Ductile iron manhole covers are a type of ductile iron product. Ductile iron is produced through spheroidal graphite treatment and inoculation, resulting in spherical graphite structures that significantly enhance the material's mechanical properties—particularly its ductility and toughness—thus achieving strength levels even higher than those of carbon steel. Developed in the 1950s, ductile iron is an ultra-high-strength cast iron material whose overall performance closely rivals that of steel. Thanks to its exceptional qualities, it has been successfully used to manufacture complex components that demand high strength, excellent toughness, and superior wear resistance. Today, ductile iron has rapidly emerged as the second most widely used cast iron material after gray iron. The concept of "replacing steel with iron," when applied to engineering applications, primarily refers to the use of ductile iron.

Ductile iron manhole covers are typically available in round and square shapes. In urban road management, round covers are generally preferred because they are less likely to tilt, thereby better safeguarding the safety of both pedestrians and vehicles. The primary reason for choosing a round design is that every diameter passing through the center of the circle remains the same length. This ensures that even if the cover is lifted by a passing vehicle—no matter which direction it’s tilted—the diameter will always be slightly wider than the opening below, preventing the cover from falling into the well. In contrast, if a square cover were used, its diagonals would clearly exceed the length of each side. As a result, when such a cover is jacked up by a vehicle, it could easily slip downward along the diagonal axis of the well opening, posing a significant safety risk. Of course, if the well opening were designed to be either circular or significantly smaller than the square cover, the latter would no longer fall into the well. This situation also highlights an important issue: maximizing material efficiency while minimizing waste. The choice of well opening size depends on the actual dimensions of the opening itself. If a square cover—whose area far exceeds that of the well opening—is forcibly installed atop it, not only does this approach waste valuable materials but also fails to optimize the practicality and safety of the system. By contrast, using a round cover directly matches the well opening more efficiently, conserving resources while ensuring robust protection against potential hazards. Meanwhile, in rural areas or for cable wells, square-shaped covers are often chosen instead. This design helps prevent rainwater and other liquids from seeping into the well, offering enhanced functionality and reliability in these settings.

Ingredients:

Pig iron is an iron-carbon alloy with a carbon content exceeding 2%. Industrial-grade pig iron typically contains 2.5% to 4% carbon, along with elements such as C, Si, Mn, S, and P. It is produced by smelting iron ore in a blast furnace. Depending on the different forms in which carbon exists within the pig iron, it can be further classified into types like steelmaking pig iron, foundry pig iron, and ductile iron, among others.

The cast iron featuring spheroidal graphite appears spherical. Compared to flake graphite, the spheroidal graphite causes less disruption to the metal matrix, enabling the cast iron to achieve a strength level of 70–90% of the matrix’s inherent strength. Its tensile strength can reach up to 120 kgf/mm², while also exhibiting excellent toughness. Typically, the chemical composition of ductile iron—excluding iron—includes: 3.6–3.8% carbon, 2.0–3.0% silicon, no more than 1.5% combined manganese, phosphorus, and sulfur, along with适量 of rare earth elements, magnesium, and other nodulizing agents.

Production:

(1) Strictly control the chemical composition, requiring higher carbon and silicon content in the molten iron compared to gray cast iron, while reducing the levels of manganese, phosphorus, and sulfur in ductile iron.

(2) The molten iron is tapped at a higher temperature than gray cast iron, to compensate for the temperature loss during spheroidization and inoculation treatments.

(3) Perform spheroidizing treatment by adding a spheroidizing agent to the molten iron.

(4) Add a inoculant for inoculation treatment

(5) Ductile iron has poor fluidity and significant shrinkage, so it requires higher pouring temperatures and larger gating system dimensions. Properly utilizing risers and chills, and adopting the principle of sequential solidification, are essential for achieving high-quality castings.

(6) Perform heat treatment

Features:

1. Long lifespan: Corrosion-resistant, pollution-free, maintenance-free, and capable of lasting over 50 years.

2. High load-bearing capacity: Far surpasses other product types in load-bearing strength, providing robust resistance to pressure and effectively preventing safety incidents such as breakage or vehicle falls.

3. Anti-theft: Featuring both conventional and advanced anti-theft designs, the manhole cover and frame are securely connected using high-strength bolts, ensuring an integrated, tamper-proof structure.

4. Anti-tilt lid: Equipped with shock-absorbing rubber rings, ensuring no noise is generated when vehicles pass by, thus meeting environmental protection standards.

5. Excellent safety: The manhole covers fit tightly together, eliminating issues like bouncing, warping, rattling, or shifting. They are noise-free, ensuring a safe and reliable experience.

6. Aesthetic Appeal: Enhances the urban environment with a black asphalt coating on the exterior, giving the product a glossy and tidy appearance.

7. Slip Resistance: The manhole cover surface features a specialized anti-slip pattern that enhances friction, preventing pedestrians from slipping on surfaces covered by rain, snow, or ice.