According to the position of the cold iron in the sand mold, it can be divided into internal and external. The external cooling iron is placed on the surface of the sand mold and does not melt into the casting wall, which can speed up the cooling speed of the steel castings in contact with it. The internal cooling iron is in the cavity of the hot joint of the large steel casting, and its material must be the same as that of the steel casting. During pouring, the molten steel can melt the cooling iron into the steel casting, so as to speed up the cooling of the steel casting where the cooling iron is located. Because the cold iron is in the steel casting, it can be integrated into the steel casting itself, reducing the amount of steel filling the mold cavity, so the liquid shrinkage and solidification shrinkage of the mold will be greatly reduced, reducing the generation of shrinkage porosity and shrinkage cavity in the thick wall of the steel casting.
The external cooling iron is generally made of steel, iron and copper, and can also be non-metallic materials with high heat storage coefficient, but cast iron cannot be used to prevent the external cooling iron from fusing with the steel casting and carburizing the steel casting to produce cracks. Internal cooling iron is often used at the place where the steel casting is far from the riser or at the hot joint of the riser. When producing large steel castings with thick section, risers and internal chills will be set at the same time to make them solidify sequentially from top to bottom, improve the yield and further refine the grains. Carbon steel is often used as the material of internal cooling iron, and the carbon content is less than 0.25%. For the internal cooling iron of alloy steel castings, the material and composition shall be the same as that of steel castings. At present, the internal quality requirements of steel castings are higher and higher in production, coupled with the continuous progress of casting technology. In the production of large steel castings, the use of internal cooling iron is less and less, and more external cooling iron is used.