Laizhou Dingtai Machinery Co., Ltd.

　　Loose microstructure in ductile iron castings is one of the common defects in the casting process. Its formation is complex and involves multiple stages. The following are the main reasons and analysis:

　　1. Raw material issues

　　Improper alloy composition: unreasonable content of carbon, silicon, phosphorus, and other elements in the casting alloy material, especially too low carbon and silicon content or too high phosphorus content, will lead to insufficient shrinkage compensation during casting solidification, forming looseness.

　　Poor graphitization: insufficient graphitization or graphitization degradation will affect the density of the casting, leading to looseness defects.

　　2. Smelting process issues

　　Non-standard smelting process: insufficient heat preservation time or improper control of smelting temperature will lead to incomplete removal of gas and impurities in the molten iron, thus causing looseness.

　　Poor quality of molten iron: excessive residual aluminum, titanium, and other elements in the molten iron, or high sulfur content, will exacerbate the formation of looseness.

　　3. Casting condition issues

　　Unreasonable design of the gating system: the design of the sprue, runner, and riser is too small, or the casting pressure and flow rate are insufficient, which will lead to incomplete filling of the casting and form looseness.

　　Low compactness of the mold: insufficient compactness of the mold or local overheating will affect the solidification process of the casting, leading to blockage of the shrinkage channel and the formation of looseness.

　　4. Solidification characteristic issues

　　Blockage of micro shrinkage channels: during the solidification process of the casting, the micro shrinkage channels between dendrites and crystal arms are blocked, leading to the formation of small pores, that is, looseness.

　　Insufficient shrinkage compensation in the last solidified part: the last solidified part of the casting fails to shrink sufficiently, which will also cause looseness.

　　5. Other factors

　　High moisture content of molding sand: high moisture content of wet molding sand will increase the risk of looseness in castings.

　　Improper pouring temperature: pouring temperature that is too high or too low will affect the solidification process of castings, leading to looseness.