How is ductile iron used in anti-theft device?

The chemical and physical properties of the new nodular cast iron manhole cover are as-cast nodular cast iron QT500-7, with light weight, high strength, good toughness, corrosion resistance, fatigue resistance and appropriate cost. Compared with the gray cast iron manhole cover of the same specification, it is 40%~50% lighter and 40%~50% stronger than the old gray cast iron manhole cover. The chemical composition and physical properties of nodular cast iron and gray cast iron were compared. In the aspect of anti-theft, the new ductile iron anti-theft manhole cover adopts the form of hidden bolt, and this achievement has been applied for and obtained the national patent. The hidden bolt is connected with the thrust fixing clamp through the fixing hole and the spring shaft. When it is opened, it needs to insert a special lifting lock and rotate it clockwise for 90 degrees, so that the bolt can be pulled out, and the cover plate can be automatically locked without the handle lock, which is simple, firm and reliable. The old gray cast iron manhole cover must be embedded with iron pieces before the construction of the drainage well, and then an iron chain must be installed in front of the manhole cover. When the manhole cover is opened, it is inconvenient to operate, and the embedded iron pieces and chains are easy to be manually disconnected and cut off, losing the anti-theft function.