A15 Ductile Iron Rainwater Drainage Manhole Cover For Municipal Use

Ductile Iron Rainwater Drainage Manhole Cover For Municipal Use

The production process of ductile iron manhole covers mainly includes the following steps:

Raw material preparation:

Main material: Select pig iron, scrap steel, and recycled materials (unqualified products recovered in production, pouring risers, etc.). Pig iron provides carbon and basic iron elements, scrap steel adjusts the composition of molten iron, and recycled materials reduce costs and improve efficiency.
Auxiliary materials: Add alloy elements such as silicon, manganese, and copper to improve performance, add spheroidizing agents such as magnesium and rare earth, and inoculants such as ferrosilicon to ensure spheroidizing effects.
Inspection: Raw materials are tested at the factory to ensure that the content of elements such as carbon, silicon, manganese, phosphorus, and sulfur and the composition of spheroidizing agents and inoculants meet production requirements.

Smelting:

Charging: Load pig iron, scrap steel, and recycled materials into the smelting furnace (cupola/electric furnace) in proportion. Generally, pig iron is put first, and then scrap steel and recycled materials are put to avoid the influence of impurities.
Temperature control: Melting temperature is 1450 - 1550℃ (higher than ordinary gray cast iron), so that the raw materials are fully melted and the composition is uniform, which is conducive to subsequent processing.
Adjusting composition: Continuously detect and adjust the composition of molten iron during smelting to ensure that the content of elements such as carbon and silicon is suitable. For example, too high carbon increases brittleness, too low affects spheroidization; too high silicon reduces strength, too low affects fluidity.

Spheroidization and inoculation treatment:

Spheroidization: After the molten iron is melted, add spheroidizing agent (magnesium, rare earth, etc.) according to 1% - 2% of the mass of the molten iron, use the flushing method (put the bottom of the molten iron ladle, quickly flush the molten iron to react) or the transfer method (the molten iron is poured into the transfer ladle, and then put into the casting mold after adding the agent), react for 3 - 5 minutes, let the graphite become spherical, improve strength, toughness and wear resistance.
Inoculation: After spheroidization, add inoculant (ferrosilicon, etc.) according to 0.3% - 0.8% of the molten iron mass, use flow inoculation (add during pouring) or ladle inoculation (add in the molten iron ladle and pour after pouring) to refine the graphite balls and improve the mechanical properties. Metallographic analysis and hardness test can also be performed to detect the effect.

Casting and molding:

Mold preparation: Use sand mold (good air permeability and yieldability), and make the mold according to the manhole cover design to ensure molding and prevent cooling cracks.
Temperature control and speed regulation: Due to the poor fluidity and large shrinkage of ductile iron, the pouring temperature is 1350 - 1450℃, and the speed is moderate. Too fast and easy to splash, too slow and easy to low temperature, resulting in poor pouring.
Set riser chill: The riser stores excess molten iron to make up for solidification shrinkage; chill accelerates cooling and improves quality.

Cooling:

Method: After pouring, let the manhole cover cool naturally in the mold (several hours to dozens of hours, depending on the size and thickness), and it can also be assisted by forced cooling and spray cooling.
Speed ​​control: Cooling speed affects performance. Too fast is easy to produce white structure (reduced toughness and wear resistance), too slow is easy to coarse grains (reduced strength), and the speed needs to be reasonably controlled according to the material and size.

Post-processing:
Sand cleaning: Use a vibrating sand-dropping machine, a sandblasting sand-dropping machine, etc. to separate the casting from the sand mold, clean the surface/internal impurities and burrs, and there are mechanical (high efficiency but easy to damage the surface) and manual (maintain surface quality but slow) sand cleaning methods.
Cutting and grinding: flame and plasma cutting of large manhole covers; grinding the surface, removing burrs and flash, making the surface smooth, using grinding wheels, sand belts and other tools.
Heat treatment: annealing, normalizing, quenching and tempering, etc., to change the internal structure and performance, improve hardness, strength, wear resistance, etc.
Anti-corrosion treatment: spraying asphalt paint, galvanizing, thermal spraying, electrostatic spraying, etc., to enhance corrosion resistance and aesthetics. For example, underground manhole covers are often treated with asphalt for corrosion protection.

Quality inspection:

Appearance: Check whether the surface has cracks, pores, sand holes, whether it is smooth, and whether the size meets the standard.
Performance: tensile, bending, and impact tests are performed to measure mechanical properties; load-bearing, fatigue resistance, and corrosion resistance tests are performed according to EN124 and other standards, such as D400 grade to measure 40 tons of load bearing capacity.
Spheroidization rate: metallographic analysis measures the graphite spheroidization rate (generally required to be ≥80%) to measure the quality of ductile iron.

Finished product packaging and storage:

After passing the inspection, it is packaged with plastic film, cartons, etc. to prevent damage during transportation and storage.
Finished product warehouses are classified by specifications and models, waiting for shipment.