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The composite manhole cover can be divided into two types: BMC and SMC according to market demand, production process and materials: BMC (DMC) material is the abbreviation of Bulk (Dough) molding compounds. Often referred to as unsaturated polyester bulk molding compound. Its main raw material is a mass-shaped prepreg that is fully mixed with GF (chopped glass fiber), UP (unsaturated resin), MD (filler) and various additives. BMC materials were first used in the former West Germany and the United Kingdom in the 1960s, and then developed in the United States and Japan in the 1970s and 1980s, respectively. Because BMC bulk molding compound has excellent electrical properties, mechanical properties, heat resistance, chemical resistance, and adapts to various molding processes, it can meet the performance requirements of various products. It is widely used in automobile production and railway transportation. , Construction accessories, mechanical and electrical products and other fields.   SMC composite material is the abbreviation of Sheet molding compound. The main raw materials are composed of GF (special yarn), UP (unsaturated resin), low shrinkage additives, MD (filler) and various additives. It first appeared in Europe in the early 1960s. Around 1965, the United States and Japan developed this technology one after another. In the late 1980s, China introduced advanced foreign SMC production lines and production techniques. SMC composite materials and SMC molded products have excellent electrical insulation properties, mechanical properties, thermal stability, and chemical resistance. Therefore, the application range of SMC products is quite common.   The current development trend is SMC composite materials to replace BMC materials.

Resin manhole cover (also called polymer glass fiber reinforced plastic manhole cover/composite manhole cover) is a kind of glass fiber and its products (glass cloth, tape, felt, yarn, etc.) as reinforcing materials, and synthetic resin as matrix material, it is mainly composed of unsaturated polyester resin, fillers, initiators, thickeners, low shrinkage additives, film mold agents, pigments and reinforcing materials, etc., and then high-temperature compression molding is a new type of manhole cover product.    The main addition materials are fiber reinforced materials (glass cloth, tape, felt, yarn, etc.), which are characterized by small specific gravity, large specific strength and specific modulus. For example, carbon fiber and epoxy resin composite materials have specific strength and specific modulus several times larger than steel and aluminum alloys. They also have excellent chemical stability, friction reduction, wear resistance, self-lubrication, heat resistance, fatigue resistance, and Creep, noise reduction, electrical insulation and other properties. The composite of graphite fiber and resin can obtain a material whose expansion coefficient is almost equal to zero. Another feature of fiber reinforced materials is anisotropy, so the fiber arrangement can be designed according to the strength requirements of different parts of the product. . The aluminum-based composite material reinforced with carbon fiber and silicon carbide fiber can still maintain sufficient strength and modulus at 500°C. The composite manhole cover can be divided into two types: BMC and SMC according to market demand, production process and materials.   The characteristics of resin manhole covers play a great role in life, so they are widely used.

The ductile iron manhole cover is mainly made of ductile iron, or often called nodular iron. The quality depends on the nodularity. Anti-rust asphalt paint is commonly used in the casting process. In other words, the surface of ductile iron manhole covers are generally sprayed with asphalt for anti-rust treatment. Features of ductile iron manhole cover: 1. High strength The tensile strength of ductile iron is greater than 420Mpa; the yield strength is greater than 300MPa. Same as low carbon steel, it is more than 3 times that of gray iron. 2. Good toughness. The impact value is similar to that of carbon steel and 10 times that of gray iron. 3. Good plasticity. The elongation rate is greater than 7%, which is similar to high-carbon steel and gray iron materials. 4. Corrosion resistant. In the 90-day spray corrosion test performance of ductile iron, the corrosion was only 0.25 times that of pipelines and 0.1 times that of gray cast iron pipelines. The service life is 2 times longer than gray cast iron pipes and 5 times longer than ordinary steel pipes. In most municipal applications, such as water, salt water, steam, etc., the corrosion and oxidation resistance of cast iron exceeds that of steel. Due to the microstructure of spherical graphite cast iron, nodular graphite cast iron is better than steel in reducing vibration capabilities. Advantages of ductile iron manhole cover: 1. Low cost Low cost is an important reason why cast iron is more acceptable than steel, which makes ductile iron more popular. The casting efficiency is higher, and the processing cost of ductile iron is lower. 2. Lightweight There is another advantage of ductile iron manhole covers. Ductile iron has high strength and toughness, which makes ductile iron manhole covers 30% lighter than similar manhole covers made of gray cast iron.

