1. The chemical and physical characteristics of the new type of nodular cast iron manhole cover use QT500-7 as cast nodular cast iron, which is light in weight, high in strength, good in resistance, corrosion resistance, fatigue resistance, and suitable in cost. Compared with the gray cast iron manhole cover of the same specification and scale, it is 40%~50% lighter in weight and 40%~50% higher in strength than the old type of gray cast iron manhole cover. The old gray cast iron well cover is brittle and simple to fracture. The chemical composition and physical properties of nodular cast iron and gray cast iron are compared (see Table 1 and Table 2). From the comparison of the above chemical composition and physical property data, it can be concluded that the decisive indexes of ductile iron are much higher than that of gray cast iron in terms of tensile strength, elongation, yield strength and ultimate load indenter, and the various data of its chemical composition are much more reasonable than that of gray cast iron.

2. Anti theft equipment
In terms of anti-theft, the new nodular cast iron anti-theft manhole cover adopts the concealed latch method. This achievement has been applied for and won the national patent (patent No. ZL96224581X). The concealed latch is connected by a fixing hole, a tension spring shaft and a thrust fixing clip. When it is opened, it needs to be inserted with a special lifting latch and rotated 90 ° clockwise to make the latch withdraw from extraction. The cover plate can be automatically locked without lifting the hand lock, simple, firm and secure; The old gray cast iron well cover must be embedded with iron parts before the construction of the drainage well, and then an iron chain must be installed before the well cover. It is not convenient to operate when the well cover is opened, and the embedded iron parts are simply disconnected from the iron chain and simply cut manually, losing the anti-theft function.

3. Lifting equipment
The manhole cover will be lower than the road surface due to road maintenance, road heightening and other reasons. To make it level with the road surface, the entire manhole cover base must be dug, which is time-consuming and labor-intensive. In addition, when building, expanding or reconstructing asphalt pavement, and raising various well covers on the road, it is necessary to excavate relatively large well positions from scratch to raise the well covers after the pavement is paved, which leads to the secondary excavation of the road surface, and the public has a great opinion. In order to avoid secondary excavation and reduce the impact on the work and life of citizens, the new type of nodular cast iron anti-theft manhole cover can solve this problem. That is to say, the manhole cover shall be leveled with the road surface by overlapping the outer frame, and the whole manhole cover base shall not be excavated again during installation, saving 70% of the working hours

4. Anti shock equipment
The new type of nodular cast iron anti-theft manhole cover has increased the cooperation depth between the frame and the cover by padding the PCE pad on the joint surface of the frame and the cover. Six point contact is selected to make the cooperation between the cover and the frame tight and use the hinge cooperatively. The fastening bolt and anti-theft lock basically eliminate the noise, reduce the vibration, and basically eliminate the noise problem of the old gray cast iron manhole cover when it is impacted by the car and the phenomenon of being taken away by the car.

5. Low reuse value
The old gray cast iron manhole cover has high cast iron content and high use value from the beginning, which is often the target of thieves. A complete manhole cover is smashed into pieces and sold to private purchase stations, causing huge losses to the government. The new nodular cast iron anti-theft manhole cover is composed of several materials, which contains many impurities and has low recycling value. This is the fundamental method to effectively prevent thieves from stealing.

6. Beautiful appearance
The data used for the new type of nodular cast iron anti-theft manhole cover are high-quality nodular cast iron, coke and special nodulizing agent from a specially designated manufacturer (Hebei Jiunai Metal Products Co., Ltd. is a designated manufacturer). The nodularization grade is controlled within the range of Grade 1 to Grade 2. The appearance is precise, the color is close to the asphalt surface ratio, and the concrete well ring can not be exposed. On the premise of ensuring the flatness, The manhole cover is integrated into the road surface and the road to beautify the city. The old gray cast iron manhole cover, because of its dark color and rough appearance, the concrete well ring must expose the asphalt surface layer. The color is inconsistent with the asphalt surface layer, and the flatness is difficult to control. It is difficult to integrate with the road, which is a difficult point to beautify the city.

7. The price is reasonable according to different specifications. The price of the new type nodular cast iron anti-theft manhole cover is generally 500 yuan/set 600 yuan/set (concrete well ring is outside), which is close to the price of the old type gray cast iron manhole cover. To sum up, the new type of nodular cast iron anti-theft manhole cover has a series of advantages compared with the old type of gray cast iron manhole cover, especially has a very wide use value in anti-theft, which is currently the mainstream product vigorously promoted and applied in many cities in China.