How to prevent sand casting defect: slag hole

A variety of sand casting defects often occur in iron castings, how to prevent these defects has been a concern of sand casting plant. This article describes some knowledge of prevent the occurrence of slag hole in this area and practical experience .

Preventive measures of the slag hole

1. Increase the temperature of hot liquid iron, vermicular iron and alloy cast iron. If time permits, rest before casting form some time in order to slag floating.

2. To prevent oxidation of molten iron, iron foundry should control the nodulizer and the amount of inoculants strictly.

3. Design the rational gating system and place the filter on-chip to improve the capacity to file slag. Place the best system on casting slag bag with a constant flow when pouring.

4. When we cast sand ductile iron, the melt iron flows in the cavity of cast iron. Due to oxidation of molten iron or the various elements in iron liquid react with the material of casting and sand core, it will generate slag again. We often call it "secondary slag" (as distinct from the existence of "first slag”).

This defects are often found only on the fracture surface, on surface of finished sand castings can, are often found by magnetic particle inspection. Such inclusions are mainly consisted of the oxide (MgO, SiO2, Feo …) and sulfide (MgS, FeS, MnS ...) and other inclusions.

Preventive measures of secondary slag

1. Control the residual amount of magnesium in liquid iron strictly, (general the mass fraction is 0.035% ~ 0.055%, if the wall is thin, it should be controlled at minimum; or it should be controlled at maximum.)

2. Reduce the sulfur content of original molten iron, if condition permits, it is better to take some desulfurization methods, improve the processing temperature and pouring temperature. Desulfurization process of molten iron can substantially reduce the sulfur content which can effectively reduce the "secondary slag."

3. Improve the rare earth content in the nodulizer, and reduce the magnesium content. It can help to reduce the temperature of molten iron crusting and reduce the "secondary slag" effectively.

Slag holes will reduce the effective bearing area, cause the stress concentration around the pores and reduce casting fatigue resistance and impact resistance. No matter casting plants or persons who want to buy some sand casting should check carefully in order to avoid the defects.