There are many types of manhole covers, single-layer, double-layer, cast iron manhole covers, ductile iron manhole covers, composite manhole covers, cement concrete manhole covers, etc. Among them, ductile iron manhole covers are the most widely used. According to the En124 standard, manhole covers are divided into six grades according to the load-bearing capacity : Group 1 （A15）— areas where only pedestrians have access. Covers and gratings capable of withstanding a 15kN test load. Group 2（B125）—car parks and pedestrian areas where only occasional vehicular access is likely (incl. driveways). Covers and gratings capable of withstanding a 125kN test load. Group 3 （C250）— car parks, forecourts, industrial sites and areas with slow moving traffic. Also in highway locations up to 500mm from the kerb and up to 200mm into the verge, excluding motorways. Covers and gratings capable of withstanding a 250kN test load. Group 4 （D400）— areas where cars and lorries have access, including carriageways, hard shoulders and pedestrian areas. Covers and gratings capable of withstanding a 400kN test load. Group 5（E600） — areas where high wheel loads are imposed, such as loading areas, docks or aircraft pavements. Covers and gratings capable of withstanding a 600kN test load. Group 6（F900） — areas where particularly high wheel loads are imposed such as aircraft pavements. Covers and gratings capable of withstanding a 900kN test load.  

Resin manhole covers are used on the roads, which have the characteristics of insulation, no noise, no recycling value and natural anti-theft. They are irreplaceable for cast iron manhole covers. The resin manhole cover is made by a unique molding process, which makes the city look like a new one. The service life is basically 20-50 years. The resin composite manhole cover molded by high temperature has light weight, high strength, excellent fatigue resistance, and damage safety. , Simple molding, low rolling noise, good chemical corrosion resistance, good acid and alkali resistance and beautiful appearance, etc., and the pollutants in the wastewater are further reduced.   Now on the market, the manhole covers produced by various composite manhole cover manufacturers use different materials, but several characteristics are similar: 1. Strong anti-theft performance: composite manhole cover manufacturers generally use unsaturated resin, glass fiber and other materials to compound them through a special production process. After high temperature molding, the product has no recycling value. 2. Service life: Through the use of high-performance resin, glass fiber and special production process formula, the penetration of the composite manhole cover in the glass fiber is ensured, and the bonding force between the two is greatly enhanced, so that the material will not be affected by the cyclic load. Internal damage occurs, thereby ensuring the service life of the product and the same advantages of other resin composite manhole covers, effectively eliminating the disadvantages of poor adhesion. 3. High temperature/low temperature resistance, good insulation performance, strong corrosion resistance: the product is corrosion resistant, non-toxic and harmless. No metal additives. It can be used in complex, changeable, harsh and demanding places. It has obvious acid and alkali resistance, corrosion resistance, anti-aging and many other indicators that have reached product quality specifications. 4. 4. Beautiful and practical, high-grade: According to the needs of high-end customers, a personalized design with complex LOGO and multiple colors on the same manhole cover can be made to make the pattern delicate, bright and distinct. And according to customer needs, it can be made into a variety of imitation stone appearances and colors that are the same as various stone pavements. 5. Strong load-bearing capacity: The bottom adopts a special design structure, and the continuous reinforcing fiber yarns used are made from the material to ensure that the fiber yarns and glass fiber cloth are integrated, so that the product has a certain load-bearing capacity. 6. Environmental protection, non-slip, low noise: The manhole cover will not slip after the car is rolled, and there will be no back-ear noise and pollution. （ Electronical manhole covers）