Prevention of shrinkage porosity of nodular iron castings

1. Chemical composition control

The chemical composition of nodular cast iron for wind turbine shall be strictly controlled, especially C, Si, Mg, s, P and rare earth elements. The silicon content shall be appropriately reduced to ensure the requirements of low temperature impact energy. For main frame, wheel hub and other components with low temperature impact energy requirements of – 30 ℃, it is generally recommended to select w (%): 3.75 ~ 3.95 C, 1.8 ~ 2.3 Si, 0.1 ~ 0.3 Mn, ≤ 0.04p, ≤ 0.015 s, 0.035 ~ 0.06 mg, 0.005 ~ 0.015 re.

2. Casting process control of nodular cast iron

In order to ensure that the sand mold has sufficient strength and obtain a better surface of nodular iron castings, furan resin sand shall be used for molding. It shall be tamped during molding to ensure that the sand mold is dense and compact and dried before pouring.

When designing the gating system, the parting surface shall be reasonably selected to avoid parting at important parts of nodular iron castings, the sprue and riser shall be reasonably designed, and cold iron shall be placed at parts with thick wall and large wall thickness transition, so as to increase the feeding capacity of molten iron and realize the sequential solidification of nodular iron castings. After the gating system is designed, the casting process of nodular cast iron is simulated and analyzed by using ProCAST and other software.

3. Smelting process control

The medium frequency induction furnace is used for smelting, and the spectrometer in front of the furnace is used to detect the gas content and chemical composition of molten iron in real time and adjust them in time; Reasonably control the inoculation process and adopt the combination of pre furnace inoculation and instantaneous inoculation; The tapping temperature and pouring temperature of molten iron shall be strictly controlled. The tapping temperature shall be controlled at 1450 ± 10 ℃ and the pouring temperature shall be controlled at 1350 ± 10 ℃.