Prevention and treatment of the subcutaneous porosity in ductile iron casting

The following measures can be taken:

(1) When wet casting is adopted, the moisture content in the sand must be strictly controlled, and the maximum mass fraction shall not exceed 5,5%.

(2) Raise the pouring temperature, especially for thin-walled castings, the pouring temperature shall not be lower than 1300 ℃.

(3) After spheroidizing treatment, the slag is removed and the slag is blocked before pouring to prevent more MGS from entering the mold with the molten iron. (4) After spheroidizing treatment, the molten iron is allowed to stand for a while, which is beneficial to the floatation of MGS particles and their removal into the slag. (5) Improve the permeability of the mold, help to reduce the subcutaneous pores.

(6) The use of cryolite powder can effectively reduce the subcutaneous pores. The reaction between cryolite powder and water is as follows:

Naalf6 + 2H2O → NaAlO2 + 2haf + 4NF due to the action of cryolite and water, the action of MGS in water and molten iron is avoided.

(7) To avoid aluminum in ferrosilicon, because it is easy to react with water vapor and produce hydrogen pores: 3H2O + 2Al → Al2O3 + H2 ↑. Therefore, the mass fraction of aluminum in ferrosilicon is limited to 0,5% – 1,0%. If the mass fraction of aluminum is more than 2%, hydrogen pores will be formed easily.

(8) Adding reductive carbon additives to molding sand can prevent the formation of subcutaneous pores.

(9) Improve the design of gating system.

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