Laizhou Dingtai Machinery Co., Ltd.

　　The causes of porosity in ductile iron castings are closely related to factors such as the quality of the molten iron, molding conditions, process parameters, and material properties. A detailed analysis is as follows:

　　1. Molten Iron Quality

　　Residual Aluminum: The dangerous residual aluminum content in wet-type ductile iron castings is 0.03%-0.05%. Exceeding this range is likely to produce subsurface porosity. Aluminum mainly comes from inoculants, and excessive addition of ferrosilicon inoculants will increase the risk of porosity.

　　Residual Titanium: When residual aluminum and titanium coexist, excessive titanium (exceeding 0.01%) will aggravate the formation of pores. The combined action of titanium and aluminum will promote the reduction of interfacial water and gas, increasing the hydrogen content of the molten iron.

　　Sulfur Content: Sulfur is a harmful element. When the content exceeds 0.094%, subsurface porosity is easily produced, and the higher the sulfur content, the more serious the defect.

　　Hydrogen Content: When the hydrogen content of molten iron exceeds 4-5 ppm, pores are easily produced. It should generally be controlled below 2-2.5 ppm.

　　2. Molding Conditions

　　Mold Sand Moisture Content: The moisture in wet-type sand vaporizes at high temperatures, generating a large amount of gas. If it cannot be discharged in time, it will invade the molten iron and form pores.

　　Mold Permeability: Poor mold ventilation or unreasonable design will lead to gas retention, increasing the risk of porosity.

　　3. Process Parameters

　　Pouring Temperature: Both excessively high and low pouring temperatures will increase the risk of porosity. High temperatures increase the gas content of the molten iron, while low temperatures prevent gas from escaping.

　　Pouring Speed: Both too fast and too slow pouring speeds can cause the metal liquid flow to become turbulent, entraining gas to form pores.

　　4. Material Characteristics

　　Raw Material Impurities: Too many oxides, hydrides, and other impurities in the raw materials will release gas during smelting, increasing the risk of porosity.

　　Inoculants and Nodulizer: Excessive use of inoculants or nodulizer will increase the gas content in the molten iron, forming pores.

　　5. Other Factors

　　Mold Design: Unreasonable mold structure (such as too small a mold cavity or poor ventilation) will cause gas retention, forming pores.

　　Lubricants and Coatings: Improper use of lubricants or coatings will volatilize at high temperatures, producing gas and forming pores.

　　In summary, the generation of pores in ductile iron castings is the result of the combined action of multiple factors. Comprehensive control should be carried out from aspects such as molten iron quality, molding conditions, process parameters, and material characteristics to reduce porosity defects.