Knowledge

To determine whether ductile iron is prone to porosity, the following aspects can be considered:

I. Wall Thickness of Castings

For ductile iron castings, medium wall thickness castings (typically within the range of 8 to 15 mm) are more prone to sub-surface porosity. This is because within this wall thickness range, the chemical reaction rate at the interface, the formation and growth rate of hydrogen nuclei in the interfacial molten iron layer, and the solidification rate are more likely to reach a matching state, making the formation and growth of hydrogen bubbles easier.

II. Melting Process

Melting Temperature: Both excessively high and low melting temperatures can lead to the formation of pores. A temperature that is too high can cause elements in the molten metal to react with oxygen, generating oxides and bubbles; a temperature that is too low will affect the fluidity of the molten metal, making it difficult for gases to escape.

Use of Charge Materials:

If the amount of metallurgical reducing agents, charge materials, fluxes, and other additives added during the melting process is excessive, it will increase the gas content in the molten metal, thereby increasing the risk of pore formation.

III. Mold Design and Ventilation

Mold Design: Unreasonable design of the mold's vent holes or blockage of the vent holes can prevent gases in the mold cavity from being discharged smoothly during casting, thereby increasing the possibility of porosity.

Riser and Gate System Design: The design of the riser and gate system directly affects the fluidity of the molten metal and the exhaust effect. Improper design can lead to the accumulation of gases within the casting and the formation of porosity.

IV. Cooling Rate and Rhythm

Too rapid a cooling rate will cause the gases in the molten metal to solidify without being discharged, resulting in the formation of pores. At the same time, an uneven cooling rhythm may also lead to gases being trapped in certain local areas and forming pores.

V. Quality of Raw Materials ​​​​​​​

The impurities and gas content in raw materials are also important factors affecting the formation of porosity in ductile iron. If the quality of raw materials is poor and they contain more impurities and gases, it is more likely to produce porosity during the smelting and casting processes.

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