Casting is the first core process in the production of malleable iron pipe fittings. Essentially, it involves pouring high-temperature molten iron into a pre-prepared mold, which then cools to obtain a white cast iron billet. This step directly affects the quality of subsequent heat treatment and the final mechanical properties of the pipe fittings.
Preparation before casting: Before pouring the molten iron into the mold, two key preparations must be completed: batching and melting, and core making. Malleable iron has strict requirements for chemical composition. To ensure a white cast iron structure in the as-cast state, the carbon and silicon content of the molten iron must be controlled at low levels (carbon 2.2%-2.8%, silicon 1.0%-1.5%). Modern enterprises mostly use medium-frequency electric furnaces for melting, adjusting the composition in real time using a pre-furnace spectrometer to ensure the molten iron meets quality standards.
Simultaneously, since most pipe fittings are hollow structures (such as elbows and tees), sand cores need to be prepared in advance to form the inner cavity. The core-making machine injects coated sand into the core box, heats and solidifies it to obtain a sand core with sufficient strength, and then assembles it with the upper and lower sand boxes to prepare for receiving molten iron.
Gating System Design
The gating system is the channel through which molten iron enters the mold cavity, typically consisting of a pouring cup, sprue, runner, and ingate. Given the thin walls and complex shapes of malleable iron pipe fittings, the gating system must ensure rapid and stable filling of the mold with molten iron to prevent defects such as cold shuts, insufficient filling, or sand inclusions. Simultaneously, due to the solidification shrinkage of the molten iron, risers are required to compensate for the shrinkage and ensure a dense microstructure at the pipe joints.
Pouring Process Control
The key to the pouring operation lies in temperature and flow rate control. The temperature of the molten iron exiting the furnace is typically controlled between 1450℃ and 1480℃, while the pouring temperature is adjusted between 1360℃ and 1420℃ depending on the pipe wall thickness. Excessive temperature can easily lead to porosity and sand adhesion, while insufficient temperature results in poor fluidity and inability to fill thin-walled areas.
During pouring, the worker manipulates the ladle to smoothly pour the molten iron into the pouring cup. The entire process must be rapid, continuous, and stable, avoiding interruptions and splashing. After pouring, molten iron should be added to the riser as needed to compensate for shrinkage.
The finished casting cools and solidifies in the sand mold, then enters the sand cleaning process to remove surface sand and the riser, resulting in a rough-surfaced white iron billet, ready for the next step of graphitization annealing, ultimately transforming it into malleable iron pipe fittings with good toughness.
Post time: Mar-11-2026