How to eliminate sand hole and skin pores in ductile iron castings?

Skin pores and sand hole are common metal casting defects, which has a serious impact on their performance. How to eliminate sand hole and skin pores in ductile iron casting? According to the experience of Dandong Foundry, we will start from factors to look for the answers.

1. Water content of sand

The main factors affecting the skin pores is the water content of sand which should be controlled lower. 3 to 5% is the reasonable range (to ensure the performance of wet sand).

2. The content of Sulfur

The second major factor is the S content. S in liquid iron reacts with Mg in nodulizer we can get MgS. MgS is reduced by the water in sand generating H2S gas. If the casting speed is too fast, the gas is not completely discharged in time. It will produce the skin porosity under the epidermis in the casting.
So, firstly iron foundry should try to use iron ball that has low-sulfur. Secondly, after processing it is better to slag quickly cleanly, to prevent the return of sulfur.

3. Reasonable gating system

The third factor is reasonable the gating system. There are many ways to form pores, such as involved pores and immersed porosity and so on. If the gating system is unreasonable, the air will involve in the casting process. Because the solidification method is fast and the thin-walled castings solidify quickly, it is difficult to emptying air completely and the skin pores generate.

4. The content of aluminum in nodulizer and iron

The dangerous residual aluminum content of wet-type ductile iron is 0.030-0.050%. It will make the skin pores. If iron foundries add more than 0.2% of aluminum in the ladle before casting (without affecting the microstructure), it can eliminate the skin pores in ductile iron casting.

5. Pouring temperature

Iron foundries should base their casting of the main wall to choose a suitable pouring temperature in order to discharge the gas in the molten iron before solidification. If the thickness of wall is less than 10, the pouring temperature should be controlled at 1380 ~ 1430. If the thickness of wall is more than 10, temperature can be controlled at 1320 ~ 1380.

6. Machining parts

If the casting is machining parts, some small pores of the skin are allowed within a reasonable amount of processing. Otherwise, if iron foundry wants to completely avoid the skin pores, it will need strict measures of multi-party and an increase in cost. That will be more harm than good; if the surface requirements of the cast is strict, it need to take great efforts to prevent the skin pores.

A qualified cast iron product requires a wide range of needs, the attention of all aspects iron foundry should take the cost, the requirement and production process into account, only in this way, can iron foundry obtain harvest.

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