, the technological methods of FRP manholes developed in China include ① resin transfer molding (RTM) process_4]. Due to the high resin content and average production power, it is not suitable for large-scale production; ② Hand lay-up production process. The manhole cover is not adjustable due to the load, it is only suitable for use in the green belt, and there is no competition advantage; ③ molding process. Manhole covers are load-bearing structural products. The FRP manhole cover is best selected by the molding process, and the product structure is relatively fine. At present, there are many domestic enterprises that use the molding process to make the manhole cover. The molding process generally uses SMC molding compound to limit the molding under a certain temperature and pressure.
3. Recycled resin composite material manhole cover: Recycled resin composite material manhole cover is made by using waste plastic and coal ash in the molten state to mix and restrict molding. The materials used in this composite manhole cover are basically waste, the low price of raw materials, and no recycling value, which are quite popular after the market.
Some domestic research institutes started the research on the blending of coal ash and waste plastics earlier, and summarized a set of effective formulas and processes for new composite materials of waste plastics and coal ash. The research has reached the international advanced level. . The resin-based composite manhole cover made of fly ash and waste plastic is rigid and flexible, beautiful in appearance, and it can save a lot of power and steel resources. It can digest a lot of fly ash and waste plastic. Claim. More than 90% of this composite manhole cover uses waste materials without any steel or other materials as the skeleton. It is 10-20% lower in cost than similar cast iron products and has obvious economic benefits. The selection of this "green manhole cover" not only deals with the anti-theft problem of the manhole cover, but also has the benefits of non-corrosion and rust, so it has a strong market competition.
The manhole cover products currently produced are mainly flat bottom, ribbed and fish belly. From the analysis of the stress structure, the design of the fish belly structure is economical and reasonable. In addition to saving raw materials and simplifying the mold, the load of the manhole cover can also be greatly adjusted.
At that time, the rapid opening of China's national economy was vigorously advancing the construction of infrastructure facilities. Due to the many applications of manhole covers in urban planning and journey creation, the market prospects were very promising. As the function and quality of the manhole cover have an important impact on public safety, the formulation and improvement of manhole cover operation standards has practical urgency and broad social implications. Load adjustment is one of the most important functions of a manhole cover.